考研英语阅读专项强化.doc

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英语阅读专项特训(1)
　　Before 1965 many scientists pictured the circulation of the ocean’s water mass as consisting of large, slow-moving currents, such as the Gulf Stream. That view, based on 100 years of observations made around the globe, produced only a rough approximation of the true circulation. But in the 1950’s and the 1960’s, researchers began to employ newly developed techniques and equipment, including subsurface floats that move with ocean currents and emit identification signals, and oceancurrent meters that record data for months at fixed locations in the ocean. These instruments disclosed an unexpected level of variability in the deep ocean. Rather than being characterized by smooth, large-scale currents that change seasonally (if at all), the seas are dominated by what oceanographers call mesoscale fields: fluctuating, energetic flows whose velocity can reach ten times the mean velocity of the major currents.
　　Mesoscale phenomena—the oceanic analogue of weather systems—often extend to distances of 100 kilometers and persist for 100 days (weather systems generally extend about 1,000 kilometers and last 3 to 5 days in any given area). More than 90 percent of the kinetic energy of the entire ocean may be accounted for by mesoscale variability rather than by largescale currents. Mesoscale phenomena may, in fact, play a significant role in oceanic mixing, air-sea interactions, and occasional—but far-reaching—climatic events such as El Nino, the atmospheric-oceanic disturbance in the equatorial Pacific that affects global weather patterns.
　　Unfortunately, it is not feasible to use conventional techniques to measure mesoscale fields. To measure them properly, monitoring equipment would have to be laid out on a grid at intervals of at most 50 kilometers, with sensors at each grid point lowered deep in the ocean and kept there for many months. Because using these techniques would be prohibitively expensive and timeconsuming, it was proposed in 1979 that tomography be adapted to measuring the physical properties of the ocean. In medical tomography X-rays map the human body’s density variations (and hence internal organs); the information from the X-rays, transmitted through the body along many different paths, is recombined to form three-dimensional images of the body’s interior. It is primarily this multiplicative increase in data obtained from the multipath transmission of signals that accounts for oceanographers’ attraction to tomography: it allows the measurement of vast areas with relatively few instruments. Researchers reasoned that low-frequency sound waves, because they are so well described mathematically and because even small perturbations in emitted sound waves can be detected, could be transmitted through the ocean over many different paths and that the properties of the ocean’s interior—its temperature, salinity, density, and speed of currents—could be deduced on the basis of how the ocean altered the signals. Their initial trials were highly successful, and ocean acoustic tomography was born. (460 words)
　　1. According to the passage, scientists are able to use ocean acoustic tomography to deduce the properties of the ocean’s interior in part because .
　　[A] density variations in the ocean are mathematically predictable.
　　[B] mesoscale phenomena are so large as to be easily detectable.
　　[C] information from sound waves can be recombined more easily than information from X-rays.
　　[D] low-frequency sound waves are well described mathematically.
　　2. Which of the following is most similar to medical tomography as it is described in the passage?
　　[A] The use of earthquake shock-wave data collected at several different locations and combined to create a three-dimensional image of the Earth’s interior.
　　[B] The use of ocean-current meters to determine the direction and velocity of the ocean’s mesoscale fields.
　　[C] The use of a grid-point sensory system to map global weather patterns.
　　[D] The use of subsurface floats to map large-scale circulation in the ocean.
　　3. Which of the following best describes the organization of the third paragraph of the passage?
　　[A] An argument is advanced, then refuted, and an alternative is suggested.
　　[B] Opposing views are presented, elaborated, and then reconciled.
　　[C] A problem is described, then a solution is discussed and its effectiveness is affirmed.
　　[D] A theory is proposed, considered and then amended.
　　4. Which of the following, if presented as the first sentence of a succeeding paragraph, would most logically continue the discussion presented in the passage?
　　[A] Ships are another possibility, but they would need to stop every 50 kilometers to lower measuring instruments.
　　[B] To understand how ocean acoustic tomography works, it is necessary to know how sound travels in the ocean.
　　[C] Timekeeping in medical tomography must be precise because the changes in travel time caused by density fluctuations are slight.
　　[D] These variations amount to only about 2 to 3 percent of the average speed of sound in water, which is about 1500 meters per second.
　　5. The author mentions EL Nino primarily in order to emphasize .
　　[A] the difficulty of measuring the ocean’s largescale currents.
　　[B] the variability of mesoscale phenomena.
　　[C] the brief duration of weather patterns.
　　[D] the possible impact of mesoscale fields on weather conditions.
　　1965年以前，科学家们认为海水的循环主要由缓慢的洋流构成，如海湾洋流等。这种观点虽然是建立在对全球海水100多年的观察基础之上，却只是对真实情况的近似描绘。但是到了二十世纪五六十年代，研究者们开始使用新技术和新设备进行研究，其中包括：能够跟随洋流移动并发射出辨识信号的水下漂流仪器和能够在海洋中的一个固定地点持续数月纪录数据的洋流仪表。这些仪器向人们揭示，海洋深处的变化程度远比人们预想的剧烈。海洋不是平稳的，其中有大规模的洋流按季节变化，但主要是一种海洋学家们称之为所谓“紊流”区域的一种汹涌澎湃的、速度能达到主要洋流平均速度十倍的水流。
　　紊流现象本来是天气用语，这里把它类比用于海洋系统，它经常延续100公里，持续100天(在天气系统，它经常延续1000公里，在所有地区持续3到5天)。海洋90%多的动能都包含在剧烈变化的紊流中，而不是包含在大规模的洋流中。事实上，紊流现象可能在空气和海洋的互相影响中扮演了重要角色，也在一些偶尔发生但却影响深远的气候现象中扮演重要角色，比如厄尔尼诺就是这样一种在赤道太平洋地区通过大气和海洋的相互干扰来影响全球气候的现象。
　　不幸的是，用常规的技术无法实现紊流的测量。为了准确测量紊流，必须在海洋中每隔至多五十公里就放置一个方格，在每个方格中摆放监视设备，其中传感器要深放水下达数月之久。由于运用这样的技术太过昂贵，而且耗时太长，所以在1975年，有人建议采用X射线断层摄影技术来测量海洋的物理性质。在医学上X射线断层摄影技术应用X射线通过测量人体的密度变化情况，来间接测量人体的内部器官。X射线通过多条路径穿过人体，把它所携带的信息与其他技术结合，就能够形成人体内部的三维影像。从信号的多条传输路径中获得的数据可以成倍增加，正是这一点说明了X射线断层射影技术引起海洋学家注意的原因：它可以使用较少的设备测量广大的区域。研究人员推测说，低频声波可以很好地从数学上加以描绘，即使是非常微小的干扰也能够发现，因此可以发射低频声波使它通过多条路径在海洋中行进，从而海洋内部的性质，如温度、盐度、密度和水流速度等，都能够通过海洋对声波信号的影响推断出来。他们的首次试验非常成功，海洋声学X线断层射影技术就这样诞生了。
　　第一段：首先指出使用新技术和新设备研究表明，海水的循环不是主要由缓慢的洋流构成，而是一种汹涌澎湃的、速度能达到主要洋流平均速度十倍的水流，海洋学家们称之为“紊流”。
　　第二段：具体介绍了紊流现象并指出其重要性。
　　第三段：先说明测量紊流的难度很大，然后介绍了利用医学X射线断层摄影技术的原理来测量紊流的方法，从而推断海洋内部的性质，如温度、盐度、密度和水流速度等。最后引出海洋声学X线断层摄影技术的诞生。( D A C B D )