题目内容
TEXT A An airliner travelling from London to New York may take from five to fifteen hours to cross the Atlantic, while a space capsule makes one complete circuit of the earth in about ninety minutes. The sequence of events is very similar in both types of flight: the vehicle must take off, climb to a suitable height, fly in the right direction at a relatively constant speed for an appropriate time, descend, and land at the destination. Yet although flights to New York are routine affairs which almost anyone may safely undertake, a flight into space is a hazardous adventure for which only a few selected men are at present considered suitable. The most obvious difference between an aircraft and a space vehicle is that of speed, but this alone cannot account for the greater stamina required of astronauts. The human body is unaffected by speed alone and we are normally quite unconscious of the earth’s rotation on its axis, or of its rapid motion around the Sun. Of much greater importance is the rate at which the final speed is achieved, for the body is extremely sensitive to alterations of velocity, or accelerations, especially if they are sudden. An airliner can take a comparatively long time to reach its cruising speed of, say, 400mph, and its passengers will experience acceleration only to a mild degree. The space capsule, however, must be hurled through the atmosphere to reach its final speed of 18,000 mph as quickly as possible, and the acceleration applied by the launching rocket must be correspondingly high. The first problem of manned space flight, therefore, is to match the performance of the rocket to the body’s tolerance for acceleration, and this naturally involves a study of the physiological effects of acceleration. Like all other accelerations, gravity acts upon objects to produce a force, and this force is experienced as weight, or as pressure. It is usual and convenient to regard the earth’s gravity as a standard unit, referred to as lg, and also to use the expressions "force" and "acceleration" as interchangeable. Most of our knowledge of the physiological effects of acceleration has come from studies on human centrifuges, in which acceleration is produced by rotation instead of by changing speed. It has been found that human tolerance is greatly affected by the direction in which the force acts. When the acceleration is applied in line with the long axis of the body, the early symptoms are merely of difficulty in lifting the arms and legs, and of being thrust down into the seat. If the acceleration is raised to 3g or so, vision becomes slightly misty or veiled. As the stress is increased further, the field of view contracts from the edges, until at about 4.5g only a small patch of central vision remains. With yet higher accelerations, even this small area is lost, and this is the state well known to fighter pilots as "black-out". Finally, at about 5.5g to 6g consciousness is lost. The remedy follows logically: if tolerance depends upon the ability of the heart to push blood to the head, it should be possible to reduce the load by shortening the distance between heart and brain. Crouching, or bending the head forward, would be one solution, but an even more satisfactory result can be achieved by placing the body across the line of thrust. The effort needed to pump blood to the brain is then quite small, for the heavy fluid does not have to be lifted very far. In this position men have. withstood an acceleration of 17g for a period of three or four minutes without loss of consciousness. Gravity and acceleration become important once more during the re-entry of the space capsule through the earth’s atmosphere. In this phase, all the speed acquired at the cost of so much fuel during the launch must be lost. Deceleration has exactly the same properties and physiological effects as acceleration, and the same precautions must be taken to avoid exceeding the limits of tolerance. This is why the American plan involves turning the whole capsule round shortly before re-entry, so that the man is again pressed back into his protective couch. The highest, and shortest, deceleration of the entire flight comes at the moment of impact with the land or water. Here the last remnants of the speed must be lost very suddenly, and forces of up to 30g can easily accompany descent to an unyielding surface. The duration of this final insult is so short, however, that its physiological effects are negligible. No doubt the astronaut would regard the jolt as a welcome indication of his return to a normal 1g environment. Which of the following statements is NOT true about acceleration
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TEXT B Christmas is a sad season. The phrase came to Charlie an instant after the alarm clock had woken him and named for him an amorphous depression that had troubled him all the previous even hag. The sky outside his window was black. He sat up in-bed and pulled the light chain that hung in front of his nose. Christmas is a very sad day of the year, he thought. Of all the millions of people in New York, I am practically the only one who has to get up in the cold black of 6 a.m. on Christmas Day in the morning; I am practically the only one. He dressed, and when he went downstairs from the top floor of the rooming house in which he lived, the only sounds he heard were the coarse sounds of sleep; the only lights burning were lights that had been forgotten. Charlie ate some breakfast in an all-night lunch wagon and took an elevated train uptown. From Third Avenue, he walked over to Sutton Place. The neighbourhood was dark. House after house put into the shine of the streetlights a wall of black windows. Millions and millions were sleeping, and this general loss of consciousness generated an impression of abandonment, as if this were the fall of the city, the end of time. He opened the iron-and-glass doors of the apartment building where he had been working for six months as an elevator operator, and went through the elegant lobby to a locker room at the back. He put on a striped vest with brass buttons, a false ascot, a pair of pants with a light blue stripe on the seam, and a coat. The night elevator man was dozing on the little bench in the car. Charlie woke him. The night elevator man told him thickly that the day doorman had been taken sick and wouldn’t be in that day. With the doorman sick, Charlie wouldn’t have any relief for lunch, and a lot of people would expect him to whistle for cabs. Charlie had been on duty a few minutes when 14 rang-Mrs. Hewing, who, he happened to know, was kind of immoral. Mrs, Hewing hadn’t been to bed yet, and she got into the elevator wearing a long dress under her fur coat. She was followed by her two funny looking dogs. He took her down and watched her go out into the dark and take her dogs to the curb. She was outside for only a few minutes. Then she came in and he took her up to 14 again. When she got off the elevator, she said, "Merry Christmas, Charlie." "Well, it isn’t much a holiday for me, Mrs. Hewing," he said. "I think Christmas is a very sad season of the year. It isn’t that people around here ain’t generous--I mean I got plenty of tips--but, you see, I live alone in a furnished room and I don’t have any family or anything, and Christmas isn’t much of a holiday for me." "I’m sorry, Charlie," Mrs. Hewing said. "I don’t have any family myself, It is kind of sad when you’re alone, isn’t it" she called her dogs and followed them into her apartment. He went down. It was quiet then, and Charlie lit a cigarette. The heating plant in the basement encompassed the building at that hour in a regular and profound vibration, and the sullen noises of arriving steam heat began to resound, first in the lobby and then to reverberate up through all the sixteen stories, but this was a mechanical awakening, and it didn’t lighten his loneliness or his petulance. The black air outside the glass doors had begun to turn blue, but the blue light seemed to have no source; it appeared in the middle of the air. It was a tearful light, and he wanted to cry. Then a cab drove up, and the Walsers got out, drunk and dressed in evening clothes, and he took them up to their penthouse. The Walsers got him to brood about the difference between his life in a furnished room and the lives of the people overhead. It was terrible. All the following statements may account for the sadness felt by Charlie on Christmas EXCEPT______.
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