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机械专业论文中英文Gearbox Noise —— Correlation with Transmission Error and Influence of Bearing Preload变速箱噪声——相关的传输错误和轴承预压的影响摘要ABSTRACTThe five appended papers all deal with gearbox noise and vibration. The first paper presents a review of previously published literature on gearbox noise and vibration.The second paper describes a test rig that was specially designed and built for noise testing of gears. Finite element analysis was used to predict the dynamic properties of the test rig, and experimental modal analysis of the gearbox housing was used to verify the theoretical predictions of natural frequencies.In the third paper, the influence of gear finishing method and gear deviations on gearbox noise is investigated in what is primarily an experimental study. Eleven test gear pairs were manufactured using three different finishing methods. Transmission error, which is considered to be an important excitation mechanism for gear noise, was measured as well as predicted. The test rig was used to measure gearbox noise and vibration for the different test gear pairs. The measured noise and vibration levels were compared with the predicted and measured transmission error. Most of the experimental results can be interpreted in terms of measured and predicted transmission error. However, it does not seem possible to identify one single parameter,such as measuredpeak-to-peak transmission error, that can be directly related to measured noise and vibration. The measurements also show that disassembly and reassembly of the gearbox with the same gear pair can change the levels of measured noise andvibration considerably.This finding indicates that other factors besides the gears affect gear noise.In the fourth paper, the influence of bearing endplay or preload on gearbox noise and vibration is investigated. Vibration measurements were carried out at torque levels of 140 Nm and 400Nm, with 0.15 mm and 0 mm bearing endplay, and with 0.15 mm bearing preload. The results show that the bearing endplay and preload influence the gearbox vibrations. With preloaded bearings, the vibrations increase at speeds over 2000 rpm and decrease at speeds below 2000 rpm, compared with bearings with endplay. Finite element simulations show the same tendencies as the measurements.The fifth paper describes how gearbox noise is reduced by optimizing the gear geometry for decreased transmission error. Robustness with respect to gear deviations and varying torque is considered in order to find a gear geometry giving low noise in an appropriate torque range despite deviations from the nominal geometry due to manufacturing tolerances. Static and dynamic transmission error, noise, and housing vibrations were measured. The correlation between dynamic transmission error, housing vibrations and noise was investigated in speed sweeps from 500 to 2500 rpm at constant torque. No correlation was found between dynamic transmission error and noise. Static loaded transmission error seems to be correlated with the ability of the gear pair to excite vibration in the gearbox dynamic system.论文描述了该试验台是专门设计和建造噪音齿轮测试。
入舵市安恙阳光实验学校成功与失败Ⅰ.语境填词1.I wasn’t (success)，so they looked down on me.2.The child was found (被抛弃的) but unharmed.3.Iran says its nuclear ambitions are for peaceful (目的).4.They said that they (试图) to finish the task before July.5.We are learning how to confront death instead of (逃避) its reality.Ⅱ.单项填空6.How you the challenge in the second half will determine what you become after the game，whether you are a winner or a loser.A.respond toB.submit tomit toD.stick to7.I have always to China，and now my dream has .A.dream coming；come trueB.dreamt of coming；come trueC.dreamed to come；realizedD.dreamed coming；realizing8.The WFP has launched a new app called Share The Meal， the potential，people believe，is enormous as it allows smart phone users to make donatio ns with a simple tap on their phone.(2017·南通如东、徐州联考)A.whoseB.thatC.whichD.of which9.Even with the gift of 10,000，it was difficult for her to a mortgage，but she eventually found a lender and a house.A.payB.obtainC.cancelD.accept10.A notice was in order to remind the students of the changed lecture time.A.sent upB.given upC.set upD.put upⅠ.阅读理解They say a cat has nine lives，and I think that possible since I am now living my third life and I’m not even a cat.My father died when I was 15，and we had a hard struggle to make a living.And my mother，who was seriously ill in her last years，died while still in her 60s.My sister married soon after，and I followed her example within the year.This was when I began to enjoy my first life.I was very happy，in excellent health.I had a good job in San Jose and a beautiful home up the peninsula(半岛) in San Carlos.Life was a pleasant dream.Then the dream ended.I became afflicted(使苦恼) with a slowly progressive disease of the motor nerves，affecting first my right arm and leg，and then my other side.Thus began my second life...In spite of my disease I still drove to and from work each day，with the aid of special equipment installed in my car.And I managed to keep my health and optimism，to a degree，because of 14 steps.Crazy？Not at all.Our home was an affair with 14 steps leading up from the garage to the kitchen door.Those steps were a standard measure of life.They were my yardstick，my challenge to continue living.I felt that if the day arrived when I was unable to lift one foot up one step and then drag the other painfully after it—repeating the process 14 times，I would be through—I could then admit defeat and lie down and die.Then on a dark night in August,1971，I began my third life.It was raining when I started home that night；strong winds and slashing rain beat down on the car as I drove slowly down one of the lesstrav elled roads.Suddenly the steering wheel jerked(猝然一动).In the same instant I heard the bang of a blowout.It was impossible for me to change that tire！Utterly impossible!I started the engine and thumped slowly along until I came to the dirt road，where I turned in and where I found lighted windows welcomed me to a house and pulled into the driveway and honked the horn.The door opened and a little girl stood there.When she knew what happened to me，she went into the house and a moment later came out，followed by a man who called a cheerful greeting.I sat there comfortable and dry，and felt a bit sorry for the man and the little girl working so hard in the storm.About an hour later，the man’s voice was heard，“This is a bad night for car trouble，but you’re all set now.”“Thanks，” I said，“How much do I owe you？” He shook his head，“Nothing.Cynthia told me you were a cripple.Glad to be of help.I know you’d do the same for me.There’s no charge，friend.” I held out a fivedollar bill，“No！I like to pay my way.” He made no ef fort to take it and the little girl stepped closer to the window and said quietly，“Grandpa can’t see it.”1.“A cat has nine lives” here means “”.A.a cat can live nine times longer than any other animalB.a cat can die ninthC.a lucky man can not die easilyD.the author will live nine times2.What do you think of the man who helped change the tire?A.Old，warmhearted but pitiable.B.Blind，but warmhearted and happy.C.A blind old man that has nothing to do every day.D.A poor old man that is always ready to help others.3.How do you understand the underlined sentence “I followed her example within the year”？A.He listened to his sister carefully.B.Mother told him that he must get the agreement from his sister for whatever he would do.C.His sister got married.He，too.D.His sister was a great woman.He must learn from her.Ⅱ.任务型阅读The most common use of intelligence test scores is to predict degree of academic success.Such scores are used in some communities as bases for admitting able children to schools at ages younger than normal，and they are very generally used to determine admissions to schools beyond public secondary school.Another commonuse in elementary schools involves comparing such scores with performances in various subjects to identify children who are working below capacity.The greatest problem in using intelligence tests for the purpose of prediction is that no dependable criterion of their accuracyexists.The ideal criteria would be objective and reliable achievement tests following instructions in each subject，but there are few such tests，especially at the college level.Studies have shown that correlations(相关性) between intelligence tests and achievement tests in various subjects through secondary school range roughly from 0.5 to 0.8.Such correlations are fairly high，but they do not suggest anywhere near complete agreement.At the college level there are two major tests used as criteria of admission.By far the more important is the College Entrance Examination，constructed by the Educational Testing Service authorized by the College Entrance Examination Board.These tests are returned to the Educational Testing Service for scoring，and the results are then made available to the various colleges authorized by the students to receive them.The second test of this type is the American College Test，which operates in essentially the same fashion.Both tests constitute(组成) measures of certain skills，abilities，and knowledge that have been found to be related to success in college.Their correlations with academic success are limited for three outstanding reasons.First，measures of achievement in college are themselves perhaps no more reliable than those in elementary and secondary schools.Second，intellectual factors do not alone determine academic success，especially at the college level.Many students drop out of schools because they are inadequately motivated or because they dislike the instructional programme.Third，correlations are lowered because the use of such tests for denying admission to some students means that the range of scores for those admitted is restricted，and such restrictions tend to reduce correlations.答案精析高考高频单词与短语识记排查跟踪训练Ⅰ.1.successful 2.abandoned 3.purposes 4.attempted 5.avoiding Ⅱ.6.A [句意为：你对下半场如何反应将会决定比赛后你成为成功者还是失败者。
Unit 1science and scientists59. leadership ['liːdəʃɪp] n. ____________60. trace [treɪs] v. ____________n. ____________61. outstanding [aʊt'stændɪŋ] adj. ____________62. gifted ['ɡɪftɪd] adj. ____________63. come down ____________64. abstract ['æbstrækt] adj. _________n. ________65. steady ['stedi] adj. ____________66. concept ['kɒnsept] n. ____________67. astronomer [ə'strɒnəmə(r)] n. ____________68. astronomy [ə'strɒnəmi] n. ____________69. telescope ['telɪskəʊp] n. ____________70. besides [bɪ'saɪdz] prep. _______adv. _________71. brilliant ['brɪljənt] adj. ____________72. furthermore [ˌfɜːðə'mɔː(r)] adv. ____________73. above all ____________74. fault [fɔːlt] n. ____________75. shift [ʃɪft] v. ____________n. ____________76. vivid ['vɪvɪd]: adj. ____________II.汉译英1. ____________n. 霍乱2. ____________adj. 极为恶劣的; 十分严重的; 严厉的3. ____________n. 腹泻4. ____________n. 脱水5. ____________adj. 懊恼的; 沮丧的; 失意的6. ________________ 最终地; 彻底地7. ____________adj. 相互矛盾的; 对立的; 不一致的8. ____________n. 感染；传染9. ____________v. 使感染; 传染10. ___________n 微生物; 细菌; 病菌11. ___________v. 认购(股份); 定期订购; 定期缴纳(会费)12. ________________同意; 赞同13. ___________n. 证据; 证明; 检验14. ___________adj. 数量多的; 多种多样的15. ___________n. 泵; 抽水机; 打气筒16. ________________水泵17. ___________n. 一家人; 家庭; 同住一套(所)房子的人18. __________v. 怀疑; 疑有; 不信任n. 犯罪嫌疑人; 可疑对象19. __________v. 把…归咎于...; 责怪; 指责n. 责备; 指责20. __________n. 把手; 拉手; 柄 v. 处理; 搬动; 操纵(车辆/动物/工具等)21. __________n. 介入; 出面; 干涉22. __________n. 联系; 纽带v. 把...连接起来; 相关联23. __________adj. 未煮的; 生的; 未经处理的; 原始的24. __________adj. 干净的; 纯的; 纯粹的25. __________adj. 大量的; 价值巨大的; 重大的26. __________v. 减少; 减小; 降低n. 减少; 降低: 减少量27. ________________ 幸亏; 由于28. ___________n. (复数)统计数字; 统计资料; 统计学29. ___________v. 使改观; 使改变形态; 改变; 转变30. ___________n. 流行病学31. ___________n. 显微镜32. ___________n. 思想; 思维; 见解33. ___________n. 蛋白质34. ___________n. 细胞; 小房间; 单间牢房35. ___________n. 病毒36. ___________n. 发现; 调查结果; (法律)判决37. ___________adj. 最初的; 开始的; 第一的38. ___________n. 疫苗39. ___________n. 框架; 结构40. ________________ 理论框架41. ___________adj. 可靠的; 固体的; 坚实的n. 固体42. ___________v. 投射; 投掷; 向...投以(视线/笑容等)43. ___________n. 阴影; 影子; 背光处1.frustrate vt.使懊丧；使懊恼；使沮丧→__________adj.懊恼的；沮丧的；失意的→__________adj.令人懊恼的；令人沮丧的→__________n．懊丧；懊恼；沮丧2.infect vt.使感染；传染→__________ n．感染；传染→__________adj.传染性的，感染的，有感染力的3.contradict v.反驳;相矛盾;相反→__________adj.相互矛盾的；对立的；不一致的→__________n.矛盾；对立；不一致4.prove vt.证明→__________n．证据；证明；检验5.intervene vt.介入；出面；干涉→__________n．介入；出面；干涉6.subscribe v. 认购(股份); 定期订购; 定期缴纳(会费)→__________n.订阅费，订购款，订阅，订购；定期捐款；会员费→__________n.订阅人，订购者，订户；定期捐款者，定期捐助者7.suspect v. 怀疑; 疑有; 不信任→__________adj.怀疑的→__________n.怀疑8.pure adj.干净的；纯的；纯粹的→__________n.纯洁；纯净；纯粹→_________vt.使纯净；使洁净→__________n.净化(作用)；提纯9.substance n.物质；物品；主旨；要点；实质→__________adj. 大量的; 价值巨大的; 重大的→__________adv.非常；大大地；基本上；大体上；总的来说10.transform vt.v. 使改观; 使改变形态; 改变; 转变→_____________n.变化，改观，转变，改革→_____________adj.变革的；改革的11.virus n.病毒→__________adj.病毒的；病毒性的；病毒引起的12.theory n.理论→__________adj. 理论上的13.solid adj.可靠的; 固体的; 坚实的→__________n.固态;可靠性;坚固性14.initial adj.最初的；开始的；第一的→________ adv.开始；最初15.patriotic adj. 爱国的→__________adv.爱国地;忧国地→__________n.爱国主义→__________n.爱国者16.defend vt.保卫；防守；辩解→__________n．防御；防务→__________adj.防御的；保护的；保卫的；戒备的；怀有戒心的17.assist vt.帮助；协助→__________n.帮助；协助→__________n.助手；助理18.lead v.领导；导致；通向→__________n．领导者→__________n．领导；领导地位；领导才能→__________adj.最重要的；一流的→__________adj.误导的;引入歧途的19.steady adj.稳定的；平稳的；稳步的→__________adj.不稳定的→________adv.稳定地；坚固地20.vivid adj.生动的；鲜明的；丰富的→________adv.生动地Keys:1.frustrated;frustrating;frustration2.infection;infectious3.contradictory;contradiction4.proof5.intervention6.subscription;subscriber7.suspicious;suspicion8.purity;purify;purification9.substantial;substantially 10.transformation;transformative 11.virus 12.theoretical 13.solidity14.initially 15.patriotically;patriotism;patriotic 16.defence/defense;defensive 17.assistance;assistant18.leader;leadership;leading;misleading 19.unsteady；steadily 20.vividly1.raise a question★提出问题2.from a new angle 从新的角度3.creative imagination 创造性的想象力4.(be) related to★与……有关5.take a photo / picture★拍照6.in the future★在将来;今后7.scientific research 科学研究8.draw / arrive at / come to / reach a conclusion★得出结论9.collect data★收集资料ed to be ★过去是11.in time 经过一段时间之后;迟早;及时12.rise to become a famous doctor 成为名医13.attend to★照料;处理;接待14.give birth (to sb) ★生孩子;生下(某人)15.the desire to do sth★做某事的渴望16.once and for all 最终地;彻底地17.in general★大体上;一般地18.cause a disease 引起疾病19.subscribe to 同意;赞同20.be determined / make up one's mind to do sth ★决心做某事21.begin by doing sth 首先做某事22.water pump 水泵23.such as ★例如24.be to blame (for sth)★ (对某事)负有责任25.what is more 更为重要的是;更有甚者26.It seems (that) ...★似乎……;看样子……27.have sth done★让(他人)为你做(某事)28.as a result (of)★作为(……的)结果;由于……29.be able / unable to do sth★能够做某事/不能够做某事30.stop in one’s tracks (尤指因惊吓而)突然停下31.a link between ... and ...★…和…之间的联系32.raw waste 未经处理的废弃物33.be likely to do sth★可能做某事34.get cholera 感染上霍乱35.pure / boiled water 纯净水/开水36.tireless efforts 不懈努力37.substantial decrease 大幅降低38.thanks to★幸亏;由于39.consider ... (to be) sth★认为……是……40.It is believed (that) ... 人们认为……;据信……41.write out 填写42.suspect sb of (doing) sth 怀疑某人(做)某事43.be linked to / with ★与……有关联/联系44.serve dinner 供应晚饭45.fight the common cold 抵抗普通感冒46.rather than / instead of★而不是;代替47.make sense★有意义;讲得通48.resistance to medicine 抗药能力49.work on★致力于;从事于50.side effects (药物的)副作用51.make substantial advances in 在……领域取得重大进展52.make sure 确保;弄清楚e sth as sth 把某物用作某物54.initial stage / period 初期55.depend upon / on ★信赖;依靠;取决于56.carry out / conduct / do research ★进行研究57.in the first place 一开始;起初58.theoretical framework 理论框架59.calm down ★(使)平静下来;(使)镇静下来60.get down to doing sth ★开始做某事;开始认真对待某61.in the end ★最后;终于62.focus on / upon★集中(注意力、精力等)于63.at times ★有时;间或64.in a whisper ★低声地65.for a while 一会儿66.move around / about 四处走动;经常搬动67.cast / throw a shadow ★投下影子68.in fact/effect/reality/practice★实际上;事实上69.as soon as / the moment / instant (that)★一……就……70.make a great scientist 成为伟大的科学家71.the father of China's aerospace 中国航天之父72.have an impact / effect / influence on★对……有影响73.be described as 被描述为….74.an extremely well-respected man 极受尊敬的人75.attend school上学76.make / take a decision★作出决定77.switch to 转换;转向;转变78.air force 空军79.protect and defend the country 保卫国家80.rocket propulsion 火箭推进力81.overcome difficulties★克服困难82.receive a hero's welcome 受到英雄般的欢迎83.in charge of★主管;掌管84.discourage sb from doing sth 阻止某人做某事85.take on 接受(工作):呈现:雇用:承担(责任);与……较量86.under sb's leadership 在某人的领导下87.trace sth (back) to sth ★把某物追溯到某物上88.earn the name of 获得……的(美)名89.be saddened by 对……感到难过/伤心90.be familiar with★熟悉……e down with患(病);染上(小病)92.achieve / gain / acquire / win fame获得名声93.the origin of the universe 宇宙起源94.the steady state theory 稳态理论95.the big bang theory 大爆炸理论96.stand up / rise to one's feet★站起身来97.point out 指出;指明98.make a mistake★犯错误99.be willing to do sth★乐意/愿意做某事100.be afraid / scared / frightened to do sth★害怕做某事101.dream of / about (doing) sth 梦想(做)某事102.a fight / struggle against★与……的斗争103.above all★最重要的是;尤其是104.because of / due to ★由于;因为105.personal interest 个人爱好106.even though / if ★尽管;即使107.apart / aside from ★s 除……外(尚有);除……外(别无108.personal qualities★个人品质109.make up★组成;构成;编造110.statistical analysis 统计分析111.settle the conflict 解决冲突112.think outside the box 跳出框框思考;不拘一格地思考113.a vivid imagination★丰富的想象力114.start out as 起初(是);最初(是)115.be gifted with 天生具有……116.benefit from★从……中受益;得益于117.solve / settle / resolve / overcome a problem 解决问题118.give sb advice★给某人建议119.have the ability to do sth★有能力做某事e up with★想出;想到121.at first / in the beginning★起初;起先122.serve as ★充当;担当123.suffer from ★遭受;患……病124.refuse to do sth★拒绝做某事125.turn into★ (使)变成;(使)成为126.be proud of 为……而自豪127.be part of sth★是某事物的一部分(局部)128.human nature 人性129.be curious about ★对……感到好奇★在某人看来V1. To raise new questions, new possibilities, to regard old problems from a new angle requires creative imagination and marks real advance in science. 一 Albert Einstein & LeopoldInfeld(P1)提出新问题，发现新可能，从新角度审视已存在的问题，这些需要创造性的想象力，并标志着科学的真正进步。
2021年雅思阅读模拟题精选及答案（卷八）雅思阅读文本：The spectacular aurora light displays that appear in Earth's atmosphere around the north and south magnetic poles were once mysterious phenomena. Now, scientists have data from sat ellites and ground-based observations from which we know that the aurora brilliance is an immense electrical discharge similar to that occurring in a neon sign.To understand the cause of auroras, first picture the Earth enclosed by its magnetosphere, a huge region created by the Earth's magnetic field. Outside the magnetosphere, blasting toward the earth is the solar wind, a swiftly moving plasma of ionized gases with its own magnetic filed.Charged particles in this solar wind speed earthward along the solar wind's magnetic lines of force with a spiraling motion. The Earth's magnetosphere is a barrier to the solar winds, and forces the charged particles of the solar wind to flow around the magnetosphere itself. But in the polar regions, the magnetic lines of force of the Earth and of the solar wind bunch together. Here many of the solar wind's charged particles break through the magnetosphere and enter Earth's magnetic field. They then spiral back and forth between the Earth's magnetic poles very rapidly. In the polar regions, electrons from the solar wind ionizeand excite the atoms and molecules of the upper atmosphere, causing them to emit aurora radiations of visible light.The colors of an aurora depend on the atoms emitting them. The dominant greenish white light comes from low energy excitation of oxygen atoms. During huge magnetic storms oxygen atoms also undergo high energy excitation and emit crimson light. Excited nitrogen atoms contribute bands of color varying from blue to violet. Viewed from outer space, auroras can be seen as dimly glowing belts wrapped around each of the Earth's magnetic poles. Each aurora hangs like a curtain of light stretching over the polar regions and into the higher latitudes. When the solar flares that result in magnetic storms and aurora activity are very intense, aurora displays may extend as far as the southern regions of the United States.Studies of auroras have given physicists new information about the behavior of plasmas,which has helped to explain the nature of outer space and is being applied in attempts to harness energy from the fusion of atoms.雅思阅读题目：1. What does the passage mainly discuss?(A) The methods used to observe auroras from outer space(B) The formation and appearance of auroras around the Earth's poles(C) The factors that cause the variety of colors in auroras(D) The periodic variation in the display of auroras2. The word "phenomena" in line 2 is closest in meaning to(A) ideas(B) stars(C) events(D) colors3. The word "picture" in line 5 is closest in meaning to(A) frame(B) imagine(C) describe(D) explain4. The passage describes the magnetosphere as a barrier (line 10) because(A) its position makes it difficult to be observed from Earth(B) it prevents particles from the solar wind from easily entering Earth's atmosphere(C) it increases the speed of particles from the solar wind(D) it is strongest in the polar regions5. The word "them" in line 16 refers to(A) polar regions(B) electrons(C) atoms and molecules(D) aurora radiations6.According to the passage , which color appears most frequently in an aurora display?(A) greenish-white(B) crimson(C) blue(D) violet7. The word "emit" in line 20 is closest in meaning to(A) change from(B) connect with(C) add to(D) give off8. The word "glowing" in line 22 is closest in meaning to(A) shining(B) moving(C) charging(D) hanging9.Auroras may be seen in the southern regions of the United Sates when(A) magnetic storms do not affect Earth(B) solar flares are very intense(C) the speed of the solar wind is reduced(D) the excitation of atoms is low10. The passage supports which of the following statements about scientists' understanding ofauroras?(A) Before advances in technology, including satellites, scientists knew little about auroras.(B) New knowledge about the fusion of atoms allowed scientists to learn more about auroras.(C) Scientists cannot explain the cause of the different colors in auroras.(D) Until scientists learn more about plasma physics, little knowledge about auroras will beavailable.11. Which of the following terms is defined in the passage ?(A) "magnetosphere" (line 6)(B) "electrons" (line 15)(C) "ionize" (line 15)(D) "fusion" (line 29)雅思阅读答案：BCBBCADABAAEconomic EvolutionA Living along the Orinoco River that borders Brazil and Venezuela are the Yanomam people, hunter-gatherers whose average annual income has been estimated at the equivalent of $90 per person per year. Living along the Hudson River that borders New York State and New Jersey are the Manhattan people, consumer traders whose average annual income has been estimated at $36,000 per person per year. That dramatic difference of 400 times, however, pales in comparison to the differences in Stock Keeping Units (SKUs, a measure of the number of types of retail products available), which has been estimated at 300 for the Yanomam and 10 billion for the Manhattans, a difference of 33 million times.B How did this happen? According to economist Eric D. Beinhocker, who published these calculations in his revelatory work The Origin of Wealth (Harvard Business School Press, 2006), the explanation is to be found in complexity theory. Evolution and economics are not just analogous to each other, but they are actually two forms of a larger phenomenon called complex adaptive systems, in which individual elements, parts or agents interact, then process information and adapt their behavior to changing conditions. Immune systems, ecosystems, language, the law and the Internet are all examples of complex adaptive systems.C In biological evolution, nature selects from the variation producedby random genetic mutations and the mixing of parental genes. Out of that process of cumulative selection emerges complexity and diversity. In economic evolution, our material economy proceeds through the production and selection of numerous permutations of countless products. Those 10 billion products in the Manhattan village represent only those variations that made it to market, after which there is a cumulative selection by consumers in the marketplace for those deemed most useful:VHS over Betamax, DVDs over VHS, CDs over vinyl records, flip phones over brick phones, computers over typewriters, Google over Altavista, SUVs over station wagons, paper books over e-books (still), and Internet news over network news (soon).Those that are purchased “survive”and "reproduce" into the future through repetitive use and remanufacturing.D As with living organisms and ecosystems, the economy looks designed—so just as humans naturally deduce the existence of a top-down intelligent designer, humans also (understandably) infer that a top-down government designer is needed in nearly every aspect of the economy. But just as living organisms are shaped from the bottom up by natural selection, the economy is molded from the bottom up by the invisible hand. The correspondence between evolution and economics is not perfect, because some top-down institutional rules and laws are needed to provide a structure within which free and fair trade can occur.But too much top-down interference into the marketplace makes trade neither free nor fair. When such attempts have been made in the past they have failed—because markets are far too complex, interactive and autocatalytic to be designed from the top down. In his 1922 book, Socialism, Ludwig Von Mises spelled out the reasons why, most notably the problem of “economic calculation”in a planned socialist economy. In capitalism, prices are in constant and rapid flux and are determined from below by individuals freely exchanging in the marketplace. Money is a means of exchange, and prices are the information people use to guide their choices. Von Mises demonstrated that socialist economies depend on capitalist economies to determine what prices should be assigned to goods and services. And they do so cumbersomely and inefficiently. Relatively free markets are, ultimately, the only way to find out what buyers are willing to pay and what sellers are willing to accept.E Economics helps to explain how Yanomam-like hunter-gatherers evolved into Manhattan-like consumer-traders. In the Nineteenth century French economist Frederic Bastiat well captured the principle: “Where goods do not cross frontiers, armies will." In addition to being fierce warriors, the Yanomam are also sophisticated traders, and the more they trade the less they fight. The reason is that trade is a powerful social adhesive that creates political alliances. One village cannot go to another village and announce that they are worried about beingconquered by a third, more powerful village—that would reveal weakness. Instead they mask the real motives for alliance through trade and reciprocal feasting. And, as a result, not only gain military protection but also initiate a system of trade that—in the long run—leads to an increase in both wealth and SKUs.F Free and fair trade occurs in societies where most individuals interact in ways that provide mutual benefit. The necessary rules weren't generated by wise men in a sacred temple, or lawmakers in congress, but rather evolved over generations and were widely accepted and practiced before the law was ever written. Laws that fail this test are ignored. If enforcement becomes too onerous, there is rebellion. Yet the concept that human interaction must, and can be controlled by a higher force is universal. Interestingly, there is no widespread agreement on who the "higher force" is. Religious people ascribe good behavior to god's law. They cannot conceive of an orderly society of atheists. Secular people credit the government. They consider anarchy to be synonymous with barbarity. Everyone seems to agree on the concept that orderly society requires an omnipotent force. Yet, everywhere there is evidence that this is not so. An important distinction between spontaneous social order and social anarchy is that the former is developed by work and investment, under the rule of law and with a set of evolved morals while the latter is chaos. The classical liberal tradition of von Mises and Hayeknever makes the claim that the complete absence of top-down rules leads to the optimal social order. It simply says we should be skeptical about our ability to manage them in the name of social justice, equality, or progress.Questions 1-5Do the following statements agree with the information given in Reading Passage 1?In boxes 1-5 on your answer sheet, writeTRUE if the statement is trueFALSE if the statement if falseNOT GIVEN if the information is not given in the passageSKUs is a more precise measurement to demonstrate the economic level of a community.No concrete examples are presented when the author makes the statement concerning economic evolution.Evolution and economics show a defective homolog.Martial actions might be taken to cross the borders if trades do not work.Profit is the invisible hand to guide the market.Questions 6-8Choose the correct letter, A, B, C or D.Write your answers in boxes 6-8 on your answer sheet.6 What ought to play a vital role in each field the economy?A a strict ruleB a smart strategyC a tightly managed authorityD a powerful legislation7-8 Which two of the following tools are used to pretend to ask for union according to one explanation from the perspective of economicsA an official announcementB a diplomatic eventC the exchange of goodsD certain written correspondenceE some enjoyable treatment in a win-win situationQuestions 9-13SummaryComplete the following summary of the paragraphs of Reading Passage, using no more than three words from the Reading Passage for each answer. Write your answers in boxes 9-13 on your answer sheet.In response to the search of reasons for the phenomenon shown by the huge difference in the income between two groups of people both dwelling near the rivers, several researchers made their effort and gave certain explanations. One attributes 9 to the interesting change claiming that it is not as simple as it seems to be in appearance that therelationship between 10 which is a good example of 11 , which involve in the interaction of separate factors for the processing of information as well as the behavioral adaptation to unstable conditions. As far as the biological transformation is concerned, both 12 and the blend of genes from the last generation bring about the difference. The economic counterpart shows how generating and choosing the 13 of innumerable goods moves forward the material-oriented economy.文章题目：经济进化论篇章结构体裁论说文题目经济进化论结构A段：Yanomam人和曼哈顿人在年收入及库存单位上存在巨大差异B段：介绍复杂适应系统C段：物质经济通过产品生产和产品选择完成进化D段：经济由下而上进行选择E段：经济进化论解释了采猎者如何进化为贸易者F段：贸易可以自由演化，也可以由更高力量来控制试题分析Question 1-13题目类型：LIST OF HEADINGS题号定位词文中对应点题目解析1 SKUs A段第三句A段提到SKUs(库存单位)，只是将Yanomam 人和曼哈顿人在年收入和库存单位上的差异做了一个比较，并未说明SKUs是否能够衡量经济发展水平。
Ⅰ.阅读单词——会意1．tutor n．(英国大学中的)助教；导师；家庭教师v t.辅导2．cite v t.引用；引述3．messenger n．送信人；信使4．edition n．(报纸、杂志)一份；(广播、电视节目)一期、一辑；版次5．culture shock文化冲击6．zone n．(有别于周围的)地区；地带；区域7．comfort zone舒适区；舒适范围8．overwhelming adj.无法抗拒的；巨大的；压倒性的9．homesickness n．思乡病；乡愁10．setting n．环境；背景；(小说等的)情节背景11．tremendous adj.巨大的；极大的12．mature adj.成熟的13．boom v i.&n．迅速发展；繁荣14．perspective n．(思考问题的)角度；观点15．envoy n．使者；使节；代表16．outlook n．前景；可能性；观点17．belt n．腰带；地带18．initiative n．倡议；新方案Ⅱ.重点单词——记形1．complex adj.复杂的；难懂的；(语法)复合的2．recall v t.&v i.记起；回想起3．presentation n．报告；陈述；出示；拿出4．firm n．公司；商行；事务所adj.结实的；牢固的；坚定的5．insight n．洞察力；眼光6．grasp v t.理解；领会；抓紧7．expense n．费用；花费；开销8．deny v t.否认；否定；拒绝9．gain v t.获得；赢得；取得；增加n．好处；增加10．angle n．角；角度；立场11．sincerely ad v.真诚地；诚实地12．budget n．预算13．outcome n．结果；效果Ⅲ.拓展单词——悉变1．qualification n．(通过考试或学习课程取得的)资格；学历→qualify v t.&v i.(使)具备资格；(使)合格→qualified adj.有资格的；称职的2．ambition n．追求的目标；夙愿；野心；抱负→ambitious adj.有野心的；有雄心的3．adaptation n．适应；改编本→adapt v t.使适应；改编v i.适应4．comfort n．安慰；令人感到安慰的人或事物；舒服；安逸v t.安慰；抚慰→comfortable adj.令人舒适的；舒服的→uncomfortable adj.不舒服的5．participate v i.参加；参与→participation n．参加；参与→participant n．参与者6．engage v i.参加；参与(活动)v t.吸引(注意力、兴趣)；雇用→engaged adj.忙于；从事于；已订婚的→engagement n．订婚；约定7．involve v t.包含；需要；涉及；影响；(使)参加→involved adj.参与的；投入的→involvement n．参与8．motivated adj.积极的；主动的→motivation n．动力；积极性；动机→motivate v t.成为……的动机；激发；激励9．advisor n．(also-ser)顾问→advise v t.&v i.建议；劝告→advice n．建议；忠告10．reasonable adj.有道理的；合情理的→reasonably ad v.明智地；合理地→reason n．原因；道理v t.&v i.推理，推断v i.理解→unreasonable adj.不合理的；不公正的11．expectation n．期望；预期；期待→expect v t.预料；期望12．applicant n．申请人→apply v i.申请v t.应用；使用；涂；敷→application n．申请(书)；应用(程序)13．exposure n．接触；体验；暴露；揭露→expose v t.使接触；使体验；显露；使暴露于(险境)14．departure n．离开；启程；出发→depart v i.&v t.离开；启程；出发15．dramatic adj.巨大的；突然的；急剧的；戏剧(般)的→dramatically ad v.突然地；戏剧地；引人注目地→drama n．戏剧；戏剧性事件16．behave v t.表现v i.&v t.表现得体；有礼貌→behaviour/behavior n．行为；举止17．surroundings n．[pl.]环境；周围的事物→surrounding adj.周围的；附近的→surround v t.包围；围绕18．depressed adj.沮丧的；意志消沉的→depress v t.使沮丧；使忧愁→depression n．沮丧；抑郁19．strengthen v i.&v t.加强；增强；巩固→strong adj.强壮的→strength n．体力；优点20．optimistic adj.乐观的→optimism n．乐观主义21．competence n．能力；胜任；本领→competent adj.有能力的；称职的22．cooperate v i.合作；协作；配合→cooperation n．合作；协作23．logical adj.合乎逻辑的；合情合理的→logically ad v.合乎逻辑地→logic n．逻辑(学)；道理1．bully/'bʊli/n．恃强凌弱者；横行霸道者vt.恐吓；胁迫2．attentive/ə'tent I v/adj.专心的；留意的；体贴的3．exert/Iɡ'zɜːt/vt.施加；运用4．rebellious/r I'beljəs/adj.叛逆的；反抗的；难对付的5．impose/I m'pəʊz/vt.&vi.把……强加于；强制推行6．immense/I'mens/adj.巨大的；无穷的7．unity/'juːnəti/n．团结；联合；统一8．universal/ˌjuːn I'vɜːsl/adj.全体的；通用的；普遍的9．personnel/ˌpɜːsə'nel/n．全体人员；职员；人事部门10．expertise/ˌekspɜː'tiːz/n．专门知识(或技能)；专长Ⅳ.背核心短语1．participate in参加；参与2．speak up大声点说；明确表态3．feel at home舒服自在；不拘束4．engage in(使)从事；参与5．get involved in参与；卷入；与……有关联6．cost an arm and a leg(使)花一大笔钱7．side with支持；站在……的一边8．as far as I know据我所知9．as far as I am concerned就我而言；依我看来10．in summary总的来说；总之11．generally speaking一般来说Ⅴ.悟经典句式1．It was the first time that she had left China.(It was the first time that＋过去完成时)这是她第一次离开中国。
In all cases, the length distributions have a negative exponential shape (Figs. 6 and7), but the negative exponent magnitudes tend to be smaller (ranging from about –0.01 to –0.17) than those generated in the simulations (ranging from –0.1 to –1.5). The exception is the Oil Mountain microcrack data (Fig. 7), which has an extremely high magnitude exponent of negative 136. It is possible that natural rock is less flawed than we modeled, or more likely most flaws in rock are too small to impact the propagation of largerfractures. In the numerical model the flaws are quite large, on the order of 0.2 m. Another factor that is important to consider is that fracture length is exceptionally difficult toquantify in the field because of the segmented nature of most natural fractures.13Depending on the detail level of the data collection, fracture length observations may overestimate the abundance of longer fractures by overlooking their segmented nature at smaller scales.Fracture Spacing.As with fracture length, fracture spacing is significantly affected by variations in subcritical index (Figs. 5 and8). (The results are from the same 400 crack simulations used for the length discussion above, and we exclude flaws that have not propagated from the spacing analysis.) The first overall spacing attribute is whether or not the fractures are clustered. As mentioned above, the cases with subcritical indices of 40 and 80 show strong fracture clustering, while those with lower ndo not. The nominal correlation of fracture spacing with bed thickness (i.e. fracture height) is evident in the fracture pattern for the non-clustered cases of n ≤20, where the maximum spacing of 3.5 to 4 meters is close to the bed thickness of 4 meters (Fig. 8). Increasing the subcritical index from 5 to 20 increases the median spacing (taken at a cumulative frequency of 0.5) from 0.7 to 2.3 meters. However, for the clustered cases, the median spacing goes back down, such that the median spacing for n=80 is 0.5 meters, which is less than that for any other case. However, if fracture trace length were the measure of fracture intensity, the trace maps (Fig. 5) clearly show that the n=5 case is the most highly fractured.Relating Fracture Length to Aperture.A theoretical model for fracture length distributions is important because fracture length is difficult to observe in core data. Correlation of length with a more easily measured parameter would also be beneficial for fracture attribute determination. One attribute just discussed is the spacing, which has been shown to behave similarly to fracture length as the subcritical index for the fracturing material is changed. Another important flow related parameter that can be correlated with length is the aperture (fracture opening), more specifically the maximum aperture. For the simplified conditions of two-dimensional, plane-strain elasticity, maximum fracture aperture (Iu ∆) can be described as a linear function of fracture length (2a) as (9)where E is Young’s modulus and νis Poisson’s ratio. Eq. 9 also requires that the crack is straight, uniformly loaded, and not interacting with its neighbors. For a population of fractures of different length to show linear aperture to length scaling, all of those fractures must also be experiencing the same driving stress, I σ∆. Since crack propagation is inherently unstable under constant stress loading (which is implied by constant driving stress), such conditions are unlikely to be long-lived in nature. A better model, although still idealized, is to assume the driving stress varies from crack to crack to maintain a constant stress intensity factor, KI, equal to the rock’s fracture toughness, KIc, such that each crack is just at the point of propagation, where (10)Solving this expression for driving stress and substituting it into Eq. 9 results in a new aperture to length expression that predicts square-root instead of linear scaling. (11)A more illustrative expression is to describe the fracture aspect ratio, (12)which shows that aspect ratio is expected to decrease with increasing fracture length. This trend can be readily seen in examples of outcrop data, such as the Shiprock dike data described earlier as well as veins from other sandstone and granite outcrops. The data depicted in Fig. 9show a best-fit, power-law curve with a negative exponent of 0.6, which is very close to the inverse square-root relationship predicted in Eq. 12. Further work is required to examine how fracture interaction and other effects influence aperture to length scaling, particularly the effects of limited fracture height. However, this simple analysis brings into question the validity of the linear scaling law and suggests sub-linear scaling may be a more reasonable model.Core-based Measurements of Fracture Mechanics PropertiesGeomechanical predictions of fracture attributes need some constraints to be used for subsurface reservoir characterization. One parameter we have identified that strongly controls fracture pattern development is the subcritical crack index. The laboratory measurement of subcritical crack behavior in rock is performed using the double torsion testing method.A large number of subcritical index measurements have been reported for a variety of rock types,but few measurements have been made from subsurface reservoir rocks and no systematic studies of petrographic or diagenetic controls of subcritical crack propagation have been reported.In ongoing studies of natural fractures in sedimentary rock, we are carrying out suites of measurements on core and outcrop samples from several different formations in which there are known variations in petrographic properties such as porosity, mineralogy, and intergranular cement. Correlations between the subcritical index and petrographic properties are needed to predict mechanical properties where measurements are not available and to correct present-day measurements for the diagenetic changes that have occurred since the time of fracturing.以断裂力学核心属性为基础的测量断裂力学预测需要一些可用于地下储层特征的约束属性。
托福阅读文章结构划分最全解读托福阅读如何才能快速又高效呢?本文将详细解答托福阅读文章的结构划分，帮助正在备考托福中认为托福阅读索然无趣的同学，快速找到解答托福阅读的方法。
托福阅读文章结构划分最全解读在官方指南当中，ETS给出了托福阅读的常见四种结构，下面我们就来分别看一看：第一种，因果类文章结构，也就是全文都是围绕着某个现象进行解释。
典型文章desert formation，在文章开头的第一段就出现这样的内容：The deserts, which already occupy approximately a fourth of the Earth's land surface, have in recent decades been increasing at an alarming pace. The expansion of desert-like conditions into areas where they did not previously exist is called desertification. 首先对沙漠的现状进行了描述，紧接着就赶紧扣题下定义，告诉我们什么是沙漠化。
现象交代完了之后，出题段的第三段就迅速展开了原因的描述，我们发现第三段和第五段开头分别是这样的：Even in the areas that retain a soil cover, the reduction of vegetation typically results in the loss of the soil's ability to absorb substantial quantities of water. 以及There is little doubt, however, that desertification in most areas results primarily from human activities rather than natural processes.这样就交代了两个原因，分别是loss of vegetation和soil’s ability to absorb water. 同学们读到这里就要开始有预判断了，预料下面是否开始说一些其他的原因呢?带着这样的疑问去看，发现第六段说的是：Four specific activities have been identified as major contributors to the desertification processes: overcultivation, overgrazing, firewood gathering, and overirrigation. 第九段针对overirrigation展开论述。
Correlations between Ground and Excited State Spectra of a Quantum DotD.R. Stewart*†, D. Sprinzak‡†, C.M. Marcus†, C.I. Duruöz*, J.S. Harris Jr.** Department of Electrical Engineering, Stanford University, Stanford CA 94305, USA† Department of Physics, Stanford University, Stanford CA 94305, USA‡ Braun Center for Submicron Research, Department of Condensed Matter, Weizmann Institute of Science,Rehovot 76100, IsraelWe have studied the ground and excited state spectra of a semiconductor quantum dot for successive numbers of electron occupancy using linear and nonlinear magnetoconductance measurements. We present the first observation of direct correlation between the m th excited state of the N electron system and the ground state of the N+m electron system for m up to 4. Results are consistent with a non-spin-degenerate single particle picture of the filling of levels. Electron-electron interaction effects are also observed as a perturbation to this model. Magnetoconductance fluctuations of ground states are shown as anticrossings where wavefunction characteristics are exchanged between adjacent levels.Quantum dots (QDs) are small electrically conducting regions, typically a micrometer or less in size, containing from one to a few thousand electrons (1). Due to the small volume, the allowed electron energies within the dot are quantized, forming a discrete spectrum of quantum states, not unlike the energy levels of an atom. However, in contrast to the ordered shell structure of atomic spectra—a consequence of the spherically symmetric potential that binds the electrons—the generic energy spectrum of a QD (lacking any special symmetry) shows no shell structure, but instead possesses universal statistical properties associated with the underlying universality of quantum chaos (2).Disordered or irregularly-shaped QDs are examples of so-called mesoscopic systems—small electronic structures intermediate in size between atoms and macroscopic (classical) objects that possess universal spectral and transport properties, independent of material, shape or disorder. In the past few years, a remarkable set of connections between mesoscopic systems, complex quantum systems such as heavy nuclei (where the statistical approach to spectra was first developed), quantum systems whose classical analogs are chaotic, and random matrix theory has emerged, providing deep theoretical insight into the generic properties of quantum systems (2). These connections are based principally on noninteracting single-particle spectral properties; only recently has attention been focused on mesoscopic systems in which interactions between particles and interference play equally important roles. It is in this context that the generic spectral features of multi-electron QDs are of great interest.The electronic spectra of QDs are governed by the interplay of two energy scales: the Coloumb interaction or charging energy associated with adding a single electron to the dot, and the confinement energy associated with quantization due to the confining potential. In lateral semiconductor QDs the charging energy is typically an order of magnitude larger than the quantum confinement energy, leading one to expect that the quantum spectrum of the N+1 electron QD should be uncorrelated with the spectrum of the N electron QD (1).Previous investigation of QD spectra via transport and capacitance spectroscopy has concentrated on analysis of the 'addition' energy spectrum composed of the ground states of the QD for successive numbers of electrons (1,3,4,5). Several experiments (6,7,8,9) have also probed the 'excitation' spectrum of quantum levels in the QD for fixed electron number using nonlinear conductance measurements. These measurements showed spectral features attributed to electron-electron interactions such as spin blockade (8) and clusters of resonances identified with a single excited state (9). Many-body calculations for few electron systems (N≤5) have explained some of the experimentally observed features in terms of spin and spatial selection rules (10), spectrally dominant center-of-mass excitation modes (11) and non-equilibrium effects (12). Very recently, ground and excited state spectra were both investigated in a circular, few-electron quantum dot (13).We present an experimental study of correlations between ground state addition spectra and excitation spectra of an irregularly shaped QD containing several hundred electrons. We find that excitation and addition spectra for successive electron occupancies are remarkably correlated, agreeing in many respects with a non-interacting picture in which electrons simply fill the excited states, so that addition and excitation spectra coincide. Departures from this single particle model are also observed, giving insight into the electron-electron interaction strength. Additionally, we observe that spin degeneracy appears absent in the QD spectrum.Measurements were performed on a quantum dot defined by applying ~ -0.3 V to Cr/Au electrostatic gates on the surface of a GaAs/AlGaAs heterostructure (inset Fig. 1B), depleting a two dimensional electron gas (2DEG) 900Å below the surface. The ungated2DEG mobility and density were 1.4x105cm2/Vs and2.0x1011cm-2 at 4.2K. Differential conductanceg = dI/dV DS of the QD in the Coulomb blockade (CB) regime (1) was measured in a dilution refrigerator using ac lock-in techniques with a 6 µV ac excitation added to a dc bias in the range ±1.5 mV. Measurements were made as a function of gate voltage (V G), drain-source d c bias (V DS) and magnetic field (B) applied perpendicular to the 2DEG plane. The experimental gate voltage was scaled to dot energy using both the nonlinear CB peak width (~ eV DS+3.5k B T) at finite V DS and independently by a fit of CB peak widths at V DS = 0 as a function of temperature (14). The electron temperature in the dot was 90±10mK (k B T ~ 8 µeV) as determined from the FWHM of linear CB peaks. The mean energy level spacing in the dot measured from the excited state spectra (discussed below) is ∆ ~ 35 µeV, providing an estimate of the dot area, A m=πh2/*∆ ~ 0.1 µm2 (m* is the electron effective mass). This area is consistent with the lithographic area allowing ~ 150 nm lateral depletion, and yields an occupancy of electrons in the dot N ~ 200. All magnetoconductance measurements were performed in the regime g < 0.3 e2/h, and in the regime of single electron transport, i.e. 0 < |eV DS| < E C, where E C ~ 730 µeV is the classical charging energy of the QD measured from linear CB peak spacings.A typical nonlinear differential conductance measurement through the QD as a function of V G and V DS is shown in Fig. 1A. At V DS = 0 we observe the familiar CB peaks, approximately equally spaced in V G. Increasing V DS results in broadening of the CB peaks to form multiple peak structures (6, 7) enclosing so-called 'Coulomb diamonds'. The central areas of the Coulomb diamonds (white in Fig. 1A) correspond to the blockade regime of zero conductance and fixed electron number. Dark stripes parallel to the Coulomb diamond edges in Fig. 1A are peaks in the differential conductance; each stripe represents the transmission resonance of a single QD level aligned with the source or drain Fermi levels (8). For positive V DS we identify the resonances parallel to the negative slope Coulomb diamond edge as unoccupied QD levels in resonance with the source, namely such peaks correspond to electrons tunneling into subsequent unoccupied states of the QD.The first evidence of correlations between the excitation spectra of the N and N+1 electron systems can be seen in Fig. 1B, where the dark stripes of Fig. 1A are visible as multiple resonances on the left edge of each broadened CB peak. Each broadened CB peak shows a tall peak with one, two, three or four smaller peaks to its left. We identify the tall peak as the first, second, third or fourth excited state resonance of the N+3, N+2, N+1, or N electron system, respectively. At low temperature, k B T « ∆(∆/k B T ~ 4 in our dot) the peak height for each resonance is simply modeled as proportional to the overlap of the wave function in the dot with the source and drain wave functions (14).Thus, the shift of the distinctive tall peak by one position in each successive excitation spectrum suggests that the particular electron wave function associated with this peak and the overall level structure of the dot near the Fermi surface are only weakly perturbed as electrons are removed one by one.In order to confirm this correlation between excitation spectra of adjacent CB peaks, we follow the evolution of each resonance within a broadened CB peak as a function of magnetic field, B. The continuous evolution of resonance position and height with B yields a distinct signature or 'fingerprint' for each quantum level, and collectively for each excitation spectrum. Figure 2 shows three broadened CB peaks evolving with B, at fixed V DS. We observe the striking effect that the fingerprints of the N-1, N, and N+1 excitation spectra display shifted versions of the same level structure; for each electron removed from the dot one extra level is visible at the top of each spectrum. This shifting agrees with a non-interacting description of the QD in which a fixed spectrum is filled one level at a time.Figures 2B and 2C detail the labeling of the QD levels for the data of Figs. 1 and 2A. The dark stripes of Fig. 1A are identified by color as subsequent QD levels in resonance with the source fermi level. Figure 2B shows the state of the system after an electron has tunneled onto the QD from the source and before it has tunneled off to the drain, for the V G bias which aligns each ground state with the source. Increasing V G (lowering the dot potential well) brings higher excited states into resonance with the source. For the broadened CB peak separating the N-2 and N-1 Coulomb diamonds (red in Fig. 2A) we label these higher resonances as excited states of the N-1 electron system, and show the B field fingerprint of this N-1 excitation spectrum in Fig. 2A. This sequential labeling is understood to be approximately correct (we neglect non-equilibrium effects, which are not resolvable presumably due to thermal broadening (8, 12)). Negative differential conductance peaks are also observed in our data but will not be described here.Further understanding of the QD spectral properties is obtained by comparing the fingerprints of ground state addition spectra measured at V DS = 0 to that of neighboring excitation spectra, measured at finite V DS. Six peaks, labeled N-3 to N+2 in Fig. 3A (where peak N represents the degeneracy between electron numbers N and N-1) show the fingerprints of several consecutive ground states, for different surface gate voltages and thus a different QD shape than in Figs. 1 and 2. Individual ground states show large peak height and position fluctuations, with the expected symmetry about B = 0. In Fig. 3C we collapse this group of levels, originally separated by E C, by shifting each trace in energy (gate voltage) until they best align with adjacent levels. By doing so we assume a Coulomb interaction independent of B. Remarkably, such translation of the ground states produces a recognizable spectrum coherent over manylevels, in which the fluctuations of height and position are visible as anti-crossings of neighboring levels. The specific signature of each anti-crossing is that two successive levels appear to trade both conductances and velocities ∂E/∂B as they pass through their point of closest approach (15). This assembled spectrum of fluctuating ground states appears to be composed of slowly varying wave functions as followed through anti-crossings, slightly perturbed into the measured anti-crossed level structure.Finally, we compare the assembled ground state spectrum to measured excited state spectra of the same peaks. Figures 4A and 4B compare the N th CB peak at finite bias, showing structure that corresponds to the excited state spectrum of the N-electron QD, to the N th and N+1th peaks at zero-bias shifted in the same way as in the assembled spectrum of Fig. 3C. One can observe that the magnetoconductance fingerprint of the N th zero-bias CB peak matches the resonances at both the top and bottom of the N th finite bias CB peak, since all three are identified with the ground state of the N electron system. More significantly, the N+1th zero-bias CB peak (ground state) matches closely the second resonance (first excited state) of the N th finite bias peak in position, height and relative spacing between the levels. We emphasize that the observed correspondence between the N+1th ground state and the N th first excited state is trivially implied by a non-interacting electron model, but is not obvious in a strongly interacting system.Despite the overall consistency of the observed addition and excitation spectra with a single-particle picture, there are some important departures that arise presumably due to electron-electron interactions. Figure 4C shows the finite bias structure corresponding to the excited states spectrum of the N-1 electron system, while Fig. 4D displays the N-1th, N th and N+1th zero bias peaks shifted in energy from Fig. 3B to best match the N-1 excited state spectrum. The relative position of the N th and N+1th levels in Fig. 4D differs considerably from that in Fig. 4B. The N+1th ground state has been shifted from its alignment of Fig. 4B (same as Fig. 3C) until it is overlapping and even changing places with the N th ground state. This apparent 30 µeV shift of the N+1th level is comparable to the average level spacing of 35 µeV, and indicates that while levels may undergo an overall shift in energy as one electron is added, the level ‘fingerprint’ (position and height fluctuations in B) appears largely unchanged. Smaller, similar shifts in level spacings exist in almost all neighboring excitation spectra. Additionally, some resonances show a trend of broadening at higher excited state energies similar to (9).Another departure from the simple single particle picture is the absence of spin-degenerate pairs of levels. Previous measurements on few-electron semiconductor QDs (5) and ultrasmall metal QDs (9) showed spin degenerate level spectra, whereas in-plane magnetic field measurements of a multi-electron semiconductor QD suggested no spin degeneracy (8). In our results the appearance of one new resonance in the excitation spectrum per electron removed from the QD indicates that energy levels in the dot are not spin degenerate. To estimate the energy splitting between spin paired levels, we examine the spectrum for levels with identical fingerprints. Figure 3B shows that each ground state level has a different fingerprint, implying none are spin paired. In Fig. 3C however, some of the slowly varying wave functions followed through anti-crossings do appear parallel suggesting that spin pairing may be visible in this underlying spectrum. We infer in either case that the energy splitting between spin paired wave -functions is larger than the mean single particle spacing,∆ ~ 35 µeV. This energy splitting determines the scale of the spin-orbit (16) or electron-electron interaction responsible for the absence of degeneracy.In conclusion, we have demonstrated for the first time that strong correlations exist between the QD energy level spectra of successive electron numbers in the dot, probed via magnetotransport measurements. The excitation spectra of adjacent CB peaks are found to be shifted versions of a very similar spectrum, with the addition of one excited state per electron removed from the dot. These results suggest a single particle model of the QD spectrum with no spin degeneracy. Departures from this single particle model are attributed to electron-electron interactions.We thank B. Altshuler, D. Ralph and M. Heiblum for useful discussions. We thank S. Patel and A. Huibers for valuable help throughout the measurements. We gratefully acknowledge support from JSEP under Grant DAAH04-94-G-0058, the Army Research Office under Grant DAAH04-95-1-0331, the Office of Naval Research YIP program under Grant N00014-94-1-0622, and the NSF-NYI program. One of us (DS) acknowledges the support of MINERVA grant. ____________________________________________ 1.L. P. Kouwenhoven, et al., in Proceedings of theAdvanced Study Institute on Mesoscopic Electron Transport L. L. Sohn et al. Eds. (Kluwer, 1997);U. Meirav, E. B. Foxman, Semiconductor Science and Technology10, 255-284 (1995).2.For recent reviews discussing the connectionbetween mesoscopic physics and quantum chaos, see: B. L. Altshuler and B. D. Simons, in Mesoscopic Quantum Physics, edited by E.Akkermans, G. Montambaux, J.-L. Pichard, and J.Zinn-Justin (Elsevier, Amsterdam, 1995); T. Guhr,A. Mueller-Groeling, and H. A. Weidenmueller,cond-mat/9707301, (1997); Mesoscopic physics and random matrix theory are discussed in C. W. J.Beenakker, Rev. Mod. Phys. 69, 731 (1997). For a general introduction to quantum chaos, see: M. C.Gutzwiller, Chaos in Classical and Quantum Mechanics (Springer-Verlag, New York, 1990).3.P. L. McEuen, et al., Phys. Rev. Lett.66, 1926(1991); P. L. McEuen, et al., Phys Rev. B45,11419-11422 (1992).4.R. C. Ashoori, et al., Surface Science305, 558-565 (1994).5.S. Tarucha, D. G. Austing, T. Honda, R. J. van derHage, L. P. Kouwenhoven, Physical Review Letters77, 3613-3616 (1996).6. A. T. Johnson, L. P. Kouwenhoven, W. de Jong,N. C. van der Vaart, C. J. P. M. Harmans, Physical Review Letters69, 1592-5 (1992).7. E. B. Foxman, et al., Physical Review B(Condensed Matter)47, 10020-10023 (1993); P.L. McEuen, et al., Physica B189, 70-79 (1993).8.J. Weis, R. J. Haug, K. von Klitzing, K. Ploog,Physical Review Letters71, 4019-4022 (1993). 9. D. C. Ralph, C. T. Black, M. Tinkham, PhysicalReview Letters78, 4087-4090 (1997).10.K. Jauregui, W. Häusler, D. Weinmann, B. Kramer,Physical Review B (Condensed Matter)53, R1713-R1716 (1996); D. Weinmann, W. Häusler, B.Kramer, Physical Review Letters74, 984-987(1995).11.D. Pfannkuche, S. E. Ulloa, Physical ReviewLetters74, 1194-1197 (1995).12.O. Agam, N. S. Wingreen, B. L. Altshuler, D. C.Ralph, M. Tinkham, Physical Review Letters78, 1956-1959 (1997).13. L. P. Kouwenhoven, T. H. Oosterkamp, M. W. S.Danoesastro, M. Eto, D. G. Austing, T. Honda, S.Tarucha, condmat/970822914.C. W. J. Beenakker, Physical Review B (CondensedMatter)44, 1646-56 (1991).15.T. Takami, Physical Review Letters68, 3371-3374(1992).16.P. Pfeffer, W. Zawadzki, Physical Review B52,R14332-R14335 (1995).Figure 1. Coulomb diamonds: (A) Differential conductance, g, as a function of drain-source voltage, V DS, and gate voltage, V G, in a gray scale where black is large g. The white diamonds are blockade regions where electron number is fixed. Dark diagonal stripes (peaks) parallel to the diamond edges correspond to QD levels in resonance with the source or drain fermi levels. The magnetic field is 30 mT. (B) One trace from Fig. A at V DS = 570 µV. The distinctive high peak appears as the 2nd resonance from the left (1st excited state) on the rightmost CB peak and shifts to the 3rd, 4th and 5th (not resolvable) resonance (2nd, 3rd and 4th excited states) as the electron number decreases. Decreasing average g is attributed to capacitive coupling between V G and adjacent surface gates. Inset: A scanning electron micrograph of the QD studied.Figure 2. Excitation spectracorrelations: (A) Differential conductance, g, of the three broadened CB peaks separating the N-2, N-1, N and N+1 Coulomb diamonds as a function of gate voltage, V G ,and applied magnetic field, B, in color scale where yellow is large g. Fixed drain-source bias V DS = 570 µV. The resonance pattern of each CB peak corresponds to the excitation spectrum of the N-1,N or N+1 electron QD. As each electron is removed a new resonance is introduced and the rest of the spectrum shifts by one level. Energy scale is inverted in this figure only. (B)Schematic energy diagrams of the source-QD-drain system,with N-1, N or N+1 electrons in the QD. Filled circles indicate occupied levels in the dot. The QD is illustrated with the N-1, N or N+1 level in resonance with the source fermi level.Increasing V G increases the dot potential well depth and brings higher levels into resonance with the source. (C) Coulomb diamond schematic, with colored stripes corresponding to colored levels in Fig. B, and black squares illustrating the specific gate bias V G of each diagram in Fig. B. The three yellow planes correspond to the data of Fig. A. Resonance stripes parallel to the positive slope Coulomb diamond edge are not illustrated as they are not clearly resolved in our data.G-105-20-15-10-50.1-200-10010020030252015DSDSDS(B)(A)Figure 3. Ground state spectra: (A) Six adjacent CB peaks at V DS = 0 in gray scale showing both position and height fluctuations as a function of B. The gray scale of g for each trace is normalized to the maximum g of that trace. (B) Trace N shown as raw data and the corresponding gray scale plot. (C) The six traces of Fig. A are shifted vertically to best align with each other, forming a spectrum with visible anti-crossings of adjacent levels.Figure 4. Comparing ground and excited state spectra: (A) The magnetic ‘fingerprint’ of the N th CB peak at V DS = 570 µV. Visible resonances at the bottom of the peak correspond to the excitation spectrum of the N electron QD. (B) The N th and N+1th zero bias CB peaks, shifted as in Fig. 3C. The N th peak matches both edges of the finite bias peak in A, and the N+1th peak matches the second resonance (first excited state) in Fig. A. A similar match between the excitation spectrum of the N-1 electron system and the N-1, N, N+1 ground states is done in (C) and (D). Note the relative position of the N th and N+1th peaks is different than in Fig. B.。
