毕业设计中的外文翻译

本科生毕业设计 (论文)
外文翻译
原文标题
Worlds Collide:
Exploring the Use of Social Media Technologies for
Online Learning
译文标题
世界的碰撞：
探索社交媒体技术在在线学习的应用
作者所在系别计算机科学与工程系作者所在专业计算机科学与技术作者所在班级
作者姓名
作者学号
指导教师姓名
指导教师职称讲师
完成时间2013年2月
北华航天工业学院教务处制
注：1. 指导教师对译文进行评阅时应注意以下几个方面：①翻译的外文文献与毕业设计（论文）的主题是否高度相关，并作为外文参考文献列入毕业设计（论文）的参考文献；②翻译的外文文献字数是否达到规定数量（3 000字以上）；③译文语言是否准确、通顺、具有参考价值。

2. 外文原文应以附件的方式置于译文之后。

毕业设计(论文）外文文献翻译院系：财务与会计学院年级专业：201＊级财务管理姓名:学号：132148*＊*附件: 财务风险管理【Abstract】Although financial risk has increased significantly in recent years risk and risk management are not contemporary issues。

The result of increasingly global markets is that risk may originate with events thousands of miles away that have nothing to do with the domestic market。

Information is available instantaneously which means that change and subsequent market reactions occur very quickly。

The economic climate and markets can be affected very quickly by changes in exchange rates interest rates and commodity prices。

Counterparties can rapidly become problematic。

As a result it is important to ensure financial risks are identified and managed appropriately. Preparation is a key component of risk management。

【Key Words】Financial risk，Risk management，YieldsI. Financial risks arising1.1What Is Risk1.1.1The concept of riskRisk provides the basis for opportunity. The terms risk and exposure have subtle differences in their meaning. Risk refers to the probability of loss while exposure is the possibility of loss although they are often used interchangeably。

1 英文文献翻译1.1 Modern PackagingAuthor：Abstract1. Changing Needs and New RolesLooking back, historical changes are understandable and obvious. That all of them have had an impact on the way products are brought, consumed and packaged is also obvious. What is not so obvious is what tomorrow will bring. Yet, it is to the needs, markets, and conditions of tomorrow that packaging professionals must always turn their attention.The forces that drove packaging during the Industry Revolution continue to operate today. The consumer society continues to grow and is possibly best described by a 1988s bumper sticker, “Born to Shop”. We consume goods today at a rate 4 to 5 times greater than we did as recently as 1935. Most of these goods are not essential to survival; they constitute what we may call “the good life”.In the second half of the 20th century， the proliferation of goods was so high that packaging was forced into an entirely new role, that of providing the motivation rather than presenting the goods itself. On a shelf of 10 competing products, all of them similar in performance and quality, the only method of differentiating became the package itself. Marketer aimed at lifestyles, emotional values, subliminal images, features, and advantages beyond the basic product rather than the competitor’s. In some in instances, the package has become the product, and occasionally packaging has become entertainment.A brand product to carry the product manufacturer or product sales of theretailer’s label, usually by the buyer as a quality assessment guidance. In some cases, competing brands of product quality is almost no difference, a difference is the sale of its packaging. An interesting visually attractive packaging can give a key marketing advantage and convince impulse spending. However, the packaging should accurately reflect the quality of products/brand value in order to avoid the disappointment of consumers, encourage repeat purchases and build brand loyalty. Ideally, the product should exceed customer expectations.2. Packaging and the Modern Industrial SocietyThe importance of packaging to a modern industrial society is most evident when we examine the food-packaging sector. Food is organic in nature, having an animal or plant source. One characteristic of such organic matter is that, by and large, it has a limited natural biological life.A cut of meat, left to itself, might be unfit for human consumption by the next day. Some animal protein products, such as seafood, can deteriorate within hours.The natural shelf life of plant-based food depends on the species and plant involved. Pulpy fruit portions tend to have a short life span, while seed parts, which in nature have to survive at least separated from the living plant are usually short-lived.In addition to having a limited natural shelf life, most food is geographically and season-ally specific. Thus, potatoes and apples are grown in a few North American geographical regions and harvest during a short maturation period. In a world without packaging，we would need to live at the point of harvest to enjoy these products, and our enjoyment of them would be restricted to the natural biological life span of each. It is by proper storage, packaging and transport techniques that we are able to deliver fresh potatoes and apples, or the products derived from them, throughout the year and throughout the country. Potato-whole,canned, powdered, flaked, chipped, frozen, and instant is available, anytime, anywhere. This ability gives a society great freedom and mobility. Unlike less-developed societies, we are no longer restricted in our choice of where to live, since we are no longer tied to the food-producing ability of an area. Food production becomes more specialized and efficient with the growth of packaging. Crops and animal husbandry are moved to where their production is most economical, without regard to the proximity of a market. Most important, we are free of the natural cycles of feast and famine that are typical of societies dependent on natural regional food-producing cycles.Central processing allows value recovery from what would normally be waste by products of the processed food industry from the basis of other sub-industries. Chicken feathers are high in protein and, properly mill and treated, can be fed back to the next generation of chickens. Vegetable waste is fed to cattle or pigs. Bagasse, the waste cane from sugar pressing, is a source of fiber for papermaking. Fish scales are refined to make additives for paints and nail polish.The economical manufacture of durable goods also depends on good packaging.A product's cost is directly related to production volume. The business drive to reduce costs in the supply chain must be carefully balanced against the fundamental technical requirements for food safety and product integrity, as well as the need to ensure an. efficient logistics service. In addition, there is a requirement to meet the aims of marketing to protect and project brand image through value-added pack design. The latter may involve design inputs that communicate distinctive, aesthetically pleasing, ergonomic, functional and/or environmentally aware attributes. But for a national or international bicycle producer to succeed, it must be a way of getting the product to a market, which may be half a world away. Again, sound packaging, in this case distributionpackaging, is a key part of the system.Some industries could not exist without an international market. For example, Canada is a manufacturer of irradiation equipment, but the Canadian market (which would account for perhaps one unit every several years) could not possibly support such a manufacturing capability. However, by selling to the world, a manufacturing facility becomes viable. In addition to needing packaging for the irradiation machinery and instrumentation, the sale of irradiation equipment requires the sale packaging and transport of radioactive isotopes, a separate challenge in itself. In response to changing consumer lifestyles, the large retail groups and the food service industry development. Their success has been involved in a competition fierce hybrid logistics, trade, marketing and customer service expertise, all of which is dependent on the quality of packaging. They have in part led to the expansion of the dramatic range of products offered, technology innovation, including those in the packaging. Supply retail, food processing and packaging industry will continue to expand its international operations. Sourcing products around the world more and more to assist in reducing trade barriers. The impact of the decline has been increased competition and price pressure. Increased competition led to the rationalization of industrial structure, often in the form of mergers and acquisitions. Packaging, it means that new materials and shapes, increased automation, packaging, size range extension of lower unit cost. Another manufacturer and mergers and acquisitions, the Group's brand of retail packaging and packaging design re-evaluation of the growing development of market segmentation and global food supply chain to promote the use of advanced logistics and packaging systems packaging logistics system is an integral part of, and played an important role in prevention in the food supply or reduce waste generation.3. World Packaging.This discussion has referred to primitive packaging and the evolution of packaging functions. However, humankind's global progress is such that virtually every stage in the development of society and packaging is present somewhere in the world today. Thus, a packager in a highly developed country will agonize over choice of package type, hire expensive marketing groups to develop images to entice the targeted buyer and spend lavishly on graphics. In less-developed countries, consumers are happy to have food, regardless of the package. At the extreme, consumers will bring their own packages or will consume food on the spot, just as they did 2000 years ago.Packagers from the more developed countries sometimes have difficulty working with less-developed nations, for the simple reason that they fail to understand that their respective packaging priorities are completely different. Similarly, developing nations trying to sell goods to North American markets cannot understand our preoccupation with package and graphics.The significant difference is that packaging plays a different role in a market where rice will sell solely because it is available. In the North American market, the consumer may be confronted by five different companies offering rice in 30 or so variations. If all the rice is good and none is inferior, how does a seller create a preference for his particular rice? How does he differentiate? The package plays a large role in this process.The package-intensive developed countries are sometimes criticized for over packaging, and certainly over-packaging does exist. However, North Americans also enjoy the world's cheapest food, requiring only about 11 to 14% of our disposable income. European food costs are about 20% of disposable income, and in the less-developed countries food can take 95%of family income.4. The status and development trend of domestic and international packaging machineryWorldwide, the history of the development of the packaging machinery industry is relatively short, science and technology developed in Europe and America in general started in the 20th century until the 1950s the pace greatly accelerated.From the early 20th century, before the end of World War II World War II，medicine，food, cigarettes，matches，household chemicals and other industrial sectors, the mechanization of the packaging operations; the 1950s, the packaging machine widely used common electric switches and tube for the main components of the control system to achieve the primary automation; 1960s, Electrical and optical liquid-gas technology is significantly increased in the packaging machine, machines to further expand on this basis a dedicated automated packaging line; the 1970s, the micro- electronic technology into the automation of packaging machines and packaging lines, computer control packing production process; from the 1980s to the early 1990s, in some field of packaging, computer, robot application for service, testing and management, in preparation for the over-flexible automatic packaging lines and "no" automatic packaging workshop.Actively promoted and strong co-ordination of all aspects of society, and gradually establish a packaging material, packaging, printing, packaging machinery and other production sectors, and corresponding to the research, design, education, academic, management and organization, and thus the formation of independent and complete. The packaging of light industrial system, and occupies an important place in the national economy as a whole.Based on recent years data that members of the World Packaging Alliance output value of the packaging industry accounts for about 2% of the total output value of the national economy; in which the proportion of packaging machinery, though not large, but the rapid development of an annual average of almost growing at a rate of about 10%. Put into use at the packaging machine is now more than thousand species of packaging joint machines and automated equipment has been stand-alone equate. According to the new technological revolution in the world development trend is expected to packaging materials and packaging process and packaging machinery will be closely related to obtain the breakthrough of a new step, and bring more sectors into the packaging industry.China Packaging Technology Association was established in 1980. Soon, the China National Packaging Corporation have been born. Since then, one after another in the country organized a national and international packaging machinery exhibition, seminars, also published I had the first ever "China Packaging Yearbook and other packaging technology books. All this indicates that China is creating a new packaging historical perio d.1.2中文翻译现代包装1、不断变化的需求和新的角色,回顾以往,包装所带来明显的历史性变化是可以理解的, 一个产品包装方式的给他们的销量带来的影响也是显而易见的。

毕业设计外文文献翻译专业学生姓名班级学号指导教师优集学院外文资料名称：Knowledge-Based Engineeri--ng Design Methodology外文资料出处：Int.J.Engng Ed.Vol.16.No.1附件： 1.外文资料翻译译文2.外文原文基于知识工程(KBE)设计方法D. E. CALKINS1.背景复杂系统的发展需要很多工程和管理方面的知识、决策，它要满足很多竞争性的要求。

设计被认为是决定产品最终形态、成本、可靠性、市场接受程度的首要因素。

高级别的工程设计和分析过程(概念设计阶段)特别重要，因为大多数的生命周期成本和整体系统的质量都在这个阶段。

产品成本的压缩最可能发生在产品设计的最初阶段。

整个生命周期阶段大约百分之七十的成本花费在概念设计阶段结束时，缩短设计周期的关键是缩短概念设计阶段，这样同时也减少了工程的重新设计工作量。

工程权衡过程中采用良好的估计和非正式的启发进行概念设计。

传统CAD工具对概念设计阶段的支持非常有限。

有必要，进行涉及多个学科的交流合作来快速进行设计分析(包括性能，成本，可靠性等)。

最后，必须能够管理大量的特定领域的知识。

解决方案是在概念设计阶段包含进更过资源，通过消除重新设计来缩短整个产品的时间。

所有这些因素都主张采取综合设计工具和环境，以在早期的综合设计阶段提供帮助。

这种集成设计工具能够使由不同学科的工程师、设计者在面对复杂的需求和约束时能够对设计意图达成共识。

那个设计工具可以让设计团队研究在更高级别上的更多配置细节。

问题就是架构一个设计工具，以满足所有这些要求。

2.虚拟(数字)原型模型现在需要是一种代表产品设计为得到一将允许一产品的早发展和评价的真实事实上原型的过程的方式。

虚拟样机将取代传统的物理样机，并允许设计工程师，研究“假设”的情况，同时反复更新他们的设计。

真正的虚拟原型，不仅代表形状和形式，即几何形状，它也代表如重量，材料，性能和制造工艺的非几何属性。

（Sheaｒ waｌl ｓt ｒuctural desigｎ ofh ｉgh-ｌev ｅl fr ａmeworkＷｕ Jiche ｎgＡbstract ： In t ｈis pape ｒ the basic c ｏｎcepts of ｍａn ｐow ｅr ｆｒom th ｅ ｆra ｍｅ sh ｅａr w ａｌl str ｕc ｔｕｒｅ, analy ｓis of the ｓtruct ｕr ａｌ des ｉgn ｏf th ｅ c ｏnt ｅnt ｏｆ t ｈe fr ａme she ａr wall, in ｃｌudi ｎg the ｓeism ｉc wa ｌl she ａr spa本科毕业设计外文文献翻译学校代码： 10128学 号：题 目：Shear wall structural design of high-level framework 学生姓名： 学 院：土木工程学院 系 别：建筑工程系 专 业：土木工程专业（建筑工程方向） 班 级：土木08-（5）班 指导教师： (副教授)ｎratiｏdesign, ａnd a concrｅtｅｓtruｃtuｒe in thｅmｏst co ｍmonｌy useｄframe shear walｌstｒｕcturｅtｈｅdesign of p ｏiｎｔs to note.Keyworｄs: cｏncrｅｔｅ; fｒaｍｅshｅａｒwall sｔｒucｔｕre；hiｇh－risｅbuildｉｎｇsThe wall is aｍoｄern high－rｉｓe buiｌdiｎgs is an iｍpo ｒｔant buiｌdinｇconｔｅnt, the ｓize of thｅfraｍe sheａr wall must comｐly with buildｉng reguｌａtｉons. The pｒｉnｃipｌe is ｔhat the largeｒsｉzｅbｕt the thｉｃknessｍuｓt ｂｅsmaller gｅoｍetric featｕrｅｓshoｕlｄｂe ｐｒeｓented ｔo the pｌatｅ,ｔｈe forｃe is close to cylｉndrｉcal.Ｔhe waｌl sｈｅar wa ｌl strｕｃｔure ｉs a flaｔcomｐonent. Itｓeｘposure to tｈe force aｌoｎg ｔhe ｐlane leｖｅl of theｒole ofｓｈear and momｅｎt, must also take ｉｎtｏａccounｔthe veｒｔical preｓsure.Opeｒate unｄer thｅcomｂiｎed actｉｏn oｆbenｄing momeｎts and axial force aｎｄsheａr forcｅbｙthe caｎtilｅｖｅr deep beａm uｎder ｔｈe acｔion of the force leveｌｔo lｏo ｋinto ｔｈe bottom mouｎted on ｔhe basｉs of. Sheaｒｗaｌl ｉｓdiｖidｅｄinｔo a whole walｌand ｔheａssoｃiated ｓｈeａr wall in thｅactual project,a wholｅwａlｌfor ｅxａmpl ｅ, suｃh as ｇenｅraｌhｏusiｎｇｃonstｒuction in tｈe gablｅｏr fish bｏne strｕcture ｆｉlｍwａｌls ａnd small opｅningｓwall.Cｏupled Sｈeａr ｗalls are ｃonnｅcted bｙｔhｅcｏupｌing ｂeam shｅａr wall.Buｔｂecause tｈeｇｅnerａlｃｏupling beaｍstｉｆfness is less thaｎｔhe wall stiｆfnｅsｓof the lｉmbs，ｓｏ. Wａlｌliｍb aｌonｅis obviｏus.The ｃｅntral beam of tｈeｉnflｅｃtion pｏｉnｔtｏpay aｔtenｔiｏｎto tｈeｗaｌl pressｕre thａn the limiｔs of the lｉmb axis. Will forｍa shortｗiｄe beａms，widｅcolｕmn wａll liｍｂｓhear wａll ｏpｅnings toｏlarge ｃomｐonｅnt aｔbothｅn ｄs ｗith jｕst the domain of vａｒiabｌe crosｓ－ｓecｔｉon ro ｄin ｔhe intｅrｎａｌforcｅｓｕnder tｈｅaｃtioｎof maｎy Ｗalｌlｉmb iｎflｅcｔion point Ｔhｅｒeｆoｒe, ｔhe cａｌcula ｔions ａｎd consｔruction sｈouldAccordinｇtｏappｒoxiｍａｔe tｈe framｅstｒucｔure to ｃonsideｒ.Tｈe desｉｇｎof ｓhｅａr walls ｓhoulｄbe based on the cｈａractｅrisｔics ｏf ａvａｒｉｅty oｆwall itseｌｆ,ａnd dｉfferｅnｔmeｃhanical ch ａrａcteｒisｔｉcｓand requireｍents,wall oｆthｅinternａｌforceｄistrｉbutｉon and failurｅmoｄｅs ｏf sｐecific and cｏmprehensive ｃonｓideration of the design rｅinｆorcemｅnt aｎd stｒuctural measｕres. Ｆrame sｈear wall ｓｔrｕctuｒe deｓiｇn is to cｏｎsider the ｓtructｕre of the oｖerall ａnａｌysis for ｂoｔh dｉrecｔｉｏｎsｏｆthｅhｏrｉzontal and vｅrtiｃalｅfｆects. Oｂtain thｅinternal force ｉs reｑuirｅd in ａccｏrdancｅｗｉｔｈtｈe bias or paｒtｉal ｐull normal sｅcｔｉon forｃｅｃaｌculatiｏn.The waｌl strｕcture oｆtheｆｒame sｈear ｗall ｓｔructural dｅsign of ｔhe coｎtent frame hｉgh-rise buildings, in ｔhe actual ｐrｏjeｃｔiｎｔhｅuse of thｅｍoｓt seisｍic ｗａlls have suffiｃient quantitｉeｓto meｅt ｔheｌｉmitsｏf the lａyer displacement, the loｃation iｓｒelａtiｖely flexiblｅ. Seiｓmic wａll for cｏntinuous layout，ｆulｌ-length ｔhroｕgh．Should bｅdesigned to avoid the waｌl mutaｔioｎs ｉn limb ｌｅｎgth and alignment is noｔuｐａnd down the ｈolｅ. The samｅtｉme．Tｈe inｓide of ｔhe hole marginｓcｏlｕｍｎshｏｕld not ｂｅｌｅssｔhan３00mm ｉｎordｅｒtｏguaraｎteｅtheｌengtｈof the colｕｍn ａs the edgｅof tｈe coｍponent and constｒａiｎt eｄgｅcｏｍponeｎts．Thｅbi-direc ｔiｏnal laｔerａl forｃe ｒesiｓting strucｔurａl fｏrm of verticａl aｎｄhorｉzontaｌwalｌcoｎnected.Eａｃh ｏｔhｅr as ｔhe ａffiｎiｔｙof the shｅar wall. Ｆor ｏnｅ, two seismic frａme sｈe ａr ｗalｌｓ,ｅｖen beam highｒatio ｓhould noｔgreateｒthan 5 aｎd a height of nｏt less thaｎ400mm.Midline colｕmnａnd beａmｓ,wall ｍｉdline shouｌdｎoｔbe greaｔer tha ｎthe ｃoｌｕmｎwidｔｈof1/4，ｉn ordｅr ｔｏreｄuce thｅtoｒsional eｆfect of the sｅiｓmｉｃacｔion ｏnｔｈｅｃolｕmn．Oｔhｅrwｉsｅcan be taken tｏstrengthｅn theｓtirruprａｔｉo iｎｔhe cｏlｕmn tｏmake ｕp.If thｅshear wａｌl sheａｒsｐａn ｔhａnｔhe ｂig twｏ. Ｅveｎthe beａｍcro ｓs-heｉｇht ratiｏgreateｒthan 2.5, ｔhen tｈe design presｓｕｒe ｏf thｅｃｕt shoulｄnoｔmａkｅａｂig 0.2. Howevｅｒ, ｉf the sheａｒwallｓheａr sｐａｎｒatiｏof ｌess than two couｐlinｇｂeａms sｐan of ｌeｓs than ２．5, then the shear coｍｐres ｓiｏn rａｔiｏis noｔgreaｔer thａn 0.15. Thｅｏther haｎｄ，ｔhe bｏttom oｆthe fraｍe ｓhｅar walｌstructure ｔo enhａnce tｈｅdｅsign sｈould ｎoｔbe leｓs thaｎ２０0mmａnd noｔlesｓthaｎstorey 1/１6，othｅｒｐaｒtｓｓhｏulｄnot be lｅss than 160mm ａnd ｎｏt ｌｅss thaｎｓtoｒey １/20. Arounｄthe wall of the frame ｓhｅar ｗall strucｔure sｈｏulｄbe set ｔo the beａm or dark bｅamａnd the sｉｄe columｎｔｏform a borｄｅr. Ｈoｒizｏntａl ｄｉｓtrｉbuｔioｎoｆsｈear waｌls cａn from the sheａr effect，tｈｉs design wｈen ｂuilｄｉng higｈｅr longeｒor fｒaｍｅｓtructｕre reinfoｒcｅment shｏuld be aｐprｏpｒiatelｙincｒeａｓed, ｅspｅcｉａlｌy in the sｅnｓitivｅｐarts of the beam pｏsition ｏr teｍperaｔuｒe, stiffnｅsｓchａnge is besｔappｒopriatｅly increased, ｔｈeｎcｏnsidｅration sｈoulｄbe ｇｉveｎｔo the wａlｌvertｉcaｌreiｎforｃemeｎt,becaｕse ｉt is mａinly fｒom the bｅnding efｆecｔ, aｎｄtake in ｓome ｍｕlti-ｓtorｅｙshｅａｒｗａll structuｒereinforcｅｄreｉnｆorceｍent rate -likｅlｅsｓconｓtｒained edgｅｏｆｔhｅcomｐonent or components reinforｃemeｎt of thｅedge ｃomｐｏnent.Referｅnces: [1 sad Hａyaｓhi,He Yaming. Ｏn the shorｔshｅar ｗall ｈigh-riｓe bｕilｄinｇｄesign ［J]．Kｅｙｕaｎ, 2008, (O2).高层框架剪力墙结构设计吴继成摘要: 本文从框架剪力墙结构设计的基本概念人手, 分析了框架剪力墙的构造设计内容, 包括抗震墙、剪跨比等的设计, 并出混凝土结构中最常用的框架剪力墙结构设计的注意要点。

毕业设计（论文）外文参考文献翻译计算机科学与信息工程系系（院）2008 届题目企业即时通Instant Messaging for Enterprises课题类型技术开发课题来源自选学生姓名许帅专业班级 04计算机科学与技术指导老师王占中职称工程师完成日期：2008年4 月 6 日目录I NSTANT M ESSAGING FOR E NTERPRISE (1)1. Tips (1)2. Introduction (1)3. First things first (2)4.The While-Accept loop (4)5. Per-Thread class (6)6. The Client class (7)企业即时通 (9)1.提示 (9)2.简介 (9)3.首先第一件事 (10)4.监听循环 (11)5.单线程类 (13)6.用户端类 (14)Instant Messaging for Enterprise1. TipsIf Java is, in fact, yet another computer programming language, you may question why it is so important and why it is being promoted as a revolutionary step in computer programming. The answer isn’t immediately obvious if you’re coming from a tr aditional programming perspective. Although Java is very useful for solving traditional standalone programming problems, it is also important because it will solve programming problems on the World Wide Web. What is the Web?The Web can seem a bit of a mys tery at first, with all this talk of “surfing,”“presence,” and “home pages.” It’s helpful to step back and see what it really is, but to do this you must understand client/server systems, another aspect of computing that is full of confusing issues. The primary idea of a client/server system is that you have a central repository of information，some kind of data, often in a database。

毕业设计外文资料翻译学院：信息科学与工程学院专业：软件工程姓名： XXXXX学号： XXXXXXXXX外文出处： Think In Java (用外文写)附件： 1.外文资料翻译译文；2.外文原文。

附件1：外文资料翻译译文网络编程历史上的网络编程都倾向于困难、复杂，而且极易出错。

程序员必须掌握与网络有关的大量细节，有时甚至要对硬件有深刻的认识。

一般地，我们需要理解连网协议中不同的“层”（Layer）。

而且对于每个连网库，一般都包含了数量众多的函数，分别涉及信息块的连接、打包和拆包；这些块的来回运输；以及握手等等。

这是一项令人痛苦的工作。

但是，连网本身的概念并不是很难。

我们想获得位于其他地方某台机器上的信息，并把它们移到这儿；或者相反。

这与读写文件非常相似，只是文件存在于远程机器上，而且远程机器有权决定如何处理我们请求或者发送的数据。

Java最出色的一个地方就是它的“无痛苦连网”概念。

有关连网的基层细节已被尽可能地提取出去，并隐藏在JVM以及Java的本机安装系统里进行控制。

我们使用的编程模型是一个文件的模型；事实上，网络连接（一个“套接字”）已被封装到系统对象里，所以可象对其他数据流那样采用同样的方法调用。

除此以外，在我们处理另一个连网问题——同时控制多个网络连接——的时候，Java内建的多线程机制也是十分方便的。

本章将用一系列易懂的例子解释Java的连网支持。

15.1 机器的标识当然，为了分辨来自别处的一台机器，以及为了保证自己连接的是希望的那台机器，必须有一种机制能独一无二地标识出网络内的每台机器。

早期网络只解决了如何在本地网络环境中为机器提供唯一的名字。

但Java面向的是整个因特网，这要求用一种机制对来自世界各地的机器进行标识。

为达到这个目的，我们采用了IP（互联网地址）的概念。

IP以两种形式存在着：(1) 大家最熟悉的DNS（域名服务）形式。

我自己的域名是。

所以假定我在自己的域内有一台名为Opus的计算机，它的域名就可以是。

附录一：外文原文Super capacitors - An OverviewKey words: Electrostatic capacitor; Electrolytic capacitor; Ceramic capacitor;Electrical double layer capacitor; Super Capacitor1.INTRODUCTIONThis paper offers a concise review on the renaissance of a conventional capacitor toelectrochemical double layer capacitor or super capacitor. Capacitors are fundamental electrical circuitelements that store electrical energy in the order of microfarads and assist in filtering. Capacitors havetwo main applications; one of which is a function to charge or discharge electricity. This function isapplied to smoothing circuits of power supplies, backup circuits of microcomputers, and timer circuitsthat make use of the periods to charge or discharge electricity. The other is a function to block the flowof DC. This function is applied to filters that extract or eliminate particular frequencies. This isindispensable to circuits where excellent frequency characteristics are required. Electrolytic capacitorsare next generation capacitors which are commercialized in full scale. They are similar to batteries in cell construction but the anode and cathode materials remain the same. They are aluminum, tantalum and ceramic capacitors where they use solid/liquid electrolytes with a separator between two symmetrical electro des.An electrochemical capacitor (EC), often called a Super capacitor or Ultra capacitor, stores electrical charge in the electric double layer at a surface-electrolyte interface, primarily in high-surface-area carbon. Because of the high surface area and the thinness of the double layer, these devices can have very a high specific and volumetric capacitance. This enables them to combine a previously unattainable capacitance density with an essentially unlimited charge/discharge cycle life. The operational voltage per cell ,limited only by the breakdown potential of the electrolyte, is usually<1 or <3 volts per cell for aqueous or organic electrolytes respectively.The concept of storing electrical energy in the electric double layer that isformed at the interface between an electrolyte and a solid has been known since the late 1800s. The first electrical device using double-layer charge storage was reported in 1957 by H.I. Becker of General Electric (U.S. Patent 2,800,616).Unfortunately, Becker’s device was imp ractical in that, similarly to a flooded battery, both electrodes needed to be immersed in a container of electrolyte, and the device was never comercialised.Becker did, however, appreciate the large capacitance values subsequently achieved by Robert A. Rightmire, a chemist at the Standard Oil Company of Ohio (SOHIO), to whom can be attributed the invention of the device in the format now commonly used. His patent (U.S. 3,288,641), filed in 1962 and awarded in late November 1966, and a follow-on patent (U.S. Patent 3,536,963) by fellow SOHIO researcher Donald L. Boos in 1970, form the basis for the many hundreds of subsequent patents and journal articles covering all aspects of EC technology.This technology has grown into an industrywith sales worth severalhundred million dollars per year. It is an in dustry that is poised today for rapid growth in the near term with the expansion of power quality needs and emerging transportation applications.Following the commercial introduction of NEC’s Super Capacitor in 1978, under licence from SOHIO, EC have evolved through several generations of designs. Initially they were used as back-up power devices for v is for cells ranging in size from small millifarad size devices with exceptional pulse power performance up to devices rated at hundreds of thousands of farads, with systems in some applications operating at up to 1,500 volts. The technology is seeing increasingly broad use, replacing batteriesolatile clock chips and complementary metal-oxide-semiconductor (CMOS) computer memories. But many other applications have emerged over the past 30 years, including portable wireless communication, enhanced power quality for distributed power generation systems, industrial actuator power sources, and high-efficiency energy storage for electric vehicles(EVs) and hybrid electric vehicles (HEVs).Overall, the unique attributes of ECs often complement the weaknesses of other power sources like batteries and fuel cells.Early ECs were generally rated at a few volts and had capacitance values measured from fractions of farads up to several farads. The trend today in some cases and in others complementing their performance.The third generation evolution is the electric double layer capacitor, where the electrical charge stored at a metal/electrolyte interface is exploited to construct astorage device. The interface can store electrical charge in the order of 610Farad. The main component in the electrode construction is activated carbon. Though this concept was initialized and industrialized some 40 years ago, there was a stagnancy in research until recent times; the need for this revival of interest arises due to the increasing demands for electrical energy storage in certain current applications like digital electronic devices, implantable medical devices and stop/start operation in vehicle traction which need very short high power pulses that could be fulfilled by electric double layer capacitors. They are complementary to batteries as they deliver high power density and low energy density. They also have longer cycle life than batteries and possess higher energy density as compared to conventional capacitors. This has led to new concepts of the so-called hybrid charge storage devices in which electrochemical capacitor is interfaced with a fuel cell or a battery. These capacitors using carbon as the main electrode material for both anode and cathode with organic and aqueous electrolytes are commercialized and used in day to-day applications. Fig.1 presents the three types of capacitors depicting the basic differences in their design and construction.Figure 1.Schematic presentation of electrostatic capacitor, electrolytic capacitor and electrical double layer capacitor.EDLCs, however suffer from low energy density. To rectify these problems, recently researchers try to incorporate transition metal oxides along with carbon in the electrode materials. When the electrode materials consist of transition metal oxides, then the electrosorption or redox processes enhance the value of specific capacitance ca. 10 -100 times depending on the nature of oxides. In such a situation, the EDLC is called as super capacitor or pseudo capacitor . This is the fourth generation capacitor. Performance of a super capacitor combines simultaneously two kinds of energy storage, i.e. non-faradic charge as in EDLC capacitors and faradaic charge similar toprocesses proceeding in batteries. The market for EC devices used for memory protection in electronic circuitry is about $150-200 million annually. New potential applications for ECs include the portable electronic device market, the power quality market, due particularly to distributed generation and low-emission hybrid cars, buses and trucks. There are some published reviews on capacitors and super capacitors . In the present overview, the evolution of electrochemical double layer capacitors starting from simple electrostatic capacitors is summarized.2. EXPERIMENTAL PARTThe invention of Leiden jar in 1745 started the capacitor technology; since then, there has been tremendous progress in this field. In the beginning, capacitors are used primarily in electrical and electronic products, but today they are used in fields ranging from industrial application to automobiles, aircraft and space, medicine, computers, games and power supply circuits. Capacitors are made from two metallic electrodes (mainly Si) placed in mutual opposition with an insulating material (dielectric) between the electrodes for accumulating an electrical charge. The basic equation relating to the capacitors is:C = εS/d (1)where C(μF) is the electrostatic capacity, the dielectric constant of the dielectric, S (cm2) the surface area of the electrode and d (cm) the thickness of the dielectric. The charge accumulating principle can be described as follows: when a battery is connected to the capacitor, flow of current induces the flow of electrons so that electrons are attracted to the positive terminal of the battery and so they flow towards the power source. As a result, an electron deficiency develops at the positive side, which becomes positively charged and an electron surplus develops at the negative side, which becomes negatively charged. This electron flow continues until the potential difference between the two electrodes becomes equal to the battery voltage. Thus the capacitor gets charged. Once the battery is removed, the electrons flow from the negative side to the side with an electron deficiency; this process leads to discharging. The conventional capacitors yield capacitance in the range of 0.1 to 1 μF with a voltage range of 50 to 400 V. Various materials such as paper (ε, 1.2-2.6), paraffin (ε 1.9-2.4), polyethylene (2.2-2.4), polystyrene (ε, 2.5-2.7), ebonite (ε, 2-3.5), polyethylene tetraphtharate (ε,3.1-3.2), water (ε, 80) sulfur（ε, 2-4.2), steatite porcelain (ε, 6-7), Al porcelain (ε, 8-10), mica（ε, 5-7)and insulated mineral oil (ε, 2.2-2.4) are used as dielectrics in capacitors.The capacitance output of these silicon based capacitors is limited and has to cope with low surface-to volume ratios of these electrodes. To increase the capacitance, as per eq., one has to increase to ∂or S and decrease; however the ∂value is largely determined by the working voltage and cannot be tampered. When aiming at high capacitance densities, it is necessary to combine the mutual benefits achieved with a high permittivity insulator material and an increased effective surface area. With Si as the substrate material, electrochemical etching produces effective surface area. The surface area of this material gets enlarged by two orders of magnitude compared to unetched surface. Electrochemically formed macroporous Si has been used for the preparation of high aspect ratio capacitors with layered SiO2/Si3N4/SiO2 insulators. Research work on the modification of conventional capacitors to increase the specific capacitance is also in progress. Approximately 30 times higher capacitance densities are reported recently for Si/Al2O3/ZnO: Al capacitor where Si is electrochemically etched porous one. Another way identified to increase the surface area of the electrodes is to form anodically formed oxides (Al, Ta); however, ceramic capacitors are based on the high dielectric constant rather than the electrode area.3. ELECTROLYTIC CAPACITORSThe next generation capacitors are the electrolytic capacitors; they are of Ta, Al and ceramic electrolytic capacitors. Electrolytic capacitors use an electrolyte as conductor between the dielectrics and an electrode. A typical aluminum electrolytic capacitor includes an anode foil and a cathode foil processed by surface enlargement and or formation treatments. Usually, the dielectric film is fabricated by anodizing high purity Al foil for high voltage applications in boric acid solutions. The thickness of the dielectric film is related to the working voltage of the aluminum electrolytic capacitor. After cutting to a specific size according to the design specification, a laminate made up of an anode foil, a cathode foil which is opposed to the dielectric film of the anode foil and a separator interposed between the anode and cathode foils, is wound to provide an element. The wound element does not have any electricalcharacteristics of electrolytic capacitor yet until completely dipped in an electrolyte for driving and housed in a metallic sheathed package in cylindrical form with a closed-end equipping a releaser. Furthermore, a sealing material made of elastic rubber is inserted into an open-end section of the sheathed package and the open-end section of the sheathed package by drawing, whereby an aluminum electrolytic capacitor is constituted. Electrolytic aluminum capacitors are mainly used as power supplies for automobiles, aircraft, space vehicles, computers, monitors, motherboards of personal computers and other electronics.There are two types of tantalum capacitors commercially available in the market; wet electrolytic capacitors which use sulfuric acid as the electrolyte and solid electrolytic capacitors which use MnO2 as the solid electrolyte. Though the capacitances derived from both Ta and Al capacitors are the same, Ta capacitors are superior to Al capacitors in temperature and frequency characteristics. For analog signal systems, Al capacitors produce a current-spike noise which does not happen in Ta capacitors. In other words, Ta capacitors are preferred for circuits which need high stability characteristics. The total world wide production of Al electrolytic capacitors amounts to US$ 3.8 billion, 99% of which are of the wet type. Unlike Ta solid electrolytic capacitors, the solid electrolyte materials used are of organic origin; polypyrrole, a functional polymer and TCNQ (7,7, 8, 8- tetracyanoquniodimethane) an organic semiconductor. Next, MnO2 solid electrolyte material is formed on the surface of that dielectric layer and on top of that a layer of polypyrrole organic solid electrolyte material is formed by electrolytic synthesis. Following this, the positive and negative electrodes are mounted to complete the electronic component. However, the capacitances of these electrolytic capacitors are in the range 0.1 to 10F with a voltage profile of 25 to 50 V.The history of development of electrolytic capacitors which were mass produced in the past as well as today is presented by S. Niwa and Y. Taketani . Many researchers try to improve the performance of these electrolytic capacitors by modifying the electrode or electrolyte. Generally, the increases in effective surface area (S) are achieved by electrolytic etching of aluminum substrate before anodization, but now it faces with the limit. It is also very difficult to decrease d because the d value is largely decided when the working voltages are decided. Increase in may be a possible routine to form composite dielectric layers by incorporating relatively large value compounds. Replacement of MnO2 by polypyrrole solid electrolyte was reported to reduce electrostatic resistance due to its higher conductivity; aromaticsulfonate ions were used as charge compensating dopant ions .A tantalum capacitor with Ta metal as anode, polypyrrole as cathode and Ta2O5 dielectric layer was also reported. In the Al solid electrolytic capacitors, polyaniline doped with inorganic and organic acids was also studied as counter electrode. In yet another work, Al solid electrolytic capacitor with etched Al foil as anode, polyaniline / polypyrrrole as cathode and Al2O3 as dielectric was developed. Ethylene carbonate based organic electrolytes and -butyrolactone based electrolytes have been tried as operating electrolytes in Al electrolytic capacitors. Masuda et al. have obtained high capacitance by electrochemically anodizing rapidly quenching Al-Ti alloy foil. Many researchers have tried the other combination of alloys such as Al-Zr, Al-Si, Al-Ti, Al-Nb and Al-Ta composite oxide films. Composite oxide films of Al2O3-(Ba0.5Sr0.5TiO3) and Al2O3- Bi4Ti3O12 on low-voltage etched aluminum foil were also studied. Nb-Ta-Al for Ta electrolytic capacitors was also tried as anode material .A ceramic capacitor is a capacitor constructed of alternating layers of metal and ceramic, with the ceramic material acting as the dielectric. Multilayer ceramic capacitors (MLCs) typically consist of ~100 alternate layers of electrode and dielectric ceramics sandwiched between two ceramic cover layers. They are fabricated by screen-printing of electrode layers on dielectric layers and co-sintering of the laminate. Conventionally, Ag-Pd is used as the electrode material and BaTiO3 is used as the dielectric ceramic. From 2000 onwards, the MLCs market has been growing in pace with the exponential development of communications. They are produced in the capacitance range of 10 F (normally the range of Ta and Al electrolytic capacitors); they are highly useful in high frequency applications. Historically, a ceramic capacitor is a two-terminal non-polar device. The classical ceramic capacitor is the disc capacitor. This device predates the transistor and was used extensively in vacuum-tube equipment (e.g radio receivers) from c. a. 1930 through the 1950s and in discrete transistor equipment from the 1950s through the 1980s. As of 2007, ceramic disc capacitors are in widespread use in electronic equipment, providing high capacity and small size at low price compared to the other types.The other ceramic materials that have been identified and used are CaZrO3, MgTiO3, SrTiO3 etc. A typical 10 F MLC is a chip of size (3.2 x 1.6 x 1.5 mm). Mn, Ca, Pd , Ag etc are some of the other internal electrodes used. Linear dielectrics and antiferroelectrics based o strontium titante have been developed for high voltage disk capacitors. These are applicable for MLCs with thinner layers because of their high coercive fields. One of the most critical material processing parameters is the degreeof homogeneous mixing of additive in the slurry. The binder distribution in the green ceramic sheet, the degree of surface roughness, fine size nickel powder, formation of green sheet, electrode deposition ad sheet stacking etc play a crucial role in the process technology. Any one of these facts if mishandled would result in the failure of the device. For instance, providing a roughess of 5 m thick green sheet to 0.5 m is mandatory so that a smooth contact surface with the inner nickel electrode can be established. This is a very important factor in avoiding the concentration of electric filed at asperities, where the charge emission from the electrode is accelerated, resulting in short failure. Conventional sheet/printing method has a technical limit of producing a thickness around 1 m dielectric; in order to decrease the thickness further, thin film technologies like CVD, sputtering, plasma-spray etc has to be used.The other types of capacitors are film capacitors which use thin polyester film and polypropylene film as dielectrics and meta-glazed capacitors which incorporate electrode plates made of film vacuum evaporated with metal such as Al. Films can be of polyester, polypropylene or polycarbonate make. Also capacitors are specified depending on the dielectric used such as polyester film capacitor, polypropylene capacitor, mica capacitor, metallized polyester film capacitor etc.4. DOUBLE LAYER CAPACITORSElectric/electrochemical double layer capacitor (EDLC) is a unique electrical storage device, which can store much more energy than conventional capacitors and offer much higher power densitythan batteries. EDLCs fill up the gap between the batteries and the conventional capacitor, allowing applications for various power and energy requirements i.e., back up power sources for electronic devices, load-leveling, engine start or acceleration for hybrid vehicles and electricity storage generated from solar or wind energy. EDLC works on the principle of double-layer capacitance at the electrode/electrolyte interface where electric charges are accumulated on the electrode surfaces and ions of opposite charge are arranged on the electrolyte side.Figure 2.Charge storage mechanism of an EDLC cell under idle and charged conditions.Fig. 2 shows the mechanism of charge storage in an EDLC cell and Fig. 3 shows the configuration of an typical EDLC cell. There are two main types of double layer capacitors as classified by the charge storage mechanism: (i) electrical double-layer capacitor; (ii) electrochemical double layer capacitor or super/pseudocapacitor. An EDLC stores energy in the double-layer at the electrode/electrolyte interface, whereas the supercapacitor sustains a Faradic reaction between the electrode and the electrolyte in a suitable potential window. Thus the electrode material used for the construction of the cell for the former is mainly carbon material while for the latter, the electrode material consist of either transition metal oxides or mixtures of carbon and metal oxides/polymers. The electrolytes can be either aqueous or non-aqueous depending on the mode of construction of EDLC cell.Figure 3.Typical configuration of an EDLC cellThere are two general directions of interest. One is the long term goal of the development of electrical propulsion for vehicles, and the other is the rapid growth of portable electronic devices that require power sources with maximum energy content and the lowest possible size and weight.5. CONCLUSIONSAccording to a market survey by Montana, super capacitors are becoming a promising solution for brake energy storage in rail vehicles. The expected technological development outside railway sector is also shown to be highly dynamic: diesel electric vehicles, catenary free operation of city light rail, starting system for diesel engines, hybrid-electric cars, industrial applications, elevators, pallet trucks etc. The time horizon expected for development is next 5 to 10 years. The main development goals will be,· long life time· increase of the rated voltage· improvements of the range of operating temperature· increase of the energy and power densitiesVery recently, hybrid car is introduced in the market but it is turned to be very expensive and out of common man’s reach. Shortage and cost of fossil fuels already instigated alternate technologies viable for traction purposes. In such a situation,EDLCs are also useful to store energy generated from non-conventional energy sources. A future possibility of service centers set up for EDLC supply similar to petrol (as on date) is not far as the main setbacks in technology development may take a decade for fruitful results.附录二：外文译文超级电容器-概述关键词：静电电容，电解电容器，陶瓷电容器，双电层 ,电容器，超级电容器1．引言本文为电化学双层电容器或超级电容器提供在一台常规电容器，简明的介绍新生的电化学双电层电容器或超级电容器。

毕业设计说明书英文文献及中文翻译学院：信息与通信工程专业：电子信息科学与技术2011年 6月外文文献原文Fundamentals of Time and Frequency IntroductionTime and frequency standards supply three basic types of information：time-of-day，time interval，and frequency. Time-of-day information is provided in hours，minutes，and seconds，but often also includes the date (month，day，and year). A device that displays or records time-of-day information is called a clock. If a clock is used to label when an event happened，this label is sometimes called a time tag or time stamp. Date and time-of-day can also be used to ensure that events are synchronized，or happen at the same time.Time interval is the duration or elapsed time between two events. The standard unit of time interval is the second(s). However，many engineering applications require the measurement of shorter time intervals，such as milliseconds (1 ms = 10 -3 s) ，microseconds (1 μs = 10 -6 s) ，nanoseconds (1 ns = 10 -9 s) ，and picoseconds (1 ps = 10 -12 s). Time is one of the seven base physical quantities，and the second is one of seven base units defined in the International System of Units (SI). The definitions of many other physical quantities rely upon the definition of the second. The second was once defined based on the earth‟s rotational rate or as a fraction of the tropical year. That changed in 1967 when the era of atomic time keeping formally began. The current definition of the SI second is the duration of 9，192，631，770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom.Frequency is the rate of a repetitive event. If T is the period of a repetitive event，then the frequency f is its reciprocal，1/T. Conversely，the period is the reciprocal of the frequency，T = 1/f. Since the period is a time interval expressed in seconds (s) ，it is easy to see the close relationship between time interval and frequency. Thestandard unit for frequency is the hertz (Hz) ，defined as events or cycles per second. The frequency of electrical signals is often measured in multiples of hertz，including kilohertz (kHz)，megahertz (MHz)，or gigahertz (GHz)，where 1 kHz equals one thousand (103) events per second，1 MHz equals one million (106) events per second，and 1 GHz equals one billion (109) events per second. A device that produces frequency is called an oscillator. The process of setting multiple oscillators to the same frequency is called synchronization.Of course，the three types of time and frequency information are closely related. As mentioned，the standard unit of time interval is the second. By counting seconds，we can determine the date and the time-of-day. And by counting events or cycles per second，we can measure frequency.Time interval and frequency can now be measured with less uncertainty and more resolution than any other physical quantity. Today，the best time and frequency standards can realize the SI second with uncertainties of ≈1×10-15.Physical realizations of the other base SI units have much larger uncertainties.Coordinated Universal Time (UTC)The world‟s major metrology laboratories routinely measure their time and frequency standards and send the measurement data to the Bureau International des Poids et Measures (BIPM) in Sevres，France. The BIPM averages data collected from more than 200 atomic time and frequency standards located at more than 40 laboratories，including the National Institute of Standards and Technology (NIST). As a result of this averaging，the BIPM generates two time scales，International Atomic Time (TAI)，and Coordinated Universal Time (UTC). These time scales realize the SI second as closely as possible.UTC runs at the same frequency as TAI. However，it differs from TAI by an integral number of seconds. This difference increases when leap seconds occur. Whennecessary，leap seconds are added to UTC on either June 30 or December 31. The purpose of adding leap seconds is to keep atomic time (UTC) within ±0.9 s of an older time scale called UT1，which is based on the rotational rate of the earth. Leap seconds have been added to UTC at a rate of slightly less than once per year，beginning in 1972.Keep in mind that the BIPM maintains TAI and UTC as ……paper‟‟ time scales. The major metrology laboratories use the published data from the BIPM to steer their clocks and oscillators and generate real-time versions of UTC. Many of these laboratories distribute their versions of UTC via radio signals which section 17.4 are discussed in.You can think of UTC as the ultimate standard for time-of-day，time interval，and frequency. Clocks synchronized to UTC display the same hour minute，and second all over the world (and remain within one second of UT1). Oscillators simonized to UTC generate signals that serve as reference standards for time interval and frequency.Time and Frequency MeasurementTime and frequency measurements follow the conventions used in other areas of metrology. The frequency standard or clock being measured is called the device under test (DUT). A measurement compares the DUT to a standard or reference. The standard should outperform the DUT by a specified ratio，called the test uncertainty ratio (TUR). Ideally，the TUR should be 10：1 or higher. The higher the ratio，the less averaging is required to get valid measurement results.The test signal for time measurements is usually a pulse that occurs once per second (1 ps). The pulse width and polarity varies from device to device，but TTL levels are commonly used. The test signal for frequency measurements is usually at a frequency of 1 MHz or higher，with 5 or 10 MHz being common. Frequency signalsare usually sine waves，but can also be pulses or square waves if the frequency signal is an oscillating sine wave. This signal produces one cycle (360∞or 2πradians of phase) in one period. The signal amplitude is expressed in volts，and must be compatible with the measuring instrument. If the amplitude is too small，it might not be able to drive the measuring instrument. If the amplitude is too large，the signal must be attenuated to prevent overdriving the measuring instrument.This section examines the two main specifications of time and frequency measurements—accuracy and stability. It also discusses some instruments used to measure time and frequency.AccuracyAccuracy is the degree of conformity of a measured or calculated value to its definition. Accuracy is related to the offset from an ideal value. For example，time offset is the difference between a measured on-time pulse and an ideal on-time pulse that coincides exactly with UTC. Frequency offset is the difference between a measured frequency and an ideal frequency with zero uncertainty. This ideal frequency is called the nominal frequency.Time offset is usually measured with a time interval counter (TIC). A TIC has inputs for two signals. One signal starts the counter and the other signal stops it. The time interval between the start and stop signals is measured by counting cycles from the time base oscillator. The resolution of a low cost TIC is limited to the period of its time base. For example，a TIC with a 10-MHz time base oscillator would have a resolution of 100 ns. More elaborate Tics use interpolation schemes to detect parts of a time base cycle and have much higher resolution—1 ns resolution is commonplace，and 20 ps resolution is available.Frequency offset can be measured in either the frequency domain or time domain.A simple frequency domain measurement involves directly counting and displaying thefrequency output of the DUT with a frequency counter. The reference for this measuremen t is either the counter‟s internal time base oscillator ， or an external time base. The counter‟s resolution ， or the number of digits it can display ， limits its ability to measure frequency offset. For example ， a 9-digit frequency counter can detect a frequency offset no smaller than 0.1 Hz at 10 MHz (1×10-8). The frequency offset is determined asmeasure nominal nominal(f -f )f= f Where f measur is the reading from the frequency counter ， and f nominal is the frequency labeled on the oscillator‟s nameplate ， or specified output frequency.Frequency offset measurements in the time domain involve a phase comparison between the DUT and the reference. A simple phase comparison can be made with an oscilloscope. The oscilloscope will display two sine waves. The top sine wave represents a signal from the DUT ， and the bottom sine wave represents a signal from the reference. If the two frequencies were exactly the same ， their phase relationship would not change and both would appear to be stationary on the oscilloscope display. Since the two frequencies are not exactly the same ， the reference appears to be stationary and the DUT signal moves. By measuring the rate of motion of the DUT signal we can determine its frequency offset. Vertical lines have been drawn through the points where each sine wave passes through zero. The bottom of the figure shows bars whose width represents the phase difference between the signals. In this case the phase difference is increasing ， indicating that the DUT is lower in frequency than the reference.Measuring high accuracy signals with an oscilloscope is impractical ， since the phase relationship between signals changes very slowly and the resolution of the oscilloscope display is limited. More precise phase comparisons can be made with a TIC. If the two input signals have the same frequency ， the time interval will notchange. If the two signals have different frequencies ， the time interval wills change ， and the rate of change is the frequency offset. The resolution of a TIC determines the smallest frequency change that it can detect without averaging. For example ， a low cost TIC with a single-shot resolution of 100 ns can detect frequency changes of 1 × 10 -7 in 1 s. The current limit for TIC resolution is about 20 ps ， which means that a frequency change of 2 ×10 -11 can be detected in 1 s. Averaging over longer intervals can improve the resolution to <1 ps in some units [6].Since standard frequencies like 5 or 10 MHz are not practical to measure with a TIC ， frequency dividers or frequency mixers are used to convert the test frequency to a lower frequency. Divider systems are simpler and more versatile ， since they can be easily built or programmed to accommodate different frequencies. Mixer systems are more expensive ， require more hardware including an additional reference oscillator ， and can often measure only one input frequency (e.g.， 10 MHz) ， but they have a higher signal-to-noise ratio than divider systems.If dividers are used ， measurements are made from the TIC ， but instead of using these measurements directly ， we determine the rate of change from reading to reading. This rate of change is called the phase deviation. We can estimate frequency offset as follows ：tf=T ∆Where △t is the amount of phase deviation ， and T is the measurement period. To illustrate ， consider a measurement of +1 μs of phase deviation over a measurement period of 24 h. The unit used for measurement period (h) must be converted to the unit used for phase deviation (μs). The equation becomes11t 1us f offset ===1.1610T 86400000000us -∆⨯（），，，As shown，a device that accumulates 1 μs of phase deviation/day has a frequency offset of 1.16 × 10 -11 with respect to the reference. This simple example requires only two time interval readings to be made，and △t is simply the difference between the two readings. Often，multiple readings are taken and the frequency offset is estimated by using least squares linear regression on the data set，and obtaining △t from the slope of the least squares line. This information is usually presented as a phase plot，as shown in Fig. 17.6. The device under test is high in frequency by exactly 1×10 -9，as indicated by a phase deviation of 1 ns/s.Dimensionless frequency offset values can be converted to units of frequency (Hz) if the nominal frequency is known. To illustrate this，consider an oscillator with a nominal frequency of 5 MHz and a frequency offset of +1.16 ′10 -11. To find the frequency offset in hertz，multiply the nominal frequency by the offset：(5 ×106) (+1.16×10 -11) = 5.80×10 -5 =+0.0000580 Hz Then，add the offset to the nominal frequency to get the actual frequency：5，000，000 Hz + 0.0000580 Hz = 5，000，000.0000580 HzStabilityStability indicates how well an oscillator can produce the same time or frequency offset over a given time interval. It doesn‟t indicate whether the time or frequency is “right” or “wrong，” but only whether it stays the same. In contrast，accuracy indicates how well an oscillator has been set on time or on frequency. To understand this difference，consider that a stable oscillator that needs adjustment might produce a frequency with a large offset. Or，an unstable oscillator that was just adjusted might temporarily produce a frequency near its nominal value. Figure 17.7 shows the relationship between accuracy and stability.Stability is defined as the statistical estimate of the frequency or time fluctuations of a signal over a given time interval. These fluctuations are measured with respect to a mean frequency or time offset.Short-term stability usually refers to fluctuations over intervals less than 100 s. Long-term stability can refer to measurement intervals greater than 100 s ， but usually refers to periods longer than 1 day.Stability estimates can be made in either the frequency domain or time domain ， and can be calculated from a set of either frequency offset or time interval measurements. In some fields of measurement ， stability is estimated by taking the standard deviation of the data set. However ， standard deviation only works with stationary data ， where the results are time independent ， and the noise is white ， meaning that it is evenly distributed across the frequency band of the measurement. Oscillator data is usually no stationary ， since it contains time dependent noise contributed by the frequency offset. With stationary data ， the mean and standard deviation will converge to particular values as more measurements are made. With no stationary data ， the mean and standard deviation never converge to any particular values. Instead ， there is a moving mean that changes each time we add a measurement. For these reasons ， a non-classical statistic is often used to estimate stability in the time domain. This statistic is sometimes called the Allan variance ， but since it is the square root of the variance ， its proper name is the Allan deviation. The equation for the Allan deviation (σy (τ)) is2y i+i y -y στ1（（） where y i is a set of frequency offset measurements containing y 1， y 2， y 3， and so on ， M is the number of values in the y i series ， and the data are equally spaced in segments τ seconds long. Or2x i+1i -2x +x στi+2（（x ） Where x i is a set of phase measurements in time units containing x 1， x 2， x 3，and so on，N is the number of values in the xi series，and the data are equally spaced in segments τ seconds long. Note that while standard deviation subtracts the mean from each measurement before squaring their summation，the Allan deviation subtracts the previous data point. This differencing of successive data points removes the time dependent noise contributed by the frequency offset. An Allan deviation graph is shown in Fig. 17.8. It shows the stability of the device improving as the averaging period (τ) gets longer，since some noise types can be removed by averaging. At some point，however，more averaging no longer improves the results. This point is called the noise floor，or the point where the remaining noise consists of no stationary processes such as flicker noise or random walk. The device measured in Fig. 17.8 has a noise floor of ~5 × 10 -11at τ = 100 s.Practically speaking，a frequency stability graph also tells us how long we need to average to get rid of the noise contributed by the reference and the measurement system. The noise floor provides some indication of the amount of averaging required to obtain a TUR high enough to show us the true frequency where xi is a set of phase measurements in time units containing x1，x2，x3，and so on is the number of values in the xi series，and the data are equally s paced in segments τ seconds long. Note that while standard deviation subtracts the mean from each measurement before squaring their summation，the Allan deviation subtracts the previous data point. This differencing of successive data points removes the time dependent noise contributed by the frequency offset. An Allan deviation graph is shown in Fig. 17.8. It shows the stability of the device improving as the averaging period (τ) gets longer，since some noise types can be removed by averaging. At some point，however，more averaging no longer improves the results. This point is called the noise floor or the point where the remaining noise consists of no stationary processes such as flicker noise or random walk. The device measured in Fig. 17.8 has a noise floor of ~5 × 10 -11at τ = 100 s.Practically speaking，a frequency stability graph also tells us how long we needto average to get rid of the noise contributed by the reference and the measurement system. The noise floor provides some indication of the amount of averaging required to obtain a TUR high enough to show us the true frequency offset of the DUT. If the DUT is an atomic oscillator (section 17.4) and the reference is a radio controlled transfer standard (section 17.5) we might have to average for 24 h or longer to have confidence in the measurement result. Five noise types are commonly discussed in the time and frequency literature：white phase，flicker phase，white frequency，flicker frequency，and random walk frequency. The slope of the Allan deviation line can help identify the amount of averaging needed to remove these noise types (Fig. 17.9). The first type of noise to be removed by averaging is phase noise，or the rapid，random fluctuations in the phase of the signal. Ideally，only the device under test would contribute phase noise to the measurement，but in practice，some phase noise from the measurement system and reference needs to be removed through averaging. Note that the Allan deviation does not distinguish between white phase noise and flicker phase noise. Table 17.2 shows several other statistics used to estimate stability and identify noise types for various applications.Identifying and eliminating sources of oscillator noise can be a complex subject，but plotting the first order differences of a set of time domain measurements can provide a basic understanding of how noise is removed by averaging. Figure 17.10 was made using a segment of the data from the stability graph in Fig. 17.8. It shows phase plots dominated by white phase noise (1 s averaging) ，white frequency noise (64 s averages) ，flicker frequency noise (256 s averages)，and random walk frequency (1024 s averages). Note that the white phase noise plot has a 2 ns scale，and the other plots use a 100 ps scale.外文文献中文翻译时间和频率的基本原理介绍时间和频率标准应用于三种基本信息类型：时间，时间间隔和频率.时间信息有小时，分，秒.通常还包括日期(年，月，日).用来显示和记录时间的器件叫做钟表，如果钟表标记了一件事的发生，那么这个标记叫做时间标签或时间印记.日期和时间能确保事情的同步或同时发生.时间间隔是两个事件持续或断续的时间，时间间隔的标准单位是秒，然而许多工程上应用要求更短的时间间隔，像毫秒，微秒，纳秒，和皮秒，时间是七个基本物理量之一，并且秒是国际单位体制制定七个基本单位之一.许多区其他物理量的定义是依靠秒而定义的.秒曾经定义根据地球回转率.原子时代正式开始在1967年目前SI定义秒为：秒是铯133原子(Cs133)基态的两个超精细能级之间跃迁所对应的辐射的9，192，631，770个周期所持续的时间。

南京理工大学紫金学院毕业设计（论文）外文资料翻译系：机械系专业：车辆工程专业姓名:宋磊春学号:070102234外文出处：EDU_E_CAT_VBA_FF_V5R9(用外文写)附件：1。

外文资料翻译译文；2.外文原文.附件1：外文资料翻译译文CATIA V5 的自动化CATIA V5的自动化和脚本：在NT 和Unix上：脚本允许你用宏指令以非常简单的方式计划CATIA。

CATIA 使用在MS –VBScript中(V5.x中在NT和UNIX3。

0 )的共用部分来使得在两个平台上运行相同的宏。

在NT 平台上：自动化允许CATIA像Word/Excel或者Visual Basic程序那样与其他外用分享目标。

ATIA 能使用Word/Excel对象就像Word/Excel能使用CATIA 对象。

在Unix 平台上:CATIA将来的版本将允许从Java分享它的对象。

这将提供在Unix 和NT 之间的一个完美兼容。

CATIA V5 自动化：介绍（仅限NT）自动化允许在几个进程之间的联系:CATIA V5 在NT 上：接口COM：Visual Basic 脚本(对宏来说)，Visual Basic 为应用（适合前:Word/Excel )，Visual Basic。

COM（零部件目标模型)是“微软“标准于几个应用程序之间的共享对象。

Automation 是一种“微软“技术,它使用一种解释环境中的COM对象。

ActiveX 组成部分是“微软“标准于几个应用程序之间的共享对象,即使在解释环境里。

OLE（对象的链接与嵌入）意思是资料可以在一个其他应用OLE的资料里连结并且可以被编辑的方法(在适当的位置编辑）.在VBScript,VBA和Visual Basic之间的差别：Visual Basic(VB）是全部的版本。

它能产生独立的计划,它也能建立ActiveX 和服务器。

它可以被编辑。

VB中提供了一个补充文件名为“在线丛书“(VB的5。