Communication Networks 2012 年期末考卷

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无线通信原理与应用期末考试题

第一章1 短距离无线通信的特点1)无线发射功率在uW到100mW量级2)通信距离在几厘米到几百米3)应用场景众多，特别是频率资源稀缺情况4)使用全向天线和线路板天线5)不需申请频率资源使用许可证6)无中心，自组网7)电池供电2 频分复用和时分复用的特点和区别？频分复用（FDD）同时为用户和基站提供了无线电传输信道，这样可以在发送信号的同时接收到来的信号。

在基站中，使用不同的发射天线和接收天线以对应分离的信道。

然而在用户单元中，使用单个天线来传输和接收信号，并使用一种称为双工器的设备来实现同一天线上的信号传输与接收。

对于FDD系统，发送和接收的信道频率至少要间隔标称频率的5%，以保证在廉价的制造成本下能够提供具备足够隔离度的双工器时分复用（TDD）方式即在时间上分享一条信道，将其一部分时间用于从基站向用户发送信息，而其余的时间用于从用户向基站发送信息。

如果信道的数据传输速率远大于终端用户的数据速率，就可以通过存储用户数据然后突发的方式来实现单一信道上的全双工操作。

TDD只在数字传输和数字调制时才可以使用，并且对定时很敏感。

3 蜂窝移动电话系统的结构和各部分的作用？蜂窝电话系统为在无线覆盖范围内的、任何地点的用户提供公用电话交换网的无线接入。

蜂窝系统能在有限的频带范围中于很大的地理范围内容纳大量用户，它提供了和有线电话系统相当的高通话质量。

获得高容量的原因，是由于它将每个基站发射站的覆盖范围限制到称为“小区”的小块地理区域。

这样，相距不远的另一个基站里可以使用相同的无线信道。

一种称为“切换”的复杂的交换技术，确保了当用户从一个小区移动到另一个小区时不会中断通话。

一个蜂窝移动电话系统包括移动台、基站和移动交换中心（MSC）。

移动交换中心负责在蜂窝系统中将所有的移动用户连接到公用电话交换网上，有时MSC也称为移动电话交换局（MTSO）。

每个移动用户通过无线链路和某一个基站通信，在通话过程中，可能会切换到其他任何一个基站。

计算机网络试卷

A. DemultiplexingB. MultiplexingC. TDMD. FDM(6)Consider sending a 999 byte datagram into a link that has an MTU of 500 bytes ,( B )A.2 fragments are created with offset field value 0,500, respectivelyB. 3 fragments are created with offset field value 0, 480, 960, respectivelyC. 3 fragments are created with offset field value 0, 60, 120, respectivelyD.None of these above(7)About the encapsulation relationships of segment、datagram and frame, which ofthe following is correct? ( C )A. Segment is encapsulated within the frame, and the frame is encapsulatedwithin the datagram.B. Datagram is encapsulated within the Segment, and the Segment isencapsulated within the frame.C. Segment is encapsulated within the datagram, and the datagram isencapsulated within the frame.D. Frame is encapsulated within the datagram, and the datagram is encapsulatedwithin the segment.(8)TCP has which of the following characteristics: ( D )A. Flow controlB. Connection establishmentC. Congestion controlD. All of the above(9)What is the ICMP used for ？( C )A. Error reportingB. Used by pingC. A and BD. None above.(10)A taking-turns MAC protocol has which of the following characteristics:( B )A. there is no single point failureB. it does not generate collisionsC. there is no master nodeD. all of the above(11)I n the Ethernet two-layer switches, how is the forwarding table established?( B )A. Manual configurationB. Self-learningC. Routing algorithmD. Destination address learning(12)W hich are the error detection and correction techniques used often in link layer?( A )A. CRCB. ChecksumC. Parity checksD. None of the above(13)I n routing among ASs, which of the following issues dominants? ( A )A. Routing PolicyB. Geographical distance between AssC. Current congestion levels in the ASsD. Number of ASs traversed(14)A n ARP query packet is encapsulated in ( B )A. a link-layer frame addressed to a specific adapterB. a link-layer broadcast frameC. an IP datagramD. none of the above(15)T wo important reasons that the Internet is organized as a hierarchy of networksfor the purposes of routing are ( C )A. Least cost and maximum free circuit availabilityB. Message complexity and speed of convergenceC. Scale and administrative autonomyD. Link cost changes and link failure2.Fill the blank. (10 scores, every blank is 1 score )(1)The task of the data link layer is providing data transmission services between_________Adjacent nodes__________; The task of the network layer is providing data transmission services between _______hosts___________; and the task of transport layer is providing data transmission services between ________processes___________.(2)The two key functions of network layer are _______Forwarding________ and________routing__________.(3)Two routing protocols have been used extensively for routing within anautonomous system in the Internet: RIP protocol and __OSPF____ protocol. (4)The header of IP datagram has a _____TTL______ field, when the value of thefield is 0, the datagram transmitted will be discarded.(5)RIP advertisements typically announce the number of hops to variousdestination; BGP updates, on the other hand, announce the ________Sequence of ASs on the routes___________to the various destinations.(6)TCP provides a ________Flow control________service to its application toeliminate the possibility of the sender overwhelming the receiver.(7)The tool (command) that can be used to determine the number of hops to adestination and the round trip time (RTT) for each hop is ______Traceroute________.3.Judge the following questions as true or false. (10 scores, everyone is 1 scores)(1)When a user request a Web page that consists of some text and two images. Forthis page, the client will send one request message and receive three response message.(2)With a window size of 1, SR, GBN, and the alternating bit protocol arefunctionally equivalent.(3)When using distance vector route algorithm, the complete network topologyinformation must be known by a router.(4)In a P2P file-sharing application, there is no notion of client and server sides ofa communication session.(5)All nodes connected to the Internet must implement UDP.(6)Media Access Control is a function of the data-link layer.(7)Emails are delivered to receiver's server using POP3 protocol.(8)Both CIDR and NAT can lead to much more efficient use of the available IPv4address space.(9)Collisions will not occur under CSMA/CD MAC protocol.(10)When a TCP segment arrives to a host, the socket to which the segment isdirected depends on the destination port number and the destination IP address.4.Answer the following questions briefly. (30 scores, every one is 6scores)(1)Consider sending a packet from a source host to a destination host over a fixed the four factors of delay for the packet. Is the delay constant ? Why or why not? Identify which factor will most likely predominate (i.e. ,be the largest factor ) for 1M Byte Packets in a flow on the following different links.a) 10 Mb/s LAN segment between two PCs in the same buildingb) 1 Mb/s geosynchronous-orbit satellite (同步轨道卫星) link between the USand Chinac) on the Internet between the US and China(2) Domain Name System (DNS) uses a distributed approach as opposed to a single server. Why? Assume a client needs to find the IP address of using the DNS. And assume the client has a local DNS server, but that server does not have any addresses cached. What are the DNS servers that are queried (in order) to find the IP address?(3)Try to describe the main principles of reliable data transfer for GBN as figure 1.Figure 1 GBN window mechanism(4) Consider a subnet with prefix 222.201.130.64/26. Give an example of one IPaddress(of form xxx.xxx.xxx.xxx) that can be assigned to an interface in this network. Suppose an ISP owns the block of addresses of the form 222.201.130.64/26. And suppose it wants to create four subnets from this block, with each block having the same number of IP addresses. What are the prefixes(of form a.b.c.d/x) for the four subnets?(5) As figure 2, suppose Host A sends a datagram to Host B via router R. Please drawup the source and destination MAC addresses, and source and destination IP addresses in the frame as required below:1.From A to the R2.From R to B.F igure 25. Comprehensive Questions (20 scores, every one is 10 scores)(1) Consider the following network. With the indicated link costs, use Dijkstra’s shortest path algorithm to compute the shortest path from x to all network nodes. While selecting the next node, if several nodes have the same min cost, select the one with lowest id, (e.g., if t and v have the same min cost, then select t).R1A-23-F9-CD-06-9B222.222.222.220111.111.111.11E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D111.111.111.112111.111.111.111A74-29-9C-E8-FF-55222.222.222.221B222.222.222.22249-BD-D2-C7-56-2A88-B2-2F-54-1A-0FFigure 4Figure 3Please show how the algorithm works by filling out the following table.(2) Assume the following graph shows the behavior of a TCP congestion control, answer each question with a short discussion justifying your answer.a) Identify the intervals of time when TCP slow start is operating.b) Identify the intervals of time when TCP congestion avoidance is operating.c)After 14th transmission round,is segment loss detected by a triple duplicate ACK or by a timeout? And which version of TCP protocol(Reno or Tahoe) is used base on this information?d) During what transmission round is the 50th segment sent?e) Assuming a packet loss is detected after the 23rd round by the receipt of a triple duplicate ACKs, what will be the values of the congestion window size andThreshold?,考试作弊将带来严重后果！华南理工大学期末考试《 Computer Networks 》A 试卷Select the correct choice. (30 scores, every one is 2 scores)Fill the blank. (10 scores, every blank is 1 score )Adjacent nodes; hosts ; processes Forwarding , routing OSPF TTLSequence of ASs on the routes Flow control Traceroute (Tracert)Judge the following questions as true or false. (10 scores, every one is 1 scores) Answer the following questions briefly. (30 scores, every one is 6 scores)nodal processing delay, queuing delay, transmission delay .Propagation delay.a) transmission delay b) propagation delay c) queuing delay(2) Why: A distributed hierarchy of servers gives better scalability and does not present a single point of failure.In order: Local -Root Top level(org) Authoritative () DNS server(3)i.“window” of up to N, consecutive unack’ed pkts allowed.ii.ACK(n): ACKs all pkts up to, including seq # n - “cumulative ACK”a)may receive duplicate ACKs (see receiver)b)Only a single timer for the oldest transmitted but not yet acknowleged. timeout(n): retransmit pkt n and all higher seq # pkts in window(4) 222.201.130. 64~ 222.201.130.127Four subnets: 222.201.130.64/28222.201.130.80/28222.201.130.96/28222.201.130.112/28(5)i.From A to R: Source MAC address: 74-29-9C-E8-FF-55Destination MAC address: E6-E9-00-17-BB-4BSource IP: 111.111.111.111Destination IP: 222.222.222.222ii.From R to B: Source MAC address: 1A-23-F9-CD-06-9BDestination MAC address: 49-BD-D2-C7-56-2ASource IP: 111.111.111.111Destination IP: 222.222.222.22210.C omprehensive Questions (20 scores, every one is 10 scores) (1)1x∞∞8,x5,x1,x5,x2xy3,y∞4,y5,x4,y 3xyt4,t4,y5,x4,y 4xytu4,y5,x4,y 5xytuv5,x4,y 6xytuvz5,x7xytuvzw 3,y4,t4,y5,x1,x4,y(2)a)[1,6],[20,23]b) [6,14],[15,19]c)A triple duplicate Ack; Renod) 6e) 4, 4。

2012年通信专业实务-传输与接入真题下午试卷

试题一【问题1】一段3km长的光纤，输入光功率为1mW（波长为1310nm）时，输出光功率为0.8mW。

请计算这段光纤在该波长下的损耗系数为多少？若该类型光纤在1550nm波长下的损耗系数为0.25dB/km，那么1mW的1550nm波长光信号经10km长该类型光纤传输后，输出光信号功率为多少？[解析]：光纤损耗用损耗系数α(λ)表示，单位为dB/km，即单位长度（km）的光功率损耗（dB）值。

由于光功率随长度是按指数规律衰减的，定义p0 为注入光纤的功率，L为光纤的长度，pL为光纤传输距离L后的光功率。

【问题2】（8分，每题1分。

请对下列说法进行判断，将“√”（判为正确）或“×”（判为错误）写在答题纸对应栏内）1、对于G.652光纤（常规单模光纤），若光信号波长大于零色散波长，那么由于光纤色散，光信号长波长部分较短波长部分传输得慢。

[答案] 错误[解析]：常规单模光纤在1.27nm波长处色散为零，大于1.27nm时色散为正，小于1.27nm时色散为负，随波长增加传播速率变快。

(V=λf)2、密集波分复用系统中的光纤线路只采用G.655光纤。

[答案]：错误[解析]：说的太绝对，其实还有具有更大有效面积、超低损耗和非线性折射率效应的G.654光纤，用于DWDM 长距离海底系统，可以减少EDFA的数量；消除了OH离子吸收峰的全波光纤G.656，应用波长范围得到了极大拓展。

由于G.655光纤非零色散的特性，能够避免FWM的影响，适用于DWDM环境。

3、半导体激光器是光纤通信常用的光源。

[答案]：正确[解析]：光纤通信最简单的光源有半导体发光二极管和半导体激光器4、I层采用InGaAs材料的PIN光电二极管能将850nm波长的光信号转换成电信号。

[答案]：错误[解析]：Si光电二极管的波长响应范围为0.5～1.0μm，适用于短波长波段；InGaAs的波长响应范围为1.1～1.6μm，适应于长波长波段。

2012年考研英语一真题及答案完整解析 - 副本

2012年全国硕士研究生入学统一考试英语（一）Section I Use of EnglishDirections:Read the following text. Choose the best word(s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1. (10 points)Read the following text. Choose the best word(s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1. (10 points)The ethical judgments of the Supreme Court justices have become an important issue recently. The court cannot _1_ its legitimacy as guardian of the rule of law _2_ justices behave like politicians. Yet, in several instances, justices acted in ways that _3_ the court’s reputation for being independent and impartial.Justice Antonin Scalia, for example, appeared at political events. That kind of activity makes it less likely that the court’s decisi ons will be _4_ as impartial judgments. Part of the problem is that the justices are not _5_by an ethics code. At the very least, the court should make itself _6_to the code of conduct that _7_to the rest of the federal judiciary.This and other similar cases _8_the question of whether there is still a_9_between the court and politics.The framers of the Constitution envisioned law _10_having authority apart from politics. They gave justices permanent positions _11_they would be free to _12_ those in power and have no need to _13_ political support. Our legal system was designed to set law apart from politics precisely because they are so closely _14_.Constitutional law is political because it results from choices rooted in fundamental social _15_ like liberty and property. When the court deals with social policy decisions, the law it _16_ is inescapably political-which is why decisions split along ideological lines are so easily _17_ as unjust.The justices must _18_ doubts about the court’s legitimacy by making themselves _19_ to the code of conduct. That would make rulings more likely to be seen as separate from politics and, _20_, convincing as law.1. [A]emphasize [B]maintain [C]modify [D] recognize2. [A]when [B]lest [C]before [D] unless3. [A]restored [B]weakened [C]established [D] eliminated4. [A]challenged [B]compromised [C]suspected [D] accepted5. [A]advanced [B]caught [C]bound [D]founded6. [A]resistant [B]subject [C]immune [D]prone7. [A]resorts [B]sticks [C]loads [D]applies8. [A]evade [B]raise [C]deny [D]settle9. [A]line [B]barrier [C]similarity [D]conflict10. [A]by [B]as [C]though [D]towards11. [A]so [B]since [C]provided [D]though12. [A]serve [B]satisfy [C]upset [D]replace13. [A]confirm [B]express [C]cultivate [D]offer14. [A]guarded [B]followed [C]studied [D]tied15. [A]concepts [B]theories [C]divisions [D]conceptions16. [A]excludes [B]questions [C]shapes [D]controls17. [A]dismissed [B]released [C]ranked [D]distorted18. [A]suppress [B]exploit [C]address [D]ignore19. [A]accessible [B]amiable [C]agreeable [D]accountable20. [A]by all mesns [B]atall costs [C]in a word [D]as a resultSection II Reading ComprehensionPart ADirections:Read the following four texts. Answer the questions below each text by choosing A, B, C or D. Mark your answers on ANSWER SHEET 1. (40 points)Text 1Come on –Everybody’s doing it. That whispered message, half invitation and half forcing, is what most of us think of when we hear the words peer pressure. It usually leads to no good-drinking, drugs and casual sex. But in her new book Join the Club, Tina Rosenberg contends that peer pressure can also be a positive force through what she calls the social cure, in which organizations and officials use the power of group dynamics to help individuals improve their lives and possibly the word.Rosenberg, the recipient of a Pulitzer Prize, offers a host of example of the social cure in action: In South Carolina, a state-sponsored antismoking program called Rage Against the Haze sets out to make cigarettes uncool. In South Africa, an HIV-prevention initiative known as LoveLife recruits young people to promote safe sex among their peers.The idea seems promising，and Rosenberg is a perceptive observer. Her critique of the lameness of many pubic-health campaigns is spot-on: they fail to mobilize peer pressure for healthy habits, and they demonstrate a seriously flawed understanding of psychology.” Dare to be different, please don’t smoke!” pleads one billboard campaign aimed at reducing smoking amongteenagers-teenagers, who desire nothing more than fitting in. Rosenberg argues convincingly that public-health advocates ought to take a page from advertisers, so skilled at applying peer pressure.But on the general effectiveness of the social cure, Rosenberg is less persuasive. Join the Club is filled with too much irrelevant detail and not enough exploration of the social and biological factors that make peer pressure so powerful. The most glaring flaw of the social cure as it’s presented here is that it doesn’t work very well for very long. Rage Against the Haze failed once state funding was cut. Evidence that the LoveLife program produces lasting changes is limited and mixed.There’s no doubt that our peer groups exert enormous influence on our behavior. An emerging body of research shows that positive health habits-as well as negative ones-spread through networks of friends via social communication. This is a subtle form of peer pressure: we unconsciously imitate the behavior we see every day.Far less certain, however, is how successfully experts and bureaucrats can select our peer groups and steer their activities in virtuous directions. It’s like the teacher w ho breaks up the troublemakers in the back row by pairing them with better-behaved classmates. The tactic never really works. And that’s the problem with a social cure engineered from the outside: in the real world, as in school, we insist on choosing our own friends.21. According to the first paragraph, peer pressure often emerges as[A] a supplement to the social cure[B] a stimulus to group dynamics[C] an obstacle to school progress[D] a cause of undesirable behaviors22. Rosenberg holds that public advocates should[A] recruit professional advertisers[B] learn from advertisers’ experience[C] stay away from commercial advertisers[D] recognize the limitations of advertisements23. In the author’s view, Rosenberg’s book fails to[A] adequately probe social and biological factors[B] effectively evade the flaws of the social cure[C] illustrate the functions of state funding[D]produce a long-lasting social effect24. Paragraph 5shows that our imitation of behaviors[A] is harmful to our networks of friends[B] will mislead behavioral studies[C] occurs without our realizing it[D] can produce negative health habits25. The author suggests in the last paragraph that the effect of peer pressure is[A] harmful[B] desirable[C] profound[D] questionableText 2A deal is a deal-except, apparently ,when Entergy is involved. The company, a major energy supplier in New England, provoked justified outrage in Vermont last week when it announced it was reneging on a longstanding commitment to abide by the strict nuclear regulations.Instead, the company has done precisely what it had long promised it would not challenge the constitutionality of Vermont’s rules in the federal court, as part of a desperate effort to keep its Vermont Yankee nuclear powe r plant running. It’s a stunning move.The conflict has been surfacing since 2002, when the corporation bought Vermont’s only nuclear power plant, an aging reactor in Vernon. As a condition of receiving state approval for the sale, the company agreed to seek permission from state regulators tooperate past 2012. In 2006, the state went a step further, requiring that any extension of the plant’s license be subject to Vermont legislature’s approval. Then, too, the company went along.Either Entergy never real ly intended to live by those commitments, or it simply didn’t foresee what would happen next. A string of accidents, including the partial collapse of a cooling tower in 207 and the discovery of an underground pipe system leakage, raised serious questions about both Vermont Yankee’s safety and Entergy’s management–especially after the company made misleading statements about the pipe. Enraged by Entergy’s behavior, the Vermont Senate voted 26 to 4 last year against allowing an extension.Now the company is suddenly claiming that the 2002 agreement is invalid because of the 2006 legislation, and that only the federal government has regulatory power over nuclear issues. The legal issues in the case are obscure: whereas the Supreme Court has ruled that states do have some regulatory authority over nuclear power, legal scholars say that Vermont case will offer a precedent-setting test of how far those powers extend. Certainly, there are valid concerns about the patchwork regulations that could result if every state sets its own rules. But had Entergy kept its word, that debate would be beside the point.The company seems to have concluded that its reputation in Vermont is already so damaged that it has noting left to lose by going to war with the state. But there should be consequences. Permission to run a nuclear plant is a poblic trust. Entergy runs 11 other reactors in the United States, including Pilgrim Nuclear station in Plymouth. Pledging to run Pilgrim safely, the company has applied for federal permission to keep it open for another 20 years. But as the Nuclear Regulatory Commission (NRC) reviews the company’s application, it should keep it mind what promises from Entergy are worth.26. The phrase “reneging on”(Line 3.para.1) is closest in meaning to[A] condemning.[B] reaffirming.[C] dishonoring.[D] securing.27. By entering into the 2002 agreement, Entergy intended to[A] obtain protection from Vermont regulators.[B] seek favor from the federal legislature.[C] acquire an extension of its business license .[D] get permission to purchase a power plant.28. According to Paragraph 4, Entergy seems to have problems with its[A] managerial practices.[B] technical innovativeness.[C] financial goals.[D] business vision29. In the author’s view, th e Vermont case will test[A] Entergy’s capacity to fulfill all its promises.[B] the mature of states’ patchwork regulations.[C] the federal authority over nuclear issues .[D] the limits of states’ power over nuclear issues.30. It can be inferred from the last paragraph that[A] Entergy’s business elsewhere might be affected.[B] the authority of the NRC will be defied.[C] Entergy will withdraw its Plymouth application.[D] Vermont’s reputation might be damaged.Text 3In the idealized version of how science is done, facts about the world are waiting to be observed and collected by objective researchers who use the scientific method to carry out their work. But in the everyday practice of science, discovery frequently follows an ambiguous and complicated route. We aim to be objective, but we cannot escape the context of our unique life experience. Prior knowledge and interest influence what we experience, what we think our experiences mean, and the subsequent actions we take. Opportunities for misinterpretation, error, and self-deception abound.Consequently, discovery claims should be thought of as protoscience. Similar to newly staked mining claims, they are full of potential. But it takes collective scrutiny and acceptance to transform a discovery claim into a mature discovery. This is the credibility process, through which the individual researcher’s me, here, now becomes the community’s anyone, anywhere, anytime. Objective knowledge is the goal, not the starting point.Once a discovery claim becomes public, the discoverer receives intellectual credit. But, unlike with mining claims, the community takes control of what happens next. Within the complex social structure of the scientific community, researchers make discoveries; editors and reviewers act as gatekeepers by controlling the publication process; other scientists use the new finding to suit their own purposes; and finally, the public (including other scientists) receives the new discovery and possibly accompanying technology. As a discovery claim works it through the community, the interaction and confrontation between shared andcompeting beliefs about the science and the technology involved transforms an individual’s discovery claim into the community’s credible discovery.Two paradoxes exist throughout this credibility process. First, scientific work tends to focus on some aspect of prevailing Knowledge that is viewed as incomplete or incorrect. Little reward accompanies duplication and confirmation of what is already known and believed. The goal is new-search, not re-search. Not surprisingly, newly published discovery claims and credible discoveries that appear to be important and convincing will always be open to challenge and potential modification or refutation by future researchers. Second, novelty itself frequently provokes disbelief. Nobel Laureate and physiologist AlbertAzent-Gyorgyi once described discovery as “seeing what everybody has seen and thinking what nobody has thought.” But thinking what nobody else has thought and telling others what they have missed may not change their views. Sometimes years are required for truly novel discovery claims to be accepted and appreciated.In the end, credibility “happens” to a discovery claim – a process that corresponds to what philosopher Annette Baier has described as the commons of the mind. “We reason together, challenge, revise, and complete each other’s reasoning and each other’s conceptions of reason.”31. According to the first paragraph, the process of discovery is characterized by its[A] uncertainty and complexity.[B] misconception and deceptiveness.[C] logicality and objectivity.[D] systematicness and regularity.32. It can be inferred from Paragraph 2 that credibility process requires[A] strict inspection.[B]shared efforts.[C] individual wisdom.[D]persistent innovation.33.Paragraph 3 shows that a discovery claim becomes credible after it[A] has attracted the attention of the general public.[B]has been examined by the scientific community.[C] has received recognition from editors and reviewers.[D]has been frequently quoted by peer scientists.34. Albert Szent-Györgyi would most likely agree that[A] scientific claims will survive challenges.[B]discoveries today inspire future research.[C] efforts to make discoveries are justified.[D]scientific work calls for a critical mind.35.Which of the following would be the best title of the test?[A] Novelty as an Engine of Scientific Development.[B]Collective Scrutiny in Scientific Discovery.[C] Evolution of Credibility in Doing Science.[D]Challenge to Credibility at the Gate to Science.Text 4If the trade unionist Jimmy Hoffa were alive today, he would probably represent civil servant. When Hoffa’s Teamsters were in their prime in 1960, only one in ten American government workers belonged to a union; now 36% do. In 2009 the number of unionists in America’s public sector passed that of their fellow members in the private sector. In Britain, more than half of public-sector workers but only about 15% of private-sector ones are unionized.There are three reasons for the public-sector unions’ thriving. First, they can shut things down without suffering much in the way of consequences. Second, they are mostly bright and well-educated. A quarter of America’s public-sector workers have a university degree. Third, they now dominate left-of-centre politics. Some of their ties go back a long way. Britain’s Labor Party, as its name implies, has long been associated with trade unionism. Its current leader, Ed Miliband, owes his position to votes from public-sector unions.At the state level their influence can be even more fearsome. Mark Baldassare of the Public Policy Institute of California points out that much of the state’s budget is patrolled by unions. The teachers’ unio ns keep an eye on schools, the CCPOA on prisons and a variety of labor groups on health care.In many rich countries average wages in the state sector are higher than in the private one. But the real gains come in benefits and work practices. Politicians h ave repeatedly “backloaded” public-sector pay deals, keeping the pay increases modest but adding to holidays and especially pensions that are already generous.Reform has been vigorously opposed, perhaps most egregiously in education, where charter schools, academies and merit pay all faced drawn-outbattles. Even though there is plenty of evidence that the quality of the teachers is the most important variable, teachers’ unions have fought against getting rid of bad ones and promoting good ones.As the cost to everyone else has become clearer, politicians have begun to clamp down. In Wisconsin the unions have rallied thousands of supporters against Scott Walker, the hardline Republican governor. But many within the public sector suffer under the current system, too.John Donahue at Harvard’s Kennedy School points out that the norms of culture in Western civil services suit those who want to stay put but is bad for high achievers. The only American public-sector workers who earn well above $250,000 a year are university sports coaches and the president of the United States. Bankers’ fat pay packets have attracted much criticism, but apublic-sector system that does not reward high achievers may be a much bigger problem for America.36. It can be learned from the first paragraph that[A] Teamsters still have a large body of members.[B] Jimmy Hoffa used to work as a civil servant.[C] unions have enlarged their public-sector membership.[D]the government has improved its relationship with unionists.37. Which of the following is true of Paragraph 2?[A] Public-sector unions are prudent in taking actions.[B] Education is required for public-sector union membership.[C] Labor Party has long been fighting against public-sector unions.[D]Public-sector unions seldom get in trouble for their actions.38. It can be learned from Paragraph 4 that the income in the state sector is[A] illegally secured.[B] indirectly augmented.[C] excessively increased.[D]fairly adjusted.39. The example of the unions in Wisconsin shows that unions[A]often run against the current political system.[B]can change people’s political attitudes.[C]may be a barrier to public-sector reforms.[D]are dominant in the government.40. John Donahue’s attitude towards the public-sector system is one of[A]disapproval.[B]appreciation.[C]tolerance.[D]indifference.Part BDirections:In the following text, some sentences have been removed. For Questions 41-45, choose the most suitable one from the list A-G to fit into each of the numbered blanks. There are two extra choices, which do not fit in any of the blanks. Mark your answers on ANSWER SHEET1.（10 points）Think of those fleeting moments when you look out of an aeroplane window and realise that you are flying, higher than a bird. Now think of your laptop, thinner than a brown-paper envelope, or your cellphone in the palm of your hand. Take a moment or two to wonder at those marvels. You are the lucky inheritor of a dream come true.The second half of the 20th century saw a collection of geniuses, warriors, entrepreneurs and visionaries labour to create a fabulous machine that could function as a typewriter and printing press, studio and theatre, paintbrush and gallery, piano and radio, the mail as well as the mail carrier. (41)The networked computer is an amazing device, the first media machine that serves as the mode of production, means of distribution, site of reception, and place of praise and critique. The computer is the 21st century's culture machine.But for all the reasons there are to celebrate the computer, we must also tread with caution. (42)I call it a secret war for two reasons. First, most people do not realise that there are strong commercial agendas at work to keep them in passive consumption mode. Second, the majority of people who use networked computers to upload are not even aware of the significance of what they are doing.All animals download, but only a few upload. Beavers build dams and birds make nests. Yet for the most part, the animal kingdom moves through the world downloading. Humans are unique in their capacity to not only make tools but then turn around and use them to create superfluous material goods - paintings, sculpture and architecture - and superfluous experiences - music, literature, religion and philosophy. (43)For all the possibilities of our new culture machines, most people are still stuck in download mode. Even after the advent of widespread social media, a pyramid of production remains, with a small number of people uploading material, a slightly larger groupcommenting on or modifying that content, and a huge percentage remaining content to just consume. (44)Television is a one-way tap flowing into our homes. The hardest task that television asks of anyone is to turn the power off after he has turned it on.(45)What counts as meaningful uploading? My definition revolves around the concept of "stickiness" - creations and experiences to which others adhere.[A] Of course, it is precisely these superfluous things that define human culture and ultimately what it is to be human. Downloading and consuming culture requires great skills, but failing to move beyond downloading is to strip oneself of a defining constituent of humanity.[B] Applications like , which allow users to combine pictures, words and other media in creative ways and then share them, have the potential to add stickiness by amusing, entertaining and enlightening others.[C] Not only did they develop such a device but by the turn of the millennium they had also managed to embed it in a worldwide system accessed by billions of people every day.[D] This is because the networked computer has sparked a secret war between downloading and uploading - between passive consumption and active creation - whose outcome will shape our collective future in ways we can only begin to imagine.[E] The challenge the computer mounts to television thus bears little similarity to one format being replaced by another in the manner of record players being replaced by CD players. [F] One reason for the persistence of this pyramid of production is that for the pasthalf-century, much of the world's media culture has been defined by a single medium - television - and television is defined by downloading.[G]The networked computer offers the first chance in 50 years to reverse the flow, to encourage thoughtful downloading and, even more importantly, meaningful uploading.Part CDirections:Read the following text carefully and then translate the underlined segments into Chinese. Your translation should be written clearly on ANSWER SHEET 2. (10 points)Since the days of Aristotle, a search for universal principles has characterized the scientific enterprise. In some ways, this quest for commonalities defines science. Newton’s laws of motion and Dar winian evolution each bind a host of different phenomena into a single explicatory frame work.(46)In physics, one approach takes this impulse for unification to its extreme, and seeks a theory of everything—a single generative equation for all we see.It isbecoming less clear, however, that such a theory would be a simplification, given the dimensions and universes that it might entail, nonetheless, unification of sorts remains a major goal.This tendency in the natural sciences has long been evident in the social sciences too. (47)Here, Darwinism seems to offer justification for it all humans share common origins it seems reasonable to suppose that cultural diversity could also be traced to more constrained beginnings. Just as the bewildering variety of human courtship rituals might all be considered forms of sexual selection, perhaps the world’s languages, music, social and religious customs and even history are governed by universal features. (48)To filter out what is unique from what isshared might enable us to understand how complex cultural behavior arose and what guides it in evolutionary or cognitive terms.That, at least, is the hope. But a comparative study of linguistic traits published online today supplies a reality check. Russell Gray at the University of Auckland and his colleagues consider the evolution of grammars in the light of two previous attempts to find universality in language.The most famous of these efforts was initiated by Noam Chomsky, who suggested that humans are born with an innate language—acquisition capacity that dictates a universal grammar. A few generative rules are then sufficient to unfold the entire fundamental structure of a language, which is why children can learn it so quickly.(49)The second, by Joshua Greenberg, takes a more empirical approach touniversality identifying traits (particularly in word order) shared by manylanguage which are considered to represent biases that result from cognitiveconstraintsGray and his colleagues have put them to the test by examining four family trees that between them represent more than 2,000 languages.(50)Chomsky’s grammar should show patterns of language change that are independent of the family tree or the pathway tracked through it. Whereas Greenbergian universality predicts strong co-dependencies between particular types of word-order relations.Neither of these patterns is borne out by the analysis, suggesting that thestructures of the languages are lire age-specific and not governed by universalsSection III WritingPart A51. Directions:Some internationals students are coming to your university. Write them an email in the name of the Students’ Union to1)extend your welcome and2)provide some suggestions for their campus life here.You should write about 100 words on ANSWER SHEET2.Do not sign your name at the end of the letter. Use “Li Ming” instead.Do not write the address(10 points)Part B52. Directions: write an essay of 160-200 words based on the following drawing. In your essay you should1) describe the drawing briefly2) explain its intended meaning, and3) give your commentsYou should write neatly on ANSWER SHEET2.（20 points）1.【答案】B【解析】从空后信息可以看出，这句表达的是“_ _法官表现得像政治家”的情况下，法庭就不能保持其作为法律法规的合法卫士的形象，所以应该选C,maintain“维持，保持”，其他显然语义不通。

2012年考研英语(一)试题及答案 (完整版)

2012英语考研试题Section I Use of EnglishDirections：Read the following text. Choose the best word(s) for each numbered blank and mark A， B，C or D on ANSWER SHEET 1. (10 points)Read the following text. Choose the best word(s) for each numbered blank and mark A， B，C or D on ANSWER SHEET 1. (10 points)The ethical judgments of the Supreme Court justices have become an important issue recently. The court cannot _1_ its legitimacy as guardian of the rule of law _2_ justices behave like politicians. Yet， in several instances， justices acted in ways that _3_ the court's reputation for being independent and impartial.Justice Antonin Scalia， for example， appeared at political events. That kind of activity makes it less likely that the court's decisions will be _4_ as impartial judgments. Part of the problem is that the justices are not _5_by an ethics code. At the very least， the court should make itself _6_to the code of conduct that _7_to the rest of the federal judiciary.This and other similar cases _8_the question of whether there is still a _9_between the court and politics.The framers of the Constitution envisioned law _10_having authority apart from politics. They gave justices permanent positions _11_they would be free to _12_ those in power and have no need to _13_ political support. Our legal system was designed to set law apart from politics precisely because they are so closely _14_.Constitutional law is political because it results from choices rooted in fundamental social _15_ like liberty and property. When the court deals with social policy decisions， the law it _16_ is inescapably political-which is why decisions split along ideological lines are so easily _17_ as unjust.The justices must _18_ doubts about the court's legitimacy by making themselves _19_ to the code of conduct. That would make rulings more likely to be seen as separate from politics and，_20_， convincing as law.1. [A]emphasize [B]maintain [C]modify [D] recognize2. [A]when [B]lest [C]before [D] unless3. [A]restored [B]weakened [C]established [D] eliminated4. [A]challenged [B]compromised [C]suspected [D] accepted5. [A]advanced [B]caught [C]bound [D]founded6. [A]resistant [B]subject [C]immune [D]prone7. [A]resorts [B]sticks [C]loads [D]applies8. [A]evade [B]raise [C]deny [D]settle9. [A]line [B]barrier [C]similarity [D]conflict10. [A]by [B]as [C]though [D]towards11. [A]so [B]since [C]provided [D]though12. [A]serve [B]satisfy [C]upset [D]replace13. [A]confirm [B]express [C]cultivate [D]offer14. [A]guarded [B]followed [C]studied [D]tied15. [A]concepts [B]theories [C]divisions [D]conceptions16. [A]excludes [B]questions [C]shapes [D]controls17. [A]dismissed [B]released [C]ranked [D]distorted18. [A]suppress [B]exploit [C]address [D]ignore19. [A]accessible [B]amiable [C]agreeable [D]accountable20. [A]by all mesns [B]atall costs [C]in a word [D]as a resultSection II Reading ComprehensionPart ADirections：Read the following four texts. Answer the questions below each text by choosing A， B， C or D. Mark your answers on ANSWER SHEET 1. (40 points)Text 1Come on -Everybody's doing it. That whispered message， half invitation and half forcing，is what most of us think of when we hear the words peer pressure. It usually leads to no good-drinking， drugs and casual sex. But in her new book Join the Club， Tina Rosenberg contends that peer pressure can also be a positive force through what she calls the social cure， in which organizations and officials use the power of group dynamics to help individuals improve their lives and possibly the word.Rosenberg， the recipient of a Pulitzer Prize， offers a host of example of the social cure in action： In South Carolina， a state-sponsored antismoking program called Rage Against the Haze sets out to make cigarettes uncool. In South Africa， an HIV-prevention initiative known as LoveLife recruits young people to promote safe sex among their peers.The idea seems promising，and Rosenberg is a perceptive observer. Her critique of the lameness of many pubic-health campaigns is spot-on： they fail to mobilize peer pressure for healthy habits，and they demonstrate a seriously flawed understanding of psychology.“ Dare to be different， please don't smoke！” pleads one billboard campaign aimed at reducing smoking among teenagers-teenagers， who desire nothing more than fitting in. Rosenberg argues convincingly that public-health advocates ought to take a page from advertisers， so skilled at applying peer pressure.But on the general effectiveness of the social cure， Rosenberg is less persuasive. Join the Club is filled with too much irrelevant detail and not enough exploration of the social and biological factors that make peer pressure so powerful. The most glaring flaw of the social cure as it's presented here is that it doesn't work very well for very long. Rage Against the Haze failed once state funding was cut. Evidence that the LoveLife program produces lasting changes is limited and mixed.There's no doubt that our peer groups exert enormous influence on our behavior. An emerging body of research shows that positive health habits-as well as negative ones-spread through networks of friends via social communication. This is a subtle form of peer pressure： we unconsciously imitate the behavior we see every day.Far less certain， however， is how successfully experts and bureaucrats can select our peer groups and steer their activities in virtuous directions. It's like the teacher who breaks up the troublemakers in the back row by pairing them with better-behaved classmates. The tactic never really works. And that's the problem with a social cure engineered from the outside： in the real world， as in school， we insist on choosing our own friends.21. According to the first paragraph， peer pressure often emerges as[A] a supplement to the social cure[B] a stimulus to group dynamics[C] an obstacle to school progress[D] a cause of undesirable behaviors22. Rosenberg holds that public advocates should[A] recruit professional advertisers[B] learn from advertisers' experience[C] stay away from commercial advertisers[D] recognize the limitations of advertisements23. In the author's view， Rosenberg's book fails to[A] adequately probe social and biological factors[B] effectively evade the flaws of the social cure[C] illustrate the functions of state funding[D]produce a long-lasting social effect24. Paragraph 5shows that our imitation of behaviors[A] is harmful to our networks of friends[B] will mislead behavioral studies[C] occurs without our realizing it[D] can produce negative health habits25. The author suggests in the last paragraph that the effect of peer pressure is[A] harmful[B] desirable[C] profound[D] questionableText 2A deal is a deal-except， apparently ，when Entergy is involved. The company， a major energy supplier in New England， provoked justified outrage in Vermont last week when it announced it was reneging on a longstanding commitment to abide by the strict nuclear regu lations.Instead， the company has done precisely what it had long promised it would not challenge the constitutionality of Vermont's rules in the federal court， as part of a desperate effort to keep its Vermont Yankee nuclear power plant running. It's a stunning move.The conflict has been surfacing since 2002， when the corporation bought Vermont's only nuclear power plant， an aging reactor in Vernon. As a condition of receiving state approval for the sale， the company agreed to seek permission from state regulators to operate past 2012. In 2006， the state went a step further， requiring that any extension of the plant's license be subject to Vermont legislature's approval. Then， too， the company went along.Either Entergy never really intended to live by those commitments， or it simply didn't foresee what would happen next. A string of accidents， including the partial collapse of a cooling tower in 207 and the discovery of an underground pipe system leakage， raised serious questions about both Vermont Yankee's safety and Entergy's management- especially after the company made misleading statements about the pipe. Enraged by Entergy's behavior， the Vermont Senate voted 26 to 4 last year against allowing an extension.Now the company is suddenly claiming that the 2002 agreement is invalid because of the 2006 legislation， and that only the federal government has regulatory power over nuclear issues. The legal issues in the case are obscure： whereas the Supreme Court has ruled that states do have some regulatory authority over nuclear power， legal scholars say that Vermont case will offer a precedent-setting test of how far those powers extend. Certainly， there are valid concerns about the patchwork regulations that could result if every state sets its own rules. But had Entergy kept its word， that debate would be beside the point.The company seems to have concluded that its reputation in Vermont is already so damaged that it has noting left to lose by going to war with the state. But there should be consequences. Permission to run a nuclear plant is a poblic trust. Entergy runs 11 other reactors in the United States， including Pilgrim Nuclear station in Plymouth. Pledging to run Pilgrim safely， the company has applied for federal permission to keep it open for another 20 years. But as the Nuclear Regulatory Commission (NRC) reviews the company's application， it should keep it mind what promises from Entergy are worth.26. The phrase “reneging on”(Line 3.para.1) is closest in meaning to[A] condemning.[B] reaffirming.[C] dishonoring.[D] securing.27. By entering into the 2002 agreement， Entergy intended to[A] obtain protection from Vermont regulators.[B] seek favor from the federal legislature.[C] acquire an extension of its business license .[D] get permission to purchase a power plant.28. According to Paragraph 4， Entergy seems to have problems with its[A] managerial practices.[B] technical innovativeness.[C] financial goals.[D] business vision29. In the author's view， the Vermont case will test[A] Entergy's capacity to fulfill all its promises.[B] the mature of states' patchwork regulations.[C] the federal authority over nuclear issues .[D] the limits of states' power over nuclear issues.30. It can be inferred from the last paragraph that[A] Entergy's business elsewhere might be affected.[B] the authority of the NRC will be defied.[C] Entergy will withdraw its Plymouth application.[D] Vermont's reputation might be damaged.Text 3In the idealized version of how science is done， facts about the world are waiting to be observed and collected by objective researchers who use the scientific method to carry out their work. But in the everyday practice of science， discovery frequently follows an ambiguous andcomplicated route. We aim to be objective， but we cannot escape the context of our unique life experience. Prior knowledge and interest influence what we experience， what we think our experiences mean， and the subsequent actions we take. Opportunities for misinterpretation，error， and self-deception abound.Consequently， discovery claims should be thought of as protoscience. Similar to newly staked mining claims， they are full of potential. But it takes collective scrutiny and acceptance to transform a discovery claim into a mature discovery. This is the credibility process， through which the individual researcher's me， here， now becomes the community's anyone， anywhere，anytime. Objective knowledge is the goal， not the starting point.Once a discovery claim becomes public， the discoverer receives intellectual credit. But，unlike with mining claims， the community takes control of what happens next. Within the complex social structure of the scientific community， researchers make discoveries； editors and reviewers act as gatekeepers by controlling the publication process； other scientists use the new finding to suit their own purposes； and finally， the public (including other scientists) receives the new discovery and possibly accompanying technology. As a discovery claim works it through the community， the interaction and confrontation between shared and competing beliefs about the science and the technology involved transforms an individual's discovery claim into the community's credible discovery.Two paradoxes exist throughout this credibility process. First， scientific work tends to focus on some aspect of prevailing Knowledge that is viewed as incomplete or incorrect. Little reward accompanies duplication and confirmation of what is already known and believed. The goal is new-search， not re-search. Not surprisingly， newly published discovery claims and credible discoveries that appear to be important and convincing will always be open to challenge and potential modification or refutation by future researchers. Second， novelty itself frequently provokes disbelief. Nobel Laureate and physiologist Albert Azent-Gyorgyi once described discovery as “seeing what everybody has seen and thinking what nobody has thought.” But thinking what nobody else has thought and telling others what they have missed may not change their views. Sometimes years are required for truly novel discovery claims to be accepted and appreciated.In the end，credibility “happens” to a discovery claim - a process that corresponds to what philosopher Annette Baier has described as the commons of the mind. “We reason together，challenge， revise， and complete each other's reasoning and each other's conceptions o f reason.”31. According to the first paragraph， the process of discovery is characterized by its[A] uncertainty and complexity.[B] misconception and deceptiveness.[C] logicality and objectivity.[D] systematicness and regularity.32. It can be inferred from Paragraph 2 that credibility process requires[A] strict inspection.[B]shared efforts.[C] individual wisdom.[D]persistent innovation.33.Paragraph 3 shows that a discovery claim becomes credible after it[A] has attracted the attention of the general public.[B]has been examined by the scientific community.[C] has received recognition from editors and reviewers.[D]has been frequently quoted by peer scientists.34. Albert Szent-Gy？rgyi would most likely agree that[A] scientific claims will survive challenges.[B]discoveries today inspire future research.[C] efforts to make discoveries are justified.[D]scientific work calls for a critical mind.35.Which of the following would be the best title of the test？[A] Novelty as an Engine of Scientific Development.[B]Collective Scrutiny in Scientific Discovery.[C] Evolution of Credibility in Doing Science.[D]Challenge to Credibility at the Gate to Science.Text 4If the trade unionist Jimmy Hoffa were alive today， he would probably represent civil servant. When Hoffa's Teamsters were in their prime in 1960， only one in ten American government workers belonged to a union； now 36% do. In 2009 the number of unionists in America's public sector passed that of their fellow members in the private sector. In Britain， more than half of public-sector workers but only about 15% of private-sector ones are unionized.There are three reasons for the public-sector unions' thriving. First， they can shut things down without suffering much in the way of consequences. Second， they are mostly bright and well-educated. A quarter of America's public-sector workers have a university degree. Third，they now dominate left-of-centre politics. Some of their ties go back a long way. Britain's Labor Party， as its name implies， has long been associated with trade unionism. Its current leader，Ed Miliband， owes his position to votes from public-sector unions.At the state level their influence can be even more fearsome. Mark Baldassare of the Public Policy Institute of California points out that much of the state's budget is patrolled by unions. The teachers' unions keep an eye on schools， the CCPOA on prisons and a variety of labor groups on health care.In many rich countries average wages in the state sector are higher than in the private one. But the real gains come in benefits and work practices. Politicians have repeatedly “backloaded” public-sector pay deals， keeping the pay increases modest but adding to holidays and especially pensions that are already generous.Reform has been vigorously opposed， perhaps most egregiously in education， where charter schools， academies and merit pay all faced drawn-out battles. Even though there is plenty of evidence that the quality of the teachers is the most important variable， teachers' unions have fought against getting rid of bad ones and promoting good ones.As the cost to everyone else has become clearer， politicians have begun to clamp down. In Wisconsin the unions have rallied thousands of supporters against Scott Walker， the hardline Republican governor. But many within the public sector suffer under the current system， too.John Donahue at Harvard's Kennedy School points out that the norms of culture in Western civil services suit those who want to stay put but is bad for high achievers. The only American public-sector workers who earn well above $250，000 a year are university sports coaches and the president of the United States. Bankers' fat pay packets have attracted m uch criticism，but a public-sector system that does not reward high achievers may be a much bigger problem for America.36. It can be learned from the first paragraph that[A] Teamsters still have a large body of members.[B] Jimmy Hoffa used to work as a civil servant.[C] unions have enlarged their public-sector membership.[D]the government has improved its relationship with unionists.37. Which of the following is true of Paragraph 2？[A] Public-sector unions are prudent in taking actions.[B] Education is required for public-sector union membership.[C] Labor Party has long been fighting against public-sector unions.[D]Public-sector unions seldom get in trouble for their actions.38. It can be learned from Paragraph 4 that the income in the state sector is[A] illegally secured.[B] indirectly augmented.[C] excessively increased.[D]fairly adjusted.39. The example of the unions in Wisconsin shows that unions[A]often run against the current political system.[B]can change people's political attitudes.[C]may be a barrier to public-sector reforms.[D]are dominant in the government.40. John Donahue's attitude towards the public-sector system is one of[A]disapproval.[B]appreciation.[C]tolerance.[D]indifference.Part BDirections：In the following text， some sentences have been removed. For Questions 41-45， choose the most suitable one from the list A-G to fit into each of the numbered blanks. There are two extra choices， which do not fit in any of the blanks. Mark your answers on ANSWER SHEET1.（10 points）Think of those fleeting moments when you look out of an aeroplane window and realise that you are flying， higher than a bird. Now think of your laptop， thinner than a brown-paper envelope，or your cellphone in the palm of your hand. Take a moment or two to wonder at those marvels. You are the lucky inheritor of a dream come true.The second half of the 20th century saw a collection of geniuses， warriors， entrepreneurs and visionaries labour to create a fabulous machine that could function as a typewriter and printing press， studio and theatre， paintbrush and gallery， piano and radio， the mail as well as the mail carrier. (41)The networked computer is an amazing device， the first media machine that serves as the mode of production， means of distribution， site of reception， and place of praise and critique. The computer is the 21st century's culture machine.But for all the reasons there are to celebrate the computer， we must also tread with caution.(42)I call it a secret war for two reasons. First， most people do not realise that there are strong commercial agendas at work to keep them in passive consumption mode. Second， the majority of people who use networked computers to upload are not even aware of the significance of what they are doing.All animals download， but only a few upload. Beavers build dams and birds make nests. Yet for the most part， the animal kingdom moves through the world downloading. Humans are unique in their capacity to not only make tools but then turn around and use them to create superfluous material goods - paintings， sculpture and architecture - and superfluous experiences - music，literature， religion and philosophy. (43)For all the possibilities of our new culture machines， most people are still stuck in download mode. Even after the advent of widespread social media， a pyramid of production remains， with a small number of people uploading material， a slightly larger group commenting on or modifying that content， and a huge percentage remaining content to just consume. (44)Television is a one-way tap flowing into our homes. The hardest task that television asks of anyone is to turn the power off after he has turned it on.(45)What counts as meaningful uploading？ My definition revolves around the concept of “stickiness” - creations and experiences to which others adhere.[A] Of course， it is precisely these superfluous things that define human culture and ultimately what it is to be human. Downloading and consuming culture requires great skills，but failing to move beyond downloading is to strip oneself of a defining constituent of humanity.[B] Applications like ， which allow users to combine pictures， words and other media in creative ways and then share them， have the potential to add stickiness by amusing，entertaining and enlightening others.[C] Not only did they develop such a device but by the turn of the millennium they had also managed to embed it in a worldwide system accessed by billions of people every day.[D] This is because the networked computer has sparked a secret war between downloading and uploading - between passive consumption and active creation - whose outcome will shape our collective future in ways we can only begin to imagine.[E] The challenge the computer mounts to television thus bears little similarity to one format being replaced by another in the manner of record players being replaced by CD players.[F] One reason for the persistence of this pyramid of production is that for the past half-century， much of the world's media culture has been defined by a single medium - television - and television is defined by downloading.[G]The networked computer offers the first chance in 50 years to reverse the flow， to encourage thoughtful downloading and， even more importantly， meaningful uploading.Part CDirections：Read the following text carefully and then translate the underlined segments into Chinese. Your translation should be written clearly on ANSWER SHEET 2. (10 points)Since the days of Aristotle， a search for universal principles has characterized the scientific enterprise. In some ways， this quest for commonalities defines science. Newton's laws of motion and Darwinian evolution each bind a host of different phenomena into a single explicatory frame work.(46)In physics， one approach takes this impulse for unification to its extreme， and seeksa theory of everything-a single generative equation for all we see.It is becoming less clear，however， that such a theory would be a simplification， given the dimensions and universes that it might entail， nonetheless， unification of sorts remains a major goal.This tendency in the natural sciences has long been evident in the social sciences too.(47)Here， Darwinism seems to offer justification for it all humans share common origins it seems reasonable to suppose that cultural diversity could also be traced to more constrained beginnings. Just as the bewildering variety of human courtship rituals might all be considered forms of sexual selection， perhaps the world's languages， music， social and religious customs and even history are governed by universal features. (48)To filter out what is unique from what is shared might enable us to understand how complex cultural behavior arose and what guides it in evolutionary or cognitive terms.That， at least， is the hope. But a comparative study of linguistic traits published online today supplies a reality check. Russell Gray at the University of Auckland and his colleaguesconsider the evolution of grammars in the light of two previous attempts to find universality in language.The most famous of these efforts was initiated by Noam Chomsky， who suggested that humans are born with an innate language-acquisition capacity that dictates a universal grammar. A few generative rules are then sufficient to unfold the entire fundamental structure of a language，which is why children can learn it so quickly.(49)The second， by Joshua Greenberg， takes a more empirical approach to universality identifying traits (particularly in word order) shared by many language which are considered to represent biases that result from cognitive constraintsGray and his colleagues have put them to the test by examining four family trees that between them represent more than 2，000 languages.(50)Chomsky's grammar should show patterns of language change that are independent of the family tree or the pathway tracked through it. Whereas Greenbergian universality predicts strong co-dependencies between particular types ofword-order relations. Neither of these patterns is borne out by the analysis， suggesting that the structures of the languages are lire age-specific and not governed by universalsSection III WritingPart A51. Directions：Some internationals students are coming to your university. Write them an email in the name of the Students' Union to1) extend your welcome and2) provide some suggestions for their campus life here.You should write about 100 words on ANSWER SHEET2.Do not sign your name at the end of the letter. Use “Li Ming” instead.Do not write the address(10 points)Part B52. Directions： write an essay of 160-200 words based on the following drawing. In your essay you should1) describe the drawing briefly2) explain its intended meaning， and3) give your commentsYou should write neatly on ANSWER SHEET2.（20 points）【 - 考研试题】Section I：Use of English1.B2.A3.B4.D5.C6.B7.D8.B9.A 10.B11.A 12.C 13.C 14.D 15.A 16.C 17.A 18.C 19.D 20.DSection II：Reading ComprehensionPart A21.D 22.B 23.A 24.C 25.D26.C 27.D 28.A 29.D 30.A31.A 32.B 33.B 34.D 35.D36.C 37.D 38.B 39.C 40.APart B41.C 42.D 43.A 44.F 45.GPart C2012年研究生入学考试英语一的翻译文章出自美国杂志《Nature》，题目是Universal truths。

全国2012年7月高等教育自学考试_04742通信概论试题及答案

全国2012年7月高等教育自学考试_04742通信概论试题及答案全国2012年7月高等教育自学考试通信概论试题课程代码：04742一、单项选择题(本大题共25小题，每小题1分，共25分)在每小题列出的四个备选项中只有一个是符合题目要求的，请将其代码填写在题后的括号内。

错选、多选或未选均无分。

1.观察眼图时，当“眼睛”张大时，表示码间串扰( )A.没有B.很大C.较大D.小2.在无线传输中，设发射的射频信号波长为λ，要想保证有效的辐射，所需的天线长度一般应大于( )A.λ/2B.λ/3C.λ/4D.λ/53.通信系统中接收设备的功能是放大和( )A.反变换B.压缩C.整形D.整流4.在FM和PM这两种调制过程中，都保持恒定不变的是( )A.载波的频率B.载波的相位C.载波的幅度D.载波的频率和相位5.调频信号的解调就是要产生一个与调频信号的频率呈线性关系的( )A.输入电流B.输出电压C.输入电压D.输出电流6.2DPSK系统是一种实用的数字调相系统，其抗加性白噪声性能与2PSK相比是( )A.好于2PSKB.时好时差C.相同D.差于2PSK/doc/0c12144377.html,ITT为程控数字交换机的模拟用户规定的BORSCHT功能含有( )A.6项功能B.7项功能C.8项功能D.9项功能8.在PCM时分复用一次群中，每一路基带信号占用帧内的一个( )A.时隙B.空间C.位置D.频点9.多普勒扩展引起的衰落与( )A.时间有关B.建筑物高度有关C.距离有关D.空气折射率有关10.跳时码分多址主要是用于( )A.第一代移动通信领域B.军事抗干扰通信领域C.第二代移动通信设备D.第二代半移动通信网络11.通信系统中信源是消息的发源地，其作用是通过传感器把消息转换为( )A.语音信号B.原始电信号C.IP分组D.已调信号12.通信系统中发送设备的功能是将信道匹配于( )A.交换设备B.信源C.传输设备D.信号13.幅度调制中，调制的实质是进行( )A.频谱搬移B.幅度缩小C.幅度放大D.频率扩大14.对于模拟信号，信号带宽与信道带宽的关系是( )A.前者大于后者B.两者相等C.前者小于后者D.前者大于等于后者15.夜晚，在天波传播中电离层反射高频电磁波主要是在( )A.A层B.D层C.E层D.F层16.若抽样速率f S＜2f H，则会产生( )A.叠加失真B.混合失真C.相对失真D.混叠失真17.理想抽样频谱的包络是( )A.一条曲线B.一条水平线C.一条垂线D.一条斜线18.在PCM中，对于语音、图像等随机信号，量化误差是( )A.随机的B.固定的C.预知的D.可计算出来的19.在脉冲编码调制过程中，每增加一位编码位数，平均量化信噪比就提高( )A.9dBB.8dBC.6dBD.3dB20.增量调制可看成是量化电平数为2的( )A.PCMB.DCMC.TCMD.DPCM21.高速率DWDM系统和相干检测系统中必须采用光的( )A.内腔调制B.幅度调制C.频率调制D.外腔调制22.在单模光纤中，只传输m值( )A.大于零的单模B.小于零的单模C.等于零的单模D.必须大于1的单模23.1.55μm光纤的损耗通常只有( )A.0.4dBB.0.2dBC.0.1dBD.0.05dB24.VSAT入向信道上采用的随机分配方式主要是( )A.帧ALOHAB.同步ALOHAC.时隙ALOHAD.时隙ALAHO25.我国的支线或专用网微波通信常用( )A.3、4、5GHz频段B.1、5、6、7GHz频段C.2、7、8GHz频段D.2、7、8、11GHz频段二、填空题(本大题共10小题，每小题1分，共10分)请在每小题的空格中填上正确答案。

2012年1月通信原理自考试卷

2012年1月通信原理自考试卷2012年1月湖北省高等教育自学考试通信原理试卷课程代码：02363一、单项选择题（本大题共20小题，每小题1分，共20分）在每小题列出的四个备选项中只有一个是符合题目要求的，请将其代码填写在题后的括号内。

错选、多选或未选均无分。

1.通信系统中传输的信号，如果是时间信号的连续函数时，称为( )A.时间信号B.模拟信号C.连续信号D.自然信号2.在广义信道中除了传输媒介外，还包含有关的( )A.信号电缆B.光缆C.部件和电路D.编码格式3.计算机网络中常用的五类UTP电缆的带宽( )A.20Mb/sB.40 Mb/sC.100 Mb/sD.200 Mb/s4.理想无失真信号传输条件要求系统带宽是( )A.信号带宽的2倍B.相同与信号带宽C.有限宽D.无限宽5.AM信号中的载波分量体现的是信号源的( )A.最大幅度B.直流分量C.冲击信号D.交流分量6.如果对信号带宽为W的低通信号进行来奎斯特抽样，需要的抽样频率为( )A.0.5WB.1WC.2WD.4W7.PCM编码的8位码中第一位码是用来表示信号的( )A.类型B.大小C.极性D.压扩8.适合通信传输特性的码称为( )A.线路码B.基带码C.单极性码D.双极性码9.2FSK需要的载波数目为( )A.1个B.2个C.4个D.5个10.对时间和带宽都没有限制的多址方式是( )A.CDMAB.FDMAC.SDMAD.ALOHA11.载波同步的频域插入法需要插入的导频是( )A.正弦信号B.余弦信号C.正交信号D.直流信号12.接收端恢复码元序列的同步是( )A.载波同步B.位同步C.帧同步D.信号同步13.差错控制的引入再同步传输率下，信息码元传输速率 ( )A.增加B.降低C.不变D.时增时减14.如采用偶校验，序列11110000和11110010后应分别加入( )A.0,0B.0,1C.1,0D.1,115.如果数据传输发生一个错误，接收方校验和与数据的和应该是( )A.全0B. 全1C.不全为0D. 数据的反16.SSB 和VSB 信号通过相干调制器后输出信噪比是传输信噪比的( )A.不变B.2倍C.3倍D.4倍17.以下四种数字调制方式中判决电平最难设置的是( )A.ASKB.FSKC.PSKD.DPSK18.为了使接收信号不失真，需要增大滤波器带宽，同时对输入噪声功率的影响是() A.减小 B.不变C.增大D.不相关19.数据帧传输速率的控制被叫做( )A.码元速率控制B. 交换控制C.线路规则D. 流程控制20.计算机通信网中不同功能层之间的通信规约称为 ( )A.通道B.接口C.协议D.约定二、填空题（本大题共5小题，每小题2分，共10分）请在每小题的空格中填上正确答案。

2012级研究生考试《电网络分析》试卷

g
2

图2
二、（20 分）图 2 为以节点 3 为公共端的二端口网络，用不定导纳矩阵分析法求该二端口网络的短路导纳矩阵 Ysc s 。
三（ 20 分）图 3 所示线性非常态网络中，已知 R1 R2 0.5 ， L1 L2 0.5 H ，
学号
C1 C2 0.5 F ， iS t 5cos 2t A， uS t 10cos 2t V。（1）请选择一个规范树，列出
该网络的以电容 C1 的电压 uC1 和电感 L2 的电流 iL 2 为状态变量的状态方程（矩阵形式）。（2）写出以 iR1 、 iL1 和 uC 2 作为网络输出变量的输出方程（矩阵形式）。
姓名
《电网络分析》试卷第 1 页共 2 页
iL 2
iL1
L2
L1
C1

iR1
R1
R2
iS t

uC 2
C2
uC1

uS t
图3 四、（20 分）已知某二端口网络的开路阻抗矩阵 Z oc ，用信号流图分析法求该网络的出传输参数矩阵 T 。其中：
U1 z11 z12 I1 I1 U z z I Z 0 c I 2 21 22 2 2
………………………………………密………………………………………………封………………………………………线…………………………………… ………………………………
华南理工大学研究生课程考试
《电网络分析》试卷
考试时间： 2013 年 1 月 16 日上午 9 时至 11 时
任课教师
注意事项：1. 请将答案写在答题纸上，请考生考前将密封线内各项信息填写在答题纸上； 2. 考试形式：闭卷（√）开卷（）； 3. 本试卷共六大题，满分 100 分，考试时间为 150 分钟。

计算机网络与通信期末考试_毕业生

四川大学期考试试题（A）
（200 ——200 学年第 2 学期）
课程号：30306230课序号：0 3课程名称：计算机网络与通信任课教师：等成绩：适用专业年级：学生人数：印题份数：学号：姓名：
2 题间不留空，一般应题卷分开教务处试题编号：
3务必用A4纸打印
注：1试题字迹务必清晰，书写工整。

本题 4 页，本页为第 2 页
2 题间不留空，一般应题卷分开教务处试题编号：
3务必用A4纸打印
注：1试题字迹务必清晰，书写工整。

本题 4 页，本页为第 3 页
2 题间不留空，一般应题卷分开教务处试题编号：
3务必用A4纸打印
2 题间不留空，一般应题卷分开教务处试题编号：3务必用A4纸打印。

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THE UNIVERSITY OF MELBOURNESemester II AssessmentNovember,2012Department of Electrical and Electronic EngineeringELEN90061COMMUNICATION NETWORKSTime allowed:180minutesReading time:15minutesThis paper has8pagesAuthorised materials:Non-programmable electronic calculators are permitted in accordance with the rules of the Dept.of Electrical and Electronic Engineering.Drawing instruments are permitted.Instructions to invigilators:NONE.Instructions to students:Students should attempt ALL QUESTIONS.The total marks of the examination paper is100.You are free to choose the order in which the questions are answered.All the script books will be collected at the end of the three hours examination period.Lodging of paper with the Baillieu Library:Paper should be reproduced and lodged with the Baillieu Library.Some useful formulasM/M/1:¯N q=ρ2 1−ρM/M/m:¯N q=(mρ)mρm!(1−ρ)2p0p0= m−1k=0(mρ)kk!+(mρ)mm!11−ρ−1ρ=λmµM/G/1:W=λX2 2(1−ρ)Question1(2+2+2+3+2+2+2=15marks)(a)(i)Brieﬂy explain how the Poisson distribution and the Poisson process are related.(ii)Consider an M/M/1queue with utilization factorρ<1.In an exam a student has correctly computed the expected number in system¯N.The student then computes the expected number in queue¯N q using the relation¯N q=¯N−1.What is wrong with the student’s reasoning?(iii)In the study of queueing networks,what is the diﬀerence between an open queueing network and a closed queueing network?(b)(i)Consider an M/M/3queue with arrival rateλ=8per second,and service rate per server ofµ=3per pute the average number in system¯N and average time spent in system T.(ii)Next consider an M/M/1system withλ=8per second andµ=9per second. Compute¯N and T.(iii)Now consider a system consisting of three separate M/M/1queues each withµ=3 per second,with arriving customers(of rateλ=8per second)randomly allocated to each queue with probability1/pute¯N and T.(iv)Compare the values of¯N and T for the systems in(b)(i)-(iii).Question2(3+1+6+2+2+2+2+1+1=20marks)(a)Consider an M/M/2/4system with arrival rateλand service rateµper server. (i)Draw the state transition rate diagram of the system.(ii)What requirements are there onλandµfor stability?(iii)Let p i be the steady state probability ofﬁnding i customers in the queueing system. Write down a set of detailed balance equations,and then use them to show thatp0=11+ρ+12ρ2+14ρ3+18ρ4whereρ=λ/µ.(b)A small company has4telephone lines and2receptionists.If both receptionists are busy and the four lines are not all occupied,then an incoming call is put on hold.If all four lines are busy,then an incoming call is blocked.Incoming calls follow a Poisson process with rate10per hour.The length of each call is exponentially distributed with mean5minutes.(i)Explain how an M/M/2/4system can be used to model the above situation.(ii)Compute the steady state probabilities p i for i=0, (4)(iii)What is the fraction of time where the system has customers on hold?(iv)What is the probability that an incoming call is put on hold?(v)What is the probability that an incoming call is blocked?(vi)What is the probability that both receptionists are free?Question3(5+5+3+2=15marks)(a)Consider an M/G/1system with Poisson arrivals of rateλ,and the service time consists of aﬁxed time d plus an exponentially distributed time with mean1/µ.Derive an expression for the average waiting time W in terms ofλ,d,andµ.(Recall that an exponential random variable of mean1/µhas variance1/µ2.)(b)Consider a system where customers arrive according to a Poisson process of rate6 per hour.20%of the customers require aﬁxed service time of8minutes,while80% of the customers require an exponentially distributed service time of mean7minutes. Customers are served in the order in which they arrive.Show that the average delay(i.e. average system time T)in this M/G/1queue is around23.49minutes.(c)Brieﬂy describe the nonpreemptive priority and preemptive resume priority queueing schemes.(d)In(b),suppose the customers withﬁxed service times and the customers with expo-nentially distributed service times are put into diﬀerent priority ing nonpre-emptive priority queueing,how should the priority classes be ordered in order to minimize the average delay(averaged over both priority classes)?Give a reason for your answer, by quoting a suitable result from the lectures.Question4(3+8+3+2=16marks)(a)User Datagram Protocol(i)UDP belongs to what layer in the Internet’s protocol architecture?What is the key, essential service that the UDP protocol provides?Give an example of a service that is highly suitable for UDP’s layer that UDP does not itself provide.(ii)What kinds of applications typically use UDP,and why?What happens if a UDP segment is lost?(iii)Clearly and completely describe how UDP checksums are calculated.(b)Transport Control Protocol(i)TCP belongs to what layer in the Internet’s protocol architecture?What is the key, essential service that the TCP protocol provides?Give an example of a service that is highly suitable for TCP’s layer that TCP does not itself provide.(ii)Explain the slow start and congestion avoidance phases of TCP.Include in your description of the aims of the two phases,and how the protocol transitions from one to the other.(iii)Two of the functions of TCP areﬂow control and congestion control.Explain succinctly but clearly the key diﬀerences between these.Include in your description the aims of these functions,the key state variables used to support them,and the feedback to the client side that is needed and how it is accomplished(assume TCP Reno,the loss oriented TCP variant focussed on in lectures).(c)Internet Protocol(i)The Internet Protocol is one of the three main components comprising the network layer of the Internet.What are the other two?(ii)What is IP fragmentation,and why is it necessary?(iii)Consider a company who has been allocated the IP address space:210.35.42.0/22. How many network interfaces can be allocated a unique IP address?If these aren’t suﬃcient,what are the two options available to the company to connect more interfaces?(d)Link LayerA Cyclic Redundancy Check(CRC)code of a data word D is deﬁned by D∗2r⊕R=nG where⊕represents the XOR operation and R is a carefully chosen remainder.Assume that the remainder R transmitted over the network is3bits long.What is the value of R if the data to be transmitted D equals110001and the generator is G=1011?Show all working.Question5(12+6=18marks)(a)TCP dynamicsConsider two hosts A and B communicating over a single Ethernet link400metres long. The Ethernet link has a capacity of10Mbps.The RTT is supposed constant and equals 20milliseconds.The two hosts are communicating using the Renoﬂavour of the TCP protocol,which halves its congestion window if triple duplicate acknowledgements are detected.(ignore the window inﬂation by3MSS incorporated into fast recovery).The maximum segment size of the TCP connection is assumed to be200bytes.A andB initial sequence numbers are respectively400and1100and both hosts have an initial congestion avoidance threshold set to12MSS.In the following we assume A is transmitting a web page of size1500bytes to host B, beginning from the start of the three way handshake.Assume that data is sent as soon as possible.(i)Considering connection establishment,slow start and congestion avoidance phases, but no losses or delayed ACKs,what would A sequence number be just after four RTTs? (ii)What is the size of A’s congestion window just after four RTTs?(iii)Without any packet loss,when would Aﬁrst enter its congestion avoidance phase? (iv)What would be the size of A’s congestion window after detecting a triple duplicate ACK after eight RTT?(v)What would be the size of A’s congestion window if its last unacknowledged sequence number times out before nine RTTs?(vi)Without losses or triple duplicate ACKs,what is the average throughput of this connection over theﬁrst six RTTs?(b)PerformanceRemember that the Ethernet header is16bytes long and that the IP and TCP headers are both20bytes long.(i)Assuming the speed of the electrical signal in the Ethernet link is2×108km/s,what is the propagation delay between A and B?(ii)Without slow start or congestion avoidance,how much time would it take for A to transmit the entire web page to B if sending all Ethernet frames back to back?Justify your answer.(iii)Using the same assumptions as in(ii),what is throughput seen by the transport layer?What is the application layer level goodput?Question6(12+4=16marks)(a)Dijkstra Routing algorithmUse the network described inﬁgure1and Dijkstra’s routing algorithm pseudo-code below to compute the forwarding table of node B.Show all steps.Figure1:Network Graph with link costs.1I n i t i a l i z a t i o n:2N’={u}3for a l l nodes v4i f v a d j a c e n t to u then5D(v)=c(u,v)6e l s e7D(v)=i n f i n i t y89Loop10f i n d w not in N’such t h a t D(w)i s a minimum11add w to N’12update D(v)for a l l v a d j a c e n t to w and not in N’:13D(v)=min(D(v),D(w)+c(w,v))14until a l l nodes in N’(b)Hierarchical RoutingAnswer with True or False.(i)RIP and OSPF are both intra-AS routing protocols(ii)OSPF is a distance-vector based protocol.(iii)BGP comprises eBGP,an inter-AS protocol connecting routers from diﬀerent ASes, and iBGP,an intra-AS protocol connecting routers within a single AS.(iv)The NEXT-HOP BGP attribute gives the IP address of the next interface within the current AS along the path to the gateway router linking the current AS to the AS which has advertised the route in question.End of Examination Paper。