01.Introduction

合集下载

英语介绍泉州

2
History
History
Quanzhou has a history dating back over 1700 years. It was founded in the year 260 and has since become an important port city in Chinese history. During the Tang Dynasty, Quanzhou became a major international port
ancient history with modern development. Whether you are interested in history, culture, or just enjoying a vacation on
the beach, Quanzhou has something to offer everyone
its literature, with many famous writers and poets having lived or worked here. In addition, Quanzhou is home to a variety of traditional crafts, such as embroidery, paper-cutting, and陶瓷 (ceramics)
Quanzhou, located on the southeast coast of Fujian Province, is a city with a long history and rich cultural and historical heritage. It is famous for its ancient city, beautiful scenery, and delicious food. In this article, we will introduce Quanzhou from several aspects, including its history, culture, tourism, and food

电力电子英文课件01

12
II.
The history
Application of fast-switching Invention of fully-controlled Thyristor semiconductor devices GTO GTR Mercury arc rectifier Power MOSFET Power diode Vacuum-tube rectifier Thyristor Thyristor Thyratron (microprocessor)
Feedback/ Feed forward
Controller
Reference
Power
-heating -power converter -other electric or electronic equipment
The task of power electronics has been recently extended to also ensuring the currents and power consumed by power converters and loads to meet the requirement of electric energy sources.
Power electronics: to process electric power
Other classifications of electronics
Power
Electronics
Vacuum electronics: using vacuum devices, e.g, vacuum tubes devices Solid (Solid state) electronics: using solid state devices, e.g, semiconductor devices Physical electronics: physics,material,fabrication, and manufacturing of electronic devices Applied electronics: application of electronic devices to various areas 9

Handbook of Railway Vehicle Dynamics_01 Introduction

1IntroductionSimon IwnickiCONTENTSI.Aims (1)II.Structure of the Handbook (2)I.AIMSThe principal aim of this handbook is to present a detailed introduction to the main issues inﬂuencing the dynamic behaviour of railway vehicles and a summary of the history and state of the art of the analytical and computer tools and techniques that are used in thisﬁeld around the world. The level of technical detail is intended to be sufﬁcient to allow analysis of common practical situations but references are made to other published material for those who need more detail in speciﬁc areas.The main readership will be engineers working in the railway industry worldwide and researchers working on issues connected with railway vehicle behaviour,but it should also prove useful to those wishing to gain a basic knowledge of topics outside their specialist technical area.Although in the very earliest days of the railways(as described in Chapter2)an individual was responsible for all aspects of the design of a railway,for most of the historical period of railways the vehicles(or rolling stock)have been under the control of mechanical engineers whereas the track has been seen as the domain of civil engineers.The focus of this book being on the vehicles would tend to put itﬁrmly in the mechanical domain,but in fact,in recent years this rather artiﬁcial divide has been lessened as engineers have been forced to consider the railway as a system with the wheel–rail interface at its centre.Increasing use of electrical and electronic components to power, control(or in some cases replace)the basic mechanical components has brought electrical, electronic,mechatronic and control engineers into the teams.The development of equations that represent the complex interactions between a vehicle and the track and of computers able to provide fast solutions to these equations has relied upon the expertise of software engineers and even mathematicians.The topics covered in this handbook are the main areas which impact on the dynamic behaviour of railway vehicles.These include the analysis of the wheel–rail interface,suspension and suspension component design,simulation and testing of electrical and mechanical systems, interaction with the surrounding infrastructure,and noise generation.Some related areas,such as aerodynamics or crashworthiness,are not covered as they tend to use different techniques and tools and have been extensively developed for road or air transport and are reported on elsewhere.The handbook is international in scope and draws examples from around the world,but several chapters have a more speciﬁc focus where a particular local limitation or need has led to the development of new techniques or tools.For instance,the chapter on longitudinal dynamics mainly uses Australian examples as the issues related to longitudinal dynamics cause most problems in heavy haul lines such as those in Australia where very long trains are used to transport bulk freight with extremely high axle loads,sometimes on narrow gauge track.Similarly,the issue of structure1gauging largely uses the U.K.as a case study,because here the historic lines through dense population centres have resulted in a very restricted loading gauge.The desire to run high-speed trains in this situation has led to the use of highly developed techniques to permit full advantage of the loading gauge to be taken.The issue of standards has been a tricky one due to the vast number of different organisations who set and control railway standards.It has not been possible to provide comprehensive guidance in this area but typical examples of the application of standards have been brought into the handbook where appropriate.For example,AAR Chapter XI standards for derailment in the U.S.and UIC518for limits on wheel–rail forces in the E.U.are presented.It should be stressed that these are intended only as illustrative examples of how the results of vehicle dynamic analyses can be used,and those with responsibility for safety should check carefully what the relevant current standards are for their work.II.STRUCTURE OF THE HANDBOOKThe history of the ﬁeld is presented by Alan Wickens in Chapter 2,from the earliest thoughts of George Stephenson about the dynamic behaviour of a wheelset through the development of theoretical principles to the application of modern computing techniques.Professor Wickens was one of the pioneers of these methods and,as director of research at British Rail Research,played a key role in the practical application of vehicle dynamics knowledge to high-speed freight and passenger vehicles.In Chapter 3,Anna Orlova and Yuri Boronenko outline and explain the basic structure of the railway vehicle and the different types of running gear that are commonly used.Each of the relevant components is described and the advantages and disadvantages of the different types explained.The key area of any study of railway vehicle behaviour is the contact between the wheels and the rails.All the forces that support and guide the vehicle pass through this small contact patch,and an understanding of the nature of these forces is vital to any analysis of the general vehicle behaviour.The equations that govern these forces are developed by Hugues Chollet and Jean-Bernard Ayasse in Chapter 4.They include an analysis of the normal contact that governs the size and shape of the contact patch and the stresses in the wheel and rail and also the tangential problem where slippage or creep in the contact patch produces the creep forces which accelerate,brake,and guide the vehicle.The speciﬁc area of tribology applied to the wheel–rail contact is explained by Ulf Olofson and Roger Lewis in Chapter 5.The science of tribology is not a new one but has only recently been linked to vehicle dynamics to allow effective prediction of wheel and rail wear,and examples of this from the Stockholm local railway network are presented.Although the main focus of railway vehicle dynamics is traditionally on the vehicle,the track is a key part of the system and in Chapter 6Tore Dahlberg clearly explains the way that track dynamics can be understood.The contribution of each of the main components that make up the track to its overall dynamic behaviour is also presented.Chapter 7covers the unique railway problem of gauging,where the movement of a railway vehicle means that it sweeps through a space that is larger than it would occupy if it moved in a perfectly straight or curved path.Precise knowledge of this space or envelope is essential to avoid vehicles hitting parts of the surrounding infrastructure or each other.David M.Johnson has developed computer techniques that allow the gauging process to be carried out to permit vehicle designers and operators to ensure safety at the same time as maximising vehicle size and speed,and in this chapter he explains these philosophies and techniques.Of fundamental concern to all railway engineers is the avoidance of derailment and its potentially catastrophic consequences.Huimin Wu and Nicholas Wilson start Chapter 8with some statistics from the U.S.that show the main causes of derailment.They go on to summarise the limits Handbook of Railway Vehicle Dynamics 2Introduction3 that have been set by standards to try to prevent these occurrences,and cover the special case of independently rotating wheels and several possible preventative measures that can be taken.Longitudinal train dynamics are covered by Colin Cole in Chapter9.This is an aspect of vehicle dynamics that is sometimes ignored,but it becomes of major importance in heavy haul railways where very long and heavy trains lead to extremely high coupling forces between vehicles. This chapter also covers rolling resistance and braking systems.Chapter10deals with noise and vibration problems,which have become of greater concern in recent years.David Thompson and Chris Jones explain the key issues including rolling noise caused by rail surface roughness,impact noise,and curve squeal.They outline the basic theory required for a study in this area and also show how computer tools can be used to reduce the problem of noise. The effect of vibrations on human comfort is also discussed and the inﬂuence of vehicle design considered.In Chapter11,R.M.Goodall and T.X.Mei summarise the possible ways in which active suspensions can allow vehicle designers to provide advantages that are not possible with passive suspensions.The basic concepts from tilting bodies to active secondary and primary suspension components are explained in detail and with examples.Recent tests on a prototype actively controlled bogie are presented and limitations of the current actuators and sensors are explored before conclusions are drawn about the technology that will be seen in future vehicles.Computer tools are now widely used in vehicle dynamics and some specialist software packages allow all aspects of vehicle–track interaction to be simulated.Oldrich Polach,Mats Berg, and Simon Iwnicki have joined forces in Chapter12to explain the historical development and state of the art of the methods that can be used to set up models of railway vehicles and to predict their behaviour as they run on typical track or over speciﬁc irregularities or defects.Material in previous chapters is drawn upon to inform the models of suspension elements and wheel–rail contact,and the types of analysis that are typically carried out are described.Typical simulation tasks are presented from the viewpoint of a vehicle designer attempting to optimise suspension performance.Chapter13takes these principles into theﬁeld and describes the main test procedures that can be carried out during the design or modiﬁcation of a vehicle,or as part of an acceptance process to demonstrate safe operation.Julian Stow and Evert Andersson outline the range of transducers available to the test engineer and the ways that these can be most effectively used to obtain valid and useful data.The necessaryﬁltering,corrections,and compensations that are normally made are explained,and data acquisition system requirements are covered.The chapter includes examples of the most commonly carried out laboratory andﬁeld tests.An alternative toﬁeld testing is to use a roller rig,on which,a vehicle can be run in relative safety with conditions being varied in a controlled manner and instrumentation can be easily installed.Weihua Zhang and his colleagues at Southwest Jiaotong University in China operate what is probably the most important roller rig in the world today and they outline the characteristics of this and other roller rigs and the ways in which they are used.Chapter14also reviews the history of roller rigs,giving summaries of the key details of examples of the main types.Chapter15extends the theme to scale testing,which has been used effectively for research into wheel–rail contact.In this chapter P.D.Allen describes the possible scaling philosophies that can be used and how these have been applied to scale roller rigs.In compiling this handbook I have been fortunate in being able to bring together some of the leading experts in each of the areas that make up theﬁeld of railway vehicle dynamics.I and my coauthors hope that this handbook,together with its companion volume,Road and Off-Road Vehicle Dynamics,will be a valuable introduction for newcomers and a useful reference text for those working in theﬁeld.Simon IwnickiManchester。

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。

Chap.01_Introduction

23
As early as 1816, the vitalistic theory received a heavy blow when Michel Chevreul (米切尔· 欧仁· 谢弗勒) found that soap, prepared by the reaction of alkali with animal fat, could be separated into several pure organic compounds. Without the intervention of an outside vital force.
NH4CN
O NH2 C NH2
By the mid-nineteenth century, the weight of evidence was clearly against the vitalistic theory. H. Kolbe (柯尔柏), 1844，Acetic acid.
M. Berthelort (柏赛罗), 1854, Oil and Fat
Caudate nucleus 尾状核
13
14
Ian Robertson is of Psychology at Trinity College, Dublin “Power and success work through the same circuit as sex and cocaine; it’s a basic, primitive reward system.”
18
History: In Zhou Dynasty, there were some people named “染人”, “醯人” in charge of staining, making wine and making vinegar. But the foundations of organic chemistry date from the mid-eighteenth century, when chemistry was evolving from an alchemist’s art into modern science. At that time, unexplainable differences were noted between substances obtained from living sources and those obtained from minerals.

01-Introduction to Bioinformatics(生物信息学国外教程2010版) PPT课件

Textbook
The course textbook has no required textbook. I wrote Bioinformatics and Functional Genomics (Wiley-Blackwell, 2nd edition 2009). The lectures in this course correspond closely to chapters.
The textbook website is: This has powerpoints, URLs, etc. organized by chapter. This is most useful to find “web documents” corresponding to each chapter.
I will make pdfs of the chapters available to everyone.
You can also purchase a copy at the bookstore, at (now $60), or at Wiley with a 20% discount through the book’s website .
Literature references
You are encouraged to read original source articles (posted on moodle). They will enhance your understanding of the material. Readings are optional but recommended.
Web sites
The course website is reached via moodle: /moodle (or Google “moodle bioinformatics”) --This site contains the powerpoints for each lecture, including black & white versions for printing --The weekly quizzes are here --You can ask questions via the forum --Audio files of each lecture will be posted here

SMT-01_Introduction_CD

4. Flat Grinding
5. Wafer Slicing
8. Wafer Etching
Slurry
9. Polishong
Polishing table
10. Wafer Inspection
Polishing head
(Note: Terms in Figure 1.7 are explained in Chapter 4.)
After studying the material in this chapter, you will be able to:
1. Describe the current economic state and the technical roots of the semiconductor industry.
2000
1981
1975
1987
1992
1965
50 mm 100 mm 125 mm 150 mm 200 mm
Figure 1.4
300 mm
Devices and Layers from a Silicon Chip
Top protective layer Metal layer
Insulation layers
Microprocessor Chips
Photo courtesy of Advanced Micro Devices
Photo 1.1
Photo courtesy of Intel Corporation
Development of an Industry
• Industry Roots
– Vacuum Tubes – Radio Communications – Mechanical Tabulators – Inventors – Disadvantages

苏司兰风力发电1.25 MW零部件简介

C. Tower
塔身
2
01. INTRODUCTION
简介
Course Objectives 课程目的
• The course objective is to ensure learning by participants about the Introduction of 1.25 MW WTG Components 课程目的为保证参与者对 1.25MW 风力发电机简介的掌握。 Upon completion of this training the participants will be able to identify and can distinguish functional importance of 1.25 MW WTG Components 培训结束后参与者应可以识别和区别 1.25MW 风力发电机的功能重要性。 They will also be able to apply it in understanding and implementing various technical functions of parts of 1.25 MW WTG 同时也能够将其用于了解和执行 1.25MW 风力发电机各组成部件的不同技术功能。
8
6.
7.
8.
9.
03. TECHNICAL FEATURES
技术特征（继续）
(Contd.)
10. Rotor brake system consists of Aerodynamic brake and Mechanical brake working under braking programs which ensures safe running of the Wind Turbine in all working and environmental conditions 叶轮制动系统包括空气动力制动和机械制动，制动系统保障任何工作和环境条件下发电机的安全运作 11. Pitching also used for the Aerodynamic Braking 空气动力制动亦采用变桨 12. On the Gearbox high-speed shaft, disc brake calipers with hydraulic drive system ensures Fail-safe Mechanical Braking of the rotor. Thus, it protects Wind Turbine against any Operational failure and unforeseen environmental hazards 齿轮箱的高速轴上，盘式制动器配水力驱动系统，保障叶轮自动防故障制动。因此，在任何操作故障和无法预料的环境威胁下保护了发电机 13. Manually activated hydraulically driven Hub-lock 手动开启水压式轮毂锁 14. A multi-stage planetary and helical gears ensures highest possible mechanical efficiency and power 多阶段行星式和螺旋状齿轮保障最高效的机械效率和动力 15. A permanent, mechanical driven oil pump supplies the oil to gearbox and main shaft bearing with pressure lubrication 永久的机械驱动油泵提供油给齿轮箱和主轴承以强制润滑

王力宏所有歌曲

10.follow me
十四、专辑《盖世英雄》
01.在梅边
02.花田错
03.盖世英雄
04.Kiss Goodbye
05.完美的互动
06.大城小爱
07.第一个清晨
08.哥儿们
09.让开
10.爱因为在心中
十五、专辑《改变自己》
01.改变自己
02.落叶归根
03.我们的歌
04.Julia
05.感情副作用
06.打开爱
07.不降落的滑翔翼
08.失去了你
09.你爱过没有.Mary Says（流泪手心英文版）
八、专辑《永远的第一天》
01.Introduction
02.永远的第一天
03.龙的传人
04.不要害怕
05.狂想世界
01.公转自转
02.爱你等于爱自己
03.信任
04.不管怎样
05.你以为我是谁
06.梦想被冷冻
07.One Of These Days
08.我的情歌
09.2000年
10.Please Come Back To Me
七、专辑《不可能错过你》
01.钓灵感
02.不可能错过你
03.流泪手心
05. ふるえる心(Japanese Version)（不要害怕）
06. 永远のはじまり（永远的第一天）
07. モノローグ（你不在）
08. Hear My Voice（你和我）
09. 仆等になれなくて(Japanese Version)（两个人不等于我们）
10. 君の知らない空へ（你可以告诉我（你还爱谁））

英语听力教案及

Employees need to listen effectively to understand instructions, customer requirements, and communication among colleagues.
Interpersonal relationships
Using background knowledge
Applying prior knowledge and experience to make inquiries about the listening text's content
Inferring the speaker's attribute
Resources • Summary and Outlook
01
Introduction to Listening Skills
The definition and importance of listening skills
Definition
Listening skills refer to the ability to receive and understand oral communication through the ear
Comprehension listening
The ability to understand the general meaning of a passage or conversation
Analytical listening
The ability to analyze specific information or details from a passage or conversation

01. Introduction to M580 - CN

● BME NOC 0301 and BME NOC 0311 以太网通信模块作为通信接口，支持在M580 PAC 与使用如下协议的其他以太网设备间的通信:
● EtherNet/IP ● Modbus/TCP
● BME 模块的功能类似于已经在M340 PLC中使用的BMX NOC
● BME NOC 03*1 模块已经内置了网络安全功能，用来提高在M580架构中抵御网络攻击的能力
12
远程子站适配器- BME CRA 312 10
● 与背板的双连接:
● X-Bus (1) ● 以太网 (2)
● 适配孔可以防止模块安装在BMX的老机架上 (3)
M580 Configuration V1.0
Schneider Electric | Industry Business | Training | March 20, 2020
描述 4槽以太网背板 8槽以太网背板 12槽以太网背板
Ethernet & X-Bus 槽数 4
8
8
仅X-Bus 槽数 0 0 4
● 在M580架构中，以太网背板在任何时候都不能被用于扩展机架
M580 Configuration V1.0
Schneider Electric | Industry Business | Training | March 20, 2020
15
HART 模块 – BME AH* 0*12
● 提供2个HART 模块, 这些是应用新以太网背板的第一个新X80模块 :
● BME AHI 0812 – 8 通道模拟量输入模块 4 – 20 mA ● BME AHO 0412 – 4 通道模拟量输出模块 4 – 20 mA

甘肃地震英文版的

The local power supply, water supply, and communication systems wer
02.
e also affected, which led to power shutdowns and communication failures in some areas. In addition, some local hospitals and schools
2
were damaged, affecting the medical and educational services in the
area
3
Response
Response
The Chinese government quickly responded to the earthquake. The State Council sent a rescue team to the affected areas to support the local governments in rescue
Introduction
On the evening of July 22, 2023, a strong earthquake occurred in
Gansu Province, China. The epicenter was located in the border area between Qingyang
organizations also provided support and assistance to the
affected areas
4
International Assistance
International Assistance

01 Introduction to Psychology

Chapter 1: Introduction to Psychology
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 1: Introduction to Psychology
The Subfields of Psychology
Understanding change and individual differences
– Developmental psychology
• Changes in behavior over the life span (womb to tomb)
The Subfields of Psychology
Physical and mental health
– Health psychology
• Explores relationship between psychological factors and physical ailments or disease
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 1: Introduction to Psychology
Module 1: Psychologist at Work
外显行为反应的一门学科
心理学是系统地研究心理过程和行为的科学
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1.introduction

免疫学概论
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

01 - Introduction

TelecommunicationsN.WangLecturer: D.Room CF612 Ext. 6163Main Chapters:1.Introduction2.Signal Analysis3.Amplitude modulation4.Angle Modulation5.Pulse Modulation6.Digital Communications7.Optical Fiber CommunicationsLaboratory ExperimentsThe experiments will be performed in the Control and Signal Processing Laboratory in EF401.Two experiments need to be done. The experiments will be on:(1) Amplitude Modulation (AM) System(2) Pulse Code Modulation (PCM)You will be informed of the schedule of the labs in due course.Method of AssessmentCoursework: 40%Test (25%)Home work or in class exercises (5%)Lab. (10%): One lab report chosen from one of the two experiments needs to be handed in at least one week before the exam.Examination: 60%The duration will be 3 hours. All questions will be compulsory.Intended Subject Learning Outcomes:•To understand the fundamentals of telecommunication systems.•To appreciate the advantages and limitations of different telecommunication systems•To learn from theory to practice by doing laboratory experiments on important telecommunication techniquesIntroductionObjectives:•To provide a broad overview of communication systems•To describe the main components of a general communication system•To discuss signal and noise in communication system•To explain the importance of modulation in communication systems•To describe the classification of communications•To describe the key factors to evaluate the performance of a communication systemWhat does telecommunication mean?Telecommunications is made up of the words “tele” which means “over a distance” and “communication” which means “the process of exchanging information”. Thus, telecommunication means the process of exchanging information over a distance. Information is an intelligence signal which changes unpredictably with time.During communication, the message is transmitted from its source to a destination. This transmission is achieved by the use of a communication system.(Lathi) What are the components of a telephone system?Person who talks on a phone (message source)↓Telephone (transducer in which speech message is converted into electrical signal)↓Wire (transmission channel)↓Telephone (transducer in which electrical signal is converted back into speech message)↓Person who talks on a phone (message destination)What are the components of a television system?Person who dances (message source)↓Video camera (transducer in which image message is converted into electrical signal)↓Antenna (transmitter in which signal is modified for efficient transmission)↓Free space (transmission channel)↓Television (transducer in which electrical signal is received and converted back into image message)↓Person who watches television (message destination)In communication, the physical message, such as sound, word, picture, etc., is converted into an electrical message called signal and this electrical signal is conveyed at the distant place, where it is reconverted into the physical message through some media. Thus, a communication system has following components:The function of communication system componentsSource originates a message, such as a human voice, a television picture, or data.If the message is not electrical, it should be converted by an input transducer into an electrical waveform referred to as the baseband signal or message signal.e.g. in a telephone system, human voice is converted into an electric current variation.The transmitter modifies the message signal for efficient transmission.The channel is a medium such as wire, coaxial cable, an optical fiber, or free space – for signal transmission.The receiver reprocesses (demodulate) the output signal from the channel. The receiver output is fed to the output transducer, which converts the electrical signal into its original form, the message.The destination is the unit to which the message is communicated.In a communication system, a message must be converted into a signal before it can be transmitted in the transmission channel.What is a signal?A Signal is a set of information or data and is usually a function of time.A typical example of signal is the variation of electric current that contains message.During the signal transmission, noise will be added and it will affect the signal.Noise refers to undesired signal which carries no information. It is random and unpredictable signal produced by the natural processes both internal and external to the system. When such random variations are superimposed on an information-bearing signal and if the noise amplitude is larger than that of the signal, the message may cause signal distortion, which leads that the information cannot be correctly received.Distortion is waveform perturbation caused by imperfect response of the system to the desired signal itself. Unlike noise, distortion disappears when the signal is turned off.There are two types of noises, external noise and internal noise.The electrical noise that is introduced in the transmitting medium is termed external noise.The noise introduced by the components in the transmitter and receiver is known as internal noise. External NoiseMan-made noise: produced by electromagnetic waves generated by things like electric motors, power lines, etc. These waves will be converted by receiving antenna into electrical signals.Atmospheric noise: caused by naturally occurring disturbances in the earth’s atmosphere due to, e.g. lightning, etc.Internal NoiseInternal noise is produced by electronic circuits.There are two types of internal noise: thermal noise and shot noise.Thermal NoiseThermal noise is generated in a resistive component due to the rapid and random motion of electrons and atoms inside the component. This motion increases with increasing temperature (hence, “thermal”).This random motion of electrons produces an unpredictable component in a current passing through a resistor (hence, “noise”). Its frequency content is spread uniformly throughout the usable spectrum, hence it is also known as white noise. It is sometimes referred to as Johnson noise, after its discoverer.Thermal noise generationAt any temperature above absolute zero, thermal energy causes charged particles to exhibit random motion. The random motion of charged particles such as electrons generates random currents or voltages called thermal noise. Thermal noise exists in every communication system.Shot NoiseShot noise exists in all active devices, especially in transistors . It is caused by random variations in the arrival rate of electrons or holes (due to spontaneous recombination and generation) at the output of the device.There are other types of internal noise but they are relatively unimportant and hence will not be considered here.Shot noise and thermal noise are additive .Noise is one of the basic factors that set the limit of communication system performance.Signal-to-Noise Ratio (SNR or S/N) provides a comparison of noise and signal powers at the same point. It is defined asand in decibel form asQuestions1.Can you increase the SNR by amplifying the signal before the receiver? Why or why not?2. What type of noise does a transistor has?3. Find the SNR in dB if the ratio of signal power to noise power is:(a) 10 ?(b) 100 ?ModulationModulation is defined as the process by which some parameter of the high frequency carrier is varied in accordance with the message signal. This parameter may be the amplitude, the frequency or the phase ofthe carrier wave.S N P Signal Power SNR Noise Power P ==10()10log S N P SNR dB P =Notice that after modulation the signal transmission takes place at the high frequency carrier which has been modified to carry the lower-frequency message signal.What is the carrier wave?A sinusoidal wave of high frequency and one of its parameters is varied in proportion to the message signal In a communication system, the transmitter modifies the message signal for efficient transmission.How to perform modulation?In modulation, the information is carried on a high frequency “carrier” and the transmission takes place at the carrier frequency. Thus, the modulation can be performed by multiplying the message signal by a carrier wave (sinusoidal signal).e.g. g(t) = m(t) cos(ωc t)where m(t) is the message signal, or baseband signal, or modulating signal (signal before modulation), cos(ωc t) is the carrier wave, and g(t) is the modulated signal (signal after modulation).A modulator is a product device, it systematically alters the carrier wave in correspondence with the variations of the modulation signal and the resulting modulated signal “carries” the message information. Why modulation is needed? Why not just transmit the signal directly?The primary purpose of modulation in a communication system is to generate a modulated signal suited to the characteristics of the transmission channel. Actually, there are several practical benefits and applications of modulation briefly discussed below.Efficient transmission:Signal transmission over long distance always involves a traveling electromagnetic wave, with or without a guiding medium. The efficiency of any particular transmission method depends upon the frequency of the signal being transmitted. By the use of modulation, message information can be impressed on a carrier whose frequency has been selected for the desired transmission method.For efficient radiation of electromagnetic energy, the radiating antenna should have the physical dimension of at least 1/10 of the signal’s wavelength. For many baseband signals, the wavelengths are too large for reasonable antenna dimensions. For example, the frequency of a speech signal is in the range of 100 to 3000 Hz (in open space, fλ = c, where c is the light propagation velocity) and the corresponding wavelength is 100 to 3000 km. This long wavelength indicates an impracticably large antenna. By use of modulation, the low frequency speech signals can be used to modulate a high frequency carrier wave, thus translating the signal spectrum to the range of carrier frequencies that corresponds to a much higher frequency or in other words, much smaller wavelength.Frequency allocation:Modulation can effectively shift the frequency spectrum of the signal to the location centered on the carrier frequency.When you tune a radio or television set to a particular station, you are selecting one of the many signals being propagated at that time. Since each station has a different assigned carrier frequency, the desired signal can be separated from the others by filtering. Were it not for modulation, only one station could broadcast in a given area; otherwise, two or more broadcast stations would create a hopeless interference.Efficient spectrum utilization:The channel bandwidth may be much larger than the signal bandwidth. It would be wasteful if only one signal is transmitted over the channel. One way to solve this problem is to use modulation, which allows each signal spectrum be moved to its assigned frequency range without overlapping and thus will not interfere with each other. Thus several signals can be transmitted simultaneously in the same channel. This is known as Frequency Domain Multiplexing (FDM).MultiplexingBandwidth:Bandwidth (BW) is the portion of electromagnetic spectrum occupied by a signal.e.g. A signal frequency range is 902 to 928 MHz. What is the signal bandwidth?f1 = 902 MHz, f2 = 928 MHz, thenBW = f2 – f1 = 26 MHzWhat is the relation ship between the signal bandwidth and channel bandwidth (transmission bandwidth)? When a signal changes rapidly with time, its frequency is high or its spectrum extends over a wide range and hence the signal has a large bandwidth.Similarly, the ability of a system to follow signal variation is reflected in its frequency response or transmission (channel) bandwidth.A rapid signal variation ⇒ a large signal bandwidth ⇒ a large channel bandwidth requiredThe two fundamental limitations of information transmission are bandwidth and noise.The concept of bandwidth applies to both signals and systems. When a signal changes rapidly with time, its frequency content or spectrum extends over a wide range and we say that the signal has a large bandwidth. Similarly, the ability of a system to follow signal variation is reflected in its frequency response or transmission bandwidth.What is the consequence of insufficient transmission bandwidth?Communication under real-time conditions requires sufficient transmission bandwidth to accommodate the signal spectrum; otherwise, severe distortion will result.Every communication system has limited bandwidth that limits the signal speed.Noise imposes a second limitation on information transmission.Both the bandwidth and the noise limit the communication system performance.Classification of communication systems:A communication system is divided into two categories depending on the transmission media (channel) used: line communication system, and wireless communication system.In line communication, transmission is carried out on the transmission line.Examples of transmission line: wire, coaxial cable, optical fiber, etc.In wireless communication, signals from various sources are transmitted through a common media – open space.Examples of wireless communication: radio, microwave, etc.A communication system can be divided into analog communication system and digital communication system, according to the characteristics of transmitted signals.How to evaluate the performance of a communication system?The performance of a communication system is usually evaluated by two key factors:1.Efficiency determines the capacity of transmission channel;2.Reliability determines the signal quality.In an analog communication system, efficiency is measured by transmission channel bandwidth, B, and reliability is measured by system output signal-to-noise ratio (S/N).e.g. a single sideband telephone system requires 4 kHz bandwidth but a double sideband or a conventional amplitude modulation telephone system requires 8 kHz bandwidth, so that single sideband system has a higher efficiency than a double sideband or a conventional amplitude modulation system.e.g. a telephone system requires a S/N at least 20 dB and a TV picture needs its S/N above 40 dB.In a digital communication system, efficiency is measured by bit rate, R, and reliability is measured by bit error rate, P b.Bit rate: R = n/T (bits/sec) where n is the number of bits sent in T secondsBit error rate (BER): P b = number of error bits / total number of bitse.g. a digital telephone system requires P b < 10-3∼ 10-6 and data communication requires P b < 10-9.Review Questions1.What are the main components in a basic communication system?2.What is a transducer? What is a signal? What is a carrier?3.What are main types of internal noise?4.Why modulation is important in a communication system?5.Distinguish between message and signal.6.Define modulating signal and modulated signal.7.How to evaluate a communication system?Reference Books:1.J. J. O’Reilly, “Telecommunication Principles”, Chapman & Hill, 19942. B. P. Lathi, “Modern Digital and Analogue Communication Systems”, Oxford University Express,19983.Simon Haykin, “Communication systems”, John Willey, 20014.Ferrel G. Stremler, Introduction to Communication Systems”, Addison Welsey, 19905.John M. Senior, “Optical Fiber Communications: Principle and Applications”, Second Edition,Prentice Hall, 19926.L. Frenzel, Communication Electronics”, Second Edition, McGraw-Hill, 19947.H. P. Hsu, “Analog and Digital Communications, McGraw-Hill, 20038.G. Miller, “Modern Electronic Communication”, Third Edition, Prentice-Hall, 1989。

01-Introduction to Bioinformatics(生物信息学国外教程2010版)

Grading
60% moodle quizzes (your top 6 out of 7 quizzes). Quizzes are taken at the moodle website, and are due one week after the relevant lecture. Special extended due date for quizzes due immediately after Thanksgiving and the New Year. 40% final exam Monday, January 10 (in class). Closed book, cumulative, no computer, short answer / multiple choice. Past exams will be made available ahead of time.
Outline for the course (all on Mondays)
1. Accessing information about DNA and proteins Nov. 15
2. Pairwise alignment
3. BLAST 4. Multiple sequence alignment
Literature references
You are encouraged to read original source articles (posted on moodle). They will enhance your understanding of the material. Readings are optional but recommended.
Nov. 22

茶文化英语_讲稿模板

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