单选集
单选集
Electrical conductivity（）
A:电导率 B:载流子数 C:载流子迁移率
Passage One
The making of glass is a very old industry--at least 4,500 years old. Glass has many extraordinary qualities and it is frequently being used in new ways.
One of the most interesting new uses for glass is in telephone communication. Scientists have developed glass fibers as thin as human hair, which are designed to can-y light signals. When the light reaches the other end, it is first changed into electrical signals, which are in turn converted into sound messages.
Called light wave communication, the new system was used successfully in an experiment in Chicago in 1997. During the experiment, two glass fibers were able to carry 672 conversations at the same time. The lightwave cable, containing 144 glass fibers, has the capacity to carry 50,000 conversations at the same time.
The lightwave communication system has two important advantages. First, the glass fiber cables are smaller and weigh less than copper. Second, they cost less.
Perhaps it can be said that telephone communication has entered the age of light.
A:electrical signals must first be changed' into light signals and then into sound B:the light signals have to be changed directly into sound C:light must first be changed into electrical signals and then into sound D:neither the light nor the electrical signals have to be changed in any way
Passage One
The making of glass is a very old industry--at least 4,500 years old. Glass has many extraordinary qualities and it is frequently being used in new ways.
One of the most interesting new uses for glass is in telephone communication. Scientists have developed glass fibers as thin as human hair, which are designed to can-y light signals. When the light reaches the other end, it is first changed into electrical signals, which are in turn converted into sound messages.
Called light wave communication, the new system was used successfully in an experiment in Chicago in 1997. During the experiment, two glass fibers were able to carry 672 conversations at the same time. The lightwave cable, containing 144 glass fibers, has the capacity to carry 50,000 conversations at the same time.
The lightwave communication system has two important advantages. First, the glass fiber cables are smaller and weigh less than copper. Second, they cost less.
Perhaps it can be said that telephone communication has entered the age of light.
A:sound signals B:light signals C:electrical signals D:any signals
A:the electricity thief who steals electricity at one’s home. B:electricity to power electrical appliances even when they are turned off. C:electricity to power electrical appliances when they are turned on. D:electricity waiting to be used when electrical appliances are turned of
{{B}}第三篇{{/B}}
| {{B}}? ? ? ? ? ?
?Controlling Robots with the Mind{{/B}} ? ?Belle, our tiny monkey, was seated in her special chair inside a chamber at our Duke University lab. Her right hand grasped a joystick (操纵杆) as she watched a horizontal series of lights on a display panel. She knew that if a light suddenly shone and she moved the joystick left or right to correspond to its position, she would be sent a drop of fruit juice into her mouth. ? ?Belle wore a cap glued to her head. Under it were four plastic connectors, which fed arrays of microwires - each wire finer than the finest sewing thread- into different regions of Belle’s motor cortex (脑皮层), the brain tissue that plans movements and sends instructions. Each of the 100 microwires lay beside a single motor neuron (神经元). When a neuron produced an electrical discharge, the adjacent microwire would capture the currant and send it up through a small wiring bundle that ran from Belle’s cap to a box of electronics on a table next to the booth. The box, in turn, was linked to two computers, one next door and the other half a country away. ? ?After months of hard work, we were about to test the idea that we could reliably translate the raw electrical activity in a living being’s brain - Belle’s mere thoughts - into signals that could direct the actions of a robot. We had assembled a multijointed robot arm in this room, away from Belle’s view, which she would control for the first time. As soon as Belle’s brain sensed a lit spot on the panel, electronics in the box running two real-time mathematical models would rapidly analyze the tiny action potentials produced by her brain cells. Our lab computer would convert the electrical patterns into instructions that would direct the robot arm. Six hundred miles north, in Cambridge, Mass, a different computer would produce the same actions in another robot arm built by Mandayam A. Srinivasan. If we had done everything correctly, the two robot arms would behave as Belle’s arm did, at exactly the same time. ? ?Finally the moment came. We randomly switched on lights in front of Belle, and she immediately moved her joystick back and forth to correspond to them. Our robot arm moved similarly to Belle’s real arm. So did Srinivasan’s. Belle and the robots moved in synchrony (同步), like dancers choreographed (设计舞蹈动作) by the electrical impulses sparking in Belle’s mind. ? ?In the two years since that day, our labs and several others have advanced neuroscience, computer science and microelectronics to create ways for rats, monkeys and eventually humans to control mechanical and electronic machines purely by "thinking through," or imagining the motions. Our immediate goal is to help a person who has been unable to move by a neurological (神经的) disorder or spinal cord (脊髓) injury, but whose motor cortex is spared, to operate a wheelchair or a robotic limb. |
A:It was directed by signals converted from the electrical activity in Belle’s brain. B:It converted the electrical patterns into instructions for the other robot. C:It was six hundred miles away from where Belle was. D:It could perform the same function as Belle did.
Compared to common electrical conductors, superconductors
A:have little or no electrical resistance. B:can be used for a long time. C:are not energy-efficient. D:can be made easily.
第二篇 Superconductor Ceramic(陶瓷) An underground revolution begins this winter．with the flip(轻击)of a switch，30，000 homes in one part of Detroit will soon become the first in the country to receive electricity transmitted by ice．cold high．performance cables．Other American cities are expected to follow Detroit’s example in the years ahead．which could conserve enormous amounts of power． The new electrical cables at the Frisbie power station in Detroit are revolutionary because they are made of superconductors．A superconductor is a material that transmits electricity with little or no resistance．Resistance is the degree to which a substance resists electric current．All common electrical conductors have a certain amount of electrical resistance．They convert at least some of the electrical energy passing through them into waste heat．Superconductors don’t?No one understands how superconductivity works．It just does． Making superconductors isn’t easy．A superconductor material has to be cooled to an extremely low temperature to 10se its resistance．The first superconductors，made more than 50 years ago，had to be cooled to-263 degrees Celsius before they lost their resistance．Newer superconducting materials 10se their resistance at-143 degrees Celsius． The superconductors cable installed at the Frisbie station is made of a ceramic material that contains copper．oxygen．bismuth(铋)。strontium(锶)．and calcium(钙)．A ceramic is a hard．strong compound made from clay or minerals．The superconducting ceramic has been fashioned into a tape that is wrapped lengthwise around a long tube filled with liquid nitrogen．Liquid nitrogen is supercold and lowers the temperature of the ceramic tape to the point where it conveys electricity with zero resistance． The United States loses an enormous amount of electricity each year to resistance．Because cooled superconductors have no resistance．they waste much less power．0ther cities are watching the Frisbie experiment in the hope that they might switch to superconducting cable and conserve power．too． Compared to common electrical conductors，superconductors
A:have little or no electrical resistance． B:Can be used for along time． C:are not energy-efficient． D:can be made easily．
Don’t fail to get medical attention for a jolt of electricity (for instance, from lightning, a power line, or home electrical cords), even if no damage is evident. An electrical bum can cause invisible (and serious) injury deeper inside the body. More than 500 Americans die every year from electrical burns.
Do go to the ER immediately.
Be sure to get medical attention for electrical burns even if there is no obvious damage because.
A:there might be an invisible injury deeper inside the body. B:many Americans die each year from electrical burns. C:lightning is too much for a person to endure. D:electrical bums will always lead to serious injury inside the body.
Don’t fail to get medical attention for a jolt of electricity (for instance, from lightning, a power line, or home electrical cords), even if no damage is evident. An electrical bum can cause invisible (and serious) injury deeper inside the body. More than 500 Americans die every year from electrical burns.
Do go to the ER immediately.
Be sure to get medical attention for electrical burns even if there is no obvious damage because.
A:there might be an invisible injury deeper inside the body. B:many Americans die each year from electrical burns. C:lightning is too much for a person to endure. D:electrical bums will always lead to serious injury inside the body.
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