A New Measurement of the Energy Dependence of Nuclear Transparency for Large Momentum Trans

小学上册英语第1单元期末试卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The _______ can help create a relaxing environment.2.What is the name of the famous painting of a woman with a mysterious smile?A. The ScreamB. The Birth of VenusC. The Girl with a Pearl EarringD. The Mona LisaD3.The _______ (兔子) hops quickly away.4.Cleopatra was the last active ruler of _______.5.Understanding a plant's ______ helps in its proper care. (了解植物的需求有助于正确照顾它。

)6.The __________ (大萧条) caused widespread unemployment in the 1930s.7.What is the opposite of day?A. MorningB. NightC. EveningD. AfternoonB8.We need to __________ our project.9.My friend is very ________.10.My uncle loves to share his __________ (经验) in cooking.11.What do we call a group of stars forming a pattern?A. GalaxyB. ConstellationC. NebulaD. ClusterB12.The turtle moves very _______ (乌龟的动作很_______).13.She is a _____ (模特) in fashion shows.14.What is the capital city of Kenya?A. NairobiB. KampalaC. Addis AbabaD. Dar es SalaamA15.sh-American War resulted in the U.S. acquiring ________ (菲律宾). The Sphi16.I enjoy _____ (reading/writing) stories.17.The _____ (电脑) is new.18.What is the capital of Nigeria?A. AbujaB. LagosC. Port HarcourtD. KanoA19. A ______ is a natural opening in the Earth’s crust through which gases and lava escape.20.What is the name of the famous painting of a woman with a mysterious smile?A. The Girl with a Pearl EarringB. Mona LisaC. The Birth of VenusD. The Last SupperB21.I want to learn how to _______ (游泳) better.22.Which of these is a type of nut?A. AlmondB. PotatoC. AppleD. CarrotA23.The main gas produced during cellular respiration is _______.24.The capital city of Bhutan is ________ (不丹的首都城市是________).25.My teacher has a ______ (鹈鹕) that catches fish.26.My cousin is a great ____ (chef).27.What do you call a young crocodile?A. HatchlingB. PupC. CalfD. Kit28.The _____ (hill) is covered in wildflowers.29.The ancient Egyptians worshipped many _____.30.We have a _______ (家庭聚会) this Saturday.31.My friend is very ________.32.The movie was very ___. (funny)33. A ________ is a large area of land with few trees.34.What do we call a person who studies the origins of words?A. EtymologistB. LinguistC. LexicographerD. PhilologistA35.I can ________ my toys.36.My friend is my silly _______ who makes me laugh.37.My ________ (玩具名称) is a fun way to express myself.38.The ________ (workshop) enhances learning.39.The _____ (ancient) Greeks made significant contributions to philosophy.40.My cousin is a great __________ (活动组织者).41.How do you say "friend" in German?A. FreundB. AmigoC. PalsD. Compagnon42.I like to ________ in the rain.43.I love to play in the _________ (游乐场) with my _________ (玩具).44.We are having ______ at the picnic tomorrow. (sandwiches)45.The chemical symbol for gallium is _______.46.The Sahara is the largest ________ in the world.47.My father helps me with my __________. (作业)48.The unit of measurement for mass is called a ______.49.What is the main gas we breathe?A. OxygenB. Carbon DioxideC. NitrogenD. HydrogenA50.The main gas produced during cellular respiration is ______.51.The ______ helps with the digestion of carbohydrates.52.The _______ (Amendments) to the Constitution are the changes made to the original document.53.The chemical properties of a substance depend on its _____.54.The ancient Egyptians had a unique system of ________ (书写).55.What is the capital of the United Kingdom?A. LondonB. EdinburghC. DublinD. Cardiff56.The _______ (山羊) bleats softly.57.The __________ (历史的传承) shapes future identity.58.What is the name of the famous American musician known for "Purple Rain"?A. Michael JacksonB. PrinceC. Bruce SpringsteenD. Elvis PresleyB59.The ancient Egyptians believed in many _______. (神灵)60.The dog is _____ (barking).61.The bear hibernates during the _____ winter.62.The chemical symbol for calcium is _______.63.What is 3 x 3?A. 6B. 7C. 8D. 9D64.I see a _____ frog by the pond. (green)65.The discovery of ________ has had wide-ranging impacts on industry.66.The pizza is very _____. (yummy)67.My cousin is a great __________ (作曲家).68.What do you call a type of music with a strong rhythm?A. ClassicalB. JazzC. RockD. Pop69.What is the capital of the United States?A. New YorkB. Washington D.C. C. Los AngelesD. Chicago70.The ______ is known for her environmental advocacy.71.I have a _____ (手链) that I made with colorful beads. 我有一个用彩色珠子制作的手链。

Professional and Academic Skills(PAS)-2Week-3Quantitative Data Analysis- Questionnaire Design andLevel MeasurementDate: 10/02/2020v Collecting Quantitative Data using Questionnaire v Questionnaire Designv Pilot Questionnairev Level of Measurement: Categorical Variable and Continuous Variablev Identify the main issues that you need to consider when preparing quantitative data for analysisCollecting Primary Data using QuestionnaireØQuestionnaire:“is a method/technique of data collection in which each person is asked to respond to same set of questions in a predetermined order”(De Vaus, 2014)Ø “It also widely used as an instrument” (Ekinci, 2015)ØIt provides efficient way of collecting responses from a large sample prior to quantitative analysisTypes of QuestionnaireSource: Saunders (2016)Advantages and disadvantages of questionnaireAdvantages◦Large sample size – can be collected relatively quickly◦Cost effective- large sample of the population can be contacted at relative cost◦Analysis easier and visualisation – closed questions are easier to analyse◦Anonymity- allows respondents to maintain their anonymity◦If completed anonymously and in private then personal questions may receive more valid answersDisadvantages◦Difficult for respondents to provide deep reasons behind consumers behaviour◦Unanswered questions- some questions will be ignored and left unanswered◦Dishonest answer- they may not be 100% truthful with their answers◦Respondents under no/little pressure to complete and return◦No flexibility re questions posed and no supplementary options available-Things to Consider to Produce a Good QuestionnaireüTo ensure that it will collect precise data that you require to answer your research question(s) and your research objectivesüYou are unlikely to have more than one opportunity to collect the dataüDesign of your questionnaire will affect the response rate and the reliability of the data you collect (clear, specific and unambiguous)üEasy questions at the start and open questions at endüFar more closed than open questionsü Types of questions you need to ask to collect your dataüNumber of questions you need to ask to collect your dataüVisual presentation of the questionnaire- Colourful, artistic appearance of the questionnaireValidity and ReliabilityValidity: refers to the ability of your questionnaire to measure what you intend to measure also know as measurement validity.Reliability- refers to the consistency of the research method used, For example if the same method was used again would it lead to the same data collected.For a questionnaire to be valid it must be reliableValidity and reliability of the data you collect and the response rate you achieve depend largely on the:- Design of your questions- Structure of your questionnaire- and the rigor of your pilot testingFactors that can impact ReliabilityØParticipants errorØParticipants biasØResearcher errorØResearcher biasHow many questions should a questionnaire have?◦For your MA dissertation time taken to complete the questionnaire should not exceed 10 -12 minutes.◦Effective design of the questions should allow you to include all necessary questions for your final project and should consist maximum 15-20 questions.How many need to be collected ?◦Around a minimum of 100 for your MA dissertation when conducting a mono method.Constructing your Questions- Closed and Open questionsOpen questions- refer to as open ended questions, allow respondents to give answers in their own wayFink (2013) Closed questions- refer to closed-ended questions or forced-choice questions, provide a number of alternative answers from which the respondent is instructed to choose. It is easier,quicker and require minimal writingThere are 6 types of closed questions:List question: where the respondent is offered a list of items, any of which may be selectedCategory question: where only one response can be selected from a given set of categoriesRanking question: where the respondent is asked to place something in orderRating question: in which a rating device is used to record responsesQuantity question: to which the response is a number giving the amountMatrix question: where responses to two or more questions can be collected using the same gridSource: Saunders, 2016Rating /Likert Scale questionsCategory questionQuantity questionSemantic differential Rating question- Series of bi-polar adjectives between which underlined spaces areprovided for the recipient to record their views/feelings.Example of Rank questionExample of Matrix QuestionConstructing the QuestionnaireØExplaining the purpose of the questionnairev Covering letter or welcome screen:self-completed questionnaires should be accompanied by a covering letter, email, text or SMS message which explains the purpose of of the surveyv Introducing the questionnaire- explain clearly and concisely why you want the respondents to complete the surveyExample of Introduction for Interviewer-completed questionnaire….Lavrakas, 2016Closing the QuestionnaireØ at the end of the questionnaire you will need to explain clearly what you want your respondents to do with their completed questionnaire.Example:Saunders, 2016Pilot Testing and Assessing ValidityThe purpose of the pilot testing is to refine questionnaire so that the respondents will have no problems in answering the questions and there will be no problem in recording the dataØIt helps you to obtain some assessment of the questions, validity and likely reliability of the dataØTo ensure that the data collected will enable your investigative questions to be answeredØfor student questionnaire minimum number of a pilot is 10 (Flink, 2013)To ensure questionnaire’s face validity, as part of your Pilot you should try to get additional information about (Bell and Waters, 2014)-üHow long the question took to completeüthe clarity of the instructionüWhich, if any, questions were ambiguousüWhich, if any, question the respondents felt uneasyüwhether in the layout was clear and attractiveüany other commentsInternet QuestionnaireFor both Web and Mobile questionnaire:ØIt is important to have clear timetable that identifies the tasks need to be doneØA good response will depend on the recipient being motivated to answer the questionnaire and to send it backØEmail or SMS message and visual appearance will help to ensure a high level of responseØQuestionnaire design must be clear across all display mediaData collection- what to measureIf you intend to undertake quantitative analysis then you should consider:v The number of cases of data (sample size)v Type or types of data (scale of measurement)v Data layout and format required by the analysis softwarev Impact of data coding on subsequent analysis (for different types ofdata)v Process and checking the data error (checking your data for out of range values)When you collect data you need to decide on two thingsv What to measurev How to measureWhat to Measurev Usually we collect several measures on each person or thing of interestv Each thing we collect data about is called an observationv Each observation can be a person or an organisation, a product or a period in time Factual or demographic variables- age, gender, education, occupation, incomeAttitudes or opinion variables- record how respondents feel about something, or what they think is true or falsev Behaviour or event variables- contain data about what people did or what happened in past, happening or will happen in the future.Data collection- what to measure continue …..VariablesObservations Age SexIncome Brand preference 20Female 10,000Zara 30Female 35,000Cartier25Male 25,000 SuperdryLevel of MeasurementLevel of measurement: is the relationship between what is being measured and the numbers that represent what is being measured Variables can take many forms and levels. Quantitative data can be divided into two distinct groups:v Categorical variable◦Descriptive or Nominal data◦Ranked datav Numerical variable◦Continuous data◦Discrete DataCategorical DataCategorical data- refer to data whose values can not be measured numerically but can be classified into sets (categories) according to the characteristics that identify or describe the variable or placed in rank order (Brown and Saunders, 2008)i.e. your species (human, domestic cat, fruit bat), race, sex, age group, and educational levelv Descriptive/Nominal data- these data simply count the number of occurrences in each category of a variable. (a car manufacturer may categorize the types of cars as hatchback, Saloon and estate)Binary/dichotomous variable: a sub-type of nominal scale with only two categories.It names two distinct types of things such as: Male or Female, Dead or Alive; Yes or NoCategorical Data continuous…….v Ranked/ordinal variable- precise form of categorical data. When categories are ordered, the variable is known as an ordinal variable.v Ordinal variables will tell us the things that happenedv The order in which things occurredv But this data will not tell us differences between the values/points on a scaleExample 1- beauty pageant winners- first, second and thirdExample-2 : satisfaction levelUnsatisfied Very unsatisfied Very Satisfied Satisfied Somewhatsatisfied123 45Examples of Nominal and ordinal DataNumerical Variablev Numerical variables are those whose values are measured or counted numerically as quantities . (Brown and Saunders, 2008).v These data are more precise than categorical data as you can assign each data valuea position on a numerical scaleTypes of Numerical variable:v Continuous variable-a variable that has a changing value and it can take on infinitely many, uncountable number. i.e. time, a person’s weight, Age, number of customers etcv Interval data: for data to be interval, we must be certain that data on scalerepresent equal differences in the property being measured. (i.e. measure averageday time temperature during summer in London- 60-70 degrees Fahrenheit, 80-90….)Numerical Data continues ……v Ratio data : a ratio variable has all the properties of an interval variable, and also has an absolute value of 0.v Discrete variable- can take only certain values. Usually the whole number on the scale. i.e.v Example:rating your confidence level on 5 point scale.Number of Customers-12Number of shops- 10Number of friends- 8Stress Level0 1 2 3 4 5 6 7 8 9 10Seminar ActivityActivity-1:Demonstrate your choice of data collection method(s) that you plan to adopt in your study.Activity-2-In small groups, discuss about different types of questionnaire and which one you are likely to use.- What are the main attributes of questionnaires discussed on this PPT?-What scale of measurement questions you are likely to use in you questionnaire, provide at least three examples of Rating scales questions.。

新《物理专业英语》范围单词篇1 、加速度acceleration2 、速度 velocity3 、角速度 angular velocity4 、角动量angular momentum5 、热量 amount of heat6 、热力学第一定律 the first law of thermodynamics7 、干涉 interference8 、反射 reflection9 、折射 refraction10 、振幅 amplitude11 、机械运动 mechanical motion12、保守场 conservative field13 、向心力 centripetal force14、保守力 conservative force15、摩擦力 friction force16 、面积area17 、体积 volume18、阿伏加德罗常数 Avogadro constant19 、绝对零度 absolute zero20 、电势能 energy of position21、重力势能 gravitational potential energy22 、重力场 the field of gravity force23 、真空中的磁场 magnetic field in a vacuum24 、电磁波 electromagnetic wave25 、电流的相互作用interaction of current1、（第3页）第四段的第3句A typical problem of mechanics consists in determining the states of a system at all the following moments of time t when we know the state of the system at a certain initial moment to and also the law governing the motion.翻译：机械运动的一个典型的问题的构成取决于一个系统在接下来的时间间隔t的状态，（因此）当我们知道了一个确切的最初的系统状态时，也可以知道运动的规律。

核专业英语段落翻译南华大学，核科学技术学院，崔爽OUR MA TERIAL world is composed of many substances distinguished by their chemical, mechanical, and electrical properties. They are found in nature in various physical states—the familiar solid, liquid, and gas, along with the ionic “plasma.” However, the apparent diversity of kinds and forms of material is reduced by the knowledge that there are only a little more than 100 distinct chemical elements and that the chemical and physical features of substances depend merely on the strength of force bonds between atoms.We recall that this energy may be released by heating of solids, as in the wire of a light bulb; by electrical oscillations, as in radio or television transmitters; or by atomic interactions, as in the sun. The radiation can be viewed in either of two ways—as a wave or as a particle—depending on the process under study. In the wave view it is a combination of electric and magnetic vibrations moving through space. In the particle view it is a compact moving uncharged object, the photon, which is a bundle of pure energy, having mass only by virtue of its motion.A COMPLETE understanding of the microscopic structure of matter and the exact nature of the forces acting is yet to be realized. However, excellent models have been developed to predict behavior to an adequate degree of accuracy for most practical purposes. These models are descriptive or mathematical, often based on analogy with large-scale processes, on experimental data, or on advanced theory.The emission and absorption of light from incandescent hydrogen gas was first explained by Bohr with a novel model of the hydrogen atom. He assumed that the atom consists of a single electron moving at constant speed in a circular orbit about a nucleus—the proton成。

•短语英汉互译• 1. parameter design 参数设计• 2. quality engineering 质量工程• 3. loss function 损失函数• 4. process capability index 过程能力指数• 5. standard deviation 标准差，均方差• 6. tolerance interval 容许区间•7. normal distribution 正态分布•8. correction coefficient 校正系数•9. data bank 数据库•10. chance variable 随机变量•短语英汉互译•11. parameter design 参数设计•12. probability density function 概率密度函数•13. tolerance design 公差设计•14. preventive maintenance 预防性维修，定期维修•15. data processing 数据处理•16. coefficient of regression 回归系数•17. quality loss 质量损失•18. chance error 随机误差•19. product planning 产品策划•20. system design 系统设计•短语英汉互译•21. specification 规格•22. percent defective 不合格率•23. variance 方差•24. probability distribution 概率分布•25. bilateral tolerance 双向公差•26. dimension 尺寸，维度•27. product design 产品设计•28. service after purchase 售后服务•29. classified variable 分类变量•30. common variance 公共方差•31. characteristic vector 特征向量•短文英译汉•Top management shall review the organization’s quality management system at planned intervals to ensureits continuing suitability, adequacy and effectiveness. This review shall include assessing opportunities forimprovement and the need for changes to the quality management system, including the quality policy and quality objectives. Record from management review shall be maintained.•短文英译汉•最高管理者应按策划的时间间隔评审质量管理体系，以确保其持续的适宜性、充分性和有效性。

考研翻译必背词汇（红色部分为必背词汇）1990 年英译汉试题People have wondered for a long time how their personalities，and behaviors are formed. It is not easy to explain why one person is intelligent and another is not，or why one is cooperative and another is competitive.Social scientists are，of course，extremely interested in these types of questions.(61)They want to explain why we possess certain characteristics and exhibit certain behaviors. There are no clear answers yet，but two distinct schools of thought on the matter have developed. As one might expect ，the two approaches are very different from each other. The controversy is often conveniently referred to as” nature vs. nurture”.(62)Those who support the “nature” side of the conflict believe that our personalities and behavior patterns are largely determined by biological factors.(63)That our environment has little，if anything ，to do with our abilities ，characteristics and behavior is central to this theory. Taken to an extreme，this theory maintain s that our behavior is predetermined to such a great degree that we are almost completely govern ed by our instinct s.Those who support the “nurture” theory，that is，they advocate education，are often called behaviorists. They claim that our environment is more important than our biologically based instincts in determining how we will act. A behaviorist，B.F. Skinner，sees humans as beings whose behavior is almost completely shaped by their surroundings. The behaviorists maintain that，like machines，humans respond to environmental stimuli as the basis of their behavior.Let us examine the different explanations about one human characteristic ，intelligence ，offered by the two theories. Supporters of the “nature” theory insist that we are born with a certain capacity for learning that is biologically determined. Needless to say ，they don’t believe that factors in the environment have much influence on what is basically a predetermined characteristic. On the other hand，behaviorists argue that our intelligence levels are the product of our experiences.(64)Behaviorists suggest that the child who is raise d in an environment where there are many stimuli which develop his or her capacity for appropriate responses will experience greater intellectual development.The social and political implication s of these two theories are profound. In the United States，blacks often score below whites on standardized intelligence tests. This lead s some “nature” proponent s to conclude that blacks are biologically inferior to whites. (65)Behaviorists ，in contrast，say that differences in scores are due to the fact that blacks are often deprived of many of the educational and other environmental advantage s that whites enjoy.Most people think neither of these theories can yet fully explain human behavior.1991 年英译汉试题The fact is that the energy crisis ，which has suddenly been officially announce d，has been with us for a long time now，and will be with us for an even longer time. Whether Arab oil flows freely or not，it is clear to everyone that world industry cannot be allowed to depend on so fragile a base. (71)The supply of oil can be shut off unexpectedly at any time，and in any case，the oil wells will all run dry in thirty years or so at the present rate of use.(72)New sources of energy must be found，and this will take time，but it is not likely to result in any situation that will ever restore that sense of cheap and plentiful energy we have had in the times past. For an indefinite period from here on，mankind is going to advance cautiously，and consider itself lucky that it can advance at all.To make the situation worse ，there is as yet no sign that any slowing of the world’s population is in sight. Although the birthrate has d ropped in some nations ，including the United States，the population of the world seems sure to pass six billion and perhaps even seven billion as the twenty-first century opens.(73)The food supply will not increase nearly enough to match this ，which means that we are heading into a crisis in the matter of producing and marketing food.Taking all this into account，what might we reasonably estimate supermarkets to be like in the year2001?To begin with，the world food supply is going to become steadily tighter over the next thirty years—even here in the United States. By2001，the population of the United States will be at least two hundred fifty million and possibly two hundred seventy million，and the nation will find it difficult to expand food production to fill the additional mouths. (74)This will be particularly true since energy pinch will make it difficult to continue agriculture in the high energy American fashion that make s it possible to combine few farmers with high yields.It seems almost certain that by2001the United States will no longer be a great food exporting nation and that，if necessity forces exports，it will be at the price of belt tightening at home.In fact，as food items will end to decline in quality and decrease in variety，there is very likely to be increasing use of flavouring additives.(75)Until such time as mankind has the sense to lower its population to the point where the planet can provide a comfortable support for all，people will have to accept more “unnatural food”.1992 年英译汉试题“Intelligence” at best is an assumptive construct—the meaning of the word has never been clear. (71)There is more agreement on the kinds of behavior referred to by the term than there is on how to interpret or classify them. But it is generallyagreed that a person of high intelligence is one who can grasp ideas readily，make distinction s，reason logically，and make use of verbal and mathematical symbols in solving problems. An intelligence test is a rough measure of a child’s c apacity for learning the kinds of things required in school. It does not measure character，social adjustment，physical endurance，manual skills，or artistic abilities. It is not supposed to—it was not designed for such purposes. (72)To criticise it for such failure is roughly comparable to criticizing a thermometer for not measuring wind velocity.The other thing we have to notice is that the assessment of the intelligence of any subject is essentially a comparative affair.(73)Now since the assessment of intelligence is a comparative matter we must be sure that the scale with which we are comparing our subjects provides a “valid” or “fair” comparison. It is here that some of the difficulties which interest us begin. Any test perform ed involve s at least three factors: the intention to do one’s best，the knowledge require d for understanding what you have to do，and the intellectual ability to do it. (74)The first two must be equal for all who are being compared，if any comparison in terms of intelligence is to be made. In school populations in our culture these assumption s can be made fair and reasonable，and the value of intelligence testing has been proved thoroughly. Its value lie s，of course，in its providing a satisfactory basis for prediction. No one is in the least interested in the marks a little child gets on his test; what we are interested in is whether we can conclude from his mark on the test that the child will do better or worse than other children of his age at tasks which we think re quire “generalintelligence”. (75)On the whole such a conclusion can be drawn with a certain degree of confidence，but only if the child can be assumed to have had the same attitude towards the test as the others with whom he is being compared，and only if he was not punished by lack of relevant information which they possess ed. 1993 年英译汉试题(71)The method of scientific investigation is nothing but the expression of the necessary mode of working of the human mind; it is simply the mode by which all phenomena are reason ed about and given precise and exact explanation. There is no more difference，but there is just the same kind of difference ，between the mental operations of a man of science and those of an ordinary person ，as there is between the operations and methods of a baker or of a butcher weighing out his goods in common scale s ，and the operations of a chemist in perform ing a difficult and complex analysis by means of his balance and finely graded weights. (72)It is not that the scales in the one case ，and the balance in the other ，differ in the principle s of their construction or manner of working; but that the latter is much finer apparatus and of course much more accurate in its measurement than the former.You will understand this better，perhaps，if I give you some familiar examples.(73)You have all heard it repeated that men of science work by means of induction（归纳法）and deduction，that by the help of these operations ，they，in a sort of sense，manage to extract from Nature certain natural laws，and that out of these，by some special skill of their own，they build up their theories. (74)And it is imagined by many that the operations of the common mind can be by no means compared with these processes，and that they have to be acquired by a sort of special training. To hear all these large words，you would think that the mind of a man of science must be constitute d differently from that of his fellow men; but if you will not be frightened by terms ，you will discover that you are quite wrong ，and that all these terrible apparatus are being used by yourselves every day and every hour of your lives.There is a well-known incident in one of Moliere’s plays ，where the author makes the hero express unbounded delight on being told that he had been talking prose（散文）during the whole of his life. In the same way，I trust that you will take comfort，and be delighted with yourselves，on the discovery that you have been acting on the principle s of inductive and deductive philosophy during the same period.(75)Probably there is not one here who has not in the course of the day had occasion to set in motion a complex train of reasoning，of the very same kind ，though differing in degree ，as that which a scientific man goes through in tracing the causes of natural phenomena.1994 年英译汉试题According to the new school of scientists, technology is an overlooked force in expand ing the horizons of scientific knowledge. (71)Science moves forward, they say, not so much through the insight s of great men of genius as because of more ordinary things like improve d technique s and tools.(72) “In short”, a leader of the new school contend s, “the scientific revolution, as we call it, was largely the improvement and invention and use of a series of instruments that expanded the reach of science in innumerable directions.”(73) Over the years, tools and technology themselves as a source of fundamental innovation have largely been ignored by historians and philosophers of science.The modern school that hails technology argue s that such master s as Galileo, Newton, Maxwell, Einstein, and inventors such as Edison attached great importance to, and derive d great benefit from, craft information and technological devices of different kinds that were usable in scientific experiments. The centerpiece of the argument of a technology-yes, genius-no advocate was an analysis of Galileo's role at the start of the scientific revolution. The wisdom of the day was derived from Ptolemy, an astronomer of the second century, whose elaborate system of the sky put Earth at the center of all heavenly motions. (74)Galileo's greatest glory was that in 1609 he was the first person to turn the newly invented telescope on the heavens to prove that theplanets revolve around the sun rather than around the Earth. But the real hero of the story, according to the new school of scientists, was the long evolution in the improvement of machinery for making eyeglasses.Federal policy is necessarily involved in the technology vs. genius dispute.(75)Whether the Government should increase the financing of pure science at the expense of technology or vice versa often depends on the issue of which is seen as the driving force.1995 年英译汉试题The standardized educational or psychological tests that are widely used to aid in selecting, classifying, assigning, or promoting students, employees, and military personnel have been the target of recent attacks in books, magazines, the daily press, and even in congress. (71) The target is wrong, for in attacking the tests, critics divert attention from the fault that lies with ill-informed or incompetent users. The tests themselves are merely tools, with characteristics that can be measure d with reasonable precision under specified conditions. Whether the results will be valuable, meaningless, or even misleading depends partly upon the tool itself but largely upon the user.All informed predictions of future performance are based upon some knowledge of relevant past performance: school grades research productive, sales records, or whatever is appropriate. (72) How well the predictions will be validate d by later performance depends upon the amount, reliability, and appropriateness of the information used and on the skill and wisdom with which it is interpreted. Anyone who keeps careful score knows that the information available is always incomplete and that the predictions are always subject to error.Standardized tests should be considered in this context. They provide a quick, objective method of getting some kids of information about what a person learned, the skills he has developed, or the kinds of person he is. The information so obtain ed has, qualitatively, the same advantages and shortcomings as other kinds of information. (73) Whether to use tests, other kinds of information, or both in a particular situation depends, therefore, upon the evidence from experience concerning comparative validity and upon such factors as cost and availability. (74)In general, the tests work most effectively when the qualities to be measured can be most precisely define d and least effectively when what is to be measured or predicted can not be well defined.Properly used, they provide a rapid mean s of getting comparable information about many people. Sometimes they identify students whose high potential has not been previous ly recognized, but there are many things they do not do.(75) For example, they do not compensate for gross social inequality, and thus do not tell how able an underprivileged youngster might have been had he grown up under more favorable circumstance s.1996 年英译汉试题The differences in relative growth of various areas of scientific research have several cause s. (71)Some of these causes are completely reasonable result s of social needs. Others are reasonable consequence s of particular advances in science being to some extent self-accelerating.Some, however, are less reasonable processes of different growth in which preconception s of the form scientific theory ought to take, by persons in authority, act to alter the growth pattern of different areas. This is a new problem probably not yet unavoidable; but it is a frightening trend. (72)This trend began during the Second World War, when several governments came to the conclusion that the specific demands that a government wants to make of its scientific establishment cannot generally be foreseen in detail. It can be predicted, however, that from time to time questions will arise which will require specific scientific answers. It is therefore generally valuable to treat the scientific establishment as a resource or machine to be kept in functional order.(73)This seems mostly effectively done by supporting a certain amount of research not related to immediate goals but of possible consequence in the future.This kind of support, like all government support, requires decisions about the appropriate recipient s of funds. Decisions based on utility as opposed to lack of utility are straightforward. But a decision among projects none of which has immediate utility is more difficult. The goal of the supporting agencies is the praisable one of supporting “good ” as opposed to “bad” science, but a valid determination is difficult to make. Generally, the idea of good science tends to become confused with the capacity of the field in question to generate an elegant theory. (74)However, the world is so made that elegant systems are in principle unable to deal with some of the world's more fascinating and delightful aspects.(75)New forms of thought as well as new subjects for thought must arise in the future as they have in the past, giving rise to new standards of elegance.1997 年英译汉试题Do animals have rights? This is how the question is usually put. It sounds like a useful, ground-clearing way to start. (71)Actually, it isn't, because it assume s that there is an agreed account of human rights, which is something the world does not have.On one view of rights, to be sure, it necessarily follows that animals have none.(72)Some philosophers argue that rights exist only within a social contract, as part of an exchange of duties and entitlements. Therefore, animals cannot have rights. The idea of punishing a tiger that kills somebody is absurd; for exactly the same reason, so is the idea that tigers have rights. However, this is only one account, andby no means an uncontested one. It denies rights not only to animals but also to some people—for instance, to infants, the mentally incapable and future generations. In addition, it is unclear what force a contract can have for people who never consented to it: how do you reply to somebody who says “I don't like this contract”?The point is this: without agreement on the rights of people, arguing about the rights of animals is fruitless. (73)It leads the discussion to extremes at the outset: it invites you to think that animals should be treated either with the consideration humans extend to other humans, or with no consideration at all.This is a false choice. Better to start with another, more fundamental, question: is the way we treat animals a moral issue at all?Many deny it. (74)Arguing from the view that humans are different from animals in every relevant respect, extremists of this kind think that animals lie outside the area of moral choice . Any regard for the suffering of animals is seen as a mistake—a sentimental displacement of feeling that should properly be directed to other humans.This view, which hold s that torturing a monkey is morally equivalent to chopping wood, may seem bravely “logical”. In fact it is simply shallow: the confused centre is right to reject it. The most elementary form of moral reasoning—the ethical equivalent of learning to crawl—is to weigh others' interests against one's own. This in turn requires sympathy and imagination: without which there is no capacity for moral thought. To see an animal in pain is enough, for most, to engage sympathy.(75)When that happens, it is not a mistake: it is mankind's instinct for moral reasoning in action, an instinct that should be encouraged rather than laughed at. 1998 年英译汉试题They were,by far, the largest and most distant objects that scientists had ever detect ed: a strip of enormous cosmic clouds some 15 billion light-years from earth.(71)But even more important, it was the farthest that scientists had been able to look into the past, for what they were seeing were the patterns and structures that existed 15 billion years ago. That was just about the moment that the universe was born. What the researchers found was at once both amazing and expect ed; the US National Aeronautics and Space Administration's Cosmic Background Explorer satellite—Cobe—had discovered landmark evidence that the universe did in fact begin with the primeval explosion that has become known as the Big Bang (the theory that the universe originated in an explosion from a single mass of energy.) (72)The existence of the giant clouds was virtually required for the Big Bang, first put forward in the 1920s, to maintain its reign as the dominant explanation of the cosmos. According to the theory, the universe burst into being as a submicroscopic, unimaginable dense knot of pure energy that flew outward in all directions, emitting radiation as it went, condensing into particles and then into atoms of gas. Overbillions of years, the gas was compressed by gravity into galaxies, stars, plants and eventfully, even humans.Cobe is designed to see just the biggest structures, but astronomers would like to see much smaller hot spots as well, the seeds of local objects like clusters and superclusters of galaxies. They shouldn't have long to wait.(73)Astrophysicists working with ground-based detectors at the South Pole and balloon-borne instruments are closing in on such structures, and may report their findings soon. (74)If the small hot spots look as expected, that will be a triumph for yet another scientific idea, a refinement of the Big Bang called the inflationary universe theory. Inflation says that very early on, the universe expanded in size by more than a trillion trillion trillion trillionfold in much less than a second, propelled by a sort of antigravity.(75)Odd though it sounds, cosmic inflation is a scientifically plausible consequence of some respected ideas in elementary-particle physics, and many astrophysicists have been convinced for the better part of a decade that it is true. 1999 年英译汉试题(71) While there are almost as many definition s of history as there are historians, modern practice most closely conforms to one that sees history as the attempt to recreate and explain the significant events of the past. Caught in the web of its own time and place, each generation of historians determine s anew what is significant for it in the past. In this search the evidence found is always incomplete and scattered; it is also frequently partial or partisan. The irony of the historian's craft is that its practitioners always know that their efforts are but contributions to an unending process.(72) Interest in historical methods has arise n less through external challenge to the validity of history as an intellectual discipline and more from internal quarrels among historians themselves. While history once revered its affinity to literature and philosophy, the emerging social sciences seemed to afford greater opportunities for asking new questions and providing rewarding approach es to an understanding of the past. Social science methodologies had to be adapted to a discipline governed by the primacy of historical sources rather than the imperatives of the contemporary world. (73)During this transfer, traditional historical methods were augment ed by additional methodologies designed to interpret the new forms of evidence in the historical study.Methodolgy is a term that remains inherently ambiguous in the historical profession.(74) There is no agreement whether methodology refers to the concepts peculiar to historical work in general or to the research technique s appropriate to the various branches of historical inquiry. Historians, especially those so blinded by their research interests that they have been accused of“tunnel method,” frequently fall victim to the “technicist fallacy.”Also common in the natural sciences, the technicist fallacy mistakenly identifies the discipline as a wholewith certain parts of its technical implementation.(75) It applies equally to traditional historians who view history as only the external and internal criticism of sources, and to social science historians who equate their activity with specific techniques.2000 年英译汉试题Governments throughout the world act on the assumption that the welfare of their people depends largely on the economic strength and wealth of the community.(71) Under modern conditions, this require s varying measure s of centralized control and hence the help of specialized scientists such as economists and operational research experts. (72)Furthermore, it is obvious that the strength of a country's economy is directly bound up with the efficiency of its agriculture and industry, and that this in turn rests upon the efforts of scientists and technologists of all kinds. It also mean s that governments are increasingly compelled to interfere in these sectors in order to step up production and ensure that it is utilized to the best advantage. For example, they may encourage research in various ways, including the setting up of their own research centers; they may alter the structure of education, or interfere in order to reduce the wastage of natural resources or tap resources hitherto unexploited; or they may cooperate directly in the growing number of international projects related to science, economics and industry. In any case,all such interventions are heavily dependent on scientific advice and also scientific and technological manpower of all kinds.(73)Owing to the remarkable development in mass communications, people everywhere are feeling new wants and are being exposed to new customs and ideas, while governments are often forced to introduce still further innovation s for the reasons given above.At the same time, the normal rate of social change throughout the world is taking place at a vastly accelerate d speed compared with the past. For example,(74) in the early industrialized countries of Europe the process of industrialization—with all the far reaching changes in social patterns that followed—was spread over nearly a century, whereas nowadays a developing nation may undergo the same process in a decade or so. All this has the effect of building up unusual pressures and tensions within the community and consequently presents serious problems for the governments concerned.(75)Additional social stresses may also occur because of the population explosion or problems arising from mass migration movements—themselves made relatively easy nowadays by modern means of transport. As a result of all these factors, governments are becoming increasingly dependent on biologists and social scientists for planning the appropriate programs and putting them into effect.2001 年英译汉试题In less than 30 years' time the Star Trek holodeck will be a reality. Direct link s between the brain's nervous system and a computer will also create full sensory virtual environments, allowing virtual vacations like those inthe film Total Recall.(71) There will be television chat shows hosted by robots, and cars with pollution monitors that will disable them when they offend. (72) Children will play with dolls equipped with personality chips, computers with in-built personalities will be regarded as workmates rather than tools, relaxation will be in front of smell-television, and digital age will have arrived.According to BT's futurologist, Ian Pearson, these are among the developments scheduled for the first few decades of the new millennium (a period of 1,000 years), when supercomputers will dramatically accelerate progress in all areas of life. (73)Pearson has pieced together the work of hundreds of researchers around the world to produce a unique millennium technology calendar that gives the latest dates when we can expect hundreds of key breakthroughs and discoveries to take place.Some of the biggest developments will be in medicine, including an extended life expectancy and dozens of artificial organs coming into use between now and 2040.Pearson also predict s a breakthrough in computer-human links. “By linking directly to our nervous system, computers could pick up what we feel and, hopefully, simulate feeling too so that we can start to develop full sensory environments, rather like the holidays in Total Recall or the Star Trek holodeck,” he says. (74) But that, Pearson points out,is only the start of man-machine integration:“It will be the beginning of the long process of integration that will ultimately lead to a fully electronic human befor e the end of the next century.”Through his research, Pearson is able to put dates to most of the breakthroughs that can be predicted. However, there are still no forecasts for when faster-than-light travel will be available, or when human cloning will be perfected, or when time travel will be possible. But he does expect social problems as a result of technological advances. A boom in neighborhood surveillance cameras will, for example, cause problems in 2010, while the arrival of synthetic lifelike robots will mean people may not be able to distinguish between their human friends and the droids. (75)And home appliances will also become so smart that controlling and operating them will result in the breakout of a new psychological disorder—kitchen rage.2002 年英译汉试题Almost all our major problems involve human behavior, and they cannot be solved by physical and biological technology alone. What is needed is a technology of behavior, but we have been slow to develop the science from which such a。

外文资料与中文翻译外文资料：Intelligent thermal energy meter controllerAbstractA microcontroller based, thermal energy meter cum controller (TEMC) suitable for solar thermal systems has been developed. It monitors solar radiation, ambient temperature,fluid flow rate, and temperature of fluid at various locations of the system and computes the energy transfer rate. It also controls the operation of the fluid-circulating pumpdepending on the temperature difference across the solar collector field. The accuracyof energy measurement is ±1.5%. The instrument has been tested in a solar water heatingsystem. Its operation became automatic with savings in electrical energy consumption ofpump by 30% on cloudy days.1 IntroductionSolar water heating systems find wide applications in industry to conserve fossil fuel like oil, coal etc. They employ motor driven pumps for circulating water with on-offcontrollers and calls for automatic operation. Reliability and performance of the system depend on the instrumentation and controls employed. Multi-channel temperature recorders, flow meters, thermal energy meters are the essential instruments for monitoring andevaluating the performance of these systems. A differential temperature controller (DTC) is required in a solar water heating system for an automatic and efficient operation ofthe system. To meet all these requirements, a microcontroller based instrument wasdeveloped. Shoji Kusui and Tetsuo Nagai [1] developed an electronic heat meter formeasuring thermal energy using thermistors as temperature sensors and turbine flow meter as flow sensor.2 Instrument detailsThe block diagram of the microcontroller (Intel 80C31) based thermal energy meter cum controller is shown in Fig. 1. RTD (PT100, 4-wire) sensors are used for the temperaturemeasurement of water at the collector field inlet, outlet and in the tank with appropriate signal conditioners designed with low-drift operational amplifiers. A precision semiconductor temperature sensor (LM335) is used for ambient temperature measurement. A pyranometer, having an output voltage of 8.33 mV/kW/m2, is used for measuring the incident solar radiation. To monitor the circulating fluid pressure, a sensor with 4–20 mA output is used. This output is converted into voltage using an I-V converter. All these outputsignals are fed to an 8-channel analog multiplexer (CD4051). Its output is fed to adual-slope 12-bit A/D converter (ICL7109). It is controlled by the microcontroller through the Programmable Peripheral Interface (PPI-82C55).Fig. 1. Block diagram of thermal energy meter cum controller.A flow sensor (turbine type) is used with a signal conditioner to measure the flowrate. Its output is fed to the counter input of the microcontroller. It is programmed tomonitor all the multiplexed signals every minute, compute the temperature difference,energy transfer rate and integrated energy. A real-time clock with MM58167 is interfacedto the microcontroller to time-stamp the logged data. An analog output (0–2 V) is provided using D/A converter (DAC-08) to plot both the measured and computed parameters. A 4×4 matrix keyboard is interfaced to the microcontroller to enter the parameters like specificheat of liquid, data log rate etc. An alphanumeric LCD display (24-character) is alsointerfaced with the microcontroller to display the measured variables. The serialcommunication port of the microcontroller is fed to the serial line driver and receiver(MAX232). It enables the instrument to interface with the computer for down-loading thelogged data. A battery-backed static memory of 56K bytes is provided to store the measured parameters. Besides data logging, the instrument serves as a DTC. This has been achievedby interfacing a relay to the PPI. The system software is developed to accept thedifferential temperature set points (ΔT on and ΔT off) from the keyboard. An algorithmsuitable for on-off control having two set-points is implemented to control the relays.3 Instrument calibrationThe amount of energy transferred (Q) is :Where = mass flows rate of liquid kg/s ; V = volumetric flow rate (l/h) ; ρ= density of water (kg/l) ; Cp = specific heat (kJ/kg°C); and ΔT = temperature difference between hot and cold (°C).The accuracy in energy measurement depends on the measurement accuracy of individual parameters. Temperature measurement accuracy depends on the initial error in the sensorand the error introduced due to temperature drifts in the signal conditioners and the A/D converter. The temperature sensor is immersed in a constant temperature bath (HAAKE B ath-K, German), whose temperature can be var ied in steps of 0.1°C. A mercury glass thermometer (ARNO A MARELL, Germany) with a resolution of 0.05°C is also placed along with PT100 sensor in the bath. This is compared with the instrument readings. The accuracy of the instrument in temperature measurem ent is ±0.1°C. Hence, the accuracy in differential temperature measurement is ±0.2°C.The flow sensor having a maximum flow rate of 1250 l/h is used for flow measurement.It is calibrated by fixing it in the upstream of a pipeline of length 8 m. The sensor output is connected to a digital frequency counter to monitor the number of pulses generated withdifferent flow rates. Water collected at the sensor outlet over a period is used forestimating the flow rate. The K-factor of the sensor is 3975 pulses/l. The uncertaintyin flow measurement is ±0.25% at 675 l/h. Uncertainties in density and specific heat ofwater are ±0.006 kg/l and ±0.011 kJ/kg°C respectively.Maximum amount of energy collection (Q) = 675×0.98×4.184×15/3600 = 11.53kW. Uncertainty in energy measurementωq/Q = [(ωv/V)2 + (ωρ/ρ)2 + (ωcp/Cp)2+(ωt/T )2]1/2.Inaccuracy in electronic circuitry is ±0.03 kW.The net inaccuracy in energy measurement is ±1.5%4 Field testThe instrument is incorporated in a solar water heating system as shown in Fig. 2.It consists of five solar flat plate collectors having an absorber area of 1.6 m2 each. The absorber is a fin and tube extruded from aluminium and painted with matt black paint. The collectors are mounted on a rigid frame facing south at an angle equal to the latitude of Bangalore (13°N). They are arranged in parallel configuration and connected to athermally insulated 500 l capacity storage tank. A 0.25 hp pump is used for circulatingthe water through the collector field. All the pipelines are thermally insulated. Thetemperature sensors and the flow sensor are incorporated in the system as shown in Fig.2. The data on solar radiation, ambient temperature, water flow rate, solar collector inlet and outlet temperatures and the system heat output are monitored at regular intervals.Fig. 2. Solar water heating system with thermal energy meter cum controller.The performance of the solar water heating system with TEMC on a partial cloudy dayis shown in Fig. 3. It is observed that DTC switched OFF the pump around 14:40 h as thereis no further energy gain by the collector field. This in turn reduced the heat lossesfrom the collector to ambient. Experiments are conducted with and without DTC o n both sunny and cloudy days. The DTC operated system shows the savings in electrical energy by 30%on a partial cloudy day and 8% on a sunny day. The variation in system output with andwithout DTC i s around 3%. Thus the controller has not only served as an energy conservation device, but also switches ON/OFF the system automatically depending on the availabilityof solar radiation. The collector field output (shown in Fig. 3) is calculated by measuring the fluid flow rate using volumetric method and the temperature difference with anotherpair of standard thermometers. It is 16.86 kWh. It is compared with the instrument reading 17.18 kWh. Thus, the deviation is 1.9%. Fig. 3 shows that the solar collector fieldefficiency is 54% when the incident solar irradiation is 31.75 kWh.Fig. 3. Performance of SWH system with TEMC on a partial cloudy day.5 Concluding remarksTEMC is used as on-line instrument in solar water heating systems for the measurement of thermal energy, temperature, flow rate with simultaneous control on the operation ofthe pump t o save electrical energy and enhance the thermal energy collection. Since several options are provided in the instrument, it can be used for monitoring the energy transfer rate in other thermal systems.AcknowledgementsThe authors are thankful to Department of Science and Technology, Govt. of India forproviding the financial assistance to carry out the above work.References1. Shoji Kusui, Tetsuo Nagai. An electronic integrating heat meter. IEEE Trans. onInstrumentation and Measurement, 1990;39(5):785-789.中文翻译：智能热能表控制器摘要适用于太阳能热系统的单片机热能表控制器（TEMC）已经研制成功。

外文文献RURAL TOURISM AND SUSTAINABLE DEVELOPMENTINTRODUCTIONRural tourism is a segment of the total tourist industry which is particularly important in Hungary, in a country with no spectacular natural attractions, without seaside，high mountains, rainforest or herds of exotic animals. However，its attractive cultural landscapes with small villages，thermal springs，rivers and lakes，combined with the traditional hospitality，are able to offer pleasant experiences to the kind of tourist who is looking for relaxation and recreation in a calm setting。

On one hand，rural tourism development can play an important role in the diversification of the Hungarian tourist supply and in the creation of a more complex and colourful country image. On the other hand，rural tourism is not only the end, but the means to stimulate economic growth，to increase the viability of underdeveloped regions, and to improve the living standards of local populations。

NCEP数据资料获取地⾯抬升指数美国国家环境预报中⼼（NCEP）和国家⼤⽓研究中⼼（NCAR）联合执⾏的全球⼤⽓40年资料再分析计划通过CDC（Climate Dianogistic Center）利⽤磁带的形式向外发⾏。

地⾯抬升指数抬升指数是⼀种表⽰⼤⽓对流性不稳定的指数，指⼀个⽓块从地⾯出发，上升到500百帕（海拔5500⽶左右⾼度）处所具有的温度被该处实际⼤⽓温度所减得到的差值。

The lifted index (LI) is the difference between the environment Te(p) and an lifted Tp(p) at a given pressure height in the (lowest layer where most weather occurs) of the , usually 500 (). The temperature is measured in Celsius. When the value is positive, the atmosphere (at the respective height) is stable and when the value is negative, the atmosphere is .LI can be computed using computer algorithms but can also be determined graphically. To do this, generally, the is lifted from the portion of the (PBL) that lies below the morning . The air here should be about 60 to 65% , which is then lifted along the dry adiabat (see also ) to the , which is the intersection of that curve with the average in the boundary layer. Once the LCL is found, the parcel is lifted along the moist adiabat to 500 mb. It is then that one finds LI = Te(p) - Tp(p).LI is generally scaled as follows:LI 6 or Greater, Very Stable ConditionsLI Between 1 and 6 : Stable Conditions, Thunderstorms Not LikelyLI Between 0 and -2 : Slightly Unstable, Thunderstorms Possible, With Lifting Mechanism (i.e., cold front, daytime heating, ...)LI Between -2 and -6 : Unstable, Thunderstorms Likely, Some Severe With Lifting MechanismLI Less Than -6: Very Unstable, Severe Thunderstorms Likely With Lifting MechanismThe lifted index can be used in forecasting, however, (CAPE) is considered by most as a superior measurement of instability and is preferred by many meteorologists for convection forecasting. However, LI is easier and faster to determine without using a computer, as determining CAPE requires integration from one level to another.Reanalysis output includes two lifted indices. the surface lifted index (LFTX) and the best (4-layer) lifted index (4LFTX).The surface lifted index is computed by finding the temperature of an air parcel lifted from the lowest layer to 500 mb and subtractingthe ambient 500 mb temperature.The best lifted index is computed by lifting the parcel from the layer with the warmest equivalent potential temperature to 500 mband subtracting the ambient 500 mb temperature.最暖等效位温For computation, the vertical profile was converted to six layers of depth of 30 mb starting from the surface.Stability of the AtmosphereLifted Index (LI)The LI is a commonly utilized measure of stability which measures the difference between a lifted parcel's temperature at 500 mb and the environmental temperature at 500 mb. It incorporates moisture and lapse rate (static stability) into one number, which is less vulnerable to observations at individual pressure levels. However, LI values do depend on the level from which a parcel is lifted, and rally cannot account for details in th environmental temperature curve above the LCL and below 500 mb. LI was originally intended to utilize average moisture and temperature properties within the planetary boundary layer.LI = T(500 mb envir) - T(500 mb parcel)in degrees C, where T (500 mb envir) represents the 500 mb environmental temperature and T (500 mb parcel) is the rising air parcel's 500 mb temperature.LI over 0:Stable but weak convection possible for LI = 1-3 if strong lifting is present.LI = 0 to -3:Marginally unstable.Moderately unstable.LI = -3 to -6:LI = -6 to -9:Very unstable.LI below -9:Extremely unstable.These LI values are based on lifted parcels using the average lowest 50 to 100 mb moisture and temperature values (i.e., the boundary layer). Variations exist on how LI values are calculated, as discussed below.Surfaced-based LI:Surface-based LIs can be calculated hourly, and assume a parcel is lifted from the surface using surface-based moisture and temperature values, as well as assigned environmental temperatures at 500 mb. This method is valid for a well-mixed nearly dry adiabatic afternoon boundary layer where surface characteristics are similar to those in the lowest 50 to 100 mb layer. However, these values would not be representative of the ambient elevated instability if a nocturnal inversion or shallow cool air to the north of a frontal boundary is present. In these cases, more instability resides above the surface, and parcels may be lifted to form thunderstorms from the top of the inversion.Best LI:The Best LI represents the lowest (most unstable) LI computed from a series of levels from the surface to about 850 mb. This index is most useful during cases when shallow cool air exists north of a frontal boundary resulting in surface conditions and boundary layer-based LI values that are relatively stable. However, the airmass at the top of the inversion, from which lifting may occur, is potentially unstable. An example of this would be elevated ("overrunning") convection (possibly a nocturnal MCS).。

小学下册英语第6单元自测题英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The __________ (人际沟通) facilitates relationships.2.The ____ digs tunnels and is often seen in the grass.3.The chemical equation for respiration includes glucose and _____.4. A peacock shows off its ______ (羽毛).5.The chemical symbol for lead is _______.6.What do we call the study of ancient cultures through artifacts?A. AnthropologyB. ArchaeologyC. HistoryD. SociologyB7.Which planet has the most moons?A. EarthB. JupiterC. SaturnD. Neptune8.My favorite fruit is ________ because it is sweet.9.The city of Sydney is located in _______.10.My cousin is a great __________ (厨师).11.My favorite musician is _______.12. A tortoise can live for over a ________________ (百年).13.I like to ______ my friends' birthdays. (celebrate)14.Which fruit is known for having seeds on the outside?A. BananaB. StrawberryC. AppleD. GrapeB15.The fire is ___ (crackling).16.The ______ (小鸟) builds a nest to keep its eggs safe.17.I enjoy watching ________ on television.18.My friend loves to share __________ (故事) with others.19.What is 7 + 2?A. 8B. 9C. 10D. 11B20.The __________ (历史的连接) unites us.21.What do we call a large body of freshwater?A. OceanB. SeaC. LakeD. RiverC22.I have a _____ (拼图) of a beautiful landscape that I enjoy completing. 我有一个美丽风景的拼图，喜欢完成它。

小学上册英语第6单元自测题(有答案)英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.I enjoy ______ during my free time.2.My brother is ______ than me. (taller)3.The study of Earth's geological history is important for understanding ______.4.My teacher is ______ (善良). She always helps us with our ______ (功课).5.I have _______ (many) friends at school.6. A _______ is a process that requires careful measurement.7.Certain plants can ______ (提供) shelter for animals.8.I want to ___ (learn/know) more about it.9.Sulfuric acid is commonly used in ______.10.She wears a _____ (裙子) to the party.11.We have a ______ (精彩的) student exhibition each year.12.The _______ of a shadow depends on the position of the light source.13.Which food is made from milk?A. BreadB. CheeseC. RiceD. Noodles答案:B14.The car is parked _____ (in front/behind) the house.15.What is 3 + 7?A. 9B. 10C. 11D. 12答案:B 1016.The ice cream is _____ (cold/hot) and delicious.17.What shape has four equal sides?A. RectangleB. TriangleC. SquareD. Circle答案:C18.The __________ is a region known for its rich soil.19.The ancient Greeks believed in _______. (神话)20.The ________ was a key battle in the narrative of independence.21.The bat uses its _______ (回声定位) to navigate.22.This fruit is very _______ (甜).23.Which of these animals is a reptile?A. FishB. BirdC. SnakeD. Elephant答案:C Snake24.I have a toy ________ that dances.25.Read and colour.(看词涂色.)26.What is the process of converting a liquid into a gas?A. EvaporationB. CondensationC. FreezingD. Melting答案:A.Evaporation27.What do you call a group of stars?A. GalaxyB. UniverseC. ClusterD. Solar System答案: A28.We are going to ________ (旅行) next month.29.The process of changing from liquid to gas is called ______.30.My friend likes to take ____ (photos) of nature.31.The _______ (Spanish Flu) pandemic occurred in 1918-1919.32.What is the capital city of Argentina?A. Buenos AiresB. SantiagoC. LimaD. Bogotá答案: A33.The rainbow has ______ colors. (seven)34._____ (农村社区) often depend on agriculture.35.What is the name of the famous novel written by Mark Twain?A. Moby DickB. The Adventures of Tom SawyerC. The Great GatsbyD. To Kill a Mockingbird答案:B.The Adventures of Tom Sawyer36.My ________ (玩具名称) is made of soft fabric.37.My sister is talented at ____.38.The fish swims _____ (fast/slow) in the water.39.The school bell _____ (rings/turns) at AM.40.Which animal can fly?A. FishB. ElephantC. BirdD. Snake答案: C41.We like to ________ (play) outside.42.He is very _____ (细心) about his work.43.The porcupine has sharp _______ (刺).44.The _______ of light can be affected by the surface it strikes.45.I keep my toys in a ________.46.The hawk is a _________ bird of prey. (强壮的)47.What do we call the main character in a play?A. ActorB. ProtagonistC. DirectorD. Producer答案: B48.Acidic substances have a pH level less than ______.49.为下列对话选择相符的图片。

NoiseIntroductionAircraft noise is hardly a new subject as evidenced by the following note received by a predecessor of United Airlines in about 1927.Although internal noise was the major preoccupation of aircraft acoustic engineers for many years and still is important, the noise produced by the aircraft engine and experienced on the ground has become a dominant factor in the acceptability of the airplane. With the development of high bypass ratio engines, noise due to other sources has become important as well.Internal noise is treated by placing the engines to minimize the noise directly radiated to the cabin, (e.g. using the wing as a shield) and by providing insulating material over the entire surface of the flight and passenger compartments. If the engines are mounted on the fuselage, vibration isolation is an important feature. In the late 1980's when prop-fans were being developed, internal noise become an important consideration again. It was, at one point, estimated that 2000 lbs of additional acoustic insulation would be required to reduce cabin noise levels to those of conventional jets if prop-fans were placed on the aircraft wings. This is one reason why many prop-fan aircraft were designed as aft-mounted pusher configurations.External noise is affected by the location of the source and observer,the engine thrust, and a number of factors that influence the overall configuration design. These will be discussed in detail later in this chapter, but first we must understand the origins of noise and its measurement.The Nature of NoiseA sound wave carries with it a certain energy in the direction of propagation. The sound becomes audible because of energy which originates at the source of the sound vibrations and which is transported by the sound waves. The changes in air pressure which reach the eardrum set it vibrating; the greater these changes, the louder is the sound.The intensity of sound, I, is the quantity of energy transferred by a sound wave in 1 sec through an area of 1 cm. For a plane sine wave:I = p2 / 2 ρ cwhere:p = the amplitude of the varying acoustic excess pressureρ = air densityc = speed of soundI is usually expressed in ergs per cm2 per sec. (mW/m2)The human ear responds to a frequency range of about 10 octaves. It responds to air vibrations whose amplitude is hardly more than molecular size; it also responds without damage to sounds of intensity 1013 to 1014 times greater without damage.The response of the ear is not proportional to the intensity, however. It is more nearly proportional to the logarithm of the intensity. If sound intensity is increased in steps of what seem to be equal increments of loudness, we find that the intensities form a sequence of the sort 1, 2, 4, 8, 16, .... or 1, 10, 100, 1000 not 1, 2, 3, 4, ... or 1, 10, 19, 28, ... . Since the ear responds differently to different frequencies, the logarithmic relation of intensity to loudness is not generally perfect, but it is easier to handle than the enormous numbers involved in the audible intensity range. Therefore, the intensity level of sound is defined in decibels as 10 times the logarithm of the ratio of the intensity of a sound, I, to a reference level defined as 10-9 erg/cm2/sec.I / 10-9Thus: Sound intensity level (SPL), decibels = 10 log10The response of the ear is not exactly proportional to the decibel scale. In addition to the physical quantities, intensity and frequency, thepsycho-physiological quantities of loudness and pitch must be considered. The loudness of a sound depends both on intensity level and frequency; pitch depends chiefly on frequency but to some extent on intensity. Contours of equal loudness for the average person are plotted in the following figure from Ref. 2. The actual contour values are the values of SPL at 1 kHz.Contours of equal loudness, plotted against intensity and frequency for the average ear.The db(A) ScaleIn an attempt to develop a noise measuring scale more responsive to these characteristics of the ear, the "A" scale was defined to weight noise at frequencies above 1000 Hz more heavily. Noise measured on this scale is given in units of db(A).Frequency response weighting for the "A" scale. (From Peterson and Gross, 1967, p.9).The Perceived Noise Level Scale PNdb and EPNdbThe scale most often used for aircraft noise measurement is the Perceived Noise Level (PNL) scale. The scale requires that the SPL be measured in each of nine contiguous frequency ranges and combined according to a special prescription, not too different from the A-weighting method, to provide a noise indication level. The units are PNdb.The effective perceived noise level, EPNL, accounts for duration and presence of discrete frequency tones. It involves a correction factor that adds to the PNL when there are discrete tones in the noise spectrum. It also includes a correction obtained by integrating the PNL over a 10 second time interval. (Details are given in the full text of FAR Part 36.)The effective perceived noise level correlates with people's perceived noisiness as shown in the figures below.Subjective Reactions to Various Noise LevelsThe fact that people's perception of noise varies logarithmically with sound intensity results in some interesting relations. Note that asintensity is reduced by 50% the SPL changes by 10 log I1/I2= -3db. Fromthe plot above this reduction would be only barely perceptible. This is why noise reduction is a challenge. To make something seem about half as noisy requires a reduction in SPL by about 10 db. This is a reduction in I of about 90%!.People's reactions also depend on how often such noises occur and a variety of methods for averaging noisiness have been used. Sound exposure levels(SEL), noise exposure forecasts (NEF), and Day-Night-Levels all involve some kind of averaging of multiple noise events, usually with higher weightings (e.g. 10-20 times) for night flights. These are intended to capture the community response in a statistical way. (See figure below.)Community Response to Different Noise LevelsFootprintsThe U.S. Environmental Protection Agency (EPA) uses a Day-Night Average A-Weighted Sound Level metric known as DNL as a method for predicting the effects on a population of the long term exposure to environmental noise. The DNL metric is legislated to be the single system for measuring aircraft noise impact and for determining land use compatibility.Noise maps typically depict the DNL 65dB contour as this is identified by federal guidelines as the threshold level of aviation and community noise that is "significant". In general, most land uses are considered to be compatible with DNLs less than 65 dB.Sample of Estimated Noise Footprints Atlanta Airport in Jan. 2000Contours of constant DNL or EPNdB are often plotted to determine the areas affected at a given levels. Different aircraft may have very different footprints, this is especially obvious when comparing 2 vs. 4 engine aircraft, because of different climb rates.Sources of NoiseAircraft noise is generally divided into two sources: that due to the engines, and that associated with the airframe itself. As higher bypass ratio engines have become more common and aircraft have become larger, interest in airframe-related noise has grown, but engine noise still accounts for most of the aircraft external noise. The relative importance of various noise sources is shown in the figure below.Propulsion-Related Noise SourcesEngine noise includes that generated at the fan inlet and exit, the combustor core, the turbine, and that caused by jet mixing. While jet noise, caused by the turbulent mixing of the high speed exhaust with the ambient air, is a broad band noise source, with most of the energy directed aft of the engine at a 45 degree angle from the engine axis, the turbomachinery noise often includes discrete tones associated with blade passage frequencies and their harmonics.Jet noise levels vary as the sixth to eighth power of the jet exhaust velocity as shown in the figure below. Early turbojet engines had exhaustvelocities of nearly 2000 ft/sec and noise suppressors were used to try to obtain better mixing and lower the noise associated with the strong shear. Such suppressors were effective in reducing the low frequency noise, but often not the high frequencies and added weight and cost to the design.The jet velocity was reduced considerably as the bypass ratio increased. This is indicated by the figure below that applies to older engines, but is still representative of the trend observed for larger modern engines.The net result is a substantial reduction in the noise due to jet mixing. At the same time, though, the larger fan noise become more significantas seen from the figure below.Computational aerodynamics is getting to the point of predicting such effects in a practical way, but it is a very complex problem, involving internal unsteady flows and propagation estimates.Without such CFD tools, one can still estimate the effects of engine thrust levels, separation distances, and number of engines by scaling experimental results according to the fundamental physics of the problem as described in the following sections.Non-propulsive noiseIn addition to the engine noise, the shear of the boundary layer and unsteady vortex shedding from landing gear, landing gear doors, and other separated flows as well as flap edge flows contribute a significant part of the acoustic energy, especially for large aircraft on approach.The figure on the right shows that these noise sources were still well below the requirement, but the figure was drawn in 1974. Stage 3 noise regulations now make airframe noise a significant issue.Noise ReductionWith substantially more stringent noise regulations and a desire to reduce community environmental impact, engine companies, aircraft manufacturers, and government agencies have continued to look for ways to reduce aircraft noise.NASA work as part of their advanced subsonic technology program includes the objective of 10 decibel (dB) community noise reduction relative to 1992 production technology. This includes:∙ 6 dB engine noise reduction∙50% improvement in nacelle liner efficiency∙ 4 dB airframe noise reduction∙Community noise impact minimization through operations∙ 6 dB interior noise reductionTo accomplish this, engineers are developing higher bypass ratio engines to reduce exhaust velocities, continuing to improve nacelle treatments, and operating the aircraft with take-off power cutbacks and 2-segment approaches.The picture below shows a large acoustic test facility used by NASA Lewis as part of their work on engine noise reduction.The RegulationsNoise regulations in FAR Part 36 Stage 3 include restrictions on noise in 3 conditions. The take-off noise is defined as the noise measured at a distance of 21,325 ft (6500 m) from the start of the take-off roll, directly under the airplane. The sideline noise is measured 1476 ft (450 m) from the runway centerline at a point where the noise level after liftoff is greatest. The approach noise is also measured under the airplane when it is at a distance of 6562 ft (2000 m) from the runway threshold. For each of these conditions the maximum noise level is a function of maximum takeoff gross weight, and for the take-off case the limits depend also on the number of engines. The figures below summarize the requirements.Stage 4 noise regulations are applicable to new type designs introduced after January 1, 2006. Existing aircraft will be able to operate under Stage 3 regulations. This new Standard will be "Chapter 4" in ICAO Annex 16 and are related to the Stage 3 / Chapter 3 regulations as follows: - A cumulative margin of 10 dB relative to Chapter 3- A minimum sum of 2 dB at any two conditions- No trades allowedEstimating Aircraft Noise for Advanced DesignWe start with a measurement of the noise due to a known engine at a known distance away. For example, a 25,000 lb (sea level static take-off thrust) turbofan engine with a bypass ratio of 6 produces a noise of about 101 PNdb at a distance of 1000 ft. This assumes some level of noise suppression (about 5PNdb). We might also infer a baseline engine noise from measured data such as that provided by GE and shown below:Examples of measured noise data form reference (from GE)We are interested in the effect of design changes on the noise, so starting from the reference value, we make corrections for thrust level, distance,ground attenuation, and noise duration. These effects are shown in the plots below and further described by an example computation that follows.The effect of thrust level on noise is obtained by simply scaling the sound intensity (I) by the ratio of thrust to reference thrust. This correction is applied to scale the engine size or the number of engines. This means that if the engine technology is similar, reducing the installed thrust by 50% will lead to a noise reduction of about 3db. (10 log (1/2) = -3)If thrust is reduced, not by scaling the engines, but by reducing the throttle setting, the noise is reduced much more because the fan tip speeds and exhaust velocity are reduced.The sound intensity varies roughly as the inverse square of the distance from the source. This means that for each doubling of the distance, we expect a 6db reduction in the noise level. However, atmospheric attenuation adds about 1.2 db of reduction per 1000 ft so that increasing the distance from 1000 ft to 2000 ft results in about 7.2db attenuation. Both of these effects are included in the above plot. The presence of various obstacles and absorbing material near the ground is sometimes taken into account by adding 25% to the actual distance and considering this an effective distance.To obtain EPNdb we typically reduce the PNdb level by about 4db for the take-off and sideline calculations and by about 5db on approach. (This reflects typical tone and duration corrections under these conditions.)Finally we add the airframe noise which is very difficult to estimate, but which we take here to be related to the log of the aircraft weight: Airframe Noise (db) = 40 + 10 log W, where W is the aircraft weight in lbs. This fit is based on some simple scaling rules suggested by energy considerations and some empirical data from NASA and Lockheed measurements. It is very rough and applicable only on approach, but usually is not the major part of the noise contribution.Example Computations (DC-10)Take-off:Base = 101 PNdb, 25,000 lb thrust, 1 engine, 1000ft+ 4.8 for 3 engines+ 1.9 for 40,000 lb SLS thrust engines- 4.0 for 1500 ft altitude at 6500m from start of take-off- 4.0 correction to EPNdb on take-off----------Total: 99.7 EPNdb (Flight measurement shows 98 db)Sideline:Base = 101 PNdb, 25,000 lb thrust, 1 engine, 1000ft+ 4.8 for 3 engines+ 1.9 for 40,000 lb SLS thrust engines- 6.5 for 1476 ft (450m) from centerline (effective distance = 1476*1.25 = 1845ft)- 4.0 correction to EPNdb on take-off----------Total: 97.2 EPNdb (Flight measurement shows 96 db)Approach:Base = 101 PNdb, 25,000 lb thrust, 1 engine, 1000ft+ 4.8 for 3 engines+ 1.9 for 40,000 lb SLS thrust engines+ 9.1 for 370 ft altitude at 6562 ft (2000m) from runway- 7.0 correction for 45% throttle- 5.0 correction to EPNdb on approachEngine subtotal: 104.8 dbAirframe: 94.8 db at a landing weight of 300,000 lbs----------Total (add I's): 105.2 EPNdb (Flight measurement shows 106 db)。

统计学里总集的英语The concept of the total population in statistics is a fundamental one that underpins many of the core principles and techniques used in data analysis and inference. In its most basic form, the total population refers to the complete set of individuals, objects, or observations that are of interest for a particular study or investigation. This can encompass a wide range of entities, from the entire human population of a country or the world, to the universe of all possible product sales within a specific market, to the complete set of measurements taken from a scientific experiment.Regardless of the specific context, the total population represents the broadest and most comprehensive representation of the phenomenon or subject under study. It is the starting point from which all statistical analysis and inference must be derived, as it provides the foundation for understanding the true nature and characteristics of the population as a whole.One of the key reasons why the total population is so important in statistics is that it allows researchers and analysts to make reliableand generalizable conclusions about the larger group based on the information and data collected from a smaller, representative sample. By studying the properties and behaviors of a carefully selected subset of the total population, statisticians can draw inferences and make predictions about the population as a whole with a high degree of confidence.This process of sampling and inference is at the heart of much of the work done in fields such as market research, public health, and social science. For example, a political pollster might survey a sample of registered voters to gauge public opinion on a particular issue, with the goal of making accurate predictions about the voting behavior of the entire electorate. Similarly, a medical researcher might conduct a clinical trial with a group of patients to evaluate the efficacy of a new drug, with the ultimate aim of understanding how the drug would perform when administered to the broader patient population.In both of these cases, the total population represents the complete set of individuals or observations that are relevant to the study, and the sample is a carefully selected subset that is used to make inferences about the larger group. The validity and reliability of these inferences, in turn, depend heavily on the degree to which the sample is representative of the total population and the appropriateness of the statistical methods used to analyze the data.It is important to note that the total population is not always directly observable or accessible to researchers. In many cases, the true size and characteristics of the population may be unknown or difficult to determine with certainty. This is particularly true in situations where the population is large, dispersed, or constantly changing, such as the global population of internet users or the universe of all possible financial transactions.In such cases, statisticians must rely on various techniques and assumptions to estimate the properties of the total population based on the information that is available. This may involve the use of sampling methods, statistical modeling, and other analytical approaches to make informed inferences about the population as a whole.One common technique used in this context is the concept of the "target population," which represents the specific group of individuals or observations that the researcher is ultimately interested in studying or making inferences about. The target population may be a subset of the total population, but it is the group that the researcher ultimately wants to understand and draw conclusions about.For example, in a study of consumer spending habits, the total population might include all individuals who have made purchases ina particular market, while the target population might be a specific demographic group, such as middle-income households in a particular geographic region. By focusing on the target population, the researcher can tailor their sampling and analysis methods to better address the specific research questions and objectives of the study.Another important consideration in the context of the total population is the issue of sampling bias and the potential for errors or distortions in the data. Because researchers can rarely study the entire total population directly, they must rely on samples that may not be perfectly representative of the larger group. This can introduce a variety of biases, such as selection bias, non-response bias, or measurement error, which can compromise the validity and generalizability of the findings.To address these challenges, statisticians have developed a range of techniques and strategies for designing and implementing sampling methods that minimize the risk of bias and maximize the representativeness of the sample. This may involve the use of random sampling, stratified sampling, or other advanced sampling approaches, as well as the application of statistical weighting and adjustment methods to correct for any biases or errors that may be present in the data.Overall, the concept of the total population is a fundamental and indispensable part of the field of statistics, as it provides the foundation for understanding the broader context and implications of any data-driven investigation or analysis. By carefully defining and studying the total population, researchers can gain valuable insights into the underlying patterns, trends, and relationships that govern the phenomena they are investigating, and use this knowledge to make informed decisions and drive meaningful change in a wide range of domains.。

分散剂折光率的英文Refractive Index of Dispersants.Dispersants are substances that are added to adispersion to prevent the particles from agglomerating and settling out. They work by coating the particles with alayer of material that prevents them from interacting with each other. The refractive index of a dispersant is an important property that can affect its performance.What is Refractive Index?The refractive index of a material is a measure of how much light is bent when it passes from one material to another. It is defined as the ratio of the speed of lightin a vacuum to the speed of light in the material. The higher the refractive index, the more light is bent.How Does Refractive Index Affect Dispersant Performance?The refractive index of a dispersant can affect its performance in several ways.Particle Interaction: The refractive index of a dispersant can affect the way that particles interact with each other. If the refractive index of the dispersant is close to the refractive index of the particles, then the particles will experience less electrostatic repulsion and will be more likely to agglomerate.Light Scattering: The refractive index of a dispersant can also affect the way that light is scattered by the dispersion. If the refractive index of the dispersant is close to the refractive index of the particles, then the particles will scatter less light and the dispersion will be more transparent.Flocculation: The refractive index of a dispersant can also affect the flocculation of the particles. Flocculation is the process by which particles aggregate into larger, more easily removed flocs. If the refractive index of the dispersant is close to the refractive index of theparticles, then the particles will be less likely to flocculate.How to Choose the Right Refractive Index for a Dispersant.The ideal refractive index for a dispersant will depend on the specific application. In general, however, a dispersant with a refractive index that is close to the refractive index of the particles will be more effective.Measurement of Refractive Index.The refractive index of a dispersant can be measured using a refractometer. A refractometer is a device that measures the angle of refraction of light as it passes from one material to another. The refractive index of the material can be calculated from the angle of refraction.Conclusion.The refractive index of a dispersant is an importantproperty that can affect its performance. By understanding how refractive index affects dispersant performance, you can choose the right dispersant for your application.。

International Journal of Impact Engineering 24(2000)613}629A further study of plastic shear failure of impulsively loadedclamped beamsT.X.Yu *,F.L.ChenDepartment of Mechanical Engineering,Hong Kong Uni v ersity of Science and Technology,Clear Water Bay,Kowloon,Hong KongReceived 20March 1999;received in revised form 29June 1999AbstractAs early as in 1973,Menkes and Opat (Exp Mech 1973;13:480}6)conducted an experimental investigation on the dynamic plastic response and failure of fully clamped metal beams subjected to a uniformly distributed impulsive loading and identi "ed three basic failure modes:large inelastic deformation (Mode I),tensile tearing (Mode II)and transverse shear failure at the supports (Mode III).A rigid-plastic analysis was later carried out by Jones (Trans ASME J Eng Ind 1976;98(B1):131}6),in which an elementary failure criterion was adopted to estimate the threshold impulsive velocities at the onset of Mode II or Mode III failure.A deep understanding of these three basic failure modes is of fundamental importance to failure analyses of various structures under intense dynamic loading.The present paper re-examines the plastic shear failure (Mode III)of impulsively loaded clamped beams,with focus on two e !ects:(i)the interaction between the shear force and bending moment;and (ii)the weakening of the sliding sections during the failing process.A dimensional analysis is "rst performed to obtain a general form of the threshold impulsive velocity,which overlooks succeeding concrete analyses.The elementary failure criterion is then modi "ed to incorporate the sliding sections 'weakening e !ect.Interaction between the shear force and the bending moment at the supporting ends is considered by using circular yield curve (Robinson,Int J Solids Struct 1973;9:819),Hodge 's curve (J Appl Mech 1957;24:453}6),or a yield condition based on slip-line solutions.By taking into account the variation with time of the shear force and the bending moment over the failing cross-sections,the plastic deformation and failure process of the beams are traced and the ratio of plastic shear dissipation to the total plastic dissipation is thus calculated.This is followed by a discussion on a shear strain failure criterion.Finally,the predictions from various approaches are compared with each other as well as with relevant experimental results. 2000Elsevier Science Ltd.All rights reserved.Keywords:Shear failure;Rigid-plastic beam;Dynamic failure criterion;Interactive yield condition;Weakening e !ect *Corresponding author.Tel.:#852-2358-8652;fax:#852-2358-1543.E-mail address:metxyu @ust.hk (T.X.Yu).0734-743X/00/$-see front matter 2000Elsevier Science Ltd.All rights reserved.PII:S 0734-743X (99)00038-X614T.X.Yu,F.L.Chen/International Journal of Impact Engineering24(2000)613}6291.IntroductionStudy of structural failure under intense dynamic loading is of importance for the safety andhazard assessments in many engineering"elds.Simple structural members,such as beams,platesand thin shells,may fail due to di!erent modes under su$ciently intense dynamic loads[1].Severalexperimental and theoretical studies[2}8]have examined the onset of these failure modes in orderto estimate the structural capacities of sustaining impact loading.As early as1973,Menkes and Opat[2]conducted an experimental investigation on the dynamicplastic response and failure of fully clamped metal beams subjected to a uniformly distributedimpulsive loading and identi"ed three basic failure modes,rge inelastic deformation(Mode I),tensile tearing(Mode II)and transverse shear failure at the supports(Mode III).Later,a theoreticalrigid-plastic analysis provided by Jones[3}5]showed reasonable agreement with the experimentalresults[2]on the threshold impulsive velocities at the onset of Mode II or Mode III failure.In thisanalysis,square yield criteria relating either the axial force to the bending moment or the transverseshear force to the bending moment,and elementary failure criteria were adopted.It is evident thatthe foundation of the simple formulations employed,especially those for Mode III failure,needs tobe further validated.In the1990s,an energy density criterion was proposed by Shen and Jones[8]which caters to thesimultaneous in#uence of the bending moment,the axial force as well as the transverse shear in thestructural response.According to this criterion rupture occurs in a rigid-plastic structure whenthe absorption of plastic work per unit volume, ,reaches a critical value;and further if the ratio ofthe plastic work absorbed through shearing deformation to the total plastic work done by all thestress components, ,reaches a critical value, "0.45,a structure su!ers a Mode III failure.The merit of the energy density criterion is that it may be universally applicable for a large class ofdynamic structural problems.Nevertheless,it has been noted that some problems associated withthis criterion remain unanswered,e.g.(i)in a rigid-plastic analysis,the calculation of the energydensity depends upon the length of a plastic hinge;(ii)in FE calculations,the energy density ismesh-dependent;and(iii)it is unclear how to determine the critical ratio .It was suggested that "0.45,but this value disagrees with0.857from the theoretical prediction in[3],refer to Fig.11 in[8].A clearance is needed.Transverse shear failure becomes increasingly important and dominant when intensity of thedynamic loading increases.Until now,several analyses[3,8}12]have been concerned with thisfailure mode by employing the concept of`plastic shear sliding a or`plastic shear hinge a.In a rigid,perfectly plastic beam,it is generally assumed that a plastic shear hinge has an in"nitesimal length,that is,transverse shear sliding is treated as a transverse-displacement discontinuity which is theidealization of abrupt change in transverse displacement across a short segment of a beam[5].Onthe other hand,Wang and Jones[13]found that in a rigid-linear hardening beam subjected toimpulsive loading,the location of the shear hinge travels a"nite distance¸ during the failure process.A penetrating understanding of these basic failure modes is of fundamental importance to thefailure analyses of various structures under intense dynamic loading.Two important e!ects,however,have been ignored in all previous investigations:(i)the interaction between the shear forceand bending moment;and(ii)the weakening of the sliding sections during the failure process.Thus,the present paper is aimed at re-examining the shear failure problem of impulsively loaded beamsby various approaches,but focusing on these two factors.In addition to further comments and modi "cations on the elementary failure criterion,the interaction between the shear force and the bending moment at the sliding sections will be considered by adopting circular yield curve [14],Hodge 's curve [15],or a yield condition based on slip-line "eld solutions [16].The variation of the shear force and the bending moment over the sliding cross-sections during the beam 's deformation process will also be taken into account.2.Mode III failure of impulsively loaded clamped beams :general considerationConsider a clamped beam of length 2¸and of rectangular cross-section with thickness H and width B ,subjected to uniformly distributed initial velocity over the entire span,as shown in Fig.1.For a simply supported beam subjected to an impulsive velocity,Jones et al.[11,4]found that dimensionless ratio "Q ¸/2M with M and Q denoting the fully plastic bending moment and the fully plastic shear force of the cross-section,respectively,is an important parameter;di !erent transverse shear response modes occur when 41or '1.Obviously,this parameter mainly depends on the geometry of the beam.Nevertheless,it is of importance merely for some special beam cross-sectional shapes,such as wide-#anged I-beam or sandwich beam,where &1.As for the rectangular cross-sectional beam considered here, "¸/H 1.For instance,in the experiments conducted by Menkes and Opat [2], ranged from 5.33to 21.4.It was observed that,unlike tearing failure (Mode II)which followed the large de #ection of the beam (Mode I),transverse shear failure (Mode III)was characterized by insigni "cant #exural deformation at most cross-sections.There-fore,shear failure occurs at the supports in the early stage of the beam 's response and generally exhibits a type of localized behaviour,while the Mode III thresholds does not depend on the length of the beam.Thus,with the length of the beam being excluded from the theoretical description,if a rigid-plastic model is adopted,the maximum shear sliding at the supports, ,can be expressed as a function of impulsive velocity < ,yield stress >,density and thickness H of the beam: " (<,>, ,H ).(1)From the -theorem of dimensional analysis,we haveH "f < (>/ "f (( ).(2)Here non-dimensional parameter " < />is termed the damage number which is commonly used to specify the severity of impact,according to Johnson [17].Hence,if we adopt a criterion forFig.1.An impulsively loaded clamped beam.T.X.Yu,F.L.Chen /International Journal of Impact Engineering 24(2000)613}629615shear failure in form"kH (3)with k being a constant determined by experimental measurement or theoretical consideration,the threshold impulsive velocity for transverse shear failure (i.e.Mode III failure)can be expressed as< "f \ (k ) > .(4)It transpires that for rectangular cross-sectional beam with ¸/H 1,the threshold impulsive velocity for a Mode III failure does not depend on geometry of the beam but only on material properties.3.Elementary failure criterion (EFC )With the aid of the velocity "eld shown in Fig.2where sliding occurs at the supports of the beam having a "nite shear strength Q ,Jones [3]employed a simple rigid-plastic procedure to estimate the threshold velocity for the onset of a mode III failure as< " 2Q 3 BM.(5)In this simple theoretical analysis,an elementary failure criterion for complete severance at the supports of a beam" R<Q d t "H (6)was adopted.Condition (6)can be regarded as an extreme case of Eq.(3)with k "1.If von Mises yield criterion is adopted,then for a beam of rectangular cross-section,M ">BH /4and Q">BH /(3,so that < "2(23 > "0.943 > .(7)Fig.2.Velocity "eld for the impulsively loaded clamped beam with shear sliding at supports.616T.X.Yu,F.L.Chen /International Journal of Impact Engineering 24(2000)613}6294.Modi 5ed elementary failure criterionIt is observed in a few recent experiments [18,19]that in most cases the realistic shear failure is caused by a combination of shear sliding and crack propagation.In these cases,the elementary failure criterion (6)can be straightforwardly modi "ed to the form (3).The factor k (0(k 41)slightly depends on the material properties,geometric constraint of the structure as well as loading conditions.One may easily conjecture that the value of k for a tough material is larger than that for a brittle material [20].However,for a wide range of situations k can be approximately taken as a constant,say k "0.3.Using modi "ed elementary failure criterion (3)and following the same derivation given by Jones[3],the modi "ed threshold velocity for the onset of a Mode III failure is obtained as< " 2kQ 3 BM(8)which can be rewritten as< "2(23 k > "0.943 k > (9)for beams of rectangular cross-section.These two expressions predict a lower value of the threshold velocity < by a factor of (k .If k takes 0.3,(k "0.548,and consequently < "0.517(>/ .Both Eqs.(5)and (8)are based on the assumption that during the beam 's deformation process,the bending strength M and shear strength Q of the sliding section A (see Fig.2)remain constants M and Q and the same situation occurs at D.In other words,the internal force state of sections A and D is always located at the corner G (M ,Q )on the square yield locus (Fig.3(a)).This is,undoubtedly,a quite rough approximation,refer to the con "gurations sketched in Fig.4.The sketch suggests a weakening e !ect of shear sliding on the bending and shear strengthsof Fig.3.Yield loci on the m }q plane:(a)a square yield locus for intact sections and a rectangular yield locus for the sliding sections;(b)a yield circle for intact sections and yield ellipses for the sliding sections;(c)interactive yield curves based on slip-line "eld solutions for the sliding sections.T.X.Yu,F.L.Chen /International Journal of Impact Engineering 24(2000)613}629617Fig.4.Shear sliding takes place (a)over a cross-section;(b)over a "nite width.sections A and D,that is,M " M and Q " Q ,where the weakening factor depends on the shear sliding: " ( ).If the weakened bending moment M and the weakened shear force Q are incorporated into the deformation mechanism shown in Fig.2,then the conservation of linear momentum of segment AB demands< !< "2 R Q d t ,(10)while the conservation of angular momentum requires< !< "6 R (M #M )d t BHz .(11)It is noted that at interior hinges B and C,M "M and Q "0,so that the mid-portion of the beam,BC,moves at a constant velocity <.Eqs.(10)and (11)therefore result in the length of segment AB,z "3 R (M #M )d t R Q d t "3M Q R ( #1)d t Rd t 56M Q .(12)Eq.(12)indicates that two interior hinges B and C travel towards the mid-point as decreases from 1during the beam 's plastic deformation process.This is di !erent from the prediction that hinges B and C remain stationary until < "0based on the assumption of constant bending and shear strengths at the sliding sections A and D.Substituting Eq.(12)into Eq.(10)yieldsd d t "< "< !2Q 3 BHM R d t R ( #1)d t .(13)618T.X.Yu,F.L.Chen /International Journal of Impact Engineering 24(2000)613}629For rectangular cross-sectional beam,by introducing non-dimensional variables,, H , ,t H /< (14)Eq.(13)is recast into non-dimensional formd d "1!89 ( O d ) O( #1)d .(15)where is Johnson 's damage number mentioned before.Fig.4shows two con "gurations of the plastic shear deformation region.(a)The shear sliding is treated as a stationary,strong discontinuity,as introduced by Nonaka [9],Symonds [10]and Jones [3];then by assuming a statically admissible stress "eld at sliding sections A and D,we "nd "1! /H "1! .(b)A "nite width of shear sliding is considered.Experiments [2,18,19]and some theoretical models indicate that this width w is usually very small.For example,in the plastic shear band model shown in Section 7,only half of its total width,i.e.e ,lies outside the clamp "xture,so that the e !ective width of plastic shear deformation region of the beam,w ,could be taken as e "((3/8)H "0.216H .Referring to Fig.4(b),the maximum shear force then occurs over straight line E F provided 50.049H .Since "E F "+H ! ,it is seen that +1! /H "1! .Consequently,for both con "gurations (a)and (b),Eq.(15)can be rewritten asd d "1!89 O (1! )dO[(1! ) #1]d .(16)Eq.(16)is an integral-di !erential equation,which can be transformed into a standard set of "rst-order di !erential equations ready to be integrated numerically by means of a second-order Runge }Kutta procedure to obtain the maximum sliding as a function of , ( ).The calculated results are depicted in Fig.5,where the variation of the "nal value of the weakening factor, ,with is also exhibited.Recalling failure criterion (3),that is "k ,the threshold impulsive velocity for shear failure of the beam is thus determined as a function of parameter k , (k ).If the valueof Fig.5.The variation of the "nal value of the weakening factor and shear sliding with impulsive loading parameter .T.X.Yu,F.L.Chen /International Journal of Impact Engineering 24(2000)613}629619k in criterion (3)is speci "ed,a threshold value of can be determined accordingly.For example,if k "0.3,we "nd "0.221,and accordingly < "0.447(>/ .In addition,it can be seen from Fig.5that when approaches a critical value "0.369,the maximum shear sliding increases from 0.7H to 1.0H rapidly.Thus,a critical impulsive velocity is identi "ed as< " > "0.607 > .(17)It is 0.644times the value given by Eq.(7)but is 1.17times that by Eq.(9)for k "0.3.The di !erences re #ect the in #uence of the reductions of M and Q during the beam 's deformation process.5.Interaction between transverse shear and bending moment at sliding sectionsOn bending moment-shear force plane,interactive yield curves,rather than the square ones,provide better representations of the yield condition.Although interaction between shear force and bending moment is intricate,several interactive yield curves for beams of rectangular cross-section have been proposed from various postulations.5.1.Circular yield cur v e (CYC )A typical one of these interactive yield curves is a circlem #q "1(18)with m "M /M and q "Q /Q ,as shown in Fig.3(b).This was found by Robinson [14]from an approximation to Ilyushin }Shapiro 's yield surface [21,22]and is the special case of m (1!q ) #n #q "1with n "0,which was derived from a uniform stress distribution in a rectangular cross-section [23].According to the associated #ow rule,the generalized velocity vector (< Q , M)must be normal to the yield curve,that is,M Q < "(34H < "! q(19)where denotes the angular velocity about the generalized plastic hinge A.Di !erentiating Eq.(18)givesq m "!(1!q ) q.(20)For any given value of q / m ,q can be determined from this equation,and then m can be calculated from yield condition (18)as follows:m "(1!q) (21)so that the location of the internal force state on the yield circle can be determined.620T.X.Yu,F.L.Chen /International Journal of Impact Engineering 24(2000)613}629Applying the velocity "eld shown in Fig.2,Eqs.(10)and (11)provide< "< 1!8 9(22)and"< !< z "< H 32 27(3,(23)where, O q d ,v , O(m #1)d .(24)Substitution of Eqs.(22)and (23)into Eq.(19)results inq"!8 27 !24 .(25)Eq.(22)is then recast intod d "1!8 9 .(26)With the help of (24),(25),(20)and (21),Eq.(26)is numerically integrated by means of a second-order Runge }Kutta procedure starting from initial conditions "0,q "1,m "0at "0.The results reveal that on the yield circle,the internal force state of sections A and D moves from point R counterclockwise in the early stage and approaches point S in the later stage.The prediction on the "nal shear sliding obtained from Eq.(26),as marked by `CYC a in Fig.6(a),is larger by around 25%than that given by Jones [3]based on the assumption of constant shear force and bending moment at sections A and D.To reach "k "1, " "0.706and correspond-ingly < "0.840(>/ ;or to reach "k "0.3, " "0.212and correspondingly < "0.460(>/ .In the foregoing analysis,the weakening e !ect of the shear sliding on the interactive yield condition is neglected.If this weakening e !ect is incorporated,as discussed in the later part of Section 4,the bending and shear strengths of the sliding sections may be expressed as M " M and Q " Q,with weakening factor "1! .Then,the yield condition (18)is modi "ed as m # q"1(27)and accordingly Eqs.(20)and (21)are replaced byq m "! 1! q q (28)T.X.Yu,F.L.Chen /International Journal of Impact Engineering 24(2000)613}629621Fig.6.A comparison with the result given in Ref.[3]on the predictions of the "nal shear sliding from various interactive yield curves with the weakening e !ect of the shear sliding incorporated:(a)circular yield curve (CYC)and Hodge 's yield curve (HYC);(b)yield curve based upon slip-line "eld solutions (SLF).andm " 1! q (29)whilst Eqs.(24)}(26)remain valid.As a result,the internal force state moves along the yield curve while the yield condition of sliding sections A and D progressively shrinks on the q }m plane:R P P P P P2,as sketched in Fig.3(b).Predictions on the "nal shear sliding are marked by `CYC-W a in Fig.6(a).Yet when approaches a critical value "0.396,the "nal shear sliding increases from 0.65H to 1.0H rapidly,so that a critical impulsive velocity is identi "ed as < "(>/ "0.629(>/ .5.2.Hodge 's yield cur v e (HYC )With the help of a variational method,Hodge [15]obtained another interactive yield curve between shear force and bending moment for beams of rectangular cross-section asq "ln ((1# # )/ (30a)622T.X.Yu,F.L.Chen /International Journal of Impact Engineering 24(2000)613}629andm "((1# !q )/(30b)with serving as a parameter.It can be well approximated by [24]m # q #q "1.(31)This yield curve closely circumscribes the yield circle (18),but inscribes the square yield condition.Similar to the analysis in Section 5.1,by taking account of weakening e !ect of the sliding sections,another critical impulsive velocity is obtained as < "(>/ "(0.415>/ "0.644(>/ .5.3.Slip-line x eld solutions (SLF )Based on slip-line "elds constructed in the root region of cantilever beams under various loading conditions,Yu and Hua [16]obtained an interactive yield curve between m and q at the beam 's root,which can be "tted by a single approximationm !2.106q #4.632q !1.526q !1"0(32)with error less than 1%,as depicted in Fig.3(c).Adopting this interactive yield,we can get clear deformation patterns for the plastic shear failure of the dynamically loaded beams.Eqs.(20)and (21)and (27)}(29)are accordingly replaced byqm"(1#2.106q !4.632q #1.526q ) 1.053!4.632q #2.289q ,(33)m "(1#2.106q !4.632q #1.526q ) (34)andm!2.106 q #4.632 q !1.526 q!1"0,(35) q m "[1#2.106(q / )!4.632(q / ) #1.526(q / ) ] [1.053!4.632(q / )#2.289(q/ ) ],(36)m " 1#2.106 q !4.632 q #1.526 q.(37)Hence,the beam 's shear failure progress can also be traced as in Section 5.1.Fig.7exhibits the history of the shear force and the bending moment at sliding section A.Similar variation trends are obtained as adopting circular or Hodge 's yield curves in these sections.From the prediction on the "nal shear sliding shown in Fig.6(b),it is found that when approaches a critical value"0.410,the "nal shear sliding increases from 0.65H to 1.0H rapidly,so thata critical impulsive velocity is also identi "ed as < "(>/ "0.641(>/ .For a speci "ed ,Fig.7.The history of shear force and bending moment at end A(sliding section)based on SLF.this interactive yield condition results in a slightly smaller prediction on the"nal shear sliding compared with that from circular or Hodge's yield curves.The reason is that the slip-line solution is an upper bound while the latter two are lower bounds of the true yield condition.6.Plastic dissipation at sliding sectionsWith regard to the deformation mechanism shown in Fig.2,the increment of plastic dissipation merely due to shear deformation at sliding sections A and D isd E "Q d "q Q H d ,(38) while the increment of plastic dissipation due to bending isd E "M < !<zd t"m Q H(d !d )3.(39)Hence,the history of plastic dissipation can be traced by using each of the foregoing approaches. The ratio of plastic dissipation merely due to shear deformation to the total dissipation due to both bending and shear,de"ned by,EE "EE #E(40)can then be calculated.Fig.8(a)shows the variation of the ratio with time for three representative values of .For any speci"ed values of (4 ), decreases quickly from1.0in the very early stage after impact,then it approaches gradually to its"nal value at< "0,when the shear sliding ceases.In other words, shear sliding dominates the plastic dissipation in the very early stage,but this stage swiftly transits to the stage of shear-bending deformation.In correspondence to each of the critical values obtained from various approaches,the critical values of ,denoted by ,based on these approaches can be obtained and summarized in Table1.A & curve calculated from CYC withFig.8.(a)The variation history of ratio with time;(b)the variation of "nal value of with impulsive loading parameter (CYC-W).the weakening e !ect of shear sliding being considered is shown in Fig.8(b).It can be seen that when ( ,the calculated values of are notably less than,that is,at the end of dynamic response ofthe beam,shear sliding only dissipates a small portion of the total energy,so at the supports shear failure will not take place.Based on a comparison with the experimental results conducted by Menkes and Opat [2],Shen and Jones [8]suggested that the critical value of at the onset of Mode III failure,,could beestimated as 0.45.On the other hand,as shown in Table 1,our study indicates that the values ofcalculated from the square yield condition range from 0.85to 0.94,around double of 0.45,but those calculated from the interactive yield curves range from 0.44to 0.66,fairly close to"0.45suggested in Ref.[8].7.Shear strain failure criterionThe shear sliding at the supports of a beam subjected to impulsive load may be expressed as [25]" e(41)where shear sliding is an accumulative quantity over the shear band, is the average shear strain and e is the half-width of the shear band as de "ned in Fig.9.As mentioned in Section 4,although the shear band has a total width of 2e ,only half of its width lies outside the clamp "xture;so the e !ective width of plastic shear deformation region of the beam should be e ,see Ref.[26]for details.From the elementary beam theory,it can be deduced [26]that e "M2Q"(38H .(42)Substituting Eq.(42)into Eq.(41)yields"(38H .(43)Fig.9.Shear bands located at the supporting ends.Thus,when transverse shear failure occurs at the supports,a critical shear slidingis reached,i.e."(38H ,(44)whereis the rupture shear strain of the beam material,which may be taken a typical value of 0.5for aluminum alloy and 0.8for mild steel [25].Hence,if expressed in uniform form (3),it is found that k "((3/8)"0.108and 0.173,respectively.As in Ref.[26],it is assumed that the displacement pro "le of a clamped beam after impulsively loading as="= [1!(x /¸) ]for 41,=[1!(x /¸) ? ]for 51,(45)where "I /I with Ibeing the critical input impulse at which the beam fails by tensile tearing.Byexploiting the principle of equivalent work done,the critical input impulse Irequired to causetransverse shear failure of the beam can be deduced as (refer to Eq.(35b)in Ref.[26])I >B H "4!3(H /¸) 4(H /¸) # (1#n )(H /¸)(46)so that the threshold impulsive velocity is found to be<"4!3(H /¸) 16#(H /¸)4(1#n )>(47)in which n is the work-hardening index of the material.It slightly depends on the rupture shearstrainand the thickness-to-length ratio H /¸.As H /¸P 0,it has a limit value<"0.5>.(48)It is interesting to note that this limit threshold velocity is very close to that given by Eq.(9)for k "0.3.。