1. Introduction
英语写作第一节课introduction
18
Comparing some terms
―subject‖, ―topic‖ and ―title‖
19
―subject‖, ―topic‖ and ―title‖
• Subject: is the thing, person, idea or event that is being discussed, written about, or considered. e.g. the subject of a discussion, letter, book • Topic: The topic is a particular subject that is written about or discussed. • Title: The title of a book, play, piece of music is the name given to it by the person who wrote it or composed it, or the name by which it is usually known.
Choose which are subjects and topics? sports, foreign students in U.S Universities, what makes a champion soccer player, education, why I play soccer, my first trip abroad, open classrooms and traditional classrooms, one tour in the USA, world travel, music in elementary school
It moves down and up conforming to the Writing task Meanwhile, her double chin is her rhythm. another great feature, which seems to give her voice more power. Above all, you can see what an extraordinary woman she is, so can you guess who she is?
英语论文分析学习 第1节 introduction
What Is an Introduction?
What questions will readers ask when reading an essay: 1. What topic am I going to learn about? 2. Why is that topic important? 3. Do I know the topic already? What do I know already? An introduction aims to answer these 3 questions.
Contents of an introduction
Example:
"Numerous studies on the utilization of plant proteins as a partial or complete replacement for fish meal in diets have been conducted using various freshwater and marines fishes (Lovell, 1987; Tacon et al., 1983; Murai et al., 1989a; Cowey et al., 1974).
Contents of an introduction
Q: What are the ways to establish a topic? A: Claiming centrality General to specific Previous research Describing of the background Definition of key words
[英语学习]unit-1-Introduction
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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
introduction 造句
introduction 造句introduction 造句:1.He made theself-introduction and everyone shook hands with him.他作了自我介绍，大家都与他握了手。
2.Please be aware that this is only a selection of essential requirements ofthe organic standards, meant as an introduction.请注意，这只是一个有机标准必需要求的精选摘要，仅作介绍。
3.The article givessort of a general introduction concerning the back story of the game, and the general feel .文章整体介绍了游戏故事背景和对其的印象。
4.Therefore,the enemy would like to ask all the detailed re-usedan introduction.所以想问问都用过的冤家详细的再引荐下。
5.About this trip here first simple introduction, the specific content, everybody can consult brochure or visit our websit e to understand.关于这次旅程就先简单介绍到这里，具体的内容，大家可以参照小册子或是登陆我们的网站进行了解。
6.I also wonder if it is possible for research articles to be produced by a historical and popular introduction.我想，是否有可能通过历史的、通俗的介绍来撰写研究论文。
unit_1_introduction[1]
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1.1 Text(2)
• According to the information direction transmitted in channel, modern communication systems can be divided into the simplex communication systems, half-duplex communication systems, and full-duplex communication systems; • According to the number of information communicating approaches, modern communication systems can be divided into the serial communication systems and the parallel communication systems; • According to the control methods of information transmitted in channels, modern communication systems can be divided into the synchronous communication systems and the asynchronous communication systems; • According to the line connecting modes and signal interacting ways between signal source and destination, modern systems can be divided into point-to-point communication systems, one-to-multi-points communication systems and multi-to-multi-points communication systems.
1 INTRODUCTION 传感与检测技术
1 INTRODUCTION TO SENSORBASED MEASUREMENT SYSTEM
1.1 GENERAL CONCEPTS AND TERMINOLOGY 1.1.1 Measurement Systems System: a combination of two or more elements, subsystems, and parts necessary to carry out one or more functions. The function of a measurement system: the objective and empirical assignment of a number to a property or quality of an object or event in order to describe it.
The best approach is to design systems insensitive to interference.
1.3 GENERAL INPUT-OUTPUT CONFIGRATION
Common method: . negative feedback.
y ( x yH ( s ))G ( s ) Y ( s) G ( s) 1 X (s) 1 G (s) H (s) H x
1.3 GENERAL INPUT-OUTPUT CONFIGRATION
1.3.2 Compensation Techniques Reduce the effects of interfering and modifying inputs:
• Change the system design • Add new elements to it
1.Introduction+structures
I. Classification of Writings
A. Literature Writings B. Scientific Writings (factual writings)
II. Principles for Good Scientific Writing (1)
Content: original Organization/Structure: complete, coherent Language: correct 文风有独创性；主题 处理好； 中心思想明确； 行文逻辑严密；选辞精确；句子、段落表达 完整；阅读效果好；没有错别字及语法、标 点符号的错误。
Brief & Simple
Though I usually go to the country for a walk during the weekend, I decided to spend the whole day in the city for a change last Sunday. I went to the Tian’anmen Square and the Zhongshan Park. It was so early when I left home that the streets around my neighborhood were deserted. Without the usual crowds and traffic, everything was strangely quiet.
Writing Suggestions:
Plan your writing (audience awareness / target readers). Ignore the language. Write and rewrite. Find readers. Keep writing. Find suitable methods from handbooks and guides. There is many a way to write.
情景英语1(introduction)
Scene 1: You are the new comer to the office. You meet your new coworker Peter Smith in the office. Please introduce each other and have a very nice greeting.
A: David! It’s great to see you! you look as young as ever And you must B: Philip, ___________________________. be Roger. C: Hi. A: Yes, this is my youngest son Roger. Roger, I want you to meet the king dancer of tango of Harvard— David Lin. C: Nice to meet you, Mr. Lin. B: Well, you are so tall. How old are you this year? C: Seven. we haven’t seen each other for years since our graduation, B: So ______________________________________________, Philip. Well, how’ve you been? A: Oh, working too hard.
A: Good evening, Mr. Wu. B: Good evening, Mr. Smith. A: Have you met my wife, Juliet? I haven’t had the pleasure B: No,______________________________. A: Mary, this is Mr. Wu, my Chinese friend. C: How do you do, Mr. Wu? Welcome. B: How do you do? Have a glass of wine Mr. Wu. A:_____________________, let me introduce you to some of my guests. And___________________________________________. B: Thank you.
1.introduction 简介
Introduction
1、生物化学的概念 2、生物化学的发展简史
3、生物化学的主要研究内容 4、生物化学与其它学科的关系
生物化学的概念
生物化学是研究生命 化学的学科，它在分子水 平上探讨生命的本质，即 研究生物体的分子结构与 功能，物质代谢与调节， 及其在生命活动中的作用。
①吴宪
在血液化学分析方面创 立了血滤液的制备和血糖测定法； ②蛋白质方面，提出了蛋白质变 性学说； ③免疫学方面，研究抗原抗体的 反应机制；
④1965年，首先人工合成具
有生物活性的胰岛素； ⑤1981年，成功合成酵母丙 氨酰tRNA; ⑥完成人类基因组计划工作 的1％。
生物化学的研究内容
静态生物化学 动态生物化学 1、 功能生物化学 分子生物学 2、生物化学的研究采用化 学的原理和方法； 3、生物化学与细胞学、遗传学、 生理学关系密切；
生物化学的发展简史
1、初级阶段
2、发展阶段 3、分子生物学阶段
4、现状
初级阶段
1、对糖类、脂类、氨基酸作
了比较系统的研究； 2、发现了核酸； 3、化学合成了简单多肽； 4、酵母发酵过程中可溶性催 化剂的发现奠定了酶学的基础。
1、生物大分子的结构与功能； 2、物质代谢及其调节； 3、基因信息的传递及其调控。
生物大分子：由某些 基本结构单位按照一定的 顺序和方式连接所形成的 多聚体。 分子量一般在104以上
生物化学与其他学科的关系
1、与农业的关系 2、与工业的关系 3、与药学的关系 4、与医学的关系
与农业的关系
人类基因组计划
科学研究证明，人类的生老病死
都与基因有关，如果能够破译人 类基因的序列和功能，就有可能 真正有效地预防、诊断和治疗各 种疾病。因此，1990年正式启动 的人类基因组计划一开始就引起 了全世界的广泛关注。
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:
Chapter 1 - Introduction
Chapter 1 - I ntroductionEcho sounding is a technique for measuring water depths by transmitting acoustic pulses from the ocean surface and listening for their reflection (or echo) from the sea floor. This technique has been used since the early twentieth century to provide the vital depth input to charts that now map most of the world’s water-covered areas. These charts have permitted ships to navigate safely through the world’s oceans. In addition, information derived from echo sounding has aided in laying trans-oceanic telephone cables, exploring and drilling for off-shore oil, locating important underwater mineral deposits, and improving our understanding of the Earth’s geological processes. Until the early 1960s most depth sounding used single-beam echo sounders. These devices make a single depth measurement with each acoustic pulse (or ping) and include both wide and narrow beam systems. Relatively inexpensive wide-beam “unstabilized” sounders detect echoes within a large solid angle under a vessel and are useful for finding potential hazards to safe navigation. However, these devices are unable to provide much detailed information about the sea bottom. On the other hand, more expensive narrow-beam “stabilized” sounders are capable of providing high spatial resolution with the small solid angle encompassed by their beam, but can cover only a limited survey area with each ping. Neither system provides a method for creating detailed maps of the sea floor that minimizes ship time and is thus cost-effective. The unstabilized systems lack the necessary spatial resolution, while the stabilized systems map too little area with each ping.In 1964, SeaBeam Instruments—at the time the Harris Anti-Submarine Warfare Division of General Instrument Corporation—patented a technique for multiple narrow-beam depth sounding. The first such systems to use this technique were built by SeaBeam for the US Navy and were known as Sonar Array Sounding Systems (SASS). SASS employed two separate sonar arrays oriented orthogonal to one another—one for transmitting and one for receiving—an arrangement called a Mills Cross Array. The arrays and the associated analog electronics provided 90 1°-wide unstabilized beams. Roll and pitch compensation produced 60 1°-wide stabilized beams, which permitted mapping a 60° “fan” of the sea floor with each ping. This system allowed survey vessels to produce high-resolution coverage of wide swaths of the ocean bottom in far less ship time than would have been required for a single-beam echo sounder, greatly reducing the costs of such mapping endeavors.Figure Chapter 1 - -1: Contour Map of Perth CanyonMost multibeam bathymetry systems still use the Mills Cross technique for beam forming. However, as faster computers and Large Scale Integrated (LSI) digital chips have become available, most of the signal processing, including beam forming, moved from analog signal processing into the digital (discrete) signal processing (DSP) domain using digital signal microprocessor (DSPµP) chips. The availability of fast DSPµPs has also permitted the implementation of sophisticated detection algorithms. As a result, survey vessels today can do on-board real-time multibeam processing and display of bathymetry data in a manner impossible only a few years ago. Figure Chapter 1 - -1 shows a sample of a high-quality ocean floor map produced by a SEA BEAM 2100 Multibeam Survey System, the latest generation of multibeam sonar from SeaBeam Instruments.The SEA BEAM 2100 system represents the culmination of over a third of a century of design, development, and production experience by SeaBeam Instruments in the area of multibeam bathymetric systems. With added sophistication, this latest generation multibeam sonar system has added capabilities and complexity. It is necessary to have a basic theoretical understanding of the way multibeam bathymetry systems in general, and the SEA BEAM 2100 in particular, work in order to both:•Operate the system in a manner that maximizes coverage and data quality•Evaluate the system performance for signs of system degradationOrganization of this DocumentThis manual provides a general explanation of the way a multibeam sonar system works and describes in detail the implementation of multibeam technology represented by the SEA BEAM 2100 system.Chapter 2, “Sonar Concepts,” introduces the concepts and definitions involved in echo sounding, using a description of a simple single-beam echo sounder as an example. Characteristics of the creation and transmission of acoustic pulses in water and their echoes off the ocean bottom are discussed. This chapter also explains some of the limitations of a single-beam sonar.Chapter 3, “Introduction to Multibeam Sonar: Projector and Hydrophone Systems,” describes the Mills Cross technique, including the processes of beam forming and beam steering and how it is applied to sonar and to the SEA BEAM 2100 in particular. The chapter discusses how systems that employ the Mills Cross technique can make up for many of the short-comings of single-beam echo sounders.Chapter 4, “Detection Processing and Range Calculation,” describes how the SEA BEAM 2100 extracts signals and determines the location of the sea floor from multibeam echoes. The processes used for ship motion compensation and the formation of stable beams and the implementation of sound velocity profiles are discussed.Chapter 5, “Sidescan Sonar,” discusses sea floor imaging using sidescan sonars and how the SEA BEAM 2100 can be used simultaneously as a depth-finding and sidescan sonar.A glossary of the terminology of multibeam sonar technology is included as an appendix. Scope of this DocumentMultibeam technology involves a number of disciplines including underwater acoustics, digital signal processing, and detection theory statistics. Many excellent texts are available that provide in-depth mathematical treatment of each of these fields. The purpose of this document is not to cover all related topics in rigorous mathematical detail, but instead to present you with a simple, clear understanding of the fundamental concepts required to develop the full potential of a multibeam sonar system. Ideas are presented in a graphical and descriptive way, with minimal use of complex mathematics. Where appropriate, references to texts are provided so you can pursue topics in greater detail. While directed at users of the SEA BEAM 2100 system in particular, most of the concepts explained in this document are common to all multibeam sonars, so much of this information can be applied to any commercially available multibeam system.。
DASA说明书CH1.introduction_iMS-J__cn
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大学英语综合教程第三册unit1分析
Unit objectives
Objectives: The unit aims to help students
Apply critical thinking to different writing tasks, such as essays, reports, and reviews.
Improve their writing skills, including essay structure, argumentation, and language use.
02
text analysis
Topic of the text
Topic
The text is about the topic of "The Secret of Success". It mainly discusses the factors that lead to success, including perseverance, hard work, positive attitude, and good habits.
Text Organization
Introduction
Body
The text begins with an introduction that sets the scene and introduces the topic of "The Secret of Success". It also provides a brief overview of the main points that will be covered in the text.
1. Introduction
This section provides an overview of the unit and introduces the theme of critical thinking and writing.
1.introduction
Introduction to Immunology
Liu chun 2016 – 03 – 01
1
一、发展史：
古老： 16世纪 人痘预防天花
① 接触法 ② 痘浆法 ③ 旱苗法 ④ 水苗法
18世纪 牛痘预防天花 ( Jenner )
Edward Jenner discovered that cowpox vaccination protected against smallpox in 1796. Officially smallpox eradicated in 1979.
中 枢
2、未成熟 LC克隆遇Ag 刺激后发生克隆清除; 成 熟 LC克隆遇Ag刺激后则 活化增殖分化，并清除Ag； 3、由于未成熟 LC克隆 在胸腺、骨髓中与自身Ag 相遇而致自身反应性LC克 隆清除；所以成熟LC克隆 主要针对外来Ag。因而免
疫系统能区别自己与非己。
外 周
7
克隆选择学说 ( Burnet )
44
20世纪获得诺贝尔医学生理学奖的免疫学家
年代 1901 1905 1908 1912 1913 1919 1930 1951 1957 1960 1972 1977 1980 学者姓名 Behring Koch Ehrlich Metchnikoff Carrel Richet Bordet Landsteiner Theler Bovet Burnet Medawar Edelman Porter Yalow Dausset Snell Benacerraf Jerne Kohler Milstein Tonegawa Murray Thomas Doherty Zinkernagel 国家 德国 德国 德国 俄国 法国 法国 比利时 奥地利 南非 意大利 澳大利亚 英国 美国 英国 美国 法国 美国 美国 丹麦 德国 阿根廷 日本 美国 美国 澳大利亚 瑞士 获奖成就 发现抗毒素，开创免疫血清疗法 发现结核杆菌，发明诊断结核病的结核菌素 提出抗体生成侧链学说和体液免疫学说 发现细胞吞噬作用，提出细胞免疫学说 器官移植 发现过敏现象 发现补体, 建立补体结合试验 发现人红细胞血型 发明黄热病疫苗 抗组胺药治疗超敏反应 提出抗体生成的克隆选择学说 发现获得性移植免疫耐受性 阐明抗体的化学结构 阐明抗体的化学结构 创立放射免疫测定法 发现人白细胞抗原 发现小鼠H-2系统 发现免疫应答的遗传控制 提出天然抗体选择学说和免疫网络学说 杂交瘤技术制备单克隆抗体 单克隆抗体技术及Ig基因表达的遗传控制 抗体多样性的遗传基础 第一例肾移植成功 第一例骨髓移植成功 提出MHC限制性，即T细胞的双识别模式 提出MHC限制性，即T细胞的双识别模式
新视角研究生英语 读说写 课后题答案1
It is ironical since in these positions that women do the same jobs and wear the same or similar uniforms as men, and this sameness implies that women should not be differentiated from men. However, such a presupposition has been broken by the reality that many women are suffering from gender bias.
Unit 9: Structure of the text
Text Outline
2. Body (Paras. 5–12)
1) The on-the-job gender discrimination (Paras. 2–7)
A. Wage bias, which means___________________________ employees are paid less those of the opposite gender for doing the same work ________________________________________________. it is difficult B. The glass ceiling, which means _____________________ for women to advance up the corporate ladder. _______________________________________________ .
戴语言学1-INTRODUCTION
INTRODUCTION1.1 What is linguistics?1.1.1 DefinitionLinguistics is generally defined as the scientific study of language. It tries to answer the basic questions "What is language?" and "How does language work?" It probes into various problems related to language such as "What do all languages have in common?", "What range of variation is found among languages?", "What makes language change?", "To what extent are social class differences reflected in language?", "How does a child acquire his mother tongue?", and many others.Linguistics studies not a n y particular language, e.g. English, Chinese, Arabic, and Latin, but it studies languages in general. It is a scientific study because it is based on the systematic investigation of linguistic data, conducted with reference to some general theory of language structure. In order to discover the nature and rules of the underlying language system, what the linguist has to do first is to collect and observe language facts, which are found to display some similarities, and generalizations are made about them; then he formulates some hypotheses about the language structure. But the hypotheses thus formed have to be checked repeatedly against the observed facts to fully prove their validity. In linguistics, as in any other discipline, data and theory stand in a dialectical complementation; that is, a theory without the support of data can hardly claim validity, and data without being explained by some theory remain a muddled mass of things.★Four criteria of doing linguistics: objectivity, rigorousness(accuracy), explicitness, and adequacy (信息充分).▲(Linguistics is generally defined as the scientific study of language.Linguistics studies not any particular language, but languages in general. The process of linguistic study is: first, certain linguistic facts are observed, and generalizations are made about them; second, based on these generalizations, hypotheses are formed to account for these facts; third, the hypotheses are tested by further observations; and finally, a linguistic theory is constructed about what language is and how it works.)1.1.2 The scope of linguisticsThe study of language as a whole is often called general linguistics. This deals with the basic concepts, theories, descriptions, models and methods applicable in any linguistic study, in contrast to those branches of study which relate linguistics to the research of other areas.Language is a complicated entity with multiple layers and facets, so it is hardly possible for the linguists to deal with it all at once. They have to concentrate on one aspect of it at a time. This has given rise to a number of relatively independent branches within the area of linguistics.What first drew the attention of the linguists were the sounds used in languages. The study of sounds used in linguistic communication led to the establishment of phonetics.Then, as linguists became interested in how sounds are put together and used to convey meaning in communication, they developed another branch of study related tosounds called phonology. (the study of sound patterns)The sounds used in linguistic communication are represented by symbols, i. e. morphemes. The study of the way in which these symbols are arranged and combined to form words has constituted the branch of study called morphology.Then the combination of words to form grammatically permissible sentences in languages is governed by rules. The study of these rules constitutes a major branch of linguistic studies called syntax. (★The study of sentence structure; it attempts to describe what is grammatical in a particular language in terms of rules)But the ultimate objective of language is not just to create grammatically well-formed sentences. In most general terms language is used to convey meaning. The study of meaning is known as semantics.Language communication does not occur in a vacuum, it always occurs in a context. When the study of meaning is conducted, not in isolation, but in the context of language use, it becomes another branch of linguistic study called pragmatics.The study of all these aspects of language form the core of linguistics.Then, language is not an isolated phenomenon; it is a social activity carried out in a certain social environment by human beings. Naturally, in the course of time the study of language has established close links with other branches of social studies, resulting in some interdisciplinary branches of linguistic study.Language and society are closely connected. The language a person uses often reveals his social background, and there exist social norms that determine the type of language to be used on a certain occasion; and language changes are often caused by social changes. The study of all these social aspects of language and its relation with society form the core of the branch called sociolin guistics.Psycholinguistics relates the study of language to psychology. It aims to answer such questions as how the human mind works when we use language, how we as infants acquire our mother tongue, how we memorize, and how we process the information we receive in the course of communication.Findings in linguistic studies can often be applied to the solution of such practical problems as the recovery of speech ability. The study of such applications is generallyBut in a narrow sense applied linguistics refers to the application of linguistic theories and principles to language teaching, especially the teaching of foreign and second languages.▲(Other branches of linguistics include anthropological linguistics, neurological linguistics, mathematical linguistics, and computational linguistics.)Prescriptive and descriptive represent two different types of linguistic study. If a linguistic study aims to describe and analyze the language people actually use, it is said to be descriptive; if the linguistic study aims to lay down rules for "correct and standard" behaviour in using language, i.e. to tell people what they should say and what they should not say, it is said to be prescriptive.Modern linguistics is mostly descriptive. It differs from earlier studies of language normally known as "grammar" in that the latter is based on "high" (religious, literary) written language. It aims to set models for language users to follow. On the other hand, modern linguistics is supposed to be scientific and objective and its task is to describe the language people actually use, be it "correct" or not. Modern linguists believe that whatever occurs in the language people use should be described and analyzed in their investigation.▲(Modern linguistics is descriptive, not prescriptive. The major task of a linguist is to describe language in an objective way. His investigations are based on authentic, and mainly spoken language data. Traditional grammar is prescriptive in the sense that it tries to lay down a series of grammatical rules and these grammatical rules are then forced on the language users. Any use of language which conforms to the prescribed rules is labelled as correct, otherwise, it will be lablled as incorrect.)★高:All languages are systems of conventions, not systems of natural laws.The first and essential step in the study of any language is observing and setting down precisely what happens when native speakers speak it. Each language is unique in its pronunciation, grammar, and vocabulary. It cannot be described in terms of logic or of some theoretical, ideal language. It cannot be described in terms of any other language, or even in terms of its past. All languages are dynamic rather than static, and hence a “rule” in any language can only be a statement of contemporary practice. “Correctness”can rest only upon usage, for the simple reason that there is nothing else for it to rest on and all usage is relative.1.1.3.2Language exists in time and changes through time. The description of a language at some point of time in history is a synchronic study; the description of a language as it changes through time is a diachronic study. A diachronic study of language is a historical study; it studies the historical development of language over a period of time.In modern linguistics, a synchronic approach seems to enjoy priority over a diachronic one. It is believed that unless the various states of a language in different historical periods are successfully studied, it would be difficult to describe the changes that have taken place in its historical development. Synchronic descriptions are often thought of as being descriptions of a language in its current existence, and most linguistic studies are of this type.1.1.3.3Speech and writing are the two major media of linguistic communication. Modern linguistics regards the spoken language as the natural or the primary medium of human language for some obvious reasons. From the point of view of linguistic evolution, speech is prior to writing. The writing system of any language is always "invented" by its users to record speech when the need arises. Even in today's world there are still many languages that can only be spoken but not written. (▲And then in terms of function, the spoken form of language is used for a wider range of purposes than the written form, and carries a larger load of communication than the written.)Then in everyday communication, speech plays a greater role than writing in terms of the amount of information conveyed. And also, speech is always the way in which every native speaker acquires his mother tongue, and writing is learned and taught later when he goes to school. For modern linguists, spoken language reveals many true features of human speech while written language is only the "revised" record of speech. Thus their data for investigation and analysis are mostly drawn from everyday speech, which they regard as authentic.1.1.3.4The distinction between langue and parole was made by the Swiss linguist F. de Saussure in the early 20th century. Langue and parole are French words. Langue refers to the abstract linguistic system shared by all the members of a speech community, and parole refers to the realization of langue in actual use. Langue is the set of conventions and rules which language users all have to abide by, and parole is the concrete use of the conventions and the application of the rules. Langue is abstract; it is not the language people actually use. Parole is concrete; it refers to the naturally occurring language events. Langue is relatively stable, it does not change frequently; while parole varies from person to person, and from situation to situation.Saussure made this distinction in order to single out one aspect of language for serious study. In his opinion, parole is simply a mass of linguistic facts, too varied and confusing for systematic investigation, and what linguists should do is to abstract langue from parole, i.e., to discover the regularities governing the actual use of language and make them the subjects of study of linguistics.1.1.3.5Similar to Saussure's distinction between langue and parole is the distinction between competence and performance, which was proposed by the American linguist N. Chomsky in the late 1950's. Chomsky defines competence as the ideal user's knowledge of the rules of his language, and performance the actual realization of this knowledge in linguistic communication. According to Chomsky, a speaker has internalized a set of rules about his language, this enables him to produce and understand an infinitely large number of sentences and recognize sentences that are ungrammatical and ambiguous. Despite his perfect knowledge of his own language, a speaker can still make mistakes in actual use, e.g., slips of the tongue, and unnecessary pauses. This imperfect performance is caused by social and psychological factors such as stress, anxiety, and embarrassment. Similar to Saussure, Chomsky thinks that what linguists should study is the ideal speaker's competence, not his performance, which is too haphazard to be studied. Although a speaker possesses an internalized set of rules and applies them in actual use, he cannot tell exactly what these rules are. So the task of the linguists is to discover and specify these rules.While Saussure's distinction and Chomsky's are very similar, they differ at least in that Saussure took a sociological view of language and his notion of langue is a matter of social conventions, and Chomsky looks at language from a psychological point of view and to him competence is a property of the mind of each individual.1.1.3.6It is generally believed that the beginning of modern linguistics was marked by the publication of F: de Saussure's book "Course in General Linguistics" in the early 20th century. But we have to be aware that before that language had been studied for centuries in Europe by such scholars as philosophers and grammarians. The general approach thus traditionally formed to the study of language over the years is roughly referred to as "traditional grammar." Modern linguistics differs from traditional grammar in several basic ways. Some of these have already been briefly mentioned before.Firstly, linguistics is descriptive while traditional grammar is prescriptive. A linguist is interested in what is said, not in what he thinks ought to be said. He describes language in all its aspects, but does not prescribe rules of "correctness". He does not believe that there is some absolute standard of correctness concerning language use which linguists or school teachers should view as their duty to maintain. Instead, he would prefer to be an observer and recorder of facts, but not a judge. He might recognize that one type of speech appears to be more socially acceptable than others because of the influence of fashion. But this will not make him think that the socially acceptable variety can replace all the other varieties, or the old words are always better than new ones or vice versa. He will regard the changes in language and language use as the result of a natural and continuous process, not something to be feared.Second, modern linguistics regards the spoken language as primary, not thewritten. Traditional grammarians, on the other hand, tended to emphasize, maybe over-emphasize, the importance of the written word, partly because of its permanence. Before the invention of sound recording, it was difficult for people to deal with utterances which existed only for seconds. Then, the traditional classical education was also partly to blame. People were encouraged to imitate the "best authors" for language usage. Many of the rules of traditional grammar apply only to the written language; they cannot be made meaningful in terms of the spoken language, without much qualification and addition.Then, modern linguistics differs from traditional grammar also in that it does not force languages into a Latin-based framework. For a long time on the European continent it was unquestionably assumed that Latin provides a universal framework into which all languages fit. As a result, other languages were forced to fit into Latin patterns and categories, especially its case system and tense divisions of past, present and future. To modern linguists, it is unthinkable to judge one language by standards of another. They are opposed to the notion that any one language can provide an adequate framework for all the others. They are trying to set up a universal framework, but that will be based on the features shared by most of the languages used by mankind.1.2 What is language?If we take linguistics to be the scientific study of language, our next question then is "What is language?" This may at first sound like a naive and simple question. Yet to this extremely familiar, everyday phenomenon, it is difficult to give a satisfactory definition. Some people probably will say "language is a tool for human communication". Far from a definition, this only tells us what language does, or what it is used f or, i.e. its function. Alternatively, one might say "language is a set of rules. " Then this tells nothing about its functions, and there are actually other systems that are also rule-governed.Modern linguists have proposed various definitions of language, some of which are quoted below:"Language is a purely human and non-instinctive method of communicating ideas, emotions and desires by means of voluntarily produced symbols." (Sapir, 1921)Language is "the institution whereby humans communicate and interact with each other by means of habitually used oral-auditory arbitrary symbols." (Hall, 1968)"From now on I will consider language to be a set (finite or infi nit e) of sentences, each finite in length and constructed out of a finite set of elements. " (Chomsky, 1957)Each of these definitions has its own special emphasis, and is not totally free from limitations. However, there are some important characteristics of human language linguists have agreed on; these are embraced in the following generally accepteddefinition:Short as it is, this definition has captured the main features of language.First of all, language is a system, i.e., elements of language are combined according to rules. This explains why "iblk" is not a possible sound combination in English, and also why "Been he wounded has " is not a grammatically acceptable sentence in English.Second, language is arbitrary in the sense that there is no intrinsic connection between a linguistic symbol and what the symbol stands for, for instance, between the word "pen" and the thing we write with. The fact that different languages have different words for the same object is a good illustration of the arbitrary nature of language. This also explains the symbolic nature of language: words are just symbols; they are associated with objects, actions, ideas, etc. by convention. This conventional nature of language is well illustrated by a famous quotation from Shakespeare's play "Romeo and Juliet": "A rose by any other name would smell as sweet. "Third, language is vocal because the primary medium for all languages is sound. All evidence points to the fact that writing systems came into being much later than the spoken forms and that they are only attempts to capture sounds and meaning on paper. The fact that children acquire spoken language before they can read or write also indicates that language is primarily vocal.The term "human" in the definition is meant to specify that language is human-specific, i.e., it is very different from the communication systems other forms of life possess, such as bird songs and bee dances.1.2.2Design features refer to the defining properties of human language that distinguish it from any animal system of communication. By comparing language with animal communication systems, we can have a better understanding of the nature of language. A framework was proposed by the American linguist Charles Hockett. He specified twelve design features, five of which will be discussed here.▲vast majority of linguistic expressions are arbitraryAs mentioned earlier, language is arbitrary. This means that there is no logical connection between meanings and sounds. A good example is the fact that different sounds are used to refer to the same object in different languages. (▲In addition, the same sound may be used to refer to different objects in different languages.) On the other hand, we should be aware that while language is arbitrary by nature, it is not entirely arbitrary; certain words are motivated. The best examples are the onomatopoeic words, such as rumble, crash, cackle, bang in English. Besides, some compound words are also not entirely arbitrary. For example while"photo" and "copy" are both arbitrary, the compound word "photocopy" is not entirely arbitrary. But, non-arbitrary words make up only a small percentage of the vocabulary of a language.The arbitrary nature of language is a sign of sophistication and it makes it possible for language to have an unlimited source of expressions.▲creativity or open-endednessLanguage is productive or creative in that it makes possible the construction and interpretation of new signals by its users. This is why they can produce and understand an infinitely large number of sentences, including sentences they have never heard before. They can send messages which no one else has ever sent before. Much of what we say and hear we are saying or hearing for the first time.Productivity is unique to human language. Most animal communication systems appear to be highly restricted with respect to the number of different signals that their users can send and receive. For example, gibbon calls are not productive, for gibbons draw all their calls from a limited repertoire, which is rapidly exhausted, making any novelty impossible. And bee dancing is used only to indicate food sources, which is the only kind of message that can be sent through the dancing.double articulation (sounds and meanings)Language is a system, which consists of two sets of structures, or two levels. At the lower or the basic level there is a structure of sounds, which are meaningless by themselves. But the sounds of language can be grouped and regrouped into a large number of units of meaning, which are found at the higher level of the system. For example, the grouping of the three sounds /k/, /a:/, and /p/ can mean either a kind of fish (carp), or a public place for rest and amusement (pa rk). Then the units at the higher level can be arranged and rearranged into an infinite number of sentences. This duality of structure or double articulation of language enables its users to talk about anything within their knowledge. No animal communication system has duality or even comes near to possessing it.▲By duality we mean that each language is organized at two levels or layers, one is sound and the other is meaning. The advantage of this division is that we can use limited number of sounds to produce unlimited number of sound combinations with distinctive meanings. e.g. in the language of English we use around 48 sounds to produce almost indefinite number of sound combinations (words). This feature is very economical for the system of language.eg. Santa Claus, Superman, mimicsLanguage can be used to refer to things which are present or not present, real or imagined matters in the past, present, or future, or in far-away places. In other words, language can be used to refer to contexts removed from the immediate situations of the speaker. This is what "displacement" means. This property provides speakers with an opportunity to talk about a wide range of things, free from barriers caused by separation in time and place.In contrast, no animal communication system possesses this feature. Animal calls are mainly uttered in response to immediate changes of situation, i.e., in contact of food, in presence of danger, or in pain. Once the danger or pain is gone, calls stop.5)While human capacity for language has a genetic basis, i.e., we were all born with the ability to acquire language, the details of any language system are not genetically transmitted, but instead have to be taught and learned anew. An English speaker and a Chinese speaker are both able to use a language, but they are not mutually intelligible. This shows that language is culturally transmitted. It is passed on from one generation to the next through teaching and learning, rather than by instinct. In contrast, animal call systems are genetically transmitted, i.e., animals are born with the capacity to produce the set of calls peculiar to their species.The sounds used in language are meaningfully distinct. e.g. the distinction between pack and back in meaning can only be due to the difference between the / p / and / b / sound in these two words.Revision exercises:1. How do you interpret the following definition of linguistics: Linguistics is the scientific study of language.2. What are the major branches of linguistics? What does each of them study?3. In what basic ways does modern linguistics differ from traditional grammar?4. Is modern linguistics mainly synchronic or diachronic? Why?5. For what reasons does modern linguistics give priority to speech rather than to writing?6. How is Saussure's distinction between langue and parole similar to Chomsky's distinction between competence and performance?7. What characteristics of language do you think should be included in a good, comprehensive definition of language?8. What are the main features of human language that have been specified by C.Hockett to show that it is essentially different from animal communication system?。
北京理工大学 人工智能导论 刘峡壁 1.Introduction
How to measure Machine Intelligence?
Two views
Behavior/action (weak AI )
• Can the machine act intelligently? • Turing test.
1. Learning Approach
John McCarthy:
Q. What about making a ``child machine'' that could improve by reading and by learning from experience? A. This idea has been proposed many times, starting in the 1940s. Eventually, it will be made to work. However, AI programs haven't yet reached the level of being able to learn much of what a child learns from physical experience. Nor do present programs understand language well enough to learn much by reading.
Exploration, modification, and extension of domains by manipulation of domain-specific constraints, or by other means.
AI:Introduction 14
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Hexagonal Close-Packing- octahedral sites
Radius ratio: r+/r- (2r-)2 + (2r-)2 = (2r- + 2r+)2 (√2-1) r- = r+ r+/r- = 0.414
Cubic Close-Packing (fcc)
Interstitial site- cubic - (2r-)2 + (2√2r-)2 = (2r- + 2r+)2 (√3-1) r- = r+ r+/r- = 0.73
Non-Close-Packing- Body-Centered Cubic (bcc)
a
Coordination number: 8 Packing efficiency: - √3a = 4r - Vunit cell = a3 = (64r3)/3√3 - Vatoms = (4/3)πr3 X 2 atoms = (8/3)πr3 - Efficiency = Vatoms/Vunit cell = √3 π /8 = 68%
Crystal Structure in Ionic Crystals
r+/r0.22 – 0.41 0.41 – 0.73 0.73 – 1.00
type
Tetrahedral Octahedral cubic
Coordination number (CN)
4 (ccp or hcp) 6 (ccp or hcp) 8 (sc)
Hexagonal Close-Packing- octahedral sites
Why hcp containing n spheres has n octahedral sites? - # of atoms: 2 atom (12 X 1/6, at 12 corners) + 1 atom ( 2 X 1/2 , at top and bottom layer) + 3 atoms (inside) = 6 atoms in unit cell - # of octahedral sites: 3 X 1 (between bottom and middle layer) + 3 X 1 (between top and middle layer) = 6 sites - 6 sites/ 6 atoms = 1
<References> 1. 결정학 개론, 정수진. 2. Introduction to Materials Science for Engineers, James F. Shackelford, 7th ed. 3. Introduction to solid state physics, Charles Kittel, 7th ed. 4. Sol-gel science: The physics and chemistry of sol-gel processing, C. Jeffrey Brinker. 4. Transmission Electron Microscopy: A Textbook for Materials Science, David B. Williams. 5. 태양전지공학, 이준신. 6. Nanochemistry, Geoffrey A. Ozin.
a
Face-centerd cubic (fcc) • √2a = 4r, a = 2√2r • Vunit cell = a3 = 16√2r3 • Vatoms = (4/3)πr3 X 4 atoms = 16/3 πr3 • Packing efficiency = Vatoms/Vunit cell = π /3√2 = 0.74 (74%) • 4 octahedral sites • 8 tetrahedral sites
Hexagonal Close-Packing- tetrahedral sites
a
Radius ratio: r+/r- a = (2r-)sin 45o = √2r- body diagonal of cubic cell = √6r- Because cations and anions are in contact, r+ + r- = √6r-/2 r+/r- = 0.225
LECTURER: Joo, Jin (주진) Office: Rm #103 E01, Phone: 950-5585, E-mail: joojin@knu.ac.kr OUTLINE This class will cover fundamentals for understanding useful properties in solid state including preparation characterization methods. TEXTBOOK Solid State Chemistry-An introduction, Lesley E. Smart, 3rd ed.
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Close-Packing
Close-packing - Most efficient way using space. - 74% packing efficiency. - Coordination number: 12 (6 in the same layer + 3 (below) + 3 (above). - Two type of interstitial sites (i) Octahedral: n spheres → n sites (ii) Tetrahedral: n spheres → 2n sitesChຫໍສະໝຸດ ice of Unit Cells
Non-Close-Packing- Primitive Cubic
Top view
Side view
Non-Close-Packing- Primitive Cubic
Coordination number: 6 The simplest way packing spheres. Packing efficiency: - a = 2r - Vunit cell = a3 = 8r3 - Vatoms = (4/3)πr3 X 1 atoms = (4/3)πr3 - Efficiency = Vatoms/Vunit cell = π/6 = 52.4% Only example is Po
GRADING Midterm Exam 100 points Final Exam 100 points Quiz 100 points Attendance 100 points (late attendance: only 20 min of late attendance is allowed!) * Absence from class more than 8 times,1/4 of whole class, will be graded F Office hour : For 1 hour after each class.
Lattices and Unit Cells
Lattice: a periodic array of “dots” (or lattice points). Unit cell: the simplest portion of a lattice that can be repeated by translation to cover the entire 1-D, 2-D, or 3-D space. Crystal structure = Lattice + Basis of the Lattice Point.
Chapters 5 Defects and Non-Stoichiometry Chapter 6 Chapter 7 Chapter 8 Chapter 9 Carbon-Based Electronics Zeolites and Related Structures Optical Properties of Solids Magnetic and Dielectric Properties
3-Dimensional Unit Cells
Four types of lattices
1. The primitive unit cell—symbol P—has a lattice point at each corner. 2. The body-centred unit cell—symbol I—has a lattice point at each corner and one at the centre of the cell. 3. The face-centred unit cell—symbol F—has a lattice point at each corner and one in the centre of each face. 4. The face-centred unit cell—symbol A, B, or C— has a lattice point at each corner, and one in the centres of one pair of opposite faces.
Hexagonal Close-Packing- tetrahedral sites
Side view
Top view
Unit cell
Tetrahedral sites
Why hcp containing n spheres has 2n tetrahedral sites? - # of atoms: 1 atom (at 8 corners) + 1 atom (between top and bottom layers) = 2 atoms in unit cell - # of tetrahedral sites: 2 X 1 (between top and middle layer) + 2 X 1 (at 4 edges) - 4 sites/ 2 atoms = 2