题目内容
But weight is not the only factor. The smaller the computer the faster it can work. The signals go to and fro at a very high but almost constant speed. So if one can scale down all dimensions to, let us say, one tenth, the average lengths of the current-paths will be reduced to one tenth. So, very roughly speaking, scaling down of all linear dimensions in the ratio of one to ten also gives a valuable bonus: the speed of operation is scaled up 10 times. Other techniques allow even further speed increases.
This increase of operation is a real advantage. There are some applications in which computers could be used which require very fast response times. Many of these are military, of course; but military applications also have applications in engineering sooner or later. For example, automatic blind landing of aircraft requires continuous computer calculations which result in control of the aircraft flight. The more immediate the responses are, the more stable that control can be.
Another advantage is that less power is required to run the computer. In space vehicles and satellites this is an important matter; but even in a trial application we need not waste power. Sometimes a computer takes so much power that cooling systems which require still more power have to be installed to keep the computer from getting too hot, which would increase the risk of faults developing. So a computer which does not need to be cooled saves power on two counts.
Another advantage is reliability. Mini-computers have been made possible by the development of integrated circuits. Instead of soldering bits of wire to join separate components such as resistors and capacitors sometimes in the most intricate networks, designers can now produce many connected circuits in one unit which involves no soldering and therefore no risk of broken joints at all.
Which of the following is NOT one of the advantages of mini-computers？
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Part A
Directions: Read the following four texts. Answer the questions below each text by choosing A, B, C or D. (40 points)
More than a hundred years ago, before the Civil War, a crew of cowboys stood outside a large horse corral. With them was their boss Bradford Grimes, a cattleman, who owned a large South Texas ranch near the Gulf of Mexico.
Just then, Mrs. Grimes, the cattleman's wife, came to the ranch house door and cried out, "Bradford! Bradford! Those Blacks are worth a thousand dollars apiece. One might get killed". The cowboys laughed, but they knew she was telling the truth. For they were all Black slaves. Bradford Grimes was their owner.
Most of the first Black cowboys were slaves, brought by their masters from the old South. On the plantations in the South, the slaves cut cotton. On the ranches in Texas they had to learn a new trade—breaking horses and handling long-horns. Some were taught by Mexican vaqueros, some by Indiana who knew the ways of horses and cattle.
Grimes was only one of hundreds of slave-owning ranchers who ran cattle in Texas. The ranchers had brought their families and slaves from Mississippi, Georgia, and other southern states. They came on horseback, on foot, and in wagons.
Some ranchers settled near the Mexican border, but there they found that it was too easy for their slaves to escape. Even slaves as far north as Austin, the capital of Texas, came to think of Mexico as the Promised Land. As early as 1845, the year that Texas became a state, a Texas newspaper reported the escape of twenty-five Blacks. "They were mounted on some of the best horses that could be found, "the story said, "and several of them were well armed". Thousands of other Black slaves escaped in the same way.
All-Black cattle crews were common throughout central and eastern Texas. There were even a few free Blacks who owned ranches before the Civil War. Aaron Ashworth was one of them, and he owned 2,500 cattle, as well as some slaves of his own. He employed a White schoolmaster to tutor his children. Black cowboys helped to tame and settle a wild country.
Most of the first Black slaves that became cowboys ______.
上市公司T日增发新股可流通部分上市交易，当日股票不设涨跌幅限制。()
Bluetooth
When you use computers, entertainment systems or telephones, the various pieces and parts of the systems make up a community of electronic devices. These devices communicate with each other using a variety of wires, cables, radio signals and infrared light(红外线) beams, and an even greater variety of connectors and plugs.
The art of connecting things is becoming more and more complex every day. And Bluetooth has now become a new popular method of connecting devices that can streamline the process. A Bluetooth connection is wireless and automatic, and it takes small-area networking to the next level by removing the need for user intervention and keeping transmission power extremely low to save battery power.
Bluetooth Operation
Bluetooth networking transmits data via 10w-power radio waves. It communicates on a frequency of 2.45 gigahertz(千兆赫)(actually between 2.402 GHz and 2.480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices(ISM).
A number of devices that you may already use fake advantage of this same radio-frequency band. Baby monitors(微型监视器), garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band.
One of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters(32 feet), cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The Walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms.
Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter(32-foot) radius; you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum.(扩展频谱) frequency that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use. 79 individual, randomly chosen frequencies within a designated range, changing from one-to another on a regular basis. In the case of Bluetooth. the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it's unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second.
Piconets(个人域网络)
Let's say you have a typical modern living room with the typical modern Stuff inside. There's an entertainment system with a stereo, a DVD player, a satellite TV receiver and a television; there's also a cordless telephone and a-personal computer. Each of these systems uses Bluetooth, and each forms its own piconet to talk between the main unit and peripheral(外围设备).
The cordless telephone has one Bluetooth transmitter in the base and another in the handset. The manufacturer has programmed each unit with an address that falls into a range of addresses it has established for a particular type of device. When the base is first turned on, it sends radio signals asking for a response from any units with an address in a particular range. Since the handset has an address in the range, it responds, and a tiny network is formed. Now, even if one of these device
企业要具有较强的偿还到期债务的能力，其现金到期债务比至少应大于1。（)A．正确B．错误C．AD．现金到期企业要具有较强的偿还到期债务的能力，其现金到期债务比至少应大于1。 ()
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