Вопрос № 1077988 - Английский язык

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Radio scanner
1. The air around you is bursting with radio waves. You know that you can flip on the AM/FM radio in your car and receive dozens of stations. You can flip on a CB radio and receive 40 more. You can flip on a TV and receive numerous broadcast channels. Cell phones can send and receive hundreds of frequencies. And this is just the tip of the radio spectrum iceberg. Literally tens of thousands of other radio broadcasts and conversations are zipping past you – police officers, firefighters, ambulance drivers, paramedics, sanitation workers, space shuttle astronauts, race car drivers, and even babies with their monitors are transmitting radio waves all around you at this very moment.
2. To tap into this ocean of electromagnetic dialogue and hear what all of these people are talking about, all you need is a scanner. A scanner is basically a radio receiver capable of receiving multiple signals. Generally, scanners pick up signals in the VHF to UHF range. Radio scanners are very portable and affordable. Scanners typically operate in three modes: scan, manual scan, and search.
3. In scan mode the receiver constantly changes frequencies in a set order looking for a frequency that has someone transmitting. The frequencies can be preprogrammed on some models or manually set on practically all models. In manual scan mode, the user taps a button or turns a dial to manually step through preprogrammed frequencies one frequency at a time. In search mode, the receiver is set to search between two sets of frequencies within a given band. This mode is useful when a user does not know a frequency, but wants to know what frequencies are active in a given area. If the frequency the scanner stops at during a search is interesting, the user can store that frequency in the radio scanner and use it in scan mode.
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What is the difference between scan mode and manual scan mode receivers?

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Radio scanner
1. The air around you is bursting with radio waves. You know that you can flip on the AM/FM radio in your car and receive dozens of stations. You can flip on a CB radio and receive 40 more. You can flip on a TV and receive numerous broadcast channels. Cell phones can send and receive hundreds of frequencies. And this is just the tip of the radio spectrum iceberg. Literally tens of thousands of other radio broadcasts and conversations are zipping past you – police officers, firefighters, ambulance drivers, paramedics, sanitation workers, space shuttle astronauts, race car drivers, and even babies with their monitors are transmitting radio waves all around you at this very moment.
2. To tap into this ocean of electromagnetic dialogue and hear what all of these people are talking about, all you need is a scanner. A scanner is basically a radio receiver capable of receiving multiple signals. Generally, scanners pick up signals in the VHF to UHF range. Radio scanners are very portable and affordable. Scanners typically operate in three modes: scan, manual scan, and search.
3. In scan mode the receiver constantly changes frequencies in a set order looking for a frequency that has someone transmitting. The frequencies can be preprogrammed on some models or manually set on practically all models. In manual scan mode, the user taps a button or turns a dial to manually step through preprogrammed frequencies one frequency at a time. In search mode, the receiver is set to search between two sets of frequencies within a given band. This mode is useful when a user does not know a frequency, but wants to know what frequencies are active in a given area. If the frequency the scanner stops at during a search is interesting, the user can store that frequency in the radio scanner and use it in scan mode.
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Lidar
1. These days, more and more police departments are using laser speed detectors. The basic element in a laser speed gun, also called a lidar gun (for light detection and ranging), is concentrated light. The lidar gun clocks the time it takes a burst of infrared light to reach a car, bounce off and return back to the starting point. By multiplying this time by the speed of light, the lidar system determines how far away the object is.
2. Unlike traditional police radar, lidar does not measure change in wave frequency. Instead, it sends out many infrared laser bursts in a short period of time to collect multiple distances. By comparing these different distance samples, the system can calculate how fast the car is moving. These guns may take several hundred samples in less than half a second, so they are extremely accurate. As it turns out, conventional radar is relatively easy to detect. The simplest radar detector is just a basic radio receiver, something like the one you use to pick up FM and AM radio stations.
3. The air is full of radio signals – they’re used for everything from television broadcasts to garage door openers – so for a receiver to be at all useful, it must pick up only signals in a certain range. The receiver in a radio is designed to pick up signals in the AM and FM frequency spectrum, whereas the receiver in a radar detector is tuned to the frequency range used by police radar guns. Periodically, the frequency range used by the police is expanded, and speedsters everywhere have to invest in new detection equipment.
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Natural and synthetic polymers
1.With names such as polytetrafluoroethyline and polyethyleneteraphthalate, it is not surpprising that polymers are usually called by by their more common name, plastic. But what, exactly, is a polymer or a plastic? Polymers are compounds made up of several elements that are chemically bound. Most compounds consist of large numbers of tiny molecules, which each contain just a few atoms. For example, a water molecule – H2O – contains two hydrogen atoms and one oxygen atom. But the molecules of polymers contain huge numbers of atoms, joined together in long chains.
2. Rubber, thanks to its many uses from rubber bands to car tyres, is one of the best-known polymers. It comes from latex, a natural liquid which comes from rubber trees. Rubber is therefore a natural polymer. However, most of the polymers used in industry are not natural, but synthetic. The term «plastic» is generally used to refer to synthetic polymers - in other words, those that are manmade.
3. Synthetic polymers can be divided into two main categories. Thermoplastics can be melted by heat, and formed in shaped containers called moulds. Thermosetting plastics, also called thermosets, can be heated and moulded like thermoplastics. They may also be mixed from cold ingredients. However; during cooling or mixing, a chemical reaction occurs, causing thermosets to cure. This means they set permanently, and cannot be moulded again. If a thermoset is heated after curing, it will burn.
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Engineers of the Imagination
1. U.S. physicist Richard Feynman first suggested the idea for nanomachines in 1959. He had given a lecture on the possibility of building devices atom by atom. Eric Drexler, another physicist, developed the idea. Beginning in 1977, Drexler wrote a series of books about nanoengineering. It was a great idea, but no one knew how to move individual atoms and put them in place. Engineers have not yet created practical nanomachines. They have developed micromachines. They have microscopic gears, wheels, and axles. These machines are no larger than a speck of dust.
2. Engineers at the U.S. Department of Energy’s Sandia National Laboratories in Albuquerque, New Mexico, have created a micromachine that has gears. Each one is smaller in diameter than a human hair. Making a tiny engine powerful enough to run one of these machines is a much more complicated problem. In 1988 engineers at the University of California – Berkeley created the world’s first micromotor. It was just 100 microns (100,000 nanometers) across. The motor was powered by static electricity. This energy made tiny gears spin at high speeds, but it wasn’t powerful enough to do any useful work.
3. Manufacturers may be able to produce these engines very cheaply, perhaps for only ten or fifteen dollars each. In 2003 Dr. Alex Zettl, a physicist at the University of California – Berkeley created the first nanomotor. It is a tiny electric motor so small that it can fit on the back of a cold virus. About two hundred of them could fit on a human hair. So far, all the motor can do is spin a tiny rotor. It has not produced enough power to run a machine. Engineers are certain, however, that they will soon develop much more powerful electric nanomotors.
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The Microwave oven
1. Shortly after the end of World War II, Percy Spencer, already known as an electronics genius and war hero, was touring one of his laboratories at the Raytheon Company. He stopped momentarily in front a magnetron, the power tube that drives a radar set. Feeling a sudden and strange sensation, Spencer noticed that the chocolate bar in his pocket had begun to melt.
2. Spencer, who obtained one hundred twenty patents in his lifetime, knew how to apply his curiosity. So he did what any good inventor would – he went for some popcorn. Spencer didn't feel like a snack, he asked for unpopped popcorn. Holding the bag of corn next to the magnetron, Spencer watched as the kernels exploded into puffy white morsels.
3. From this simple experiment, Spencer and Raytheon developed the microwave oven. The first microwave oven was very big and heavy. At first, it was used exclusively in restaurants, railroad cars and ocean liners – places where large quantities of food had to be cooked quickly. In fact, it took decades after the invention of the microwave oven for it to be refined to a point where it would be useful to the average consumer. Today, Percy Spencer's radar boxes melt chocolate and pop popcorn in millions of homes around the world.
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