题目内容
Hurricane (飓风) Katrina
A hurricane is a fiercely powerful, rotating(旋转的)form. of tropical storm that can be 124 to 1,240 miles in diameter. The term hurricane is derived from Hurican, the name of a native American storm god. Hurricanes are typical of a calm central region of low pressure between "12 to 60 miles in diameter, known as the eye. They occur in tropical regions. Over its lifetime, one of these can release as much energy as 10,000 nuclear bombs.
The seed for hurricane formation is a cluster(聚集) of thunderstorm over warm tropical waters. Hurricanes can only form. and be fed when the sea-surface temperature exceeds 27℃ and the surrounding atmosphere is calm. These requirements are met between June and November in the northern part of the world.
Under these conditions, large quantities of water evaporate (蒸发) and condense (冷凝) into clouds and rain-releasing heat in the process. It is this heat energy, combined with the rotation of the Earth, that drives a hurricane.
When the warm column of air from the sea surface first begins to rise, it causes an area of low pressure. This in turn creates wind as air is drawn into the area. This spinning wind drags up more moist air from the sea surface in a process that strengthens the storm. Cold air falls back to the ocean surface through the eye and on the outside of the storm.
Initially, when wind speeds reach 23 miles per hour, these mild, wet and grey weather systems are known as depressions, or low air pressure. Hurricane Katrina formed in this way over the southeastern Bahamas on 23 August 2005, Katrina has had a devastating impact on the Gulf Coast of the US, leaving a disaster zone of 90,000 square miles in its wake(尾迹)-almost the size of the UK. Thousands have been killed or injured and more than half a million people have become homeless in a humanitarian(人道主义的) crisis of a scale not seen in the US since the Great Depression. The cost of the damage may top $100 billion.
The eye of a hurricane refers to its ______.
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Winter is the toughest season for grasses and flowers to survive in desert.
Sleep Lets Brain File Memories
To sleep. Perchance to file？ Findings published online this week by the proceedings of the National Academy of Sciences further support the theory that the brain organizes and stows memories formed during the day while the rest of the body is catching zzz's.
Gyorgy Buzsaki of Rutgers University and his colleagues analyzed the brain waves of sleeping rats and mice. Specifically, they examined the electrical activity emanating(散发) from the somato-sensory (耳、目、口等以外的) neocortex (新大脑皮层) (an area that processes sensory information) and the hippocampus(海马), which is a center for learning and memory. The scientists found that oscillations in brain waves from the two regions appear to be intertwined. So-called sleep spindles (bursts of activity from the neocortex) were followed tens of milliseconds later by beats in the hippocampus known as ripples. The team posits that this interplay between the two brain regions is a key step in memory consolidation.
A second study, also published online this week by the proceedings of the National Academy of Sciences, links age-associated memory decline to high glucose levels.
Previous research had shown that individuals with diabetes(糖尿病，多尿症) suffer from increased memory problems. In the new work, Antonio Convit of New York University School of Medicine and his collaborators studied 30 people whose average age was 69 to investigate whether sugar levels, which tend to increase with age, affect memory in healthy people as well. The scientists administered recall tests, brain scans (细看，审视，浏览，扫描) and glucose tolerance tests, which measure how quickly sugar is absorbed from the blood by the body's tissues. Subjects with the poorest memory recollection, the team discovered, also displayed the poorest glucose tolerance. In addition, their brain scans showed more hippocampus shrinkage than those of subjects better able to absorb blood sugar.
"Our study suggests that this impairment (损害、损伤) may contribute to the memory deficits (赤字、不足额) that occur as people age. " Convit says. "And it raises the intriguing possibility that improving glucose tolerance could reverse some age-associated problems in cognition. " Exercise and weight control can help keep glucose levels in check(阻止、制止), so there may be one more reason to go to the gym.
Which of the following statements is nearest in meaning to the sentence "To sleep. Perchance to file？"
A．to confrontB．confrontedC．confrontingD．being confronted
Plants in Desert
Only special plants can survive the terrible climate of a desert, for these are regions where the annual range of the soil temperature can be over 75℃. Furthermore, during the summer there are few clouds in the sky to protect plants from the sun's ray. Another problem is the fact that there are frequently strong winds which drive small, sharp particles of sand into the plants, tearing and damaging them. The most difficult problem for all forms of plant life, however, is the fact that the entire annual rainfall occurs during a few days or weeks in spring.
Grasses and flowers in desert survive from one year to the next by existing through the long, hot, dry season in the form. of seeds. These seeds remain inactive unless the right amount of rain falls. If no rain falls, or if insufficient rain falls, they wait until the next year, or even still the next. Another factor that helps these plants to survive is the fact that their life cycles are short. By the time that the water from the spring rains disappears—just a few weeks after it falls—such plants no longer need any.
The perennials have special features which enable them to survive as plants for several years. Thus, nearly all desert perennials have extensive root systems below ground and a small shoot system above ground. The large root network enables the plant to absorb as much water as possible in a short time. The small shoot system, on the other hand, considerably limits water loss by evaporation.
Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long, dry season, just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season. Then, in next rainy season, they come fully alive once more, and grow new branches, leaves and flowers, just as the grasses and flowers in desert do.
Ordinary plants are unable to survive in the desert mainly because of the changeable weather.
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