星火英语巅峰阅读100篇.doc

PartA-Text1 The sun-that power plant in the sky-bathes Earth in ample energyto fulfill all the worlds power needs many times over. It doesnt give off carbon dioxide emissions. It wont run out. And its free. So how on Earth can people turn this bounty of sunbeams into useful electricity?The suns light (and all light) contains energy. Usually, when light hits an object the energy turns into heat, like the warmth you feel while sitting in the sun. But when light hits certain materials the energy turns into an electrical current instead, which we can then harness for power. 1Old-school solar technology uses large crystals made out of silicon, which produces an electrical current when struck by light. Silicon can do this because the electrons in the crystal get up and move when exposed to light instead of just jiggling in place to make heat. The silicon turns a good portion of light energy into electricity, but it is expensive because big crystals are hard to grow. Newer materials use smaller, cheaper crystals, such as copper-indium-gallium-selenide, that can be shaped into flexible films. This “thin-film” solar technology, however, is not as good as silicon at turning light into electricity.2In order to have a hope of replacing fossil fuels, scientists need to develop materials that can be easily mass-produced and convert enough sunlight to electricity to be worth the investment. A solar cell is a device people can make that takes the energy of sunlight and converts it into electricity. In a crystal, the bonds between silicon atoms are made of electrons that are shared between all of the atoms of the crystal. The light gets absorbed, and one of the electrons thats in one of the bonds gets excited up to a higher energy level and can move around more freely than when it was bound. That electron can then move around the crystal freely, and we can get a current. Imagine that you have a ledge, like a shelf on the wall, and you take a ball and you throw it up on that ledge. Thats like promoting an electron to a higher energy level, and it cant fall down. A photon packet of light energy comes in, and it bumps up the electron onto the ledge representing the higher energy level and it stays there until we can come and collect the energy by using the electricity.1.Which of the following can best describe the features of the solar energy?A.Sufficient and enduringB.Clean and free of charge C.Available and accessibleD.Inexhaustible and pollution-free2.What plays a key role in the process of turning light energy into electricity?A.The atoms.B.The siliconC.The crystalsD.The electrons3.Compared with old-school solar technology, thin film solar technologyA.Can be spread far and wideB.Is likely to replace the siliconC.Is less advanced and more expensiveD.Cant convert enough sunlight to electricity4.We can get an electrical current whenA.a solar cell is exposed to light B.enough sun light hit the crystalsC.silicon atoms are bound in the crystalD.the electrons move freely in the crystal5.The author illustrates in the last paragraph thatA.how easy it is to turn sunlight into electricityB.how we can use th eelectricity in our daily lifeC.how an electron is promoted to a higher energy levelD.how we can collect the energy converted by a photonPartA-Text2A new study on mice uncovers some answers that could someday offer a powerful target for eliminating the recurrence of bad memories in humans, especially known to those who suffer from post-traumatic stress disorder (PTSD: mental disorder caused by accidents of emergency). Fear memories are the most robust memories-they can last over a lifetime, says Nadine Gogolla, a biologist at Harvard University and lead author on the paper published recently in the journal Science. You can push them far back, but spontaneous recovery and relapses will happen. Until now, science has been unable to stop this process-in humans or in mice.2By repeating the previously reported rat findings, Gogolla and her colleagues found that at some point during a young mouses development-between about 16 and 23 days postnatal-a molecular net of sorts is cast over a region of the brain called the amygdale, effectively crystallizing formerly changeable memories. It looks just like what you would expect from a fishermans net, says Gogolla of the protein matrix (a living part in which something is formed) under the microscope. And it acts as a structural constraint on the cells. How it does that, nobody really knows. But the result is that memories are held inside. What the researchers did learn was that by cutting that net-with an injection of an enzyme that digests the chains linking the matrix together-memories could be once again destabilized. The drug cuts the net into its pieces, Gogolla says, just like when you cut the strings of a net and it falls apart. Then, for a couple weeks, the original youthful plasticity in the neuronal circuits of the amygdala is regained and any bad memory formed after the matrix digestion could be subsequently eliminated through extinction therapy, a common treatment during which a patient is presented with the original fear trigger but in a context that is not fearful. When the treatment was given after a mouse underwent fear conditioning, however, extinction was unable cut out that memory completely. Because the treatment has to occur before a traumatic event, its hard to make it immediately available, notes Gogolla. But it does help us in finding the underlying mechanisms. Eventually, she hopes tools can be found that can be applied after fear-inducing experiences, and that translate from mice to humans. 1This would be welcome relief for the approximately 20 percent of all military personnel who have returned from Iraq and Afghanistan reporting symptoms of PTSD, not to mention for heartbroken couples. 1.What is said about the fearful memories in the passage?2.According to Gogolla and her colleagues, fearful memories_.3.What was confirmed by Gogollas study on extinction therapy?4. The findings of Gogollas study will be most probably applied to_.5.It can be inferred from the passage that_.Text3As Gilbert White, Darwin, and others observed long ago, all species appear to have the innate capacity to increase their numbers from generation to generation. The task for ecologists is to untangle the environmental and biological factors that hold this intrinsic capacity for population growth in check over the long run. The great variety of dynamic behaviors exhibited by different populations makes this task more difficult: some populations remain roughly constant from year to year; others exhibit regular cycles of abundance and scarcity; still others vary wildly, with outbreaks and crashes that are in some cases plainly correlated with the weather, and in other cases not.To impose some order on this kaleidoscope of patterns, one school of thought proposes dividing populations into two groups. These ecologists posit that the relatively steady populations have “ density-dependent ” growth parameters; that is, rates of birth, death, and migration which depend strongly on population density. The highly varying populations have “ density-independent ” growth parameters, with vital rates buffeted by environmental events; these rates fluctuate in a way that is wholly independent of population density.This dichotomy has its uses, but it can cause problems if taken too literally. For one thing, no population can be driven entirely by density-independent factors all the time. No matter how severely or unpredictably birth, death and migration rates may be fluctuating around their long-term averages, if there were no density-dependent effects, the population would, in the long run, either increase or decrease without bound (barring a miracle by which gains and losses canceled exactly). Put another way, it may be that on average 99 percent of all deaths in a population arise from density-independent causes, and only one percent from factors varying with density. The factors making up the one percent may seem unimportant, and their cause may be correspondingly hard to determine. Yet, whether recognized or not, they will usually determine the long-term average population density.1In order to understand the nature of the ecologists investigation, we may think of the density-dependent effects on growth parameters as the “signal” ecologists are trying to isolate and interpret, one that tends to make the population increase from relatively low values or decrease from relatively high ones, while the density-independent effects act to produce “noise” in the population dynamics. For populations that remain relatively constant, or that oscillate around repeated cycles, the signal can be fairly easily characterized and its effects described, even though the causative biological mechanism may remain unknown. For irregularly fluctuating populations, we are likely to have too few observations to have any hope of extracting the signal from the overwhelming noise. But it now seems clear that all populations are regulated by a mixture of density-dependent and density-independent effects in varying proportions.1.The author of the passage is primarily concerned with2.According to the passage, which of the following behaviors has been exhibited by different populations ?3.The author considers the dichotomy discussed in the second paragraph to be4.Which of the following statements can be inferred from the last paragraph?5.Which of the following is true according to the passage?Text4The intensive work of materials scientists and solid-state physicists has given rise to a class of solids known as amorphous metallic alloys, or glassy metals. There is a growing interest among theoretical and applied researchers alike in the structural properties of these materials.When a molten metal or metallic alloy is cooled to a solid, a crystalline structure is formed that depends on the particular alloy composition. In contrast, molten nonmetallic glass-forming materials, when cooled, do not assume a crystalline structure, but instead retain a structure somewhat like that of the liquid-an amorphous structure. At room temperature, the natural long-term tendency for both types of materials is to assume the crystalline structure. The difference between the two is in the kinetics or rate of formation of the crystalline structure, which is controlled by factors such as the nature of the chemical bonding and the ease with which atoms move relative to each other. 1Thus, in metals, the kinetics favors rapid formation of a crystalline structure, whereas in nonmetallic glasses the rate of formation is so slow that almost any cooling rate is sufficient to result in an amorphous structure. For glassy metals to be formed, the molten metal must be cooled extremely rapidly so that crystallization is suppressed.The structure of glassy metals is thought to be similar to that of liquid metals. One of the first attempts to model the structure of a liquid was that by the late J. D. Bernal of the University of London, who packed hard spheres into a rubber vessel in such a way as to obtain the maximum possible density. The resulting dense, random-packed structure was the basis for many attempts to model the structure of glassy metals. Calculations of the density of alloys based on Bernal-type models of the alloys metal component agreed fairly well with the experimentally determined values from measurements on alloys consisting of a noble metal together with a metalloid, such as alloys of palladium and silicon, or alloys consisting of iron, phosphorus, and carbon, although small discrepancies remained. One difference between real alloys and the hard spheres used in Bernal models is that the components of an alloy have different sizes, so that models based on two sizes of spheres are more appropriate for a binary alloy, for example. The smaller metalloid atoms of the alloy might fit into holes in the dense, random-packed structure of the larger metal atoms.One of the most promising properties of glassy metals is their high strength combined with high malleability. In usual crystalline materials, one finds an inverse relation between the two properties, whereas for many practical applications simultaneous presence of both properties is desirable. 2One residual obstacle to practical applications that is likely to be overcome is the fact that glassy metals will crystallize at relatively low temperatures when heated slightly. Text5Aided by the recent ability to analyze samples of air trapped in glaciers, scientists now have a clearer idea of the relationship between atmospheric composition and global temperature change over the past 160,000 years. In particular, determination of atmospheric composition during periods of glacial expansion and retreat (cooling and warming) is possible using data from the 2,000 meter Vostok ice core drilled in Antarctica. The technique involved is similar to that used in analyzing cores of marine sediments, where the ratio of the two common isotopes of oxygen, 18O and 16O, accurately reflects past temperature changes. Isotopic analysis of oxygen in the Vostok core suggests mean global temperature fluctuations of up to 10 degrees centigrade over the past 160,000 years.Data from the Vostok core also indicate that the amount of carbon dioxide has fluctuated with temperature over the same period: the higher the temperature, the higher the concentration of carbon dioxide and the lower the temperature, the lower the concentration. Although change in carbon dioxide content closely follows change in temperature during periods of deglaciation, it apparently lags behind temperature during periods of cooling. The correlation of carbon dioxide with temperature, of course, does not establish whether changes in atmospheric composition caused the warming and cooling trends or were caused by their.The correlation between carbon dioxide and temperature throughout the Vostok record is consistent and predictable. The absolute temperature changes, however, are from 5 to 14 times greater than would be expected on the basis of carbon dioxides own ability to absorb infrared radiation, or radiant heat. This reaction suggests that, quite aside from changes in heat-trapping gases, commonly known as greenhouse gases, certain positive feedbacks are also amplifying the temperature change. Such feedbacks might involve ice on land and sea, clouds, or water vapor, which also absorb radiant heat.Other data from the Vostok core show that methane gas also correlates closely with temperature and carbon dioxide. The methane concentration nearly doubled, for example, between the peak of the penultimate glacial period and the following interglacial period. Within the present interglacial period it has more than doubled in just the past 300 years and is rising rapidly. Although the concentration of atmospheric methane is more than two orders of magnitude lower than that of carbon dioxide, it cannot be ignored: the radiative properties of methane make it 20 times more effective, molecule for molecule, than carbon dioxide in absorbing radiant heat. 1On the basis of a simulation model that climatological researchers have developed, methane appears to have been about 25 percent as important as carbon dioxide in the warming that took place during the most recent glacial retreat 8,000 to 10,000 years ago.6Forests planted with a diverse species of trees will be better able to withstand pest infestation than those that are sown plantation-style with just one species, a newly released study said.1A diversity of trees will support a greater range of insects than a single species, ensuring that there are more predators to keep down the numbers of a pest that, unchecked, could decimate a swath of woodland in an outbreak year.“Mixed forests have a greater flexibility than plantation-style forests ,” explained Eldon Eveleigh, an entomologist with the Canadian Forest Service in Fredericton, New Brunswick.The findings have implications for the management of forestry lands, and also commercial plantations.Eveleigh and colleagues studied three patches of the Arcadian Forest in the eastern Canadian province of New Brunswick as part of an effort to examine how biodiversity could protect forests from pest damage. They looked at three sections of forest: one was almost entirely composed of balsam fir, which is a favourite target of a moth called the spruce budworm. Budworm is one of the most destructive native insects in the northern spruce and fir forests of the eastern United States and Canada.The other two plots were varying mixtures of balsam fir and hardwood species such as birch, maple and deciduous varieties.2The Canadian researchers found that the budworm thrived in the plot that was almost entirely balsam fir, laying twice as many larvae per square meter than in either of the two other plots during a peak reproductive year. The results were devastating, with tree mortality averaging 65 percent in this plot-almost three times higher than the mortality rates seen in either of the other two chunks of forest.Separately, the scientists also noticed that as the abundance of budworms increased, so too did the numbers of other plant-eating insects or parasites that feed on the moth. The so-called “birdfeeder” effect continued on up the food chain, with other higher-order insects flocking to the area in search of more plentiful food sources.However the abundance of these higher-order predators was much greater in the plots with several species of tree, suggestin