请说出什么是反馈控制系统,开环控制系统和闭环控制系统各有什么优缺点?
反馈控制系统即闭环控制系统,在一个控制系统,将系统的输出量通过某测量机构对其进行实时测量,并将该测量值与输入量进行比较,形成一个反馈通道,从而形成一个封闭的控制系统;开环系统优点:结构简单,缺点:控制的精度较差;闭环控制系统优点:控制精度高,缺点:结构复杂、设计分析麻烦,制造成本高
暂无解析
下图是三种典型多址方式的示意图, 请标出三个图分别是哪种多址方式, 并且对于每种多址 方式举出一个典型的网络类型。
Locate a contract
If you are willing to buy the whole lot once and for all ,we can grant you a discount of 8% on the price.
所有国家都在争夺供应不足的能源。
我们认为你的还盘不合理,因为这种材料的价格目前呈上升趋势We should be please to allow you the requested discount of 5% ,if you will to raise your order to 50,000 pieces.
Selling Digital Music without Copy-protection Makes Sense
A. It was uncharacteristically low-key for the industry’s greatest showman. But the essay published this week by Steve Jobs, the boss of Apple, on his firm’s website under the unassuming title “Thoughts on Music” has nonetheless provoked a vigorous debate about the future of digital music, which Apple dominates with its iPod music-player and iTunes music-store. At issue is “digital rights management” (DRM)—the technology guarding downloaded music against theft. Since there is no common standard for DRM, it also has the side-effect that songs purchased for one type of music-player may not work on another. Apple’s DRM system, called FairPlay, is the most widespread. So it came as a surprise when Mr. Jobs called for DRM for digital music to be abolished.
B. This is a change of tack for Apple. It has come under fire from European regulators who claim that its refusal to license FairPlay to other firms has “locked in” customers. Since music from the iTunes store cannot be played on non-iPod music-players (at least not without a lot of fiddling), any iTunes buyer will be deterred from switching to a device made by a rival firm, such as Sony or Microsoft. When French lawmakers drafted a bill last year compelling Apple to open up FairPlay to rivals, the company warned of “state-sponsored piracy”. Only DRM, it implied, could keep the pirates at bay.
C. This week Mr. Jobs gave another explanation for his former defence of DRM: the record companies made him do it. They would make their music available to the iTunes store only if Apple agreed to protect it using DRM. They can still withdraw their catalogues if the DRM system is compromised. Apple cannot license FairPlay to others, says Mr Jobs, because it would depend on them to produce security fixes promptly. All DRM does is restrict consumer choice and provide a barrier to entry, says Mr Jobs; without it there would be far more stores and players, and far more innovation. So, he suggests, why not do away with DRM and sell music unprotected? “This is clearly the best alternative for consumers,” he declares, “and Apple would embrace it in a heartbeat.”
D. Why the sudden change of heart? Mr Jobs seems chiefly concerned with getting Europe’s regulators off his back. Rather than complaining to Apple about its use of DRM, he suggests, “those unhappy with the current situation should redirect their energies towards persuading the music companies to sell their music DRM-free.” Two and a half of the four big record companies, he helpfully points out, are European-owned. Mr Jobs also hopes to paint himself as a consumer champion. Apple resents accusations that it has become the Microsoft of digital music.
E. Apple can afford to embrace open competition in music players and online stores. Consumers would gravitate to the best player and the best store, and at the moment that still means Apple’s. Mr Jobs is evidently unfazed by rivals to the iPod. Since only 3% of the music in a typical iTunes library is protected, most of it can already be used on other players today, he notes. (And even the protected tracks can be burned onto a CD and then re-ripped.) So Apple’s dominance evidently depends far more on branding and ease of use than DRM-related “lock in”.
F. The music giants are trying DRM-free downloads. Lots of smaller labels already sell music that way. Having seen which way the wind is blowing, Mr Jobs now wants to be seen not as DRM’s defender, but as a consumer champion who helped in its downfall. Wouldn’t it lead to a surge in piracy? No, because most music is still sold unprotected on CDs, people wishing to steal music already can do so. Indeed, scrapping DRM would probably increase online-music sales by reducing confusion and incompatibility. With the leading online store, Apple would benefit most. Mr Jobs’s argument, in short, is transparently self-serving. It also happens to be right.
Notes to Reading Passage 1
1. low-key:
抑制的,受约束的,屈服的
2. showman:
开展览会的人, 出风头的人物
3. unassuming:
谦逊的, 不夸耀的, 不装腔作势的
4. iPod:
(苹果公司出产的)音乐播放器
5. iTunes store:
(苹果公司出产的)在线音乐商店
6. get off person’s back:
不再找某人的麻烦,摆脱某人的纠缠
7. gravitate:
受吸引,倾向于
8. unfazed:
不再担忧,不被打扰
Questions 1-7
Do the following statemets reflect the claims of the writer in Reading Passage 1?
Write your answer in Boxes 1-7 on your answer sheet.
TRUE if the statement reflets the claims of the writer
FALSE if the statement contradicts the claims of the writer
NOT GIVEN if it is impossbile to say what the writer thinks about this
1. Apple enjoys a controlling position in digital music market with its iPod music-player and iTunes music-store.
2. DRM is a government decree issued with a purpose to protect downloaded music from theft by consumers.
3. Lack of standardization in DRM makes songs bought for one kind of music player may not function on another.
4. Apple has been criticized by European regulators since it has refused to grant a license FairPlay to other firms.
5. All music can be easily played on non-iPod music devices from Sony or Microsoft without too much fiddling.
6. Apple depends far more on DRM rather than branding for its dominance of the digital music devices.
7. If DRM was cancelled, Sony would certainly dominate the international digital music market.
Questions 8-10
Choose the appropriate letters A-D and write them in boxes 8-10 on your answe sheet.
8. Which of the following statements about Mr. Jobs’ idea of DRM is NOT TRUE?
A. DRM places restrictions on consumer’ choice of digital music products available.
B. DRM comples iTunes buyers to switch to a device made by Sony or Microsoft.
C. DRM constitutes a barrier for potential consumers to enter digital music markets.
D. DRM hinders development of more stores and players and technical innovation.
9. The word “unfazed” in line 3 of paragraph E, means___________.
A. refused
B. welcomed
C. not bothered
D. not well received
10. Which of the following statements is TRUE if DRM was scapped?
A. Sony would gain the most profit.
B. More customers would be “locked in”.
C. A sudden increase in piracy would occur.
D. Online-music sales would probably decrease.
Questions 11-14
Complete the notes below.
Choose NO MORE THAN THREE WORDS from Reading Passage 1 for each answer.
Write your answers in boxes 11-14 on your answer sheet.
Mr. Steve Jobs, the boss of Apple, explains the reason why he used to defend DRM, saying that the company was forced to do so: the record companies would make their music accessible to …11...only if they agreed to protect it using DRM; they can still…12…if the DRM system is compromised. He also provides the reason why Apple did not license FairPlay to others: the company relies on them to …13….But now he changes his mind with a possible expectation that Europe’s regulators would not trouble him any more in the future. He proposes that those who are unsatisfactory with the current situation in digital music market should …14… towards persuade the music companies to sell their music DRM-free.
Payment of the purchase is to be effected by an irrevocable letter of credit in our favour, payable by draft at sight in pounds sterling in London.
We are introducing ourselves as one of the leading exporters of the same line of business.
Nutritious refreshment
题目:通过自荐信建立商务关系。