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各单位销毁会计档案由档案部门自行完成。 ()
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Earth's Inner Core
Scientists have long struggled to understand what lies at the planet's center. Direct observation of its center is impossible, so researchers must(51) to other evidence.
In 1889, a German scientist detected a severe earthquake in Japan. Geophysicists concluded that shock waves(52) jolts (晃动)from one side of Earth through the center to the other side. Then in 1936, Danish geophysicist lnge Lehmann studied the waves'(53) to determine that within Earth's core of molten (熔化了的)iron lies a solid inner core - but(54) that core was made of eluded (难倒)her. Other geophysicists quickly determined that Lehmann's inner core was composed mostly(55) iron. Since then, Lehmann's discovery has(56) conventional Earth science.
But now scientists are challenging traditional theory with new and radical(57) . For example, Earth's center could actually contain an "inner core within the inner core," claim Ishii and colleague Adam Dziewonski.
Analyzing hundreds of thousands of earthquake wave(58) , they maintain that the inner core has at its heart a tiny, even more solid sphere (球体). This sphere "may be the oldest fossil(59) from the formation of Earth," says Dziewonski.
Dziewonski and Ishii speculate that shortly(60) Earth formed around 4.8 billion years ago, a giant asteroid (小行星)smashed into the young planet and nearly melted it. But Earth's center didn't quite melt; it(61) mass as the planet cooled. The core within a core may be the kernel (核心)that endured. "its presence could change our basic ideas about the(62) of the planet," Dziewonski says.
Dziewonski's idea is tame (温和的)compared to the(63) theories of independent geophysicist J. Marvin Herndon. Earth's inner core is made not of iron, he claims, but a(64) of nickel and silicon. Herndon has a truly revolutionary notion: Within the nickel silicide (硅化物)inner core is also an "inner" inner core - an 8 km-wide ball of the element uranium. Uranium is radioactive. Herndon thinks the uranium releases heat energy as its atoms(65) fission-split and crash into one another in a chain reaction. In other words, we may live on top of a gigantic, "natural" nuclear power plant.
登记各种明细分类账是根据原始凭证、汇总原始凭证和记账凭证等进行的。 ()
Laughter
There is an old saying in English: "Laughter is the best medicine". Until recently, few people took the saying very seriously. Now, however, doctors have begun to investigate laughter and the effects it has on the human body. They have found evidence that laughter really can improve people's health.
Tests were carried out to study the effects of laughter on the body. People watched funny films, while doctors checked their heart rate, blood pressure, breathing and muscies. It was found that laughter has similar effects to physical exercise. It increases blood pressure, the heart rate and the rate of breathing; it also works several groups of muscles in the face, the stomach, and even the feet. If laughter exercises the body, it must be beneficial.
Other tests have shown that laughter appears to be capable of reducing the effect of pain on the body. In one experiment doctors produced pain in groups of students who listened to different radio programs. The group which tolerated the pain for the longest time was the group which listened to a funny program. The reason why laughter can reduce pain seems to be that it helps to produce endorphins (内啡肽) in the brain. These are natural chemicals which diminish both stress and pain.
There is also some evidence to suggest that laughter helps the body's immune system, that is, the system which fights infection. In an experiment, one group of students watched a funny video while another group served as the control group-in other words, a group with which to compare the first group. Doctors checked the blood of the students in both groups and found that the people in the group that watched the video had an increase in the activity of their white blood cells, that is, the cells which fight infection.
As a result of these discoveries, some doctors and psychiatrists (精神病学家) in the United States now hold laughter clinics, in which they try to improve their patients' condition by encouraging them to laugh. They have found that even if their patients do not really feel like laughing, making them smile is enough to produce beneficial effects similar to those caused by laughter.
We learn from the first paragraph that laughter
A Dolphin and an Astronomer
One day in 1963, a dolphin named Elvar and a famous astronomer, Carl Sagan, were playing a little game. The astronomer was visitin9 an institute which was looking into the way dolphins communicate with each other. Sagan was standing on the edge of one of the tanks where several of these friendly, highly intelligent creatures were kept. EIvar had just swum up alongside him and had turned on his back.
The dolphin wanted Sagan to scratch his stomach again, as the astronomer had done twice before. Elvar looked up at Sagan, waiting. Then, after a minute or so, the dolphin leapt up through the water and made a sound just like the word 'more'. The astonished astronomer went to the director of the institute and told him about the incident. 'Oh, yes. That's one of the Words he knows,' the director said, showing no Surprise at all.
Dolphins have bigger brains in proportion to their body size than humans have, and it has been known for a long time that they can make a number of sounds, What is more, these sounds seem to have different functions, such as warning each other of danger. Sound travels much faster and much further in water than it does in air. That is why the parts of the brain that deal with sound are much better developed in dolphins than in humans. But can it be said that dolphins have a 'language', in the real sense of the word？ Scientists don't agree on this.
A language is not just a collection of sounds, or even words. A language has a structure and what we call a grammar. The structure and grammar of a language help to give it meaning. For example, the two questions 'Who loves Mary？' and 'Who does Mary love？' mean very different things. If you stop to think about it, you will see that this difference doesn't come from the words the question but from the difference in structure. That is why the question 'Can dolphins speak？' can't be answered until we find out if dolphins not only make sounds but also arrange them in a grammatical order which affects their meaning.
The astronomer was not interested in the way dolphins communicate with each other.
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