1+Introduction
§1 The objective of mechanics of materials
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§1 The objective of mechanics of materials
Under the request that the strength, rigidity, stability are satisfied, offer the necessary theoretical foundation and calculation method for determining reasonable shapes and dimensions, choosing proper materials for the components at the most economic price.
Foreign teacher lesson 15%, Final Exam 65%,
Tutor Details
Lecturer : Dr. Zongjian-Yao（姚宗健） Email: 39189611@ Tel: 13256769973
Mechanics of Materials
刚度 : 杆件在外载作用下，抵抗弹性变形的能力。
稳定性 : 杆件在压力外载作用下，保持其原有平衡状态的能力。
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§1 The objective of mechanics of materials
Problems about the strength, rigidity and stability of engineering structures
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§1 The objective of mechanics of materials
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§1 The objective of mechanics of materials
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§1 The objective of mechanics of materials
Problems about the strength, rigidity and stability in large bridges.
Mechanics of Materials 材料力学
Course Details
Activity: 80classes, 72Lectures and 8 Laboratory Sessions Assessment: Attendance 10%, Assignments 5%, Experiment 5%,
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(a)
(b)
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§1 The objective of mechanics of materials
Strength :
Capacity to resist failure of a component or an element.
Rigidity : Capacity to resist deformations of a component or an element.
strength
Problems about
rigidity
stability
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§1 The objective of mechanics of materials
工程结构的强度、 刚度和稳定问题 强 稳刚 度 定度 问 题
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§1 The objective of mechanics of materials
Stability : Capacity to remain the original state in equilibrium of a component or an element
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§1 The objective of mechanics of materials
强度 : 杆件在外载作用下，抵抗断裂或过量塑性变形的能力。
Strength of Materials and Mechanics of Deformable Bodies
Physics and Theoretical Mechanics: The general rule of movement（Particle、Rigid Body）
Particle:mass Rigid Body: mass and volume Deformable Body: mass, volume and deformation
Particle —— Rigid Body —— Deformable Body The result of the development of mechanics
Mechanics of Materials
Chapter 1 Introduction and Basic Concepts
§1 The objective of mechThe objective of mechanics of materials
Strength(强度): Capacity to resist failure of a component or an element.
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§1 The objective of mechanics of materials
Determine the stresses, strains and displacements in structural members due to the loads acting on them Make sure the member or the structure is stable Strength、 Rigidity、 Stability
There are problems about the strength, rigidity and stability in a bicycle structure too
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§1 The objective of mechanics of materials
自行车结构也有强度、 刚度和稳定问题
Rigidity(刚度): Capacity to resist deformations of a component or an element.
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§1 The objective of mechanics of materials
Stability(稳定性): Capacity to remain the original state in equilibrium of a component or an element
Chapter 1 Introduction
Chapter 1 IntroductionⅠ. Decide whether each of the following statements is True or False:1. Linguistics is generally defined as the scientific study of language.2. Linguistics studies particular language, not languages in general.3. A scientific study of language is based on what the linguist thinks.4. In the study of linguistics, hypotheses formed should be based on language facts and checked against the observed facts.5. General linguistics is generally the study of language as a whole.6. General linguistics, which relates itself to the research of other areas, studies the basic concepts, theories, descriptions, models and methods applicable in any linguistic study.7. Phonetics is different from phonology in that the latter studies the combinations of the sounds to convey meaning in communication.8. Morphology studies how words can be formed to produce meaningful sentences.9. The study of the ways in which morphemes can be combined to form words is called morphology.10. Syntax is different from morphology in that the former not only studies the morphemes, but also the combination of morphemes into words and words into sentences.11. The study of meaning in language is known as semantics.12. Both semantics and pragmatics study meanings.13. Pragmatics is different from semantics in that pragmatics studies meaning not in isolation, but in context.14. Social changes can often bring about language changes.15. Sociolinguistics is the study of language in relation to society.16. Modern linguistics is mostly prescriptive, but sometimes descriptive.17. Modern linguistics is different from traditional grammar.18. A diachronic study of language is the description of language at some point in time.19. Modern linguistics regards the written language as primary, not the written language.20. The distinction between competence and performance was proposed by F. de Saussure.Ⅱ. Fill in each of the following blanks with one word which begins with the letter given:21. Chomsky defines “competence” as the ideal user’s k__________ of the rules of his language.22. Langue refers to the a__________ linguistic system shared by all the members of a speech community while the parole is the concrete use of the conventions and application of the rules.23. D_________ is one of the design features of human language which refers to the phenomenon that language consists of two levels: a lowerlevel of meaningless individual sounds and a higher level of meaningful units.24. Language is a system of a_________ vocal symbols used for human communication.25. The discipline that studies the rules governing the formation of words into permissible sentences in languages is called s________. 26. Human capacity for language has a g_______ basis, but the details of language have to be taught and learned.27. P _______ refers to the realization of langue in actual use.28. Findings in linguistic studies can often be applied to the settlement of some practical problems. The study of such applications is generally known as a________ linguistics.29. Language is p___________ in that it makes possible the construction and interpretation of new signals by its users. In other words, they can produce and understand an infinitely large number of sentences which they have never heard before.30. Linguistics is generally defined as the s _______ study of language.Ⅲ. There are four choices following each statement. Mark the choice that can best complete the statement:31. If a linguistic study describes and analyzes the language people actually use, it is said to be _______.A. prescriptiveB. analyticC. descriptiveD. linguistic32. Which of the following is not a design feature of human language?A. ArbitrarinessB. DisplacementC. DualityD. Meaningfulness33. Modern linguistics regards the written language as _______.A. primaryB. correctC. secondaryD. stable34. In modern linguistics, speech is regarded as more basic than writing, because _______.A. in linguistic evolution, speech is prior to writingB. speech plays a greater role than writing in terms of the amount of information conveyedC. speech is always the way in which every native speaker acquires his mother tongueD. All of the above35. A historical study of language is a _______ study of language.A. synchronicB. diachronicC. prescriptiveD. comparative36. Saussure took a(n) _______ view of language, while Chomsky looks at language from a ________ point of view.A. sociological psychologicalB. psychological sociologicalC. applied pragmaticD.semantic linguistic37. According to F. de Saussure, _______ refers to the abstract linguistic system shared by all the mem- bers of a speech community.A. paroleB. performanceC. langueD. Language38. Language is said to be arbitrary because there is no logical connection between _______ and meanings.A. senseB. soundsC. objectsD. ideas39. Language can be used to refer to contexts removed from the immediate situations of the speaker. This feature is called _______,A. displacementB. dualityC. flexibilityD. cultural transmission40. The details of any language system is passed on from one generation to the next through _______, rather than by instinct.A. learningB. teachingC. booksD. both A and BⅣ. Define the following terms:41. Linguistics42. Phonology43. Syntax44. Pragmatics45. Psycholinguistics46. Language47. Phonetics48. Morphology49. Semantics50. Sociolinguistics51. Applied Linguistics52. Arbitrariness53. Productivity54. Displacement55. Duality56. Design Features57. Competence58. Performance59. Langue60. ParoleⅤ. Answer the following questions as comprehensively as possible. Give examples for illustration if necessary:62. What are the design features of human language? Illustrate them with examples.63. How is modern linguistics different from traditional grammar?。
考研 1 introduction_of_Linguistics
Arbitrariness ---任意性，最先由
Saussure提出，语言学之父。 Arbitrary relationship between the sound of a morpheme and its meaning.
Duality（二重性） 语言是层级性的，主要是由
syllables morphemes word phrase sentence discourse这么个系统组成的。 (浙大）问答题：Explain what the term duality means as it is used to describe a property of human lg.
讲义一 Introduction to Linguistics
Grace Tan
T/F
1.The relation between form and meaning in human
language is natural. 2.When lg is used to get information from others , it serves an informative function. 3.The reason for French to use Cheval and English to use horse to refer to the same animal is inexplicable. 4.Most animal communication systems lack the primary level of articulation. 5.Halliday′s linguistic potential is similar to the notions of parole and performance. 6.Descriptive linguistics are concerned with how lgs work, not with how they can be improved.
[英语学习]unit-1-Introduction
![[英语学习]unit-1-Introduction](https://360docs-1393072327.cos.ap-beijing.myqcloud.com/c54459bff7ec4afe05a1df71.webp)
展。
• a Panorama of Publishing 出版业概况 • book industry 图书出版业 • book community 书业团体
Questions on part 1
• 1 [+ obj] : to prepare and produce (a book, magazine, etc.) for sale ▪ It's a small company that only publishes about four books a year. ▪ The university press publishes academic titles. ▪ The newspaper is published daily. 2 : to have something you wrote included in a book, magazine, newspaper, etc. [no obj] ▪ There is a lot of pressure for professors to publish regularly. [+ obj] ▪ He has not published anything for a long time. 3 [+ obj] : to include (an article, letter, photograph, etc.) in a magazine or newspaper ▪ The magazine published two of my stories.
3. intriguing
1-introduction (s)(1-简介)
Marketing is so much more than that!（营销远 不止这些）
Packaging（包装） Strategy（策略） Competitive Strategies（竞 Sales, Sales-force 争优势） （销售，销售队伍） Market Penetration（市场 Brand Management 渗透） （品牌管理） Quality（质量）
Meaning:
Creating customer value and satisfaction are at the heart of modern marketing thinking A very simple definition of marketing is the delivery of customer satisfaction at a profit. Goals of marketing are to attract new customers by promising superior value and to keep and grow current customers by delivering satisfaction. Marketing is much more than selling and advertising. It is about understanding and satisfying customer needs.
Logistics（物流） Location（定位） Distribution Channels（分销渠道） Pricing Considerations（价格策略）
Globalization（全球化）
New Product Develop（新产品开发） Service Delivery（服务交付）
1Introduction
主要内容 (Outline)• 绪论小规模集成电路三（SSI）• 逻辑函数基础 门电路个• 组合逻辑电路模 块中规模集成电路 （MSI）• 集成触发器 • 时序逻辑电路大规模集成电路 • 半导体存储器（LSI）• 数模、模数转换电路绪论 (Introduction)一、数字(digital)信号和模拟(analog)信号 数字量和模拟量 数字电路和模拟电路二、数字信号相关概念 二进制数 Binary Digits 数字信号的逻辑电平 Logic Levels 数字信号波形 Digital Waveforms一、Digital Signal and Analog Signal Digital and Analog Quantities电子 电路 中的 信号模拟信号: 连续analogue signal value数字信号: 离散digital signal valuetime time模拟信号T( C) 30采样信号T( C)sampled3025离散化 2520202 4 6 8 10 12 2 4 6 8 10 12 t (h)A.M.P.M.2 4 6 8 10 12 2 4 6 8 10 12 t (h)A.M.P.M.数字化－表示 为由0、1组成 的二进制码Analog Electronic SystemDigital and Analog Electronic System★ 工作在模拟信号下的电子电路是模拟电路。
研究模拟电路时，注重电路输入、输出信号 间的大小、相位关系。
包括交直流放大器、 滤波器、信号发生器等。
★ 模拟电路中，晶体管一般工作在放大状态。
★ 工作在数字信号下的电子电路是数字电路。
研究数字电路时，注重电路输出、输入间的逻 辑关系。
主要的分析工具是逻辑代数，电路的 功能用真值表、逻辑表达式或波形图表示。
★ 在数字电路中，三极管工作在开关状态， 即工作在饱和状态或截止状态。
Lecture 1 Introduction
LOGO
（4）Expressiveness
It is the East, and Juliet is the sun! Arise, fair sun, and kill the envious moon… (Shakespeare, Romeo and Juliet) 那就是东方, 朱丽叶就是太阳! 起来吧,美丽的太阳! 赶走那妒忌的月亮……(朱生豪译)
这是莎士比亚名剧《罗密欧与朱丽叶》 中罗密欧的一段台词.正是通过这种直接 的抒情, 表现了罗密欧炽热而真挚的情 怀,以及他对朱丽叶的仰慕之情.这是一 种直抒胸臆的表达方法.
LOGO
Shall I compare thee to a summer‟s day? Thou art more lovely and more temperate: Rough winds do shake the darling buds of May, And summer‟s lease hath all too short a date 我可能把你和夏天相比拟？ 你比夏天更可爱更温和： 狂风会把五月的花苞吹落地 夏天也嫌太短促，匆匆而过。(梁实秋译)
LOGO
The child is father of the man. (Wordsworth) 儿童是成人之父 童年的经历可决定成年后的性格. Then her soul sat on her lips，and language flowed， from what source I cannot tell．(Jane Eye，Chapter 8) 译文一：于是她能把思想表达出来，话流露出来了， 从什么地方来的我却不知道。(李霁野，1990：84) 译文二：接着，她的心灵就像坐在她的嘴唇上似的， 话语滔滔不绝地流出来；我也说不出它是从哪个源头流 出来的。(祝庆英，1980：90)
Topic 1 Introduction
Trygve Haavelmo (Norway)
1980 Nobel Laureates in Economics
Lawrence R. Klein (University of Pennsylvania), “For the creation of econometric models and their application to the analysis of economic fluctuations and economic policies”
Topic 1: Introduction to Econometrics
What is econometrics? Why study econometrics? Types of econometrics Nobel Prize and Econometrics Methodology of econometrics
2. Specification of the Mathematical Model 1) Specification of variables e.g. consumption (income) inflation (money supply of the previous period, GDP growth rate) income (qualification, IQ, EQ, gender, etc.) weight (height, gender, race, age, etc.) * It should be based on economic theory and analysis of economic phenomena * Data availability * The relationship among variables: independence
unit1_introduction
The aim/ purpose of this report is to… This present report sets out to… My purpose in writing/ My purpose of writing this report is to… In writing this report, I aim to… It has been found out that… The findings show that… I found out that…
an insurance policy covering loss of movable property (e.g. jewelry) regardless of its location
Floating policy is of great importance for export trade; it is, in fact, a convenient method of insuring goods where a number of similar export transactions are intended, e.g. where the insured has to supply an oversea importer under an exclusive sales agreement or maintains sales representatives or subsidiary companies abroad. 统保单对出口贸易至关重要。它实际上是货物保险中 的一种便利的办法， 特别适用于分不同的时间出口的 一批类似的货物，如， 被保险方根据独家代理协议书 向国外的进口方供货，或在国外委任了销售代表设立 分支机构时使用。
1. INTRODUCTION
1. INTRODUCTION1.1. WHY USE ELECTRONS?Why should we use an electron microscope? Historically, TEMs were developed because of the limited image resolution in light microscopes, which is imposed by the wavelength of visible light. Only after electron microscopes were developed was it realized that there are many other equally sound reasons for using electrons, most of which are utilized to some extent in a modern TEM. By way of introduction to the topic let's look at how the TEM developed and the pros and cons of using such an instrument.1.1.A. An Extremely Brief HistoryLouis de Broglie (1925) first theorized that the electron had wave-like characteristics, with a wavelength substantially less than visible light. Then Davisson and Germer (1927) and Thompson and Reid (1927) independently carried out their classic electron diffraction experiments which demonstrated the wave nature of electrons. It didn't take long for the idea of an electron microscope to be proposed, and the term was first used in the paper of Knoll and Ruska (1932). In this paper they developed the idea of electron lenses into a practical reality, and demonstrated electron images taken on the instrument shown in Figure 1.1. This was a most crucial step, for which Ruska received the Nobel Prize, somewhat late, in 1986. Within a year of Knoll and Ruska's publication, the resolution limit of the light microscope was surpassed. Ruska, surprisingly, revealed that he hadn't heard of de Broglie's ideas about electron waves and thought that the wavelength limit didn't apply to electrons. TEMs were developed by commercial companies only four years later. The Metropolitan-Vickers EM 1 was the first commercial TEM. It was built in the UK in 1936, but apparently it didn't work very well and regular production was really started by Siemens and Halske in Germany in 1939. TEMs became widely available from several other sources (Hitachi, JEOL, Philips and RCA, inter alia) after the conclusion of World War II.For materials scientists a most important development took place in the late 1940s when Heidenreich (1949) first thinned metal foils to electron transparency. This work was followed up by Bollman in Switzerland and Hirsch and co-workers in Cambridge. Because so much of the early TEM work examined metal specimens, the word "foil" has come to be synonymous with "specimen." In addition, the Cambridge group also developed the theory of electron diffraction contrast with which we can now identify, often in a quantitative manner, all known line and planar crystal defects in TEM images. This theoretical work is summarized in a formidable but essential text often referred to as the "Bible" of TEM (Hirsch et al. 1977). For the materials scientist,practical applications of the TEM for the solution of materials problems were pioneered in the United States by Thomas and first clearly expounded in his text (Thomas 1962). Other materials-oriented texts followed, e.g., Edington (1976) and Thomas and Goringe (1979).Today, TEMs constitute arguably the most efficient and versatile tools for the characterization of materials. If you want to read a history of the TEM, the book by Marton (1968) is a compact, personal monograph and that edited by Hawkes (1985) contains a series of individual reminiscences. Fujita (1986) emphasizes the contribution of Japan to the development of the instrument. The field is now at the point where many of the pioneers have put their memoirs down on paper, or Festschrifts have been organized in their honor (e.g., Cosslett 1979, Ruska 1980, and Hashimoto 1986) which detail their contributions over the decades, and compile some useful overview papers of the field. If you enjoy reading about the history of science, we strongly recommend the review of Fifty Years of Electron Diffraction, edited by Goodman (1981), and Fifty Years of X-ray Diffraction, edited by Ewald (1962). (The spelling of X-ray is discussed in the CBE Manual, 1994.)Figure 1.1. The electron microscope built by Ruska and Knoll in Berlin in the early 1930s.1.1.B. Microscopy and the Concept of ResolutionWhen asked what a "microscope" is, most people would answer that it is an instrument for magnifying things too small to see with the naked eye, and most likely they would be referring to the visible-light microscope. Because of the general familiarity with the concept of the light microscope, we will draw analogies between electron and visible-light microscopes wherever it's instructive.The smallest distance between two points that we can resolve with our eyes is about 0.1-0.2 mm, depending on how good our eyes are, and assuming that there's sufficient illumination to see by. This distance is the resolution or resolving power of our eyes. So any instrument that can show us pictures (or "images" as we'll refer to them) revealing detail finer than 0.1 mm could be described as a microscope, and its highest useful magnification is governed by its resolution. A major attraction to the early developers of the TEM was that, since electrons are smaller than atoms, it would be possible, at least theoretically, to build a microscope that could "see" detail well below the atomic level. The idea of being able to "see" with electrons may be confusing to you. Our eyes are not sensitive to electrons. If a beam of high-energy electrons was aimed into your eye, you would most likely be blinded as the electrons killed the retinal cells, but you wouldn't see anything! So an integral part of any electron microscope is a viewing screen of some form, which translates electron intensity to light intensity, and which we observe or record photographically. We'll discuss these screens and other ways of recording electron images in later chapter.The resolution of a TEM means different things for different functions of the instrument, and we'll discuss them in the appropriate chapters. It's easiest to think of the image resolution in TEM in terms of the classical Rayleigh criterion for light microscopy, which states that the smallest distance that can be resolved, , is given approximately by δβµλ=δsin 61.0 [1.1]In equation 1.1, is the wavelength of the radiation, is the refractive index of the viewing medium, and is the semiangle of collection of the magnifying lens. For the sake of simplicity we can approximate sin (which is sometimes called the numerical aperture) to unity and so the resolution is equal to about half the wavelength of light. For green light in the middle of the visible spectrum, is about 550 nm (5500Å), and so the resolution of a good light microscope is about 300 nm. In TEMs we can approximate the resolution in equation 1.1 to 0.61/ which, as we'll see later, is very small.λµβµβλλβNow although 300 nm is a small dimension to us it corresponds to about 1000 atom diameters, and therefore many of the features that control the properties of materials are on a scale well below the resolution of the light microscope. So there's a real need to image detail down to the atomic level if we want to understand the properties of materials, and that's a major reason why TEMs are so useful.We'll try to use nanometers throughout this book, but you'll find that many microscopists still insist on using Angstroms rather than the SI units. However, the Angstrom is close to the atomic diameter and so is a more convenient unit because it saves us using convoluted phrases like “three tenths of a nanometer.”This limit of light microscopy was well understood at the turn of this century and prompted Ernst Abbe, one of the giants in the field, to complain that "it is poor comfort to hope that human ingenuity will find ways and means of overcoming this limit." (He was right to be so depressed because he died in 1905, some 20 years before de Broglie's ingenuity solved the problem.) Now de Broglie's famous equation shows that the wavelength of electrons is related to their energy, E, and if we ignore relativistic effects we can show approximately (and exactly in Section 1.4 below) that2/122.1~Eλ [1.2]In this equation E is in electron volts (eV) and in nm. Remember that we should be precise in our use of the units V and eV: the former represents the accelerating voltage of the microscope while the latter refers to the energy of the electrons in the microscope. So for a 100-keV electron, we find that ~ 4 pm (0.004 nm), which is much smaller than the diameter of an atom.λλFigure 1.2. A twin boundary in spinel stepping from one {111} plane to another parallel plane. The white dots are columns of atoms. The change in atomic orientation across the twin boundary can be readily seen, even if we do not know what causes the white dots or why, indeed, they are white.We'll see later that we are nowhere near building TEMs that approach this wavelength limit of resolution, because we can't make perfect electron lenses (see Section 2). But progress was rapid after Ruska's early work on lenses and, since the mid-1970s, many commercial TEMs have been capable of resolving individual columns of atoms in crystals, creating the field of "high-resolution transmission electron microscopy," or HRTEM. A typical HRTEM image is shown in Figure 1.2. The advantages of shorter wavelengths led in the 1960s to the development of high voltage electron microscopes (HVEMs), with accelerating potentials between 1 MV and 3 MV . In fact, most of these instruments were used to introduce controlled amounts of radiation damage into specimens in an attempt to simulate nuclear reactor environments, but changes in the emphasis of energy research mean there is not much call for such instruments today. While we can still improve the resolution byincremental amounts, the drive for much better resolution is now no longer paramount and the TEM is developing in other ways. In fact, only one HVEM (1 MV) for HRTEM imaging was constructed in the 1980s and three 1.25-MV machines in the 1990s. Intermediate voltage electron microscopes (IVEMs) were introduced in the 1980s. These TEMs operate at 300 or 400 kV, but still offer very high resolution, close to that achieved at 1 MV.1.1.C. Interaction of Electrons with MatterElectrons are one type of "ionizing radiation," which is the general term given to radiation that is capable of removing one of the tightly bound inner-shell electrons from the attractive field of the nucleus.One of the advantages to using ionizing radiation is that it produces a wide range of secondary signals from the specimen, and some of these are summarized in Figure 1.3. Many of these signals are used in "analytical electron microscopy,'' or AEM, giving us chemical information and a lot of other detail about our samples. AEM uses X-ray energy dispersive spectrometry (XEDS) and electron energy-loss spectrometry (EELS). For example, Figure 1.4A is an X-ray spectrum from a very small region of a TEM specimen showing characteristic peaks which identify the elements present. We can transform such spectra into quantitative data describing elemental changes associated with inhomogeneous microstructures as also shown in Figures 1.4B and C. In contrast, microscopes using nonionizing radiation such as visible light usually only generate light (but not much heat, which is good). AEMs generally offer improved performance at intermediate voltages, similar to HRTEMs.Figure 1.3. Signals generated when a high-energy beam of electrons interacts with a thin specimen. Most of these signals can be detected in different types of TEM. The directions shown for each signal do not always represent the physical direction of the signal but indicate, in a relative manner, where the signal is strongest or where it is detected.In order to get the best signal out of our specimens we have to put the best signal in, and so the electron source is critical. We are now very accomplished in this respect as you'll see in Section 4, so modern TEMs are very good signal-generating instruments. To localize these signals we need to get our TEM to form a very fine electron beam, typically <10 nm and at best <1 nm in diameter. We accomplish this by combining TEM and scanning electron microscope (SEM) technology to create a scanning transmission electron microscope (STEM). The STEM is both the basis for AEMs and a unique scanning imaging microscope in its own right. In fact there are instruments that are only capable of operating in scanning mode and these are sometimes referred to as "dedicated STEMs," or DSTEMs.1.1.D. Depth of FieldThe depth of field of a microscope is a measure of how much of the object we are looking at remains "in focus" at the same time. Like the resolution, this property is governed by the lenses in the microscope. The best electron lens is not a very good one, as we've already mentioned, and has been compared to using the bottom of a Coca-Cola bottle as a lens for light microscopy. To minimize this problem we have to use very small limiting apertures in the lenses, narrowing the beam down to a thin "pencil" of electrons which at most is a few micrometers across. These apertures cut down the intensity of the electron beam, but also act to increase the depth of focus of the images that we produce. Remember that "depth of field" refers to the specimen while "depth of focus" refers to the image.While this large depth of field is chiefly used in the SEM to produce 3D-like images of the surfaces of specimens with large changes in topography, it is also critical in the TEM. It turns out that in the TEM, all of the specimen is usually in focus at the same time, independent of the specimen topography, as long as it's electron transparent! Figure 1.5 shows a TEM image of some dislocations in a crystal. The dislocations appear to start and finish in the specimen, but in fact they are threading their way through the specimen from the top to the bottom, and they remain in sharp focus at all times. Furthermore, we can record the final image at different positions below the final lens of the instrument and it will still be in focus. Compare this with the visible-light microscope where, as you probably know, unless the surface of the specimen is flat to within the wavelength of light, it is not all in focus at the same time. This aspect of TEM gives us both advantages and disadvantages in comparison to the visible-light microscope.A BC Figure 1.4. (A) An X-ray spectrum from asmall biotite crystal showing peaks atenergies that are characteristic of theelements present in the region thatinteracts with the electron beam. Themajor peaks from left to right are for Mg,Al, Si, K, Fe, and the Cu support grid. (B)A TEM image of a precipitate-free zone(PFZ) in an aged Al-16 wt% Ag alloy. (C)The Ag profile across the PFZ in (B),obtained through X-ray spectrometry inthe TEM showing the depletion of Agresponsible for the PFZ formation.Figure 1.5. TEM image of dislocations in GaAs. A band of dislocations threads through the thin specimen from the top to the bottom but remains in focus through the foil thickness.1.1.E. DiffractionThompson and Reid showed that electrons could be diffracted when passing through thin crystals of nickel, and the possibility of combining electron diffraction into TEMs was realized by Kossel and Mollenstedt (1939). Today, electron diffraction is an indispensable part of TEM and is arguably the most useful aspect of TEM for materials scientists. Figure 1.6 shows a TEM diffraction pattern which contains information on the crystal structure, lattice repeat distance, and specimen shape, as well as being a most striking pattern. We'll see that the pattern can always be related to the image of the area of the specimen from which it came, in this case shown in the inset. In addition to the things we just listed, you can conduct a complete crystallographic symmetry analysis of minuscule crystals, including such esoteric aspects as point-group and space-group determination, and at all times the crystallography can be related to the image of your specimen. There is no similar capability on a light microscope because of the relatively large wavelength of visible light.So an electron microscope can produce atomic level images, can generate a variety of signals telling you about your sample chemistry and crystallography, and you can always produce images that are in focus. There are many other good reasons why you should use electron microscopes. We hope they will become evident as you read through this book. At the same time there are many reasons why you should not always seek to solve your problems with the TEM, and it is most important that you realize what the instrument cannot do, as well as knowing its capabilities.Figure 1.6. TEM diffraction pattern from a thin foil of A1-Li-Cu containing various precipitate phases, shown in the inset image. The central spot (X) contains electrons that come directly through the foil and the other spots and lines are diffracted electrons which are scattered from different crystal planes.。
unit_1_Introduction_and_greeting
I will choose two groups to present!
Dialog 1
• • • • • • Read the dialog together. Find out the elements below: Who: Where: When: What:
• Page 6. Act Out.
forms and ceremonies seriously; freedom from constraint or embarrassment 非正式，不拘礼节
a garrulous informality that is explosive, intense and distinctly American. 他29岁，有着深蓝色的眼镜，絮絮叨叨不拘礼节，是个活 泼、热情、典型的美国人。
Part I: Intensive Reading Task1: Topic: Ways Americans greet, introduce and
say goodbye to people.
Section Learning
Main ideas:
1) In the American society, informality is valued very highly. 2) When you greet people who you already know, you are expected to show a certain amount of informality toward them.
e.g: He is 29 years old, with quiet blue eyes and
Section Learning
Language Points: