英文文章素材5000字

About Temperature This document was prepared for the middle school math teachers who are taking part in Project Skymath. It is also hoped that the general public will find it interesting. Disponible en espanol, toque aqui. Contents (click on star) What is Temperature The Development of Thermometers and Temperature Scales Heat and Thermodynamics The Kinetic Theory Thermal Radiation 3 K - The Temperature of the Universe Summary Acknowledgments References What is Temperature? In a qualitative manner, we can describe the temperature of an object as that which determines the sensation of warmth or coldness felt from contact with it. It is easy to demonstrate that when two objectsof the same material are placed together (physicists say when they are put in thermal contact), the object with the higher temperature cools while the cooler object becomes warmer until a point is reached after which no more change occurs, and to our senses, they feel the same. When the thermal changes have stopped, we say that the two objects (physicists define them more rigorously as systems) are in thermal equilibrium . We can then define the temperature of the system by saying that the temperature is that quantity which is the same for both systems when they are in thermal equilibrium. If we experiment further with more than two systems, we find that many systems can be brought into thermal equilibrium with each other; thermal equilibrium does not depend on the kind of object used. Put more precisely, if two systems are separately in thermal equilibrium with a third, then they must also be in thermal equilibrium with each other, and they all have the same temperature regardless of the kind of systems they are. The statement in italics, called the zeroth law of thermodynamics may be restated as follows: If three or more systems are in thermal contact with each other and all in equilibrium together, then any two taken separately are in equilibrium with one another. (quote from T. J. Quinn's monograph Temperature) Now one of the three systems could be an instrument calibrated to measure the temperature - . a thermometer. When a calibrated thermometer is put in thermal contact with a system and reaches thermal equilibrium, we then have a quantitative measure of the temperature of the system. For example, a mercury-in-glass clinical thermometer is put under the tongue of a patient and allowed to reach thermal equilibrium in the patient's mouth - we then see by how much the silvery mercury has expanded in the stem and read the scale of the thermometer to find the patient's temperature. What is a Thermometer? A thermometer is an instrument that measures the temperature of a system in a quantitative way. The easiest way to do this is to find a substance having a property that changes in a regular way with its temperature. The most direct 'regular' way is a linear one: t(x) = ax + b, where t is the temperature of the substance and changes as the property x of the substance changes. The constants a and b depend on the substance used and may be evaluated by specifying two temperature points on the scale, such as 32° for the freezing point of water and 212° for its boiling point. For example, the element mercury is liquid in the temperature range of ° C to ° C (we'll discuss the Celsius ° C scale later). As a liquid, mercury expands as it gets warmer, its expansion rate is linear and can be accurately calibrated. The mercury-in-glass thermometer illustrated in the above figure contains a bulb filled with mercury that is allowed to expand into a capillary. Its rate of expansion is calibrated on the glass scale. The Development of Thermometers and Temperature Scales The historical highlights in the development of thermometers and their scales given here are based on "Temperature" by T. J. Quinn and "Heat" by James M. Cork. One of the first attempts to make a standard temperature scale occurred about AD 170, when Galen, in his medical writings, proposed a standard "neutral" temperature made up of equal quantities of boiling water and ice; on either side of this temperature were four degrees of heat and four degrees of cold, respectively. The earliest devices used to measure the temperature were called thermoscopes. They consisted of a glass bulb having a long tube extending downward into a container of colored water, although Galileo in 1610 is supposed to have used wine. Some of the air in the bulb was expelled before placing it in the liquid, causing the liquid to rise into the tube. As the remaining air in the bulb was heated or cooled, the level of the liquid in the tube would vary reflecting the change in the air temperature. An engraved scale on the tube allowed for a quantitative measure of the fluctuations. The air in the bulb is referred to as the thermometric medium, . the medium whose property changes with temperature. In 1641, the first sealed thermometer that used liquid rather than air as the thermometric medium was developed for Ferdinand II, Grand Duke of Tuscany. His thermometer used a sealed alcohol-in-glass device, with 50 "degree" marks on its stem but no "fixed point" was used to zero the scale. These were referred to as "spirit" thermometers. Robert Hook, Curator of the Royal Society, in 1664 used a red dye in the alcohol . His scale, for which every degree represented an equal increment of volume equivalent to about 1/500 part of the volume of the thermometer liquid, needed only one fixed point. He selected the freezing point of water. By scaling it in this way, Hook showed that a standard scale could be established for thermometers of a variety of sizes. Hook's original thermometer became known as the standard of Gresham College and was used by the Royal Society until 1709. (The first intelligible meteorological records used this scale). In 1702, the astronomer Ole Roemer of Copenhagen based his scale upon two fixed points: snow (or crushed ice) and the boiling point of water, and he recorded the daily temperatures at Copenhagen in 1708- 1709 with this thermometer. It was in 1724 that Gabriel Fahrenheit, an instrument maker of Däanzig and Amsterdam, used mercury as the thermometric liquid. Mercury's thermal expansion is large and fairly uniform, it does not adhere to the glass, and it remains a liquid over a wide range of temperatures. Its silvery appearance makes it easy to read. Fahrenheit described how he calibrated the scale of his mercury thermometer: "placing the thermometer in a mixture of sal ammoniac or sea salt, ice, and water a point on the scale will be found which is denoted as zero. A second point is obtained if the same mixture is used without salt. Denote this position as 30. A third point, designated as 96, is obtained if the thermometer is placed in the mouth so as to acquire the heat of a healthy man." (D. G. Fahrenheit,Phil. Trans. (London) 33, 78, 1724) On this scale, Fahrenheit measured the boiling point of water to be 212. Later he adjusted the freezing point of water to 32 so that the interval between the boiling and freezing points of water could be represented by the more rational number 180. Temperatures measured on this scale are designated as degrees Fahrenheit (° F). In 1745, Carolus Linnaeus of Upsula, Sweden, described a scale in which the freezing point of water was zero, and the boiling point 100, making it a centigrade (one hundred steps) scale. Anders Celsius (1701-1744) used the reverse scale in which 100 represented the freezing point and zero the boiling point of water, still, of course, with 100 degrees between the two defining points. In 1948 use of the Centigrade scale was dropped in favor of a new scale using degrees Celsius (° C). The Celsius scale is defined by the following two items that will be discussed later in this essay: (i) The triple point of water is defined to be ° C. (ii) A degree Celsius equals the same temperature change as a degree on the ideal-gas scale. On the Celsius scale the boiling point of water at standard atmospheric pressure is C in contrast to the 100 degrees defined by the Centigrade scale. To convert from Celsius to Fahrenheit: multiply by and add 32. ° F = ° C + 32 ° K = ° C + 273. (Or, you can get someone else to do it for you!) In 1780, J. A. C. Charles, a French physician, showed that for the same increase in temperature, all gases exhibited the same increase in volume. Because the expansion coefficient of gases is so very nearly the same, it is possible to establish a temperature scale based on a single fixed point rather than the two fixed- point scales, such as the Fahrenheit and Celsius scales. This brings us back to a thermometer that uses a gas as the thermometric medium. In a constant volume gas thermometer a large bulb B of gas, hydrogen for example, under a set pressure connects with a mercury-filled "manometer" by means of a tube of very small volume. (The Bulb B is the temperature-sensing portion and should contain almost all of the hydrogen). The level of mercury at C may be adjusted by raising or lowering the mercury reservoir R. The pressure of the hydrogen gas, which is the "x" variable in the linear relation with temperature, is the difference between the levels D and C plus the pressure above D. P. Chappuis in 1887 conducted extensive studies of gas thermometers with constant pressure or with constant volume using hydrogen, nitrogen, and carbon dioxide as the thermometric medium. Based on his results, the Comité International des Poids et Mesures adopted the constant-volume hydrogen scale based on fixed points at the ice point (0° C) and the steam point (100° C) as the practical scale for international meteorology. Experiments with gas thermometers have shown that there is very little difference in the temperature scale for different gases. Thus, it is possible to set up a temperature scale that is independent of the thermometric medium if it is a gas at low pressure. In this case, all gases behave like an "Ideal Gas" and have a very simple relation between their pressure, volume, and temperature: pV= (constant)T. This temperature is called the thermodynamic temperature and is now accepted as the fundamental measure of temperature. Note that there is a naturally-defined zero on this scale - it is the point at which the pressure of an ideal gas is zero, making the temperature also zero. We will continue a discussion of "absolute zero" in a later section. With this as one point on the scale, only one other fixed point need be defined. In 1933, the International Committee of Weights and Measures adopted this fixed point as the triple point of water , the temperature at which water, ice, and water vapor coexist in equilibrium); its value is set as . The unit of temperature on this scale is called the kelvin, after Lord Kelvin (William Thompson), 1824-1907, and its symbol is K (no degree symbol used). To convert from Celsius to Kelvin, add 273. K = ° C + 273. Thermodynamic temperature is the fundamental temperature; its unit is the kelvin which is defined as the fraction 1/ of the thermodynamic temperature of the triple point of water. Sir William Siemens, in 1871, proposed a thermometer whose thermometric medium is a metallic conductor whose resistance changes with temperature. The element platinum does not oxidize at high temperatures and has a relatively uniform change in resistance with temperature over a large range. The Platinum Resistance Thermometer is now widely used as a thermoelectric thermometer and covers the temperature range from about -260° C to 1235° C. Several temperatures were adopted as Primary reference points so as to define the International Practical Temperature Scale of 1968. The International Temperature Scale of 1990 was adopted by the International Committee of Weights and Measures at its meeting in 1989. Between and , the temperature is defined in terms of the vapor pressure - temperature relations of the isotopes of helium. Between and the triple point of neon () the temperature is defined by means of a helium gas thermometer. Between the triple point of hydrogen () and the freezing point of silver (°K) the temperature is defined by means of platinum resistance thermometers. Above the freezing point of silver the temperature is defined in terms of the Planck radiation law. T. J. Seebeck, in 1826, discovered that when wires of different metals are fused at one end and heated, a current flows from one to the other. The electromotive force generated can be quantitatively related to the temperature and hence, the system can be used as a thermometer - known as a thermocouple. The thermocouple is used in industry and many different metals are used - platinum and platinum/rhodium, nickel-chromium and nickel-aluminum, for example. The National Institute of Standards and Technology (NIST) maintains databases for standardizing thermometers. For the measurement of very low temperatures, the magnetic susceptibility of a paramagnetic substance is used as the thermometric physical quantity. For some substances, the magnetic susceptibility varies inversely as the temperature. Crystals such as cerrous magnesium nitrate and chromic potassium alum have been used to measure temperatures down to K; these crystals are calibrated in the liquid helium range. This diagram and the last illustration in this text were taken from the Low Temperature Laboratory, Helsinki University of Technology's picture archive. For these very low, and even lower, temperatures, the thermometer is also the mechanism for cooling. Several low-temperature laboratories conduct interesting applied and theoretical research on how to reach the lowest possible temperatures and how work at these temperatures may find application. Heat and Thermodynamics Prior to the 19th century, it was believed that the sense of how hot or cold an object felt was determined by how much "heat" it contained. Heat was envisioned as a liquid that flowed from a hotter to a colder object; this weightless fluid was called "caloric", and until the writings of Joseph Black (1728-1799), no distinction was made between heat and temperature. Black distinguished between the quantity (caloric) and the intensity (temperature) of heat. Benjamin Thomson, Count Rumford, published a paper in 1798 entitled "an Inquiry Concerning the Source of Heat which is Excited by Friction". Rumford had noticed the large amount of heat generated when a cannon was drilled. He doubted that a material substance was flowing into the cannon and concluded "it appears to me to be extremely difficult if not impossible to form any distinct idea of anything capable of being excited and communicated in the manner the heat was excited and communicated in these experiments except motion." But it was not until J. P. Joule published a definitive paper in 1847 that the the caloric idea was abandoned. Joule conclusively showed that heat was a form of energy. As a result of the experiments of Rumford, Joule, and others, it was demonstrated (explicitly stated by Helmholtz in 1847), that the various forms of energy can be transformed one into another. When heat is transformed into any other form of energy, or when other forms of energy are transformed into heat, the total amount of energy (heat plus other forms) in the system is constant. This is the first law of thermodynamics, the conservation of energy. To express it another way: it is in no way possible either by mechanical, thermal, chemical, or other means, to obtain a perpetual motion machine; ., one that creates its own energy (except in the fantasy world of Maurits Escher's "Waterfall"!) A second statement may also be made about how machines operate. A steam engine uses a source of heat to produce work. Is it possible to completely convert the heat energy into work, making it a 100% efficient machine? The answer is to be found in the second law of thermodynamics: No cyclic machine can convert heat energy wholly into other forms of energy. It is not possible to construct a cyclic machine that does nothing but withdraw heat energy and convert it into mechanical energy. The second law of thermodynamics implies the irreversibility of certain processes - that of converting all heat into mechanical energy, although it is possible to have a cyclic machine that does nothing but convert mechanical energy into heat! Sadi Carnot (1796-1832) conducted theoretical studies of the efficiencies of heat engines (a machine which converts some of its heat into useful work). He was trying to model the most efficient heat engine possible. His theoretical work provided the basis for practical improvements in the steam engine and also laid the foundations of thermodynamics. He described an ideal engine, called the Carnot engine, that is the most efficient way an engine can be constructed. He showed that the efficiency of such an engine is given by efficiency = 1 - T"/T', where the temperatures, T' and T" , are the hot and cold "reservoirs" , respectively, between which the machine operates. On this temperature scale, a heat engine whose coldest reservoir is zero degrees would operate with 100% efficiency. This is one definition of absolute zero, and it can be shown to be identical to the absolute zero we discussed previously. The temperature scale is called the absolute, the thermodynamic , or the kelvin scale. The way that the gas temperature scale and the thermodynamic temperature scale are shown to be identical is based on the microscopic interpretation of temperature, which postulates that the macroscopic measurable quantity called temperature is a result of the random motions of the microscopic particles that make up a system. The Kinetic Theory This brief summary is abridged from a more detailed discussion to be found in Quinn's "Temperature" About the same time that thermodynamics was evolving, James Clerk Maxwell (1831-1879) and Ludwig Boltzmann (1844-1906) developed a theory describing the way molecules moved - molecular dynamics. The molecules that make up a perfect gas move about, colliding with each other like billiard balls and bouncing off the surface of the container holding the gas. The energy associated with motion is called Kinetic Energy and this kinetic approach to the behavior of ideal gases led to an interpretation of the concept of temperature on a microscopic scale. 温度 -------------------------------------------------- ----------- ------------------- 什么是温度 发展的温度计和温度秤 热和热力学 动力学理论 热辐射 3 K -温度的宇宙 摘要 致谢 参考资料 什么是温度？ 在定性的方式，我们可以描述一个物体的温度所决定的感觉温暖 或冷漠感到从联系。 很容易证明，当两个相同的材料放在一起（物理学家说，当他们 把在接触） ，对象与较高的温度变冷，而凉爽的对象变得温暖， 直到点后达成的，没有更多的变化发生时，和我们的理智，他们 同样的感觉。当热的变化已经停止，我们说，这两个物体（物理 学家更严格地界定他们的系统）的热平衡。然后，我们便可确定 该系统的温度说，温度是数量是相同的系统时，在热平衡。 如果我们的实验进一步有两个以上的系统，我们发现，许多系统 可以使热平衡彼此;热平衡并不取决于种对象使用。提出更确切地 说， 如果两个系统分别在热平衡的三分之一，那么他们也必须在热平 衡彼此，他们都具有相同的温度，无论什么样的制度中都。 声明楷体字，称为零定律热力学可重如下： 如果三个或更多的系统，热相互联系和共同所有的平衡，那么任何两个单独的平衡彼此。 （引自苏灿奎因的专着，温度） 现在是三个系统可以是一个工具校准测量温度-即温度计。当校...文字超过了10000字，发不了了，不好意思

我从这个网站找的，，有好多，，，下面是我自己选的，，觉得比较好珍惜每一天(Everyday is A Gift) My brother-in-law opened the bottom drawer of my sister's bureau and lifted out a tissue-wrapped package. "This", he said, "is not a slip. This is lingerie." He discarded the tissue and handed me the slip.妹夫打开了妹妹衣柜最底层抽屉，拿出一个用纸包装的包裹。“这个，”他说，“不是件普通内衣，而是一件豪华内衣。”他把薄纸撕开，递给了我那件内衣。It was exquisite, silk, handmade and trimmed with a cobweb of lace. The price tag with an astronomical figure on it was still attached. 它的确精致无比，丝质、全手工缝制，周围还有一圈网状蕾丝花边。价签都尚未拆去，上面的数字高得惊人。"Jan bought this the first time we went to New York, at least 8 or 9 years ago. She never wore it. She was saving it for a special occasion.“这是我们第一次去纽约时简买的，至少已是八、九年前的事了。她从没有穿过它。她想等一个特殊的日子再穿它。”Well, I guess this is the occasion.唉，我想现在便是那特殊的日子了。He took the slip from me and put it on the bed, with the other clothes we were taking to the mortician. His hands lingered on the soft material for a moment, then he slammed the drawer shut and turned to me, "Don't ever save anything for a special occasion. Every day you' re alive is a special occasion."妹夫从我手中拿过内衣放在床上，和其他我们要带给殡仪服务人员的衣服放在一起。他的手在那柔软织物上徘徊了一会儿，随即砰然关上抽屉，转身对我说：“永远不要把任何东西留给什么特殊日子。你活着的每一天就是一个特殊的日子。”I remembered those words through the funeral and the days that followed when I helped him and my niece attend to all the sad chores that follow an unexpected death. I thought about them on the plane returning to California from the midwestern town where my sister's family lives. I thought about all the things that she hadn't seen or heard or done. I thought about the things that she had done without realizing that they were special.这两句话久久在我耳边回响着，伴我度过了葬礼和帮妹夫、侄女处理妹妹意外死亡后的伤心后事的那几天。我从位处中西部的妹妹家返回加州时，在飞机上还是在想这两句话。我想到妹妹未曾有机会看到、听到或去做的事。我想到她淡然做过，但却没有意识到其特殊性的事。I'm still thinking about his words, and they've changed the weeds in the garden. I'm spending more time with my family and friends and less time in committee meetings. Whenever possible, life should be a pattern of experience to savour, not endure. I'm trying to recognize these moment now and cherish them.我至今还在想着妹夫说的话，正是它们改变了我的心境。我花了更多的时间与家人朋友在一起，而少花些时间在那些工作会议上。无论何时，生活应当是一种“品味”而非一种“忍受”。我在学习欣赏每一刻，并珍惜每一刻。I'm not "saving" anything; we use our good china and crystal for every special. Event such as losing a pound, getting the sink unstopped, the first camellia blossom… I wear my good blazer to the market if I feel like it. My theory is if I look prosperous, I can shell out $28. 49 for one small bag of groceries without wincing. I'm not saving my good perfume for special parties; clerks in hardware stores and tellers in banks have noses that function as well as my party going friends.我不再去“珍藏”任何东西；只要有一点好事，我们就不吝啬使用精美的瓷器和水晶制品，比如说当体重减了一磅时，当厨房水槽堵塞通了时，当第一朵山茶花绽放时……如果我想穿，我就穿上我名牌衣服去市场购物。我的理论是：如果我看上去还富足的话，我可以毫不心疼地为一小袋杂货付出美元。我不再为特殊的派对而珍藏我上好的香水；五金店售货员和银行出纳员们的嗅觉，不会比派对上朋友们来得差。"Someday" and "one of these days" are losing their grip on my vocabulary. If it's worth seeing or hearing or doing, I want to see and hear and do it now. I' m not sure what my sister would've done had she know that she wouldn't be here for the tomorrow we all take for granted.“有朝一日”和“终有一天”这样的词正从我的常用词汇中淡出。如果值得去看、去听或去做，我当即就要去看、去听或去做。人们总是理所当然的以为自己必然有明天，不知假如妹妹知道她将没有明日，她会做些什么。I think she would have called family members and a few close friends. She might have called a few former friends to apologize, and mend fences for past squabbles. I like to think she would have gone out for a Chinese dinner, her favorite food. I'm guessing. I'll never know.我想她会给家人和几位密友打电话。她可能还会给几位昔日朋友打电话主动道歉，摒弃前嫌。我想她可能会外出吃顿她喜欢的中餐。我只是猜想而已。我永远也不会知道。It's those little things left undone that would make me angry if I knew that my hours were limited. Angry because I put off seeing good friends whom I was going to get in touch with someday. Angry because I hadn't written certain letters that I intended to write one of these days. Angry and sorry that I didn't tell my husband and daughter often enough how much I truly love them.假如我知道我的时间不多了，那些没来得及做的小事会让我恼火。恼火是因为我一拖再拖没能去看看“有朝一日”会去看的好友们。恼火是因为我还没有写出我“终有一天”要写的信。恼火与内疚是因为我没能更经常地告诉我的丈夫和女儿：我是多么真切地爱他们。I'm trying very hard not to put off, hold back, or save anything that would add laughter and luster to our lives. And every morning when I open my eyes, I tell myself that every day, every minute, every breath truly, is... a gift from God.我正努力不再拖延、保留或珍藏那些能给我们生活带来欢笑和光彩的东西。每天清晨当我睁开双眼，我便告诉自己每一天、每一分钟、每一瞬间都真是……上帝赐予的礼物。

What is a Computer?A computer is a programmable machine. The two principal characteristics of a computer are: it responds to a specific set of instructions in a well-defined manner and it can execute a prerecorded list of instructions (a program).Modern Computers DefinedModern computers are electronic and digital. The actual machinery -- wires, transistors, and circuits -- is called hardware; the instructions and data are called general-purpose computers require the following hardware components:memory: enables a computer to store, at least temporarily, data and storage device: allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape device: usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a device: a display screen, printer, or other device that lets you see what the computer has processing unit (CPU): the heart of the computer, this is the component that actually executes addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to Classification, By Size and PowerComputers can be generally classified by size and power as follows, though there is considerable overlap:personal computer: a small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving : a powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality : a multi-user computer capable of supporting from 10 to hundreds of users : a powerful multi-user computer capable of supporting many hundreds or thousands of users : an extremely fast computer that can perform hundreds of millions of instructions per Related Questions1. What is computer history?2. What is computer hardware?3. What is computer software?4. What is computer science?5. What is computer interface?1. What is computer history?The history of computer development is often referred to in reference to the different generations of computing devices. Each of the five generations of computers is characterized by a major technological development that fundamentally changed the way computers history of computer development is often referred to in reference to the different generations of computing devices. Each of the five generations of computers is characterized by a major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, more powerful and more efficient and reliable computing this Webopedia reference article you'll learn about each of the five generations of computers and the technology developments that have led to the current devices that we use today. Our journey starts in 1940 with vacuum tube circuitry and goes to the present day -- and beyond -- with artificial Webopedia Definitions: computer, magnetic drums, binary, integrated circuit, semiconductor, nanotechnologyFirst Generation (1940-1956) Vacuum TubesThe first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of generation computers relied on machine language, the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. Input was based on punched cards and paper tape, and output was displayed on UNIVAC and ENIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the . Census Bureau in UNIVAC computer at the Census BureauA UNIVAC computer at the Census Source: United States Census BureauSecond Generation (1956-1963) TransistorsTransistors replaced vacuum tubes and ushered in the second generation of computers. The transistor was invented in 1947 but did not see widespread use in computers until the late 1950s. The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable than their first-generation predecessors. Though the transistor still generated a great deal of heat that subjected the computer to damage, it was a vast improvement over the vacuum tube. Second-generation computers still relied on punched cards for input and printouts for computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN. These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core first computers of this generation were developed for the atomic energy Generation (1964-1971) Integrated CircuitsThe development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their Generation (1971-Present) MicroprocessorsThe microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The Intel 4004 chip, developed in 1971, located all the components of the computer—from the central processing unit and memory to input/output controls—on a single 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh. Microprocessors also moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. Fourth generation computers also saw the development of GUIs, the mouse and handheld Generation (Present and Beyond) Artificial IntelligenceFifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and . What is computer hardware?Hardware refers to objects that you can actually touch, like disks, disk drives, display screens, keyboards, printers, boards, and chips. In contrast, software is untouchable. Software exists as ideas, concepts, and symbols, but it has no provide a useful analogy. The pages and the ink are the hardware, while the words, sentences, paragraphs, and the overall meaning are the software. A computer without software is like a book full of blank pages -- you need software to make the computer useful just as you need words to make a book . What is computer software?Software means computer instructions or data. Anything that can be stored electronically is software, in contrast to storage devices and display devices which are called terms software and hardware are used as both nouns and adjectives. For example, you can say: "The problem lies in the software," meaning that there is a problem with the program or data, not with the computer itself. You can also say: "It's a software problem."The distinction between software and hardware is sometimes confusing because they are so integrally linked. Clearly, when you purchase a program, you are buying software. But to buy the software, you need to buy the disk (hardware) on which the software is of SoftwareSoftware is often divided into two categories. Systems software includes the operating system and all the utilities that enable the computer to function. Applications software includes programs that do real work for users. For example, word processors, spreadsheets, and database management systems fall under the category of applications . What is computer science?Computer science is the study of computers, including both hardware and software design. Computer science is composed of many broad disciplines, including artificial intelligence and software engineering. Most universities now offer bachelor, master, and doctorate degrees in computer . What is computer interface?Interface is a boundary across which two independent systems meet and act on or communicate with each other. In computer technology, there are several types of interface - the keyboard, mouse, menus of a computer system. The user interface allows the user to communicate with the operating system. Also see interface - the languages and codes that the applications use to communicate with each other and with the interface - the wires, plugs and sockets that hardware devices use to communicate with each other.

珍惜每一天(Everyday is A Gift) My brother-in-law opened the bottom drawer of my sister's bureau and lifted out a tissue-wrapped package. "This", he said, "is not a slip. This is lingerie." He discarded the tissue and handed me the slip. 妹夫打开了妹妹衣柜最底层抽屉，拿出一个用纸包装的包裹。“这个，”他说，“不是件普通内衣，而是一件豪华内衣。”他把薄纸撕开，递给了我那件内衣。 It was exquisite, silk, handmade and trimmed with a cobweb of lace. The price tag with an astronomical figure on it was still attached. 它的确精致无比，丝质、全手工缝制，周围还有一圈网状蕾丝花边。价签都尚未拆去，上面的数字高得惊人。 "Jan bought this the first time we went to New York, at least 8 or 9 years ago. She never wore it. She was saving it for a special occasion. “这是我们第一次去纽约时简买的，至少已是八、九年前的事了。她从没有穿过它。她想等一个特殊的日子再穿它。” Well, I guess this is the occasion. 唉，我想现在便是那特殊的日子了。 He took the slip from me and put it on the bed, with the other clothes we were taking to the mortician. His hands lingered on the soft material for a moment, then he slammed the drawer shut and turned to me, "Don't ever save anything for a special occasion. Every day you' re alive is a special occasion." 妹夫从我手中拿过内衣放在床上，和其他我们要带给殡仪服务人员的衣服放在一起。他的手在那柔软织物上徘徊了一会儿，随即砰然关上抽屉，转身对我说：“永远不要把任何东西留给什么特殊日子。你活着的每一天就是一个特殊的日子。” I remembered those words through the funeral and the days that followed when I helped him and my niece attend to all the sad chores that follow an unexpected death. I thought about them on the plane returning to California from the midwestern town where my sister's family lives. I thought about all the things that she hadn't seen or heard or done. I thought about the things that she had done without realizing that they were special. 这两句话久久在我耳边回响着，伴我度过了葬礼和帮妹夫、侄女处理妹妹意外死亡后的伤心后事的那几天。我从位处中西部的妹妹家返回加州时，在飞机上还是在想这两句话。我想到妹妹未曾有机会看到、听到或去做的事。我想到她淡然做过，但却没有意识到其特殊性的事。 I'm still thinking about his words, and they've changed the weeds in the garden. I'm spending more time with my family and friends and less time in committee meetings. Whenever possible, life should be a pattern of experience to savour, not endure. I'm trying to recognize these moment now and cherish them. 我至今还在想着妹夫说的话，正是它们改变了我的心境。我花了更多的时间与家人朋友在一起，而少花些时间在那些工作会议上。无论何时，生活应当是一种“品味”而非一种“忍受”。我在学习欣赏每一刻，并珍惜每一刻。 I'm not "saving" anything; we use our good china and crystal for every special. Event such as losing a pound, getting the sink unstopped, the first camellia blossom… I wear my good blazer to the market if I feel like it. My theory is if I look prosperous, I can shell out $28. 49 for one small bag of groceries without wincing. I'm not saving my good perfume for special parties; clerks in hardware stores and tellers in banks have noses that function as well as my party going friends. 我不再去“珍藏”任何东西；只要有一点好事，我们就不吝啬使用精美的瓷器和水晶制品，比如说当体重减了一磅时，当厨房水槽堵塞通了时，当第一朵山茶花绽放时……如果我想穿，我就穿上我名牌衣服去市场购物。我的理论是：如果我看上去还富足的话，我可以毫不心疼地为一小袋杂货付出美元。我不再为特殊的派对而珍藏我上好的香水；五金店售货员和银行出纳员们的嗅觉，不会比派对上朋友们来得差。 "Someday" and "one of these days" are losing their grip on my vocabulary. If it's worth seeing or hearing or doing, I want to see and hear and do it now. I' m not sure what my sister would've done had she know that she wouldn't be here for the tomorrow we all take for granted. “有朝一日”和“终有一天”这样的词正从我的常用词汇中淡出。如果值得去看、去听或去做，我当即就要去看、去听或去做。人们总是理所当然的以为自己必然有明天，不知假如妹妹知道她将没有明日，她会做些什么。 I think she would have called family members and a few close friends. She might have called a few former friends to apologize, and mend fences for past squabbles. I like to think she would have gone out for a Chinese dinner, her favorite food. I'm guessing. I'll never know. 我想她会给家人和几位密友打电话。她可能还会给几位昔日朋友打电话主动道歉，摒弃前嫌。我想她可能会外出吃顿她喜欢的中餐。我只是猜想而已。我永远也不会知道。 It's those little things left undone that would make me angry if I knew that my hours were limited. Angry because I put off seeing good friends whom I was going to get in touch with someday. Angry because I hadn't written certain letters that I intended to write one of these days. Angry and sorry that I didn't tell my husband and daughter often enough how much I truly love them. 假如我知道我的时间不多了，那些没来得及做的小事会让我恼火。恼火是因为我一拖再拖没能去看看“有朝一日”会去看的好友们。恼火是因为我还没有写出我“终有一天”要写的信。恼火与内疚是因为我没能更经常地告诉我的丈夫和女儿：我是多么真切地爱他们。 I'm trying very hard not to put off, hold back, or save anything that would add laughter and luster to our lives. And every morning when I open my eyes, I tell myself that every day, every minute, every breath truly, is... a gift from God. 我正努力不再拖延、保留或珍藏那些能给我们生活带来欢笑和光彩的东西。每天清晨当我睁开双眼，我便告诉自己每一天、每一分钟、每一瞬间都真是……上帝赐予的礼物。 希望对你有帮助哦！！！！！！！！！