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复习的近四个半月, 英语底子一般, 能考出这个成绩很满意..... 感谢中国人民大学2006年企业管理硕士班级一起奋战出国的兄弟姐妹Dong qi\ Liu Fang\ He yu Hong -----, 感谢CD, 感谢各个兄弟姐妹的JJ帮助....... 你们的帮助让非NN才有今天的math51以及verbal的41. 废话少说, 这里贡献自己的一点机经, 主要在阅读把, 在前人的机经基础上进行修改, 我自己做了根据昨天的感觉做了一下整理 1 广告 第一段：当时传统的人们为, 广告要起作用的话, 必须要通过不断影响消费者, 促使其购买产品。如何评价advertisement的effectiveness呢？第一句说了one view，是直接评价advertisement的投入和产出（input and marketing/sales），但另外有人提出广告其实可以是建立一个model来分步
(stage) 分析advertisement在每一步的effectiveness, 在真正有demand之前，还有一些步骤如brand awareness之类的东西，所以就有第二种衡量广告的多层model，并建议用hierarchical 模型来对消费者进行渗透影响。传统的广告model只重视广告与销售的关系，也就是广告的费用和带来的销售增长之间的关系，而新的广告model则表明广告不仅仅和销售有关系，而且应该和XX有关系。 第二段：第二个理论有很多的模型，但是大部分模型都有两个缺陷：一个是市场，另一个是广告针对的特定群体。然后某个人提出了一种新模式，和传统的继承理论有些不一样，这种模式说明广告对以下三个阶段的用户都有作用：一是对此广告不了解的客户；一个是想使用该产品的客户；还有一个是以前用过该产品并且对产品满意的客户。而传统模式则认为广告本身让客户在此三种模式中向上移动，这是不对的。 2 成本理论
第一段：说以前的cost理论。管理人员现在日常的生产经营决策还在使用以前的cost理论，这个老的cost理论只考虑direct material and labor cost. 这种传统的会计核算成本的方法适合于原先企业生产产品单一，labor 和material cost好算的情况. 但现在企业往往都有多条生产线，生产很多产品，这种方法核算就会产生错误，因为它忽略了除人力和原料以外的成本，由于有更多staff、maintenance cost等，计算的时候把这些费用摊在每一个产品上就会导致错误。 第二段：举了个例子，plant1和plant2，plant 1生产蓝圆珠笔，plant 2生产蓝圆珠笔和彩色圆珠笔。plant 2因为产品结构比较复杂，有多条生产线，存在一些overhead cost——在企业里除了生产一线以外的其它工人的工资、maintenance cost、还有其它一些维持企业必须的费用就比较高。虽然可能plant2每生产per unit blue的费用要低于1生产per只，但根据老的cost理论把所有的费用（含overhead费用）分摊到每每只笔上去，账面上plant2生产的blue pen就比plant1的成本高。 第三\四\五段：Plant2有生产蓝色原子笔和彩色原子笔，由于蓝色原子笔作为一种常规产品，制造流程较简单，实际成本低；彩色原子笔的流程较复杂，实际成本高。在传统计算成本的方法下，混在一块算，用成本去除产量是不准确的，会导致蓝色原子笔成本被高估和利润被低估，而彩色原子笔会因此成本被低估和利润被高估。在竞争压力下，这样plant 2会误以为它生产的蓝圆珠笔的成本比生产单一产品的厂商高（plant1)，给它带来的利润---profit margin比较低（卖价一样），而停止生产蓝圆珠笔，生产其它的圆珠笔。但是实际上plant2生产blue pen的成本是比plant1低的，这样一来plant2反而放弃了有比较优势的产品，生产了更多其它产品。 3 地震第一段：讲一个Long-established theory，传统地质学家认为：（1）由于地幔中的高温和压力使岩石成流质状或plastic状，大多数地震都是在高温高压下facture断裂，在地表less than 30 miles的地方发生；（2）地表深处的pressure导致处于此深度物质转变过程较慢从而形成不了地震。现实的情况也显示，确实绝大多数地震发生在浅地表。 第二段：然而有个学者发现有些地震发生得离地表很深，即存在一个puzzle是每年都有几百个地震发生在深层120mile--300mile，说原来的理论应该包括（involve）另一种地表深处的变化情况等。这个人develop了两个理论用来解释：（1）第一个理论是地下的温度和压力使岩石中的crystal结构发生变化，然而这种变化发生得太慢而不太可能成为地震的成因；（2）这个人又提出了另一个理论，是地下的激变使岩石中的crystal结构被压塌，却还是连在一起的，恰好解释了深层地震。这里提到一点, 这两个理论都强调岩石结构发生了变化,考试出到了一题什么是true, 我敢肯定是这个... Why earthquake can happen in deep ground. The first paragraph says common sense tells us the earthquake happened in the place close to the ground, because the deep ground has very high press and makes the mantle ductile which can bring out earthquake. The second paragraph explains why the earth can happen in deep ground. 4 定价策略第一段：整段就是在解释两种定价策略。传统的定价是固定价格定价，但由于近年来经济的快速发展，以前用的Stable pricing的定价方法已经不适用了。现在推出新产品时候多用两种浮动价格定价法：Pricing strategy----Skimming pricing and penetrate pricing. Skimming pricing就是在产品刚上市的短期以内，趁着产品还很有竞争优势，maximize short-term price, 等别人的产品优势也赶上来了时再减价（先把价格定在利润最大化价格或者最大化价格，以图在短期取得最大的利润，然后慢慢降价）；Penetrate pricing就是在产品上市时定一个比较低的价格，目标在于争取顾客，争取市场份额。 第二段：讲由于现在的市场竞争太激烈，产品竞争优势很难保持，更加适用close to利润最大化价格的定价策略，即还是采用skimming pricing比较好：（1）因为现在新商品刚出来的那会的时间在减少-----即新商品刚开发出来的时候别的竞争者海没有开发出于起竞争的商品的时间在减少，直接导致产品的生命周期很短, 所以在最短时间内就把成本回收比较好, 虽然在这之后商品常常降的比预期的快。企业采用Skimming pricing则能从maximize short-term price中来recover research and development costs 的时间就比较短；（2）采用penetrate pricing的目标在于保持长期的优势，但是现在产品在更替太快，所以长期根本都不存在。当然skimming pricing也有缺点，作者在最后一句话说，skimming虽然牺牲了long-term的发展, 但是作者认为没关系, 因为这些产品no future，意思应该是指产品周期很短, 根本没有未来可言, 当然是尽量在短时间内回收成本, 再投入研发新产品比较重要。 以下是自己复习的时候找的一些背景材料给大家参考, 大家以参考为主......可能不是考试主要的...... So far, the earth has warmed an average of 0.6°C above pre-industrial levels, which does not sound like very much. However, the warming is not uniform in all parts of the planet. It is much greater in the Polar Regions, and this is already having serious consequences. Land and water absorb most of the solar energy that reaches it, whereas ice reflects most of it back into space. The increase in greenhouse gases warms the atmosphere, with the result that less snow and ice form and they melt more quickly. A cycle is created: as the ice and snow melt, the sea and land absorb an increasing amount of heat, causing even more melting. In the Arctic, this process has recently speeded up to the point where it is happening at a rate 10 to 15 times faster than it had been for the previous several decades. Huge chunks of the polar ice caps are breaking off, accelerating the process even further and causing the sea level to rise. Effect of Greenhouse Effect Provide the consistence of Greenhouse Effect gases increases continuously, the climate will be changed with increase of surface temperature. Its influences contain: The winter in the Northern Hemisphere will be shortened with colder and wetter climate, while the summer will be longer with dryer and hotter climate. The semitropical area will be dryer, while the tropical area will be wetter. The temperature increase speeds up water evaporation. The global rain fall will decrease year by year, and rain fall type in each area will change. It can change distribution and growth of plants and crops to cause soil depletion by speeding up growth. The restrain on crop growth will destroy ecologic environment and balanced indirectly. The sea will become warmer than before and seal level will increase by 15-95 cm in 2100 to cause sea water encroachment in low-lying areas. About 1/3 of world population along sea coast will be threatened by it. It can change resources distribution in areas to cause supply unbalance of food, water and finishing etc., which will trigger economic and social problems internationally.
Effects of Carbon Dioxide Emissions on Hydrological CycleExcessive emissions of carbon dioxide, which causes global warming, will negatively affect the water tables in California. Already there has been a decrease in groundwater levels due to temperature increase, and in the future, it is predicted that there will be an even greater change. Several sources agree that there have already been changes in the hydrologic cycle in the western United States including an increase in cold season precipitation, reduced snow cover flooding and a decrease in runoff from the mountains. The increased temperature in California has led to changes in the precipitation patterns as well as the overall climate. Although there has been a slight increase in overall cold-season precipitation, the form that it is falling in has also changed presenting a greater issue later seen in the spring. There is more rainfall precipitation at the cost of snow precipitation. The snowfall in the California
Coastal
Range and the Sierra Nevada mountains accumulate into snow packs (Kim 2004). These snow packs slowly melt in the spring and summer in a time release fashion that is beneficial to agriculture. These changes will have its societal impacts, some of which are being felt now. As the winter months see more rainfall and less snow, it is upon the soil to absorb the rain. Soil saturation rates vary in the summer and winter months. During the summer, the sun heats the soil, drying it up and allowing saturation whenever rain falls. However in the winter, the sun does not do the same. Since the sun has less intensity in the winter months, the soil tends to remain cold and already wet because the conditions are not right for substantial evaporation. (Kim 2004) This directly leads to flooding in the low-lying regions at the base of the mountains. An increase in temperature is already affecting the San Francisco estuary— California’s primary source of freshwater. Flooding may occur in the winter months because of the winter precipitation is falling in the form of rain. Due to the loss of snow pack, the estuary will not replenish in the spring months as it used to in the past. Also salinity levels in the estuary are expected to increase as the water flow decreases. Furthermore recent models suggest that warming will increase with elevation. This means that temperature zones are not just shifting north, but also up. It this happens that the snow packs that were once out of reach from accelerated melting, now are susceptible to melting. In the long run, this could lead to the end of the Sierra Nevada’s snow packs and thus ending summer replenishing of the estuary, and local reservoirs. If rising sea levels continue at its projected rate, this would devastate the estuary, causing it fill with salt water, and cause the salinity level to the too high for human consumption or agricultural use. If warming trends continue, it is expected that the effects on the estuary will only intensify. California’s reservoirs depend on the year-round water flow from the melting snow packs to recharge. If the reservoirs cannot recharge, than the water level will easily dwindle until it empties out completely. As California’s population continues to increase as rapidly as it currently is, than these societal impacts may be felt sooner as Californians may eventually have to look elsewhere for fresh water. Hydrological Cycle In the natural environment, precipitation either falls directly onto the ground or is intercepted by the leaves, branches and trunks of vegetation, eventually moving to the ground or evaporating into the atmosphere. Some of the precipitation that falls directly on land runs into rivers, lakes or oceans. Other water reaching the ground is absorbed by leaf litter or stored in depressions and cracks. Water from precipitation also filters into the upper layer of soil at a rate that depends on the soil's characteristics and the amount of water already in the soil. Generally, if there is more precipitation than the soil can absorb, it runs off the surface ( overland flow or run-off ) or enters the upper soil layers where it moves laterally. Water generally moves from the upper layers of the soil through transpiration by trees and other vegetation, or by percolation into even deeper ground layers. Water that percolates into groundwater reserves may take months, years or even hundreds of years to pass back to the surface. Nevertheless, groundwater reserves play a major role in sustaining flows in streams between surface recharge events (such as rainfall) and are the main source of stream flow during dry periods. The hydrologic (or water) cycle continues as the heat of the sun returns water from the earth's surface to the atmosphere through evaporation. Geographical features-land and water formations-have a large influence on the hydrologic cycle, particularly on rainfall. For example, when moisture-laden air is forced upwards over a mountain range, the vapour cools and usually falls as rain, hail or snow on the windward side of the range (DLWC 2000). Various human activities affect the hydrologic cycle (Figure 2). Land use has an impact on evaporation rates, the amount of water infiltrating to ground water, the rate of run-off and erosion, and the quality of water reaching water bodies. The amount of water absorbed into the ground and the quantity and purity of run-off vary with different soil and vegetation types. Cities and roads contain less open ground to absorb water, so run-off is greater in these areas. 2 寄生The original article dodder
Consuelo De Moraes, assistant professor of entomology, studies green, leafy things that are, at a glance, lovely and benign. But she will be the first to tell you that even in the most lush and pastoral setting, it's a jungle out there in the plant world. For the past decade, the focus of De Morales' work has been chemical ecology — specifically, the way that plants and insects communicate with each other. Her latest research, published in the Sept. 29, 2006 issue of Science, examines the parasitic nature of a weed called dodder (of the genus Cuscuta) and reveals a plant intelligence not seen before. Dodder has the ability not only to recognize its prey by scent but also to move toward it with a remarkable accuracy and efficiency. "We tend to think of plants as static," she says. "But then we see dodder, which exhibits an almost animal-like behavior." The behavior De Moraes describes is dodder's assault on its victim, which in her study was the tomato plant, and it occurs with military precision. Dodder, also known as strangleweed, lovevine, and hellbind, is a viney plant, in the same family as the morning glory. It attacks its quarry by sending out strangling tendrils that wind around the host. Dodder acquires energy and nutrients by sucking out the host's phloem (pronounced "flow-um"), the essential fluid that gives a plant life. Dodder can weaken without killing, although its effects are often crippling. But for such a pernicious predator, it has a rather short range—seedlings can only grow about four inches before finding a host. Unlike most plants, dodder can't produce its own food through photosynthesis and does not put down roots, so host plants serve as its only source of nutrition. In order for dodder to survive, it must choose wisely. Tomato plants provide more nutrients than others, and are preferred, but a dodder will latch onto another plant if it is the only thing available. Dodder relies on its capability to smell the tomato plant, De Moraes explains. During the normal process of transpiration— the process by which a plant releases watery vapors through its membranes—the tomato releases compounds known as volatiles. Adds De Moraes, "Volatiles are made up of alcohol, aldehydes, and terpenes—which is pretty much what you would find in a bottle of perfume."
Hooked on Plant Perfume De Moraes began studying volatiles when she was a Ph.D. student at the University of Georgia in the early 1990s. At the time, she remembers, she read a paper by entomologist Ted Turlings (then at University of Florida and now at the University of Neuchâtel in Switzerland) that described how plants under attack by certain insects released specific volatiles. Tomato seedling with parasitic dodder. Photo by Justin Runyon; Courtesy De Moraes and Mescher Labs. "I have been hooked ever since then," she says. "When I started this course of study, it was already known that plants responded to insects. At the time everyone thought the release of volatiles through transpiration was a general response. But if the plant can tell you not only 'someone feeding on me,' but who is feeding, the signal from the plant is very specific." One of De Moraes' first research projects examined how a nicotine plant being attacked by moths sent out a signal to wasps, who in turn, attacked the moths. Calling in the cavalry, as it were. This early work looked at the insect attack-plant reaction phenomenon, and through it De Moraes discovered that plants release different volatiles when they are stressed. Between transpiration and stress reactions, says De Moraes, "We haven't found any plants yet that don't release volatiles. The most amazing thing for me, though, is that not only can parasitic plants perceive volatiles, they can distinguish among them." The dodder study, spearheaded by De Moraes and collaborator Mark Mescher, another assistant professor of entomology, was instigated by a proposal from one of their graduate students. Justin Runyon, who is working on a Ph.D. in entomology, was interested in looking at how host plants like the tomato responded to the stress of being strangled by dodder. "Dodder is well known," says De Moraes. "We asked the question, 'How does dodder find the host plant in the first place?' But when we started searching the literature for the answer, we were surprised that no one knew. Mark Mescher suggested that maybe they were using volatiles."
Not Easily Tricked In search of the mechanism that triggered dodder's attraction to the tomato, De Moraes, Mescher, and Runyon followed their collective hunch that the release of volatiles gave away the unsuspecting tomato's location. But to prove their hypothesis, the team gave dodder (specifically Cuscuta pentagona) choices of other potential prey. "We wanted to know if the plants were using visual cues or something else," says De Moraes. "Our first question was, 'Would it find the host plant?' If you blocked the plant, would the dodder still go to it?" The selective dodder showed absolutely no interest in an ersatz tomato plant fashioned from felt and pipe cleaners, nor was it drawn toward vials of red—or green—colored water. But when the researchers extracted scent chemicals from the actual tomato and applied them to a piece of rubber, the dodder plant immediately shot out tendrils in the direction of the scent. Remarkably, dodder plants also displayed an ability to choose among potential hosts. When given the option of tomato or wheat, dodder choose tomato if it is available. If there is no choice, dodder will lean toward wheat, but the team also discovered that one of the volatiles released by wheat repels dodder, which, in the long run, may help researchers discover a way to control dodder infestation. Just in the state of California, Cuscata pentagona costs farmers an estimated $4 million in reduced tomato crops each year. And there are 150 species of dodder, which attack many other cash crops, including carrots, cranberries, onions, citrus trees, and alfalfa. Farmers have a difficult time eliminating it because the herbicides that kill it also destroy the host plants. Tomato seedling with dodder wrapping around stem. Photos by Justin Runyon; Courtesy De Moraes and Mescher Labs. IN SHORT - The Earth's interior is structured into a core, a 'mantle', and a crust. The core, further, is mostly metallic as it's parted into a solid inner core and an outer liquid one. The mantle is composed of semi-molten rock as the crust is the thin, outermost layer, with a thickness varying between 3 and 19 miles (5-30 km). The total diameter of the Earth is of 7,900 miles (12,750 km) with the core having a radius of 2,165 mi (3,483 km), and the mantle a thickness of 2,100 mi (3,400 km). Earth formed like any other planetary body in the solar system by accretion of planetesimals, heating and differentiation. Due to impacts, radioactivity or tidal gravitational effects, a part of primitive Earth's material melted and that material differentiated into three layers due to density differences: heavier material sank to planet's center forming a planet core, lighter material (mostly basalt and silicates) formed what is called a "mantle", as lightest material floated atop and cooled, forming a thin crust. Hence Earth has a layered structure: a core, a mantle and a crust. Earth has a diameter of 7,900 mi (12,750 km) （1）Core of the Earth is the densest part of Earth as it is mostly metallic (iron-nickel alloy). It parts into a solid inner core, and an outer liquid core. Inner core has a temperature of 7,800° F (4,300° C) and a radius of 795 mi (1,278 km). It is solid because of the press ion existing at Earth's center. It is mostly made of iron. Outer core is 1,370 mi (2,200 km) wide, has a temperature of 6,700° F (3,700° C), is liquid iron and 10 percent sulfur. It's the liquid outer core rotation about inner core which yields Earth's magnetic field. This works like a dynamo. （2）Mantle is a dense, hot layer of semi-molten rock. It is about mi 2,100 mi (3,400 km) thick. It contains iron, magnesium, calcium, silicon, and oxygen. Mantle is plastic as temperature and pression are high at his depth. （3）Crust is the outermost, thin layer of Earth. Its thickness varies from 3 mi (5 km) under the oceans, to about 19 mi (30 km) at the continents. It may reach up to 62 mi (100 km) under the large mountain ranges. There crust goes deeper. It is rich in oxygen and silicon with lesser amounts of miscellaneous materials like aluminum, iron, magnesium, calcium, potassium, or sodium. Oceanic crust is made of basalt as continental crust is made of lower density rocks like andesite or granite. This model is further complicated as the uppermost, cooler, part of the mantle is somehow jointed to the crust which is just above it and they behave similarly. Together they are forming the "lithosphere" , which is 50 mi (80 km) thick in average. The lithosphere has been broken into the plates plate tectonics is about. The next layer of the mantle forms the "asthenosphere" . The asthenosphere is found just beneath the lithosphere. It's a narrow, mobile zone made of hot, semi-solid material which can soften and flow after subjected to high temperature and pressure over geologic time. It's the various motions of this system which yields the plate tectonics; asthenosphere is slowly moving. The more rigid lithosphere is floating above, or about it. Banner fails to tell us precisely how Indians viewed property. Sometimes, he seems to suggest that their conceptions of property were not all that different from those of whites. Yet he also notes that no market in real estate existed before the coming of the Europeans. Indians did not buy and sell land among themselves. Most tribes seem to have allocated plots to individual families, while unclaimed land remained free for the taking. Since villages tended to move when soil was depleted, the European notion of a fenced-off piece of land belonging for ever to a single family didn’t make much sense. Nor did the idea of accumulating more and more land as a way of enhancing one’s wealth. Certainly, Indians familiarised themselves over time with the colonists’ definition of landed property. Well into the 19th century, however, Banner notes, ‘individuals owned rights to use land, not the land itself.’ This use-right, he insists, ‘was property’. But he never examines the implications – legal, economic and ideological – of differences between white and Indian conceptions of property. SLEEP deprivation is an uncomfortable experience. In drivers and workers it can lead to fatal accidents. In those under interrogation it can lead to confession. But why it does what it does is mysterious—as, indeed, is the purpose of sleep itself. 睡眠被剥夺是很不舒服的经历。这在司机或工人身上可能引发致命的事故。在那些被审讯的人身上则迫使其招供。但为什么会有这种效果却仍然是一个谜——正如实际上睡眠的目的本身也是个谜。 Many theories have been proposed to explain why the pressure to sleep builds up until it becomes irresistible. The latest, presented at the recent annual meeting of the Organization for Human Brain Mapping, in Florence, Italy, starts from the obvious proposition that the longer you stay awake, the more you learn. Giulio Tononi of the University of Wisconsin proposes that this extra learning makes the brain more and more expensive to maintain. Sleep prunes back the grey matter so that, come the morning, the brain is once again economical to run. If this pruning cannot take place, the organ becomes less and less efficient, and dire consequences result. 形形色色的理论被提出，试图解释为什么睡意逐渐袭来直至不可抗拒。最新的理论在最近于意大利的佛罗伦萨举行的人脑制图组织的年会上发表，它基于一个显而易见的命题，即一个人清醒的时间越长那么学习得就越多。来自威斯康星大学的朱利奥托诺尼提出，这额外的学习时间会使大脑维持正常运行的消耗越来越大。睡眠对于灰质[1]的剪裁使大脑在第二天早上再次轻装上阵。而如果这种剪裁不能进行，那么这个器官将越来越低效直至后果不堪设想。 Even at rest, the brain is costly to run, consuming 20% of the body's energy production. Most of this energy goes towards maintaining synapses, the junctions across which impulses jump from nerve cell to nerve cell, keeping the brain alert even when it is not doing anything. When a person learns something new, certain synapses are strengthened relative to others. Over the course of the day, there is a net increase in the strength and number of the brain's synapses. And, as Dr Tononi observes, stronger synapses consume more energy. In addition, making them requires more protein and fats and they take up more space. Given that an organism has limited supplies of all of these things, something must happen to prevent the cost of having a brain from gradually spiralling out of control. That something, Dr Tononi believes, is non-rapid eye movement (non-REM) or slow-wave sleep. 即便在休息时大脑的运行也代价高昂，它消耗人体产生的20%的能量。其中大部分用来维持突触，让大脑即使在无事可做时也保持警觉。突触是神经细胞间的连结，脉冲信号通过它们在细胞间传导。当一个人学到新知识的时候一部分特定的突触相对地被增强了。一天之中大脑突触的数量和连结强度都有净增长。并且如托诺尼博士所观察到的，越强的突触消耗越多能量。不仅如此，突触的增加还需要更多的蛋白质、脂肪和更大的空间。考虑到所有这些在一个生物体中都是有限的，所以必然存在某种机制来预防大脑的消耗逐渐超出负荷。这种机制在托诺尼博士看来就是非快速动眼睡眠或称慢波睡眠。 Until recently, most sleep research focused on REM sleep. This is the time when people dream, and dreams have had a grip on the scientific imagination since the days of Freud, and on the popular imagination at least since biblical times. Lately, though, researchers have started to wonder whether they have been looking in the wrong place for the significance of sleep, for REMming occupies only about a fifth of the night. 直到最近，大多数对于睡眠的研究都关注于快速动眼睡眠[3]。这种睡眠是人们做梦的时段，而这些梦深深吸引了自佛洛伊德时代以来的科学想象及自圣经时代以来的大众的想象力。后来研究者们开始怀疑他们是否在寻找睡眠意义的过程中步入误区，因为快速动眼睡眠仅在晚上的五份之一时间里发生。 During the other 80% of sleep—the part that is non-REM—the firing pattern of the brain's nerve cells sets up slow electrical waves that start at different points in the cerebral cortex and travel across it. These travelling waves occur hundreds of times a night, and most commonly at a frequency, 1 cycle per second, which has been shown to depress the activity of synapses. 在其余的80%的非快速动眼睡眠时间里，脑神经细胞的兴奋模式产生的慢速的电波从大脑皮层的不同的区域开始扩布。这些扩布的电波一晚上会产生上百次，大多数的频率是每秒钟扩布一轮，它们使突触的活动减弱。 Within an hour of a person falling asleep, slow waves will have covered his entire cortex, affecting every nerve cell in it. At first, these waves are big and powerful, but their size decreases through the night. Dr Tononi believes that the function of these slow waves is to “downscale” synapses, reducing their size, chemical activity and electrical activity—and thus the strength with which they connect their nerve cells together—all over the brain. 在人入睡后的一小时内慢波将覆盖其整个大脑皮层，并影响其中的每个神经细胞。这些慢波起初很强但波幅随时间推移逐渐减弱。托诺尼博士认为这些慢波的功用是削弱突触，减小它们的尺寸、化学活动和电活动，从而在整个大脑范围内减弱神经细胞间的联系。 The trick, he thinks, is that this downscaling is done in proportion to the existing strength of each synapse. When a sleeper awakens, the strength of each synapse is thus the same relative to all the others, but all synapses are weaker than they were when he went to sleep. Indeed, the weakest of them may vanish completely, taking part of the previous day's memory with them. 他认为其中的奥妙在于这种削弱是与每个突触原有的强度成比例的。因此当人苏醒时每个突触的相对强度是不变的，但所有的突触强度比之睡前都减弱了。实际上其中最弱的突触已经带着前一天的记忆片断一起完全消失了。 In earlier experiments, designed to replicate normal learning, Dr Tononi found that the part of the brain showing most slow-wave activity during sleep was the same as the part that had been activated during the experiment. This fitted the prediction that the downscaling slow-waves would be strongest in those parts of the brain where the most changes had taken place during the day. 在先前模拟正常的学习过程的试验中，托诺尼博士发现大脑中在睡眠时慢波最活跃的部分正是在试验中被激活的部分。这与预测相吻合，即大脑中被慢波削弱最显着的部分是在白天变化最大的。
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发表于 2007-12-7 14:23:00
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