英文文献 科技类 原文及翻译 64
科技文献中英文对照翻译
Sensing Human Activity:GPS Tracking感应人类活动:GPS跟踪Stefan van der Spek1,*,Jeroen van Schaick1,Peter de Bois1,2and Remco de Haan1Abstract:The enhancement of GPS technology enables the use of GPS devices not only as navigation and orientation tools,but also as instruments used to capture travelled routes:assensors that measure activity on a city scale or the regional scale.TU Delft developed aprocess and database architecture for collecting data on pedestrian movement in threeEuropean city centres,Norwich,Rouen and Koblenz,and in another experiment forcollecting activity data of13families in Almere(The Netherlands)for one week.Thequestion posed in this paper is:what is the value of GPS as‘sensor technology’measuringactivities of people?The conclusion is that GPS offers a widely useable instrument tocollect invaluable spatial-temporal data on different scales and in different settings addingnew layers of knowledge to urban studies,but the use of GPS-technology and deploymentof GPS-devices still offers significant challenges for future research.摘要：增强GPS技术支持使用GPS设备不仅作为导航和定位工具,但也为仪器用来捕捉旅行路线:作为传感器,测量活动在一个城市或区域范围内规模。
科技英语原文及简单翻译
科技英语原文及简单翻译How ASIMO WorksIntroduction to How ASIMO WorksWant a robot to cook your dinner, do your homework, clean your house, or get your groceries? Robots already do a lot of the jobs that we humans don't want to do, can't do, or simply can't do as well as our robotic counterparts.Honda engineers have been busy creating the ASIMO robot for more than 20 years. In this article, we'll find out what makes ASIMO the most advanced humanoid robot to date.The Honda Motor Company developed ASIMO, which stands for Advanced Step in Innovative Mobility, and is the most advanced humanoid robot in the world. According to the ASIMO Web site, ASIMO is the first humanoid robot in the world that can walk independently and climb stairs.Rather than building a robot that would be another toy, Honda wanted to create a robot that would be a helper for people -- a robot to help around the house, help the elderly, or help someone confined to a wheelchair or bed. ASIMO is 4 feet 3 inches (1.3 meters) high, This allows ASIMO to do the jobs it was created to do without being too big and menacing.ASIMO's Motion: Walk Like a HumanHonda researchers began by studying the legs of insects, mammals, and the motion of a mountain climber with prosthetic legs to better understand the physiology and all of the things that take place when we walk -- particularly in the joints. For example, the fact that we shift our weight using our bodies and especially our arms inorder to balance was very important in getting ASIMO's walking mechanism right. The fact that we have toes that help with our balance was also taken intoconsideration: ASIMO actually has soft projections on its feet that play a similar role to the one our toes play when we walk. This soft material also absorbs impact on the joints, just as our soft tissues do when we walk.ASIMO has hip, knee, and foot joints. Robots have joints that researchers refer to as \degrees of freedom.\A single degree of freedom allows movement either right and left or up and down. ASIMO has 34 degrees of freedom spread over different points of its body in order to allow it to move freely. There are three degrees of freedom in ASIMO's neck, seven on each arm and six on each leg. The number of degrees offreedom necessary for ASIMO's legs was decided by measuring human joint movement while walking on flat ground, climbing stairs and running.ASIMO also has a speed sensor and a gyroscope sensor mounted on its body. They perform the tasks of:? ?sensing the position of ASIMO's body and the speed at which it is moving relaying adjustments for balance to the central computer These sensors work similarly to our inner ears in the way they maintain balance and orientation.ASIMO also has floor surface sensors in its feet and six ultrasonic sensors in its midsection. These sensors enhance ASIMO's ability to interact with its environment by detecting objects around ASIMO and comparing gathered information with maps of the area stored in ASIMO's memory.To accomplish the job our muscles and skin do in sensing muscle power, pressure and joint angles, ASIMO has both joint-angle sensors and a six-axis force sensor.Unless you know a lot about robotics, you may not fully grasp the incredible milestone it is that ASIMO walks as we do. The most significant part of ASIMO's walk is the turning capabilities. Rather than having to stop and shuffle, stop and shuffle, and stop and shuffle into a new direction, ASIMO leans and smoothly turns just like a human. ASIMO can also self-adjust its steps in case it stumbles, is pushed, or otherwise encounters something that alters normal walking.In order to accomplish this, ASIMO's engineers had to find a way to work with the inertial forces created when walking. For example, the earth's gravity creates a force, as does the speed at which you walk. Those two forces are called the \inertial force.\ground, called the \posture has to work to make it happen. This is called the \zero moment point\(ZMP). To control ASIMO's posture, engineers worked on three areas of control:? ?Floor reaction control means that the soles of the feet absorb floor unevenness while still maintaining a firm stance.Target ZMP control means that when ASIMO can't stand firmly and its body begins to fall forward, it maintains position by moving its upper body in the direction opposite the impending fall. At the same time, it speeds up its walking to quickly counterbalance the fall.?Foot-planting location control kicks in when the target ZMP control has been activated. It adjusts the length of the step to regain the right relationship between the position and speed of the body and the length of the step.ASIMO's Motion: Smooth MovesASIMO can sense falling movements and react to them quickly; but ASIMO's engineers wanted more. They wanted the robot to have a smooth gait as well as do something that other robots can't do -- turn without stopping.When we walk around corners, we shift our center of gravity into the turn. ASIMO uses a technology called \predictive movement control,\Intelligent Real-Time Flexible Walking Technology or I-Walk, to accomplish that same thing. ASIMO predicts how much it should shift its center of gravity to the inside of the turn and how long that shift should be maintained. Because this technolgy works in real time, ASIMO can do this without stopping between steps, which other robots must do.Essentially, with every step ASIMO takes, it has to determine its inertia and then predict how its weight needs to be shifted for the next step in order to walk and turn smoothly. It adjusts any of the following factors in order to maintain the right position:? ? ? ?the length of its steps its body position its speedthe direction in which it is steppingWhile reproducing a human-like walk is an amazing achievement, ASIMO can now run at speeds up to 3.7 miles per hour (6 kilometers per hour). In order to qualify as a true running robot, ASIMO must have both feet off the ground for an instant in each step. ASIMO manages to be airborne for .08 seconds with each step while running. Honda engineers encountered an entirely new set of challenges while trying to give ASIMO the ability to run. They gave ASIMO’s torso a degree of freedom to aid in bending and twisting so that the robot could adjust its posture while airborne. Without this ability, ASIMOwould lose control while airborne, possibly spinning in the air or tripping when landing.In order to make turns smoothly while running, the engineers enhanced ASIMO's ability to tilt its center of gravity inside turns to maintain balance and counteractcentrifugal force. ASIMO could even anticipate turns and begin to lean into them before starting the turn, much like you would if you were skiing or skating.ASIMO如何工作介绍如何工作。
外文文献翻译原文及译文
华北电力大学毕业设计（论文）附件外文文献翻译学号： 200701000324 姓名:杨曦所在院系：电力工程系专业班级：电气化0707指导教师：安勃原文标题： Research on Smart Grid in China2011年06月20日对中国智能电网的研究1摘要——智能电网是电力系统的未来发展的新方向。
在本文中，首先是智能电网的背景，意义，以及概念和结构。
典型的智能电网图如下所示.然后,在美国和欧洲智能电网的发展现状进行了描述，并对这些国家未来发展思路的趋势进行了总结和比较及分析。
此外，分析了中国智能电网发展的必要性，详细介绍了在目前与中国与有关项目，并对特高压电网和智能电网之间的的关系进行了讨论。
最后，对智能电网在未来在中国电网的潜在作用进行了展望和并为中国的智能电网发展指明新方向.索引词,智能电网，特高压电网，规划,经营，管理一导言随着世界经济全球化的推广,石油价格一直维持在一个上升的趋势。
还值得注意的是世界范围内的的能源供应短缺，对资源和环境的压力越来越大,同时，由于目前电网的低效率，在能源输送过程中损失了巨大的电力。
此外,由于不断增长的电力需求和用户对电力可靠性和质量日益增长的要求，电力工业正面临着前所未有的挑战和机遇。
因此，一个有环境友好,经济，高性能，低投资，安全性，可靠性和灵活性特点的的电力系统一直是电力工程师的目标。
尽管如此，基础设施和先进的仪表出现互联网更广泛地的使用加速了这个过程[1］。
自1990年以来随着分布式发电越来越多地使用，已经对对电网的强度提出更多的需求和要求［2][3]。
对于这些问题，为了找出最佳的解决方案，电力公司应接受新的思路，采用新技术，对现有的能源系统进行潜力挖掘，对技术和应用加以改进。
来自不同国家的学者和专家已经达成共识：未来电网的必须能够满足不同的需求及能源发电，高度市场化的电力交易的需求，由此可以满足客户的自我选择。
所有这些都将成为未来智能电网的发展方向。
科技文献翻译
科技文献翻译Technology has transformed every aspect of our lives, from the way we communicate and work to how we shop and entertain ourselves. With the rapid advancement of technology, there is a growing demand for accurate translations of technology-related literature. This article aims to provide a translation of a technology paper consisting of 700 words.The paper titled "The Role of Artificial Intelligence in Autonomous Vehicles" explores the impact of AI in self-driving cars. Autonomous vehicles have gained significant attention in recent years due to their potential to revolutionize transportation. This paper discusses how AI technologies, such as deep learning and machine vision, have contributed to the development of autonomous vehicles.一项名为“人工智能在自动驾驶汽车中的角色”的研究探讨了AI在无人驾驶汽车中的影响。
在过去几年中，由于其改变出行方式的潜力，自动驾驶汽车引起了广泛关注。
科技文献中英文翻译
Intelligent Power Supply英文With the rapid development of electronic technology, application field of electronic system is more and more extensive, electronic equipment, there are more and more people work with electronic equipment, life is increasingly close relationship. Any electronic equipment are inseparable from reliable power supply for power requirements, they more and more is also high. Electronic equipment miniaturized and low cost in the power of light and thin,small and efficient for development direction. The traditional transistors series adjustment manostat is continuous control linear manostat. This traditional manostat technology more mature, and there has been a large number of integrated linear manostat module, has the stable performance is good, output ripple voltage small, reliable operation, etc. But usually need are bulky and heavy industrial frequency transformer and bulk and weight are big filter.In the 1950s, NASA to miniaturization, light weight as the goal, for a rocket carrying the switch power development. In almost half a century of development process, switch power because of is small volume, light weight, high efficiency, wide range, voltage advantages in electric, control, computer, and many other areas of electronic equipment has been widely used. In the 1980s, a computer is made up of all of switch power supply, the first complete computer power generation. Throughout the 1990s, switching power supply in electronics,electrical equipment, into the rapid development. In addition, large scale integrated circuit technology, and the rapid development of switch power supply with a qualitative leap, raised high frequency power products of, miniaturization, modular tide.Power switch tube, PWM controller and high-frequency transformer is an indispensable part of the switch power supply. The traditional switch power supply is normally made by using high frequency power switch tube division and the pins, such as using PWM integrated controller UC3842 + MOSFET is domestic small power switch power supply, the design method of a more popularity.Since the 1970s, emerged in many function complete integrated control circuit, switch power supply circuit increasingly simplified, working frequency enhancesunceasingly, improving efficiency, and for power miniaturization provides the broad prospect. Three end off-line pulse width modulation monolithic integrated circuit TOP (Three switch Line) will Terminal Off with power switch MOSFET PWM controller one package together, has become the mainstream of switch power lC development. Adopt TOP switch lC design switch power, can make the circuitsimplified,volume further narrowing, cost also is decreased obviousiy.Monolithic switching power supply has the monolithic integrated, the minimalist peripheral circuit, best performance index, no work frequency transformer can constitute a significant advantage switching power supply, etc. American Pl (with) company in Power in the mid 1990s first launched the new high frequency switching Power supply chip, known as the "top switch Power", with low cost, simple circuit, higher efficiency. The first generation of products launched in 1994 represented TOP100/200 series, the second generation product is the TOPSwitch - debuted in 1997 П .The above products once appeared showed strong vitality and he greatly simplifies the design of 150W following switching power supply and the development of new products for the new job, also, high efficiency and low cost switch power supply promotion and popularization created good condition, which can be widely used in instrumentation, notebook computers, mobile phones, TV, VCD and DVD, perturbation VCR, mobile phone battery chargers, power amplifier and other fields, and form various miniaturization, density, on price can compete with the linear manostat AC/DC power transformation module.Switching power supply to integrated direction of future development will be the main trend, power density will more and more big, to process requirements will increasingly high. In semiconductor devices and magnetic materials, no new breakthrough technology progress before major might find it hard to achieve, technology innovation will focus on how to improve the efficiency and focus on reducing weight. Therefore, craft level will be in the position of power supply manufacturing higher in. In addition, the application of digital control IC is the future direction of the development of a switch power. This trust in DSP for speed and anti-interference technology unceasing enhancement. As for advanced control method, now the individual feels haven't seen practicability of the method appears particularly strong, perhaps with the popularity of digital control, and there are some new control theory into switching power supply.(1) The technology: with high frequency switching frequencies increase, switchconverter volume also decrease,power density has also been boosted, dynamic response improved. Small power DC - DC converter switch frequency will rise to MHz. But as the switch frequency unceasing enhancement, switch components and passive components loss increases, high-frequency parasitic parameters and high-frequency EMI and so on the new issues will also be caused．(2) Soft switching technologies: in order to improve the efficiency of non-linearity of various soft switch, commutation technical application and hygiene, representative of soft switch technology is passive and active soft switch technology, mainly including zero voltage switch/zero current switch (ZVS/ZCS) resonance, quasi resonant, zero voltage/zero current pulse width modulation technology (ZVS/ZCS - PWM) and zero voltage transition/zero current transition pulse width modulation (PWM) ZVT/ZCT - technical, etc. By means of soft switch technology can effectively reduce switch loss and switch stress, help converter transformation efficiency.(3) Power factor correction technology (IC simplifies PFC). At present mainly divided into IC simplifies PFC technology passive and active IC simplifies PFC technology using IC simplifies PFC technology two kinds big, IG simplifies PFC technology can improve AC - DC change device input power factor, reduce the harmonic pollution of power grid.(4) Modular technology. Modular technology can meet the needs of the distributed power system, enhance the system reliability.(5) Low output voltage technology. With the continuous development of semiconductor manufacturing technology, microprocessor and portable electronic devices work more and more low, this requires future DC - DG converter can provide low output voltage to adapt microprocessor and power supply requirement of portable electronic devicesPeople in switching power supply technical fields are edge developing related power electronics device, the side of frequency conversion technology, development of switch between mutual promotion push switch power supply with more than two year growth toward light, digital small, thin, low noise and high reliability, anti-interference direction. Switching power supply can be divided into the AC/DC and DC/DC two kinds big, also have AC/AC DC/AC as inverter DC/DC converter is now realize modular, and design technology and production process at home and abroad, are mature and standardization, and has approved by users, but the AC/DC modular, because of its own characteristics in the process of making modular, meetmore complex technology and craft manufacture problems. The following two types of switch power supply respectively on the structure and properties of this.Switching power supply is the development direction of high frequency, high reliability, low consumption, low noise, anti-jamming and modular. Because light switch power, small, thin key techniques are changed, so high overseas each big switch power supply manufacturer are devoted to the development of new high intelligent synchronous rectifier, especially the improvement of secondary devices of the device, and power loss of Zn ferrite (Mn) material? By increasing scientific and technological innovation, to enhance in high frequency and larger magnetic flux density (Bs) can get high magnetic under the miniaturization of, and capacitor is a key technology. SMT technology application makes switching power supply has made considerable progress, both sides in the circuit board to ensure that decorate components of switch power supply light, small, thin. The high frequency switching power supply of the traditional PWM must innovate switch technology, to realize the ZCS ZVS, soft switch technology has become the mainstream of switch power supply technical, and greatly improve the efficiency of switch power. For high reliability index, America's switch power producers, reduce by lowering operating current measures such as junction temperature of the device, in order to reduce stress the reliability of products made greatly increased．Modularity is of the general development of switch power supply trend can be modular power component distributed power system, can be designed to N + 1 redundant system, and realize the capacity expansion parallel. According to switch power running large noise this one defect, if separate the pursuit of high frequency noise will increase its with the partial resonance, and transform circuit technology, high frequency can be realized in theory and can reduce the noise, but part of the practical application of resonant conversion technology still have a technical problem, so in this area still need to carry out a lot of work, in order to make the technology to practional utilization.Power electronic technology unceasing innovation, switch power supply industry has broad prospects for development. To speed up the development of switch power industry in China, we must walk speed of technological innovation road, combination with Chinese characteristics in the joint development path, for the high-speed development of national economy to make the contribution.中文智能开关电源随着电子技术的高速发展，电子系统的应用领域越来越广泛，电子设备的种类也越来越多，电子设备与人们的工作、生活的关系口益密切。
英语科技文翻译
Protein Filaments Caught in the Act蛋白质细丝的行为Grant J. Jensen*C ells can be thought of as little chemical processing plants, but they also 细胞可以被看做小型化工加工工厂，但他们也能完成一些了不起的物accomplish some marvelous physical and mechanical tasks such as理和机械工作，例如把自己塑造成特有的形状，朝营养素处移动，组shaping themselves into characteristic forms, moving toward nutrients, 织复杂的内部结构，复制、分离DNA。
organizing their complex interiors, replicating and then segregating their DNA, and dividing (1). It has long been understood how in 人们很早就认识到真核细胞中的大部分工作是由它的细胞骨架细丝----一种细胞eukaryotes most of this work is done by cytoskeletal filaments –long中的细丝网状或束状的长的蛋白质聚合物来担当的。
protein polymers that are used like cables, tracks, and bea ms in the machinery of the cell. But until about a decade ago, it was a 但是直到大约十年前，细菌细胞如何完成同样的工作仍是个谜团。
mystery as to how bacterial cells did the same tasks. None of the 当时任何一种科技，包括传统的电子显微学方法，都不能令人信服地existing technologies, including "traditional" electronmicroscopy在细菌细胞中发现类似的细胞骨架细丝。
经济学人科技类文章中英双语（5篇范例）
经济学人科技类文章中英双语（5篇范例）第一篇：经济学人科技类文章中英双语The Brain Activity Map绘制大脑活动地图Hard cell 棘手的细胞An ambitious project to map the brain is in the works.Possibly too ambitious 一个绘制大脑活动地图的宏伟计划正在准备当中，或许有些太宏伟了 NEWS of what protagonists hope will be America’s next big science project continues to dribble out.有关其发起人心中下一个科学大工程的新闻报道层出不穷。
A leak to the New York Times, published on February 17th, let the cat out of the bag, with a report that Barack Obama’s administration is thinking of sponsoring what will be known as the Brain Activity Map.2月17日，《纽约时报》刊登的一位线人报告终于泄露了秘密，报告称奥巴马政府正在考虑赞助将被称为“大脑活动地图”的计划。
And on March 7th several of those protagonists published a manifesto for the project in Science.3月7日，部分发起人在《科学》杂志上发表声明证实了这一计划。
The purpose of BAM is to change the scale at which the brain is understood.“大脑活动地图”计划的目标是改变人们在认知大脑时采用的度量方法。
英文文献科技类原文及翻译
本科毕业设计(论文)外文翻译姓名: 王文超学号： 200715010220专业: 电气工程及其自动化班级: 电气071502指导教师: 智泽英职称：副教授日期: 2011年6月12日电子信息工程学院The basics of Computer Numerical ControlWhile the specific intention and application for CNC machines vary from machine type toanother, all forms of CNC have common benefits. Though the thrust of this presentation is to teach you CNC usage, it helps to understand why these sophisticated machines have become so popular. Here are but a few of the more important benefits offered by CNC equipment.The first benefit offered by all forms of CNC machine tools is improved automation. The operator intervention related to producing workpieces can be reduced or eliminated. Many CNC machines can run unattended during their entire machining cycle, freeing the operator to do other tasks. This gives the CNC user several side benefits including reduced operator fatigue, fewer mistakes caused by human error, and consistent and predictable machining time for each workpiece. Since the machine will be running under program control, the skill level required of the a CNC operator (related to basic machining practice) is also reduced as compared to a machinist producing workpieces with conventional machine tools.The second major benefit of CNC technology is consistent and accurate workpieces. Today’s CNC machines boast almost unbelievable accuracy and repeatability specifications. This means that once a program is verified, two, ten, or one thousand identical workpieces can be easily produced with precision and consistency.A third benefit offered by most forms of CNC machine tools is flexibility. Since these machines are run from programs, running a different workpiece is almost as easy as loading a different program. Once a program has been verified and executed for one production run, it can be easily recalled the next time the workpiece is to be run. This leads to yet another benefit, fast change-overs. Since these machines are very easy to setup and run, and since programs can be easily loaded, they allow very short setup time. This is imperative with today’s Just-In-Time product requirements.1. Motion control-the heart of CNCThe most basic function of any CNC machine is automatic, precise, and consistent motion. Rather than applying completely mechanicaldevices to cause motion as is required on most conventional machine tools, CNC machines allow motion control in a revolutionary manner. All forms of CNC equipment have two or more directions of motion, called axes. These axes can be precisely and automatically positioned alongtheir lengths of travel. The two most common axis types are linear (driven along a straight path) and rotary (driven along a circular path).Instead of causing motion by turning cranks and handwheels as is required on conventional machine tools, CNC machines allow motions to be commanded through programmed commands. Generally speaking, the motion type (rapid, linear, and circular), the axes to move, the amount of motion and the motion rate (feedrate) are programmable with almost all CNC machine tools.Accurate positioning is accomplished by the operator counting the number of revolutions made on the handwheel plus the graduations on the dial. The drive motor is rotated a corresponding amount, which in turn drives the ball screw, causing linear motion of the axis. A feedback device confirms that the proper amount of ball screw revolutions has occurred.A CNC command executed within the control (commonly through a program) tells the drive motor to rotate a precise number of times. The rotation of the drive motor in turn rotates the ball screw. And the ball screw causes drives the linear axis. A feedback device at the opposite end of the ball screw allows the control to confirm that the commanded number of rotations has taken place.Though a rather crude analogy, the same basic linear motion can be found on a common table vise. As you rotate the vise crank, you rotate a lead screw that, in turn, drives the movable jaw on the vise. By comparison, a linear axis on a CNC machine tool is extremely precise. The number of revolutions of the axis drive motor precisely controls the amount of linear motion along the axis.How axis motion is commanded-understanding coordinate systems. It would be infeasible for the CNC user to cause axis motion by trying to tell each axis drive motor how many times to rotate in order to command a given linear motion amount. (This would be like having to figure out how many turns of the handle on a table vise will cause the movable jaw to move exactly one inch!) Instead, all CNC controls allow axis motion to be commanded in a much simpler and more logical way by utilizing some form of coordinate system. The two most popular coordinate systems used with CNC machines are the rectangular coordinate system and the polar coordinate system. By far, the move popular of these two is the rectangular coordinate system, and we’ll use it for all discussions made during this presentation.。
英文科技文献翻译
英文文献翻译二〇一二年五月三十日Integrated wiring systemModern science and technology progress has made rapid development of computer and network technology, provides a more powerful computer processing capacity and network communication ability. The computer and network communication technology can greatly improve the modern enterprise production management efficiency, reduce the operation cost, and makes the modern enterprise can obtain more effectively and timely decision market information, provide more quickly, more satisfactory service to customers, in the competition. The computer and network communication technology has become a key factor in the success of the company.Integrated cabling system in order to meet the development needs is specially designed a set of cabling system. For modern buildings, such as the body, it adopted a series of nerve of high quality standard, modular combinations of material, the voice, data and image and control signal system using uniform transmission media, through comprehensive, integrated unified planning design in a set of standard cabling system in modern architecture, the three subsystems will connect organically, and system integration for the modern architecture provides a physical medium. Structured cabling system can directly related to the success of the modernization of the building, choose a high quality of integrated wiring system is of vital importance.Computer and communication networks are dependent on wiring system as the physical basis of network connections and information transmission channel. The traditional single application on a particular special layout techniques, lack of flexibility and development of, can not meet the rapid development of modern business needs of network applications. The new generation of structured cabling systems provide the user the required data, voice, fax, video and other information service connections, which allows voice and data communications equipment, switching equipment, information management systems and equipment control system , security system connected to each other, but also to make these devices with external communication networks. It includes the building to the external network or phone line connection Bureau,with the work area of voice or data terminals associated with all the cables and wiring components. Cabling system composed by different series of components, including: transmission media, line management of hardware, connectors, sockets, plugs, adapters, transmission electronic circuits, electrical protection equipment and support. Compared with the previous wiring, cabling system features can be summarized as:Practicality: after the implementation of cabling systems will be able to adapt to the modern and future communication technology development and implementation of voice, data, unified communications, signal transmission.Flexibility: wiring system can satisfy the requirements of various applications, information points to any connection of different types of terminal equipment, such as telephone, computer, printer, computer terminal, electric machine, various sensors and image monitoring equipment.Modularity: integrated cabling system in fixed in buildings, the level of all cable connectors are basic type of the standard, all voice, data and interconnection of building automation, network and image, with convenient use, equipment, change, management and expansion.Scalability: integrated wiring system is for future expansion, more use, easy to expand into new equipment.Economy: the integrated wiring system enables managers, and at the same time, reduce the modular structure, work because of the difficulty of future changes greatly reduced the cost or moving system.General: to meet the standard of international communication and computer network topology structure, can adapt different transmission speed communication can adapt to the requirement, can support and accommodate various computer network operation.1 workspace subsystemPurpose is to realize the workspace terminal equipment and level of connections between subsystems, the terminal devices connected to the information socket connection cables. Workspace used computer, networkequipment is distributed (on), telephone, or may alarm detector, camera, monitors, acoustics, etc.2 Horizontal subsystemPurpose is to realize information socket and management subsystem (jumper wire connection between frame), will lead to the management subsystem of user workspace, and to provide users with one accord with international standard pronunciation, satisfy the requirements and the high-speed data transmission information points. The subsystem of information from a job, decorate the socket to the inside of the administrative levels of the cable distribution frames. In the system of transmission medium of UTP (4) shielding twisted-pair cable, it can support the most modern communication equipment. If you need some broadband application, you can use fiber. Information ISDN8 for export by core RJ45 jack (standard), each information socket outlets can be flexibly according to actual application requirements and optional change purposes.3 the management subsystemThis sub-system connected by a cross, composed of interconnect patch panel. Management point of connection means to connect to other subsystems. Cross-connect and interconnect allows communication lines locate or relocate to different parts of the building to make it easier to manage communication lines, so that when the mobile terminal device easily plug. Interconnection distribution frame connections under different hardware sub-floor distribution frame (box) IDF and MDF (box) MDF, IDF can be installed on each floor of the trunk connection between, MDF is usually installed in the equipment room.4 vertical lines subsystemPurpose is to achieve the computer equipment, pabx (PBX), with the management subsystem of control center is building a connection between the main cable, routing. This is usually between two units subsystem, especially in the central point in the public system provides more line facilities. By building the system all vertical lines and more logarithmic cable support hardware, toprovide total distribution frames and main equipment room wiring between floors between the main distribution frames routing. Common medium is multi-cores cable and optical fiber cable twisted-pair.5.Equipment room subsystemThis subsystem is mainly from the devices in the cable, connectors and related hardware support, the role of the computer, PBX, cameras, monitors and other weak and connected to the interconnection of equipment up on the main distribution frame. Equipment includes computer systems, network hub (Hub), network switches (Switch), program-controlled switchboards (PBX), audio output devices, CCTV control devices and alarm control center, etc.6 Buildings subsystem (Campus):The subsystem will be extended to cable a building complex of other buildings of the communications equipment and devices, is part of a structured cabling system to support the provision of buildings in the hardware required for communication between. It consists of cables, fiber optic cable and into the Building Department, over-current over-voltage protection equipment and other related electrical hardware, commonly used medium is optical fiber. Compared with the traditional routing, integrated wiring construction as a modern information transmission system, its main advantages are: Traditional wiring specification due to lack of a unified, user must choose a variety of different application types of cables, connectors and wiring, resulting in duplication of cable laying waste, lack of flexibility and can not support the development needs of the user application re-wiring; integrated wiring system integration requirements of modern architecture transmission of voice, data, video and other information, using international standardized information interface and performance specifications, to support multi-vendor equipment and protocols to meet the rapid development of modern enterprise information application needs.Integrated wiring system, the user can according to actual needs or changing office environment, flexible and convenient way to achieve change and restructuring routes, adjusting the mode of building the network required to fully meet user business needs.Structured cabling system is the star topology wiring methods and standard interfaces, which greatly improves over all network reliability and manageability, significantly reduce system management and maintenance costs. The modular system design to provide a good system scalability and future-oriented application development support, fully guaranteed the user's investment in cabling, providing customers a long-term benefits.Cabling System can solve the traditional wiring methods exist many problems, provides long-term benefits of advanced and reliable solutions. With the rapid development of modern information technology, integrated wiring system will be indispensable to modern intelligent building infrastructure.综合布线系统现代科技的进步使计算机及网络技术飞速发展，提供越来越强大的计算机处理能力和网络通信能力。
科技文献中英文对照翻译
Human Geomatics in Urban Design—Two Case Studies在城市设计中的人类地理信息学——两个案例研究Małgorzata Hanzl1,*,Karol Dzik2,Paulina Kowalczyk2,Krystian Kwieciński2,Ewa Stankiewicz2and AgataŁ.Wierzbicka2Abstract:The mapping of different aspects of urban phenomena and their relation to thephysical cityscape has been greatly extended by the use of geomatics.The tradition to basereasoning on‗understanding the world‘dates from the time of Aristotle.The extensionplan for Barcelona(Eixample),developed by Cerdà,which opened the era of modern urbanplanning,was preceded by analyses of rich data,describing both detailed demographicissues and physical structures.The contemporary,postmodernist city planning continuesthis tradition,although a shift towards analyses of more human-related issues can beobserved,covering,inter alia,citizens‘perception,cultural differences and patterns ofhuman activities with regard to distinct social groups.The change towards a morehuman-related perspective and the inclusion of urban morphology analyses are directconsequences of this trend.The required data may be gathered within a crowd-sourcingparticipation process.According to communicative planning theory,communication withthe wider public is indispensable in order to achieve the best results,and can be realizedwith the use of sophisticated IT tools.Evidence-based reasoning may be supported byimages of significant aesthetic values,which inspire immediate reactions.Keywords:GIS;crowd-sourcing;mash-up;education;urban planning;urban analyses摘要：不同方面的城市现象及其与物理城市景观的关系映射经由地理信息学的使用已经大大扩展了。
科技类文章中英文对照范文带翻译
科技类文章中英文对照范文带翻译印度首富百亿美元建4G网免费向全国提供India's richest man is rolling out a $20 billion mobile network that could bring lightning-fast Internet to hundreds of millions of people.印度首富正斥资200亿美元建设移动网络，或可使十亿人高速连接互联网。
Indian consumers are already celebrating the arrival of Mukesh Ambani's new Reliance Jio service, seizing on the billionaire's promise to deliver rock bottom prices and download speeds thatwill enable streaming video.印度消费者已经在庆祝穆克什•安巴尼新推出的瑞来斯Jio网络服务。
这位亿万富翁承诺，该网络会以最低价格提供满足流媒体使用的下载速度。
The 4G network, which reaches more than 80% of the country, officially went live Monday with a set of generous introductory offers.这个覆盖印度超过80%地区的4G网络于周一正式开通，同时慷慨附送试用套餐。
Indians will be able to use Jio for free until the end of 2021, and pay as little as 149 rupees $2.25 a month for data after that.印度人到今年年底都可免费使用Jio网络，之后的网费也只有每月149卢比2.25美金。
英语科技文双语版
科技文1.单心室辅助人工心脏应用于实验动物山羊，存活11天又23小时。
在存活期间，动物心电图，中心静脉压，呼吸，体温等参数基本正常。
石泵分流量可调，驱动装置连续工作11天，性能稳定可靠。
动物死后的病理解剖表明，死亡的主要原因是肾动脉的广泛性血栓引起的急性肾功能衰竭。
A univentricular assistant artificial heart was applied to the experiment goat, which survived for 11 days and 23 hours. During the period of survival, the parameters such as E.C.G., central venous blood pressure, respiration and temperature appeared to be essentially normal. The necessary amount of blood flow was well regulated by the pump. The driving system worked continuously, smoothly and reliably for 11 days. Postmortem patho-anatomy revealed that the chief cause of the animal’s death was acute renal failure as a result of widespread multiple embolism of renal arteries.2. 中国已经成功地发射了第一颗试验通信卫星。
这颗卫星是由三级火箭推动的，一直运转正常。
它标志着我国运载工具和电子技术方面进入了一个新阶段。
The successful launching of China’s first experimental communication satellite, which was propelled by a three-stage rocket and has been in operation ever since, indicates that our nation has entered a new stage in the development of carrier rockets and electronics.3.石墨晶体结构遭到破坏时，总是碎化为微小尺寸的片状粉末。
经典翻译范文之科技篇中英文对照
中国热门科技词汇科学发展观concept of scientific development全民科学文化素质scientific and cultural qualities of the entire people发展科技scientific and technological advancement科教兴国revitalize China through science and education农业技术agricultural technology[扩展]白色农业white agriculture （microbiological agriculture and biological cell agriculture）超级杂交水稻super-hybrid rice技术下乡spreading the application of science and technology in rural areas节水农业water-saving agriculture立体农业3-D agriculture农产品加工及转化the processing and commercialization of agro-products农业科技agro-science农作物良种seeds of high-quality crop农作物新品种选育the selection and breeding of new crops生态农业environmental-friendly agriculture无土栽培soil -less cultivationBP机，传呼beeper, pager背投屏幕rear projection screen不明飞行物unidentified flying object （UFO）operating system 操作系统产品科技含量technological element of a product创新innovation电话会议teleconference电话留言机answering machine对讲机talkie and walkie多媒体multimedia二期the second phase防抱死系统ABS （anti-lock braking system）孵化器incubator高产优质high yield and high quality高技术产业化apply high technology to production高科技板块high-tech sector高科技园high-tech park个人数字助理PDA （personal digital assistant）工业园区industrial park国家质量技术监督局the State Bureau of Quality and Technical Supervision 国家重点实验室national key laboratories火炬计划Torch Program （a plan to develop new and high technology）计算机中央处理器central processing unit（CPU）技术产权technology property right技术交底confide a technological secret to someone.technology-intensive product 技术密集产品交叉学科interdisciplinary branch of science科技成果转化为生产力transfer of scientific and technological achievements into productive forces科技含量technology content科技基础设施science and technology infrastructure科技是第一生产力Science and technology constitute a primary productive force科技体制改革reform of the science and technology management system科技与经济脱节science and technology are out of line from the economy科教兴国rejuvenate the country through science and education可持续发展战略strategy of sustainable development纳米nanometer三峡水利枢纽工程the key water control project at the Three Gorges on the Yangtze River物种起源origin of species新兴学科new branch of science研究成果research results在孵企业incubated enterprises自动取款机automatic teller machine （ATM）自然科学与社会科学的交叉融合integration of natural and social sciencesIT 信息技术[扩展]信息港info port信息高地information highland信息高速公路information superhighway信息革命information revolution信息含量information content信息化informationization信息技术处理ITA - Information Technology Agreement信息检索information retri办公自动化OA （Office Automation）笔记本电脑laptop / notebook / portable computer电脑病毒computer virus电脑犯罪computer crime电子管理e-management电子货币e-currency电子商务e-business; e-commerce电子商务认证e-business certification电子邮件E-mail非对称数字用户环路ADSL （Asymmetrical Digital Subscriber Loop）高速宽带互联网high-speed broadband networks公告板BBS （bulletin board system）光盘杂志CD-ROM magazine广域网WAN （wide area net word）汉字处理软件Chinese character processing softwarehacker 黑客计算机2000年问题Y2K problem计算机辅助教育CAI -computer assisted instruction计算机辅助设计CAD-computer assisted design计算机合成制造CAM-computer assisted manufacturing计算机中央处理器CPU - central processing unit超文本传送协议hypertext transfer protocol （HTTP）界面interface金融电子化computerized financial services局域网LAN - local area network互联网服务提供商ISP （Internet Service Provider）全球移动通信系统（全球通）global system for mobile communications （GSM）刻录机CD burner宽带接入broadband access宽带网broadband networks内联网、局域网（计算机）Intranet垃圾邮件junk mail千年问题、千年虫millennium bug; Y2K bug人工智能AI - artificial intelligence人机交互human - computer interaction人机交互human-computer interaction虚拟人visual humanvirtual net 虚拟网虚拟网virtual net虚拟现实virtual reality虚拟银行virtual bank因特网服务提供商ISP- internet service provider万维网World Wide Web（WWW）应用软件internet applications域名domain在线on line掌上电脑palm computer政府上网工程Government Online Project只读存储器read-only-memory （ROM）智能感知技术perceptive technology智能终端intelligent terminal中文信息处理系统Chinese information processing system 数码科技digital technology高保真Hi-Fi （High Fidelity）高清晰度电视high definition TV （HDTV）光谷optical valley光通讯optical communication蓝光光盘Blue -ray Disc数码港cyber portdigital globe 数字地球数字蜂窝移动通信digital cellular mobile telecommunications三维电影three-dimensional movie三维动画three-dimensional animation[详析] “蓝光光盘”利用蓝色的激光束来刻录数据。
科技英语原文翻译
Calls in the WildMidday sun scorches1 the plains of northern Namibia, and a female elephant just coming into estrus2 is making a racket3. With a rumble loud enough to rival a jackhammer4, she broadcasts her availability for mating. But gusty winds and turbulence5 created by heat shimmering through the atmosphere tend to break up the sound waves she generates, so her signal carries little more than half a mile. The odds6 are slim that a mature male in his own period of reproductive7 readiness will be close enough to hear her call.Hours pass. Dusk settles over the flat sand veld8. Winds calm, and air near the ground becomes cooler than the warm air above it, effectively creating a channel for sound. Now the low-frequency end of the eager female’s cries can carry six miles in all directions, reaching the ears of elephants spread over a range of more than 110 square miles. The chance that a tall, strong mate will come swaggering her way is now a pretty sure thing.To understand how elephants make the switch from local to long-distance calling, it helps to know something about weather. Wind and heat -- along with rough terrain and dense vegetation -- limit animal calling ranges because they disrupt sound waves. Wind can also be a problem for the receiver: Gusts9 blustering10over elephants’ massive heads and floppy11ears can make it difficult for these distinctly non-aerodynamic12animals to hear any signal clearly. High frequencies (think bird whistles and chimp chatter) are even more easily disturbed than low frequencies (elephant rumbles and lion roars).The link between weather and sound has long intrigued Michael Garstang, a University of Virginia meteorologist13with a tool kit14full of weather instruments, a detailed grasp of how atmospheric15patterns can affect acoustics16 -- and a fondness for elephants.Garstang became curious about whether elephants waste energy bellowing17 against the wind, or whether they take advantage of daily atmospheric changes that can boost bass tones like the woofers18 in stereo speakers. To find answers, he assembled a team of researchers and headed to Etosha National Park in Namibia, home to a healthy and growing elephant population. Hills and forests aren’t part of Etosha’s savanna19 habitat, so Garstang knew that weather, rather than terrain, would be the most significant environmental factor affecting the elephants’lowest pitched communications.Daytime temperatures at the site rose to over 110, and the wind regularly blew at more than 20 miles an hour. In the evening, temperatures dropped below 40, and for hours the air was almost still. Ninety-six percent of the infrasonic20signals Garstang’s team recorded occurred in the cool calm between dusk and dawn. The greatest number of calls happened from an hour before sunset to three hours after, with another talkative period in the first two hours after sunrise.Those early morning and early evening peaks in calls support the idea that elephants have indeed adapted their behavior to match patterns of change in the atmosphere. Garstang succinctly21 sums up his findings: “Elephants talk most when conditions are best.”That adaptation is crucial, since calling range helps determine the size of the area used by elephants at any given time. Long-distance vocalizations keep group members bonded as they trade information about resources and dangers and seek breeding partners across pachyderm22-scale areas. Knowledge about how elephants communicate, Garstang says, can help us protect their habitat -- and their future.中午的太阳scorches1纳米比亚北部平原，和雌性大象刚刚进入estrus2正在racket3。
英文文献小短文(原文加汉语翻译)
A fern that hyperaccumulates arsenic(这是题目，百度一下就能找到原文好，原文还有表格，我没有翻译)A hardy, versatile, fast-growing plant helps to remove arsenic from contaminated soilsContamination of soils with arsenic,which is both toxic and carcinogenic, is widespread1. We have discovered that the fern Pteris vittata (brake fern) is extremely efficient in extracting arsenic from soils and translocating it into its above-ground biomass. This plant —which, to our knowledge, is the first known arsenic hyperaccumulator as well as the first fern found to function as a hyperaccumulator— has many attributes that recommend it for use in the remediation of arsenic-contaminated soils.We found brake fern growing on a site in Central Florida contaminated with chromated copper arsenate (Fig. 1a). We analysed the fronds of plants growing at the site for total arsenic by graphite furnace atomic absorption spectroscopy. Of 14 plant species studied, only brake fern contained large amounts of arsenic (As;3,280–4,980 We collected additional samples of the plant and soil from the contaminated site –1,603 As) and from an uncontaminated site –As). Brake fern extracted arsenic efficiently from these soils into its fronds: plantsgrowing in the contaminated site contained 1,442–7,526 Arsenic and those from the uncontaminated site contained –These values are much higher than those typical for plants growing in normal soil, which contain less than of arsenic3.As well as being tolerant of soils containing as much as 1,500 arsenic, brake fern can take up large amounts of arsenic into its fronds in a short time (Table 1). Arsenic concentration in fern fronds growing in soil spiked with 1,500 Arsenic increased from to 15,861 in two weeks. Furthermore, in the same period, ferns growing in soil containing just 6 arsenic accumulated 755 Of arsenic in their fronds, a 126-fold enrichment. Arsenic concentrations in brake fernroots were less than 303 whereas those in the fronds reached 7,234 of 100 Arsenic significantly stimulated fern growth, resulting in a 40% increase in biomass compared with the control (data not shown).After 20 weeks of growth, the plant was extracted using a solution of 1:1 methanol:water to speciate arsenic with high-performance liquid chromatography–inductively coupled plasma mass spectrometry. Almost all arsenic was present as relatively toxic inorganic forms, with little detectable organoarsenic species4. The concentration of As(III) was greater in the fronds (47–80%) than in the roots %), indicating that As(V)was converted to As(III) during translocation from roots to fronds.As well as removing arsenic from soils containing different concentrations of arsenic (Table 1), brake fern also removed arsenic from soils containing different arsenic species (Fig. 1c). Again, up to 93% of the arsenic was concentrated in the fronds. Although both FeAsO4 and AlAsO4 are relatively insoluble in soils1, brake fern hyperaccumulated arsenic derived from these compounds into its fronds (136–315 levels 3–6 times greater than soil arsenic.Brake fern is mesophytic and is widely cultivated and naturalized in many areas with a mild climate. In the United States, it grows in the southeast and in southern California5. The fern is versatile and hardy, and prefers sunny (unusual for a fern) and alkaline environments (where arsenic is more available). It has considerable biomass, and is fast growing, easy to propagate,and perennial.We believe this is the first report of significant arsenic hyperaccumulation by an unmanipulated plant. Brake fern has great potential to remediate arsenic-contaminated soils cheaply and could also aid studies of arsenic uptake, translocation, speciation, distribution anddetoxification in plants.*Soil and Water Science Department, University ofFlorida, Gainesville, Florida 32611-0290, USAe-mail†Cooperative Extension Service, University ofGeorgia, Terrell County, PO Box 271, Dawson,Georgia 31742, USA‡Department of Chemistry & SoutheastEnvironmental Research Center, FloridaInternational University, Miami, Florida 33199,1. Nriagu, J. O. (ed.) Arsenic in the Environment Part 1: Cycling and Characterization (Wiley, New York, 1994).2. Brooks, R. R. (ed.) Plants that Hyperaccumulate Heavy Metals (Cambridge Univ. Press, 1998).3. Kabata-Pendias, A. & Pendias, H. in Trace Elements in Soils and Plants 203–209 (CRC, Boca Raton, 1991).4. Koch, I., Wang, L., Ollson, C. A., Cullen, W. R. & Reimer, K. J. Envir. Sci. Technol. 34, 22–26 (2000).5. Jones, D. L. Encyclopaedia of Ferns (Lothian, Melbourne, 1987).积累砷的蕨类植物耐寒，多功能，生长快速的植物，有助于从污染土壤去除砷有毒和致癌的土壤砷污染是非常广泛的。
科技外文文献译文
流动的：一个快速的，多平台的开放源码的同步化多媒体整合语言唱机Dick C.A. Bulterman, Jack Jansen, Kleanthis Kleanthous, Kees Blom and Daniel Benden CWI: Centrum voor Wiskunde en InformaticaKruislaan 4131098 SJ Amsterdam, The Netherlands+31 20 592 43 00Dick.Bulterman@cwi.nl摘要：本文概述了一个出现在早期的流动性的同步化多媒体唱机。
不同于其它同步化的实现，早期的播放器是一个可重组的同步化引擎，可以定制作为一个实验媒体播放器的核心。
同步化唱机是一个引用了同步化多媒体引擎并可以集成在一个广泛的媒体播放器的项目。
本文是以我们要创造一个新的同步化引擎为动机的综述开始的。
然后论述的是早期媒体播放器的核心架构（包括可扩展性，播放器自定义的集成装置）。
我们以一个关于我们在windows，Mac，Linux版本应用于台式机以及PDA设备上实施流动性例子的体验的讨论结束。
类别和主题描述符：H.5.2 多媒体的信息系统。
H.5.4 超级文本/超级媒体。
一般词汇：试验，性能，验证。
关键词：同步化多媒体整合语言，唱机，公开源代码，演示。
1.动机：早期公开的同步化媒体播放器是一个非常有特色的公开源代码的同步化 2.0播放器，它以研究团体的意图被使用（在我们的研究团体内外）目的是为了研究项目的团体在需要源代码的时候可以访问生产特性的同步化播放器的网站。
它也被用作一个独立的不需要专有的媒体格式的同步化播放器使用，播放器支持一系列同步化2.0配置文件（包括台式机和移动的配置）可以被分配利用在Linux，Macintosh，windows系统的台式机，PDA设备和掌上电脑。
同时现存的几个同步化播放器，包括网络视频播放软件,IE浏览器,小型同步化播放器, GRiNS ,X- GRiNS ，以及各种各样专有移动设备，我们发展流动性唱机有三个原因：准许制作数字以及个人或者课堂使用中的的全部硬拷贝即时没有提供拷贝权限或者商业性的利益分摊，而且在第一页有这种拷贝的注意事项。
英文科技文献以及翻译
科技翻译原文题目：Struts In Action译文题目：支杆的应用指导教师：邱保志职称：教授学生姓名：郑豪学号：20137670459专业：计算机科学与技术（软件方向）院（系）：信息工程学院完成时间：2017年5月30日Struts In Action1What is struts (2)2Who makes the Struts software (2)2.1Why is Struts open source (2)2.2Why is it called Struts (3)3What are application frameworks (3)3.1Other types of frameworks (3)3.2Enabling technologies (4)3.2.1Hypertext Transfer Protocol(HTTP) (4)3.2.2Common Gateway Interface(CGI) (5)3.2.3Java servlets (6)3.2.4JavaServer Pages (6)3.3Enabling technologies11 (7)3.4.1JSP tags (7)3.4.1JavaBeans (8)3.4Enabling technologies111 (9)4Struts from30,000feet (10)1What is strutsStruts is open source software that helps developers build web applicationsquickly and easily.Struts relies on standard technologies—such as JavaBeans,Javaservlets,and Java Server Pages(JSP)—that most developers already know how touse.By taking a standards-based,“fill-in-the-blanks”approach to software development,Struts can alleviate much of the time-consuming grunt work that comeswith every new project.2Who makes the Struts softwareStruts is hosted by the Apache Software Foundation(ASF)as part of its Jakartaproject. Besides Struts,Jakarta hosts several successful open source products,including Tomcat, Ant,and Velocity.The initial Struts codebase was developed between May2000and June 2001when version1.0was released.More than30developers contributed to the Struts distribution,and thousands more follow the Struts mailing lists.The Struts codebase is managed by a team of volunteer“Committers.”By2002,the Struts team included nine active Committers.The primary architect and developer of the Struts framework is Craig R.McClanahan.Craig is also the primary architect of Tomcat4and the implementationarchitect of the Java Web Services Developer Pack.He is now Sun’s specification lead for JavaServer Faces(JSR-127)as well as the Web Layer Architect for the Java2Enterprise Edition(J2EE)platform.Struts is available to the public at no charge under the Apache Software License[ASF,License].There are no acquisition or other recurring costs for using the software.Unlike some other open source licenses,the Apache Software License is business-friendly.You can use Struts to create a commercial project and distribute the Struts binary without any red tape,fees,or other hassles.You can also integrate the Struts components into your own framework just as if they were written in-house.For complete details,see the Apache Software License at/LICENSE.2.1Why is Struts open sourceMost of the leading Java utilities and frameworks are now open source projects.Many of the developers working on these projects do so as part of their regular jobs with companies like IBM,Sun Microsystems,and Apple.Collaborating openly on this type of software benefits the entire marketplace.Today,many open source components are integrated into commercial panies then sell professional documentation, guaranteed support levels,and other valuable aftermarket services to their clients.When software is freely available,it becomes much easier for the marketplace to support.Strutsis a prime example of this.Although still a youngster,it has already been featured in dozens of articles and seminars,not to mention books like this one.Many development teams do not like to use software that was not“invented”in-house.Open source components provide all the benefits of writing the same software in-house but do not lock you into a proprietary solution that only your team understands.Open source frameworks are a win-win for everyone.2.2Why is it called StrutsThe framework is called“Struts”to remind us of the invisible underpinnings that hold up our houses,buildings,bridges,and,indeed,ourselves when we are on stilts.This is an excellent description of the role Struts plays in developing web applications.When raising physical structures,construction engineers use struts to provide support for each floor of a building.Likewise,software engineers use Struts to support each layer of a business application.3What are application frameworksA framework is a reusable,semi-complete application that can be specialized to produce custom applications[Johnson].Like people,software applications are more alike than they are different.They run on the same computers,expect input from the same devices, output to the same displays,and save data to the same hard disks.Developers working on conventional desktop applications are accustomed to toolkits and development environments that leverage the sameness between applications.Application frameworks build on this common ground to provide developers with a reusable structure that can serve as the foundation for their own products.A framework provides developers with a set of backbone components that have the following characteristics:_They are known to work well in other applications._They are ready to use with the next project._They can also be used by other teams in the organization.Frameworks are the classic build-versus-buy proposition.If you build it,you will understand it when you are done—but how long will it be before you can roll your own?If you buy it,you will have to climb the learning curve—and how long is that going to take? There is no right answer here,but most observers would agree that frameworks such as Struts provide a significant return on investment compared to starting from scratch, especially for larger projects.3.1Other types of frameworksThe idea of a framework applies not only to applications but to application components as well.Throughout this book,we introduce other types of frameworks that you can use withStruts.These include the Lucene search engine,the Scaffold toolkit,the Struts validator, and the Tiles tag library.Like application frameworks,these tools provide semi-complete versions of a subsystem that can be specialized to provide a custom component.Some frameworks have been linked to a proprietary development environment.This is not the case with Struts or any of the other frameworks shown in this book.You can use any development environment with Struts:Visual Age for Java,JBuilder,Eclipse,Emacs,and Textpad are all popular choices among Struts developers.If you can use it with Java,you can use it with Struts.3.2Enabling technologiesApplications developed with Struts are based on a number of enabling technologies.These components are not specific to Struts and underlie every Java web application.A reason that developers use frameworks like Struts is to hide the nasty details behind acronyms like HTTP,CGI,and JSP.As a Struts developer,you don’t need to be an alphabet soup guru,but a working knowledge of these base technologies can help you devise creative solutions to tricky problems.3.2.1Hypertext Transfer Protocol(HTTP)When mediating talks between nations,diplomats often follow a formalprotocol.Diplomatic protocols are designed to avoid misunderstandings and to keep negotiations from breaking down.In a similar vein,when computers need to talk,they also follow a formal protocol.The protocol defines how data is transmitted and how to decode it once it arrives.Web applications use the Hypertext Transfer Protocol(HTTP)to move data between the browser running on your computer and the application running on the server.Many server applications communicate using protocols other than HTTP.Some of these maintain an ongoing connection between the computers.The application server knows exactly who is connected at all times and can tell when a connection is dropped. Because they know the state of each connection and the identity of each person using it, these are known as stateful protocols.By contrast,HTTP is known as a stateless protocol. An HTTP server will accept any request from any client and will always provide some type of response,even if the response is just to say no.Without the overhead of negotiating and retaining a connection,stateless protocols can handle a large volume of requests. This is one reason why the Internet has been able to scale to millions ofcomputers.Another reason HTTP has become the universal standard is its simplicity.An HTTP request looks like an ordinary text document.This has made it easy for applications to make HTTP requests.You can even send an HTTP request by hand using a standard utility such as Telnet.When the HTTP response comes back,it is also in plain text that developers can read.The first line in the HTTP request contains the method,followed by the location of the requested resource and the version of HTTP.Zero or more HTTP request headers follow the initial line.The HTTP headers provide additional information to the server.This can include the browser type and version,acceptable document types,and the browser’s cookies,just to name a few.Of the seven request methods,GET and POST are by far the most popular.Once the server has received and serviced the request, it will issue an HTTP response.The first line in the response is called the status line and carries the HTTP protocol version,a numeric status,and a brief description of the status. Following the status line,the server will return a set of HTTP response headers that work in a way similar to the request headers.As we mentioned,HTTP does not preserve state information between requests.The server logs the request,sends the response,and goes blissfully on to the next request.While simple and efficient,a stateless protocol is problematic for dynamic applications that need to keep track of their users.(Ignorance is not always bliss.)Cookies and URL rewriting are two common ways to keep track of users between requests.A cookie is a special packet of information on the user’s computer.URL rewriting stores a special reference in the page address that a Java server can use to track users.Neither approach is seamless,and using either means extra work when developing a web application.On its own,a standard HTTP web server does not traffic in dynamic content.It mainly uses the request to locate a file and then returns that file in the response.The file is typically formatted using Hypertext Markup Language(HTML)[W3C, HTML]that the web browser can format and display.The HTML page often includes hypertext links to other web pages and may display any number of other goodies,such as images and videos.The user clicks a link to make another request,and the process begins anew.Standard web servers handle static content and images quite well but need a helping hand to provide users with a customized,dynamic response.DEFINITION Static content on the Web comes directly from text or data files,like HTML or JPEG files.These files might be changed from time to time,but they are not altered automatically when requested by a web browser.Dynamic content,on the other hand,is generated on the fly,typically in response to an individualized request from a browser.3.2.2Common Gateway Interface(CGI)The first widely used standard for producing dynamic content was the Common Gateway Interface(CGI).CGI uses standard operating system features,such as environment variables and standard input and output,to create a bridge,or gateway,between the web server and other applications on the host machine.The other applications can look at the request sent to them by the web server and create a customized response.When a web server receives a request that’s intended for a CGI program,it runs that program and provides the program with information from the incoming request.The CGI program runs and sends its output back to the server.The web server then relays the response to the browser.CGI defines a set of conventions regarding what information it will pass as environment variables and how it expects standard input and output to be used.Like HTTP, CGI is flexible and easy to implement,and a great number of CGI-awareprograms have been written.The main drawback to CGI is that it must run a new copy of the CGI-aware program for each request.This is a relatively expensive process that can bog down high-volume sites where thousands of requests are serviced per minute. Another drawback is that CGI programs tend to be platform dependent.A CGI program written for one operating system may not run on another.3.2.3Java servletsSun’s Java Servlet platform directly addresses the two main drawbacks of CGI programs.First,servlets offer better performance and utilization of resources than conventional CGI programs.Second,the write-once,run-anywhere nature of Java means that servlets are portable between operating systems that have a Java Virtual Machine (JVM).A servlet looks and feels like a miniature web server.It receives a request and renders a response.But,unlike conventional web servers,the servlet application programming interface(API)is specifically designed to help Java developers create dynamic applications.The servlet itself is simply a Java class that has been compiled into byte code,like any other Java object.The servlet has access to a rich API of HTTP-specific services,but it is still just another Java object running in an application and can leverage all your other Java assets.To give conventional web servers access to servlets,the servlets are plugged into containers.The servlet container is attached to the web server. Each servlet can declare what URL patterns it would like to handle.When a request matching a registered pattern arrives,the web server passes the request to the container, and the container invokes the servlet.But unlike CGI programs,a new servlet is not created for each request.Once the container instantiates the servlet,it will just create a new thread for each request.Java threads are much less expensive than the server processes used by CGI programs.Once the servlet has been created,using it for additional requests incursn very little overhead.Servlet developers can use the init() method to hold references to expensive resources,such as database connections or EJB Home Interfaces,so that they can be shared between requests.Acquiring resources like these can take several seconds—which is longer than many surfers are willing to wait.The other edge of the sword is that,since servlets are multithreaded,servlet developers must take special care to be sure their servlets are thread-safe.To learn more about servlet programming,we recommend Java Servlets by Example,by Alan R.Williamson [Williamson].The definitive source for Servlet information is the Java Servlet Specification [Sun,JST].3.2.4JavaServer PagesWhile Java servlets are a big step up from CGI programs,they are not a panacea.To generate the response,developers are still stuck with using println statements to render the HTML.Code that looks likeout.println("<P>One line of HTML.</P>");out.println("<P>Another line of HTML.</P>");is all too common in servlets that generate the HTTP response.There are libraries that can help you generate HTML,but as applications grow more complex,Java developers end up being cast into the role of HTML page designers.Meanwhile,given the choice,most project managers prefer to divide development teams into specialized groups.They like HTML designers to be working on the presentation while Java engineers sweat the business ing servlets alone encourages mixing markup with business logic,making itdifficult for team members to specialize.To solve this problem,Sun turned to the idea of using server pages to combine scripting and templating technologies into a single component.To build Java-Server Pages,developers start by creating HTML pages in the same old way,using the same old HTML syntax.To bring dynamic content into the page, the developer can also place JSP scripting elements on the page.Scripting elements are tags that encapsulate logic that is recognized by the JSP.You can easily pick out scripting elements on JSP pages by looking for code that begins with<%and ends with%>.For instance,to display the last modified date on the page,the developer would place the following code in the page:<B>This page was accessed at<%=new Date()%></B>There are three different types of scripting elements:expressions,scriptlets,and declarations,as shown in table1.1.Table1.1JSP scripting elementsElement PurposeExpressions Java code,bound by<%=and%>,used to evaluate Java language statements andinsert the result into the servlet’s outputScriptlets Java code,bound by<%and%>,often used to create dynamic content Declarations Java code,bound by<%!and%>,used to add code to the body of the servlet class3.3Enabling technologies11To be seen as a JSP page,the file just needs to be saved with an extension of.jsp.When a client requests the JSP page,the container translates the page into a source code file for a Java servlet and compiles the source into a Java class file—just as you would do if you were writing a servlet from scratch.At runtime,the container can also check the last modified date of the JSP file against the class file.If the JSP file has changed since it was last compiled,the container will retranslate and rebuild the page all over again.Project managers can now assign the presentation layer to HTML developers,who then pass on their work to Java developers to complete the business-logic portion.The important thing to remember is that a JSP page is really just a servlet.Anything you can do with a servlet, you can do with a JSP.3.3.1JSP tagsScripting elements are only one of the two ways to generate dynamic JSP content. Scriptlets are quick,easy,and powerful but require that developers mix Java code with HTML.Experience has taught us that embedding logic into JSP pages leads tonon-maintainable applications with minimal opportunity for reuse.A popular alternative is to use JSP tags.JSP tags are mixed in with the HTML markup and can be used as if they were ordinary HTML tags.A single JSP tag may represent dozens of Java statements,but all the developer needs to know is to how to insert the tag.The programming code is hidden away in a Java class file.To use the same code on another page,the developer only has to insert the tag markup again.If the code for the tag changes,all the tags willautomatically use the updated version.The JSP page using the tag does not need to be revised.JSP tags provide much better reuse than scriptlets and can be easier for page developersJSPs vs.ASPsMicrosoft and Sun both offer their own brand of server pages.Sun offers JavaServer Pages and Microsoft offers Active Server Pages(ASP).Both JSP s and ASPs are designed so that developers can create dynamic web pages customized with back-office data.While similar on the surface,there are several differenc es between ASP s and JSP s:_ JSP s are platform independent—write once,run anywhere._Developers have input to the direction of JSP s through the Java Community Process(JCP)._JSP developers can extend the JSP tag set with custom tags._JavaBeans and Enterprise JavaBeans(EJB)can be used with JSP s to increase reusability and reduce maintenance._JSPs can access many other Java libraries,including Java Database Connectivity(JDBC),Java Mail,Java Message Service(JMS),and Java Naming and Directory Interface(JNDI)._JSP s are compiled into a binary class file and do not need to be interpreted for every request._JSP s find wide support with tool vendors,containers,and web servers.to use, since they look like the familiar HTML tags.A number of prebuilt JSP tags libraries are available that will perform useful functionality for developers.Among these is the new JSP Standard Tag Library(JSTL).This new standard provides a rich library of reusable JSP tags.For more on JSTL,we highly recommend JSTL in Action,by Shawn Bayern[Bayern]. Struts works well with JSTL and other publicly available tag libraries,as well as any you might write yourself.For more on JSP and JSP pages,we highly recommend Web Development with JavaServer Pages,by Duane K.Fields,Mark A.Kolb,and Shawn Bayern[Fields].The definitive source for JSP information is the JavaServer Pages Specification[Sun,JSP].JSP pages are an integral part of the Struts developer’s toolbox. Most Struts developers use JSP pages and custom tags to create all the dynamic content for their applications.3.3.2JavaBeansJavaBeans are Java classes which conform to a set of design patterns that make them easier to use with development tools and other components.DEFINITION A JavaBean is a reusable software component written in Java.To qualify as a JavaBean,the class must be concrete and public,and have a noargument constructor. JavaBeans expose internal fields as properties by providing public methods that follow a consistent design pattern.Knowing that the property names follow this pattern,other Java classes are able to use introspection to discover and manipulate JavaBean properties. Rolling your own1Create a class that implementsjavax.servlet.jsp.tagext.TagSupportor javax.servlet.jsp.tagext.BodyTagSupport by implementing the doStart()or doEnd()method.These methods obtain a JspWriter object to write out any valid HTML content you need.2Create a tag library descriptor(TLD)file to map the classes you just created to a JSP tag name.3Define your<taglib>elements in the web application descriptor file(web.xml).Tell the JSP page that you will be using your tags by placing a@taglib statement at the top of the page:<%@taglib uri="/tags/app.tld prefix="app"%>4This statement imports the library for use on this page and assigns it a tag prefix.For more,see the JSP Tag Library technology page.3.4Enabling technologies111The JavaBean design patterns provide access to the bean’s internal state through two flavors of methods:accessors are used to read a JavaBean’s state;mutators are used to change a JavaBean’s state.Mutators are always prefixed with lowercase token set followed by the property name.The first character in the property name must be uppercase.The return value is always void—mutators only change property values;they do not retrieve them.The mutator for a simple property takes only one parameter in its signature,which can be of any type.Mutators are often nicknamed setters after their prefix.The mutator method signature for a weight property of the type Double would be public void setWeight(Double weight)A similar design pattern is used to create the accessor method signature.Accessor methods are always prefixed with the lowercase token get,followed by the property name.The first character in the property name must be uppercase.The return value will match the method parameter in the corresponding mutator.Accessors for simple properties cannot accept parameters in their method signature.Not surprisingly, accessors are often called getters.The accessor method signature for our weight property is public Double getWeight()If the accessor returns a logical value,there is a variant pattern. Instead of using the lowercase token get,a logical property can use the prefix is,followed by the property name.The first character in the property name must be uppercase.The return value will always be a logical value—either boolean or Boolean.Logical accessors cannot accept parameters in their method signature.The boolean accessor method signature for an on property would be public boolean isOn()The canonical method signatures play an important role when working with Java-Beans.Other components are able to use the Java Reflection API to discover a JavaBean’s properties by looking for methods prefixed by set,is,or get.If a component finds such a signature on a JavaBean,it knows that the method can be used to access or change the bean’s properties.Sun introduced JavaBeans to work with GUI components,but they are now used with every aspect of Java development,including web applications.When Sun engineers developed the JSP tag extension classes,they designed them to work with JavaBeans.The dynamic data for a page can be passed as a JavaBean,and the JSP tag can then use the bean’s properties to customize the output.For more on JavaBeans,we highly recommend The Awesome Power of JavaBeans,by Lawrence H.Rodrigues[Rodrigues].The definitive source for JavaBean information is the JavaBean Specification[Sun,JBS].Model2The0.92release of the Servlet/JSP Specification described Model2as an architecture that uses servlets and JSP pages together in the same application.The term Model2 disappeared from later releases,but it remains in popular use among Java web developers.Under Model2,servlets handle the data access and navigational flow,while JSP pages handle the presentation.Model2lets Java engineers and HTML developers each work on their own part of the application.A change in one part of a Model2 application does not mandate a change to another part of the application.HTML developers can often change the look and feel of an application without changing how the back-office servlets work.The Struts framework is based on the Model2architecture.It provides a controller servlet to handle the navigational flow and special classes to helpwith the data access.A substantial custom tag library is bundled with the framework to make Struts easy to use with JSP pages.4Struts from30,000feetHold on to your hats!Now that we’ve covered the basics,it’s time for a whirlwind tour of Struts.Before we try to get into the nuts and bolts of the framework components,let’s start with the big picture.Struts uses a Model2architecture.The Struts ActionServlet controls the navigational flow.Another Struts class,the Action,is used to access the business classes.When the ActionServlet receives a request from the container,it uses the URI(or “path”)to determine which Action it will use to handle the request.An Action can validate input and access the business layer to retrieve information from databases and other data services.To validate input or use the input to update a database,the Action needs to know what values were submitted.Rather than force each Action to pull these values out of the request,the ActionServlet bundles the input into a JavaBean.The input beans are subclasses of the Struts ActionForm class.The ActionServlet can determine which ActionForm to use by looking at the path of the request,in Struts from30,000feet15the same way the Action was selected.An ActionForm extendsorg.apache.struts.action.ActionForm.Each HTTP request must be answered with an HTTP ually,a Struts Action does not render the response itself but forwards the request on to another resource,such as a JSP page.Struts provides an ActionForward class that can be used to store the path to a page under a logical name.When it has completed the business logic,the Action selects and returns an ActionForward to the servlet.The servlet then uses the path stored in the ActionForward object to call the page and complete the response.Struts bundles these details together into an ActionMapping object.Each ActionMapping is related to a specific path.When that path is requested,the servlet retrieves the ActionMapping object.The mapping tells the servlet which Actions, ActionForms,and ActionForwards to use.All of these details,the Actions,ActionForms, ActionForwards,ActionMappings,and some other things,are declared in thestruts-config.xml file.The Action-Servlet reads this file at startup and creates a database of configuration objects.At runtime,Struts refers to the objects created with the configuration file,not the file itself.Figure1.illustrates how these components fit together.Believe it or not,you already know enough about Struts to assemble a simple application.It won’t do much,but it will illustrate how Struts actually works.Figure1Struts from30,000feetBelieve it or not,you already know enough about Struts to assemble a simple application. It won’t do much,but it will illustrate how Struts actually works.。
英文科技文献及翻译
外文翻译DC GENENRATORS1. INTRODUCTIONFor all practical purposes, the direct-current generator is only used for special applications and local dc power generation. This limitation is due to the commutator required to rectify the internal generated ac voltage, thereby making largescale dc power generators not feasible.Consequently, all electrical energy produced commercially is generated and distributed in the form of three-phase ac power. The use of solid state converters nowadays makes conversion to dc economical. However, the operating characteristics of dc generators are still important, because most concepts can be applied to all other machines.2. FIELD WINDING CONNECTIONSThe general arrangement of brushes and field winding for a four-pole machine is as shown in Fig.1. The four brushes ride on the commutator. The positive brusher are connected to terminal A1 while the negative brushes are connected to terminal A2 of the machine. As indicated in the sketch, the brushes are positioned approximately midway under the poles. They make contact with coils that have little or no EMF induced in them, since their sides are situated between poles.Figure 1 Sketch of four-pole dc matchineThe four excitation or field poles are usually joined in series and their ends brought out to terminals marked F1 and F2. They are connected such that they produce north and south poles alternately.The type of dc generator is characterized by the manner in which the fieldexcitation is provided. In general, the method employed to connect the field and armature windings falls into the following groups (see Fig.2):Figure2 Field connections for dc generators:(a)separately excited generator;(b)self-excited,shunt generator;(c)series generator;(d)compound generator;short-shunt connection;(e)compoundgenerator,long-shunt connection.The shunt field contains many turns of relatively fine wire and carries a comparatively small current, only a few percent of rated current. The series field winding, on the other hand, has few turns of heavy wire since it is in series with the armature and therefore carries the load current.Before discussing the dc generator terminal characteristics, let us examine the relationship between the generated voltage and excitation current of a generator on no load. The generated EMF is proportional to both the flux per pole and the speed at which the generator is driven, EG=kn. By holding the speed constant it can be shown the EG depends directly on the flux. To test this dependency on actual generators is not very practical, as it involves a magnetic flux measurement. The flux is produced by the ampere-turns of the field coils: in turn, the flux must depend on the amount of field current flowing since the number of turns on the field winding is constant. This relationship is not linear because of magnetic saturation after the field current reaches a certain value. The variation of EG versus the field current If may be shown by a curve known as the magnetization curve or open-circuit characteristic. For this a given generator is driven at a constant speed, is not delivering load current, and has its fieldwinding separately excited.The value of EG appearing at the machine terminals is measured as If is progressively increased from zero to a value well above rated voltage of that machine. The resulting curve is shown is Fig.3. When Ij=0, that is, with the field circuit open circuited, a small voltage Et is measured, due to residual magnetism. As the field current increases, the generated EMF increases linearly up to the knee of the magnetization curve. Beyond this point, increasing the field current still further causes saturation of the magnetic structure to set in.Figure 3 Magnetization curve or open-circuit characteristic of a separately excited dc machine The means that a larger increase in field current is required to produce a given increase in voltage.Since the generated voltage EG is also directly proportional to the speed, a magnetization curve can be drawn for any other speed once the curve is determined. This merely requires an adjustment of all points on the curve according ton n x E E G G ''where the quantities values at the various speeds.3. VOLTAGE REGULATIONLet us next consider adding a load on generator. The terminal voltage will then decrease (because the armature winding ha resistance) unless some provision is made to keep it constant. A curve that shows the value of terminal voltage for various load currents is called the load or characteristic of the generator.Figure 4 (a) directs current it to urge the generator load characteristics; (b) circuit diagramFig.4 shows the external characteristic of a separately excited generator. The decrease in the terminal voltage is due mainly to the armature circuit resistance RA. In general,A A G t R I E V -=where Vt is the terminal voltage and IA is the armature current (or load current IL) supplied by the generator to the load.Another factor that contributes to the decrease in terminal voltage is the decrease in flux due to armature reaction. The armature current established an MMF that distorts the main flux, resulting in a weakened flux, especially in noninterpole machines. This effect is called armature reaction. As Fig.4 shows, the terminal voltage versus load current curve does not drop off linearly since the iron behaves nonlinear. Because armature reaction depends on the armature current it gives the curve its drooping characteristic.4. SHUNT OR SELF-EXCIITED GENRATORSA shunt generator has its shunt field winding connected in parallel with the armature so that the machine provides its own excitation, as indicated in Fig.5. The question arises whether the machine will generate a voltage and what determines the voltage.For voltage to “build up ” as it is called, there must be some remanent magnetism in the field poles. Ordinarily, if the generator has been used previously, there will be some remanent magnetism. We have seen in Section 3 that if the field would be disconnected, there will be small voltage Ef generated due to this remanent magnetism, provided that the generator is driven at some speed. Connecting the field for self-excitation, this small voltage will be applied to the shunts field and drive a small current through the field circuit. If this resulting small current in the shunt field is of such a direction that it weakens the residual flux, the voltage remains near zeroand the terminal voltage does not build up. In this situation the weak main pole flux opposes the residual flux.Figure 5 Shunt generator:(a)circuit;(b)load characteristicIf the connection is such that the weak main pole flux aids the residual flux, the induced voltage increases rapidly to a large, constant value. The build-up process is readily seen to be cumulanve. That is, more voltage increases the field current, which in turn increases the voltage, and so on. The fact that this process terminates at a finite voltage is due to the nonlinear behavior of the magnctic circuit. In steady state the generated voltage is causes a field current to flow that is just sufficient to develop a flux required for the generated EMF that causes the field current to flow.The circuit carries only dc current, so that the field current depends only on the field circuit resistance, Rf. This may consist of the field circuit resistance Rf, the field current depends on the generated voltage in accordance with Ohm ’s law.It should be evident that on a new machine or one that has lost its residual flux because of a long idle period, some magnetism must be created. This is usually done by connecting the field winding only to a separate dc source for a few seconds. This procedure is generally known as flashing the field.Series GeneratorsAs mentioned previously, the field winding of a series generator is in series with the armature. Since it carries the load current the series field winding consists of only a few turns of thick wire. At no load, the generated voltage is small due to residual field flux only. When a load is added, the flux increases, and so does the generated voltage. Fig.7 shows the load characteristic of a series generator driven at a certain speed. The dashed line indicates the generated EMF of the same machine with the armature open-circuited and the field separately excited. The difference between the two curves is simply the IR drop in the series field and armature winding, such that)(S A A G t R R I E V +-=where RS is the series field winding resistance.Figure 7 Series generator: (a)circuit diagram;(b)load characteristicsCompound Generators The compound generator has both a shunt and a series field winding, the latter winding wound on top of the shunt winding. Fig.8 shows the circuit diagram. The two windings are usually connected such that their ampere-turns act in the same direction. As such the generator is said to be cumulatively compounded.The shunt connection illustrated in Fig.8 is called a long shunt connection. If the shunt field winding is directly connected across the armature terminals, the connection is referred to as a short shunt. In practice the connection used is of little consequence, since the shunt field winding carries a small current compared to the full-load current. Furthermore, the number of turns on the series field winding. This implies it has a low resistance value and the corresponding voltage drop across it at full load is minimal.Curves in Fig.9 represents the terminal characteristic of the shunt field winding alone. By the addition of a small series field winding the drop in terminal voltage with increased loading is reduced as indicated. Such a generator is said to be undercompounded. By increasing the number of series turns, the no-load and full-load terminal voltage can be made equal; the generator is then said to be flatcompounded. If the number of series turns is more than necessary to compensate for the voltage drop, the generator is overcome pounded. In that case the full-load voltage is higher than the no-load voltage.Figure 9 Terminal characteristics of compound generators compared with that of the shunt generatorThe overcompounded generator may be used in instances where the load is at some distance from the generator. The voltage drops in the feeder lines are the compensated for with increased loading. Reversing the polarity of the series field in relation to the shunt field, the fields will oppose each other more and more as the load current increase. Such a generator is said to be differentially compounded. It is used in applications where feeder lines could occur approaching those of a short circuit. An example would be where feeder lines could break and short circuit the generator. The short-circuit current, however, is then limited to a “safe”value. The terminal characteristic for this type of generator is also shown in Fig.9. Compound generators are used more extensively than the other types because they may be designed to have a wide varity of terminal characteristics.As illustrated, the full-load terminal voltage can be maintained at the no-load value by the proper degree of compounding. Other methods of voltage control are the use of rheostats, for instance, in the field circuit. However, with changing loads it requires a constant adjustment of the field rheostat to maintain the voltage. A more useful arrangement, which is now common practice, is to use an automatic voltage regulator with the generator. In essence, the voltage regulator is a feedback control system. The generator output voltage is sensed and compared to a fixed reference voltage deviation from the reference voltage gives an error signal that is fed to a power amplifier. The power amplifier supplies the field excitation current. If the error signal is positive, for example, the output voltage is larger than desired and the amplifier will reduce its current drive. In doing so the error signal will be reduced to zero.中文翻译直流发电机1.介绍对于所有实际目的来说，直流发电机仅用于特殊场合和地方性发电厂。
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13.3.3 C类放大器在C类功率放大器中，栅的偏压设成使晶体管在小于一半的时间内导通。
因此，漏极电流是由周期性的一串脉冲构成的。
传统上用正弦的上面部分来近似这些脉冲以便于进行直接分析②。
特别是我们假设漏极电流具有如下的形式：式中，偏置值I DC类似于线性放大器中的偏置电流，它对于C类放大器实际上是负值。
自然，整个漏极电流i D心总是为正或为零。
也就是说，漏极电流在晶体管导通时是一段正弦波，而在晶体管截止时为零。
我们继续假设晶体管在任何时候的工作情况都像是一个电流源(高输出阻抗)③。
由于我们仍然有一个高Q值的输出振荡回路，所以在负载两端的电压基本上保持为正弦，因此漏极电压和漏极电流如图13.4所示。
在以下的推导中，不必担心能否重复所有的这些细节。
正如我们将要看到的，我们如何设计这样的放大器与这些公式本身的含义有显著的不同，所以重点要放在所得到的一般结论而不是一些具体细节上。
我们从求解漏极电流不为零时总的导通角开始。
为了简化得到这一答案所需要的步骤，我们首先用余弦而不是正弦来重新写出漏极电流的表达式：显然，这样做没有任何改变，因为时间原点总是任选的。
在经过这样的修改之后，电流脉冲就如图13．5所示。
使电流等于零并求出总的导通角2中得到：我们现在可以计算平均漏极电流为:在用I DC的表达式替换后得到:我们将很快用这个表达式来推导效率作为导通角函数的公式。
我们需要的另一个量是传送到负载的功率的一般表达式。
正如与B类放大器一样由于高Q值的振荡回路而被简化，所以我们只需要计算傅里叶级数中的基波项：利用我们通过负载的基波电流的表达式，我们可以很容易地推导出最大输出电压摆幅的公式：上式允许我们求解用V DD表示的电流irf:峰值漏极电流为irf与偏置项的和为：上式可简化为:对于固定的输出电压，当脉冲宽度减小至零时，峰值漏极电流接近无穷大。
利用我们刚刚推导的公式可以很容易地计算出漏极效率为：当导通角缩小至零时，效率接近100％。
虽然这看起来很有希望，但输出功率也同时趋向于零，这是因为在漏极电流越来越窄的长条波形中基波分量也在缩小，而且从峰值漏极电流的公式中很清楚地看出，随着导通角接近于零，C类放大器归一化的功率传递能力也接近于零。
所有这些综合考虑使得实际上只得到小于100％的效率，因为除了高效率之外我们一般还希望有一个合理数量的输出功率。
在进行了前面的推导之后，我们也许会很失望，即这些推导在设计C类功率放大器的实际过程中一般不会用得很多。
一个理由是对栅偏压几乎没有几种方便的选择，但零伏是一种特别方便的选择。
因此栅驱动信号分量要选择得足够大从而能产生所希望的输出功率，所以导通角和效率通常不是直接的设计参数，而只是选择零偏压及输出功率设计的结果。
另一个理由是所做的假设(例如正弦电流尖峰脉冲，晶体管的电流源特性)并不总能充分地满足以使我们可以在定量上相信这些公式。
同样，在进行推导中最主要的优点是建立起对设计非常有用的某些一般的直观感觉——主要是效率可以很高，但这是以减少功率传递能力、增益和线性度为代价的。
13.3.4 AB类放大器我们已经看到A类放大器在100％的时间里导通，B类放大器在50％的时间里导通，而C类放大器则在0和50％之间的某段时间内导通。
AB类放大器，正如从它的名字可以联想到的，是在一个周期的50％和100％之间的某段时间内导通，这取决于所选择的偏置大小。
结果它的效率和线性度在A类和B类放大器之间。
这一折中常常是令人满意的，这从这类功率放大器的使用非常普遍就可以看出。
我们不必单独推导这一放大器的公式，因为C类放大器的公式也可以在这里应用(这些公式也包括A类和B类的情形)，惟一的差别就是偏置电流是正值而不是负值。
13.4 D类放大器至今介绍的功率放大器采用了有源器件作为控制电流源。
另一种方法是采用器件作为开关，其理由是，开关在理想上不消牦任何功率，因为或者开关两端的电压为零，或者通过它的电流为零。
因而开关的V-I乘积总是为零，所以晶体管不消耗任何功率并且其效率必定为100％。
利用这一想法的一类放大器是D类放大器。
初看起来(见图13.6)，它好像就是一个推挽式、变压器耦合的B类放大器。
与我们通常见到的并联振荡槽路不同，在这一放大器的输出端采用了一个串联的RLC网络，这是因为开关模式的放大器与前面学习过的电流模式的放大器相对偶，所以输出滤波器也互为对偶。
输入的连接方式保证了在一给定时间只有一个晶体管被驱动，其中一个晶体管在正半周工作而另一个在负半周工作，就像在推拉式B类放大器中那样。
这里所不同的是晶体管被充分驱动使它们的工作如同开关而不是如同线性(或准线性)放大器。
由于开关作用，输出变压器T2的每个初级终端被交替地驱动至地，从而在初级绕组(因而正在次级)两端产生一个方波电压。
当一个(晶体管的)漏极为零伏时，变压器的作用使另一个(晶体管的)漏极电压为2V DD。
输出滤波器则只允许这一方波的基波分量流人到负载中。
由于在次级电路中只有基波电流，所以初级电流也是正弦的，因此每个开关在它导通的半周期中见到的是一个正弦波，所以变压器的电流和电压如图13.7和图13．8所示。
由于晶体管的作用如同开关，所以D类放大器的理论效率为100％。
这个放大器归一化的功率传递能力即为①：它比B类推拉放大器要好，并且比A类放大器要好得多。
当然，D类放大器通常不能提供线性调制，但它却有可能提供高效率并且不会对器件产生过高的电压或电流。
这类(或任何其他开关)功率放大器的一个实际问题是并没有像理想开关这样的部件。
在开关过程中非零的饱和电压肯定会产生静态功耗，而有限的开关速度也意味着开关的V-I积在过渡期间不为零。
因此，开关模式的功率放大器只有在频率明显低于f r的情况下才能很好地工作。
而且，如果应用双极型晶体管由于晶体管在饱和区的电荷存储使一个晶体管导通之前另一个晶体管于能完全关断，那么效率的降低就会特别严重。
于是变压器的作用就会使全部电源电压加在还没有关断的器件上，从而V-I的乘积可能非常大。
13.5 E类放大器正如我们已经看到的，采用晶体管作为开关有可能提供大为改善的效率，但由于现实开关的不完全理想使得在实际中实现这一可能性并不总是那么容易。
相关的功耗将使效率降低。
为了防止总的损耗，开关相对于工作频率必须非常快。
当载波频率很高时，满足这一要求的困难将会更大。
如果有一种方法可以修改电路使得在切换瞬间附近的一段不为零的时间间隔内开关两端的电压为零，那么功耗就会降低。
E类放大器采用高阶电抗网络提供足够的自由度来改变开关电压波形，使它在开关导通时的值和斜率均为零，从而降低了开关损耗。
可惜的是它对于关断过渡没有任何作用，而关断过渡的边沿常常是更成问题的，至少在双极型设计中是如此。
正如我们后面将要看到的，另一个问题是E类放大器具有很差的归一化功率传递能力(事实上比A类放大器还差)，因此尽管这一类型的放大器可能有很高的效率(理论上在理想开关时为100％)，但它却要求采用更大尺寸的器件把一定数量的功率传送到负载。
E类放大器的主要优点是很容易设计。
不同于典型的C类放大器，它的实际实现几乎在设计后不会有什么问题就可以满意地工作。
在进行了先前这番讨论之后，现在让我们来看一下图13．9所示的E类放大器电路。
与在前面的例子中一样，BFL提供了一条至电源的直流通路而在RF 时近似为开路。
另外，我们注意到电容C1处于很方便的位置，因为任何器件的输出电容都可以被它吸收。
图13．9 E类放大器设计公式的推导太复杂了，在此不多加论述。
想要详细了解的读者可以参考Sokal的经典论文①。
设计公式如下：为了得到最大的效率，我们需要有与所希望的带宽相一致的最大Q值。
在实际中可以达到的Q值常常大大低于那些能显著地限制带宽所要求的Q值。
一旦Q值选定，E类功率放大器的设计就可以采用所给出的公式直接进行下去。
遗憾的是，漏极电流和电压波形的计算是很困难的。
然而如果各处都调整好的话，那么这些波形看上去如图13.10所示。
注意，在导通时漏极电压的斜率为零，然而在开关关断时电流却接近最大。
因此如果开关不是无限快(如多数会遇到的大多数开关的情形)，那么在这一过渡期间开关的功耗可以抵消掉在过渡到“导通”状态时通过减少功耗所得到的大部分改善。
此外注意每一波形都有相当大的峰值对平均值的比。
事实上细节分析表明，峰值漏极电压近似为3．6V DD，而峰值漏极电流大致为1.7V DD／R。
传送到负载上的最大输出功率为：因此归一化功率输出能力为：正如你可以看到的，E类放大器对开关特性提出了甚至比A类放大器更高的要求：由于开关关断损耗使功率传递能力较差和效率降低①，E类放大器的实际实现并没有显示出比设计得很好的其他类型放大器(如下面要介绍的F类放大器)具有明显高的效率。
此外，由于承受较大的开关强度电压，E类放大器也不能按照低功耗(并且由此而来的较低的击穿电压)工艺的趋势缩小尺寸而又能可靠地工作。
由于这些理由，类放大器并没有得到广泛的应用，只是在最初的几篇论文之后引起了人们的极大兴趣。
另一种形式的F类放大器拓扑结构图13．11所示的连接方式虽然很好，但在许多应用中传输线可能会很长而很不方便。
而且在基波主外的奇次谐波处有无穷大(或接近无穷大)阻抗的优点常常在实际中会被晶体管本身的输出电容所消除。
因此采用集总元件近似常常几乎可以与传输线的工作情况一样好。
为了建立这样的集总近似，可以用串联起来的许多并联谐振滤波器来代替传输线。
每个谐振器调谐到载波频率不同的奇次皆波上。
常常只需一个振荡回路调谐到3WO就已经足够了。
在超过13.13所示的两个振荡回路时很少会发现效率有明显的改善。
13.7.1A、AB、B、C、E、F类调制A类或B类放大器是很容易的，因为输出电压直接与漏极电流信号分量的幅值心成正比。
因此如果心本身正比于输入驱动，那么就能实现线性调制。
采用短沟MOS器件可以很容易地实现对这一比例关系很好的近似，因为当有足够的栅电压时，短沟MOS器件具有恒跨导。
双极型开器件由于有串联基极电阻也能提供合理的线性度，这一串联基极电阻或者由外部提供，或者就是器件本身的电阻。
C类放大器提出了更为明显的挑战，这可以通过研究前面推导出的输出电流公式来理解：不管形式上如何，流过电阻负载的电流基波分量一般并不与i rf成线性比例三角函数项也与i rf有关①。
因此，C类放大器通常并不提供线性调制能力值调制，至少当被调制的载波驱动栅电路时是如此。
这是因为在括号内的因此一般不适合于幅为了调制C类(或E或F类)放大器，我们可以把调制信号叠加在电源电压上，这一技术称为漏极调制。
只要调制信号的幅值与电源电压相比时不是太大，就能实现合理的线性调制。
最后对于所有这些方法，都可以采用负反馈来减少失真。
为了降低对反馈回路增益—带宽积的要求，我们可以采样输出信号并对它进行解调，然后运用这个被解调的信号来闭合回路，如同图13．14所示。