听力音频[宝典]

听力音频[宝典] Cells and Temperature 细胞与温度 much narrower limits mark the boundaries of effective functioning. Enzyme systems of mammals and birds are most efficient only within a narrow range around 37C;a departure of a few degrees from this value seriously impairs their functioning. Even though cells can survive wider fluctuations the integrated actions of bodily systems are impaired. Other animals have a wider tolerance for changes of bodily temperature. centuries it has been recognized that mammals and birds differ from For other animals in the way they regulate body temperature. Ways of characterizing the difference have become more accurate and meaningful over time, but popular terminology still reflects the old division into “warm-blooded” and “cold-blooded” species; warm-blooded included mammals and birds whereas all other creatures were considered cold-blooded. As more species were studied, it became evident that this each classification was inadequate. A fence lizard or a desert iguana— cold-blooded----usually has a body temperature only a degree or two below that of humans and so is not cold. Therefore the next distinction was made between animals that maintain a constant body temperature, called home0therms, and those whose body temperature varies with their environments, called poikilotherms. But this classification also proved inadequate, because among mammals there are many that vary their body temperatures during hibernation. Furthermore, many invertebrates that live in the depths of the ocean never experience change in the depths of the ocean never experience change in the chill of the deep water, and their body temperatures remain constant. 细胞只能在一定的温度范围内存活，而进一步保证它们有效工作的温度范围就更小了。哺乳 动物和鸟类的酶系统只能在37?左右的很小范围内才能有效工作。与此 相差仅几度的温度 都会大大削弱它们的工作效率。尽管温度变化更大时细胞仍能存活，但机体系统的整体运行 能力却被削弱了。其它动物对体温的变化有更强的适应 性。 几个世纪以来，人们就认识到哺乳动物和鸟类调节体温的方式与其它动物不同。随着时间的 推移，人们对这种差异的描述越来越精确和有意义，但是"暖血动物" 和"冷血动物"这一古 老的分类方式至今仍在大众词汇中有所反映。暖血动物包括哺乳动物和鸟类，其它动物统统 被视为冷血动物。但是对更多物种进行的研究 表 关于同志近三年现实表现材料材料类招标技术评分表图表与交易pdf视力表打印pdf用图表说话 pdf 明 这种分类显然是不适当的。美洲一种小 型蜥蜴和沙漠鬣蜥同属冷血动物，但实际上它们的体温通常只比人类的体温低1,2度，因 此并不是真正的冷血。因此又出现 了恒温动物(即保持恒定体温的动物)和变温动物(即体温 随外界环境的变化而改变的动物)这一区分方式。但这种分类也不恰当。因为有不少哺乳动 物在冬眠期间 会改变体温，而许多生活在深海的无脊椎动物在寒冷的深海水域中体温并不 变化，而是恒定的。 Sleep 睡眠 (2)Sleep is part of a person’s daily activity cycle. There are several different stages of sleep, and they too occur in cycles. If you are an average sleeper, your sleep cycle is as follows. When you first drift off into slumber, your eyes will roll about a bit, you temperature will drop slightly, your muscles will relax, and your breathing will slow and become quite regular. Your brain waves slow and become quite regular. Your brain waves slow down a bit too, with the alpha rhythm of rather fast waves for a few minutes. This is called stage 1 sleep.. For the next half hour or so, as you relax more and more, you will drift down through stage 2 and stage 3 sleep. The lower your stage of sleep. slower your brain waves will be. Then about 40 to 60 minutes after you lose consciousness you will have reached the deepest sleep of all. Your brain will show the large slow waves that are known as the delta rhythm. This is stage 4 sleep. You do not remain at this deep fourth stage all night long, but instead about 80 minutes after you fall into slumber, your brain activity level will increase again slightly. The delta rhythm will disappear, to be replaced by the activity pattern of brain waves. Your eyes will begin to dart around under your closed eyelids as if you were looking at something occurring in front of you. This period of rapid eye movement lasts for some 8 to 15 minutes and is called REM sleep. It is during REM sleep period, your body will soon relax again, your breathing will grow slow and regular once more. Your breathing will slip gently back from stage 1 to stage 4 sleep----only to rise once again to the surface of near consciousness some 80 minutes later. 睡眠是人每天日常活动循环的一部分。人的睡眠分几个阶段，而这些阶段也是 循环发生的。如果你是一个正常的睡眠者，你的睡眠循环会这样进行。 在你开始昏昏入睡时，你的眼睛会滚动几下，体温略有下降，肌肉放松，呼吸 变得缓慢而有节奏。除了开始几分钟比较快的α节奏外，脑电波也稍有减缓。 这被称为第一阶段睡眠。在随后约半小时内，你进一步放松，进入第二和第三 阶段睡眠。睡眠越深入，脑电波就越缓慢。大约在开始睡眠后的40到 60分钟，你将进入沉睡状态。这时的脑电波表现为巨大的缓波，被称为δ节奏。 这就是第四阶段睡眠。 但你并不是整夜都保持这种沉睡状态。入睡后约80分钟左右，你的大脑运动水 平会再度略有提高。δ节奏消失，并被脑电波的运动图形取代。你的眼睛会 在 闭着的眼睑下迅速转动，就好象你在看着眼前发生的什么事情。这种迅速的 眼球运动持续约8,15分钟，这一阶段睡眠被称之为快速眼动(REM)睡眠。在 REM 睡眠阶段，你的肢体会很快再度放松，呼吸也再次放慢并变得有节奏，你会轻 松地从第一阶段滑入第四阶段睡眠-直到大约80分钟后重新接近清醒状态。Folk Cultures 民间文化 (4)A folk culture is a small isolated, cohesive, conservative, nearly self-sufficient group that is homogeneous in custom and race with a strong or clan structure and highly developed rituals. Order is maintained family through sanctions based in the religion or family and interpersonal relationships are strong. Tradition is paramount, and change comes infrequently and slowly. There is relatively little division of labor into specialized duties. Rather, each person is expected to perform a great variety of tasks, though duties may differ between the sexes. Most goods are handmade and subsistence economy prevails. Individualism is weakly developed in folk cultures as are social classes. Unaltered folk cultures no longer exist in industrialized countries such as the United States and Canada. Perhaps the nearest modern equivalent in Anglo America is the Amish, a German American farming sect that largely renounces the products and labor saving devices of the industrial age. In Amish areas, horse drawn buggies still serve as a local transportation device and the faithful are not permitted to own automobiles. The Amish’s central religious concept of Demut “humility”, clearly reflects the weakness of individualism and social class so typical of folk cultures and there is a corresponding strength of Amish group identity. Rarely do the Amish marry outside their sect. The religion, a variety of the Mennonite faith, provides the principal mechanism for maintaining order. By contrast a popular culture is a large heterogeneous group often highly individualistic and a pronounced many specialized professions. Secular institutions of control such as the police and army take the place of religion and family in maintaining order, and a money-based economy prevails. Because of these contrasts, “popular” may be viewed as clearly different from “folk”. The popular is replacing the folk in industrialized countries and in many developing nations. Folk-made objects give way to their popular equivalent, usually because the popular item is more quickly or cheaply produced, is easier or time saving to use or leads more prestige to the owner. 民间文化是小型的、孤立的、紧密的、保守的、近乎自给自足的群体，具有同样 的习俗、同样的人种和强有力的家庭或部族结构以及高度发展的宗教仪式。 秩序由宗教或家庭的约束来维持，成员间的关系非常紧密，传统至高无上，很少 有变动且变动缓慢。劳动专业分工相对较少。每个人都要做各类活计，尽管男女 两性 分工不同。绝大多数物品是手工制造的，经济一般为自给自足型。个人主 义和社会阶层在民间文化群体中的发展十分薄弱。在象美国和加拿大这样的工业 化国家里， 一成不变的民间文化群体已不复存在了。在当代美洲的英语区，与 民间文化最相似的群体也许算是Amish。Amish是美国的德裔农耕部落，他们基 本上拒绝 接受工业时代的大多数产品和节省劳力的设施。在Amish地区，轻便 马车仍是当地的交通工具，信徒们不允许拥有汽车。Amish宗教中的核心观念 Demut即谦卑典型地反映了在民间文化群中个人主义和阶级的不发达。而与此同 时，Amish对群体的认同性却十分强。Amish人很少和他们宗派以外的 人通婚。 其宗教，作为Mennonite信仰的一种，提供了维护秩序的主要机制。相反，大众 文化是包含不同种族的大群体，通常高度个性化而且不断在变化。 人际关系冷 漠，劳动分工明确，由此产生了许多专门的职业。世俗的控制机构，比如警察和 军队，取代了宗教和家庭来维持秩序，而且实行的是货币经济。 大众的"与"民间的"可谓大相径庭。在工业化国家以及许由于存在着这些差异，" 多发展中国家里，大众文化正在取代民间文化。 民间制造的物品正让位于大众化产品，这通常是因为大众化的物品制造起来更 快、更便宜，用起来更容易、更方便或者是能给其所有者带来更多的威望。 Vision 视觉 (5)Human vision like that of other primates has evolved in an arboreal environment. In the dense complex world of a tropical forest, it is more important to see well than to develop an acute sense of smell. In the course of evolution members of the primate line have acquired large eyes while the snout has shrunk to give the eye an unimpeded view. Of mammals only humans and some primates enjoy color vision. The red flag is black to the bull. Horses live in a monochrome world .light visible to human eyes however occupies only a very narrow band in the whole electromagnetic spectrum. Ultraviolet rays are invisible to humans though ants and honeybees are sensitive to them. Humans though ants and honeybees are sensitive to them. Humans have no direct perception of infrared rays unlike the rattlesnake which has receptors tuned into wavelengths longer than 0.7 micron. The world would look eerily different if human eyes were sensitive to infrared radiation. Then instead of the darkness of night, we would be able to move easily in a strange shadowless world where objects glowed with varying degrees of intensity. But human eyes excel in other ways. They are in fact remarkably discerning in color gradation. The color sensitivity of normal human vision is rarely surpassed even by sophisticated technical devices. 人类的视觉，和其它灵长目动物的一样，是在丛林环境中进化出来的。在稠密、 复杂的热带丛林里，好的视觉比灵敏的嗅觉更加重要。在进化过程中，灵长目 动物的 眼睛变大，同时鼻子变小以使视野不受阻碍。在哺乳类动物中，只有人 和一些灵长目动物能够分辨颜色。红旗在公牛看来是黑色的，马则生活在一个 单色的世界里。 然而，人眼可见的光在整个光谱中只占一个非常狭窄的频段。 人是看不到紫外线的，尽管蚂蚁和蜜蜂可以感觉到。与响尾蛇不同，人也不能 直接感受到红外线。响尾 蛇的感觉器可以感受波长超过0.7微米的光线。如果 人能感受到红外线的话，这世界看上去将十分不同，而且恐怖。到那时，将与 夜的黑暗相反，我们能轻易地在 一个奇异的没有阴影的世界里走动。任何物体 都强弱不等地闪着光。然而，人眼在其它方面有优越之处。事实上，人眼对颜 色梯度具有非凡的分辨能力。普通人类的 视觉感受色彩的灵敏程度，甚至连精 密的技术装备都很难超越。 Bacteria 细菌 (3)Bacteria are extremely small living things. While we measure our own sizes in inches or centimeters, bacterial size is measured in microns. One micron is a thousandth of a millimeter: a pinhead is about a millimeter across. Rod-shaped bacteria are usually from two to four microns long, while rounded ones are generally one micron in diameter. Thus if you enlarged a rounded bacterium a thousand times, it would be just about the size of a pinhead. An adult human magnified by the same amount would be over a mile(1.6 kilometer) tall. Even with an ordinary microscope, you must look closely to see bacteria. Using a magnification of 100 times, one finds that bacteria are barely visible as tiny rods or dots. One cannot make out anything of their structure. Using special stains, one can see that some bacteria have attached to them wavy-looking “hairs” called flagella. Others have only one flagellum. The flagella rotate, pushing the bacteria through the water. Many bacteria lack flagella and cannot move about by their own power, while others can glide along over surfaces by some little-understood mechanism. From the bacteria point of view, the world is a very different place from what it is to humans. To a bacterium water is as thick as molasses is to us. Bacteria are so small that they are influenced by the movements of the chemical molecules around them. Bacteria under the microscope, even those with no flagella, often bounce about in the water. This is because they collide with the watery molecules and are pushed this way and that. Molecules move so rapidly that within a tenth of a second the molecules around a bacteria have all been replaced by new ones; even bacteria without flagella are thus constantly exposed to a changing environment. 细菌是极其微小的生物体。我们用英寸或厘米来测量自己的大小，而测量细菌却 要用微米。一微米等于千分之一毫米。针头直径大约一毫米。 棒状细菌通常有2,4微米长，而圆形细菌的直径一般只有1微米。因此，即使 你把一个圆形细菌放大1000倍，它也不过一个针头那么大。 可是如果把一个成年人放大1000倍，就会变成1英里(或1.6公里)多高。 用一般的显微镜观察细菌时，你必须仔细观察才能看见它们。使用100倍的显微 镜时，你会发现细菌不过是隐约可见的小细棒或小点点，而它们的结构你却根本 看不出来。使 用特殊的着色剂后，你会发现有的细菌上长着不少波状的"毛发"即鞭毛，而有的 细菌只有一根鞭毛。鞭毛的旋转可以推动细菌在水中行进。不少细菌没有鞭毛， 因而不能自己行进。还有些细菌却能通过某些鲜为人知的机制沿物体表面滑动。 我们所熟知的世界在细菌眼中完全是另一个样子。对于细菌来说，水就同糖浆之 于人类一样稠密。细菌是如此的微小，周围化学分子的一举一动都会对它们产生 影 响。在显微镜下，细菌，甚至包括那些没有鞭毛的细菌，经常在水中跳来跳 去。这是因为它们与水分子相撞后，被弹向各个方向。分子移动很迅速，仅0.1 秒之 隔，一个细菌周围的分子就会完全更新。因此，即使是没有鞭毛的细菌也 暴露在一个不断变化的环境中。 The source of Energy 能量的来源 (6)A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Sun’s very center. It is here that is to be found the source of the energy that the Sun constantly pours out into space as light and heat. This energy is librated at the center of the Sun as billions upon billions of nuclei of hydrogen atoms collide with each other and fuse together to form nuclei of helium, and in doing so, release some of the energy that is stored in the nuclei of atoms. The output of light and heat of the Sun requires that some 600 million tons of hydrogen be converted into helium in the Sun every second. This the Sun has been doing for several thousands of millions of year. The nuclear energy is released at the Sun’s center as high-energy gamma radiation, a form of electromagnetic radiation like light and radio waves, only of very much shorter wavelength. This gamma radiation is absorbed by atoms inside the Sun to be reemitted at slightly longer wavelengths. This radiation , in its turn is absorbed and reemitted. As the energy filters through the layers of the solar interior, it passes through the X-ray part of the spectrum eventually becoming light. At this stage, it has reached what we call the solar surface, and can escape into space without being absorbed further by solar atoms. A very small fraction of the Sun’s light and heat is emitted in such directions that after passing unhindered through interplanetary space, it hits the Earth. 说生命的物理和化学特性必须始于太阳--确切地说，是太阳的核心，而非地球。 能量来自太阳的核心。在这里，太阳不停地以光和热的形式向空间倾泻出能量。 数 十亿计的氢原子核在太阳的核心碰撞并且聚变生成氦。在此过程中一部分原 本储存于原子核中的能量被释放出来。太阳所产生的光和热需要每秒将六亿吨氢 转化为 氦。这样的转化在太阳中 已经持续几十亿年了。 核能在太阳的核心被释放为高能的伽马射线。这是一种电磁射线，就象光波和无 线电波一样，只是波长要短得多。这种伽玛射线被太阳内的原子所吸收，然后重 新释 放为波长稍长一些的光波。这新的射线再次被吸收，而后释放。在能量由 太阳内部一层层渗透出来的过程中，它经过了光谱中X射线部分，最后变成了光。 在此阶 段，能量到达我们所称的太阳表层，并且离散到空间而不再被太阳原子 所吸收。只有很小一部分太阳的光和热由此方向释放出来，并且未被阻挡，穿越 星空，来到地 球。 Obtaining Fresh water from icebergs 从冰山中获 取淡水 (7)The concept of obtaining fresh water from icebergs that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food. Glaciers are a possible source of fresh water that has been overlooked until recently. Three-quarters of the Earth’s fresh water supply is still tied up in glacial ice, a reservoir of untapped fresh water so immense that it could sustain all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes, rather, they are formed entirely on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction opposite to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To corral them and steer them to parts of the world where they are needed would not be too difficult. The difficulty arises in other technical matters, such as the prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalinization, or removing salt from water. 把冰山拖到世界上人口稠密的地区和干旱地带，再从中获取淡水，这个想法曾一 度被认为是一个笑话，更适合于卡通画，而非现实生活。然而现在，许多国家正 相当认真地考虑这件事情，特别是在科学家们发出警告之后。科学家们认为人类 将在耗尽粮食之前首先耗尽淡水资源。 冰川是一个直到最近以前一直被忽视的可能的淡水源。全球四分之三的淡水还锁 在冰川的冰块中。冰川就是一个蓄水池，其中未开发的淡水量是如此巨大，足够 支持 全世界的江河1000年。每年有7，659万亿公吨冰漂流在海洋中。它们包 含在10，000座从极地冰帽中断裂出来的冰山中。这些冰山的90%以上来自南 极。 一年四季里，覆盖在浅层大陆架上的巨大冰川生成了众多冰山。冰山和海水的冰 不同，后者是海水自身结冰形成的，而冰山则完全是在陆地上形成的。当冰川伸 展到 海水中时，冰山就断裂下来。当漂离极地地区时，冰山有时会在底层洋流 的推动下颇为神秘地逆风移动。由于冰山比小块的冰融化要慢，因此有的冰山在 大西洋中向 北飘到了赤道以南35?的地方。把冰山蓄拦起来并拖到世界上需要 它们的地方将不会太困难。 有困难的是其它的技术事宜。比如，如何防止冰山在较暖的气候中迅速融化以及 如何把大量的淡水收集到岸上去。但是，即便在拖的过程中冰山失去了一半体积， 这样做也远比从海水中脱盐取得淡水便宜。 Statistics 统计学 (8)There were two widely divergent influences on the early development of statistical methods. Statistics had a mother who was dedicated to keeping orderly records of government units (states and statistics come from the same Latin root status) and a gentlemanly gambling father who relied on mathematics to increase his skill at playing the odds in games of chance. The influence of the mother on the offspring, statistics, is represented by counting, measuring, describing, tabulating, ordering, and the taking of censuses—all of which led to modern descriptive statistics. From the influence of the father came modern inferential statistics, which is based squarely on theories of probability. Describing collections involves tabulating, depicting and describing collections of data. These data may be quantitative such as measures of height, intelligence or grade level------variables that are characterized by an underlying continuum---or the data may represent qualitative variables, such as sex, college major or personality type. Large masses of data must generally undergo a process of summarization or reduction before they are comprehensible. Descriptive statistics is a tool for describing or summarizing or reducing to comprehensible form the properties of an otherwise unwieldy mass of data. Inferential statistics is a formalized body of methods for solving another class of problems that present great of problems characteristically involves attempts to make predictions using a sample of observations. For example, a school superintendent wishes to determine the proportion of children in a large school system who come to school without breakfast, have been vaccinated for flu, or whatever. Having a little knowledge of statistics, the superintendent would know that it is unnecessary and inefficient to question each child: the proportion for the sample of as few as 100 children. Thus , the purpose of inferential statistics is to predict or estimate characteristics of a population from a knowledge of the characteristics of only a sample of the population. 统计 方法 快递客服问题件处理详细方法山木方法pdf计算方法pdf华与华方法下载八字理论方法下载 的早期发展受到两种截然不同的影响。统计学有一个"母亲"，她致力于 井井有条地记录政府机构的文件(国家和统计学这两个词源于同一个拉丁语词 根，status)，还有一个有绅士般的赌博"父亲"，他依靠数学来提高赌技，以便 在几率的游戏中取胜。"母亲"对其子女统计学的影响表现在计数、测量、 描述、 制表、归类和人口普查。所有这些导致了现代描述统计学的诞生。由于"父亲" 的影响则产生了完全基于概率论原理的现代推理统计学。 描述统计学涉及对所收集数据的制表、制图和描述。这些数据可以是数量性的数 据，如高度、智商、或者是层级性的数据--具有连续性的变量--或数据也可以代 表性质变量，如性别、大学专业或性格类型等等。数量庞大的数据通常必须经过 概括或删减的程序才能为人所理解。描述统计学就是这样一个工具，它对极其庞 杂的 数据进行描述、概括或删减，使其变成能为人理解的东西。 推理统计学是一套已定形了的方法体系，它解决的是光凭人脑极难解决的另一类 问 题 快递公司问题件快递公司问题件货款处理关于圆的周长面积重点题型关于解方程组的题及答案关于南海问题 。这类问题的显著特点是试图通过取样调查来作出预测。例如，有一位教育 督察 想知道在一个庞大的学校系统中，不吃早饭就上学的学生、已经做过防感 冒免疫的学生，或其它任何类型的学生占多大比例。若具备一些统计学的知识， 这位督察应 明白，询问每个孩子是没有必要而且没有效率的，只要用100个孩 子为样本，他就可以相当精确地得出这些孩子占整个学区的比例了。因此，推理 统计学的目的就 是通过了解一个群体中一些样本的特性，从而对整个群体的特 性进行推测和估算。 Coal-fired power plants 火力发电厂 火力发电厂 (9)The invention of the incandescent light bulb by Thomas A. Edison in 1879 created a demand for a cheap, readily available fuel with which to generate large amounts of electric power. Coal seemed to fit the bill, and it fueled the earliest power stations. (which were set up at the end of the nineteenth century by Edison himself). As more power plants were constructed throughout the country, the reliance on coal increased throughout the country, the reliance on coal increased. Since the First World War, coal-fired power plants had a combined in the United States each year. In 1986 such plants had a combined generating capacity of 289,000 megawatts and consumed 83 percent of the nearly 900 million tons of coal mined in the country that year. Given the uncertainty in the future growth of the nearly 900 million tons of coal mined in the country that year. Given the uncertainty in the future growth of nuclear power and in the supply of oil and natural gas, coal-fired power plants could well provide up to 70 percent of the electric power in the United States by the end of the century. Yet, in spite of the fact that coal has long been a source of electricity and may remain on for many years(coal represents about 80 percent of United States fossil-fuel reserves), it has actually never been the most desirable fossil fuel for power plants. Coal contains less energy per unit of weight than weight than natural gas or oil; it is difficult to transport, and it is associated with a host of environmental issues, among them acid rain. Since the late 1960’s problems of emission control and waste disposal have sharply reduced the appeal of coal-fired power plants. The cost of ameliorating these environment problems along with the rising cost of building a facility as large and complex as a coal-fired power plant, have also made such plants less attractive from a purely economic perspective. Changes in the technological base of coal-fired power plants could restore their attractiveness, however. Whereas some of these changes are intended mainly to increase the productivity of existing plants, completely new technologies for burning coal cleanly are also being developed. 托马斯爱迪生1879年发明的白炽灯导致对便宜、易得、可生产大量电能的燃料 的需求。煤似乎符合这个要求，并成为第一批电厂的燃料(正是爱迪生本人在19 世纪末建造了第一批电厂)。全国到处兴建电厂时，对煤的依赖加深了。自第一 次世界大战以来，美国每年约有一半的电力是以煤为燃料的电厂提供的。1986 年 这些电厂的总发电能力达到28，900千瓦并且消耗了当年全国开采的九亿吨 煤的83%。考虑到核能发展以及石油、天然气供应中的不确定因素，到本世纪末， 火力发电厂仍可能为美国提供多达70%的电力。 然而，尽管煤长期以来一直是电力的原料之一并且可能会继续如此(煤占美国化 石燃料储量的80%)，它却不是电厂的理想燃料。煤的单位能量含量低于石油和 天 然气，而且会导致包括酸雨在内的一系列环境问题。从1960年以来，排放控 制和垃圾处理的问题极大地削弱了燃煤电厂的魅力。由于减轻这些环境问题需要 大量 资金，而且建造庞大复杂的燃煤电厂的费用不断上涨，也使得这些电厂从 经济角度上不具备吸引力。 改变火力发电厂的基础技术却可能恢复它们的吸引力。虽然某些技术改进是渐进 的，其目的只是提高现有电厂的生产率，但人们正在开发全新的清洁燃煤的技术。 American black bears 美国黑熊 (10)American black bears appear in a variety of colors despite their name. In the eastern part of their range, most of these brown, red, or even yellow coats. To the north, the black bear is actually gray or white in color. Even in the same litter, both brown and black furred bears may be born. Black bears are the smallest of all American bears, ranging in length from five to six feet, weighing from three hundred to five hundred pounds Their eyes and ears are small and their eyesight and hearing are not as good as their sense of smell. Like all bears, the black bear is timid, clumsy, and rarely dangerous , but if attacked, most can climb trees and cover ground at great speeds. When angry or frightened, it is a formidable enemy. Black bears feed on leaves, herbs. Fruit, berries, insects, fish, and even larger animals. One of the most interesting characteristics of bears, including the black bear, is their winter sleep. Unlike squirrels, woodchucks, and many other woodland animals, bears do not actually hibernate. Although the bear does not during the winter moths, sustaining itself from body fat, its temperature remains almost normal, and it breathes regularly four or five times per minute. Most black bears live alone, except during mating season. They prefer to live in caves, hollow logs, or dense thickets. A little of one to four cubs is born in January or February after a gestation period of six to nine months, and they remain with their mother until they are fully grown or about one and a half years old. Black bears can live as long as thirty years in the wild , and even longer in game preserves set aside for them. 美国黑熊虽然被叫做黑熊但却有各种各样的颜色。在它们生活区域的东部，大部 分黑熊长有富有光泽的黑毛，但在西部，他们则长着棕色、红色甚至是黄色的毛。 在北部，黑熊其实长着灰色或白色的毛。就是在一胎所生的小熊中，都可能混杂 棕毛和黑毛。 黑熊是所有美洲熊中最小的，5,6英尺长，300,500磅重。它们的眼睛和耳朵 都很小，他们的视力和听觉不如嗅觉那样好。 像所有的熊一样，黑熊胆小，笨拙，很少具有危险性。但如果受到攻击，大部分 黑熊会以很快的速度爬上树和奔跑。当发怒或受惊吓时，黑熊会成为可怕的对手。 黑熊以树叶、草、树根、水果、浆果、昆虫、鱼，甚至更大的动物为食。熊类， 包括黑熊的最有趣的一个特点是他们的冬眠。与松鼠、旱獭和其它别的林地动物 不 同，熊并不真正地冬眠。虽然熊在冬天的几个月中不吃东西，靠体内脂肪维 持生命，但它们的体温保持正常，并有规律地一分钟呼吸4或5次。 除交配季节外，大多数黑熊独自生活。他们喜欢住在洞里、空心的大木头里或茂 密的树丛里。经过6到9个月的怀孕期后一胎1,4个小熊在1月或2月出生。 它们同母熊住在一起，直到它们完全长大，即1岁半左右。黑熊在野外可以活到 长达30年，在专门的保护区中甚至能活得更长。 Cohesion-tension Theory 内聚压力理论 (11)Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher; the sequoia tree can pump water to its very top more than 100 meters above the ground. Until the end of the nineteenth century, the movement of water in trees and other tall plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps. But many experiments demonstrated that the stems of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore, the conifers, which are among the tallest trees, have unusually low root pressures. If water is not pumped to the top of a tall tree, and if it is not pushed to the top of a tall tree, then we may ask: how does it get there According to the currently accepted cohesion-tension theory, water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves, a negative pressure, or tension, is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohesion (the attraction between water molecules) are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken. 大气压能够支持10米高的水柱，但植物可将水送得更高。美洲红杉就能把水泵 到地面以上100多米高的树顶。直到19世纪末，水在树木和其它高大植物中的 输 送还是一个谜。一些植物学家假定植物中的活细胞充当了水泵的角色。但许 多实验表明细胞都已死亡的植物茎干仍能将水输送到相当可观的高度。对于植物 中输送水 的其它解释都基于根压--植物底端的根对水的推动。但根压完全不足 以将水推到树顶。况且，最高树木中的松柏只有很低的根压。 如果水不是被泵到高树的树顶，也不是被推到树顶，那么我们会问:它是怎样到 达树顶的呢根据目前为人们所接受的内聚压力的理论，水是被拉到上面去的。一 株植 物中作用于一个正在升高的水柱之上的拉力来自该植物顶部水的蒸发。由 于水从叶子表面丧失，一个负压力，或张力就得以产生。蒸发出去的水被植物里 流动的水代 替。这些水形成水柱从植物顶端一直延伸到根部。在任何水样中造 成表面张力的力支持着这些不断的水柱。当水被限制在内径很小的管道中时，内 聚压力(水分子之 间的相互吸引力)是如此之大以致一支水柱的强度相当于一根 直径相同的钢丝的强度。这种内聚压力使得水柱被拉到非常高的地方而不会断 裂。 The Salinity of Ocean Waters 海水盐度 (12)If the salinity of ocean waters is analyzed, it is found to vary only slightly from place to place. Nevertheless, some of these small changes are important. There are three basic processes that cause a change in oceanic salinity. One of these is the subtraction of water from the ocean by means of evaporation--- conversion of liquid water to water vapor. In this manner the salinity is increased, since the salts stay behind. If this is carried to the extreme, of course, white crystals of salt would be left behind. The opposite of evaporation is precipitation, such as rain, by which water is added to the ocean. Here the ocean is being diluted so that the salinity is decreased. This may occur in areas of high rainfall or in coastal regions where rivers flow into the ocean. Thus salinity may be increased by the subtraction of water by evaporation, or decreased by the addition of fresh water by precipitation or runoff. Normally, in tropical regions where the sun is very strong, the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation. Similarly, in coastal regions where rivers dilute the sea, salinity is somewhat lower than in other oceanic areas. A third process by which salinity may be altered is associated with the formation and melting of sea ice. When sea water is frozen, the dissolved materials are left behind. In this manner, sea water directly materials are left behind. In this manner, sea water directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared. Of course, when this ice melts, it will tend to decrease the salinity of the surrounding water. In the Weddell Sea Antarctica, the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water. This heavy water sinks and is found in the deeper portions of the oceans of the world. 如果我们分析海水的盐度，会发现地区间只有轻微的变化，然而有些小的变化是 重要的。导致海洋的盐度变化的基本过程有三个，其中之一是通过蒸发的方式即 把液 态水转化为水蒸气来减少海洋中的水分。这样由于盐留了下来，所以盐度 增大。当然，如果这种方式走向极端，将会余下白色的盐晶体。 与蒸发相反的是降水，如降雨，由此水被加入海中，海水被稀释，从而盐度降低。 这种情形会发生在大量降雨的地区，或江河入海岸处。因此，盐度通过蒸发减少 水分而上升或通过降水或径流增加淡水成分而下降。 一般来说，在阳光很强烈的热带地区，海水的盐度略高于世界上其它没有热带那 样多的蒸发的地区。同理，在江河稀释海水的海岸地带，海水盐度略低于其它海 区。 第三个可以变更盐度的过程与海洋中冰的形成和融化有关。海水冻结时，溶于其 中的物质被留了下来。这样，在新形成的海水冰面的正下方的海水比在冰形成之 前有更高的盐度。当然，当冰融化的时候，会降低周围水中的盐度。 在南极洲边缘的威德尔海中，结冰过程增加低温海水的盐度，从而形成了浓度最 大的海水。这些大密度的海水下沉，可以在世界海洋的深水域发现。 Topaz 黄水晶 (13)Topaz is a hard, transparent mineral. It is a compound of aluminum, silica, and fluorine. Gem topaz is valuable. Jewelers call this variety of the stone “precious topaz”. The best-known precious topaz gems range in color from rich yellow to light brown or pinkish red. Topaz is one of the hardest gem minerals. In the mineral table of hardness, it has a rating of 8, which means that a knife cannot cut it, and that topaz will scratch quartz. The golden variety of precious topaz is quite uncommon. Most of the world’s topaz is white or blue. The white and blue crystals of topaz are large, often weighing thousands of carats. For this reason, the value of topaz does not depend so much on its size as it does with diamonds and many other precious stones, where the value increases about four times with each doubling of weight. The value of a topaz is largely determined by its quality. But color is also important: blue topaz, for instance, is often irradiated to deepen and improve its color. Blue topaz is often sold as aquamarine and a variety of brown quartz is widely sold as topaz. The quartz is much less brilliant and more plentiful than true topaz. Most of it is variety of amethyst: that heat has turned brown. 黄水晶是一种坚硬、透明的矿物质。它是铝、硅和氟的化合物。黄水晶宝石价值 不菲。珠宝商把这种石头称为"黄玉"。最出名的黄玉有各种颜色如深黄色、淡棕 色、浅红色等。黄水晶是最坚硬的宝石矿中的一种。在矿石硬度表上，它的硬度 为8，这表明刀子不能割开它而它可在石英上划痕。 金黄色的黄玉品种非常罕见。世界上大多数的黄水晶是白色或蓝色的。这些白色 或蓝色的黄水晶晶体很大，常常有数千克拉重。由于这个原因，黄水晶的价值不 像钻 石和许多其它宝石那样主要依赖于其大小，重量翻一番价值即上升约四倍。 黄水晶的价值很大程度上取决于其品质，但颜色也很重要。举例来说，蓝色的黄 水晶常需 放射处理以加深和改善其颜色。 蓝色的黄水晶常被作为海蓝宝石出售，许多种棕色石英被当作黄水晶广为贩卖。 石英光亮度远小于黄水晶，矿藏储量也远较黄水晶丰富。大多数石英是一种紫水 晶，高温使其变为棕色。 Icebergs 冰山 (14)Icebergs are among nature’s most spectacular creations, and yet most people have never seen one. A vague air of mystery envelops them. They come into being ----- somewhere ------in faraway, frigid waters, amid thunderous noise and splashing turbulence, which in most cases no one hears or sees. They exist only a short time and then slowly waste away just as unnoticed. Objects of sheerest beauty they have been called. Appearing in an endless variety of shapes, they may be dazzlingly white, or they may be glassy blue, green or purple, tinted faintly of in darker hues. They are graceful, stately, inspiring ----- in calm, sunlight seas. But they are also called frightening and dangerous, and that they are ---- in the night, in the fog, and in storms. Even in clear weather one is wise to stay a safe distance away from them. Most of their bulk is hidden below the water, so their underwater parts may extend out far beyond the visible top. Also, they may roll over unexpectedly, churning the waters around them. Icebergs are parts of glaciers that break off, drift into the water, float about awhile, and finally melt. Icebergs afloat today are made of snowflakes that have fallen over long ages of time. They embody snows that drifted down hundreds, or many thousands, or in some cases maybe a million years ago. The snows fell in polar regions and on cold mountains, where they melted only a little or not at all, and so collected to great depths over the years and centuries. As each year’s snow accumulation lay on the surface, evaporation and melting caused the snowflakes slowly to lose their feathery points and become tiny grains of ice. When new snow fell on top of the old, it too turned to icy grains. So blankets of snow and ice grains mounted layer upon layer and were of such great thickness that the weight of the upper layers compressed the lower ones. With time and pressure from above, the many small ice grains joined and changed to larger crystals, and eventually the deeper crystals merged into a solid mass of ice. 冰山是大自然最壮观的创造之一，但大多数人却从未看到过冰山，一种朦胧神秘 的气氛笼罩着它们。冰山形成于久远的、寒冷的水体中，而且伴随着雷声轰鸣般 的嘈杂和水花汹涌的风暴，但却无人耳闻目睹。冰山仅存在短短的一段时间就慢 慢地悄无声息地融化掉。 冰山具有最纯粹的美，人们如是说。冰山呈现出千姿百态，可能白得耀眼，或者 是闪耀着蓝色、绿色或紫色的玻璃般的光芒，或浓或淡。它们在平静的阳光照耀 的海水中显得优雅堂皇，令人浮想联翩。 在夜间，雾天和风暴肆但是人们亦把冰山称为恐怖的和危险的。它们的确如此-- 虐时。即便是在晴朗的天气里，与它们保持一段安全距离也是明智的。冰山的大 部分体积稳藏于水下，因此其水下部分的伸展远远超过可见的顶部。冰山也可能 出人意料地翻滚，剧烈地搅动周围的水体。 冰山是冰川的一部分，从冰川断裂漂流进水中，一段时间后融化。今天的冰山由 多年前降落的雪花形成。它们的体内是数百年，或数千年，有时甚至是数百万年 前的降雪。这些雪花落在极地或寒冷的山上，仅有少量融化或根本不融化，这样 经过许多年或许多世纪后积累了巨大的深度。 由于每年的雪花积累在表面之上，蒸发和融化使得雪花慢慢失去其羽状尖端而变 成微小的冰粒。当新的雪花降落到旧的表面上，也变成了冰粒。因而雪花覆盖层 和冰 粒层层堆积起来直到如此之大的厚度以致较上层的重量压缩较下层。在时 间和压力的作用下，许多小冰粒结合到一起变成更大的晶体，最终较底层的晶体 合并成庞大 而坚固的冰块。 Plate Tectonics and Sea-floor Spreading 板块结构与海床扩 (15)The theory of plate tectonics describes the motions of the lithosphere, the comparatively rigid outer layer of the Earth that includes all the crust and part of the underlying mantle. The lithosphere(n.[地]岩石圈)is divided into a few dozen plates of various sizes and shapes, in general the plates are in motion with respect to one another. A mid-ocean ridge is a boundary between plates where new lithospheric material is injected from below. As the plates diverge from a mid-ocean ridge they slide on a more yielding layer at the base of the lithosphere. Since the size of the Earth is essentially constant, new lithosphere can be created at the mid-ocean ridges only if an equal amount of lithospheric material is consumed elsewhere. The site of this destruction is another kind of plate boundary: a subduction zone. There one plate dives under the edge of another and is reincorporated into the mantle. Both kinds of plate boundary are associated with fault systems, earthquakes and volcanism, but the kinds of geologic activity observed at the two boundaries are quite different. The idea of sea-floor spreading actually preceded the theory of plate tectonics. In its original version, in the early 1960’s, it described the creation and destruction of the ocean floor, but it did not specify rigid lithospheric plates. The hypothesis was substantiated soon afterward by the discovery that periodic reversals of the Earth’s magnetic field are recorded in the oceanic crust. As magma rises under the mid-ocean ridge, ferromagnetic minerals in the magma become magnetized in the direction of the magma become magnetized in the direction of the geomagnetic field. When the magma cools and solidifies, the direction and the polarity of the field are preserved in the magnetized volcanic rock. Reversals of the field give rise to a series of magnetic stripes running parallel to the axis of the rift. The oceanic crust thus serves as a magnetic tape recording of the history of the geomagnetic field that can be dated independently; the width of the stripes indicates the rate of the sea-floor spreading. 板块结构理论描述岩石圈的运动。岩石圈是相对坚硬的地球外层，包括全部地壳 和部分地幔。岩石圈被划分为几十个大小不同形状各异的板块，一般而言这些板 块都 处于相对运动之中。一道中海脊是板块之间的边界，在那里新的岩石圈的 物质从下部注入。当板块从中海脊脱离时，它们滑向在岩石圈基部较易变形的地 层上。 因为地球的大小本质上是不变的，只有同等数量的岩石圈物质在其它地方被吞 没，新的岩石圈才能生成。销毁旧岩石圈的地方形成另外一种板块边界:一块潜 没的区 域。在这里，一块板块潜没到另一板块的边缘之下并结合入地幔之中。 两种板块边界均与地层系统、地震以及火山活动有关，但在两种边界处观察到的 诸般地质活动 却迥然不同。 海床扩展说实际上早于板块结构理论。在20世纪60年代它的理论雏形中，描述了海底的生成和毁灭，但没有详细介绍坚硬的岩石圈板块。这个假定不久之后为发现所证实。 该发现表明地球磁场周期性的逆转被记录在海洋地壳中。当岩浆从中海脊下涌起的时候，岩浆中的磁铁矿物质按地磁场的方向被磁化。岩浆冷却并凝固下来后，地磁 场的方向和磁极被保留在磁化了的火山岩中。磁场的逆转形成一系列与断层轴线平行的条形磁区。这样海洋壳就扮演了磁带的角色，记录下可以鉴定时间的地磁场的 历史。条形磁区的宽度表明了海底扩展的速度。