1950 Effect of change of scale on sintering phenomena
张庭伟：1950-2000年美国城市变化的因素分析及对中国城市发展的借鉴
背景及主要发现
• 结论是，讨论城市政策时，不应该、也无法局限于具体的所谓“城市问题”。城 市政策具有全局作用，带有历史影响。城市政策的成败并不完全在于城市政 策本身，而取决于更加高层、宏观的国家发展政策。国家发展政策的正确与 否，决定城市政策是否出现偏差。反之，在高度城市化的时代，城市政策对 于一个国家的经济和社会的长期发展也会产生重大、经久的反作用。制定国 家经济发展政策时，必须特别重视这些政策的空间影响、城市影响。美国的 历史教训，值得我们深刻注意
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1950-2000年影响美国大城市发展的十大因 素
• 高速公路得到汽车制造业和石油企业等大利益集团的鼓励支持，但是并没有 解决市区的交通拥挤问题，相反，沿着高速公路的郊区迅速开发，致使通往 中心区的高速公路、以及中心区内的交通反而更加拥挤。郊区开发吸引了原 来大城市周围地区的人们迁入大城市郊区。同时城市中心区出现空洞化，开 创了不可逆转的郊区化时代。 更为严重的是，由于政府几乎把所有的公共资金用于高速公路建设，对公交 的投资严重不足，公交服务质量下降，影响了居民对公交的利用率。而低下 的公交利用率，则正好成为汽车制造业等利益集团反对政府补贴公交的借 口，形成公交投资不足-使用率低下的恶性循环。 高能耗、高排放的汽车文化，不但成为美国社会的主流，也成了“现代化生 活”的标准模式，影响了包括中国的整个世界。 目前中国大力鼓励汽车消费的政策主要代表了汽车制造、石油生产等行业的 意愿，仅仅考虑当前的经济得益，具有短视性而存在着相当大的长期社会、 环境、城市代价。 在交通政策上，中国明显优于美国的最大优点是大量的轨道投资，和发达的 城市公共交通系统。
•• ••源自ht 城 tp 市 :/ 规 /w 划 ww 与 .c 交 it 通 yu 网 p. or g
新理念英语学习综合教程第三册(Unit1)卷A
综合教程部分第一单元：卷A全新版第二版综合B3U1-APart IListening Comprehension( 14 minutes )Section A1．A) TB) FScript: Mr. Doherty always dreams of writing about life on the farm so he moved to a farm with his family.正确答案：B2.A) TB) FScript: Living on the farm gives them more opportunities to enjoy outdoor activities a nd get close to nature.正确答案：A3.A) TB) FScript: Mrs. Doherty has to give up writing to maintain the farm because her husband is too busy writing to make more money.正确答案：B4.A) TB) FScript: The first winter on the farm was miserable because it was cold and boring.正确答案：B5.A) TB) FScript: Mr. Doherty decided to give up his fulltime job and depend totally on freelanc e the second year on the farm because he had to spend more time on the farm.正确答案：A6.A) TB) FScript: Mr. Doherty doesnt make enough money now to maintain their living standard in the past but their life is not seriously affected.正确答案：A7.A) TB) FScript: Three parts of our lives have changed: the way we work, the way we eat, and h e way we entertain ourselves.正确答案：A8.A) TB) FScript: Todays working men and women are commuters who travel to work early and return home late.正确答案：A9.A) TB) FScript: Fast food, takeout, and heat-and-serve dishes now take up the table of most A mericanfamilies.正确答案：A10.A) TB) FScript: The Cleavers household is a fantasy both for the 1950s and now and therefore, too ideal to learn from.正确答案：BSection BStress is the "wear and tear" our bodies experience, as we(11)_________________ to our changing environment. As a(12)_________________ influence, stress can help us take action. As a(13)_________________ influence, it can lead to health problems such as headache, insomnia, ulcers, high blood pressure and heart disease. Our goal is not to eliminate stress but to learn how to (14)_________________ it and how to use it to help us. (15)_________________ stress may make us feel bored; on the other hand, (16)_________________ stress may make us feel tied up in knots. What we need to do is to find the (17)_________________ level of stress which will(18)_________________ overwhelm us. There is no single level of stress that is optimal for all people. What is distressing to one may be a joy to another. Moreover, our (19)_________________ and the amount which we can tolerate changes with our ages. It has been revealed that most illness is related to unrelieved stress. Being aware of stress and its effect on our lives can help reduce its harmful effects. There are many sources of stress, and there are many possibilities for its management. Here are three principles as to how to manage stress:1. Become aware of your stressor and your emotional and physical reactions.2. Recognize what you can change.3. (20)_________________ of your emotional reactions to stress.Script: Stress is the "wear and tear" our bodies experience, as we adjust to our changing environment. As a positive influence, stress can help us take action. As a negative influence, it can lead to health problems such as headache, insomnia, ulcers, high blood pressure and heart disease. Our goal is not to eliminate stress but to learn how to manage it and how to use it to help us. Insufficient stress may make us feel bored; on the other hand, excessive stress may make us feel tied up in knots. What we need to do is to find the optimal level of stress which will motivate but not overwhelm us. There is no single level of stress that is optimal for all people. What is distressing to one may be a joy to another. Moreover, our personal stress requirements and the amount which we can tolerate changes with our ages. It has been revealed that most illness is related to unrelieved stress. Being aware of stress and its effect on our lives can help reduce its harmful effects. There are many sources of stress, and there are many possibilities for its management. Here are three principles as to how to manage stress: 1. Become aware of your stressor and your emotional and physical reactions. 2. Recognize what you can change. 3. Reduce the intensity of your emotional reactions to stress.正确答案：adjust正确答案：positive正确答案：negative正确答案：manage正确答案：Insufficient正确答案：excessive正确答案：optimal正确答案：motivate but not正确答案：personal stress requirements正确答案：Reduce the intensityPart IIReading Comprehension ( 25 minutes )Section AI’m not making anywhere near as much money as I did when I was employedfull time, but now we don’t need as much either. I 21 enough income to handle our $600-a-month mortgage payments plus the usual expenses for a family like ours. That includes everything from music lessons and dental bills to car repairs and college costs. When it comes to insurance, we have a poor man’s major-medical policy. We have to pay the first $500 of any medical fees for each member of the family. It 22 80% of the costs beyond that. Although we are stuck with paying minor expenses, our premium is low — only $560 a year — and we are 23 against catastrophe.24 that and the policy on our two cars at $400 a year, we have no other insurance. But we are setting aside $2,000 a year in an IRA. We’ve been able to make up the difference in income by 25 without appreciably lowering our standard of living. We continue to dine out once or twice a month, but now we patronize local restaurants 26 more expensive places in the city. We still attend the opera and ballet in Milwaukee but only a few times a year. We eat less meat, drink cheaper wine and see fewer movies. 27 Christmases are a memory, and we combine vacations with story assignments … I suspect not everyone who loves the country would be happy living the way we do. It takes a couple of special qualities. One is a 28 for solitude. Because we are so busyand on such a tight budget, we don’t entertain much. During the growing season there is no time for socializing anyway. Jim and Emily are 29 in school activities, but they too spend most of their time at home. The other requirement is energy — a lot of it. The way to make self-sufficiency work on a small scale is to resist the 30 to buy a tractor and other expensive laborsaving devices. Instead, you do the work yourself. The only machinery we own (not counting the lawn mower) is a little three-horsepower rotary cultivator and a 16-inch chain saw.A) picks upB) temptationC) givenD) generateE) involvedF) instead ofG) ExtravagantH) cutting upI) cutting backJ) enduranceK) coveredL) Aside fromM) toleranceN) exotic O) pay21. ______________________ 正确答案：D22. ______________________ 正确答案：A23. ______________________ 正确答案：K24. ______________________ 正确答案：L25. ______________________ 正确答案：I26. ______________________ 正确答案：F27. ______________________ 正确答案：G28. ______________________ 正确答案：M29. ______________________ 正确答案：E30. ______________________ 正确答案：BSection BPassage OneQuestions 31 to 35 are based on the following passage.Genetically modified foods (or GM foods) are foods derived from genetically modified organisms. Genetically modified organisms have had specific changes introduced into their DNA by genetic engineering techniques. GM foods were firstput on the market in the early 1990s. Typically, genetically modified foods are transgenic plant products: soybean, corn, canola, and cotton seed oil. Animal products have also been developed, although as of July 2010 none are currently on the market. Critics have objected to GM foods on several grounds, including safety issues, ecological concerns, and economic concerns. However, genetically-modified foods are here to stay. That’s not to sa y that food produced by conventional agriculture will disappear, but simply that food-buying patterns will polarize (两极分化): there will be a right market for conventional food just as there is for organic food. It may even be that GM food will become the food of preference because consumers come to appreciate the health benefits of reduced pesticide use. The reason GM food will not go away is that we need a three-fold increase in food production by the year 2050 to keep pace with the world’s pre dicted population growth to ten or eleven billion. It’s not just a question of more mouths to feed either. What is often forgotten is that all these extra people will take up space, reducing the overall land available for agriculture. "Genetic modification is analogous to nuclear power: nobody loves it, but climate change has made its adoption imperative," says economist Paul Collier of Oxford University. "Declining genetic modificationmakes a complicated issue more complex. Genetic modification offers both faster crop adaptation and a biological, rather than chemical, approach to yield increases." The world has 800 million hungry people. Until now, food supplies have been increased by improved varieties, pesticides and artificial fertilizers: the green revolution. Now we’re on the edge of a new revolution: a genetic one.It may well be that in the long term it is the developing world that benefits most from GM foods. It’s true that for the next ten years or so GM crops may be too expensive. But the lesson of personal computers is applicable here — once the technology has been developed for profitable crops, it will spread and become affordable for all. This doesn’t mean, unfortunately, that famines will disappear, but s everity and duration will be helped by an improved ability to produce and distribute food.31. The introduction of GM food will affect _____.A) food-pricing standardB) food-buying patternsC) food-supplies scaleD) food-production efficiency正确答案：B32 Consumers prefer GM food to conventional food because _____.A) GM food receives less pesticide applicationB) GM food is more nutritious than organic foodC) GM food is cheaper than conventional foodD) Conventional food is free from chemicals正确答案：A33. If the world population grows to ten or eleven billion by the year 2050,_____.A) a genetic revolution will take over the green revolutionB) the overall land available for agriculture will run outC) the number of hungry people will rise to 800 millionD) food production should be increased to three times that of today正确答案：D34. "But the lesson of personal computers is applicable here" (in the last paragraph) probably means that ______. A) once the technological innovation is in progress, its cost will be reducedB) once the technology has been turned into productivity, it will become popularC) once the technology has been developed for profitable products, it will enter into our daily lifeD) once the technology has been improved to meet the demands of the developing world, it will be affordable正确答案：C35. We can infer from the passage that GM food will _____A) be too expensive to affordB) keep the world from starvationC) be well-accepted by some consumersD) eventually replace conventional food正确答案：CPassage TwoQuestions 36 to 40 are based on the following passage.The radical transformation of the Soviet society had a profound impact on women’s lives. Soviet women under Stalin were also the first generation of women able togive birth in the safety of a hospital, with access to prenatal care (产检). Marxists had traditionally believed that both capitalism and the middle-class husbands exploited women. The Russian Revolution of 1917 immediately proclaimed complete equalityof rights for women. In the 1920s divorce and abortion were made easily available,and women were urged to work outside the home and liberate themselves sexually. After Stalin came to power, sexual and familial liberation was played down, and the most lasting changes for women involved work and education. These changes were truly revolutionary. Young women were constantly told that they had to be equal to men, that they could and should do everything men could do. Peasant women in Russia had long experienced the equality of backbreaking physical labor in the countryside, and they continued to enjoy that equality on collective farms. Withthe advent of the five-year-plans, millions of women also began to toil in factories and in heavy construction, building dams, roads and steel mills in summer heat and winter frost. Most of the opportunities open to men through education were also open to women. Determined women pursued their studies and entered the ranks of thebetter-paid specialists in industry and science. Medicine practically became a woman’s profession. By 1950, 75 percent of doctors in the Soviet Union were women. Thus Stalinist society gave women great opportunities but demanded great sacrificesas well. The vast majority of women simply had to work outside the home. Wages were so low that it was almost impossible for a family or couple to live only on the husband’s earnings. Moreover, the full-time working woman had a heavy burden of household tasks in her off hours, for most Soviet men in the 1930s still considered the home and the children the woman’s responsibility. Men continued to monopolize the best jobs. Finally, rapid change and economic hardship led to many broken families, creating further physical, emotional, and mental strains for women. In any event, the often-neglected human resource of women was mobilized in Stalinist society.36. The main idea of this passage is that women in Stalinist society ________.A) had economic opportunities that had never been available beforeB) had difficulty balancing their work and family responsibilitiesC) had new opportunities but also many hardshipsD) moved quickly into the highest levels of government正确答案：C37. In the last paragraph, "monopolize" probably means _____.A) hold B) earn C) leave D) pay正确答案：A38. The author’s main purpose in writing this passage is to ________.A) compare different systems of governmentB) tell stories about women in Soviet UnionC) amuse the readerD) provide information正确答案：D39. The author’s tone in this passage can best be described as ________.A) disapproving B) emotional C) objective D) sympathetic正确答案：C40.We can conclude that the economic and social status of women in Stalinist society ________.A) had been improvedB) was worse than beforeC) had not changed muchD) was better than that in capitalistic countries正确答案：APart IIIVocabulary and Structure ( 11 minutes )41. Steam turbines (涡轮机) are used for the _____ of electricity.A) construction B) manufacturing C) change D) generation 正确答案：D42 John says that his present job doesn’t provide him with enough _____ for his organizing ability.A) scope B) opening C) capacity D) range正确答案：A43. The scientists have absolute freedom as to what research they think is best to _____.A) engage B) devote C) seek D) pursue正确答案：D44. One foolish mistake can _____ you in a good deal of trouble.A) release B) involve C) evolve D) empower正确答案：B45. The doctor suggested __________ my diet with vitamins E and A.A) supplement B) supplementing C) add D) adding正确答案：B46. ____________, this essay is quite good except for a few spelling mistakes. Which one of the following choices is NOT appropriate to fill in the blank?A) On balance B) Generally C) Generally speaking D) In balance正确答案：D47. Up the chimney roared the fire, and ______ the room with its broad blaze.A) brightened B) lingered C) furnished D) fused正确答案：A48. Now the cheers and applause _____ in a single sustained roar.A) mingled B) concentrated C) assembled D) permeated正确答案：A49. They also are looking closely at what may be two key pieces of Columbia (哥伦比亚号航天飞机) _____ —a 2-foot piece of one wing and a300-pound cover of a landing gear compartment.A) debris B) garbage C) palette D) canvas正确答案：A50. "I am afraid it will not _____ my dress," she answered, "and, besides, the Chamberlain's nephew has sent me some real jewels, and everybody knows that jewels cost far more than flowers."A) settle into B) stand out C) expose to D) go with正确答案：D51. Unable to go out because of the deep snow, she felt _____ in her own house.A) isolated B) isolating C) imprisoned D) imprisoning正确答案：C52. Nobody encourages a man to dissect his appearance, feature by feature. _____ per fection, that is considered trivial —almost unmanly.A) As for B) As of C) As from D) As by正确答案：A53. "Now that you have a job and I don't," the husband said to his wife, "our situations are _____."A) remarkable B) diverged C) transferred D) reversed正确答案：D54.The street sellers repeatedly _____ their selling cries about their goods.A) advocated B) pursued C) barked D) confirmed 正确答案：C55."We are convinced that efforts for a peaceful resolution of the situation regarding Iraq should be _____ continued," Putin told journalists after talks with Chancellor Gerhar d Schroeder in Berlin.A) genetically B) normally C) persistently D) significantly 正确答案：C56. With a tremulous whisper, he broke off in the middle of a sentence, his hands flap ping at his side in a ______ shrug.A) psychic B) helpless C) capable D) tranquil正确答案：B57. During the citywide drive, doctors will provide free consultation and blood pressu re examinations in local communities. ______, medical staff at district hospitals will r eceive special training to improve their professional skills in treating hypertension pat ients.A) As a result B) On balance C) For instance D) In addition 正确答案：D58. We can _______ with four computers at the moment, but we'll need a couple more when the new staff arrive.A) go for B) go off C) get through D) get by正确答案：D59. Teachers are on strike in protest at the pay settlement _______ by the government this year.A) added B) stressed C) forced D) imposed正确答案D60. Tim is good, smart and hardworking. __________, I can't speak too highly of him.A) As a result B) In a word C) By the way D) On the contrary 正确答案：BPart IVTranslation( 10 minutes )61. Frank made his way to the door and was about to close it ____________________ (此时他一眼看见门外放着一包奇怪的东西).正确答案：when he caught sight of a strange package lying outside the door62. Bragging and never persevering to an end while doing things, _______________ _____ (每个人都认为他终将一无所成).正确答案：he is believed that he will get nowhere / amount to nothing63. ____________________ (随着工作条件的日益改善), the factory's productivity is increasing steadily.正确答案：With the working conditions improving day by day64. ____________________ (他花了两年时间走遍全国各地寻找失踪的儿子), but in vain.正确答案：He spent two years traveling all over the country in quest of his missing son65.____________________ (现在孩子们把互联网看成是理所当然的) because they think life is not enjoyable without it.正确答案：Nowadays, children take Internet for granted。
半导体制造技术
Semiconductor Manufacturing Technology半导体制造技术Instructor’s ManualMichael QuirkJulian SerdaCopyright Prentice HallTable of Contents目录OverviewI. Chapter1. Semiconductor industry overview2. Semiconductor materials3. Device technologies—IC families4. Silicon and wafer preparation5. Chemicals in the industry6. Contamination control7. Process metrology8. Process gas controls9. IC fabrication overview10. Oxidation11. Deposition12. Metallization13. Photoresist14. Exposure15. Develop16. Etch17. Ion implant18. Polish19. Test20. Assembly and packagingII. Answers to End-of-Chapter Review QuestionsIII. Test Bank (supplied on diskette)IV. Chapter illustrations, tables, bulleted lists and major topics (supplied on CD-ROM)Notes to Instructors:1)The chapter overview provides a concise summary of the main topics in each chapter.2)The correct answer for each test bank question is highlighted in bold. Test bankquestions are based on the end-of-chapter questions. If a student studies the end-of-chapter questions (which are linked to the italicized words in each chapter), then they will be successful on the test bank questions.2Chapter 1Introduction to the Semiconductor Industry Die:管芯 defective:有缺陷的Development of an Industry•The roots of the electronic industry are based on the vacuum tube and early use of silicon for signal transmission prior to World War II. The first electronic computer, the ENIAC, wasdeveloped at the University of Pennsylvania during World War II.•William Shockley, John Bardeen and Walter Brattain invented the solid-state transistor at Bell Telephone Laboratories on December 16, 1947. The semiconductor industry grew rapidly in the 1950s to commercialize the new transistor technology, with many early pioneers working inSilicon Valley in Northern California.Circuit Integration•The first integrated circuit, or IC, was independently co-invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor in 1959. An IC integrates multiple electronic components on one substrate of silicon.•Circuit integration eras are: small scale integration (SSI) with 2 - 50 components, medium scale integration (MSI) with 50 – 5k components, large scale integration (LSI) with 5k to 100kcomponents, very large scale integration (VLSI) with 100k to 1M components, and ultra large scale integration (ULSI) with > 1M components.1IC Fabrication•Chips (or die) are fabricated on a thin slice of silicon, known as a wafer (or substrate). Wafers are fabricated in a facility known as a wafer fab, or simply fab.•The five stages of IC fabrication are:Wafer preparation: silicon is purified and prepared into wafers.Wafer fabrication: microchips are fabricated in a wafer fab by either a merchant chip supplier, captive chip producer, fabless company or foundry.Wafer test: Each individual die is probed and electrically tested to sort for good or bad chips.Assembly and packaging: Each individual die is assembled into its electronic package.Final test: Each packaged IC undergoes final electrical test.•Key semiconductor trends are:Increase in chip performance through reduced critical dimensions (CD), more components per chip (Moore’s law, which predicts the doubling of components every 18-24 months) andreduced power consumption.Increase in chip reliability during usage.Reduction in chip price, with an estimated price reduction of 100 million times for the 50 years prior to 1996.The Electronic Era•The 1950s saw the development of many different types of transistor technology, and lead to the development of the silicon age.•The 1960s were an era of process development to begin the integration of ICs, with many new chip-manufacturing companies.•The 1970s were the era of medium-scale integration and saw increased competition in the industry, the development of the microprocessor and the development of equipment technology. •The 1980s introduced automation into the wafer fab and improvements in manufacturing efficiency and product quality.•The 1990s were the ULSI integration era with the volume production of a wide range of ICs with sub-micron geometries.Career paths•There are a wide range of career paths in semiconductor manufacturing, including technician, engineer and management.2Chapter 2 Characteristics of Semiconductor MaterialsAtomic Structure•The atomic model has three types of particles: neutral neutrons（不带电的中子）, positively charged protons（带正电的质子）in the nucleus and negatively charged electrons（带负电的核外电子） that orbit the nucleus. Outermost electrons are in the valence shell, and influence the chemical and physical properties of the atom. Ions form when an atom gains or loses one or more electrons.The Periodic Table•The periodic table lists all known elements. The group number of the periodic table represents the number of valence shell electrons of the element. We are primarily concerned with group numbers IA through VIIIA.•Ionic bonds are formed when valence shell electrons are transferred from the atoms of one element to another. Unstable atoms (e.g., group VIIIA atoms because they lack one electron) easily form ionic bonds.•Covalent bonds have atoms of different elements that share valence shell electrons.3Classifying Materials•There are three difference classes of materials:ConductorsInsulatorsSemiconductors•Conductor materials have low resistance to current flow, such as copper. Insulators have high resistance to current flow. Capacitance is the storage of electrical charge on two conductive plates separated by a dielectric material. The quality of the insulation material between the plates is the dielectric constant. Semiconductor materials can function as either a conductor or insulator.Silicon•Silicon is an elemental semiconductor material because of four valence shell electrons. It occurs in nature as silica and is refined and purified to make wafers.•Pure silicon is intrinsic silicon. The silicon atoms bond together in covalent bonds, which defines many of silicon’s properties. Silicon atoms bond together in set, repeatable patterns, referred to asa crystal.•Germanium was the first semiconductor material used to make chips, but it was soon replaced by silicon. The reasons for this change are:Abundance of siliconHigher melting temperature for wider processing rangeWide temperature range during semiconductor usageNatural growth of silicon dioxide•Silicon dioxide (SiO2) is a high quality, stable electrical insulator material that also serves as a good chemical barrier to protect silicon from external contaminants. The ability to grow stable, thin SiO2 is fundamental to the fabrication of Metal-Oxide-Semiconductor (MOS) devices. •Doping increases silicon conductivity by adding small amounts of other elements. Common dopant elements are from trivalent, p-type Group IIIA (boron) and pentavalent, n-type Group VA (phosphorus, arsenic and antimony).•It is the junction between the n-type and p-type doped regions (referred to as a pn junction) that permit silicon to function as a semiconductor.4Alternative Semiconductor Materials•The alternative semiconductor materials are primarily the compound semiconductors. They are formed from Group IIIA and Group VA (referred to as III-V compounds). An example is gallium arsenide (GaAs).•Some alternative semiconductors come from Group IIA and VIA, referred to as II-VI compounds. •GaAs is the most common III-V compound semiconductor material. GaAs ICs have greater electron mobility, and therefore are faster than ICs made with silicon. GaAs ICs also have higher radiation hardness than silicon, which is better for space and military applications. The primary disadvantage of GaAs is the lack of a natural oxide.5Chapter 3Device TechnologiesCircuit Types•There are two basic types of circuits: analog and digital. Analog circuits have electrical data that varies continuously over a range of voltage, current and power values. Digital circuits have operating signals that vary about two distinct voltage levels – a high and a low.Passive Component Structures•Passive components such as resistors and capacitors conduct electrical current regardless of how the component is connected. IC resistors are a passive component. They can have unwanted resistance known as parasitic resistance. IC capacitor structures can also have unintentional capacitanceActive Component Structures•Active components, such as diodes and transistors can be used to control the direction of current flow. PN junction diodes are formed when there is a region of n-type semiconductor adjacent to a region of p-type semiconductor. A difference in charge at the pn junction creates a depletion region that results in a barrier voltage that must be overcome before a diode can be operated. A bias voltage can be configured to have a reverse bias, with little or no conduction through the diode, or with a forward bias, which permits current flow.•The bipolar junction transistor (BJT) has three electrodes and two pn junctions. A BJT is configured as an npn or pnp transistor and biased for conduction mode. It is a current-amplifying device.6• A schottky diode is formed when metal is brought in contact with a lightly doped n-type semiconductor material. This diode is used in faster and more power efficient BJT circuits.•The field-effect transistor (FET), a voltage-amplifying device, is more compact and power efficient than BJT devices. A thin gate oxide located between the other two electrodes of the transistor insulates the gate on the MOSFET. There are two categories of MOSFETs, nMOS (n-channel) and pMOS (p-channel), each which is defined by its majority current carriers. There is a biasing scheme for operating each type of MOSFET in conduction mode.•For many years, nMOS transistors have been the choice of most IC manufacturers. CMOS, with both nMOS and pMOS transistors in the same IC, has been the most popular device technology since the early 1980s.•BiCMOS technology makes use of the best features of both CMOS and bipolar technology in the same IC device.•Another way to categorize FETs is in terms of enhancement mode and depletion mode. The major different is in the way the channels are doped: enhancement-mode channels are doped opposite in polarity to the source and drain regions, whereas depletion mode channels are doped the same as their respective source and drain regions.Latchup in CMOS Devices•Parasitic transistors can create a latchup condition(???????) in CMOS ICs that causes transistors to unintentionally（无心的） turn on. To control latchup, an epitaxial layer is grown on the wafer surface and an isolation barrier（隔离阻障）is placed between the transistors. An isolation layer can also be buried deep below the transistors.Integrated Circuit Productsz There are a wide range of semiconductor ICs found in electrical and electronic products. This includes the linear IC family, which operates primarily with anal3og circuit applications, and the digital IC family, which includes devices that operate with binary bits of data signals.7Chapter 4Silicon and Wafer Preparation8z Semiconductor-Grade Silicon•The highly refined silicon used for wafer fabrication is termed semiconductor-grade silicon (SGS), and sometimes referred to as electronic-grade silicon. The ultra-high purity of semiconductor-grade silicon is obtained from a multi-step process referred to as the Siemens process.Crystal Structure• A crystal is a solid material with an ordered, 3-dimensional pattern over a long range. This is different from an amorphous material that lacks a repetitive structure.•The unit cell is the most fundamental entity for the long-range order found in crystals. The silicon unit cell is a face-centered cubic diamond structure. Unit cells can be organized in a non-regular arrangement, known as a polycrystal. A monocrystal are neatly arranged unit cells.Crystal Orientation•The orientation of unit cells in a crystal is described by a set of numbers known as Miller indices.The most common crystal planes on a wafer are (100), (110), and (111). Wafers with a (100) crystal plane orientation are most common for MOS devices, whereas (111) is most common for bipolar devices.Monocrystal Silicon Growth•Silicon monocrystal ingots are grown with the Czochralski (CZ) method to achieve the correct crystal orientation and doping. A CZ crystal puller is used to grow the silicon ingots. Chunks of silicon are heated in a crucible in the furnace of the puller, while a perfect silicon crystal seed is used to start the new crystal structure.• A pull process serves to precisely replicate the seed structure. The main parameters during the ingot growth are pull rate and crystal rotation. More homogeneous crystals are achieved with a magnetic field around the silicon melt, known as magnetic CZ.•Dopant material is added to the melt to dope the silicon ingot to the desired electrical resistivity.Impurities are controlled during ingot growth. A float-zone crystal growth method is used toachieve high-purity silicon with lower oxygen content.•Large-diameter ingots are grown today, with a transition underway to produce 300-mm ingot diameters. There are cost benefits for larger diameter wafers, including more die produced on a single wafer.Crystal Defects in Silicon•Crystal defects are interruptions in the repetitive nature of the unit cell. Defect density is the number of defects per square centimeter of wafer surface.•Three general types of crystal defects are: 1) point defects, 2) dislocations, and 3) gross defects.Point defects are vacancies (or voids), interstitial (an atom located in a void) and Frenkel defects, where an atom leaves its lattice site and positions itself in a void. A form of dislocation is astacking fault, which is due to layer stacking errors. Oxygen-induced stacking faults are induced following thermal oxidation. Gross defects are related to the crystal structure (often occurring during crystal growth).Wafer Preparation•The cylindrical, single-crystal ingot undergoes a series of process steps to create wafers, including machining operations, chemical operations, surface polishing and quality checks.•The first wafer preparation steps are the shaping operations: end removal, diameter grinding, and wafer flat or notch. Once these are complete, the ingot undergoes wafer slicing, followed by wafer lapping to remove mechanical damage and an edge contour. Wafer etching is done to chemically remove damage and contamination, followed by polishing. The final steps are cleaning, wafer evaluation and packaging.Quality Measures•Wafer suppliers must produce wafers to stringent quality requirements, including: Physical dimensions: actual dimensions of the wafer (e.g., thickness, etc.).Flatness: linear thickness variation across the wafer.Microroughness: peaks and valleys found on the wafer surface.Oxygen content: excessive oxygen can affect mechanical and electrical properties.Crystal defects: must be minimized for optimum wafer quality.Particles: controlled to minimize yield loss during wafer fabrication.Bulk resistivity(电阻系数): uniform resistivity from doping during crystal growth is critical. Epitaxial Layer•An epitaxial layer (or epi layer) is grown on the wafer surface to achieve the same single crystal structure of the wafer with control over doping type of the epi layer. Epitaxy minimizes latch-up problems as device geometries continue to shrink.Chapter 5Chemicals in Semiconductor FabricationEquipment Service Chase Production BayChemical Supply Room Chemical Distribution Center Holding tank Chemical drumsProcess equipmentControl unit Pump Filter Raised and perforated floorElectronic control cablesSupply air ductDual-wall piping for leak confinement PumpFilterChemical control and leak detection Valve boxes for leak containment Exhaust air ductStates of Matter• Matter in the universe exists in 3 basic states (宇宙万物存在着三种基本形态): solid, liquid andgas. A fourth state is plasma.Properties of Materials• Material properties are the physical and chemical characteristics that describe its unique identity.• Different properties for chemicals in semiconductor manufacturing are: temperature, pressure andvacuum, condensation, vapor pressure, sublimation and deposition, density, surface tension, thermal expansion and stress.Temperature is a measure of how hot or cold a substance is relative to another substance. Pressure is the force exerted per unit area. Vacuum is the removal of gas molecules.Condensation is the process of changing a gas into a liquid. Vaporization is changing a liquidinto a gas.Vapor pressure is the pressure exerted by a vapor in a closed container at equilibrium.Sublimation is the process of changing a solid directly into a gas. Deposition is changing a gas into a solid.Density is the mass of a substance divided by its volume.Surface tension of a liquid is the energy required to increase the surface area of contact.Thermal expansion is the increase in an object’s dimension due to heating.Stress occurs when an object is exposed to a force.Process Chemicals•Semiconductor manufacturing requires extensive chemicals.• A chemical solution is a chemical mixture. The solvent is the component of the solution present in larger amount. The dissolved substances are the solutes.•Acids are solutions that contain hydrogen and dissociate in water to yield hydronium ions. A base is a substance that contains the OH chemical group and dissociates in water to yield the hydroxide ion, OH-.•The pH scale is used to assess the strength of a solution as an acid or base. The pH scale varies from 0 to 14, with 7 being the neutral point. Acids have pH below 7 and bases have pH values above 7.• A solvent is a substance capable of dissolving another substance to form a solution.• A bulk chemical distribution (BCD) system is often used to deliver liquid chemicals to the process tools. Some chemicals are not suitable for BCD and instead use point-of-use (POU) delivery, which means they are stored and used at the process station.•Gases are generally categorized as bulk gases or specialty gases. Bulk gases are the relatively simple gases to manufacture and are traditionally oxygen, nitrogen, hydrogen, helium and argon.The specialty gases, or process gases, are other important gases used in a wafer fab, and usually supplied in low volume.•Specialty gases are usually transported to the fab in metal cylinders.•The local gas distribution system requires a gas purge to flush out undesirable residual gas. Gas delivery systems have special piping and connections systems. A gas stick controls the incoming gas at the process tool.•Specialty gases may be classified as hydrides, fluorinated compounds or acid gases.Chapter 6Contamination Control in Wafer FabsIntroduction•Modern semiconductor manufacturing is performed in a cleanroom, isolated from the outside environment and contaminants.Types of contamination•Cleanroom contamination has five categories: particles, metallic impurities, organic contamination, native oxides and electrostatic discharge. Killer defects are those causes of failure where the chip fails during electrical test.Particles: objects that adhere to a wafer surface and cause yield loss. A particle is a killer defect if it is greater than one-half the minimum device feature size.Metallic impurities: the alkali metals found in common chemicals. Metallic ions are highly mobile and referred to as mobile ionic contaminants (MICs).Organic contamination: contains carbon, such as lubricants and bacteria.Native oxides: thin layer of oxide growth on the wafer surface due to exposure to air.Electrostatic discharge (ESD): uncontrolled transfer of static charge that can damage the microchip.Sources and Control of Contamination•The sources of contamination in a wafer fab are: air, humans, facility, water, process chemicals, process gases and production equipment.Air: class number designates the air quality inside a cleanroom by defining the particle size and density.Humans: a human is a particle generator. Humans wear a cleanroom garment and follow cleanroom protocol to minimize contamination.Facility: the layout is generally done as a ballroom (open space) or bay and chase design.Laminar airflow with air filtering is used to minimize particles. Electrostatic discharge iscontrolled by static-dissipative materials, grounding and air ionization.Ultrapure deiniozed (DI) water: Unacceptable contaminants are removed from DI water through filtration to maintain a resistivity of 18 megohm-cm. The zeta potential represents a charge on fine particles in water, which are trapped by a special filter. UV lamps are used for bacterial sterilization.Process chemicals: filtered to be free of contamination, either by particle filtration, microfiltration (membrane filter), ultrafiltration and reverse osmosis (or hyperfiltration).Process gases: filtered to achieve ultraclean gas.Production equipment: a significant source of particles in a fab.Workstation design: a common layout is bulkhead equipment, where the major equipment is located behind the production bay in the service chase. Wafer handling is done with robotic wafer handlers. A minienvironment is a localized environment where wafers are transferred on a pod and isolated from contamination.Wafer Wet Cleaning•The predominant wafer surface cleaning process is with wet chemistry. The industry standard wet-clean process is the RCA clean, consisting of standard clean 1 (SC-1) and standard clean 2 (SC-2).•SC-1 is a mixture of ammonium hydroxide, hydrogen peroxide and DI water and capable of removing particles and organic materials. For particles, removal is primarily through oxidation of the particle or electric repulsion.•SC-2 is a mixture of hydrochloric acid, hydrogen peroxide and DI water and used to remove metals from the wafer surface.•RCA clean has been modified with diluted cleaning chemistries. The piranha cleaning mixture combines sulfuric acid and hydrogen peroxide to remove organic and metallic impurities. Many cleaning steps include an HF last step to remove native oxide.•Megasonics(兆声清洗) is widely used for wet cleaning. It has ultrasonic energy with frequencies near 1 MHz. Spray cleaning will spray wet-cleaning chemicals onto the wafer. Scrubbing is an effective method for removing particles from the wafer surface.•Wafer rinse is done with overflow rinse, dump rinse and spray rinse. Wafer drying is done with spin dryer or IPA(异丙醇) vapor dry (isopropyl alcohol).•Some alternatives to RCA clean are dry cleaning, such as with plasma-based cleaning, ozone and cryogenic aerosol cleaning.Chapter 7Metrology and Defect InspectionIC Metrology•In a wafer fab, metrology refers to the techniques and procedures for determining physical and electrical properties of the wafer.•In-process data has traditionally been collected on monitor wafers. Measurement equipment is either stand-alone or integrated.•Yield is the percent of good parts produced out of the total group of parts started. It is an indicator of the health of the fabrication process.Quality Measures•Semiconductor quality measures define the requirements for specific aspects of wafer fabrication to ensure acceptable device performance.•Film thickness is generally divided into the measurement of opaque film or transparent film. Sheet resistance measured with a four-point probe is a common method of measuring opaque films (e.g., metal film). A contour map shows sheet resistance deviations across the wafer surface.•Ellipsometry is a nondestructive, noncontact measurement technique for transparent films. It works based on linearly polarized light that reflects off the sample and is elliptically polarized.•Reflectometry is used to measure a film thickness based on how light reflects off the top and bottom surface of the film layer. X-ray and photoacoustic technology are also used to measure film thickness.•Film stress is measured by analyzing changes in the radius of curvature of the wafer. Variations in the refractive index are used to highlight contamination in the film.•Dopant concentration is traditionally measured with a four-point probe. The latest technology is the thermal-wave system, which measures the lattice damage in the implanted wafer after ion implantation. Another method for measuring dopant concentration is spreading resistance probe. •Brightfield detection is the traditional light source for microscope equipment. An optical microscope uses light reflection to detect surface defects. Darkfield detection examines light scattered off defects on the wafer surface. Light scattering uses darkfield detection to detectsurface particles by illuminating the surface with laser light and then using optical imaging.•Critical dimensions (CDs) are measured to achieve precise control over feature size dimensions.The scanning electron microscope is often used to measure CDs.•Conformal step coverage is measured with a surface profiler that has a stylus tip.•Overlay registration measures the ability to accurately print photoresist patterns over a previously etched pattern.•Capacitance-voltage (C-V) test is used to verify acceptable charge conditions and cleanliness at the gate structure in a MOS device.Analytical Equipment•The secondary-ion mass spectrometry (SIMS) is a method of eroding a wafer surface with accelerated ions in a magnetic field to analyze the surface material composition.•The atomic force microscope (AFM) is a surface profiler that scans a small, counterbalanced tip probe over the wafer to create a 3-D surface map.•Auger electron spectroscopy (AES) measures composition on the wafer surface by measuring the energy of the auger electrons. It identifies elements to a depth of about 2 nm. Another instrument used to identify surface chemical species is X-ray photoelectron spectroscopy (XPS).•Transmission electron microscopy (TEM) uses a beam of electrons that is transmitted through a thin slice of the wafer. It is capable of quantifying very small features on a wafer, such as silicon crystal point defects.•Energy-dispersive spectrometer (EDX) is a widely used X-ray detection method for identifying elements. It is often used in conjunction with the SEM.• A focused ion beam (FIB) system is a destructive technique that focuses a beam of ions on the wafer to carve a thin cross section from any wafer area. This permits analysis of the wafermaterial.Chapter 8Gas Control in Process ChambersEtch process chambers••The process chamber is a controlled vacuum environment where intended chemical reactions take place under controlled conditions. Process chambers are often configured as a cluster tool. Vacuum•Vacuum ranges are low (rough) vacuum, medium vacuum, high vacuum and ultrahigh vacuum (UHV). When pressure is lowered in a vacuum, the mean free path(平均自由行程) increases, which is important for how gases flow through the system and for creating a plasma.Vacuum Pumps•Roughing pumps are used to achieve a low to medium vacuum and to exhaust a high vacuum pump. High vacuum pumps achieve a high to ultrahigh vacuum.•Roughing pumps are dry mechanical pumps or a blower pump (also referred to as a booster). Two common high vacuum pumps are a turbomolecular (turbo) pump and cryopump. The turbo pump is a reliable, clean pump that works on the principle of mechanical compression. The cryopump isa capture pump that removes gases from the process chamber by freezing them.。
A History of Aspirin阿司匹林的历史
Physicians, Fads, andPharmaceuticals:A History of AspirinAnne Adina Judith Andermann*, B.Sc., M.Phil. Cantab* To whom correspondence should be addressed: Faculty of Medicine, McGill University, 3655 Drummond St., Montreal, QC, Canada H3G 1Y6"Politics is not out there in society.Politics is down there in the laboratory."--Bruno Latour (1).Aspirin is a product of the late-nineteenth-century laboratory, pharmaceutical industry, and medical community. The prevailing scientific techniques, industrial approaches, and medical beliefs were instrumental in the development, promotion and reception of the drug. As a result, the present account does not extend further back than a few decades prior to the release of aspirin from the laboratories of Farbenfabriken vormals Friedrich Bayer & Co. in 1899. In contrast, much of the current literature on aspirin (2,3,4) attempts to trace the compound back to antiquity through the Ebers papyrus, the Hippocratic writings, and the works of Galen. Such histories tell a simple, linear tale of the numerous "discoveries" proposed to have led to the use of certain salicylate-containing plants, such as willow bark and wintergreen, or salicylate-related compounds, including salicilin and salicylic acid, as cures for a variety of ailments. Indeed, according to Mann and Plummer:Both [salicilin and salicylic acid] attacked fever and pain, and their partisans advocated the salicylates' use as antiseptics, mouthwashes, and water preservatives for ocean voyages; one important chemist further suggested (erroneously) that sodium salicylate, a chemical relative, would successfully treat scarlet fever, diphtheria, measles, syphilis, cholera, rabies and anthrax (5).However, it is difficult to establish what effect, if any, these examples of the "historical" uses of"proto-aspirin" had on the impetus for and modes of developing and using the actual drug called aspirin. As a matter of course, aspirin is usually described as the natural descendant from these salicylate forefathers. However, the history of aspirin is not as straightforward a tale as conventional histories suggest, but rather is a complex narrative of the people and circumstances involved in transforming a simple chemical compound into a popular pharmaceutical product that has remained one of the most widely consumed drugs for almost a century.Bayer began in 1863 as Friedrich Bayer & Co., a dye-manufacturing plant in Germany. When the dye industry began to wane during the late 1880s, Bayer made the transition into the more active and lucrative sector of pharmaceuticals by developing, producing, and marketing phenacetin (acetophenetidin) from a dye-making by-product. The company's switch from dyes to pharmaceuticals was so rapid that the first lots of the drug were alkylated in make-shift containers--empty beer bottles wrapped in towels--before the company decided to invest in suitable equipment and proper facilities for its production (6). However, despite the change in the products being manufactured, Bayer retained many of the methods used previously in the sale of dyestuffs in highly competitive markets: sales representatives, advertisements in trade journals, and the use of patents and trade names. As McTavish, a noted medical historian, remarks:By restricting its market to the pharmaceutical and medical professions, the chemical industry avoided the unseemly trappings of the nostrum trade and established itself as a member of the 'ethical' fraternity (7).From then on, McTavish affirms, "[drug production] took place in an industrial setting. Drugs were commodities similar in most respects to any other commodity: they were manufactured for profit" (7). During the 1890's, Carl Duisberg and other key figures at Bayer were busily involved in reorganizing the company, in setting up pharmaceutical laboratories for the development and standardization of drugs, and, most importantly, in establishing links with the medical world.The late nineteenth century saw an unprecedented rise in the number of new pharmaceutical products on the market. One physician in 1889 commented: "Every week, almost every day, brings its new drug, each in turn praised as being the greatest discovery of modern therapeutics" (8). McTavish attributes this tremendous influx of new products to "the increasing industrial role of the laboratory, especially in the drug industry" (7). However, the utility of these novel therapeutic products in medical practice was a source of great debate. Certain physicians staunchlyopposed what they saw as "the growing tendency among German medical men to convert the 'Republic of Science' into a commercial oligarchy for the benefit of plutocrats at the expense of suffering humanity" (7). Others were more accepting of the new developments, but remained wary of those who hailed new compounds as milestone drugs or panaceas, "lest they bring into discredit both their own calling and that of the pharmaceutical chemist" (9). In an address on the Progress of Medicine in the Nineteenth Century, Dr. F. Roberts confessed:Out of the enormous number of medicinal agents brought under our notice by puffing advertisements in the press, medical as well as lay, by pamphlets or even large books delivered by post, or by actual 'specimens for trial' which are nowadays so liberally delivered at our residences, comparatively few hold their ground, or stand a fair and candid criticism and investigation of their vaunted merits. Still a certain proportion do and I see every reason to anticipate that, as the result of the systematic researches, scientific and practical, now carried on in so many laboratories, valuable additions will be made from time to time to the medicinal agents at our disposal for the help and comfort of our patients.I only hope that in our love for the new we will not entirely throw out old friends which have done real and effective service in the past and are today as deserving of our regard as ever (10).Therefore, for those pharmaceutical companies that had managed to establish a place for themselves within the medical community, drug production became a legitimate science-based industry, whereby manufacturers and medics engaged in a profitable producer-consumer partnership. For instance, as written in the Lancet in August 1899, many new pharmaceuticals were the product of the increased attention paid "to the toleration of drugs and to the avoiding of effects which are undesirable" (11). Furthermore:Modification of the salicylates and the introduction of new morphine derivatives [which were both activities carried out in the Bayer laboratories] occur as single examples. In these matters it is satisfactory to find that the pharmacist is guided by the medical man and not solely by a knowledge of the chemistry of the principles concerned (11).Thus, the inspiration and drive to produce aspirin can be explained in terms of a medico-industrial relationship in which the pharmaceutical companies supplied products that interested the doctors, and the doctors, in turn, maintained an active interest in what the pharmaceutical companies had to offer.During the 1880s and 1890s, when physicians became intensely interested in the possible adverse effects of fever on the human body, the use of antipyretics became one of the hottest topics in therapeutic medicine. According to one pharmacology textbook published at the beginning of the 20th century:From the highest to the lowest in the profession, the fad was to regard fever as the most deleterious factor in a case, and to treat it as if it were a part of the disease, or the disease itself, instead of a symptom of almost all infections, and one which in itself is not capable of doing harm, unless it is excessive or very prolonged. [It was believed] that not only did fever, when sufficiently high, coagulate the protoplasm of vital parts, but that the patient was having his tissues burnt up, and that this excessive combustion, or conflagration, must be arrested even though the disease spent itself unaltered in its other clinical manifestations and pathological tendencies. The discovery by numerous laboratory investigations that this group of drugs decreased heat production, and increased heat dissipation, seemed to fit them in a peculiar manner to meet the therapeutic needs of the hour, and they were tested on a scale of experimental therapeutics hardly before equaled. At first, cases of untoward effects were frequently recorded, with fortunately very few fatal cases. Often these effects were due to heroic doses; in other cases, when patients in low fevers received the drug, the fall in temperature which succeeded produced collapse; while in maladies like pneumonia, with deficient aeration of the blood, or other pulmonary affectations, cyanosis, excessive sweating, and feebleness of the circulation occurred (12).Therefore, until the fever fad ended at the turn of the century, most likely as a result of the increasing popularity of the germ theory, most physicians concentrated their efforts on treating pyrexia. The drug companies responded to the medical demands of the day by catering to, and perhaps even fueling the fires of, the antipyretic era. New antipyretics and analgesics--most drugs in this class were believed to possess more or less of both properties--were introduced monthly: "those coal-tar crystalline products which have almost deluged the market as quinine substitutes, [were] being offered from time to time as analgesics, anodynes, antipyretics, as the case may be" (13). Moreover, most of these new therapeutic compounds were commonly promoted as and subsequently referred to by catchy brand names such as malarin, pyrantin, cosaprin, phesin, eupyrine, and, of course, aspirin (14).Still, it is not exactly clear how aspirin came to be. Many give the title of "discoverer of aspirin" to Felix Hoffmann, a chemist at Bayer whose father suffered from rheumatism. According to legend, Hoffmann's fatherwas taking salicylic acid, already mass-produced, widely used, and highly profitable by the end of the 1870s, to treat his rheumatic condition. Unfortunately, the drug was terribly irritating to the stomach and was associated with other ill-effects: most notably, in addition to having an unpleasant, sometimes nauseating, taste, it was believed that salicylic acid disrupted digestion and had an enfeebling action on the heart (16,17). Therefore, the dutiful son took on the task of developing a less toxic replacement. However, acetylsalicylic acid (ASA)--the common chemical name of aspirin--may have already been produced by the French chemist Charles Frédéric Gerhardt in 1853, although he called his compound acetosalicylic anhydride, which was not necessarily the same as ASA. The compound was synthesized in a purer form by Johann Kraut in 1869. Indeed, acetylsalicylic acid was already being manufactured by the Chemische Fabrik von Heyden Company in 1897, although without a brand name. Therefore, it is difficult to determine whether Hoffmann truly developed a new chemical compound or even a novel method of producing a known one, which could then have been patented in Germany.In addition to the uncertainties regarding the chemical origins of ASA, the prevailing medical opinions concerning the widely-used salicylic acid and related compounds, including acetylsalicylic acid, were mixed. Similarly, there was a wide divergence in opinion within the Bayer pharmaceutical laboratories concerning the value of the work being done on ASA in 1897. According to Mann and Plummer, there was a certain degree of animosity between Arthur Eichengrün, who ran the research and development-based Pharmaceutical Division where Hoffmann worked, and Heinrich Dreser, who was in charge of testing and standardization in the Pharmacological Division (5). Eichengrün supported Hoffmann's chemical compound, whereas Dreser initially had no interest in even testing it as a potential new drug. Apparently, Eichengrün even went so far as to surreptitiously distribute the compound to physicians for trials. However, it was Dreser who eventually published the first article on aspirin. His change of heart regarding the value of this compound likely reflects his own financial interests, since, according to Mann and Plummer:[Hoffmann and Eichengrün] had contracts with Bayer by which they would receive a royalty on any patentable product they invented. Since there was no patent, neither of them received any royalties from the sale of aspirin in Germany. However, Heinrich Dreser had an agreement with Bayer by which he would receive a royalty on any product that he introduced. Thus he received a very substantial royalty for aspirin and was able to retire early a very rich man (5).As suggested in the July 1899 issue of the Lancet:No one [in the pharmaceutical industry] would undertake the irksome task of making new products known to the medical profession without being, whether rightly or wrongly, convinced of their superior properties (17).Therefore, once Dreser finally chose to promote Hoffmann's chemical compound as aspirin, he certainly built up a strong case for its superiority over other available remedies.In his article published in the Archiv fur die Gesamte Physiologie in 1899, Dreser begins by describing the unsatisfactory nature of the drugs then available, thereby creating the need for new alternatives:In many diseases related to common cold, the use of sodium salicylate would be definitely much more popular if it would not provoke strong rejection by its disgusting sweet taste which can be corrected only to some extent (18).Dreser then suggests:Pharmacological chemistry should develop synthetically a new preparation which would avoid in addition to the disgusting sweet taste other undesirable characteristics such as the overloading of the stomach. After resorption, the active salicylate should be rapidly split off from the new product.These improvements are precisely what Dreser claims to have achieved through the synthesis of aspirin. First, the taste was refined by masking the free phenolic hydroxyl group of salicylic acid through substitution of the hydrogen atom with a methyl group. To prove that aspirin is reabsorbed and cleaved into salicylic acid, Dreser cites the work of the German scientist Lesnik published in the Archiv fur Experimentelle Pathologie und Pharmakologie to maintain that the increase of nitrogen in the urine "could be due only to the nitrogen-containing metabolic product of salicylic acid . . . also clearly shown by aspirin."Dreser then carried out comparative studies of aspirin and other salicylates to demonstrate that the former was less noxious and more beneficial than the latter. For instance, he tested the sodium salt of aspirin and sodium salicylate on normal rabbits and on cold-blooded animals, which, to his mind, "showed clearly that aspirin is less poisonous than salicylic acid." Dreser also tested aspirin on the most fine and delicate tissues, such as the gills of fish, to further demonstrate the gentleness of the compound. Finally, to put to rest any fears that aspirin might depress the heart, he conducted experiments toshow that sodium salicylate decreased cardiac output, whereas the sodium salt of aspirin increased it. Dreser concludes his article as follows:Summing up the most important pharmacologic characteristics of aspirin we may suggest the following: The aspirin has a more pleasant harsh acidic taste than sodium salicylate before resorption. It is also more protective to the stomach wall according to the above experiments. It is very advantageous, furthermore, that aspirin is split by the gastric hydrochloric acid only to a small extent (0.2%). Differences are evident between aspirin and sodium salicylate also after resorption... (18).By publishing these findings in a physiological journal, Dreser was able to provide a "scientific" and "objective" account of this new compound as a potentially powerful pharmaceutical product with few side-effects. At the same time, he was one of the top employees at Bayer, and would therefore benefit personally from the success that his pharmacological analysis had brought upon aspirin.In concert with Dreser's efforts, physicians were co-opted into supporting the effectiveness and harmlessness of aspirin. Two such doctors cited in Dreser's article were Dr. C. Witthauer, who published a paper on his experiences with aspirin in Die Heilkunde in April 1899, and Dr. Julius Wohlgemuth, who had his results published in Therapeutische Monatshefte in May of the same year. Both Witthauer's and Wohlgemuth's articles (19,20) provide a general introduction to the novel powder, corroborate Dreser's findings, and describe the results of clinical trials with aspirin. Unequivocally, they conclude that the new drug is superior to the other pharmaceutical products then available.The elegance of the early medical and pharmaceutical reports lies in their ability to ally aspirin with the already widely accepted salicylic compounds, whilst concurrently presenting aspirin as distinct from them. Thus, the new drug possessed a certain familiarity, and more importantly, the manufacturers could then claim the proven medicinal properties of salicylic acid and related compounds by association. However, it was equally important to disassociate aspirin from the negative qualities that had been attributed to these products through the development of scientific truths in the laboratory which attested to such differences. In this way, a white powder that had spent many years collecting dust on a shelf along with hundreds of other chemical compounds stored at Bayer was transformed into a substantive pharmaceutical product. Since then, each new report by members of the medical community or pharmaceutical world has expanded and altered the ever-growing narrative on aspirin.On July 22, 1899, aspirin was featured in the "Analytical Records from the Lancet Laboratory" along with several other products that had undergone the rigors of scientific analysis: an old pale cognac found to be suitable for medicinal purposes; Johannis potash water, a diuretic and alkaline treatment; Sandron's iron tonic, which was found to contain a very small quantity of iron; and finally, two specimens of Scotch whisky. The journal's announcement of The Bayer Company's latest drug resembled, in both content and intent, the articles published previously by Dreser, Witthauer, and Wohlgemuth. Within a few years, a barrage of articles singing the praises of aspirin had been published. The clinician Floeckinger even went so far as to take two large doses of aspirin himself: first 75 grains and then another 60 grains (21). After the first dose he found himself "without toxic effects, except violent headache and tinnitus" which lasted for 16 hours, until it subsided following profuse sweats. After the second dose, Floeckinger experienced "increased pulse, reduced temperature, and flashes of light before the eyes." Nonetheless, Floeckinger concludes his article as follows:[It] presents several advantages over salicylic acid. It does not irritate the stomach. There is no cardiac depression. In ordinary doses there is no tinnitus or headache...and [it] is best prescribed in wafers or sachets for acute and chronic rheumatism, polyarthritis, and pleurisy...but it is ineffective in neuralgias and pleurodynia (21).Any adverse effects experienced when taking aspirin were attributed not to this new drug, but rather to extrinsic factors, such as the medium of administration or the magnitude of the dose. Although certain physicians claimed that "some observers--Osler, for instance--recognize little or no advantage in salicylates beyond some power in relieving pain" (15), most physicians strongly supported aspirin as a valuable addition to the pharmacopoeia.Soon after its release onto the market, aspirin began to appear in the new pharmacological texts. Nonetheless, there were still many recent and reputable works that did not mention Bayer's new drug (12,22,23). Indeed, even when aspirin was included in these works, it was not always cited for use in treating ailments with which one now associate the drug. The Index of Diseases and Remedies in an American textbook on materia medica, pharmacology and therapeutics, for example, cites aspirin for the treatment of certain diseases, but does not prescribe it as a general substitute for salicylic acid and the other salicylates. The text lists salicylic acid as a drug useful for burns, eczema, ephelides (freckles), lupus vulgaris, pertussis, and ulceration. Salicilin, salol, salipyrin, and other salicylates are recommended for different disorders such as chorea, diabetes mellitus, endocarditis, fever, pharyngitis, andpleurisy, whereas aspirin is recommended, in addition to other drugs, in the treatment of influenza, neuralgia, and neuritis (24).Indeed, within the first five years after its release, aspirin was seen less and less as an antipyretic, and was increasingly prescribed for the relief of pain. By 1903, "numerous observations had been made on the analgesic effect of aspirin in neuralgias and other painful affectations," including carcinoma (25). In this way, aspirin was similar to its predecessor phenacetin, which "found its birth in what may be called the antipyretic era [of the 1880s and 1890s, and] like its relatives has come to be employed chiefly for the relief of pain" (12). The shift in interest from the antipyretic to the analgesic properties of these drugs in the early twentieth century is best summarized by the entry in the Text-book of Pharmacology and Therapeutics of 1901:As the fad for antipyresis waned by its loss of novelty, physicians began to ask each other whether these drugs which acted so well in reducing fever had any influence in shortening the course of the disease, and it was speedily determined that they did not. Simultaneously, the increasingly thorough investigations into the pathology of fever, and our increased knowledge of the life history of the organisms causing disease, made it clear that fever was a comparatively unimportant factor in a given case, unless excessive; and it begins to be apparent that fever is not only not a peculiarly harmful process, but in some cases may be actually of value... Finally, the recollection of the fact that the use of these drugs necessitates their absorption and elimination, changed or unchanged, and that in these processes they may be guilty of a deleterious influence, has still further decreased their popularity as antipyretics, while the discovery that all of them possess pain-relieving properties has also diverted attention to their use for other purposes than antipyresis (12).Thus, the uses of aspirin changed with the changing trends in the medical profession, becoming progressively less linked to the drug's initial description and indications first marketed by the pharmaceutical company. The original experiments conducted on aspirin in the Bayer laboratory were superceded by more recent clinical findings conducted by medical men not affiliated with the pharmaceutical company. Gradually, all the stories told by those who had been instrumental in presenting and promoting acetylsalicylic acid as aspirin faded into the background. By 1903, authors no longer felt the need to include comprehensive profiles of aspirin in their articles: "the remedy is now sufficiently known to make its description unnecessary here" (15). Thus, the original narrative of aspirin had been disseminated and accepted by the medical profession to such an extent that it no longer needed repeating.Aspirin had quickly become a household name around the world, finding its way even into literary works of the early twentieth century. For instance, when the young Lady Caroline Desta of Elizabeth von Arnim's 1922 novel The Enchanted April complained of a headache during a holiday in Italy, one of her companions asked, "Do you know what aspirin is in Italian?"--to which an erudite old Englishwoman interjected that "the proper remedy for headaches...is castor oil." In a similar vein, Franz Kafka once explained to his fiancée Felice Bauer, in the course of their tormented relationship, that aspirin was one of the few things that eased the unbearable pain of being (5).Aspirin has certainly been put to many different uses throughout the twentieth century, and serves as an example of one of many products of the novel and tenuous relationship that developed during the late nineteenth century between laboratory science, the manufacturing industry, and medical humanitarianism. Indeed, the early pharmaceutical industry's establishment of a close association with the medical community and its adoption of scientific techniques, or, at the very least, a scientific veneer, were instrumental in its success, "and changed the character of medical practice as much as it did the industry itself" (26). Over the years, these medico-industrial connections have consolidated to form the modern pharmaceutical industry of today, an industry that has pervaded almost all aspects of medical science and practice.The story of aspirin--its origins, popularization, and varied uses--is rather unique:Few groups of drugs have provided the manufacturers with such fortunes, physicians with such therapeutic resources, and the laity with so many semi-proprietary remedies as have the so-called antipyretic or analgesic derivatives of coal tar. Nor is there any group which illustrates so well the close relationship between chemistry and practical therapeutics, and the relation of chemical constitution to physiological action (12).Yet, the story of aspirin to a great degree epitomizes the stories of many pharmaceutical products developed both for increased therapeutic efficacy and for profit. The histories of these products generally share certain themes. The usually vague and contentious origins of a drug soon become overshadowed by the multitude of clinical reports produced with the help of medical allies. Extensive clinical trials serve to introduce new drugs to the greater medical community, to specific patient groups, and eventually, to the population at large. As the years pass, however, many drugs are used to treat diseases different from those for which the drugs were originally intended. For example, with the advent of the "anti-coagulant era," aspirin has acquired new indications as a plateletanti-aggregant, and is already widely used in the prophylaxis and treatment of strokes and myocardial infarcts. Therefore, drugs currently being produced and prescribed remain a reflection of the ever-changing state of medical knowledge and of the pharmaceutical industry's eagerness to meet the needs of the day.As the quest for more potent and less toxic drugs continues in the age of rational therapeutics, advanced technology, and designer drugs, the treatment of disease continues to be shaped by the symbiotic relationship between physicians and pharmaceutical companies forged a century ago.ACKNOWLEDGMENTSThe author wishes to acknowledge the assistance of Harmke Kamminga in the preparation of this work. She also wishes to thank the Wellcome Trust for awarding her the Masters Scholarship, and McGill University for their generous Philip F. Vineberg Travelling Fellowship, both of which made it possible to pursue this work towards an M.Phil. at the Wellcome Unit for the History of Medicine in Cambridge, England.REFERENCES1. Latour B. "The Costly Ghastly Kitchen" in Cunningham A. and Williams P., eds., The Laboratory Revolution in Medicine. Cambridge: Cambridge University Press; 1992.2. Rainsford KD. Aspirin and the Salicylates. London: Butterworths; 1984.3. Vane JR, Botting RM. Aspirin and other Salicylates. London: Chapman and Hall Medical Publishers; 1992.4. Mann J. Murder, Magic and Medicine. Oxford: Oxford University Press; 1992.5. Mann CC, Plummer ML. The Aspirin Wars: Money, Medicine, and 100 Years of Rampant Competition. Boston: Harvard Business School Press; 1991.6. Verg E, Plumpe G, Schultheis H. Meilensteine: The official Bayer publication in commemoration of the centenary of aspirin's release; 1989.7. McTavish J. What's in a name? Aspirin and the American Medical Association. Bulletin of the History of Medicine61: 364-365; 1987.8. Dr. Pope of the Leicester Infirmary and Fever House. The Lancet, April 13, 1889, p. 728.。
韦伯分布介绍
韋伯分佈韋伯分佈(Weibull distribution)以指數分佈為一特例。
其p.d.f.為其中α,β>0。
以表此分佈, 有二參數α,β, α為尺度參數, β為形狀參數。
若取β=1, 則得分佈, 以表之。
底下給出一些韋伯分佈p.d.f.之圖形。
韋伯分佈是瑞典物理學家Waloddi Weibull, 為發展強化材料的理論, 於西元1939年所引進, 是一較新的分佈。
在可靠度理論及有關壽命檢定問題裡, 常少不了韋伯分佈的影子。
分佈的分佈函數為期望值與變異數分別為Characteristic Effects of the Shape Parameter, β, for the Weibull DistributionThe Weibull shape parameter, β, is also known as the slope. This is because the value of β is equal to the slope of the regressed line in a probability plot. Different values of the shape parameter can have marked effects on the behavior of the distribution. In fact, some values of the shape parameter will cause the distribution equations to reduce to those of other distributions. For example, when β = 1, the pdf of the three-parameter Weibull reduces to that of thetwo-parameter exponential distribution or:where failure rate.The parameter β is a pure number, i.e. it is dimensionless.The Effect of β on the pdfFigure 6-1 shows the effect of different values of the shape parameter, β, on the shape of the pdf. One can see that the shape of the pdf can take on a variety of forms based on the value of β.Figure 6-1: The effect of the Weibull shape parameter on the pdf.For 0 < β1:∙As (or γ),∙As , .∙f(T) decreases monotonically and is convex as T increases beyond the value of γ.∙The mode is non-existent.For β > 1:∙f(T) = 0 at T = 0 (or γ).∙f(T) increases as (the mode) and decreases thereafter.∙For β < 2.6 the Weibull pdf is positively skewed (has a right tail), for 2.6 < β < 3.7 its coefficient of skewness approaches zero (no tail). Consequently, it may approximate the normal pdf, and for β > 3.7 it is negatively skewed (left tail).The way the value of β relates to the physical behavior of the items being modeled becomes more apparent when weobserve how its different values affect the reliability and failure rate functions. Note that for β = 0.999, f(0) = , but for β = 1.001, f(0) = 0. This abrupt shift is what complicates MLE estimation when β is close to one.The Effect ofβ on the cdf and Reliability FunctionFigure 6-2: Effect of β on the cdf on a Weibull probability plot with a fixed value of η.Figure 6-2 shows the effect of the value of β on the cdf, as manifested in the Weibull probability plot. It is easy to see why this parameter is sometimes referred to as the slope. Note that the models represented by the three lines all have the same value of η. Figure 6-3 shows the effects of these varied values of β on the reliability plot, which is a linear analog of the probability plot.Figure 6-3: The effect of values of β on the Weibull reliability plot.∙R(T) decreases sharply and monotonically for 0 < β < 1 and is convex.∙For β = 1, R(T) decreases monotonically but less sharply than for 0 < β < 1 and is convex.∙For β > 1, R(T) decreases as T increases. As wear-out sets in, the curve goes through an inflection point and decreases sharply.The Effect of β on the Weibull Failure Rate FunctionThe value of β has a marked effect on the failure rate of the Weibull distribution and inferences can be drawn about a population's failure characteristics just by considering whether the value of β is less than, equal to, or greater than one.Figure 6-4: The effect of β on the Weibull failure rate function.As indicated by Figure 6-4, populations with β < 1 exhibit a failure rate that decreases with time, populations with β = 1 have a constant failure rate (consistent with the exponential distribution) and populations with β > 1 have a failure rate that increases with time. All three life stages of the bathtub curve can be modeled with the Weibull distribution and varying values of β.The Weibull failure rate for 0 < β < 1 is unbounded at T = 0 (or γ). The failure rate, λ(T), decreases thereaftermonotonically and is convex, approaching the value of zero as or λ( ) = 0. This behavior makes it suitable for representing the failure rate of units exhibiting early-type failures, for which the failure ratedecreases with age. When encountering such behavior in a manufactured product, it may be indicative of problems in the production process, inadequate burn-in, substandard parts and components, or problems with packaging and shipping.For β = 1, λ(T) yields a constant value of or:This makes it suitable for representing the failure rate of chance-type failures and the useful life period failure rate of units.For β > 1, λ(T) increases as T increases and becomes suitable for representing the failure rate of units exhibiting wear-out type failures. For 1 < β < 2, the λ(T) curve is concave, consequently the failure rate increases at a decreasing rate as T increases.For β = 2 there emerges a straight line relationship between λ(T) and T, starting at a value of λ(T) = 0 at T = γ, andincreasing thereafter with a slope of . Consequently, the failure rate increases at a constant rate as T increases. Furthermore, if η = 1 the slope becomes equal to 2, and when γ = 0, λ(T) becomes a straight line which passes through the origin with a slope of 2. Note that at β = 2, the Weibull distribution equations reduce to that of the Rayleigh distribution.When β > 2, the λ(T) curve is convex, with its slope increasing as T increases. Consequently, the failure rate increases at an increasing rate as T increases indicating wear-out life.TopCharacteristic Effects of the Scale Parameter, η, for the Weibull DistributionFigure 6-5: The effects of η on the Weibull pdf for a common β.A change in the scale parameter η has the same effect on the distribution as a change of the abscissa scale. Increasing the value of η while holding β constant has the effect of stretching out the pdf. Since the area under a pdf curve is a constant value of one, the "peak" of the pdf curve will also decrease with the increase of η, as indicated in Figure 6-5.∙If η is increased while β and γ are kept the same, the distribution gets stretched out to the right and its height decreases, while maintaining its shape and location.∙If η is decreased while β and γ are kept the same, the distribution gets pushed in towards the left (i.e. towards its beginning or towards 0 or γ), and its height increases.∙η has the same units as T, such as hours, miles, cycles, actuations, etc.TopCharacteristic Effects of the Location Parameter, γ, for the Weibull DistributionThe location parameter, γ, as the name implies, locates the distribution along the abscissa. Changing the value of γ has the effect of "sliding" the distribution and its associated function either to the right (if γ > 0) or to the left (if γ < 0).Figure 6-6: The effect of a positive location parameter, γ, on the position of the Weibull pdf.∙When γ = 0, the distribution starts at T = 0 or at the origin.∙If γ > 0, the distribution starts at the location γ to the right of the origin.∙If γ < 0, the distribution starts at the location γ to the left of the origin.∙γ provides an estimate of the earliest time-to-failure of such units.∙The life period 0 to +γ is a failure free operating period of such units.∙The parameter γ may assume all values and provides an estimate of the earliest time a failure may be observed. A negative γ may indicate that failures have occurred prior to the beginning of the test, namelyduring production, in storage, in transit, during checkout prior to the start of a mission, or prior to actual use.∙γ has the same units as T, such as hours, miles, cycles, actuations, etc.。
Technology and Happiness 课文完整版
Technology and HappinessWhy getting more gadgets won't necessarily increase our well-being. By James SurowieckiIn the 20th century, Americans, Europeans, and East Asians enjoyed material and technological advances that were unimaginable in previous eras. In the United States, for instance, gross domestic product per capita tripled from 1950 to 2000. Life expectancy soared. The benefits of capitalism spread more widely among the population. The boom in productivity after World War II made goods better and cheaper at the same time. Things that were once luxuries, such as jet travel and long-distance phone calls, became necessities. And even though Americans seemed to work extraordinarily hard (at least compared to Europeans), their avid pursuit of entertainment turned media and leisure into multibillion-dollar industries.By most standards, then, you'd have to say that Americans are better off now than they were in the middle of the last century. Oddly, though, if you ask Americans how happy they are, you find that they’re no happier than they were in 1946 (which is when formal surveys of happiness started). In fact, the percentage of people who say they’re very happy has fallen slightly since the early 1970s -- even though the income of people born in 1940 has increased, on average, 116 percent over the course of their working lives. Nor is this a uniquely Americanphenomenon: you can find similar data for most developed countries. Perhaps the most striking example of progress having little impact on what economists call people's sense of subjective well-being is Japan. Between 1960 and the late 1980s, Japan's economy was utterly transformed, as the nation went from a low-cost supplier of cheap manufactured goods to what is perhaps the world’s most technologically sophisticated society. Over that stretch, the country's GDP quintupled. And yet by the late 1980s, the Japanese said they were no happier than they had been in 1960.Even more strikingly, life seems worse for a significant minority of citizens in the rich world. Since the 1950s, reports of major depression have increased tenfold, and while much of that increase undoubtedly represents a new willingness to diagnose mental illness, there’s a general consensus among mental-health experts that it also reflects a real development. People are more anxious, trust government and business less, and get divorced more often. In the 1960s Tom Wolfe confounded those who fretted about the gloominess of American life by insisting that Americans were in the midst of a happiness explosion. Forty years later, plenty of people would disagree.There is, though, one group of Americans that is imperturbably sunny: the Amish. Their depression rates are negligibly low relative tothe rest of society’s. Their happiness levels are consistently high. The Pennsylvania Amish, when asked how much they agree with the statement: You are satisfied with your life (using a scale of 1 to 10), turn out to be as happy as the members of the Forbes 400. The Amish, though, do without most of what we think of as modern technology. They don't rely on the automobile, don't need the Internet, and seem to prefer stability and permanence to the heady growth that propels innovation and the U.S. economy. The comparison is a little facile (the Amish have a lot of other characteristics that make people cheerful, including strong community ties, stable families, and religious faith). But it suggests an interesting question: is it possible that technology, instead of liberating us, is holding us back? Is technological progress merely a treadmill, and if so, would we be happier if we stepped off of it?Can we trust people to know what makes them happy?The relationship between happiness and technology has been a perennial subject for social critics and philosophers since the advent of the Industrial Revolution. But it’s been left largely unexamined by economists and social scientists. The attention that they have paid to the subject of happiness has involved the more capacious relationship between broad material prosperity and well-being. Gregg Easterbrook's book The Progress Paradox grappled with this question directly. Theeconomists Bruno Frey and Alois Stutzer published an academic survey of the subject in Happiness and Economics in 2001. But the truly groundbreaking work on the relationship between prosperity andwell-being was done by the economist Richard Easterlin, who in 1974 wrote a famous paper entitled “Does Economic Growth Improve the Human Lot?”Easterlin showed that when it came to developed countries, there was no real correlation between a nation's income level and its citizens' happiness. Money, Easterlin argued, could not buy happiness -- at least not after a certain point. Easterlin showed that though poverty was strongly correlated with misery, once a country was solidly middle-class, getting wealthier didn't seem to make its citizens any happier.Easterlin's work did not get much attention when it was first published, but its implications were profound. By suggesting that there was no direct link between wealth and well-being, Easterlin was challenging some basic assumptions of mainstream economics. Most economists begin with the idea that people act in their own self-interest most of the time, and that they usually understand that self-interest pretty well. The choices people make, therefore, must be better than the alternatives (or else people would make other choices). By this argument, wealth is a good thing because it increases people’s options and gives them more freedom to pursue whatever it is they want topursue. For classical economists, it was almost tautological to say that the wealthier people are, the happier they are, too.Easterlin's relatively simple study suggested that if what people said about themselves was to be believed, you could give people more choices and more wealth and not have much of an impact on their sense of well-being. Well-being is actually the central idea of economics, says Alan Krueger, an economist at Princeton University. But we’ve never really tried to measure it. We've used proxies, and we've said, If we're richer, and we have more options, we must be better off. But we haven't tried to find out if that's really true.One response to this, of course, is to say that you can't really trust what people say about themselves in surveys, no matter how well executed. Pay attention to what people do, and you’ll get a real sense of what they want. On this view, worrying about whether people say they are happy with the choices they make is nonsense. Of course they are. If people spend a lot of money and time buying and using personal computers and wireless phones and personal digital assistants, then these gadgets must make them happy.There is an inherent logic to this argument, and it has the great virtue of not asking economists to decipher people’s motives. But in the last decade or more, deciphering peoples motives (or at least theirbehavior) is something more economists have become interested in doing, and to great effect. Behavioral economists have moved away from assumptions about individual’s perfect rationality in order to develop what they think of as a more realistic model of economic behavior. They've explored the idea, hardly radical outside economics but pretty radical inside it, that people might sometimes make mistakes, and that their decisions (whether individual or collective) could actually make them unhappy. For instance, behavioral economists have shown that people’s preferences are what is sometimes called time-inconsistent. We would like to save in the long term, but in the short term we'd rather spend. Just as strikingly, behavioral economists have shown that human beings aren't very good at anticipating their own desires. Daniel Kahneman of Princeton University, who won the Nobel Prize in economics in 2002, demonstrated that students, when asked to eat a bowl of their favorite ice cream eight days in a row, had a poor sense of whether they would or would not enjoy the experience.Considering how many decisions about new technologies are based on little or no concrete evidence and involve guessing about the future, it seems plausible that people can get stuck with technologies that don't make them happy but that are hard to get rid of. Plausible, but not certain: as we’ll see, when it comes to the vexed relationship between technology and happiness, certainty is not an easy thing to come by.The question of technology: net loss or net gain?In trying to decipher how technology affects well-being, then, it's worth paying attention to a few things. First, there have been few rigorous studies of the specific relationship between technological change and how people feel about their own lives. So the question “Does more (or better) technology make people happy?”is irreducibly speculative. Second, there is something inherently unstable about people’s accounts of their own states of mind. Forget people's uncertainty about what will make them happy in the future; can we even trust that people know what makes them happy now?Most seriously, thinking about technology is hard because people adapt so quickly to the technologies that are available to them. If you had asked someone in 1870 whether she would be happier if she had a personal vehicle that would give her the freedom to travel hundreds of miles a day, in whatever direction she chose, at relatively little cost; the opportunity to fly across the ocean in a few hours; and the ability to speak to people who were thousands of miles away in real time for a few cents a minute, chances are very good that she would have said, yes, it would make her a lot happier. But today, it's the rare person who gets excited about cars, planes, and telephones. We recognize their utility, but they're also sources of frustration and stress. On balance, mostpeople would say they'd rather have cars and telephones than not, but -- and this is what makes thinking about happiness so hard –it’s not clear they really make us happier.This seems to be close to a universal phenomenon. In fact, one of happiness scholars' most important insights is that people adapt very quickly to good news. Take lottery winners. One famous study showed that although winners were very, very happy when they won, their euphoria quickly evaporated, and after a while their moods and sense of well-being were indistinguishable from what they had been before the victory. Psychologists even have a word for the phenomenon: hedonic adaptation.So, too, with technology: no matter how dramatic a new innovation is, no matter how much easier it makes our lives, it is very easy to take it for granted. You can see this principle at work in the world of technology every day, as things that once seemed miraculous soon become mundane and, worse, frustrating when they don't work perfectly. It’s hard, it turns out, to keep in mind what things were like before the new technology came along. That's why broadband users should occasionally use dial-up: it makes them appreciate just what a difference a high-speed connection really does make.Does our fast absorption of technological progress mean, then, that technology makes no difference? No. It just makes the question of technology's impact, for good and ill, more complicated. Let's start with the downside. There are certain ways in which technology makes life obviously worse. Telemarketing, traffic jams, and identity theft all come to mind. These are all phenomena that make people consciously unhappy. But for the most part, modern critiques of technology have focused not so much on specific, bad technologies as on what Heidegger called the question of technology -- that is, the impact of technology on our humanity.Those critiques have staked out two apparently opposed positions, which nonetheless share a common skepticism about peoples' ability to use technology to their own ends. The first position, which one can see in the work of the French critic Jacques Ellul or, more oddly, in the novels of Philip K. Dick, is that technological progress is leading to an ever more rigid, controlled, soulless society, in which it’s easier for people to be manipulated and monitored. The second position, which has been well articulated in books like Neil Postman's Amusing Ourselves to Death and Robert Putnam's Bowling Alone, is that technology is central to the increasing privatization of experience, which in turn is creating a fragmented, chaotic society, in which traditional relationships are harder to sustain, community isincreasingly an illusion, and people's relationships to each other, mediated as they often are by machines, grow increasingly tenuous.There’s obviously something to both arguments. Privacy has become increasingly fragile in a world of linked databases. In many workplaces, technologies like keystroke monitoring and full recordings of phone calls make it easier to watch workers. The notion that technology disrupts relationships and fractures community gained mainstream prominence as an attack on television, but in recent years it has also become central to the critique of the Internet. In Bowling Alone, Putnam suggests that TV is a chief culprit in the gradual isolation of Americans from each other and the erosion of the social capital that makes societies run smoothly. Similarly, the deleterious effects of the Internet, which supposedly further isolates people from what critics always call the real world, were pointed to early on in a famous study of 169 Pittsburgh residents, Internet Paradox: A Social Technology That Reduces Social Involvement and PsychologicalWell-Being? According to the study, published in the September 1998 issue of American Psychologist, instead of allowing them to connect with a much wider set of potential friends and exposing them to information they might otherwise never have come across, the Internet made people more depressed and lonely than they would otherwise have been.This broad criticism of technology's impact on relationships is an interesting one and is especially relevant to the question of happiness, because one of the few things we can say for certain is that the more friends and close relationships people have, the happier they tend to be. But the evidence that the Internet or even television fundamentally erodes relationships as opposed to changing them is not especially convincing. For instance, when the authors of that 1998 study revisited the question a few years later, using a slightly different methodology, they arrived at the opposite conclusion, finding that the Net had a slightly beneficial impact on people’s sociability, connections with others, and sense of well-being.Obviously, a technology as wide-ranging and ubiquitous as the Net will have myriad, immeasurable effects. But the Internet is essentially a communications technology, one that, like the telephone, allows people to expand their affective and informational networks. The Net is hardly the ideal public sphere, where all discussions are rational and everyone agrees on a definition of the common good. But it is a public sphere, and one that crucially functions without gatekeepers.The dominant critiques of technology have, then, something exaggerated about them. But one way in which technology, as a rule, does make people less happy is in its relentless generation of newness.One of the key insights of happiness studies is that people have a very hard time being content with what they have, at least when they know that others have more. Today, technological change is so rapid that when you buy something, you do so knowing that in a few months there's going to be a better, faster version of the product, and that you’re going to be stuck with the old one. Someone else, in other words, has it better. It's as if disappointment were built into acquisition from the very beginning (unless you're buying a 70-inch plasma screen, in which case you should be fine for at least a couple of years). There's no way to circumvent this drooping of the spirit, which creates dissatisfaction in the heart of the modern consumer.Technology la carte: bad food, but bigger portionsDaily stress, a nagging sense of disappointment, fear that the government knows a lot more about you than you would like it to: if these are some of the ways in which technology reduces peoples sense of well-being, how (if at all) does it increase their happiness? This is terrain that is ordinarily left to the cyber optimists and transhumanists, who believe that technology should be celebrated for the way it remakes and improves our bodies and minds. But setting flights of fancy aside, there is some intriguingly suggestive work about how certain newtechnologies make people not just objectively better off but also happier.In the marketplace, for instance, the Internet has made consumers happier not so much by cutting prices as by expanding the enormous array of choices available to them in a manageable way. In the happiness stakes, expanding consumers’options is really adouble-edged sword: consumers do have a preference for variety and novelty, and the more choices you have, the better the chance that you’ll find the thing you really want. But too much choice can actually paralyze people, leaving them, paradoxically, worse off.A well-known experiment conducted by Professors Mark Lepper and Sheena Iyengar (at Stanford and Columbia, respectively) illustrates the point: they set up two tables in a supermarket, one with 24 jars of jam and the other with six, and offered discount coupons to anyone who stopped to sample the jams. Of the people who stopped at the 24-jam table, only 3 percent went on to buy jam, while 30 percent of the people who stopped at the six-jam table did. More choices often make people frustrated because they have no reasonable way to navigate through them. What the Internet offers, at least in a nascent form, is a host of mechanisms collaborative filtering, shopbots, consumer-rating sites that give people the tools to make informed choices relatively quicklyand easily, reducing paralysis and making them happier. The important point here is that among the infinite choices that the Internet offers, one is the option of less choice.Technology has also radically changed the nature of work, or at least some people’s work. This matters because the workplace is central to people’s sense of well-being and is more important to them than anything, including family. Studies show that nothing -- not even divorce -- makes people more unhappy than unemployment. For much of the 19th and 20th centuries, technology’s impact on the workplace was ambiguous at best. While the mechanization of agriculture allowed people to escape the farm, it often propelled them straight into heavy industrial labor, which was well paying but often miserable. Technology increased the productivity of workers, but it also diminished their autonomy: superiors controlled more of the details of their working days. Even the office work of the postwar period exemplified by the endless rows of desks in Billy Wilder's The Apartment was deeply bureaucratic and controlled. But recently, the rise of the networked society, and the advent of knowledge-based businesses, means that workplaces have become less formal and more open, even while remaining efficient and productive. Already, as Arlie Hochschild points out in The Time Bind, a significant percentage of Americans find the atmosphere at work more congenial than the one at home. As thenumber of knowledge workers grows, and as companies strive to keep them happy, well-being should increase.The most important impact of technology on people’s sense ofwell-being, though, is in the field of health care. Before the Industrial Revolution, two out of every three Europeans died before the age of 30. Today, life expectancy for women in Western Europe is almost 80 years, and it continues to increase. The point is obvious, but important to note: the vast majority of people are happy to be alive, and the more time they get on earth, the better off they feel they'll be. (Remember, the point about prosperity and happiness is not that prosperity makes people unhappy; it’s that it doesn’t necessarily make them happier.) Now, the picture is a little more complicated than this. Living a few extra years as a geriatric may not be ideal. But until very recently, life for the vast majority of people was (in Hobbess formulation) nasty, brutish, and short. Technology has changed that, at least for people in the rich world. As much as we should worry about the rising cost of health care and the problem of the uninsured, it’s also worth remembering how valuable for our spirits as well as our bodies are the benefits that medical technology and pharmaceuticals have brought us.On a deeper level, what the technological improvement of our health and our longevity underscores is a paradox of any discussion ofhappiness on a national or a global level: even though people may not be happier, even though they are wealthier and possess more technology, they’re still as hungry as ever for more time. It's like that old Woody Allen joke: the food may not be so great, but we want the portions to be as big as possible.Technology may only improve the taste of the meals slightly, but it makes them a lot bigger, and for most of us, that has the promise of something like happiness.。
托福阅读OG Geology and Landscape
Geology and Landscape1. 核心词汇总结dynamic 动态的principal 主要的terrain 地形epitome 象征，缩影permanence 永久relic 遗迹，废墟comparatively 比较地altitude 高度sedimentary rocks 沉积岩fracture 折断，破裂lava 火山熔岩 extinct volcanoes 死火山 be subjected to 遭受，受...的影响 fragment 碎片 penetrate 渗透，穿透 seep 渗出 shatter 打碎，削弱 glacier 冰川 bombard 轰炸，炮击 wear 磨损2. 长难句总结(1) Hills and mountains are often regarded as the epitome of permanence, successfully resisting the destructive forces of nature, but in fact they tend to be relatively short -lived in geological terms.(2) Some mountains were formed as a result of these plates crashing into each other and forcing up the rock at the plate margins.(3) Carbon dioxide in the air reacts with the rainwater, forming a weak acid (carbonic acid) that may chemically attack the rocks.(4) Glaciers may form in permanently cold areas, and these slowly moving masses of ice cut out valleys, carrying with them huge quantities of eroded rock debris.P1: two influencesMost people consider the landscape to be unchanging, but Earth is a dynamic(动态的) body, and its surface is continually altering -slowly on the human time scale, but relatively rapidly when4,500 billion constructive processes such as uplift, which create new landscape features, and destructive forces such as erosion, which gradually wear away exposed landforms.P2: relatively short -livedHills and mountains are often regarded as the epitome(象征，缩影) of permanence(永久), successfully resisting the destructive forces of nature, but in fact they tend to be relatively short-lived in geological terms(从地质学的角度来讲). As a general rule(一般来说), the higher a mountain is, the more recently it was formed; for example, the high mountains of the Himalayas are only about 50 million years old. Lower mountains tend to be older, and are often the eroded relics(遗迹，废墟) of much higher mountain chains. About 400 million years ago, when the present-day continents of North America and Europe were joined, the Caledonian mountain chain was the same size as the modern Himalayas. Today, however, the relics of the Caledonian orogeny (mountain-building period) exist as the comparatively(比较地) low mountains of Greenland, the northern Appalachians in the United States, the Scottish Highlands, and the Norwegian coastal plateau.P3: Constructive force：plate crashing；earthquake；volcanic activityThe Earth's crust is thought to be divided into huge, movable segments, called plates, which float on a soft plastic layer of rock. 1. Some mountains were formed as a result of these plates crashing into each other and forcing up the rock at the plate margins. In this process, sedimentary rocks (沉积岩)that originally formed on the seabed may be folded upwards to altitudes(高度) of more than 26,000 feet. 2. Other mountains may be raised by earthquakes, which fracture(破裂，折断) the Earth's crust and can displace enough rock to produce block mountains. 3. A third type of mountain may be formed as a result of volcanic activity which occurs in regions of active fold mountain belts, such as in the Cascade Range of western North America. The Cascades are made up of lavas(火山熔岩) and volcanic materials. Many of the peaks are extinct volcanoes(死火山).P4: Destructive force：various weather processWhatever the reason for mountain formation, as soon as land rises above sea level it is subjected to (遭受，受...的影响)destructive forces. The exposed rocks are attacked by the various weather processes and gradually broken down into fragments(碎片), which are then carried away and later deposited as sediments. Thus, any landscape represents only a temporary stage in the continuous battle between the forces of uplift and those of erosion.P5: Destructive force：erosion-rainThe weather, in its many forms, is the main agent of erosion. Rain washes away loose soil and penetrates (渗透，穿透)cracks in the rocks. Carbon dioxide in the air reacts with the rainwater, forming a weak acid (carbonic acid) that may chemically attack the rocks. The rain seeps(渗出) underground and the water may reappear later as springs. These springs are the sources of streams and rivers, which cut through the rocks and carry away debris from the mountains to the lowlands.P6: Destructive force：erosion-windUnder very cold conditions, rocks can be shattered(打碎，削弱) by ice and frost. Glaciers(冰河，冰川) may form in permanently cold areas, and these slowly moving masses of ice cut out valleys, carrying with them huge quantities of eroded rock debris. In dry areas the wind is the principal agent of erosion. It carries fine particles of sand, which bombard(轰炸，炮击) exposed rock surfaces, thereby wearing(磨损) them into yet more sand. Even living things contribute to theformation of landscapes. Tree roots force their way into cracks in rocks and, in so doing, speed their splitting. In contrast, the roots of grasses and other small plants may help to hold loose soil fragments together, thereby helping to prevent erosion by the wind.Paragraph 1: Most people consider the landscape to be unchanging, but Earth is a dynamic body, and its surface is continually altering--slowly on the human time scale, but relatively rapidly when compared to the great age of Earth (about 4,500 billion years). There are two principal influences that shape the terrain: constructive processes such as uplift, which create new landscape features, and destructive forces such as erosion, which gradually wear away exposed landforms.1. According to paragraph 1, which of the following statements is true of changes in Earth's landscape? 细节题○They occur more often by uplift than by erosion.○They occur only at special times.○They occur less frequently now than they once did.○They occur quickly in geological terms.2. The word “relatively” in the passage is closest in meaning to 词汇题○ unusually○ comparatively○ occasionally○ naturallyParagraph 2: Hills and mountains are often regarded as the epitome of permanence, successfully resisting the destructive forces of nature, but in fact they tend to be relatively short-lived in geological terms. As a general rule, the higher a mountain is, the more recently it was formed; for example, the high mountains of the Himalayas are only about 50 million years old. Lower mountains tend to be older, and are often the eroded relics of much higher mountain chains. About 400 million years ago, when the present-day continents of North America and Europe were joined, the Caledonian mountain chain was the same size as the modern Himalayas. Today, however, the relics of the Caledonian orogeny (mountain-building period) exist as the comparatively low mountains of Greenland, the northern Appalachians in the United States, the Scottish Highlands, and the Norwegian coastal plateau.3. Which of the following can be inferred from paragraph 2 about the mountains of the Himalayas? 推断题○Their current height is not an indication of their age.○At present, they are much higher than the mountains of the Caledonian range.○They were a uniform height about 400 million years ago.○They are not as high as the Caledonian mountains were 400 million years ago.4. The word “relics” in the passage is closest in meaning to词汇题○ resemblances○ regions○ remains○ restorationsParagraph 3: The Earth's crust is thought to be divided into huge, movable segments, called plates, which float on a soft plastic layer of rock. Some mountains were formed as a result ofIn this process, sedimentary rocks that originally formed on the seabed may be folded upwards to altitudes of more than 26,000 feet. Other mountains may be raised by earthquakes, which fracture the Earth's crust and can displace enough rock to produce block mountains. A third type of mountain may be formed as a result of volcanic activity which occurs in regions of active fold mountain belts, such as in the Cascade Range of western North America. The Cascades are made up of lavas and volcanic materials. Many of the peaks are extinct volcanoes.5. According to paragraph 3, one cause of mountain formation is the细节题○ effect of climatic change on sea level○ slowing down of volcanic activity○ force of Earth's crustal plates hitting each other○ replacement of sedimentary rock with volcanic rockParagraph 5: The weather, in its many forms, is the main agent of erosion. Rain washes away loose soil and penetrates cracks in the rocks. Carbon dioxide in the air reacts with the rainwater,The rain seeps underground and the water may reappear later as springs. These springs are the sources of streams and rivers, which cut through the rocks and carry away debris from the mountains to the lowlands.6. Why does the author mention Carbon dioxide in the passage? 目的题○To explain the origin of a chemical that can erode rocks○To contrast carbon dioxide with carbonic acid○To give an example of how rainwater penetrates soil○To argue for the desirability of preventing erosion7. The word “seeps” in the passage is closest in meaning to 词汇题○ dries gradually○ flows slowly○ freezes quickly○ warms slightlyParagraph 6: Under very cold conditions, rocks can be shattered by ice and frost. Glaciers may form in permanently cold areas, and these slowly moving masses of ice cut out valleys, carryingerosion. It carries fine particles of sand, which bombard exposed rock surfaces, thereby wearingthem into yet more sand. Even living things contribute to the formation of landscapes. Tree roots force their way into cracks in rocks and, in so doing, speed their splitting. In contrast, the roots of grasses and other small plants may help to hold loose soil fragments together, thereby helping to prevent erosion by the wind.8. The word them in the passage refers to 指代题○cold areas○masses of ice○valleys○rock debrisParagraph 2: Hills and mountains are often regarded as the epitome of permanence, successfully resisting the destructive forces of nature, but in fact they tend to be relatively short-lived in geological terms. As a general rule, the higher a mountain is, the more recently it was formed; for example, the high mountains of the Himalayas are only about 50 million years old. Lower mountains tend to be older, and are often the eroded relics of much higher mountain chains. About 400 million years ago, when the present-day continents of North America and Europe were joined, the Caledonian mountain chain was the same size as the modern Himalayas. Today, however, the relics of the Caledonian orogeny (mountain-building period) exist as the comparatively low mountains of Greenland, the northern Appalachians in the United States, the Scottish Highlands, and the Norwegian coastal plateau.9. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. 句子简化题○When they are relatively young, hills and mountains successfully resist the destructive forces of nature.○Although they seem permanent, hills and mountains exist for a relatively short period of geological time.○Hills and mountains successfully resist the destructive forces of nature, but only for a short time.○Hills and mountains resist the destructive forces of nature better than other types of landforms.Paragraph 6: Under very cold conditions, rocks can be shattered by ice and frost. Glaciers may form in permanently cold areas, and these slowly moving masses of ice cut out valleys, carrying with them huge quantities of eroded rock debris. █In dry areas the wind is the principal agent of erosion. █It carries fine particles of sand, which bombard exposed rock surfaces, thereby wearingroots force their way into cracks in rocks and, in so doing, speed their splitting. In contrast, the roots of grasses and other small plants may help to hold loose soil fragments together, thereby helping to prevent erosion by the wind.10. According to paragraph 6, which of the following is both a cause and result of erosion?细节题○glacial activity○rock debris○tree roots○sand11. Look at the four squares [█] that indicate where the following sentence could be added to the passage.Under different climatic conditions, another type of destructive force contributes to erosion. Where would the sentence best fit? 句子插入题12. Directions: Three of the answer choices below are used in the passage to illustrate constructive processes and two are used to illustrate destructive processes. Complete the table by matching appropriate answer choices to the processes they are used to illustrate. This question is worth 3 points. 配对题CONSTRUCTIVE PROCESSES DESTRUCTIVE PROCESSSESAnswer ChoicesA Collision of Earth's crustal platesB Separation of continentsC Wind-driven sandD Formation of grass roots in soilE EarthquakesF Volcanic activityG Weather processesKey: D B B C C A B B B D A AEF CG。
American Economy
The United States is one of the most development countries in the world. Although it has a short history. Its achievement in economy filed is great. American people contribute to development of economy. There are many important values playing a role in economy. It worths us learning about it .The United States is currently the industrial nation in the world. It is both an economic and technological giant. It ranks first in such advance fields as computer technology, nuclear energy ,and electronics. Although its dominance is decreasing ,It produces a major portion of the world's machinery, automobiles ,oil ,electrical energy ,and chemical.The economy of the United States is a mixed economyand has maintained a stable overall GDP growth rate, a moderate unemployment rate, and high levels of research and capital investment. It has been the world's largest national economy (not including colonial empires) since at least the 1890s.Most of the economy is classified as services.I. History of American EconomyThe economic history of the United States has its roots in European settlements in the 16th, 17th, and 18th centuries. The American colonies went from marginally successful colonial economies to a small, independent farming economy, which in 1776 became the United States of America. In 180 years the United States grew to a huge, integrated, industrialized economy that still makes up over a quarter of the world economy.The main causes were a large unified market, a supportive political-legal system, vast areas of highly productive farmlands, vast natural resources (especially timber, coal and oil), a cultural landscape that valued entrepreneurship, a commitment to investing in material and human capital, and at times a willingness to exploit labor. In addition, the U.S. was able to utilize these resources due to a unique set of institutions designed to encourage utilization and extraction. As a result, the U.S.'s GDP per capita converged on and eventually surpassed that of the U.K., as well as other nations that it previously trailed economically. The economy has maintained high wages, attracting immigrants by the millions from all over the world.In the 19th century, recessions frequently coincided with financial crises.1.The Colonial PeriodEarly settlers came to the United States for various reason. some of them, Like the pilgrims of Massachusetts, Wanted to escape religious persecution .They were pious ,thrifty and had strong self -discipline Other came to the New World for profit as well as religious and political freedom, As those in virginia and pennsylvania. The Atlantic Ocean posed a great barrier to settlement in North America. In the early seventeenth century, The cost of the Atlantic passage was ￡9 to￡10 per person, more than an average English person' yearly income. Throughout most of the later colonial period, the peacetime costs of passage were￡5 to￡6. Consequently, in the seventeenth century, a majority of British or European newcomers could not and did not pay their own way to America. By 1775, however, more than half a million English, Scotch, Irish, German, and other Europeans had made the transatlantic voyage. More than 350,000 of them paid their way by borrowing and signing a unique IOU, an indenture contract.2.American IndependenceThe U.S Constitution, adopted in 1787 and in effect to this day, was in many ways a work of creative, As an economic charter, It established that the entire nation was a unified or "common"market. there were no tariffs or taxes on inter -state commerce. The constitution provided that federal government could regulated commerce with foreign its nations and amongthe states,establish uniform bankruptcy laws create mony and regulate its value, Fix standards of weights and measures establish post offices and roads , And early recognition of the importance o "intellectual property ",a matter that began assuming great importance in trade negotiations since that last 20th century .3.The 20th CenturyThe American economy in the early 20th centry experienced a period of prosperity ands then suffered the worst depression in American history following the Wall Street crash in October 1929. After World War II, American recognize the urgent need to restructure international monetary arrangements, and helped to establish the International Monetary Fund and the World Bank .By ensuring an open, capitalist, international economy, American business entered a period of consolidation during the 1950s .the 1960s and 1970swere a time of great change. By the end of 1970s ,economic growth had decreased .Unemployment and inflation continued to rise .In the early 1980s, the Reagan administration adopted new monetarist policies to fight by increasing the supply of money flowing through the economy. Central to the Reagan administration 's efforts to combat inflation was rigorous control over government spending deficit .In addition, taxes were cut to enhance economic development while interest rates were raise .These measures finally brought inflation and unemployment under control.The economy saw a recession during the administration of president George H.W Bush .Under President Clinton ,the economy grew slowly at first. Then ,measure taken during the Bush administration began to bear fruit and the economy recovered more quickly .Business earnings grew and new jobs were created .the economy had been growing continuously since the 1990s ,the longest peacetime economic expansion in history. II. Current American EconomyAccording to the current American economy, the State Statistics The American people have reached a high standard of living. American economic system has been repeatedly criticized, But it did stimulate people's land.1.AgricultureAmerican agriculture assumes a richness and variety unmatched in the most parts of the world. Because American agriculture is big business, people coined the term “agribusiness” to reflect th e large-scale nature of agricultural enterprises in the modern US economy. The term covers the entire complex of farm-related business, from the individual farmer to the multinational maker of farm chemicals. It also includes farmer cooperatives, rural banks, shippers of farm products, commodity dealers, firms that manufacture farm equipment, food-processing industries, grocery chains and many other businesses.Many big farms hire temporary workers only for a specific chore—such as picking crops. Many of these seasonal workers travel from farm to farm, staying only until the crops are picked. They are known as migrant workers.About 1/3 of the cropland in the US is planted in crops destined for export. Agricultural imports lags far behind export, leaving a surplus in the agricultural balance of The standard of living of American farmers is generally high. The readiness of many farmers to adopt new technology has been one of the strengths American agriculture.2.Manufacturing IndustryThe United States has larger manufacturing industries that employ more than 24 million workers. The manufacture of machinery, airplanes and cars has always been important. The American military industry is so highly developed that each year it makes a profit of billion ofdollars by selling military products to foreign countries .American auto companies, Other industries holding over one milling workers include food ,clothing ,electrical machinery, textiles. printing ,metal goods ,publishing and furniture , wood products and paper products.3.Service IndustryThe service industry is significant to the American economy. A clear indication can be found in its effects on employment. Employment in manufacturing and agriculture has declined since the 1970s. By contrast, tremendous growth has occurred in the service sector.The American service sector involves three categories:service for the affluent welfare banking, life insurance, real estate and law service. Welfare service include healthy care ,eduction, government and social service. Service provided by the poor usually cover two major industries: service to buildings and dwellings, and retail services, all requiring little skill.4.High-tech IndustryThe industrial Revolution brought many changes to American industry between 1776 and 1860. One key development was the introduction of the factory system, which gathered many workers together in one workplace together in one workplace and produced goods for distribution.A second development was the “Ame r ican system” of mass pro duction which originated in the firearms industry about 1800. A third development was the application of new technologies to industrial tasks. A fourth development was the emergency of new forms of business organization, notably the bank and the corporation, which facilitated the growth of industry. Finally, the construction of railroads beginning in the 1830s, marked the start of a new era for the United States.5.Foreign TradeU.S foreign trade has always been playing a significant role in the country 's economic development. In the past two centuries,particularly since World War II, It is has changed from a domestic -oriented trade pattern to a more internationally-oriented one. the U.S government has made great efforts in reducing trade barriers and coordinating the world economic system because most U.S leaders are well aware that open bilateral trade will help advance its own economic interests, enhance domestic stability as well as relationship with other nations.As for the ongoing reform and policy adjustment. The United States of reform and opening up of the road to tell us, the United States in less than 400 years , for the world's leading development from wasteland superpower, linked to reform and opening up. No reform and opening up is no American characteristic. In the modern capitalist countries, the United States of reform and opening up holding the western world.。
solutionofalarge-scaletraveling-salesmanproblem
Chapter1Solution of a Large-Scale Traveling-Salesman ProblemGeorge B.Dantzig,Delbert R.Fulkerson,and Selmer M.JohnsonIntroduction by Vaˇs ek Chv´a tal and William CookThe birth of the cutting-plane methodThe RAND Corporation in the early1950s contained“what may have been the most remarkable group of mathematicians working on optimization ever assem-bled”[6]:Arrow,Bellman,Dantzig,Flood,Ford,Fulkerson,Gale,Johnson,Nash, Orchard-Hays,Robinson,Shapley,Simon,Wagner,and other household names. Groups like this need their challenges.One of them appears to have been the travel-ing salesman problem(TSP)and particularly its instance offinding a shortest route through Washington,DC,and the48states[4,7].Dantzig’s work on the assignment problem[1]revealed a paradigm for minimiz-ing a linear function f:R n→R over afinite subset S of R n:first describe the convex hull of S by a system Ax≤b of linear constraints and then solve the linear programming problemminimize f(x)subject to Ax≤bby the simplex method.Attempts by Heller and by Kuhn to apply this paradigm to the TSP indicated that sets of linear constraints describing the convex hull of all tours are far too large to be handled directly.Undeterred,Dantzig,Fulkerson, and Johnson bashed on.The preliminary version of their paper[2]includes a dis-cussion of the convex hull of all tours,nowadays called“the TSP polytope”.The version submitted for publication four months later(and eventually published andVaˇs ek Chv´a talCanada Research Chair in Combinatorial OptimizationDepartment of Computer Science and Software Engineering,Concordia University,Canadae-mail:*********************.caWilliam CookSchool of Industrial and Systems Engineering,Georgia Institute of Technology,Atlanta,USAe-mail:****************.eduM. Jünger et al. (eds.), 50 Years of Integer Programming 1958-2008,7 DOI 10.1007/978-3-540-68279-0_1, © Springer-Verlag Berlin Heidelberg 20108George B.Dantzig,Delbert R.Fulkerson,and Selmer M.Johnson reproduced here)breaks free of the dogma:without letting the TSP polytope obscure their exposition,the authors just go ahead and solve the49-city instance.(Regarding this change,Fulkerson writes in a September2,1954,letter to Operations Research editor George Shortly“In an effort to keep the version submitted for publication elementary,we avoid going into these matters in any detail.”)This case study ushered in the cutting-plane method.To solve a problemminimize f(x)subject to x∈S(1.1) where f:R n→R is a linear function and S is afinite subset of R n,choose a system Ax≤b of linear inequalities satisfied by all points of S and use the simplex method tofind an optimal solution x∗of the linear programming problemminimize f(x)subject to Ax≤b,(1.2) called the linear programming relaxation of(1.1).If x∗belongs to S,then it is an optimal solution of(1.1);else there are linear inequalities satisfied by all points of S and violated by x∗,called cutting planes.Find one or more such inequalities,add them to Ax≤b,and iterate.(The method actually used by Dantzig,Fulkerson,and Johnson—described also in[2,3]—is a slight variation on this theme:rather than introducing cutting planes only when an optimal solution x∗of(1.2)lies outside S, they introduce them after each simplex pivot leading to a basic feasible solution x∗of(1.2)that lies outside S.)The role played by the convex hull of S in this new paradigm is only implicit: we have to be able tofind a cutting plane whenever one exists,which is the case if and only if x∗lies outside the convex hull of S.In particular,the number of linear constraints in a description of the convex hull of S is irrelevant here.Another important difference between the two paradigms is that the cutting-plane method is an engineering rather than mathematical method:unlike the simplex method,it carries no guarantee that the sequence of its iterations will terminate.(But then again,a guarantee of termination afterfinitely many iterations is a far cry from a guarantee of termination before the end of our solar system.)Our three authors write “...what we shall do is outline a way of approaching the problem that sometimes, at least,enables one tofind an optimal path and prove it so.”Until1954,no one had an inkling of a way to solve large instances of the TSP. The lament about the number of tours through n cities being too large to allow their listing one by one marked the vanguard of scientific progress on this front.Then Dantzig,Fulkerson,and Johnson let the light in and inaugurated a new era.All successful TSP solvers echo their breakthrough.This was the Big Bang.This Big Bang reverberates far beyond the narrow confines of the TSP.It provides a tempting template for coping with any NP-complete problem of minimizing a linear function over afinite set S.For each problem of this kind,the challenge lies infinding cutting planes quickly.In the special case of integer linear programming, where S consists all integer solutions of a prescribed set of linear constraints,this challenge was met with remarkable elegance(and termination afterfinitely many iterations guaranteed)by Gomory in a series of papers beginning with[5].1Solution of a Large-Scale Traveling-Salesman Problem9 Great new ideas may transform the discipline they came from so profoundly that they become hard to discern against the changed background.When terms such as “defense mechanism”and“libido”are in the common vocabulary,it is easy to forget that they came from Sigmund Freud.The cutting-plane method of George Dantzig, Ray Fulkerson,and Selmer Johnson had the same kind of impact on the discipline of mathematical programming.References1.G.B.Dantzig,Application of the simplex method to a transportation problem,Activity Analysisof Production and Allocation(T.C.Koopmans,ed.),Cowles Commission Monograph No.13.John Wiley&Sons,Inc.,New York,N.Y.;Chapman&Hall,Ltd.,London,1951,pp.359–373.2.G.B.Dantzig,D.R.Fulkerson,and S.M.Johnson,Solution of a large scale traveling salesmanproblem,Technical Report P-510,RAND Corporation,Santa Monica,California,USA,1954.3.G.B.Dantzig,D.R.Fulkerson,and S.M.Johnson,On a linear-programming,combinatorialapproach to the traveling-salesman problem,Operations Research7(1959)58–66.4.M.M.Flood,Merrill Flood(with Albert Tucker),Interview of Merrill Flood in San Franciscoon14May1984,The Princeton Mathematics Community in the1930s,Transcript Number11 (PMC11),Princeton University,1984.5.R.E.Gomory,Outline of an algorithm for integer solutions to linear programs,Bulletin of theAmerican Mathematical Society64(1958)275–278.6.M.Gr¨o tschel and G.L.Nemhauser,George Dantzig’s contributions to integer programming,Discrete Optimization5(2008)168–173.7.J.Robinson,On the Hamiltonian game(a traveling salesman problem),RAND Research Mem-orandum RM-303,RAND Corporation,Santa Monica,California,USA,1949.10George B.Dantzig,Delbert R.Fulkerson,and Selmer M.JohnsonThe following article originally appeared as:G.B.Dantzig,D.R.Fulkerson,and S.M.Johnson,Solution of a Large-Scale Travel-ing-Salesman Problem,Operations Research2(1954)393–410.Copyright c 1954by the Operations Research Society of America.Reprinted by permission from The Institute for Operations Research and the Man-agement Sciences.1Solution of a Large-Scale Traveling-Salesman Problem1112George B.Dantzig,Delbert R.Fulkerson,and Selmer M.Johnson1Solution of a Large-Scale Traveling-Salesman Problem1314George B.Dantzig,Delbert R.Fulkerson,and Selmer M.Johnson1Solution of a Large-Scale Traveling-Salesman Problem1516George B.Dantzig,Delbert R.Fulkerson,and Selmer M.Johnson1Solution of a Large-Scale Traveling-Salesman Problem2728George B.Dantzig,Delbert R.Fulkerson,and Selmer M.Johnson。
关于知识的价值Value of Knowledge_英语作文
关于知识的价值Value of Knowledge
在信息时代，知识的价值的公众意识严重影响到一个国家的经济增长。
示意图清晰地显示了知识的价值在中国发展在过去的50年。
示意图中，主要由三部分组成。
从1950年到1966年，大约一曲线直线略高于零，表明中国是一个低学历的国家则。
1966年，曲线大幅下降零度以下，向下移动，在未来11年内无望。
这一时期，正值“文革”。
那么我们的社会疯了，书籍被烧毁，学校关闭，各种学术活动被禁止。
知识造成它的主人只是灾难。
生命是一个中国知识分子，包括著名学者以及谁受过高等教育的专业一般民众或有任何与知识的噩梦。
这是一个无知的时候是一种美德和知识是一种犯罪。
人们拼命从知识了。
因此，中国落后更远落后于世界上的迅速进展。
这是在新中国历史上最黑暗的时期。
曲线恢复到原来的非1978年左右零位上升但速度缓慢。
从1984年起，它已被射击了。
开放式的政策鼓励人们学习他们的知识和渠道向市场经济。
对中国数以百万计的完善关闭他们的知识的手段和更多中享受知识的良好成果，并说再见贫穷困扰着他们几代人。
由于我们的世界正在迅速挺进信息时代，越来越多的人们认识到知识就是力量，创意就是一切。
只有当中国成为一个受过良好教育的国家，可中国是一个具有国际声望的伟大民族。
预测和控制森林火灾模型
5 5 6 7 7 9 9 13 16 18 18 19 20 20 21
6
Model to Reduce Loss of Forest Fire .................................. 16
6.1 Merchant Model ............................................................... 6.1.1 Construction of Merchant Model . . . . . . . . . . . . . . . 6.1.2 Result of Merchant Model . . . . . . . . . . . . . . . . . . . 6.2 Ecology model.................................................................. 6.2.1 Construction of Ecological Model . . . . . . . . . . . . . . 6.2.2 Result of Ecological Model . . . . . . . . . . . . . . . . . .
8 9
Strengths and Weaknesses ................................................. 24 References .......................................................................... 24
1.1 Background ..................................................................... 1.2 Problem Description .......................................................... 3 3
托福考试真题练习
托福考试真题练习托福考试真题练习2017加紧学习，抓住中心，宁精勿杂，宁专勿多。
以下是店铺为大家搜索整理的托福考试真题练习2017，希望对大家有所帮助!Most people consider the landscape to be unchanging, but Earth is a dynamic body, and itssurface is continually altering-slowly on the human time scale, but relatively rapidly whencompared to the great age of Earth (about 4,500 billion years). There are two principalinfluences that shape the terrain: constructive processes such as uplift, which create newlandscape features, and destructive forces such as erosion, which gradually wear awayexposed landforms.Hills and mountains are often regarded as the epitome of permanence, successfully resistingthe destructive forces of nature, but in fact they tend to be relatively short-lived in geologicalterms. As a general rule, the higher a mountain is, the more recently it was formed; forexample, the high mountains of the Himalayas are only about 50 million years old. Lowermountains tend to be older, and are often the eroded relics of much higher mountain chains.About 400 million years ago, when the present-day continents of North America and Europewere joined, the Caledonian mountain chain was the same size as the modern Himalayas. Today,however, the relics of the Caledonian orogeny (mountain-building period) exist as thecomparatively low mountains of Greenland, the northern Appalachians in the United States,the Scottish Highlands, and the Norwegian coastal plateau.The Earth's crust is thought to be divided into huge, movable segments, called plates, whichfloat on a soft plastic layer of rock.Some mountains were formed as a result of these platescrashing into each other and forcing up the rock at the plate margins. In this process,sedimentary rocks that originally formed on the seabed may be folded upwards to altitudes ofmore than 26,000 feet. Other mountains may be raised by earthquakes, which fracture theEarth's crust and can displace enough rock to produce block mountains. A third type ofmountain may be formed as a result of volcanic activity which occurs in regions of active foldmountain belts, such as in the Cascade Range of western North America. The Cascades aremade up of lavas and volcanic materials. Many of the peaks are extinct volcanoes.Whatever the reason for mountain formation, as soon as land rises above sea level it issubjected to destructive forces. The exposed rocks are attacked by the various weatherprocesses and gradually broken down into fragments, which are then carried away and laterdeposited as sediments. Thus, any landscape represents only a temporary stage in thecontinuous battle between the forces of uplift and those of erosion.The weather, in its many forms, is the main agent of erosion. Rain washes away loose soil andpenetrates cracks in the rocks. Carbon dioxide in the air reacts with the rainwater, forming aweak acid (carbonic acid) that may chemically attack the rocks. The rain seeps underground andthe water may reappear later as springs. These springs are the sources of streams and rivers,which cut through the rocks and carry away debris from the mountains to the lowlands.Under very cold conditions, rocks can be shattered by ice and frost. Glaciers may form inpermanently cold areas, and these slowly moving masses of ice cut out valleys, carrying withthem huge quantities of eroded rock debris. In dry areas the wind isthe principal agent oferosion. It carries fine particles of sand, which bombard exposed rock surfaces, therebywearing them into yet more sand. Even living things contribute to the formation oflandscapes. Tree roots force their way into cracks in rocks and, in so doing, speed theirsplitting. In contrast, the roots of grasses and other small plants may help to hold loose soilfragments together, thereby helping to prevent erosion by the wind.Paragraph 1: Most people consider the landscape to be unchanging, but Earth is a dynamicbody, and its surface is continually altering-slowly on the human time scale, but relativelyrapidly when compared to the great age of Earth (about 4,500 billion years). There are twoprincipal influences that shape the terrain: constructive processes such as uplift, which createnew landscape features, and destructive forces such as erosion, which gradually wear awayexposed landforms.1. According to paragraph 1, which of the following statements is true of changes in Earth'slandscape?○They occur more often by uplift than by erosion○They occur only at special times.○They occur less frequently now than they once did.○They occur quickly in geological terms.2. The word relatively in the passage is closest in meaning to○Unusually○Comparatively○Occasionally○NaturallyParagraph 2: Hills and mountains are often regarded as the epitome of permanence,successfully resisting the destructive forces of nature, but in fact they tend to be relativelyshort-lived in geological terms. As a general rule, the higher a mountain is,the more recently itwas formed; for example, the high mountains of the Himalayas are only about 50 million yearsold. Lower mountains tend to be older, and are often the eroded relics of much highermountain chains. About 400 million years ago, when the present-day continents of NorthAmerica and Europe were joined, the Caledonian mountain chain was the same size as themodern Himalayas. Today, however, the relics of the Caledonian orogeny (mountain-buildingperiod) exist as the comparatively low mountains of Greenland, the northern Appalachians inthe United States, the Scottish Highlands, and the Norwegian coastal plateau.3. Which of the following can be inferred from paragraph 2 about the mountains of theHimalayas?○Their current height is not an indication of their a ge.○At present, they are much higher than the mountains of the Caledonian range.○They were a uniform height about 400 million years ago.○They are not as high as the Caledonian mountains were 400 million years ago.4. The word relics in the passage IS closest in meaning to○Resemblances○Regions○Remains○RestorationsParagraph 3: The Earth's crust is thought to be divided into huge, movable segments, calledplates, which float on a soft plastic layer of rock. Some mountains were formed as a result ofthese plates crashing into each other and forcing up the rock at the plate margins. In thisprocess, sedimentary rocks that originally formed on the seabed may be folded upwardstoaltitudes of more than 26,000 feet. Other mountains may be raised by earthquakes, whichfracture the Earth's crust and can displace enough rock to produce block mountains. A thirdtype of mountain may be formed as a result of volcanic activity which occurs in regions ofactive fold mountain belts, such as in the Cascade Range of western North America. TheCascades are made up of lavas and volcanic materials. Many of the peaks are extinctvolcanoes.5. According to paragraph 3, one cause of mountain formation is the○effect of climatic change on sea level○slowing down of volcanic activity○fo rce of Earth's crustal plates hitting each other○replacement of sedimentary rock with volcanic rockParagraph 5: The weather, in its many forms, is the main agent of erosion. Rain washes awayloose soil and penetrates cracks in the rocks. Carbon dioxide in the air reacts with therainwater, forming a weak acid (carbonic acid) that may chemically attack the rocks. The rainseeps underground and the water may reappear later as springs. These springs are thesources of streams and rivers, which cut through the rocks and carry away debris from themountains to the lowlands.6. Why does the author mention Carbon dioxide in the passage?○To explain the origin of a chemical that can erode rocks○To contrast carbon dioxide with carbonic acid○To give an example of how r ainwater penetrates soil○To argue for the desirability of preventing erosion7. The word seeps in the passage is closest in meaning to○Dries gradually○Flows slowly○Freezes quickly○Warms slightlyParagraph 6: Under very cold conditions, rocks can be shattered by ice and frost. Glaciers mayform in permanently cold areas, and these slowly moving masses of ice cut out valleys,carrying with them huge quantities of eroded rock debris. In dry areas the wind is the principalagent of erosion. It carries fine particles of sand, which bombard exposed rock surfaces,thereby wearing them into yet more sand. Even living things contribute to the formation oflandscapes. Tree roots force their way into cracks in rocks and, in so doing, speed theirsplitting. In contrast, the roots of grasses and other small plants may help to hold loose soilfragments together, thereby helping to prevent erosion by the wind.8. The word them in the passage refers to○Cold areas○Masses of ice○Valleys○Rock debrisParagraph 2: Hills and mountains are often regarded as the epitome of permanence,successfully resisting the destructive forces of nature, but in fact they tend to be relativelyshort-lived in geological terms. As a general rule, the higher a mountain is, the more recently itwas formed; for example, the high mountains of the Himalayas are only about 50 million yearsold. Lower mountains tend to be older, and are often the eroded relics of much highermountain chains. About 400 million years ago, when the present-day continents of NorthAmerica and Europe were joined, the Caledonian mountain chain was the same size asthemodern Himalayas. Today, however, the relics of the Caledonian orogeny (mountain-buildingperiod) exist as the comparatively low mountains of Greenland, the northern Appalachians inthe United States, the Scottish Highlands, and the Norwegian coastal plateau.9. Which of the sentences below best expresses the essential information in the highlightedsentence in the passage?Incorrect choices change the meaning in important ways or leave out essential information.○When they are relatively young, hills and mountains successfully resist the destructive forcesof nature.○Although they seem permanent, hills and mountains exist for a relatively short period ofgeological time.○Hil ls and mountains successfully resist the destructive forces of nature, but only for a shorttime.○Hills and mountains resist the destructive forces of nature better than other types oflandforms.Paragraph 6: Under very cold conditions, rocks can be shattered by ice and frost. Glaciers mayform in permanently cold areas, and these slowly moving masses of ice cut out valleys,carrying with them huge quantities of eroded rock debris. █In dry areas the wind is theprincipal agent of erosion. █It carries fine particles of sand, which bombard exposed rocksurfaces, thereby wearing them into yet more sand. █Even living things contribute to theformation of landscapes. █Tree roots force their way into cracks in rocks and, in so doing,speed their splitting. In contrast, the roots of grasses and other small plants may help to holdloose soil fragments together, thereby helping to prevent erosion by the wind.10. According to paragraph 6, which of the following is botha cause and result of erosion?○Glacial activity○Rock de bris○Tree roots○Sand11. Look at the four squares [■] that indicate where the following sentence could be added tothe passage.Under different climatic conditions, another type of destructive force contributes to erosion.Where would the sentence best fit?12. Directions: Three of the answer choices below are used in the passage to illustrateconstructive processes and two are used to illustrate destructive processes. Complete thetable by matching appropriate answer choices to the processes they are used to illustrate.This question is worth 3 points.CONSTRUCTIVE PROCESSES DESTRUCTIVE PROCESSSESAnswer Choices：1.Collision of Earth's crustal plates2.Separation of continents3.Wind-driven sand4.Formation of grass roots in soil5.Earthquakes6.Volcanic activity7.Weather processes参考答案：1. ○ 4This is a Factual Information question asking for specific information that can be found inparagraph 1. The correct answer is choice 4. Sentence 1 of the paragraph explicitly states thatEarth's landscape changes relatively rapidly compared toEarth's overall age. Choice 1, on thefrequency of landscape changes, is contradicted by the paragraph. Choice 2, that landscapechanges occur only at special times, is also contradicted by the paragraph. Choice 3, thefrequency of landscape changes, is not mentioned.2. ○ 2This is a Vocabulary question. The word being tested is relatively, and it is highlightedin the passage. The correct answer is choice 2. The sentence in which relatively appears iscomparing Earth's time scale to the human time scale, so "comparatively" is the correctanswer.3. ○ 2This is an Inference question asking for an inference that can be supported by paragraph 2. Thecorrect answer choice 2, the Himalayas arc higher than the Caledonian mountains. Theparagraph states that younger mountains are general& higher than older mountains. Italso states that the Himalayas are much younger than the Caledonians. Since the Himalayas arethe younger range and Lounger mountain ranges are higher- than older ranges, we can inferthat the younger Himalayas are higher than the older Caledonians.Choices 1 and 4 are incorrect because that explicitly contradict the passage. The height of theHimalayas is an indication of their age, and the Himalayas are about the same height that theCaledonians were 400 million years ago. Choice 3 is incorrect because nothing there is nothingin the paragraph about "uniform height."4. ○ 3This is a Vocabulary question. The word being tested is relics, and it is highlighted in thepassage. Choice 3 is the correct answer.The 1.e1ic.s of the Caledonian range are what is leftof them. "Remains" means what is left of something, so it is the correct answer.5. ○ 3This is a Factual Information question asking for specific information that can be found inparagraph 3. The correct answer is choice 3, mountains are formed by crustal plates hittingeach other. The paragraph states that mountains are formed in three ways: by, crustal plateshitting each other, by earthquakes, and by volcanoes. Choices 1,2, and 4 are not among thesecauses of mountain formation, so they are therefore incorrect.6. ○ 1This is a Rhetorical Purpose question. It asks why the author mentions "carbon dioxide" in thepassage. This term is highlighted in the passage. The correct answer is choice 1; carbon dioxideis mentioned to explain the origin of a chemical that can erode rocks. The author is describing aparticular cause of erosion, and the starting point of that process is carbon dioxide.7. ○ 2This is a Vocabulary question. The word being tested is seeps, and it is highlighted in thepassage. Choice 2, "Rows slowly," is the correct answer. The sentence is describing the way inwhich rain moves underground from Earth's surface. It cannot do this by "drying" (choice 1), "freezing" (choice 3), or "warming"(choice 4).8. ○ 2This is a Reference question. The word being tested is them, and it is highlighted in thepassage. Choice 2, "masses of ice" is the correct answer. This is a simple pronoun-referentitem. The word tlze11z refers to the glaciers that are carrying eroded rock. Notice that in thiscase, a whole series of words separates thepronoun from its referent.9. ○ 2This is a Sentence Simplification question. As with all of these items, a singlesentence in thepassage is highlighted: Hills and mountains are often regarded as the epitome of permanence: successfully resistingthe destructive forces of nature, but in fact they tend to be relatively short-lived in geologicalterms.The correct answer is choice 2. That choice contains all of the essential information in thehighlighted sentence. it omits the information in the second clause of the highlighted sentence("successfully resisting the destructive forces of nature") because that information is notessential to the meaning. Choices 1, 3, and 1 are all incorrect because they change themeaning of the highlighted sentence. Choice 1 adds information on the age of a mountain thatis not mentioned in the highlighted sentence. Choice 3 introduces information about how longmountains resist forces of nature in absolute terms; the highlighted sentence says that theresistance is relatively short in geological terms, which is an entirely different meaning. Choice 4compares mountains to other land forms. The highlighted sentence does not make any suchcomparison.10. ○ 4This is a Factual Information question asking for specific information that can be found inparagraph 6. The correct answer is choice 4, "sand." Sentences 3 and 4 of that paragraphdescribe erosion in dry areas. Sand is carried by wind and bombards rock; this bombardmentbreaks down the rock, and, as a result, more sand is created. Thus sand is both the cause andthe result of erosion, so choice 4 is correct. Glacial activity (choice 1) and treeroots (choice 3)are both mentioned only as causes of erosion. Rock debris (choice 2) is mentioned only as aresult of erosion.11. ○ 1This is an Insert T ext question. You can see the four black squares in paragraph 6 thatrepresent the possible answer choices here.Under very cold conditions, rocks can be shattered by ice and frost. Glaciers may form inpermanently cold areas, and these slowly moving masses of ice cut out valleys, carrying withthem huge quantities of eroded rock debris. ■ In dry areas the wind is the principal agent oferosion. ■ It carries fine particles of sand, which bombard exposed rock surfaces, therebywearing them into yet more sand. ■ Even living things contribute to the formation oflandscapes. ■ Tree roots force their way into cracks in rocks and, in so doing, speed theirsplitting. In contrast, the roots of grasses and other small plants may help to hold loose soilfragments together, thereby helping to prevent erosion by the wind.The sentence provided, "Under different climatic conditions, another type of destructive forcecontributes to erosion,'' is best inserted at square 1.Square 1 is correct because the inserted sentence is a transitional sentence, moving thediscussion away from one set of climatic conditions (cold) to another set of climatic conditions(dryness). It is at square 1 that the transition between topics takes place.Squares 2, 3, and 4 all precede sentences that provide details of dry climatic conditions. Notransition is taking place at any of those places, so the inserted sentence is not needed.12. ○Constructive processes 1 5 6; Destructive processes 3 7This is a Fill in a Table question. It is completed correctly below. The correct choices for the"constructive processes” column are 1, 5, and 6. Choices 3 and 7 are the correct choices forthe "destructive processes" column. Choices 2 and 4 should not be used in either column.大部分人认为自然风景是一成不变的，事实上地球是一个动态的机体,他的外貌在人类文明进程中一直保持着持续缓慢的变化。
系统功能语法
Axis of Choice 选择轴 Axis of Chain链状轴
The dimension along which the utterance sequence occurs is the axis of chain; 伴 随着话语次序出现的维度是链状轴； the basic patterns along the vertical line form the basis of choice 沿着纵线出 现的基本模型则构成选择轴.
Thus, it takes actual uses of language as the object of study, in opposition to Chomsky’s TG Grammar that takes the ideal speaker’s linguistic competence as the object of study.
ห้องสมุดไป่ตู้
Thirdly, it gives a relatively high priority to description of the characteristics of particular languages and particular varieties of languages.
Fourthly, it explains a number of aspects of language in terms of clines “连续体 ”（ ungrammatical-more unusualless unusual-less usual-grammatical). Lastly, it has the categories of the system as its center.
Biological control of pests
Biological control of pestsThe continuous and reckless use of synthetic chemicals for the control of pests which pose a threat to agricultural crops and human health is proving to be counter-productive. Apart from engendering widespread ecological disorders, pesticides have contributed to the emergence of a new breed of chemical-resistant, highly lethal superbugs.According to a recent study by the Food and Agriculture Organization (FAO), more than 300species of agricultural pests have developed resistance to a wide range of potent chemicals. Not to be left behind are the disease-spreading pests, about 100 species of which have become immune to a variety of insecticides now in use.One glaring disadvantage of pesticides' application is that, while destroying harmful pests, they also wipe out many useful non-targeted organisms, which keep the growth of the pest population in check. This results in what agroecologists call the 'treadmill syndrome'. Because of their tremendous breeding potential and genetic diversity, many pests are known to withstand synthetic chemicals and bear offspring with a built-in resistance to pesticides. The havoc that the 'treadmill syndrome' can bring about is well illustrated by what happened to cotton farmers in Central America. In the early 1940s, basking in the glory of chemicalbased intensive agriculture, the farmers avidly took to pesticides as a sure measure to boost crop yield. The insecticide was applied eight times a year in the mid-1940s, rising to 28 in a season in the mid-1950s, following the sudden proliferation of three new varieties of chemicalresistant pests.By the mid-1960s, the situation took an alarming turn with the outbreak of four more new pests, necessitating pesticide spraying to such an extent that 50% of the financial outlay on cotton production was accounted for by pesticides. In the early 1970s, the spraying frequently reached 70times a season as the farmers were pushed to the wall by the invasion of genetically stronger insect species.Most of the pesticides in the market today remain inadequately tested for properties that cause cancer and mutations as well as for other adverse effects on health, says a study by United States environmental agencies. The United States National Resource Defense Council has found that DDT was the most popular of a long list of dangerous chemicals in use.In the face of the escalating perils from indiscriminate applications of pesticides, a more effective and ecologically sound strategy of biological control, involving the selective use of natural enemies of the pest population, is fast gaining popularity- though, as yet, it is a new field with limited potential. The advantage of biological control in contrast to other methods is that it provides a relatively low-cost, perpetual control system with a minimum of detrimental side-effects. When handled by experts, bio-control is safe, non-polluting and self-dispersing.The Commonwealth Institute of Biological Control (CIBC) in Bangalore, with its global network of research laboratories and field stations, is one of the most active, non-commercial research agencies engaged in pest control by setting natural predators against parasites. CIBC also serves as a clearing-house for the export and import of biological agents for pest control world-wide.CIBC successfully used a seed-feeding weevil, native to Mexico, to control the obnoxious parthenium weed, known to exert devious influence on agriculture and human health in both India and Australia. Similarly the Hyderabad-based Regional Research Laboratory (RRL), supported by CIBC, is now trying out an Argentinian weevil for the eradication of water hyacinth, another dangerous weed, which has become a nuisance in many parts of the world. According to Mrs Kaiser Jamil of RRL, 'The Argentinian weevil does not attack any other plant and a pair of adult bugs could destroy the weed in 4-5 days.' CIBC is also perfecting the technique for breeding parasites that prey on 'disapene scale' insects - notorious defoliants of fruit trees in the US and India.How effectively biological control can be pressed into service is proved by the following examples. In the late 1960s, when Sri Lanka's flourishing coconut groves were plagued by leaf-mining hispides, a larval parasite imported from Singapore brought the pest under control. A natural predator indigenous to India, Neodumetiasangawani, was found useful in controlling the Rhodes grass-scale insect that was devouring forage grass in many parts of the US. By using Neochetinabruci, a beetle native to Brazil, scientists at Kerala Agricultural University freed a 12-kilometrelong canal from the clutches of the weed Salviniamolesta, popularly called 'African Payal' in Kerala. About 30, 000 hectares of rice fields in Kerala are infested by this weed.Questions 14-17Choose the correct letter, A, B, C, or D. Write the correct letter in boxes 14-17 on your answer sheet.14 The use of pesticides has contributed toA a change in the way ecologies are classified by agroecologists.B an imbalance in many ecologies around the world.C the prevention of ecological disasters in some parts of the world.D an increase in the range of ecologies which can be usefully farmed.15 The Food and Agriculture Organisation has counted more than 300 agricultural pests whichA are no longer responding to most pesticides in use.B can be easily controlled through the use of pesticides.C continue to spread disease in a wide range of crops.D may be used as part of bio-control's replacement of pesticides.16 Cotton farmers in Central America began to use pesticidesA because of an intensive government advertising campaign.B in response to the appearance of new varieties of pest.C as a result of changes in the seasons and the climate.D to ensure more cotton was harvested from each crop.17 By the mid-1960s, cotton farmers in Central America found that pesticidesA were wiping out 50% of the pests plaguing the crops.B were destroying 50% of the crops they were meant to protect.C were causing a 50% increase in the number of new pests reported.D were costing 50% of the total amount they spent on their crops.Questions 18-21Do the following statements agree with the claims of the writer in Reading Passage 2? In boxes 18-21 on your answer sheet, write YES if the statement agrees with the claims of the writerNO if the statement contradicts the claims of the writerNOT GIVEN if it is impossible to say what the writer thinks about this18 Disease-spreading pests respond more quickly to pesticides than agricultural pests do.19 A number of pests are now born with an innate immunity to some pesticides.20 Biological control entails using synthetic chemicals to try and change the genetic make-up of the pests' offspring.21 Bio-control is free from danger under certain circumstances. Questions 22-26Complete each sentence with the correct ending, A-I, below.Write the correct letter, A-I, in boxes 22-26 on your answer sheet.22 Disapene scale insects feed on23 Neodumetiasangawani ate24 Leaf-mining hispides blighted25 An Argentinian weevil may be successful in wiping out26 Salviniamolesta plaguesA forage grass.B rice fields.C coconut trees.D fruit trees.E water hyacinth.F parthenium weed.G Brazilian beetles.H grass-scale insects.I larval parasites.。
国际贸易名词解释
国际贸易名词解释机会成本（opportunity cost）：The amount of another item must be given up in order to release sufficient resources to produce one more unit of a given item.生产某种产品而必须放弃的能够生产除此以外最大可获收益的产品的代价。
机会成本不变的存在需要两个条件：第一，两种产品生产中所使用的要素比例固定不变，并且可以相互替代；第二，所有产品中使用的同一要素都是同质的。
绝对优势（absolute advantage）If one nation is more efficient than (or has an absolute advantage over) another nation in the production of one commodity, the nation has absolute advantage in that commodity.各国间存在的生产技术存在绝对差异，以及由此造成的劳动生产率和生产成本的绝对差别，是国际分工和国际贸易的基础。
各国应集中生产并出口具有“绝对优势”的产品，进口其不具有“绝对优势”的产品，其结果比自己什么都生产更有利。
比较优势（comparative advantage）According to the law of comparative advantage, even if a nation is less efficient than the other nation in the production of both commodities, there is still a basis for mutually相互地beneficial trade. The first nation should specialize in the production of and export the commodity in which its absolute disadvantage is smaller and import the commodity in which its absolute disadvantage is greater.两国间生产技术存在相对差异，生产和贸易模式是由生产技术的相对差异以及由此产生的相对成本的差异决定的。
美国经济增长的源 1026
II .定量分析—B.计算美国的增长
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人均产出的增长率
1 ˆ y (log yt log y0 ) t
H At 1 At (13) ( ) At At
问题提出
•按照许多外生增长理论 （包括新古典增长理 论），上述变化应该导 致增长率本身的永久性 提高：短期产生“转移 动态”，长期产生“水 平效果”。
JONES（1997年）就曾指 出此现象与理论相背离。 下图显示，美国经济似 乎一直围绕其平衡增长 路径波动。
正文结构
I
II
建立模型，表示长期经济的增长受世界范围内创意的 发明驱动。全球范围内知识存量的增长最终系于全球 研究努力的进步。本文着重于此定量分析。 利用上述模型来计算美国1950-1993年的增长源泉。与 传统观点不一样，该计算结果表明，美国经济80%多的 增长与转移动态有关，不到20%处于平衡增长路径。 束下的增长。结果表明稳定增长路径依旧是一个合理 的近似。
1953多要素生产率增长率是固定的， 则可以推断出γ：
ˆ A ˆ H
II .定量分析—B.计算美国的增长
ˆ (12) yt
ˆ ˆ ˆ ˆ ˆ ( K t Yt ) ht Yt ( At n) n 1 1
（1）受教育水平增长率解释了30%的增长，其提高一个百分点，促进产出增长率提高0.63个百分点， （2）工业五国创意存量的增长解释了70%的增长，期中，超过稳态时创意存量增长的贡献为53%-70%， 稳态时就业人口解释了3-20% （3）长期增长取决于人口增长（规模效应）-〉研究人员规模的增加。但是本结果中，美国1950-1993经济增长，本国 人口规模n只能解释不到20%，80%多的增长归功于因为受教育水平和创意存量增加带来的转移动态。
大学英语六级改革适用(阅读)模拟试卷14(题后含答案及解析)
大学英语六级改革适用（阅读）模拟试卷14(题后含答案及解析) 题型有： 4. Reading ComprehensionPart III Reading ComprehensionSection BStartup Nuclear Energy Companies Augur Safer, Cheaper Atomic PowerA)Nothing captures how fashionable the startup has become quite like crowdfunding. The craze for raising contributions via websites like Kickstarter and Indiegogo is helping to launch companies from scooter manufacturers to lightbulb vendors to filmmakers. Now, even nuclear fusion is game.B)Yes, the Holy Grail of cheap, clean, safe, plentiful, low-carbon energy that has remained 40 years in the future since scientists proposed it over half a century ago has entered the crowd sourcing era. International government projects like ITER in France and the National Ignition Facility in California may have spent billions of dollars in pursuit of the technology, but that doesn’t mean there can’t be a little grassroots action, too.C)LPP Fusion, a tiny company based in Middlesex, N.J., launched in May an Indiegogo campaign to raise $200,000—loose change in this business—that it believes will help it reach a major fusion development milestone in a year and commercialize fusion reactors by 2020.D)LPP(it stands for “Lawrenceville Plasma Physics”)is representative of a new class of companies emerging to address the world’s energy crisis: Nuclear startups. Dozens of small new reactor companies are either chasing the elusive fusion dream or pursuing fission designs that trump those on the market today. All are promising to deliver a knock-out blow to the carbon-intensive fossil fuels that bedevil the world with environmental impact and volatile geopolitics and economics. Many of these innovative firms are positioning their reactors not just for electricity, but also to provide clean heat for high temperature industrial processes and for water desalination.E)While LPP might be the only crowdfunded member of the group, it is determined like its young peers to shake up the staid nuclear industry. Reactor designs have not fundamentally changed since utilities first connected fission machines to the grid in the 1950s, marking a conservatism that has mired nuclear in the era of black-and-white television while colourful possibilities abound. The startups aim to brighten the palette.F)For LPP, that would mean not only delivering fusion—melding atoms together rather than fission’ s waste-creating process of splitting them apart—but it would also eliminate the time-honoured need for costly turbines and generators. Nuclear power, including most fusion concepts, functions mechanically the same way fossil fuel plants do by creating heat to produce steam to drive a turbine. LPP is working on a type of fusion called “aneutronic”that emits charged particles for electricity.G)”The nuclear industry is stuck using the same method for making electricity that utilities have used since the days of Thomas Edison—generate heat to make steam to drive a turbine and generator,”says Eric Lerner, president of LPPFusion. “We can change all that. We can convert energy directly into electricity and slash costs.”H)First, he’ll need the $200,000 he seeks on Indiegogo(he has until July 5 to raise it), which would buy him some fancy new beryllium electrodes that would withstand rigors far better than the copper variety that LPP has been using. He hopes to install them by the end of this year in his experimental fusion reactor, which Lerner operates at the Friendly Storage premises in Middlesex, a place otherwise full of surplus boxes and furniture.I)Lerner is boldly confident that the beryllium would by the middle of next year enable his lab to overcome the problem that has vexed fusion projects forever: It would harness more energy out of its reactor than what goes into it. Additional financing might then rush in. LPP will need $50 million in total, virtually nothing next to the nearly $18 billion that ITER has budgeted for only the next 10 years of an expected 30 years of construction and development of a 20-story “tokamak” facility.J)With the financing, Lerner believes that by 2020 he could license the mass-production of small $300,000-to- $500,000 fusion machines—each the size of a one-car garage—with a capacity of 5 megawatts, enough to power 3,000 houses.K)If only he had the wherewithal of rival fusion startup Tri-Alpha Energy, which has rounded up over $140 million from Goldman Sachs, Microsoft co-founder Paul Allen, and Russian state-owned company Rusnano, among others. Like LPP, Irvine, Calif.-based Tri-Alpha hopes to develop an aneutronic machine that delivers electricity without using turbines.L)ITER and NIF, the government groups, are taking a more “conventional” fusion approach, aspiring to drive turbines with heat released by fusing isotopes of hydrogen.(In contrast, an aneutronic process tends to fuse standard hydrogen and boron.)So, too, are a number of startups that believe they can crack fusion long before the big science projects do by developing smaller machines(NIF’s facility is 3 football fields long and 10 stories tall)and deploying different technologies.M)”We liken it to the Human Genome Project or SpaceX, where large government programs were ultimately outrun by more nimble and more practical innovation in the private sector,”notes Nathan Gilliland, CEO of General Fusion near Vancouver, Canada. General Fusion has raised $32 million from sources including the Canadian oil company Cenovus and Jeff Bezos, Amazon’s chief executive.N)As intriguing as fusion is, there is probably more startup activity in fission, where novel approaches promise great improvements over the industry’s addiction to fissioning solid uranium fuel rods then cooling and moderating them with water.O)A host of startups are experimenting with different approaches including the use of liquid fuel, the use of solid fuel with different shapes(such as bricks or pebbles), and the use of alternative coolants and moderators such as salts and gases. Many of the designs draw on ideas that politics suppressed decades ago. Some, like Bill Gates-chaired TerraPower in Bellevue, Wash., are designing “fast reactors” that don’t moderate neutrons. Some envision using the element thorium instead of uranium.P)Between them, they portend leaps in safety, cut way down on nuclear waste, use “waste” as fuel, and minimize weapons proliferation risks, slash costs and tremendously boost efficiencies. Many fit the “small modular”forms that enables mass production and affordable incremental power.(Oregon startup NuScale Power recently secured $217 million in federal funds to develop a small but comparativelyconventional reactor.)Q)”There is a growing market pull for innovation in the nuclear space, so you ‘re beginning to see a blossoming of startup companies doing different things in nuclear,” says Simon Irish, CEO of startup Terrestrial Energy, Mississauga, Canada, which is developing a “molten salt” reactor(MSR)based on liquid fuel. In the U.S., Russ Wilcox, CEO of Cambridge, Mass.-based MSR developer Transatomic Power, implores the U.S. Nuclear Regulatory Commission to broaden its focus beyond conventional reactor safety, which he says “freezes progress”.R)Many observers believe that countries other than the U.S., such as Canada and China, will deploy first. Beijing is funding innovative Chinese fission projects, with collaboration from the U.S. DOE. Meanwhile, Western companies seek funds. Like Cenovus at General Fusion, more oil companies might pony up, because they want clean heat to process petroleum. As Fortune reported last month, a lack of industry funding appears to have slowed progress in DOE’s mission to develop an advanced reactor. LPP Fusion doesn’ t seem to be worried. For the young company, the next financing stage could simply be a matter of warming up the crowd.1．The aneutronic machine can generate electricity without the support of turbines.正确答案：K解析：题干意为无中子核聚变发电机不需要借助汽轮机也能发电。
一个年代的美国作文英语
一个年代的美国作文英语Title: The Transformation of American Society in the 1950s。
The 1950s in America marked a significant period of transformation across various aspects of society. From economic prosperity to cultural shifts, this decade left an indelible mark on the nation's history. Let's delve into the key facets that defined this era.Economic Prosperity:One of the most striking features of the 1950s was the unprecedented economic prosperity experienced by the United States. Coming out of the devastation of World War II, the country witnessed a remarkable period of growth and affluence. The post-war economic boom was fueled by several factors, including technological advancements, increased consumer spending, and government policies such as the GI Bill, which provided education and housing benefits toveterans.The expansion of industries such as manufacturing, automobiles, and housing construction contributed significantly to the nation's wealth. The rise of suburbs symbolized the American Dream for many families, as they sought spacious homes and a suburban lifestyle away from the urban centers.Consumer Culture:The 1950s also saw the rise of consumer culture, characterized by mass production, advertising, and the proliferation of consumer goods. Television emerged as a powerful medium for advertising, shaping consumer preferences and popularizing new products. Brands like Coca-Cola, Ford, and General Motors became household names, reflecting the pervasive influence of consumerism in American society.The advent of credit cards and installment plansfurther facilitated consumption, enabling individuals topurchase goods beyond their immediate means. This culture of conspicuous consumption not only drove economic growth but also redefined notions of status and identity.Social Conformity:Alongside economic prosperity and consumerism, the 1950s witnessed a strong emphasis on social conformity and traditional values. The post-war era was characterized by a desire for stability and normalcy, leading to a conservative backlash against perceived threats to the social order.The idealized image of the nuclear family, with a breadwinning father, homemaker mother, and obedient children, was promoted as the cornerstone of American society. Gender roles were strictly defined, with women expected to prioritize domestic duties and support their husbands' careers.The Red Scare and McCarthyism:The fear of communism permeated American society during the 1950s, fueled by the Cold War rivalry between theUnited States and the Soviet Union. Senator JosephMcCarthy's crusade against alleged communist infiltration, known as McCarthyism, led to widespread paranoia and the persecution of suspected subversives.The entertainment industry, academia, and government agencies were subjected to intense scrutiny, withindividuals accused of communist sympathies facing blacklisting and persecution. The McCarthy hearings, televised for the nation to witness, exposed the dangers of political extremism and the erosion of civil liberties inthe name of national security.Civil Rights Movement:Despite the prevailing conformity and conservatism, the 1950s also witnessed the seeds of social change,particularly in the realm of civil rights. The landmark Supreme Court decision in Brown v. Board of Education (1954) declared segregation in public schools unconstitutional,laying the groundwork for the dismantling of Jim Crow laws and racial discrimination.The Montgomery Bus Boycott (1955-1956), sparked by Rosa Parks' refusal to give up her seat to a white passenger, galvanized the African American community and ignited a mass movement for racial equality. Figures like Martin Luther King Jr. emerged as leaders in the struggle forcivil rights, advocating nonviolent resistance and social justice.Conclusion:In conclusion, the 1950s was a decade of profound change and contradiction in American society. While marked by economic prosperity and cultural conformity, it also witnessed the beginnings of social upheaval and resistance to entrenched inequalities. The legacy of this transformative era continues to shape the trajectory of the United States, serving as a reminder of the complexities inherent in the pursuit of progress and justice.。
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We shall use the term "cluster" to refer to any particle or to a number of particles which have started to grow together. Consider two partially sintered clusters which are geometrically similar, the linear dimensions of number two being A times those of number one. For example, if each cluster consists of spherical
Effect of Change of Scale on Sintering Phenomena
Conyers Herring Citation: J. Appl. Phys. 21, 301 (1950); doi: 10.1063/1.1699658 View online: /10.1063/1.1699658 View Table of Contents: /resource/1/JAPIAU/v21/i4 Published by the American Institute of Physics.
The interpretation of the Fourier series can then be carried out by the use of Eqs. (2.2)-(2.5) or combinations of these expansions. In many cases, however, the summation of the fractions of (5.2) may present insurmountable difficulties and in such cases, this method of interpretation is not applicable.
the purposes of this paper "sintering" will be FOR understood to mean any change in shape which a
mechanism of crystal growth, and it would be incorrect, at least in cases involving plane crystal facets, if growth normal to such facets required a "two-dimensional nucleation" process.!,2 It is the purpose of this note to point out that useful information can probably be obtained, both on the fundamental question of the way in which crystals grow and on the more specific question of the relative importance of the four transport mechanisms in specific cases, by a comparison of sintering rates for particles or clusters of different sizes but geometrically similar shapes.
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small particle or a cluster of particles of uniform composition undergoes when held at high temperature. In the absence of externally applied stresses, such changes are believed to be motivated by surface tension, since the surface free energy decreases as the particles grow together and assume a more compact shape. The transport of matter which is involved can take place by any of four mechanisms: viscous or plastic flow, evaporation and condensation, volume diffusion, and surface migration. With the aid of certain plausible assumptions the rates of transport by each of these mechanisms can be computed in terms of the geometrical parameters and certain constants of the material such as surface tensions, diffusion coefficients, etc.! Foremost among the assumptions involved is the assumption that the building up or tearing down of the surface can occur quite readily in response to conditions in the immediately adjoining solid or vapor phase. This assumption is closely related to the controversial problem of the
An LF(t) = Ao+ L n=!1+(nw/p)2
OC)
FIG. 4.
+- L
w
00
nBn
p n=!1+(nw/p)2
(5.2)
The success of the method of interpretation described in this discussion depends upon the possibility of effecting the summations of (5.2) by the use of the Eqs. (2.6)-(2.9) or by formulas derivable from them.
V. GENERAL CONSIDERATIONS
The general Fourier series may be written in the form:
F(t)=Ao+ I: An cos (nwt) n=!
+ I: Bn sin(nwt).
(5.1)
The coefficients A nand Bn are known functions of n. By the use of Eqs. (3.4) and (3.5), it is possible to transform (5.1) into
1 C. Herring, paper presented at the Symposium on the Physics of Powder Metallurgy organized by Sylvania Electric Products, Inc., Bayside, Long Island, New York (August 24-26, 1949). Plans have been made to publish the papers of the Symposium in book form.
2 The theory of growth by two-dimensional nucleation is summarized in the book of M. Volmer, Kinetik der Phasenbildung (Verlag von Theodor Steinkopff, Dresden and Leipzig, 1939; Edwards Brothers, Inc., Ann Arbor, 1945). An alternative theory of crystal growth has been proposed by F. C. Frank, to appear in Trans. Faraday Soc. (paper presented at the Discussion on Crystal Growth sponsored by the Faraday Society and held at Bristol, England, April, 1949).
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