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推荐第1篇:农业机械外文

Improvement and development of small agriculturalMachinery for sub-Saharan

The new government from 1950 to the 1960s, African countries after independence, a large-scale agricultural machinery imported from advanced countries to promote the modernization of agricultural policy.Now, many African countries, agriculture machinery and not the smooth management of this does not solve the economic, technical premise of the question in order to use the European and American type of mechanization of agricultural production, there are a lot of mechanization of agricultural production in Europe and America to collapse phenomenon.In which the benefit of the use of tractors, tractor makes small-scale farming in the Tianshui area into farmland by the rental contract, the small-scale farming economy, strict control, resulting in the farming work environment can not be improved.Although the advanced countries to expand investment cooperation and aistance of the African economies, but if there is no support on the actual burden of agricultural production, small-scale farming can imagine the African countries can not be real development.

This study is to improve small-scale farmers in sub-Saharan Africa working environment for the target, the agricultural status of the investigation is the right technology to the premise of the production scale of agricultural operations, agricultural surveys in the same region at the same timeway to look forward to improved and developed to ease the financial burden and labor to withstand the force of a small agricultural machinery, this study concludes that the proposal to the correct transfer of the development of improved small-scale agricultural machinery technology.First of all, to verify the independence of African countries after the implementation of European and American agricultural mechanization policy, included in the social background of sub-Saharan Africa, countries import the point of the problems caused by modern agricultural technology based on the acute and early development programs, committed to the mechanization of agriculturetendency from the advanced countries the introduction of the tractor use in agriculture, and to show small-scale farming farming summarized the discuion of the problems of small-scale farmers in African countries in general aumed.

In order to obtain full and complete investigation and the results of research should be correct and appropriate technology transfer coming in on the basis of the object region neceary survey of agricultural conditions.To survey covering sub-Saharan Africa\'s agricultural situation, we must investigate those self-sufficient pillars of small-scale farmers in the agri-environmental characteristics of the region to investigate the one hand, but also the implementation of the questionnaire surveys and personal door acce to the forms of investigation.The results of the survey, we can know that a relatively high dependence on small-scale farmers in the right economic, animal technology, pears, threshers and other small-scale agricultural machinery.In one, is Morocco, a national policy on individual farmers and groups form a team groups to use the purchase of agricultural machinery, the state has a grant system so that individuals and groups and for small-scale farmers in such as education, research, training, institutional measures and achieved substantial results, but also the transfer of agricultural technology sub-Saharan Africa also played a very good guide positive role.

Suitable starting point for small-scale farmers in the small agricultural machinery, as sub-Saharan Africa, the agricultural operations of farmers in the most need to improve, first as the

most pay attention to efficient harvesting,the same region looks forward to the popularization of improved animal farming experiment can prove the stability and maneuverability.The experiment is the same with the sub-Saharan Africa under natural environmental conditions, the experiment also in North America, Morocco, has prepared a sound and reasonable environment, the habits of this experiment as the small-scale farming agriculture methods to cover the dealer operations (cover Makers jobs: call CoverCropCultivationC.C grow wheat Lei Tian, harrowing, and cover the soil of agricultural practices) performance characteristics of the test animal farming jobs.Based on the results of this experiment to prove, instead of using the completely opposite of animal farming in China and sub-Saharan Africa, for example, might as well find a suitable method of soil improvement, animal farming and sub-Saharan Africa.In general areas such as Morocco test pear seedbed three kinds (short seedbed seedbed seedbed long) different ways of working for the safety of animal farming, animal farming from farming characteristics and operational safety inspection and improved seedbed plow hinder gradually reduce the operational safety in the right direction.In a farming in sub-Saharan Africa followed by the need for the improvement of agricultural operations on agricultural harvesting efficiency is very high on modern efficient thresher.Proceing technology, as pointed out by FAO and other agencies, as after the harvest, threshing work, is a major iue for harvesters to reduce harvest loes.On one hand, the use of straw on the threshing work is also very important.Ongoing contract work in North America, Morocco and other countries tried the improvement of Turkey\'s advanced technology, to ensure appropriate length of straw, for using the modified propeller trunk.Threshing test results using the modified propeller trunk, lo of wheat and barley, each about 3 percent, which the wheat harvest loes in North America and achieved good results.Straw loes in the Turkish manufacturing advanced machinery occasions, lo of efficiency of about 90%, while the lo of efficiency in the improved propeller trunk only 9% wheat, barley, only 10% of the harvest lo wheat and barley to meet in feed use.

Finally, in the area survey of the introduction of object technology and small-scale agricultural machinery in the examples in this paper improved on the basis of the development of the research sample, apply to the introduction of agricultural technology by small-scale farming in the African region in general type andfuture collaboration that proposals were collected.First, for technical cooperation in the sub-Saharan Africa, we can recognize in the densely detailed results of the survey is neceary to see the nature of the demand of the farmers on agricultural mechanization, and the second, are now in the proce of agricultural mechanization in the early African agricultural machinery imported premise should be to adapt to the agricultural environment of the agricultural situation in the region and the climate of the region\'s endemic, as well as the need for the development of the agricultural environment suitable animal farming and threshing machines and other small agricultural machinery, the improvement is also very important.Third, based on the popularity of the community to create small-scale agricultural machinery plays an important role, its peasants, workers, universities, research institutes and manufacturing plants to become one of the activities of groups, not as parenting groups to contribute to regional industrialization.ODA technology transferred to the site in one of the country\'s government officials, workers included in the transferred object a lot, but we also see the appropriate technology to impart to farmers should be transferred in the initial nor case.Farmers bear the burden of agriculture, rather than rely entirely on farmers in le than farmers in appropriate technology collaboration is more important, if you want on the subject can be paed.

In this thesis, and look forward to alleviate the burden of farmers in the economy and labor under the burden of the work environment to improve small-scale farmers in sub-Saharan Africa.Improvement and development of small-scale agricultural machinery while in the same region, and summarizes the correct method of technology transfer on the covers small-scale agricultural machinery.

This study is the example for the improvement and development of small-scale agricultural machinery sub-Saharan Africa, and see many African countries from Europe and the United States the use of large agricultural machinery to solve the problem in the economic conditions in the

same region and agricultural the actual state of the correct and suitable for agriculturalmachinery and well-integrated effect, we can expect to farm a good contribution to the future.Also, after the long-term ODA front-line experience on the basis of the proposal on agricultural technology transfer, through the perspective of the ODA points out the lack of respect, we can determine the future policy depends on the ODA Agricultural Technology Support Programme, it will provide important Guide to the role.

推荐第2篇:外文翻译

大连海洋大学土木工程毕业设计

外文翻译

译文题目:

原稿题目:

原稿出处:

毕业设计

译文及原稿

施工项目成本上升的因素

Construction Project Cost Escalation Factors

Engrg.Volume 25, Iue 4, pp.221-229 (October 2009)

土建08-3班 石骏 学号:080411051

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施工项目成本上升的因素

J.Mgmt.文摘:私人和公共的建设项目,一直以来有成本增长的问题。交通运输项目,在计划和建设过程中具有典型的较长生产前置时间,这在历史上是被低估的。如图所示,通过对荷兰隧道建设的经验回顾增长的成本。在美国,大约50%的现役的大型运输项目都超出他们的最初的预算。大量的研究和研究项目已经确认个体因素导致增加的工程造价。虽然这个因素能影响私人资助项目鉴定效果,但是对公共资助的项目尤其不利。公共基金用于一些项目的建设效果是有限的,并且有积累的重要的基础设施的需要。因此,如果任何项目超过预算,其他项目被从这个计划删除或降低范围以提供必要资金来抵消成本的增长。这样的行为会加剧恶化的一个国家的运输基础设施。这项研究是通过对个人作品集的深入了解,来分门别类的鉴定费用增长因素。通过超过20个州际公路机构的验证,这18种分门别类的基本影响因素对各类建设项目的成本影响都适用。这些因素描绘了有据可依成本超支问题的原因。工程师在估计未来项目的成本因素,寻求减少它们的方法时考虑这些影响因素可以,提高他们的成本估算和项目预算的准确性。

介绍:历史的大型建筑工程已经饱受成本和时间超支的困扰(Flyvbjerg李玮2002)。在很多情况下,最后的项目成本一直高于估计的成本,发布时间可能在最初工程计划时,最终设计时,抑或在开始建设时“Mega项目需要更多的前提研究来避免成本超支。” (2002)早期的项目成本估计与最终报价结果或最终工程成本可以存在显著差异。在这个时间跨度里,项目启动发展概念和最终结束之间,许多因素会影响施工项目最终成本。这段时期通常持续几年,但对于高度复杂和技术挑战性的项目可以轻易超过10年。组织面临重大挑战的项目预算控制的时间跨度将从开始一直持续到完成的项目建设。开发成本估计准确反映工程范围、经济条件、社会利益协调和宏观经济条件提供基线成本管理,可以用来传递学科的设计过程。项目可以兑现预算,但需要一个好的开始,一个估算成本超支因素的意识,及项目管理法则。当缺少法则的时候,在一个项目上显著的成本增长会毁坏整体计划,因为经费将不适应未来项目的建设。

History-Holland隧道的案例研究

过去的历史经验,可以为建设一个优质项目的预算提供更好的理解。同样使工程造价增长的问题和经验都可以从过去的事实中学到。荷兰隧道,当它在1927年开放时,是最长的水下隧道,它也是人类建筑史第一个机械通气的海底隧道。它的初始成

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本的估计是由著名的土木工程师George Washington Goethals做出的。回顾荷兰隧道工程,它突出反映了一个具有争议性的问题:关系到对复杂重大工程建设预算的估计和实际成本时,即使是最杰出的工程师也会在评估一个超过本身物理特性的工程的启动成本时遇到麻烦。许多次没有认识到工程外部物理配置的运作成本问题,纽约和新泽西委员会在1918年建设一个交通隧道在河里“敦促新隧道,哈德逊”,“让国人共用去球衣的隧道。”汽车是为主导的交通方式,隧道被决定用于通车。正因如此,隧道会使用新通风技术来净化内燃机所产生的废气。11项设计被考虑在隧道建设里,最值得注意的是,一个由工程师负责整理最近为完成巴拿马运河建设的George Washington Goethals。他想像一个单一的、二层隧道与对方的交通每一层。Goethals做出规划项目成本估计1200万美元和3年建筑时间。第一次世界大战已经耗尽了很多国家的钢铁产品,所以他的设计,利用水泥街区为隧道结构的外壳。他的设计是领先的计划“赫德森车辆管。”(1919)。但他在别处有责任,并且不是这个项目的总设计师。他以荷兰克利头工程连同董事会的5号州际公路工程咨询的名字。荷兰带着在构建地铁、隧道项目的丰富经验来到在纽约的这个项目。“Goethals”计划的估计,这个项目的成本有120万美元。荷兰基于他的研究分析,在1920年2月份发表了一份报告,报告中说:他的发现并不是什么预期的好。荷兰发现:

•原来Goethals报告中7.47米的宽度不能适应车流。 •混凝土块不能承受隧道结构附件。

•Goethals所需的施工方法的设计完全是未经证实的。 •估计的建设成本是非常低的。 •工作不能在3年内完成。

咨询工程师的一致支持了荷兰的分析。提出了一个荷兰自己的设计,支持的咨询工程师一致通过。荷兰的设计,这是一个大范围的变化,称为“双铸铁管”。一个好处是将根据建设在东方河的隧道的经验和比哈德逊河更进一步。荷兰估计费用28,669,000美元,请求28,669,000美元的球衣试验,施工时间在三年多。

讨论了隧道的设计分歧已经持续了超过一年,创造了纽约和新泽西的佣金和延缓工作一个时间表改变。一个合同授予了新泽西侧进一步推迟启动建设和增加超过一半的100万美元的成本。在纽约的建设开始于1920年10月之后,在1921年12月底,在新泽西的一部分隧道出价“允许球衣方式。”隧道委托的竣工日期是1926年12月31日。现在的施工进度已增加到5年。估计项目成本在早年的施工的蠕变、进度拖延、范围和通货膨胀上增加了多次。增加的交通量预测需要更大的出入口广场和获取更多的权利的方式“汽车隧道在增加”。然后材料和劳动力成本将另一个600万美元增加到项目的通货膨胀。在1924年,成本已经提高1400万美元,车辆隧道费用高达1400万美元。由于功能和美学的因素范围蠕变,更复杂的道路设计方法,拓宽路面

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的途径,增加了更多的成本建筑治疗范围蠕变。重新设计的通风系统加15.24公分的隧道直径及4,422,000美元的支出。荷兰也决定替代铸钢为铸铁增加强度和安全因素的多隧道范围蠕变。最后,在新泽西的通风井不得不重新设计相应的基础,随着他们的付出的代价,因为意想不到700,000美元的土地条件,所有的这些变化增加了42.5亿美元,超过估计。新的资金拨款,它被认为足以完成项目,但到了二月,另一项增加3,200,000美元,隧道申请另外3,200,000美元。委员会解释说,这是新的成本是由于增加成本挑战劳动和材料成本控制。这时荷兰总工程师死于心脏衰竭,他的助手,Milton H.Freeman接替总工程师4个月后死于肺炎。Ole Singstad,设计通风系统的设计师便成了总工程师并且把项目完成。有三个不同的总工程师,耗费5个月是可以遇见混乱。1924年4月份,水从一个裂缝冲进其中一个隧道,迫使工人匆忙逃跑的意外情况。最后一笔专用款项被使用在早期1927年工程,总造价48,400,000美元。1927年11月13日隧道正式投入使用。隧道建造工作开始于7年前。

方法论

增长的成本因素导致项目成本增长已通过大样本的研究记录,研究证实了单独或团体。每个因子的概念,提出了一种挑战,一个机构对项目的成本估计准确。作为一项大型研究试图提高成本预算和成本管理的概念,从项目的投标的一天,一个文献进行彻底的了鉴定费用估计影响因素等(2006)。文献包括勘探研究报告、出版物、政府报告、新闻文章,和其他公开来源。竣工后的文献回顾的因素进行了分析和分类的人员进入成本因素所经历的交通建设项目的增加。这是由三角在多个调查者或资料来源暗示同一因素。这种分类方法把个人因素,在先前的研究已经确定,并建立了全球框架,用于解决这个问题的工程造价升级。在最后的分类的成本因素框架是通过验证升级的数据,从采访了三角法等20多个国家SHAS公路部门先前的工程支持识别的因素包括电话采访了50个沙斯党等面谈的准备和测试仪器是最初在现场采访两个沙斯党。修订后的采访乐器被送到了沙斯党面谈前,以便他们能准备。在随访现场为五个人访谈和通过沙斯党通过一组“同伴交流”剩下的随访电话。在所有情况下,研究人员追踪采访的协议,以确保在数据采集。结果分类的成本因素可以帮助升级项目业主和工程专业人员将注意力集中在这个关键问题,导致成本估算不精确。

成本因素的分类升级

从分析方法生成的已有研究成果的基础上,认为面谈来创建一个分类的成本的原因的规模。一个更好的理解成本因素是理解升级的部队各因素的驱动因素或者来源。在这层了解可能的设计策略,为应对这些成本升级的因素。这个因素影响的评估中,每一个项目都是由自然发展阶段的内部和外部的因素在起作用,控制成本升级的机构/业主为内部,而现有的直接控制的因素外,该机构/业主分为外部。这个报告的因素

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为不应被视为暗示一水平的影响并构建提供了潜在的因素。总结成逻辑划分的因素,并帮助在可视化分类项目成本预算是如何影响。值得注意的一个因素,指出问题劳动和材料成本的估计,但是大部分的因素,是指出“影响项目范围和影响”的时机。

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Construction Project Cost Escalation Factors

J.Mgmt.

Abstract: Construction projects, private and public alike, have a long history of cost escalation.Transportation projects, which typically have long lead times between planning and construction, are historically underestimated, as shown through a review of the cost growth experienced with the Holland Tunnel.Approximately 50% of the active large transportation projects in the United States have overrun their initial budgets.A large number of studies and research projects have identified individual factors that lead to increased project cost.Although the factors identified can influence privately funded projects the effects are particularly detrimental to publicly funded projects.The public funds available for a pool of projects are limited and there is a backlog of critical infrastructure needs.Therefore, if any project exceeds its budget other projects are dropped from the program or the scope is reduced to provide the funds neceary to cover the cost growth.Such actions exacerbate the deterioration of a state’s transportation infrastructure.This study is an anthology and categorization of individual cost increase factors that were identified through an in-depth literature review.This categorization of 18 primary factors which impact the cost of all types of construction projects was verified by interviews with over 20 state highway agencies.These factors represent documented causes behind cost escalation problems.Engineers who addre these escalation factors when aeing future project cost and who seek to mitigate the influence of these factors can improve the accuracy of their cost estimates and program budgets

Introduction:Historically large construction projects have been plagued by cost and schedule overruns Flyvbjerg et al.2002.In too many cases, the final project cost has been higher than the cost estimates prepared and released during initial planning, preliminary engineering, final design, or even at the start of construction “Mega projects need more study up front to avoid cost overruns.” The ramifications of differences between early project cost estimates and bid prices or the final cost of a project can be significant.Over the time span between project initiation concept development and the completion of construction many factors may influence the final project costs.This time span is normally several years in duration but for the highly complex and technologically challenging

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projects it can easily exceed 10 years.Organizations face a major challenge in controlling project budgets over the time span between project initiation and the completion of construction.The development of cost estimates that accurately reflect project scope, economic conditions, and are attuned to community interest and the macroeconomic conditions provide a baseline cost that management can use to impart discipline into the design proce.Projects can be delivered on budget but that requires a good starting estimate, an awarene of factors that can cause cost escalation, and project management discipline.When discipline is lacking, significant cost growth on one project can raze the larger program of projects because funds will not be available for future projects that are programmed for construction History—Holland Tunnel Case Study A history of past project experiences can serve one well in understanding the challenges of delivering a quality project on budget.Repeatedly, the same problems cause project cost escalation and much wisdom can be gained by studying the past.The Holland Tunnel was, when it opened in 1927, the longest underwater tunnel ever constructed and it was also the first mechanically ventilated underwater tunnel.Its initial cost estimate was made by the renowned civil engineer George Washington Goethals.A review of the Holland Tunnel project serves to highlight the critical iues aociated with estimating the costs of large complex projects and the fact that even the most distinguished engineers have trouble aeing cost drivers beyond the physical characteristics of a project.Many times there is no recognition of the cost drivers operating outside the project’s physical configuration.A joint New York and New Jersey commiion in 1918 recommended a transportation tunnel under the river “Urges new tunnel under the Hudson.” 1918; “Ask nation to share in tunnel to Jersey.” 1918.The automobile was emerging as the predominate means of transportation and it was decided that this tunnel should be for vehicular traffic.As a result the tunnel would employ new ventilation technologies to purge the exhaust gases produced by the internal combustion engine. Eleven designs were considered for the tunnel, most notably, one by the engineer recently responsible for finishing the Panama Canal, George Washington Goethals.He envisioned a single, bilevel tunnel with opposing traffic on each level.Goethals made a planning project cost estimate of $12 million and 3 years for construction.World War I had consumed much of the nation’s steel and iron production, so his design made use of cement blocks as the tunnel’s structural shell.His design was the frontrunning plan “Hudson vehicle tube.” but he had responsibilities elsewhere and was not named chief engineer for the project.Clifford M.Holland was named to head the

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project along with a board of five consulting engineers “Name interstate tunnel engineers.” 1919.Holland came to the project with vast experience in constructing subways and tunnels in New York.The cost of the project was taken to be $12 million, Goethals’ planning estimate.Holland produced a report in February of 1920 based on his analysis of the Goethals’ design of the project.His findings were not what had been expected.Holland found • Goethals’ width of 7.47 m would not accommodate the volume of traffic.• Concrete blocks would not withstand the structural loads exerted on the tunnel.• The construction methods required by Goethals’ design were completely untried.• The estimated cost of construction was groly low.• The work could not be completed in 3 years.The board of consulting engineers gave unanimous support for Holland’s analysis.Holland then presented a design of his own which was supported unanimously by the consulting engineers.Holland’s design, which was a major scope change, called for twin cast-iron tubes.One advantage was that construction would follow established methods of tunnel construction that had been implemented for rail tunnels under the East River and further up the Hudson.Holland estimated the cost at $28,669,000 “Asks $28,669,000 for Jersey tube.” 1920 and construction time at 31/2 years.

Debate about the tunnel design continued for more than a year creating disagreements between the New York and New Jersey Commiions and delaying the work—a schedule change.A disagreement about awarding a contract on the New Jersey side further delayed the start of construction and added over half of a million dollars in cost.Construction started on the New York side in October of 1920 and in late December 1921 the New Jersey portion of the tunnel was bid “Way all cleared for Jersey tunnel.” The mandated completion date was December 31, 1926.The construction schedule had now grown to 5 years.Estimated project cost increased multiple times throughout the early years of construction as a result of scope creep, schedule delays, and inflation.Increased traffic forecast neceitate larger entrance/exit plazas and acquisition of more right of way “Vehicular tube is growing.” 1923.Then increases in material and labor costs had added another $6 million to the project inflation.By the beginning of 1924, reestimated costs had been increased by $14,000,000 “Vehicular tunnel cost up $14,000,000.” 1924 due to functional and aesthetic factors scope creep.More intricate roadway designs for approaches, widening of the approach roadways, and architectural treatments increased the costs more scope creep.Redesign of the ventilation system added 15.24 cm to the tunnel

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diameter and $4,422,000.Holland also decided to substitute cast-steel for castiron to increase the strength and safety factors of the tunnel more scope creep.Last, the New Jersey ventilation shafts had to be redesigned along with their corresponding foundations at a cost of $700,000 due to unexpected soil conditions unforeseen conditions.All of these changes increased the estimate to over $42.5 million.New funds were appropriated and it was believed that these were sufficient to complete the project, but by February of 1926, there was another increase of $3,200,000 “$3,200,000 more asked for tunnel.” The commiion explained that the new costs were due to increases in labor and material costs challenge in controlling cost.At this time Holland died of heart failure and his aistant, Milton H.Freeman, took over as chief engineer only to die of pneumonia 4 months later.Ole Singstad, the designer of the ventilation system then became chief engineer and brought the project to completion.Having three different chief engineers within 5 months created confusion unforeseen events.In April of 1924 water rushed into one of the tunnels from a leak forcing workers to make a hasty escape more unforeseen conditions.A final appropriation was requested in early 1927 brought the total project cost to $48,400,000.On November 13 of 1927 the tunnel officially opened “Work on tunnel began 7 years ago.” Methodology The cost escalation factors that lead to project cost growth have been documented through a large number of studies.Studies have identified factors individually or by groups.Each factor presents a challenge to an agency seeking to produce accurate project cost estimates.As part of a larger study seeking to improve cost estimates and management of costs from project conception to bid day, a thorough literature review was conducted to identify factors that influence cost estimates Anderson et al.2006.The literature review included exploration of research reports and publications, government reports, news articles, and other published sources.Upon completion of the literature review the factors were analyzed and categorized by the researchers into factors that drive the cost increases experienced by transportation construction projects.This was accomplished by triangulation where multiple investigators or data sources suggested the same factor.This categorization took the individual factors which had been identified in previous research and established a global framework for addreing the iue of project cost escalation.Upon final categorization the cost escalation factor framework was verified through triangulation of data from interviews with more than 20 state highway agencies SHAs around the nation .A previous project that supported identification of the factors had included telephone interviews with all 50 SHAs Schexnayder et al.2003 .An interview

8 大连海洋大学土木工程毕业设计

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instrument was prepared and tested initially during onsite interview with two SHAs.The revised interview instrument was then sent to the SHAs before the interview so that they could prepare.The interviews were conducted onsite for five SHAs through individual interviews and through a group “peer exchange.” The remaining interviews were conducted by telephone.In all cases, the researchers followed the interview protocol to ensure consistency in data collection.The resulting categorization of cost escalation factors can help project owners and engineering profeionals focus their attention on the critical iues that lead to cost estimation inaccuracy.Cost Escalation Factor Claification The triangulation analysis considered methodologies from past studies and interviews to create a categorization for the causes of cost escalation.A better understanding of the cost escalation factors is achieved through understanding the forces driving each factor or where the factor originates.With this understanding it is poible to design strategies for dealing with these cost escalation factors.The factors that affect the estimate in each project development phase are by nature internal and external.Factors that contribute to cost escalation and are controllable by the agency/owner are internal, while factors existing outside the direct control of the agency/owner are claified as external. The presentation order of the factors should not be taken as suggesting a level of influence is constructed to provide an over arching summary of the factors.It summarizes the factors into logical divisions and claifications and helps in visualizing how project cost estimates are affected.It is important to note that one of the factors points to problems with estimation of labor and material cost, but most of the factors point to “influences” that impact project scope and timing.

推荐第3篇:外文翻译

数字通信第四版

Digital Communications,Fourth Edition

作者:John Proakis 起止页码:1-10

出版日期(期刊号):2003年1月 出版单位:电子工业出版社

外文翻译译文:

第1章 引 言

在本书中,我们将介绍作为数字通信系统分析和设计基础的基本原理。数字通信的研究主题包括数字形式的信息从产生该信息的信源到一个或多个目的地的传输问题。在通信系统的分析和设计中,特别重要的是信息传输所通过的物理信道的特征。信道的特征-般会影响通信系统基本组成部分的设计。下面阐述一个通信系统的基本组成部分及其功能。

1.1数字通信系统的基本组成部分

图1-1-1 显示了一个数字通信系统的功能性框图和基本组成部分。输出的可以是模拟信号,如音频或视频信号;也可以是数字信号,如电传机的输出,该信号在时间上是离散的,并且只有有限个输出字符。在数字通信系统屮,由信源产生的消息变换成二进制数字序列。理论上,应当用尽可能少的二进制数字表示信源输出(消息)。换句话说.我们要寻求一种信源输出的有效的表示方法,使其很少产生或不产生冗余。将模拟或数宇信源的输出有效地变换成二进制数字序列的处理过程称为信源编码或数据压缩。

由信源编码器输出的二进制数字序列称为信息序列,它被传送到信道编码器。信道编码器的目的是在二进制信息序列中以受控的方式引人一些冗余,以便于在接收机中用来克服信号在信道中传输时所遭受的噪声和干扰的影响。因此,所增加的冗余是用来提高接收数据的可靠性以及改善接收信号的逼真度的。实际上,信息序列中的冗余有助于接收机译出期望的信息序列。例如,二进制信息序列的一种(平凡的)形式的编码就是将每个二进制数字简单重复m次.这里m为一个正整数。更复杂的(不平凡的)编码涉及到一次取k个信息比特,并将毎个k比特序列映射成惟一的n比特序列,该序列称为码字。以这种方式对数据编码所引人的冗余度的大小是由比率n/k作来度擞的。该比率的倒数,即k/n,称为码的速率或简称码率。信道编码器输出的二进制序列送至数宇调制器,它是通信信道的接口。因为在实际中遇到的几乎所有的通信信道都能够传输电信号(波形),所以数字调制的主要目的是将二进制信息序列映射成信号波形。为了详细说明这一点,假定已编码的信息序列以均匀速率R(b/s)―次一个比特传输,数字调制器可以简单地将二进制数字“0”映射成波形s0(t)而二进制数字“1”映射成波形s1(t)。在这种方式中,信道编码器输出的毎一比特是分别传输的。我们把它称为二进制调制。另一种方式,调制器目一次传输b个已编码的信息比特,其方法是采用M = 2s个不同的波形ST(t)i=1,2,…,M,每一个波形用来传输2s个可能的b比特序列中的一个序列。我们称这种方式为M元调制(M〉2)。注意,每b/R秒就有一个新的b比特序列进入调制器。因此,当信道比特率R固定,与一个b比特序列相应的似个波形之一的传输时间量是二进制调制系统时间周期的b倍。

图1-1-1

数字通信系统的基本模型

通信信道是用来将发送机的信号发送给接收机的物理媒质。在无线传输中,信道可以是大气(自由空间)另一方面,电话信道通常使用各种各样的物理媒质,包括有线线路、光缆和无线(微波)等。无论用什么物理媒质来传输信息,其基本特点是发送信号随机地受到各种可能机理的恶化,例如由电子器件产生的加性热噪声、人为噪声(如汽车点火噪声)及大气噪声(如在雷赛雨时的闪电)。

在数字逋信系统的接收端,数字解调器对受到信道恶化的发送波形进行处理,并将该波形还原成一个数的序列,该序列表示发送数据符号的估计值〔二进制或M元〕。这个数的序列披送至信道译码器,它根据信进编码器所用的关于码的知识及接收数据所含的冗余度重构初始的信息序列。

解调器和译码器工作性能好坏的—个度量是译码序列中发生差错的频度。更准确地说,在译码器输出端的平均比特错误概率是解调器-译码器組合性能的一个度量。一般地,错误概率是下列各种因素的函数:码特征、用来在信道上传输信息的波形的类型、发送功率信道的特征(即噪声的大小、干扰的性质等)以及解调和译码的方法。在后续各章中将详细讨论这些因素及其对性能的影晌。

作为最后一步,当需要模拟输出时,信源译码器从信道译码器接收其输出序列并根据所采用的信源编码方法的有关知识重构由信源发出的原始信号。由于信道译码的差错以及信源编码器可能引入的失真,在信源译码器输出端的信号只是原始信源输出的—个近似。在原始信号与重构信号之间的信号差或信号差的函数是数字通信系统引入失真的一种度量。

1.2通信信道及其特征

正如前面指出的,通信信道在发送机与接收机之间提供了连接。物理信道也许是携带电信号的一对明线;或是在已调光波束上携带信息的光纤;或是水下海洋信道其中信息以声波形式传输;或是自由空间,携带信息的信号通过天线在空间辐射传输。可被表征为通信信道的其他媒质是数据存储媒质如磁带、磁盘和光盘。

在信号通过任何信道传输中的一个共同的问题是加性噪声。一般地,加性噪声是由通信系统内部组成元器件所引起的,例如电阻和固态器件。有时将这种噪声称为热噪声。其他噪声和干扰源也许是系统外面引起的,例如来自信道上其他用户的干扰。当这样的噪声和干扰与期望信号占有同频带时,可通过对发送信号和接收机中解调器的适当设计来使它们的影响最小。信号在信道上传输时可能会遇到的其他类型损伤有信号衰减、幅度和相位失真、多径失真等。

可以通过增加发送信号功率的方法使噪声的影响最小。然而,设备和其他实际因素限制了发送信号的功率电平,另一个基本的限制是可用的信道带宽。带宽的限制通常是由于媒质以及发送机和接牧机中组成器件和部件的物理限制产生的。这两种限制因素限制了在任何通信信道上能可靠传输的数据量,我们将在以后各章中讨论这种情况。下面描述几种通信信道的重要特征。

1.有线信道

电话网络扩大了有线线路的应用,如话音信号传输以及数据和视频传输。双绞线和同轴电缆是基本的导向电磁信道,它能提供比较适度的带宽。通常用来连接用户和中心机房的电话线的带宽为几百千赫(khz)另一方面同轴电缆的可用宽带是几兆赫(Mhz)。信号在这样的信道上传输时,其幅度和相位都会发生失真,还受到加性噪声的恶化。双绞线信道还易受到来自物理邻近信道的串音干扰。因为在全国和全世界有线信道上通信在日常通信中占有相当大的比例,因此,人们对传输特性的表征以及对信号传输时的幅度和相位失真的减缓方法作了大量研究。在第9章中,我们将阐述最佳传输信号及其解调的设什方法。在笫10章和第11章中,我们将研究信道均衡器的设计,它是用来补偿信道的幅度和相位失真的。

2.光纤信道

光纤提供的信道带宽比同轴电缆信道大几个数量级。在过去的20年屮,已经研发出具有较低倌号衰减的光缆,以及用于信号和信号检测的可靠性光子器件。这些技术上的进展导致了光纤信道应用的快速发展,不仅应用在国内通信系统中,也应用于跨大西洋和跨太平洋的通信中。由于光纤信道具有大的可用带宽,因此有可能使电话公司为用户提供宽系列电店业务,包括话音、数据、传真和视频等。

在光纤通信系统中,发送机或调制器是一个光源.或者是发光二极管(LED)或者是激光。通过消息信号改变(调制)光源的强度来发送信息。光像光波一样通过光纤传播,并沿着传输路径被周期性地放大以补偿信号衰减(在数宇传输中,光由中继器检测和再生)。在接收机中,光的强度由光电二极管检测,它的输出电信号的变化直接与照射到光电二极管上的光的功率成正比。光纤信道中的噪声源是光电二极管和电子放大器。

3.无线电磁信道

在无线通信系统中,电磁能是通过作为辐射器的天线耦合到传播媒质的。天线的物理尺寸和配置主要决定于运行的频率。为了获得有效的电磁能量的辐射,天线必须比波长的1/10更长。因此,在调幅(AM)频段发射的无线电台,譬如说在f=1MHz时(相当于波长= C/f=300m)要求天线至少为30m。无线传输天线的其他重要特征和属性将在第5章阐述。

在大气和自由空间中,电磁波传播的模式可以划分为3种类型,即地波传播、天波传播和视线传播。在甚低频(VLF)和音频段,其波长超过10km,地球和电离层对电磁波传播的作用如同波导。在这些频段,通信信号实际上环绕地球传播,由于这个原因,这些频段主要用来在世界范围内提供从海洋到船舶的导航帮助。在此频段中可用的带宽较小(通常是中心频率的1% ~10%)因此通过这些信道传输的信息速率较低,且一般限于数字传输。在这些频率上,最主要的一种噪声是由地球上的雷暴活动产生的,特别是在热带地区。干扰来自这些频段上的用户。

在高频(HF)频段范围内,电磁波经由天波传播时经常发生的问题是信号多径。信号多径发生在发送信号经由多条传播路径以不同的延迟到达接收机的时侯,一般会引起数字通信系统中的符号间干扰。而且经由不同传播路径到达的各信号分量会相互削弱,导致信号衰落的现象.许多人在夜晚收听远地无线电台广播时会对此有体验。在夜晚,天波是主要的传播模式。HF频段的加性噪声是大气噪声和热噪声的组合。

在大约30MHZ之上的频率,即频段的边缘,就不存在天波电离层传播。然而,在30~60MHZ频段有可能进行电离层散射传播,这是由较低电离层的信号散射引起的。也可利用在40~300MHZ频率范围内的对流层散射在几百英里的距离通信。对流层散射是由在10mile或更低高度大气层中的粒子引起的信号散射造成的,一般地,电离层散射和对流层散射具有大的信号传播损耗,要求发射机功率大和天线比较长。

在30MHZ以上频率通过电离层传播具有较小的损耗,这使得卫里和超陆地通信成为可能。因此,在甚高频(VHF)频段和更高的频率,电磁传播的最主要模式是LOS传播。对于陆地通信系统这意味着发送机和接收机的天线必须是直达LOS,没有什么障碍。由于这个原因VHF和特高频(UHF)频段发射的电视台的天线安装在髙塔上,以达到更宽的覆盖区域。

一般地LOS传播所能覆盖的区域受到地球曲度的限制。如果发射天线安装在地表面之上H米的高度,并假定没有物理障碍(如山)那么到无线地平线的距离近似为d=15H KM,例如电视天线安装在300m高的塔上.它的覆盖范围大约67km另一个例子,工作在1GHZ以上频率,用来延伸电话和视频传输的微波中继系统将天线安装在离塔上或高的建筑物顶部。

对工作在VHF和UHF频率范围的通信系统限制性能的最主要噪声是接收机前端所产生的热噪声和天线接收到的宇宙噪声。在10GHZ以上的超髙频(SHF)频段,大气层环境在信号传播中担负主要角色。例如,在10GHZ频率,衰减范围从小雨时的0.003 dB/KM左右到大雨时的0.3dB/KM;在100GHZ,衰减范围从小雨时的0.1dB左右到大雨时的6dB左右。因此,在此频率范围,大雨引起了很大的传播损耗,这会导致业务中断(通信系统完全中断)。

在极高频(EHF)频段以上的频率是电磁频谱的红外区和可见光区,它们可用来提供自由空间的LOS光通信。到目前为止,这些频段已经用于实验通信系统,例如,卫星到卫星的通信链路。

4.水声信道

在过去的几十年中.海洋探险活动不断增多。与这种增多相关的是对传输数据的需求。数据是由位于水下的传感器传送到海洋表面的,从那里可能将数据经由卫星转发给数据采集中心。

除极低频率外,电磁波在水下不能长距离传播。在低频率的信号传输的延伸受到限制,因为它需要大的且功率强的发送机。电磁波在水下的衰减可以用表面深度来表示,它是信号衰减l/e的距离。对于海水,表面深度 250/f,其中f以HZ为单位。例如,在10 khz上,表面深度是2.5m。声信号能在几十甚至几百千米距离上传播。

水声信道可以表征为多径信道,这是由于海洋表面和底部对信号反射的缘故。因为波的运动,信号多径分量的传播延迟是时变的,这就导致了信号的衰落。此外,还存在与频率相关的衰减,它与信号频率的平方近似成正比。声音速度通常大约为1 500m/s,实际值将在正常值上下变化,这取决于信号传播的深度。

海洋背景噪声是由虾、鱼和各种哺乳动物引起的。在靠近港口处,除了海洋背景噪声外也有人为噪声。尽管有这些不利的环境,还是可能设计并实现有效的且高可靠性的水声通信系统,以长距离地传输数字信号。

5.存储信道

信息存储和恢复系统构成了日常数据处理工作的非常重要的部分。磁带(包括数字的声带和录像带)、用来存储大量计箅机数据的磁盘、用作计箅机数据存储器的光盘以及只读光盘都是数据存储系统的例子,它们可以表征为通信信道。在磁带或磁盘或光盘上存储数据的过程,等效于在电话或在无线信道上发送数据。回读过程以及在存储系统中恢复所存储的数据的信号处理等效于在电话和无线通信系统中恢复发送信号。

由电子元器件产生的加性噪声和来自邻近轨道的干扰一般会呈现在存储系统的回读信号中,这正如电话或无线通信系统中的情况。

所能存储的数据量一般受到磁盘或磁带尺寸及密度(每平方英寸存储的比特数)的限制,该密度是由写/读电系统和读写头确定的。例如在磁盘存储系统中,封装密度可达每平方英寸比特(1 in=2.54cm)。磁盘或磁带上的数据的读写速度也受到组成信息存储系统的机械和电子子系统的限制。

信道编码和调制是良好设计的数字磁或存储系统的最重要的组成部分。在回读过程中,信号被解调。由信道编码器引入的附加冗余度用于纠正回读信号中的差错。

1.3 通信信道的数学模型

在通过物理信道传输信息的通信系统设计中,我们发现,建立一个能反映传输媒质最重要特征的数学模型是很方便的。信道的数学模型可以用于发送机中的信道编码器和调制器,以及接收机中的解调器和信道译码器的设计。下面,我们将简要的描述信道的模型,它们常用来表征实际的物理信道。 1.加性噪声信道

通信信道最简单的数学模型是加性噪声信道,如图1-3-1所示。在这个模型中,发送信号s(t)被加性随机噪声过程n(t)恶化。在物理上,加性噪声过程由通信系统接收机中的电子元部件和放大器引起,或者由传输中的干扰引起(正如在无线电信号传输中那样)。

如果噪声主要是由接收机中的元部件和放大器引起,那么,它可以表征为热噪声。这种模型的噪声统计地表征为高斯噪声过程。因此,该信道的数学模型通常称为加性高斯噪声信道。因为这个信道模型适用于很广的物理通信信道,并且因为它在数学上易于处理,所以是在通信系统分析和设计中所用的最主要的信道模型。信道的衰减很容易加入到该模型。信号通过信道传输而受到衰减时,接收信号是

r(t)s(t)n(t) 式中,是衰减因子。

图1-3-1 加性噪声信道

2.线性滤波器信道

在某些物理信道中,例如有线电话信道,采用滤波器来保证传输信号不超过规定的带宽限制,从而不会引起相互干扰。这样的信道通常在数学上表征为带有加性噪声的线性滤波器,如图1-3-2所示。因此,如果信道输入信号为s(t),那么信道输出信号是

r(t)s(t)c(t)n(t)

c()s(t)dn(t)

式中,c()是信道的冲激响应,表示卷积。

图1-3-2 带有加性噪声的线性滤波器信道 3.线性时变滤波器信道

像水声信道和电离层无线电信道这样的物理信道,它们会导致发送信号的时变多径传播,这类物理信道在教学上可以表征为时变线性滤波器。该线性滤波器可以表征为时变信道冲激响应c(τ;t),这里c(τ;t)是信道在t-τ时刻加入冲激而在τ时刻的响应。因此,τ表示“历时(经历时间)”变量。

上面描述的三种数学模型适当的表征了实际中的绝大多数物理信道。本书将这3 种模型用于通信系统的分析和设计。

1.4 数字通信发展的回顾与展望 值得注意的是,最早的电通信形式,即电报,是一个数字通信系统。电报由S•莫尔斯研制,并在1837年进行了演示试验。莫尔斯设计出一种可变长度的二进制码,其中英文字母用点划线的序列(码字)表示。在这种码中,较频繁发生的字母用短码字表示,不常发生的字母用较长的码字表示。因此,莫尔斯码是第三章所述可变长度信源编码方法的先驱。

差不多在40年之后,1875年,E博多设计出一种电报码,其中每一个字母编成一个固定长度为5的二进制码字。在博多码中,二进制码的元素是等长度的,且指定为传号和空号。

虽然莫尔斯在研制第一个点的数字通信系统(电报)中起了重要的作用,但是现在我们所指的现代数字通信系统起源于奈奎斯特的研究。奈奎斯特研究了再给定带宽的电报信道上,无符号间干扰的最大信号传输速率。他用公式表达了一个电报系统的模型,其中发送信号的一般形式为

s(t)anng(tnT)

式中,g(t)表示基本的脉冲形状,an是以速率1/T bit/s发送的二进制数据序列。奈奎斯特提出了带宽限于W Hz的最佳脉冲形状,并且在脉冲抽样时刻Kt(k=0,1,。。。)无符号间干扰的条件下的最大比特率。他得出结论:最大脉冲速率是2W脉2,冲/s,该速率称为奈奎斯特速率。

1.INTRODUCTION In this book, we present the basic principles that underlie the analysis and design of digital communication systems.The subject of digital communications involves the transmiion of information in digital form from a source that generates the information to one or more destinations.Of particular importance in the analysis and design of communication systems are the characteristics of the physical channels through which the information is transmitted.The characteristics of the channel generally affect the design of the basic building blocks of the communication system.Below, we describe the elements of a communication system and their functions.1-1 ELEMENTS OF A DIGITAL COMMUNICATION SYSTEM Figure 1-1-1 illustrates the functional diagram and the basic elements of a digital communication system.The source output may be either an analog signal, such as audio or video signal, or a digital signal, such as the output of a teletype machine, that is discrete in time and has a finite number of output characters.In a digital communication system, the meages produced by the source are converted into a sequence of binary digits.Ideally, we should like to represent the source output (meage) by as few binary digits as poible.In other words, we seek an efficient representation of the source output that results in little or no redundancy.The proce of efficiently converting the output of either an analog or digital source into a sequence of binary digits is called source encoding or data compreion.The sequence of binary digits from the source encoder, which we call the information sequence, is paed lo the channel encoder.The purpose of the channel encoder is to introduce, in a controlled manner, some redundancy in the binary information sequence that can be used at the receiver to overcome the effects of noise and interference encountered in the transmiion of the signal through the channel.Thus, the added redundancy serves to increase the reliability of the received data and improves the fidelity of the received signal.In effect, redundancy in the information sequence aids the receiver in decoding the desired information sequence.For example, a (trivial) form of encoding of the binary information sequence is simply to repeat each binary digit m times,where m is some positive integer.More sophisticated (nontrivial) encoding involves talcing k information bits at a time and mapping each k-bit sequence into a unique n-bit sequence, called a code word.The amount of redundancy introduced by encoding the data in this manner is measured by the ratio n/k.The reciprocal of this ratio, namely k/n, is called the rate of the code or,simply, the code rate.

The binary sequence at the output of the channel encoder is paed to the digital modulator, which serves as the interface to the communications channel.Since nearly all of the communication channels encountered in practice are capable of transmitting electrical signals (waveforms), the primary purpose of the digital modulator is to map the binary information sequence into signal waveforms.To elaborate on this point, let us suppose that the coded information sequence is to be transmitted one bit at a time at some uniform rate R bits/s.The digital modulator may simply map the binary digit 0 into a waveform s0(t) and the binary digit 1 into a waveform j,(i).In this manner,each bit from the channel encoder is lransmitted separately.We call this binary modulation.Alternatively, the modulator may transmit b coded information bits at a time by using M = 2s distinct waveforms j.(r), i = 0,1

M1 MHz (corresponding to a wavelength of A = cffr = 300m).requires an antenna of at least 30m.Other important characteristics and attributes of antennas for wirele transmiion are described in Chapter 5.

Figure 1-2-2 illustrates the various frequency bands of the electromagneticspectrum.The mode of propagation of electromagnetic waves in the atmo- sphere and in free space may be subdivided into three categories, namely,ground-wave propagation, sky-wave propagation, and line-of-sight (LOS) propagation.In the VLF and audio frequency bands, where the wavelengths exceed 10 km, the earth and the ionosphere act as a waveguide for electromagnetic wave propagation.In these frequency ranges, communication signals practically propagate around the globe.For this reason, these frequency bands are primarily used to provide navigational aids from shore to ships around the world.The channel bandwidths available in these frequency bands are relatively small (usually 1-10% of the center frequency), and hence the information that is transmitted through these channels is of relatively slow speed and generally confined to digital transmiion.A dominant type of noise at these frequencies is generated from thunderstorm activity around the globe,especially in tropical regions.Interference results from the many users of these frequency bands.Ground-wave propagation, as illustrated in Fig.1-2-3, is the dominant mode of propagation for frequencies in the MF band (0.3-3 MHz).This is the frequency band used for AM broadcasting and maritime radio broadcasting.In AM broadcasting, the range with groundwave propagation of even the more powerful radio stations is limited to about 150 km.Atmospheric noise,man-made noise, and thermal noise from electronic components at the receiver are dominant disturbances for signal transmiion in the MF band.Sky-wave propagation, as illustrated in Fig.1-2-4 results from transmitted signals being reflected (bent or refracted) from the ionosphere, which consists of several layers of charged particles ranging in altitude from 50 to 400 km above the surface of the earth.During the daytime hours, the heating of the lower atmosphere by the sun causes the formation of the lower layers at altitudes below 120 km.These lower layers, especially the D-layer, serve to absorb frequencies below 2 MHz, thus severely limiting sky-wave propagation of AM radio broadcast.However, during the night-time hours, the electron density in the lower layers of the ionosphere drops sharply and the frequency absorption that occurs during the daytime is significantly reduced.As a consequence, powerful AM radio broadcast stations can propagate over large distances via sky wave over the F-layer of the ionosphere, which ranges from 140 to 400 km above the surface of the earth.

A frequently occurring problem with electromagnetic wave propagation via sky wave in the HF frequency range is signal multipath.Signal multipath occurs when the transmitted signal arrives at the receiver via multiple propagation paths at different delays, tt generally results in intersymbol interference in a digital communication system.Moreover, the signal components arriving via different propagation paths may add destructively, resulting in a phenomenon called signal fading, which most people have experienced when listening to a distant radio station at night when sky wave is the dominant propagation mode.Additive noise at HF is a combination of atmospheric noise and thermal noise.Sky-wave ionospheric propagation ceases to exist at frequencies above approximately 30 MHz, which is the end of the HF band.However, it is poible to have ionospheric scatter propagation at frequencies in the range 30-60 MHz, resulting from signal scattering from the lower ionosphere.It is also poible to communicate over distances of several hundred miles by use of tropospheric scattering at frequencies in the range 40-300 MHz.Troposcatter results from signal scattering due to particles in the atmosphere at altitudes of 10 miles or le.Generally, ionospheric scatter and tropospheric scatter involve large signal propagation loes and require a large amount of transmitter power and relatively large antennas.Frequencies above 30 MHz propagate through the ionosphere with relatively little lo and make satellite and extraterrestrial communications poible.Hence, at frequencies in the VHF band and higher, the dominant mode of electromagnetic propagation is linc-of-sight (LOS) propagation.For terrestrial communication systems, this means that the transmitter and receiver antennas must be in direct LOS with relatively little or no obstruction.For this reason, television stations transmitting in the VHF and UHF frequency bands mount their antennas on high towers to achieve a broad coverage area.

In general, the coverage area for LOS propagation is limited by the curvature of the earth.If the transmitting antenna is mounted at a height h m above the surface of the earth, the distance to the radio horizon, auming no physical obstructions such as mountains, is approximately dr Thus,r represents the \"age\" (elapsed-time) variable.

The three mathematical models described above adequately characterize the great majority of the physical channels encountered in practice.These three channel models are used in this text for the analysis and design of communication systems.1-4 A HISTORICAL PERSPECTIVE IN THE DEVELOPMENT OF DIGITAL COMMUNICATIONS It is remarkable that the earliest form of electrical communication, namely telegraphy, was a digital communication system.The electric telegraph was developed by Samuel Morse and was demonstrated in 1837.Morse devised the variable-length binary code in which letters of the English alphabet are represented by a sequence of dots and dashes (code words).In this code, more frequently occurring letters are represented by short code words, while letters occurring le frequently are represented by longer code words.Thus, the Morse code*was the precursor of the variable-length source coding methods described in Chapter 3.Nearly 40 years later, in 1875, Emile Baudot devised a code for telegraphy in which every letter was encoded into fixed-length binary code words of length 5.In the Baudot code, binary code elements are of equal length and designated as mark and space.Although Morse is responsible for the development of the first electrical digital communication system (telegraphy), the beginnings of what we now regard as modern digital communications stem from the work of Nyquist(1924), who investigated the problem of determining the maximum signaling rate that can be used over a telegraph channel of a given bandwidth without intersymbol interference.He formulated a model of a telegraph system in which a transmitted signal has the general form

s(t)anng(tnT)

where g(t)represents a basic pulse shape and an is the binary data sequence of {±1} transmitted at a rate of 1/Tbits/s.Nyquist set out to determine the optimum pulse shape that was bandlimited to W Hz and maximized the bit rate under the constraint that the pulse caused no intersymbol interference at the sampling time klT.k =0, ±1, ±2 ……His studies led him to concludc that the maximum pulse rate is 2W pulses/s.This rate is now called Nyquist rate.

推荐第4篇:外文翻译

1.简介

虽然信息披露理论表明,公司治理与信息披露之间有正相关性,实证研究提供了混合的结果(王huainey,2013)。Brown等人(2011,153)指出,由于对公司治理的文献“已经有一个成熟的程度,大部分的改进将增量”。一般而言,仅限于一个国家的经验证据,有可能减少确定和推广研究成果的说服力,限制这一研究领域的理论发展。为了更好地理解公司治理与自愿性信息披露之间的关联,我们进行了64实证研究的荟萃分析。

我们的动机是调和现有的研究结果不一致和得出来自叙事的评论可能不是很明显的见解。在这样做时,我们提出了三个新的贡献。首先,我们补充的Pomeroy和Thornton的研究(2008)和García-Meca 和 Sánchez-Ballesta(2010)的研究通过研究董事会规模和组成,首席执行官对偶与审计委员会的关系。接下来,我们依靠知识,社会,环境和网络信息披露的建议和Sánchez-Ballesta (2010, 622)。最后,我们检查在实证文献中研究信息披露指数建设,披露的方法,解释变量的定义是否影响结果的报道。

我们的荟萃分析的结果表明,国家之间的位置影响董事会规模,该协会董事会的组成,首席执行官对偶性和自愿性信息披露。此外,我们发现,投资者保护,以及类型和方法的披露的影响首席执行官对偶性和自愿性信息披露的关系。最后,我们注意到,用测量解释变量代替出现董事会组成与自愿性信息披露之间的关系。

本文的其余部分安排如下:2节进行文献回顾,制定假设,第3节介绍了数据收集,第4节提出的方法,第5节中的结果,第6节总结。 2.文献回顾与假设的发展

董事会和审计委员会的特征是企业报告政策的关键决定因素(khlif和Samaha,2014;Chau 和 Gray,2010;Chen和Jaggi,2000)。在这一部分中,我们回顾了董事会规模,董事会组成,首席执行官对偶,审计委员会与自愿性信息披露之间的关系。 2.1.董事会规模

董事会规模可能在促进企业透明度中发挥了重要作用。例如,一个大规模的董事会有利于公司由于增加专业知识和可用资源(Hidalgo等人,2011)。专家权威的概念表明,大规模董事会允许多样的经验和观点,这可能提高董事会的监督能力,从而意味着更多的自愿披露(Gandia,2008)。

另一方面,Herman(1981)认为大规模的董事会越有可能是产生副作用。Lipton 和 Lorsh(1992)表明,安排会议并在董事会议上达成共识,是董事会规模越大越难达成的。因此,董事会的监控能力可能不太有效,从而会减少自愿性信息披露。

一些实证研究表明,董事会规模与自愿性信息披露之间的正关联(例如Abeysekera,2010;Allegrini 和 Greco,2013)。然而,其他研究工作(arcay和巴斯克斯,洛伦佐和加西亚桑切斯2005和普拉多,2010)找到一个两个变量之间无关紧要的联系。因此,我们制定以下无方向性的假说::

H1:董事会规模与自愿性信息披露之间的关联。 2.2.董事会组成

代理理论表明,独立董事会对董事会的监控活动的有效性有显著的影响(1983 Fama和Jensen,)。引用声誉效应,Samaha等人(2012)和patelli和 Principe(2007)认为,外部董事作为动力市场专家监控,通过提供更多的自愿披露可以获得更大的公众的尊重来建立自己的声誉。此外,García-Meca 和 Sánchez-Ballesta(2010)认为,独立董事在董事会成员将通过更多的自愿性信息披露的改进企业报告的政策(即,“多米诺效应”)。

相比之下,patelli和Principe(2007)认为,由于外部董事通常由控制股东任命,独立董事的监督作用将是有限的(demb和 Neubauer,1992)。在这些条件下,高比例的外部董事会对自愿性信息披露产生影响 经验证据对董事会组成和自愿披露之间的关系是不确定的。而 Adams 和 Hoain(1998)和

Cheng 和 Courtenay (2006)有明显的正相关关系自愿信息披露和董事会的组成,Abdelsalam 和 Street (2007)和 Eng 和 Mak(2003)之间呈负相关文件变量。因此,我们制定以下无方向性的假说: H2:董事会的组成与自愿性信息披露之间的关联。 2.3.首席执行官的对偶性

结合领导结构可以促进首席执行官防御(Pfeffer,1981),有助于利益的偏差(Kim, Al-Shammari, Kim和 Lee,2008)。Fama 和 Jensen的代理框架(1983)表明,一个统一的领导结构降低之间的决策控制分离的重要性(董事会主席)和决策管理(首席执行官)。因此,一个统一的领导结构可以减少制衡和妥协的独立董事会管理监督(khlif和Samaha,2014;Samaha等人,2012;cerbioni和parbonetti,2007)。另一方面,CEO具有私人信息处理与企业的竞争优势和内部条件优越的知识。因此,对偶性可以限制私人信息在首席执行官和董事会之间完整传递而导致更少的自愿性信息披露的成员(Kim等人,2008)。然而,安德森和安东尼(1986)指出,对偶性使领导明确地制定和实施企业战略,从而提高效率。他们认为,一个统一的领导结构降低了首席执行官和非首席执行官主席之间产生的信息共享成本和利益之间的冲突。支持者的对偶性也强调明确的权力和命令来减少冲突,提高决策的统一的重要性(Rhoades等人,2001)。因此,首席执行官对偶性可能会导致更多的自愿性信息披露。 对自愿性信息披露和首席执行官对偶性关系的实证证据是混合的。而e Allegrini 和 Greco (2013)和Li 等人(2008)文件的一个显着的负相关性首席执行官对偶性与自愿性信息披露之间,其他的研究(例如,Cheng和Courtenay, 2006; Haniffa 和 Cooke, 2002)报告一个微不足道的或正相关的变量。因此,我们制定以下无方向性的假说: H3:首席执行官对偶性与自愿性信息披露之间的关联。 2.4.审计委员会

审计委员会的主要作用是协助董事会监督公司政策报告(Pincus等人,1989)。khlif和Samaha(2014)和Samaha等人(2012)Arcay和Vazquez(2005)表明审计委员会在明确投资者需求义务和提供信息上起重要作用。就像在高层管理控制机制,审计委员会还确保增加自愿披露数量让高层管理者决策和行为的准确评估(艾格尼和格列柯,2013)并调整管理和股东利益(拉克施曼,2008)。蓝带报告(1999)和史密斯报告(2003)也证实了审计委员会在提高信息披露和发布股价敏感信息确保股东利益保护的质量监控委员会的活动中起着举足轻重的作用。因此,审计委员预计将提高公司报告政策。 一般来说,实证研究支持审计委员会特征与自愿性信息披露之间呈正相关(沙马里和苏丹巴拉等人,2010。200

6、Ho和Wong,2001)。然而,一些研究没有发现这种关联(Allegrini 和 Greco,2013;Mangena 和 Pike,2005)。因此,我们制定了以下无方向性假设: H4:审计委员会特征与自愿披露之间的关联。

2.5.调节董事会的关联变量,审计委员会特征与自愿性信息披露 考虑到六个潜在版主对于治理属性与自愿性信息披露之间的关系,我们超越了一个简单的统计汇总。首先,我们考虑三种大致自愿性信息披露的类型:全面披露,社会和环境披露,以及智力资本披露。全面披露包括不同类型的信息,如历史,经济,社会,环境和智力资本的信息。全面自愿性信息披露是专门面向对证券市场参与者和提高投资者的能力来预测未来的收益(Gelb 和 Zarowin,2002)。历史财政信息是全面信息披露得分的主要部分(LIM等人,2007)。关于智力资本信息,目标投资者需要是因为它涉及一个公司的未来前景和提供战略和竞争优势的信息(Meet等人,1995)。相反,社会和环境的信息披露由信息对企业的社会和环境行为信息主导。因此,这类信息具体表明了公司社会的合法性(Lim等人,2007)。 虽然这三种类型的披露满足各方面信息和目标信息的不同用户,但是不同的因素都会影响每种类型的信息(Lim等人,2007)。这与股东利润最大化,而不是为其他利益相关者的利益焦点对准的董事会尤其有影响(Adams等人,2011)。Wang 和 Dewhirst (1992)认为,董事会特征(例如,首席执行官对偶性和外部董事的比例)可能会影响董事会的利益定位,并因此,影响社会和环境信息披露。

Lim等人(2007)发现董事会特征对不同类型信息披露的影响不同。鉴于审计委员会和董事会成员通常被认为是代表股东利益(Ayuso和argandona,2007),他们更可能与投资者的需求相一致,因此强调财务和战略信息披露。另一方面,一个CEO也主持董事会,可能会降低财务信息披露来保护并巩固他/她的主导董事会的地位。此外,专有成本理论预测,CEO会尽量减少社会和环境信息披露在短期内提高企业绩效和提高自己的补偿。因此,我们制定以下假设:

H5:披露类型会干预董事会,审计委员会特征与自愿性信息披露之间的关系。

我们也建议,披露方法(年度报告和公司网站)可以适度的自愿性信息披露和检查治理属性之间的关系。根据 Marston 和 Shrives(1991);Beretta和bozzolan(2004),年报报表代表信息披露的主要载体,提供给公众最全面的财务报告。这些法定年度报告正式允许公司之间内容比较。相比之下,网络披露通常对各类利益相关者的要求随意和自由,但要求企业承担额外的准备费用和更新费用。因此,董事会和审计委员会强调正规和传统的通信信道(即年度报告披露)是个期望。因此,我们制定了以下假设:

H6:披露方法(年度报告和公司网站)干预在董事会,审计委员会特征与自愿性信息披露之间的关系。 5.1.董事会规模

董事会规模有平均的相关性为0.193(Z = 8.137)在0.146和0.239之间的置信区间。因此,研究结果支持假设H1。然而,只有41.659的观测方差分了抽样误差方差。这表明高度的异质性研究。这是也很明显从显著(P<0.01)64.810卡方统计量。为了减少异质性,我们进行进一步调节变量的测试。 6。结论

在这项荟萃分析中,我们研究了董事会规模,董事会的组成,首席执行官对偶性,审计委员会与自愿性信息披露之间的关系。我们还测试被披露类型的差异调节,方法和施工是否有关;在研究环境的差异;在测量差异变量的解释。我们荟萃分析结果表明,董事会,审计委员会和自愿披露呈正相关,而首席执行官对偶性对自愿性信息披露有显著的负效应。我们的亚组的荟萃分析结果的证据表明,国家的地理位置的温和派提供了董事会规模,董事会的组成,首席执行官对偶和自愿披露之间的关系。此外,披露类型,披露的方法和投资者的水平保护适度和自愿性信息披露的首席执行官对偶之间的关联。最后,在解释变量中定义的差异 董事会的组成与自愿性信息披露之间的关联。相对于我们的敏感性分析期间提供的证据,在2002之前,首席执行官两重性有显著的负与自愿披露的关联。然而,为以下2002个时期,首席执行官对偶对自愿性信息披露的影响不显著。 总的来说,我们的荟萃分析的结果强调了需要明确地考虑一个国家的地理位置,分析了董事会特征与自愿性信息披露之间的关联。此外,首席执行官对偶性对自愿信息披露有负面影响是设置高投资者保护意味着诉讼过程更明显,高质量的司法系统,降低了管理者披露的动机信息。

我们的研究结果的一个缺陷是由经济计量方法估计的影响大小范围造成的“苹果和桔子”问题。然而,最近的会计文献中广泛应用的荟萃分析和我们的分析是按照以前荟萃分析(例如 García-Meca 和 Sánchez-Ballesta, 2010)。另外,荟萃分析技术代表两个变量之间关联的一个简单的测试和如果主要研究不控制这样一个问题而不允许我们控制内生性或反向的因果关系。由于信息披露的实证研究,包括在我们的研究,不能解决这个问题,我们无法控制的内生性。未来研究的几种途径存在。第一,关于自愿性信息披露与公司治理之间的内生性问题需要更多的研究。第二,因为几乎所有的研究公司治理对自愿性信息披露之间的影响都排除了金融公司这个样品,财务公司的公司治理对自愿性信息披露的影响与非金融公司的一个重要区别是值得研究的。最后,董事会特征中的高管薪酬与自愿性信息披露之间的关系是未来研究的一个有趣的领域。

推荐第5篇:外文翻译

微孔的加工方法

正如宏观加工一样,在微观加工中孔的加工也许也是最常用的加工之一。孔的加工方法有很多种,每一种都有其优点和缺点,这主要取决于孔的直径、深度、工作材料和设备要求。这篇文章主要介绍了内冷却钻头钻孔、无冷却钻孔、插铣、电火花以及激光加工微孔的几种方法。

易于孔加工的操作

无论孔有多大,在加工时将冷却液导入到刀尖,这都有助于排屑并能降低刀具和工件表面产生的摩擦热。尤其是在加工深细孔时,有无冷却液对加工的影响更大,因为深细孔加工的刀具比较脆弱,再加上刀具对切屑的二次切削和切屑的堆积会积累大量的热,而热量是碳化物刀具的主要“天敌”,它会加快刀具的失效速度。

当使用外冷却液时,刀具本身会阻止切削液进入切削加工位置。也就是到3-5倍的直径深度后切削液就会很难流入到刀尖。副哈维工具有限公司的副总工程师杰夫戴维斯说,这时就该选用带有内冷却液的钻头。

另外,在加工小孔时采用的外冷却液的冷却方式产生的利要大于弊,当钻头进入工件时,已经流入孔的冷却液产生的压力有时会缴坏钻头,戴维斯说。

刀具生产商提供的标准钻头的直径从0.039到 0.125英寸,能加工深度小雨12倍的直径的深孔,同时提供直径从0.002到0.020英寸的不带内冷却液的钻头。

尽管有内冷却能力,但还是不够的,冷却液需要一定的流动速度从而能够将切屑清出孔外。戴维斯强调,冷却液的最低压力应为600-800磅/平方英寸,加工状况还会随着所施加的压力的增加而提高,他补充道。

为了防止这些冷却液通口被杂物堵塞,戴维斯还推荐在钻头加上一5微米孔径或更加精密的冷却液滤清器。

另外,他还推荐在加工孔时有必要在工件的上方先技工一个定心或导向孔,以防止刀具偏斜,并有助于保证所加工孔的垂直度。当选用定心钻时,应使选择的定心钻刀尖上的坡口角小于等于其后内冷钻的坡口角。定心钻的直径还要稍微大一些。例如,如果定心钻的坡口角为120,内冷却钻头的坡口角为140,并且定心钻的直径小于内冷却钻的直径。在加工时内冷却钻的拐角处会与定心孔干涉而容易脱落,戴维斯说:这将导致钻头损坏。

虽然没加强调,但是加工细深孔时,喙式进给是一种很好的加工方式。戴维斯建议,根据工件的材料不同。每次喙式进给的深度最好为孔径的30%--50%。这种加工方式便于排出切屑,使切屑不在加工孔中堆积。 润滑及冷却

为了更加有助于徘屑,戴维斯推荐在金属加工中使用油基金属切削液代替水基冷却液,因为油具有较高的润滑效果。但是如果车间更加青睐于使用水基冷却液,液体中应该包括EP(极压)添加剂,增加润滑和减少发泡。如果产生很多泡沫,戴维斯说,“切屑就不会按着预定的方式排出。”

他还补充道,另一种提高润滑并且提高刀具寿命的方法是道具涂层,例如氮铝化钛(TiAIN)。TiAIN具有很高的硬度,当钻削像不锈钢这样的难加工金属材料时,带有TiAIN涂层的刀具能有效的减少热冲击。

威斯康星洲简斯维尔微型刀具公司的总经理大卫伯顿,对微加工刀具的小批量涂层有不同的看法,他说:“对直径小于0.020英寸的刀具涂层,会对刀具的加工质量到刀具寿命等每一加工方面都产生消极影响”。因为小刀具涂层不能做的足够薄,这样涂层就会改变刀具的前角和后角,从而不利于加工。

不过,更薄的涂层的开发正在继续,伯顿表示,现在微型刀具公司除了生产销售微型铣刀、刨刀和微型钻头外,还在和其他公司合作致力于开发一种亚细微涂层。伯顿说:“我们计划这种涂层刀君会在六月到一年的时间内上市”。

微型钻公司的产品主要是用于电路板加工钻头,但也可用于有效的切屑金属。所有的刀具都没带内冷能力。“我有一个客户想要在不锈钢上面钻一个0.004英寸的孔,他当时非常惊讶这能用一把加工电路板的钻头完成”。伯顿还补充到,采用喙式进给并选择高的主轴速度可以提高钻头的效率。

微加工刀具要使用多高的转速,这主要依赖于车间所使用的数控机床和刀具的直径,所需的转速随刀具直径的增加而加快(注:切削速度公式为 sfm=刀具直径×0.26×主轴转速)。

虽然相对较低,但伯顿的客户也成功 的应用过每分钟5000转的加工速度。伯顿说:“我们建议我们的用户找到一个震动最小的最高转速-----最佳加工速度。”

为了减少震动,在用小的切削力通过刀具的前倾面的去除适当的金属时,应使渗入到工件中的切削载荷连续而充足,如果钻头承受的切削载荷太轻,刀具前倾面的磨损速度就会加快,刀具变钝,从而影响刀具的使用寿命。这在加工细孔时应更加注意。

“用户们常常使用较轻的切削载荷来延长刀具的使用寿命,”伯顿说,“这恰恰会加快切削刃的磨损,并在刀刃宽出切屑的位置形成圆弧,刀具会变得像磨削工具一样把材料强行除掉,只能成为废刀。”伯顿认为,直径大于0.001英寸的刀具切削抗力小于0.0001时,切削力抗力就已经太小了,即使刀具不会断裂,过早的摩擦也会导致刀具寿命缩短。

太多的跳动也可能是破坏性的,但是影响有多少还值得商榷。伯顿指出,公司打算设计一台具有0.0003英寸偏差的机器,用以建立室内最坏情况下的铣削场景,还将能够加工0.004英寸宽的槽。“这迟早会实现的”。

他还补充:“你还可以试想一下0.0003英寸的跳动和只有正常水平三分之一的切削载荷,也就是说0.0001到0.00015,刀具将会立即破坏,因为刀具的一个徘屑槽会承受所有的载荷,然后徘屑槽的后面就会破坏。”

他还指出,在钻孔时,小于0.0003英寸的偏差是可以接受的,因为当钻头深入孔内时,钻头末端的切削刃在外圆柱非加工表面的引导下会继续切削。偏差的最小值随着深度和直径比值的增加而迅速减少,这是因为当钻头越深入工件,徘屑槽的吸震能力越差。最后强烈的跳动导致刀柄绕着刀具的轴线转动,而刀尖还仍然保持稳定,从而产生是刀具最终断裂的集中应力。 插铣

虽然通常没有直径小于0.002英寸的标准微型钻头,但可以用微型端铣刀来“冲”孔。“每当人们想加工一个小于0.002英寸的孔时,他们可以选用端铣刀,效果也不错。”伯顿说道。但这样加工的孔不能太深,因为刀具体不长,没有大的深度直径比率,因此一把直径为0.001英寸的端铣刀只能加工最深0.20英寸的孔,而同样直径的钻头可以加工得更深,因为钻头的设计使载荷全部作用在刀尖上,进而传到刀柄上被吸收。

市面上能提供最小5微米的端铣刀,但是并没有大量销售。“当人们想买这样的刀具时,我非常严肃的试着说服他们不要买,因为我们不喜欢制作这样的刀具。”伯顿说到。这种刀具主要问题是。不但这种刀具的硬质合金齿处于亚细微尺寸,而且当一把刀有多个齿时,每个齿的尺寸还要保持一致。伯顿道:“一把直径5微米的端铣刀在其基体上就夹持大约10个刀齿。”

他还补充说,他曾经看到过带有0.微米的粉末冶金硬质合金刀具,这是商业上能提供齿的尺寸的一半,但它还包括0.5和0.6微米的小齿。“如果齿的尺寸不统一,小齿是发挥不出作用的。” 坠电火花加工

应用坠电火花的电火花加工是一种微孔加工方式。这不同于将电导线穿过工件的电火花加工方式,应用坠电火花加工的微孔更加精密和精确,但同时花费也会很高。

坠电火花加工深细孔时,要用一根导电管作为电极。加工小而浅的孔时,需要用到一根导线或棒,“我们尽量用导管做电极。位于密歇根州的牧野公司总经理Jeff Kiszonas说道,导管的排渣孔能使加工的孔有大的深度直径比,并能够在加工中将孔底的熔渣排出孔外。他又补充道”但是另一方面,没人能制造出小于一定直径的导管。“一些供应商能提供直径小于0.003英寸的导管可以加工出0.0038英寸的孔。

现在Makino公司生产的双边坠电火花加工设备能够加工出 0.00044 英寸的微孔,这种设备主要用于孔的精加工。最近,在日本这种机床的开发人员用两分钟加工了八个这样的孔,并用四十秒穿透了0.0010英寸厚的碳化钨板。加工电极为一个因钨合金棒,由于电火花加工中再电极和工件间存在放电间隙,所以,所加工孔的直径会比电极直径大0.00020英寸。

当加工上述尺寸的孔时,旋转的导棒上包裹着通电的放电导线。精加工时需要一个w轴附件,用来夹持电极导向的模具,另外还需要一个中间导向件,当电极旋转时用来防止其弯曲和摆动。应用这种加工方式的机床适合于加工直径小于0.005英寸的孔。

另一种坠电火花加工微型孔机床是三菱VA10机床,它用精加工孔的钻摸附件来装卡和引导精制导线来腐蚀金属,伊利诺伊州的MC机械系统公司产品加工经理丹尼斯德利说:“这是一种标准的电火花加工,但是借助于安装在机器上的附件,我们同样可以加工细孔”。他还补充说在电火花加工中用2000转/分的转速旋转的导线可以加工小于0.0004英寸的孔。 钨电极电火花加工

电火花加工是一中典型的慢加工,加工微孔时这表现得也很明显。“电火花加工非常慢,并且随着加工精度的增加而减慢”Midvale公司(Midvale公司是一个位于犹他州,主要生产24伏低电压电火花加工设备和基于精密电火花加工的公司)的总裁迪恩约根森说。

钨电极的生产是应用反极性接法,经机械加工、研磨加工使之直径达到10微米、粗糙度为0.000020英寸。应用1-微米的电极加工10.5到11微米的孔,并能加工盲孔。用于加工最小孔的最大工件厚度为0.002英寸,加工50微米直径的孔时工件的厚度能达到0.004英寸。

在激光加工之后用电火花加工是生产高精度孔的一种比较不错的方法,约根森已经决定重新研发最好的加工设备。“我们需要重新研发所有电子控件、程序软件和机械”。约根森说重新研发这些软件和继续额需要花费180000到200000美元。

车间里多数精加工为100美元/小时,包括特殊金属的电火花加工,如:X射线加工金和铂、光加工不锈钢、阴极射线加工钨和钽。约根森说道,电火花加工还不适合加工半导体材料,如聚晶金刚石。 光加工

除了硬质合金和钨电极外,光也是一个不错的微孔加工的“刀具”材料。虽然大多数来钻孔的激光都是处于红外光谱范围,但是根据宾尼法尼亚州的Ex One Co。、Iiwin公司的激光技术主管兰迪吉尔摩介绍,他们采用的是绿色光柱的超脉冲技术。不像其他种类的微加工光束,超脉冲是一种纳秒级激光,它绿色光束的波长为532纳米。这种技术产生的激光一对脉冲时间为4到5纳秒,每对脉冲的间隔为50到100纳秒。这种技术的加工方式成倍的提高了加工效率。“与其他激光加工相比,这种技术大大的提高了金属去除率”。吉尔摩说:“由于这种激光脉冲短,所以很大程度上减少了对工件材料的热损伤。”

超脉冲激光加工孔的最小直径为45微米,不过这种加工最常用在H系列钢材料的柴油机喷嘴90微米到110微米孔的加工。吉尔摩提到,根据排放标准的要求这种孔的直径要缩小到50微米到70微米,因为越小的孔越能使燃料充分燃烧。

另外,这种技术加工的孔还带有一个负的锥度,就是入口直径小于出口直径,这有利于燃料的流动。

这种技术的另一种常用的应用是在航空涡轮叶片上打冷却孔。虽然叶轮只有1.5mm到2mm厚,但吉尔摩解释说,这种孔要带有25°的入口倾角,以使冷空气贴着孔壁流动,更好的起到冷却作用,这就是说钻孔的长度达到5mm。他说:“温度是航空发动机的主宰,叶轮运行的环境温度越高,燃料的利用率越高,得到的推力越大。

为了加强这技术的竞争力,Ex One 公司研发了一种专利材料,将这种材料注入中空的部件体内,可以防止光柱所加工孔以下壁体的烧伤。光加工之后,可以将这种材料完全清理掉。

“光加工的一种缺点是,光柱在遇到另一个实体之前就会一直传播”吉尔摩说:“加工柴油机喷嘴时,这会损坏相对壁的内表面”。

超脉冲加工设备的价格为650000到800000美元,虽然这要高于电火花加工设备,但是光加工不会用到电极。“激光加工用光做刀具”吉尔摩说:“它节省了电极的开支”。

根据其应用的不同,机械钻削加工、插铣、电火花加工和光加工在微孔加工中都占有一席之地。牧野公司的Kiszonas说:“用户也比较向往有更多的微孔加工方法供其选择”。

推荐第6篇:外文翻译

陕西理工学院毕业论文

职场真人秀《职来职往》节目成功要素分析

史洋

(陕西理工学院教育科学学院教育技术学专业082班,陕西 汉中 723001)

指导老师:祝传鹏

[摘要]《职来职往》自开播以来很快在社会上尤其是在大学生群体中引起关注,本文从《职来职往》的定位、包装、节目推广、以及节目营销手段等方面进行深入的研究分析,深入探讨了节目成功的多方面原因,从而为其他娱乐栏目提供借鉴经验。

[关键字]职来职往职场真人秀成功要素

引言

《职来职往》栏目是江苏卫视和中国教育频道一频道联合打造的国内首档职场娱乐真人秀节目,由李响主持,并配一位职业分析师对求职者给予正确的引导。这档以帮助求职者正确对待职场问题,协助求职者找到合适工作为目的的节目,通过不同行业、不同职位的人群,展示不同的思维和视角,理性、全面、客观地展示了求职的真实过程,也为参与的求职者打造了一个宽广的舞台,并提供了多中求职选择。自2010年开播以来,收视率不断上升,现已成为中国教育电视台的品牌节目。在众多职场真人秀节目中脱颖而出。为何该节目能够引起那么大的社会关注并获得成功呢?本文将从以下几个方面分析其原因。

1恰当的选题策划

《职来职往》的成功之处就在于节目组的工作人员对节目选题策划的正确认识,一个成功的节目,首先要确定合适的节目策划。只有策划清晰了,才能使节目的创意、制作和传播等环节有的放矢,从而取得效果最大化。《职来职往》的节目策划就很好,无论是受众定位,还是节目内容选择,栏目定位等都很新颖、准确,都符合当下的电视节目发展趋向。

1.1 抓住就业形式严峻,受众定位准确

中国教育电视台一套《职来职往》制片人马浚益表示:“有数据统计,2011年应届毕业700万

[1]将达到历史新高,就业压力也将达到史无前例的地步,求职成为社会集中关注话题。”以往的电视

求职节目,其应聘者基本上是职场的高端人才,而《职来职往》的节目受众定位于寻求工作的人群,尤其是刚毕业和面临着毕业压力大的学生。这个节目的定位可以让我们知道社会需要的是什么样的人,对于求职者来说,他们心中的理想化会被现实给理性化,这是一个难得的机会。他们可以找到自己的优势,也可以学习别人身上自己没有的东西。此外,节目还可以帮助企业来寻找他们所需要的职员,了解求职者对工作的要求,大到公司环境,小到薪资要求。节目的环节设置也很人性化 。先是自我介绍,看的是“人”,你的自我表达能力;然后是实际案例展示,你的硬件条件,你的学历、

[2]专业、工作经验;接着是人际关系看你。从而来了个短而精的相对透彻的分析。通过关注《职来

职往》可以使就业者清晰地认识自己,选择正确的职场方向,让就业者从节目中获得更多的职场经验和人生经验。

1.2节目内容寓教于乐既重娱乐性又显专业性

《职来职往》秉承着“文化教育”这根标尺,向大家提供这并不枯燥的实用性学习。通过娱乐真人秀的形式使节目内容达到了寓教于乐的目的,在轻松愉快的氛围中,让观众大有收获这种职场

[3]的电视化呈现可谓是一本结合案例与理论的职场教科书。它折射了电视人开始对社会问题、社会

现象进行冷静的观察和思考。通过《职来职往》,毕业生等求职者学到了面试的技巧,认识到了企事业单位对求职者素质和能力的要求;观看《职来职往》,在校大学生可以未雨绸缪,早日确定自己的求职方向,并进行有针对的学习实践;那些已找到工作的观众,收看这个节目,能够更进一步的了

[4]解自己的优点与不足,不断学习,从而把本职工作做得更好。正所谓“授人以鱼,不如授人以渔”,

理想的求职节目不仅仅在于“帮人找工作”,而是“教人找工作”。基于这种理念为参众、观众、大众所创办的《职来职往》节目的出现,使观众的视线不仅仅放在招聘方上,而且更多的关注求职者。这是源于节目真正的面向全民的结果。另外节目现场真实还原面试的经过,实现了真正意义上的真人秀概念。就像《职来职往》节目口号中说的那样,相信《职来职往》也会前途宽广的! 2准确的嘉宾策划

2.1求职嘉宾彰显个性魅力

随着节目收视率的提高,节目组对于求职者的选择也呈现出多样化的趋势。从过去播出的节目中不难看出,几乎每一期的5位求职者都各具特色,既有高学历的名牌高校在校生和拿着洋学历的海归,也有老实厚道的技术工人,有不愿接受父母安排而出门奋斗的“富二代”,也有住地下室吃馒头咸菜的“北漂”,甚至还有久未出门工作的家庭妇女和退居二线再就业的老阿姨等等。这些人物本身就有巨大的话题性,加上节目模式决定了其娱乐成分大大增加:脚踏实地、眼高手低、狂妄自大、过分谦卑„„形形色色的求职心态将原生态呈现在观众面前。这样的嘉宾设置,改变了以往求职节目中“参与者多是高学历,对职位要求十分苛刻,观众只能是“看客”的局面。而在《职来职往》智联招聘的网站上开通了报名专区,是求职者只需通过上网便可获得由行业达人进行职场点评的机会,大大降低了参与者的门槛,不限年龄和学历,不仅扩大了受众群,而且增加了节目讨论的话题

[5]范围。通过不同的求职者所带来的不同话题,引发大家对社会现实的思考、讨论和对自身的反思与再定位。

2.2 职场达人高调助阵

节目中站在台上的18位“面试官”,也就是主持人李响口中的“职场达人”,都是节目组精心挑选和安排的,涵盖了销售、行政、人力资源、策划、设计等多个行业、其中不乏一些青春靓丽的“80”精英。据节目制片人马浚益介绍,“对于面试官的标准,除了要求其具有个人魅力之外,更重要的是能受到观众欢迎”。确实,我们在荧屏上看到了职场达人们,除了在自己职业领域里身经百战外,更能用犀利的眼光全面扫描求职者的缺点,并一针见血的指出,发表独到的观点,具有鲜明的个人特色。如美国红帽软件公司的郑艳、北京新东方教育科技有限公司的唐宁,已经在观众中拥有了不少的粉丝。还有北京天启一方广告公司媒体部总监马丁,因在节目的曝光,他的微博粉丝已经增加到了5万,还特别成立了“马丁帮帮忙”微博粉丝群,每天都要花上3个小时专门回答青年人的求职困惑。可见,他们的出现极大的改变了大家对于以往求职节目中面试官的传统印象。

3专业的节目流程及形式策划

3.1 采用“真人秀”的表现形式,强调“平民化”

以往的求职节目因为收视率的考虑,在选手的选择上都有着特殊性的要求。这就使得节目自身

[6]与普通人有着很大的差距,其真实性和服务性就得不到彰显。在《职来职往》的舞台上,参与者

完全是常态表演。他们没有光鲜亮丽的外表,没有名利驱使的企图心,他们与电视荧屏前的观众没有区别,都是普通的求职者。他们参与节目,是为了切身体验职场压力,为自己的职业梦想而努力。他们与行业达人就当下热点话题进行激励碰撞,节目从真实、客观、全面的角度来展现职场风貌。由于他们和观众之间拥有相似的社会角色、经济状况、生活状况,因而更能增强观众的心理认同感和体验感。作家王海鴒在看过一期节目后说道:“沉静、有力量、有信息,作为作者我从中看到了真

[7] 实地人生百态。”

3.2 节目规则有趣,并设有悬念

《职来职往》节目一期90分钟左右,有五位求职者要为自己的梦想一搏,采用“环环相扣、节节过关”的真人秀形式。一个求职者面对18个来自不同行业的面试官进行问答,根据获得认可人数的多少获得相应不同的职位,9名以上可以自己挑选百家企业就职,9名以下就只能从在场对自己感兴趣的面试官的企业中挑选,全部灭灯者则淘汰,这样的规则设置很有意思体现了娱乐性元素。

节目的整个求职过程将悬念运用其中,不仅提升了观众对节目的兴趣度,而且烘托了求职现场的气氛。在《职来职往》设有三层悬念,第一层悬念设置是每个求职者最终能否求职成功;第二层悬念设置是选手获得的百强企业里是自我选择的职位还是现场达人所提供的较为被动的职位;第三层悬念是一种贯穿于始末的悬念,在每位求职者所要面对的四大环节约15分钟的时间里,什么时候会被行业达人灭掉代表求职机会的灯以及多少盏灯被灭掉。这三层悬念一直统领着整个求职的过程,每一个悬念的铺设都成为求职者职业能力的鉴定,为求职者自身的求职期盼设置了悬念,也为观众

对于结果的猜测设置了悬念。《职来职往》制造的这种悬念,既推动了求职过程,也体现了电视节目

[8]应带给观众的实用性和观赏性。

3.3 节目采用视频简历,突出了影视手段,传达了大量信息

《职来职往》中采用影视手段——视频简历,既展示了求职者的职业理想和人生经历,又有故事情节和情感内容,更容易引起观众的共鸣。

3.4 节目整体包装,媒介融合参与

《职来职往》的成功在于节目包装、宣传娴熟、大气时尚的舞台与灯光使节目“新锐式”的特色一览无余,细节处也十分考究。达人介绍、求职者登场应聘失败或成功时,背景音乐《 That is not my name》、《All We Are Ever Known》、《想飞越》、《隐形的翅膀》、《我相信》等都准确诠释了不同的

[9]节目气氛,歌曲的网络点击率随即攀升。其中在《我相信》中透过感人歌词向外界坦露求职者一

路走来的心路历程,而《隐形的翅膀》是一首国民励志歌曲,给求职者一种人生鼓励。制作优良的《职来职往》浅层次带给求职者经验教训,深层次体现了电视节目的社会功能,求职过程富有悬念与挑战。

4精心的市场策划

4.1精选播出时段

《职来职往》节目的播出时间也选择了中国教育频道和江苏卫视的黄金时段播放,使收视重点直指最大众化人群,引起了很大的社会反响,充分发挥了电视传媒优势,职场达人解答贯穿始终,并邀请职业规划师助阵,这一切手段提升了《职来职往》节目的知名度,便于打造出具有品牌特色的“教育栏目带”。

4.2 强大的经费支持,保证节目质量

任何一件事的成功都依靠在一定的经济基础之上,《职来职往》也不例外。《职来职往》利用企业冠名、赞助播出等手段在软性宣传上打造企业的品牌形象,成为《职来职往》的主要经济来源。此外节目还开通短信互动平台,方便求职者咨询,一方面提高了收视率,另一方面带动了节目的经

[10]济效益。

4.3与江苏卫视合作,借鉴非诚勿扰

如今,年轻人面临的现实问题无非两种,一是找工作,二是找对象。江苏卫视根据受众的心理需求和市场发展需要,先后举办了这两档节目,以娱乐大众,指点迷津为目的,取得了良好的成效。由于之前《非诚勿扰》这一节目模式的空前成功,致使《职来职往》沿袭了他的舞台设计、环节设置和节目包装。虽然,乍看上去,《职来职往》与《非诚勿扰》栏目有很多相似之处。但对于求职者来说,这是一种全新的尝试,与相亲类节目不同的是《职来职往》将重点放在“立业”,以提供就业

[11]服务为主。节目并不一味追求娱乐性,作为具有舆论引导作用的电视媒体,更注重社会责任感。

通过舞台上的求职过程以及求职者与面试官的言论来呈现多元化社会现状,反应社会现实。少了一些华而不实,多了一些脚踏实地。

5有效的营销策划

5.1采用多媒体合作的推广方式

《职来职往》的成功还得益于全方位多角度的宣传推广。《职来职往》平均每天在中央教育频道一套播出约20条宣传片,使更多的观众了解并收看此节目,为节目的观众注入了新鲜的血液。《职来职往》除了定期在知名报刊杂志刊登宣传广告外,还在北京的楼宇和地铁站进行户外宣传。《职来职往》注重新媒体扩大节目的受众面和知名度,定期在搜狐娱乐版、新浪娱乐新闻、新浪微博等门户网站,以及酷

六、百度奇艺网、视有网等视频网站宣传造势,并和智联招聘等大型求职网站展开

[12]深度合作。这种媒介融合的宣传手段是节目发展的需要,也是科学技术发展到一定阶段的产物,

传统媒介和新媒介相结合的方式,使节目的发展更加坚定而紧凑。此外,良好的口碑效应也使得《职来职往》的收视率节节攀升。

5.2采用校园活动进行台上台下互动

为了与成千上万名在校大学生亲密接触,2011《职来职往》校园行于近日正式启动。2011年4月27日至30日期间,《职来职往》校园行分别来到了成都与重庆、天津、济南、石家庄等各站展开活动,栏目组得到了大学生们热情的欢迎。据悉,5月份期间,《职来职往》校园行还将继续展开,届时《职来职往》的代表将会带着“行业达人”精心准备的求职课程来到大学生的身边。未来,《职

来职往》栏目组还将奔赴广州、厦门、上海以及更多城市的大学,协助“行业达人”与Mr.Job走进校园与高校就业指导中心展开互动交流,为初出茅庐的学子们进行就业指导。此外7月CCTV更是联手了人民邮电出版社策划出版了新书《职来职往--这样求职进百强》,图书作为节目的延伸在荧屏之外用事实案例向求职者传道解惑。

结束语

总之,在目前国内就业形势严峻的背景下,《职来职往》作为一档职场真人秀节目应运而生并取得成功。《职来职往》的成功得益于其在节目定位,节目特色、节目角色设置和节目宣传等方面的创新和精益求精。国内电视节目应借鉴《职来职往》的成功经验,争取做大、做强我国的电视节目,跟随《职来职往》节目的潮流,掀起一股电视求职的热潮。

参考文献

[1] 关彤.大学生就业指导[M].北京:清华大学出版社,2010.

[2] 宁迪,都城.从《职来职往》看电视求职节目的创新与发展[J].今传媒2011(9).

[3] 尹鸿等.娱乐旋风——认识电视真人秀[M].北京:中国广播电视出版社,2005.

[4] 江苏卫视官网[OL]http://,2008-06-28.

[5] 中国日报娱乐报道[OL]http://.cn/hpyl,2010-03-21.

[6] 中央电视台.绝对挑战.栏目组.绝对挑战[M].北京:人民日报出版社,2005.

[7] 孙娟妮.《从纪实性角度浅析节目的服务功能》[J].中国电视(记录),2011(6).

[8] 职来职往.[OL]新浪微博http://t.sina.com.cn/cetvzlzw.

[9] 职来职往.[OL]百度百科 http://baike.baidu.com/view/4503413.htm.

[10] 谢耕耘,陈虹.真人秀节目理论、形态和创新[M].上海:复旦大学出版社,2007.

[11] 苗隶.制作为王:《非诚勿扰》的成功之道.现代传媒,2010 (5).

[12] 黄学建.中国电视娱乐文化批评[M].北京:中国传媒大学出版社,2010.

The analysis of factors about the succe of workplace

reality show-ZhiLaiZhiWang

Shi yang

(Cla2, Grade08, Major :Education Technology, Education Science Dept.,Shaanxi University of

Technology,Han Zhong, Shaanxi, 723001)

Tutor: Zhu chuanpeng

Abstract:Since it is launch the ZhiLaiZhiWang quickly especially in groups of college students in the community concerns, this article from the vocational education to employment in the position of, package, program promotion, as well as program marketing and in-depth research and analysis, had an in-depth discuion on the various causes of program succe, to provide experience for reference for other entertainment programs.Keywords:ZhiLaiZhiWangwork place reality showSucceful factor

Text [6] CCTV.Absolute challenge.Part group.Absolute Challenge [M] Beijing: People\'s Daily Pre, 2005.

[7] Sun Juan ni.\"Analysis from a documentary point of view program service functions\" [J].Chinese TV (records), 2011 (6)

推荐第7篇:外文翻译

本科生毕业设计(论文)外文资料译文

设计(论文)题目:

学生姓名:徐凯学号:0965251027分院:信息与机电工程分院班级: 091指导教师:袁鸿斌职称:讲师填表日期:2013年3月6日

杭州师范大学钱江学院教学部制

2

3

4

推荐第8篇:外文翻译

湖北理工学院 毕业设计(论文)外文文献翻译

核电厂的液位控制系统的设计

作者:邱永胜

摘要——MSR的液位控制系统(水气分离器再热器)储油槽的关键部分是传统岛核仪器和控制设备正常运行的核电站在调节中起着非常重要的作用。这种方案是基于分布式控制系统(DCS)的设计和实现液位控制系统。设计改变了在过去MSR储油槽的核电站控制方法,选择成熟、可靠、先进的DCS控制系统来满足其要求液位控制。正常排泄水调节阀,紧急排水阀门实现独立控制和操作功能(手动/自动)。增加舒缓的水压力,温度,并调整阀门反馈信号。提供设备完整的工艺参数和自诊断功能。提高了控制系统的可用性,降低缺陷率的控制设备,控制设备转换为实现“零缺陷”,满足电站的长期安全运行。

关键字——核能计划ˈ液位控制ˈ系统配置分布式控制系统。

I介绍

我国在“十一五”计划中建立了“积极发展核电”政策,积极推进核电建设先进技术的使用。由于核能的特殊性质,仪表和控制系统的安全性和可靠性比其先进和创新更重要。

审查发生在过去重大核电站的事故中的那些相关的仪表和控制系统的问题。

II MSR

系统工作流程

气分离器再热器(MSR)用于核电站,其根本目的是提高蒸汽循环的热效率。 每一个分离器再热器再热储油槽,水平再热储油槽,II级再热储油槽,分离器储油槽,每个储油槽是提供一组基本类型监管机构控制器。控制系统控制的一个正常的排水阀,紧急排水阀控制疏水槽水位。MSR疏水液位系统的合理设计汽轮机的安全运行,具有十分重要的意义。如果不正常疏水,影响水分分离器再热器身体安全。

DAS(数据采集系统)是用于收集疏水槽的压力、温度数据信号,实时监控和显示的运行状态系统。疏水箱的水位信号(4 ~ 20 ma)被送到模拟输入卡。系统预设值比较运算符在水位信号的人机界面,通过调整PID回路,控制信号从模拟输出卡输出阀(4 ~ 20 ma),来调整阀门开度,从而达到控制的目的疏水槽水位,水位调节循环1 #、2 # MSR储油槽,分别由6组12每个正常排水监管和应急排水阀门,从各自的分段处理液位控制器控制信号来调整阀门开度,液位保持在控制范围内,控制储油 1

湖北理工学院 毕业设计(论文)外文文献翻译

槽液位稳定。

III控制系统方案

DCS需要几个控制站之间的许多工业过程控制的控制点的控制站可以通过网络交换数据连接。硬件设备主要的工作站系统处理器(WP),应用处理器(美联社),应用工作站(AW70),现场控制处理器(FCP)、通信处理器(COMMP),现场总线模块(FBM)。

DCS控制系统的硬件连接图和具体功能和配置。

A硬件需求除了满足核级仪表设备需求(1 e)安全(RCC-E(2002)标准)[2],核功率计的计算机控制系统应该是结构化,模块化,灵活,操作方便,控制网络。系统通道或保护和控制系统必须实现电气隔离和功能隔离用于光纤通信,系统必须有一个持续的在线自测诊断能力。作为一个整体,硬件系统具有较强的抗电磁干扰、高功率瞬变能力和满足电磁兼容性要求。水气分离器再热器之外的这种技术的控制系统可以被认为是通过识别的智能传感器和现场总线技术,实现信息采集和现场控制。这种技术大大简化了仪器控制布局的结构和分布的过程。 B .可靠性设计

(a)冗余设计:由于核电站的特殊性质,为了确保DCS的高可靠性要求,I / O模块,和具体的现场控制站控制器、电源、网络和服务器,将冗余配置。

(b)隔离设计:特殊要求或信号,如信号安全non-security-level DCS和DCS是一个共安全级别DCS将孤立从non-security-level DCS,避免非安全性系统导致损失的安全特性。

(c)多样性设计:多样性是一种保护的性能故障和共模故障。保护的特定功能,需要非常高的可靠性,如反应堆关闭系统,必须设置为两个相互独立的,没有属性,因此可以避免共模故障的发生。设计通常是应用于冗余系统的多样性。

(d)容错设计:设计系统的容错技术是指误动作不响应技术。至于键盘不允许键屏蔽,如运营商在操作员站不按照规则操作系统没有响应,而不是输出操作指令,或提示操作错误信息。

IV

配置控制软件的设计

控制配置,准备了一个程序(模块),设置参数,这样就可以构建所需的用户主体和额外的功能,或功能块的软连接,完成过程控制系统。

湖北理工学院 毕业设计(论文)外文文献翻译

配置软件需求: 首先,软件具有较强的可移植性,连接和互操作性; 其次、安全、高效的数据通信中,友好和视觉界面; DCS系统应用程序配置软件作为软件平台,控制工程师,从如何编写软件程序来实现控制和显示功能,并花更多的时间和精力在控制电路的设计和实际控制和显示在打印相关信息,如使用这种模块化的配置方法,可以完成各种项目的配置。

这个设计使用一个控制配置央行图。央行是包括所有仪器控制系统的控制图。 # 1 MSR正常/紧急疏水槽排水阀控制,例如,给央行的配置图和描述。液位的分段控制,即正常排水阀调节正常水平间隔,紧急排水阀高度间隔。液位控制一直很稳定,在扰动发生时,液位控制响应快,如果液面达到极限,正常和紧急陷阱都打开,关闭完全正确(高液位报警有强制性全面紧急控制水阀,低水平报警而强制关闭正常排水阀)。控制系统的失败后,设备正确响应,以确保机组的安全。

# 1 msr二级央行的正常储油槽陷阱配置图

通过配置,DCS控制程序称为中位数选择器模块、PID控制模块,两个位置控制模块,手动模块等正常排水阀是强迫开放、积极行动,紧急排水阀空气关闭,相反的效果。

使用HART协议DVC6010PD智能定位器(精度±1%)取代了现有的3582克气动阀门定位器。阀门管理安装AMS ValveLink软件和相关硬件支持# 1,# 2 msr在线和离线诊断,管理的控制阀门。

PID控制模块、模拟输入模块(AIN)和模拟输出模块(差异)连接有机地形成一个参数控制电路,。首先,是模块主要修改测量信号,FBM缩放、警报和其他操作,然后输出处理过的数据测量值输入参数PID控制模块的量。其次,PID模块考虑偏差的测量值和设置和设置p,我,d处理和调优参数,最终,传输数据量的差异模块。最后,对模块的输出数据,作为修改,然后路由到FBM的输出点。为了提高控制质量,单回路控制方案的基础上,还可以使用串级控制的程序员。串级控制回路由2模拟输入模块(AIN),2 PID控制模块和一个模拟输出模块(差异)。当循环工作状态,二级调节器的设置状态,参数的设置值是一个数据连接和通信和输出参数的主要监管机构。无扰转移到闭环控制,您通常需要将初始化二级调节器的输出信号初始化主调节器的输入信号。同时二级调节器的输出信号反演计算的输入信号传输逆计算的主要监管机构。对模块的初始化输出信号需要被转移到初始化二级调节器的输入信

湖北理工学院 毕业设计(论文)外文文献翻译

号。

V系统电源、地表和环境设计

DCS是公认的双向交流220 v±10%,50赫兹±2.5赫兹单相电源,由两个不间断电源(UPS),隔离变压器抑制高频干扰传输到网格中的力量。冗余电源配置合适的开关装置和循环保护电路。这两个主要力量提要内阁。适当的地面点的选择,完美的接地系统,接地设计,系统接地,保护接地,屏蔽地面分离。抑制噪声,确保系统的安全运行,各种抗噪声技术用于设计。这些技术包括opto-isolated、高共,必要的接地和电磁屏蔽。加强DCS系统抗干扰能力的ˈ当其他设备工作在470 mhz的频率,功率5 w,和从系统中超过1.2米,电磁干扰和射频干扰不会影响系统的稳定性。振动强度要求:5855。

[6]凡X触摸DCS系统在核电站中的应用[J]。机械和电气信息,2010(4):191 - 192。

作者的传记

邱永胜出生于西安,中国,在1973年。他收到第二炮兵工程学院BS,中国在1996年和1999年,ˈ分别。现在他是一个工程师在电子和工程学院,南京大学的职位和通讯ˈ中国。他的研究兴趣包括计算机测量和控制技术,通信技术。

湖北理工学院 毕业设计(论文)外文文献翻译

推荐第9篇:外文翻译

东 莞 理 工 学 院

本 科 毕 业 论 文

外 文 翻 译

毕业论文题目:唯美陶瓷公司普工流失的问题与对

学生姓名:李华辉

学号:20042101229

系别:工商管理系

专业班级:人力资源管理2班 指导教师姓名及职称:莫安达 起止时间:2008年1月—2008年6月

项目经理高成本的离职

你试想以下这样的一个情景,一个大型制药机构的高级经理沮丧地说:“我们公司在过去的一年里流失了很多项目经理,由此产生的问题持续影响着对股东提供的质量服务,然而我们却不知道是什么原因造成的。”这听起来很熟悉,并不陌生吧?我记得导演伍迪艾伦曾经说过“成功有80%是表面文章”。然而,更大的挑战是设法去留住那些员工。

员工离职在商业社会里面是一件很普遍的事情,员工留在企业与其共同成长和发展的日子一逝不复返。调查显示,员工进入企业里里最多五年就离职,而零离职率是没可能的,公司持续增加的离职率表明工作环境存在着严重的问题。在对项目经理进行随机调查的报告中显示,以下原因促使现今很多企业的项目经理离职变得频繁。

1、内部沟通

2、比较差的时间管理

3、人员安排和调度的问题

4、项目经理授权和经验的缺乏

5、贫乏的员工培训

6、没有项目管理工具

7、薪酬问题

公司处在日益发展的阶段,需要大量有经验和专业技能的项目经理,但是事实上招到的是大批没有经验的人到这个行业。那么为什么一些企业面临着离职率的上升?总的来说,美国劳工统计局最近发现40%的员工离职是因为他们觉得在公司里面缺乏赏识和关心,并且没有团队合作,产生严重的负荷。截至2005年2月,美国企业的员工平均流失率为3.1%,虽然这个数字看起来是很低,但如果这和美国的劳动人口相结合,那是一个多么惊人的数字,并且还有很多企业的离职率是没有统计上去的。

在今天竞争激烈的市场里,某些公司的高层只把员工离职作为日常事务的一部分,而有成本意识的成功企业应该看到离职对生产率、产品质量、服务水平等的不利影响。伯明翰认为员工离职存在六个共同点。分别如下

1、离职的必然性

2、部分员工离职是是有利的

3、离职的成本是昂贵的

4、薪酬并不是员工离职的唯一原因

5、管理是留住人才的关键的措施

6、加强组织的承诺来降低员工的离职率

上述的六个共同点也适用于专业的项目经理。

多米诺骨牌效应,在项目的任何阶段失去项目经理都是一个灾难的信号,虽然很多时候项目管理的方法是由项目管理办公室提出的,并且每个人都有着独立的系统去完成工作任务。但在剩余的时间里面因项目经理个人离职而把项目搁置下来了,在项目经理离开后,项目人员会问以下的问题。

1、他们将会去哪里?

2、谁将会来接管他们?

3、他们是有组织的吗?

4、他们对他们所做的工作了解吗?

5、按原来效率还是加快速度去完成剩余的工作?

6、是把项目经理的工作分到每个成员还是培养一个新经理更加有效?

7、股东是否被告知事件的最新发展情况?

8、财政预算是否已经超支?

事实上项目经理的离职影响以下的各项:

1、范围——那些需要完成的事情

2、时间——增加了项目的时间

3、成本——增加了加班费和培训费

4、质量——截止期限影响工程后期的质量

5、沟通——不能履行所作出的承诺

6、采购——难以选择外部供应商

因此,如何防止项目经理的离职?正如我们在开始时讨论的一样,零离职率是没可能的,并且一定的人员离职对公司来说是合理的,那样可以带来新鲜的血液,新的方法和思路,改革工作的落后环节,促进组织的发展。很多企业对员工离职没有完全了解,未能认识到高成本与离职在很大程度上密切相关。员工的离职对公司来说是一个沉重的负担,因为你要招聘、考核和培训一个新员工,并且你将会增加现有员工的负担,生产力会下降,要付出加班费,实际公司大约花费新员工薪水的三分一去替换员工。如果组织愿意花更多的时间去重视离职率,把他当成企业的重要事项,而不是日常的事务性工作,那么将会节省数万美元。

有一种办法不仅能够降低公司的离职人数,并且能够为员工离职做好准备。在这次对项目经理随机调查中显示,以下方式可以降低项目经理的离职率。

1、通过培训提高知识水平

2、评估不断变化的劳动人口文化

3、衡量公司的离职率

4、员工成本

5、雇佣合适的人选

6、设立有效的变革管理

当变革在组织中不可避免时,你可以有所准备。在日常的项目活动和突发事件中发生问题要把握好时限和团队的势头,以及维护股东的利益,变革管理在这方面起作用。变革管理能够快速的实施一个变革管理计划,产生即时反应,减少对项目发展的影响,获得成功。变革管理可以:

1、降低生产力的损失

2、鼓励抵抗变革的员工

3、尽量减少对生产力和生产质量的影响

4、减少对股东的影响

留下问题不解决会导致整个项目的破坏甚至是失败。当正在进行一个变革管理计划时,有些问题是需要考虑的。

1、故障的责任

2、额外的培训

3、需要的时间

4、更换内部人员

5、超时需要

6、谁能够作横向调动

变革管理计划是降低员工离职成本的有效办法,以至工程能够在预定的时间

和标准范围内完成,不影响公司的利益。

测量你公司的离职率吧!

很多企业对他们公司的离职率知之甚少,此外他们也不太在乎一个员工离职的所包含的成本,按照以下公式测量年职率将会变得很容易。

离职率=过去12个月离职员工总数/平均员工人数

例如:在过去的一年中有25个员工离职,而公司的平均人数是250人,那么他的离职率就是10%。

员工离职的成本可以被测量,并且在年终应该加以审核,以下的公式可以帮你计算员工离职的费用。

TC=(DHC+IHC)/T

TC:员工流失成本

DHC:直接招聘费用(广告费、摊位费、招聘人员费用等)

T:离职职位总数

我们统计出了以上需要的数据,但是员工离职这个问题在公司里面还不是很清楚,即使通过离职面谈,也可能得不到最真实的反馈,他们回答中最常见离职原因是想得到更高的薪酬或者是想找到一份更加好的工作。这就需要管理人员花费更多的时间去调查,了解存在的问题。高离职率是一个警告的标志,它预示着你公司内部存在一定的问题,其中一些原因是由于高层经理所造成的,员工的离职率得不到应有的关注,高离职率应该使你质疑工作环境如公司提供的文化、物质以及财政方面。问一问你自己这些问题:

1、这是我想去管理员工的方式吗?

2、员工能够得到金钱和感情的补偿吗?

3、公司把员工当作是成本的因素吗?

他们曾经被认为是对公司忠心耿耿,全身心为公司奉献,但是现在他们离职了,为的是更好的满足他们高质量的生活和家庭所需,这意味着现在的组织想要留住员工就要从内心去激发和鼓励他们,参与和授权是减少员工离职率的最有效工具之一。据国际发展维度收集的收据显示,如果公司有高度向心力,员工的离职率是很低的。你公司是如何维持的?

1、听取员工的意见

2、尊重员工

3、鼓励工作出色的员工

4、要求员工投入

5、信任员工

6、公平公正

7、坚定但不残暴

8、勇于承认错误

9、愉快的工作环境

10、优质的住宿环境

虽然对员工离职暂时还没有一个根本的解决方法,但是还是有很多有效的措施来降低员工的离职率,我们不能忘记那些为我们工作的员工特别是从开始到结束为公司工作的员工,我们依靠他们的知识、技能,而且他们当中的大多数人承诺及时地完成高质量的工作。作为雇主,要用时间去赞赏那些为了你公司成功而付出努力的员工,最重要的是了解他们所需要的并想办法尽力满足他们。成功有80%是表面文章,其他的20%是你用行动来留他们下来。

推荐第10篇:外文翻译

Low Voltage Flyback DC-DC Converter For

Power Supply Applications Hangzhou Liu1, John Elmes2, Kejiu Zhang1, Thomas X.Wu1, Ia Batarseh1

Department of Electrical Engineering and Computer Science, University of Central Florida, Orlando, FL 32816, USA Advanced Power Electronics Corporation, Orlando, FL 32826, USA Abstract :In this paper, we design a low voltage DC-DC converter with a flyback transformer.The converter will be used as a biased power supply to drive IGBTs.The flyback transformer using planar EI-core is designed and simulated using ANSYS PExprt software.Besides, anLT3574 IC chip from Linear Technology has been chosen for converter control.Finally, the converter modeling and simulation are presented and PCB layout is designed.Keywords:Flyback, anLT3574IC, PCB

I.INTRODUCTION The goal of this project is to develop and build a prototype of a high-efficiency, high-temperature isolated DC-DC converter to be used as a biased power supply for driving a complementary IGBT pair.It is important that the converter can deliver the required power at an ambient temperature of up to 100℃; therefore it has to be efficient so that its components do not exceed their maximum temperature ratings.The final converter will be completely sealed and potted in a metal case.The input voltage range for this converter is from 9V to 36V.The output sides have two terminals, one is﹢16V and the other one is﹣6V.In order to get the desired performance, anLT3574 IC chip from Linear Technology is used.The key to this design is the flyback transformer.The transformer using planar EI-core is designed and simulated using ANSYS PExprt software.Finally, the PCB layout of the converter will be presented.

II. KEY DESIGN OUTLINE For this flyback topology, the output voltage can be determined by both the transformer turns ratio and the flyback loop resistor pairs.Therefore, at the initial design stage, we can choose a convenient turn’s ratio for the transformer, and modify it later on if neceary to make sure the output performance is desirable and the transformer will not saturate [1].The relationship between transformers turns ratio and duty cycle can be found as

Where n is the transformer turns ratio, D is the duty cycle, VO` is the sum of the output voltage plus the rectifier drop voltage, VIN is the input voltage of the transformer.The value of feedback resistor can be calculated as

Where RREF is the reference resistor, whose value is typically 6.04kΩ; α is a constant of 0.986;VBG is the internal band gap reference voltage, 1.23V; and VTC is normally 0.55V [1].With a specific IC chosen, the converter circuit can be designed based on a demo circuit and some parameters may need to be modified if neceary to optimize the performance.Furthermore, in LT Spice, a large number of simulations need to be done with different conditions such as load resistor values and input voltage levels.It is important to make sure that the output voltage can be regulated well with all these different conditions.The most critical part of the design is the flyback transformer.With high switching frequency, the AC resistance can only be estimated based on some traditional methods such as Dowell’s curve rule [2].In order to get more accurate values of AC resistance values; we propose to use finite element electromagnetic software ANSYS PExprt to do the design [3].At the initial design stage, key parameters such as the worst-case input voltage, frequency, material, inductance values will be decided.After that, these data will be imported to the software, from which an optimized solution will be generated.III. CONVERTER SIMULATION RESULTS We choose LT3574 chip in this design.From the simulation results in Figure 1 and Table 1, it clearly shows that the output voltages which are﹢16V and -6V respectively can be regulated pretty well with the input voltage range from 9V to 36V.The voltage tolerance ranges are from ﹢15V to ﹢19V and -12V toDC converter for low voltage power supply application has been designed.The modeling and simulation results are presented.Based on the design specifications, a suitable IC from Linear Technology is chosen.A large amount of circuit simulations with different conditions such as load resistor values and input voltage levels are presented to get the desirable output voltage and current performance.The transformer has been designed including electrical, mechanical and thermal properties.With all the specific components decided, the PCB layout of the converter has been designed as well.

REFERENCE

[1] Linear Technology Application Notes , Datasheet of Isolated Flyback Converter Without an Opto-Coupler, http://cds.linear.com/docs /Datasheet/3574f.pdf.[2] P.L.Dowell, “Effect of eddy currents in transformer windings” Proceedings of the IEE, NO.8 PP.1387-1394, Aug 1966. [3] S.Xiao, “Planar Magnetics Design for Low- Voltage DC-DC Converters” MS, 2004.

[4] ANSYS Application Notes, PEmag Getting Started: A Transformer Design Example, http://www.daodoc.com/download/ EDA/Maxwell9/planarGS0601.pdf.[5] K.Zhang; T.X.Wu; H.Hu; Z.Qian; F.Chen.; K.Rustom; N.Kutkut; J.Shen; I.Batarseh; \"Analysis and design of distributed transformers for solar power conversion\" 2011 IEEE Applied Power Electronics Conference and Exposition (APEC), v l., no., pp.1692-1697, 6-11 March 2011. [6] Zhang.; T.X.Wu.; N.Kutkut; J.Shen; D.Woodburn; L.Chow; W.Wu; H.Mustain; I.Batarseh; ,\"Modeling and design optimization of planar power transformer for aerospace applic ation,\" Proceedings of the IEEE 2009 National, Aerospace & Electronics Conference (NAECON) , vol., no., pp.116-120, 21-23 July 2009. [7] Ferroxcube Application Notes, Design of Planar Power Transformer,

第11篇:外文致辞

甘粛省外事弁公室、中日友好協会、中国国際旅行者の諸先生方、友人の皆さん:

このたび愛知県日中友好協会主催の「シルクロードを巡る旅」一行は去る5月25日上海に到着し、そこから一気にウルムチに飛び、シルクロードの中心地トルファン、敦煌、酒泉、蘭州を巡り、昨日から首都北京の名所旧跡を訪ねて大半の日程を終え、明日、「北方の香港」や「アカシアの大連」という異名を持つ大連を経由して、一路帰国の途につくことになりました。

思えばこの二週間、私たちは貴国のスケールの大きさを肌で感じ、毎日が感動の連続でありました。現代化の活気あふれる大都会上海、「美しい牧場」の名を持つオアシスの町ウルムチ、唐の僧玄奘やマルコ・ポーロも訪れたという東西交易の中心地カシュガル、「砂漠の真珠」トルファン、「西遊記」の孫悟空でおなじみの火焰山、壮麗な宗教芸術を誇る敦煌を訪れ、次から次へと熱いロマンの世界を追い続ける素晴らしい旅でした。

また北京市内では、明清二代にわたる皇城となった故宮、皇帝が五穀豊穣を点に祈った天壇、北京のシンボル天安門などを見学し、歴史を秘める古都と、新生中国の二つの顔を見ることができました。

最も感動したのは、やはり万里の長城でした。月から見える唯一の地上建造物を目の当たりにしたときは、その雄大さにすっかり魅了されてしまいました。「長城に至らねば好漢にあらず」といわれているそうですが、おかげさまで、我々は全員「好男子」になることができました。

こんなに広大な大陸を二週間という短時間で駆け回ったわけですが、まことに「馬上花を見る」思いでありますが、中国を理解し、交流を深めていく第一歩としては大きな収穫でした。ことに、道中皆様と親しくなれましたことをたいへん嬉しく思います。また、行く先でいただいた本場ならではの中国料理の美味は、我々の胃袋を十二分に満たすことができましたし、今回の旅を一層盛り上げてくれました。それに、明日大連で見られるあの町を白く染めるアカシアの花とあたり一面に漂う甘酸っぱい香りも実にたのしみでございます。

私たちが、今回の旅を存分に楽しみ、滞りなく、また有意義に過ごすことができましたのも、ひとえに中国の皆様の行き届いた配慮と、至り尽くせりのお世話のおかげです。ここに私ども一行を代表して深い感謝の意を表します。申し上げます。通訳の王さん、どうもご苦労様でした。

さて、今夜はまことに粗酒粗肴ではありますが、お世話になった中国の方々とともに、酒を酌み交わし、別れを惜しんで、時間の許す限りご歓談いただきたいと存じます。

では、再びお会いできますことを祈念して、また皆さまの健康をお祈りして、乾杯をいたしたいと思います。

乾杯。

第12篇:外文致辞

在机场欢送日的本农业考察团时致辞

日本农业考察团的朋友们:

6月8日我们怀着喜悦的心情和期望来机场欢迎你们,转眼间三个星期已经过去,离别的时刻就要到来了。现在回顾一下陪同各位在中国各地与各界人士的交流活动和参观游览的情景,一幕一幕象走马灯般地浮现在我们眼前,在21世纪这种信息化时代里,通过双方的交流,日本的先进农业技术,尤其是生物工程的不断发展,肯定会为中国农业的发展提供无限的可能性。我们相信,你们在中国各地洒下的友好种子一定会生根发芽,开出绚丽的花朵,结出丰硕的果实。

各位先生尽管在生活上、饮食起居上都不太习惯,但是今天能够身体健康并且一切顺利的结束这次访问日程,并取得了可喜的成果。我们为此而感到无比高兴。但是,我们的接待工作上有许多不周到的地方,还要请各位多多见谅。

三个星期的时间并不长,但是我们已经被友谊的纽带紧紧地联结在一起了。在即将离别的时刻,我们确实感到恋恋不舍。可是,现在也只能越好下一次我们在日本在相会吧。 各位几小时后就要回到日本,回到亲友的身旁。想到这里,各位一定是归心似箭了吧。 祝各位身体健康,一路平安。

日本農業視察団の皆さん:

去る6月8日、皆さまをこの空港で大きな喜びと期待を持ってお迎えして以来、あっという間に3週間が過ぎてしまい、もうお別れの時刻が迫ってまいりました。この間を振り返りますと、皆さまとともに、中国の各地で過ごした各界との交流や観光の日々が、走馬燈の如く思い出されます。二十一世紀のこの情報化時代において、双方のこのような交流を通じて、日本の進んだ農業技術、特にバイオテクノロジーの絶えざる発展が、必ず中国農業の発展のために無限な可能性を提供してくださると思います。皆さまが中国の各地に播かれた友好交流の種は、きっと深く根を下ろし、美しい花を咲かせ、豊かな実を結ぶに違いありません。

皆さまが、不慣れな中国の生活習慣や食事などにもかかわらず、本日、全員無事、健康ですべての旅行日程を終えられ、しかも大きな成果を挙げられましたことは、何にもまして私どもの大きな喜びとするところでございます。しかし一方、私どもの接待の面で何かと不行き届きがありましたことをお許しください。

わずかに3週間の期間ではありましたが、私たちの間には、すでに強い友情の絆が結ばれました。迫り来る別れの時を前にして、誠にお名残惜しい気持ちで胸がいっぱいであります。しかしまた、今度は日本での再会の日をお約束することといたしましょう。

皆さんは、数時間後の日本でのご家族や友人との再会を思い、すでに帰心矢の如しとなっておられるのではありませんか。

ご一行の無事平安を心からお祈り申し上げて、お見送りのご挨拶といたします。

第13篇:外文致辞

尊敬的宫田先生、在座的各位先生:

此次,我们应日本外务省的邀请,于7月22日抵达成田机场,进行了为期两周的访问。 我们先后访问了东京、横滨、名古屋、京都、大阪、神户、福冈等城市,参观了工厂、企业、研究所、学校和名胜古迹,并且同有关方面的先生们进行了座谈和交流。至此我们结束了为期两周的活动日程,明天就要踏上归国的旅程了。

今天,为了表达我们对日本朋友的感谢之情,在这里举行答谢酒会,承蒙各位先生在百忙之中特地光临,对此深表感谢!

我们在日本仅仅逗留两周,不免有“走马观花”之感。尽管如此,还是基本上达到了预期的访问目的,这首先应归功于各位先生的盛情接待和精心安排的结果。我谨代表我团全体成员,向接受我们访问的各地有关人士,以及热情接待我们的朋友们表示衷心的感谢。

我们在东京逗留期间,村山先生在百忙之中特地接见了我们,并发表了高瞻远瞩的见解,是我们受益非浅,在开展今后的工作方面给予我们以极大的鼓舞。

俗话说“百闻不如一见”。通过这次访问,我们全方位地参观了先进国家日本,学到了很多东西。同时也亲眼目睹了日本朋友们在为走出“泡沫经济”崩溃后形成的暂时性的经济低谷而努力奋斗的情景,使我们十分钦佩。另一方面,中国现在正乘着入世的东风,继续大力推进对外开放政策。而日本的先进技术和雄厚的资金,对我国经济的发展具有极为重要的意义。我衷心希望中日两国在各行各业的友好合作能够不断发展下去。

通过这次访问,我们又结识了很多新朋友,这是我们最为珍贵的财富。我们衷心希望以宫田先生为首的各位日本朋友能够尽早访问中国。

我们明天就要离开东京返回中国了。在此,再一次对日本朋友们的深厚情谊表示衷心的感谢。

最后,为中日两国世世代代友好下去,

为宫里先生的健康,

为在座的朋友们的身体健康,

干杯! 尊敬する宮田先生、並びにご臨席の皆様:

私たちはこのたび、日本外務省のお招きにより、7月22日成田空港に降り立ち、二週間の友好訪問にやって参りました。以来、東京、横浜、名古屋、京都、大阪、神戸、福岡などを歴訪し、工場、企業、研究所、学校、名所旧跡などを見学し、また関係方面の方々と親しく懇談と交流を重ねてまいりました。こうして今二週間の友好交流の旅を終え、明日帰国の途に着こうとしております。

本日、私たちは皆様に対する感謝の気持ちをお伝えするために、この答礼宴会を設けました。皆様公私ご多忙の中、わざわざご出席くださり、誠にありがとうございます。

私どもの日本滞在日数はわずか二週間で、誠に「馬上花を見る」思いを免れませんが、にもかかわらず、所期の目的を基本的に達成しえましたことは、一重に関係各位の心からのご接待と、細やかなご配慮の賜物にほかなりません。訪問させていただきました各地の関係各位、またお世話にいただきました皆様に、団員一同に代わり、厚くお礼申し上げます。

また、私たちの東京滞在中には、村山先生が公務ご多忙の中、わざわざ私どもと会見してくださり、遠い未来を見通して、誠に有益なお話を聞かせてくださいました。これは今後の仕事を進めていく上で、誠に大きな励ましとなりました。

諺に「百聞は一見に如かず」と申しますが、私どもは今回の訪問を通じ、先進国日本を全面的に見学し、大変勉強になっていると共に、日本の皆様が、「バブル経済」崩壊後の一時的な不況から脱出するために奮闘努力しておられる姿をこの目で拝見し、敬服しております。一方、中国はいま、WTO加盟で勢いをつけはじめ、対外開放の政策をより一層力強く推し進めており、日本の進んだ技術と豊かな資金力は中国の経済発展のために非常に重要な役割を果たすものと思います。私は、中日両国の各分野における友好協力が今後とも続けられますよう願っております。

また、私どもは、このたびの訪問を通じ、数多くの新しい友人を得ることができましたことを、何よりも貴きとするものであります。私は宮田先生を始めとする日本友人の皆様が、できるだけ早い機会に中国を訪問されることを心から期待してやみません。

私どもは、いよいよ明日東京を発ち帰国の途につきます。ここに重ねて日本の皆様の厚い友情に感謝いたします。

では、最後に 中日両国の子々孫々までの友好を祈り、

宮田先生のご健康を祈り、

ご臨席の友人の皆様のご健康を祈って、

乾杯したしたいと思います。

乾杯!

第14篇:外文翻译

设计一个位于十字路口的智能交通灯控制系统

摘要:本文模型使用模糊本体的交通灯控制域,并把它应用到控制孤立十字路口。本文最重要的目的之一是提出一个独立的可重复使用的交通灯控制模块。通过这种方式,增加软件的独立性和为其他的软件开发活动如测试和维护,提供了便利。专家对本体论进行手动的开发和评估。此外,交通数据提取和分类路口使用的人工神经网络的图像处理算法。根据预定义的XML架构,这种信息转化为XML实例映射到适合使用模糊推理引擎的模糊规则的模糊本体。把本系统的性能与其他类似的系统性能进行比较。比较结果显示:在所有的交通条件下,在每个周期中,对每辆车它有低得多的平均延迟时间与其他的控制系统相比。

关键词:模糊本体,智能代理,智能交通系统(ITS),交通信号灯控制(TLC),孤立的十字路口,图像处理,人工神经网络

1.引言

作为城市交通增加的结果,道路网络的能力有限和发展交通工具和方法的技术方面,许多实体,关系,情况和规则已经进入交通灯控制域和转化成为一个知识领域。这个领域的建模知识帮助交通代理和应用有效地管理关于实时条件下的交通。全面知识建模领域的一个最合适的方法是使用本体概念。“本体论是一个正式的、明确的一个共享的概念化的规范。以前的模型是基本的本体建设的基础,为下列建立一个共享的语义丰富的知识域。除了本体作为概念化的形式主义的重要性,它有可能超过所代表的数据。这种能力将提高有关性能的决定和其他非智能系统的功能特点。在近年来,本体论上的研究正成为一个新的热点话题在不同的活动,如人工智能,知识管理,语义网络,电子商务和几个其他应用领域。这些领域之一是智能交通系统。一些努力已制成这个通过展示和使用本体检测交通领域拥塞,管理非城市道路气象事件,驾驶阿德福—索里系统,共享和整合一个智能交通系统。本文的目的是介绍一个红绿灯有效控制孤立交叉口这方面的知识重用的控制本体。这种新的办法适用于智能代理使用知识决策模糊。该系统采用的图像来自安装了监控摄像机拍摄的路口。这些图像处理利用图像处理算法和神经网络的方法,然后发送到一个智能代理。第2节中,我们将简要地解释了在这项工作中运用的技术包括seman-TIC网络技术,智能代理技术和交通的回地面光控制方法。在第3节,新的系统架构是基于分层语义网络架构。第4节介绍交通灯控制的模糊本体的建设。第五节从路口提取的图像信息解释。在第6节,智能系统的运作被完整描述,最后在第7节对所提出的方法进行评估,对结论进行阐述。

2.背景

本节说明在这项工作中的应用技术包括语义网络技术,特别本体和模糊本体。此外,国家的交通灯控制的艺术方法是简要介绍。 2.1.语义网络技术

语义网络被定义为当前Wed的延伸,这些网站的信息都给出明确的含义;使电脑与人更好的合作。有几层语义Web的建议源自伯纳斯滞后阶段。在此类别中的所有规则如表1所示。图.4显示输出模式的示意图。本次评选有助于智能系统,以确定下一步的阶段测序。

另一种模糊的规则类别涉及估计优化周期时间。这些规则的模糊变量是天气条件,时间,每天平均车辆拥堵情况。出于这个原因,60个模糊规则被定义了。从气象研究所取得气象条件。日期和时间也是在交通专家的知识的基础上以模糊变量形式预先定义的。图5显示日期,时间和周期时间的隶属函数。当天的参数是在日历基础上基于假期和正常的一天与周期时间量的关系预定义的。例如,假期期间的周期时间是较平日少。因此,平日的隶属度比假期多。

例如一个阶段选型的模糊规则如下所述:“如果一个路口的类型是四的方式,平均车辆拥堵低,平均行人拥堵是中等,然后相类型是简单的两阶段”。此外,为周期时间估计的模糊规则表示如下:“如果天气条件是晴天,时间是早晨,天是正常的,平均车辆拥堵是低,则周期时间短”。在此类别中的所有规则都列在附录A。

在此步骤结束时,应该对交通灯逻辑控制的项目的有效性进行评估。此功能是使用专家的意见。评价过程的主要目的是显示发展的本体和其相关的软件环境的用处。虽然所有的信息,尤其是交通灯控制规则已提取国际标准和科学交通文学,专家的知识优势是他们最后的正确性验证标准。所有模糊规则,包括优化周期时间和相位类型的规则,在这个过程中,准备以调查问卷形式和展现给一些专家包括从德黑兰警察局交通上校和两名来自德黑兰的交通组织工程师。由于德尔菲专家的意见,约有84%的淘汰型规则和优化周期时间的87%被接受。此外,所有交通逻辑控制的元素包括概念,关系,属性和公理都被这些专家进行了评估和验证。我们评估逻辑交通控制是基于理论知识的。在这个过程中进行了两项活动,包括检查的要求和能力的问题,并在目标应用环境测试本体。由于逻辑交通控制已建成的基础上,如指定要求优化循环时间,逐步淘汰型,交通的移动和优化绿灯时间,每个阶段的序列中,第一项活动是最好的结果。逻辑交通控制满足所有的交通灯控制的需求,并能回答的能力问题。绩效评估机制,可以支持这种说法。在部分实验结果我们验证了这一过程。

第15篇:外文翻译

当今时代是一个自动化时代,交通灯控制等很多行业的设备都与计算机密切相关。因此,一个好的交通灯控制系统,将给道路拥挤,违章控制等方面给予技术革新。随着大规模集成电路及计算机技术的迅速发展,以及人工智能在控制技术方面的广泛运用,智能设备有了很大的发展,是现代科技发展的主流方向。本文介绍了一个智能交通的系统的设计。该智能交通灯控制系统可以实现的功能有:对某市区的四个主要交通路口进行控制:个路口有固定的工作周期,并且在道路拥挤时中控制中心能改变其周期:对路口违章的机动车能够即时拍照,并提取车牌号。在世界范围内,一个以微电子技术,计算机和通信技术为先导的,一信息技术和信息产业为中心的信息革命方兴未艾。而计算机技术怎样 与实际应用更有效的结合并有效的发挥其作用是科学界最热门的话题,也是当今计算机应用中空前活跃的领域。本文主要从单片机的应用上来实现十字路口交通灯智能化的管理,用以控制过往车辆的正常运作。

研究交通的目的是为了优化运输,人流以及货流。由于道路使用者的不断增加,现有资源和基础设施有限,智能交通控制将成为一个非常重要的课题。但是,智能交通控制的应用还存在局限性。例如避免交通拥堵被认为是对环境和经济都有利的,但改善交通流也可能导致需求增加。交通仿真有几个不同的模型。在研究中,我们着重于微观模型,该模型能模仿单独车辆的行为,从而模仿动态的车辆组。

由于低效率的交通控制,汽车在城市交通中都经历过长时间的行进。采用先进的传感器和智能优化算法来优化交通灯控制系统,将会是非常有益的。优化交通灯开关,增加道路容量和流量,可以防止交通堵塞,交通信号灯控制是一个复杂的优化问题和几种智能算法的融合,如模糊逻辑,进化算法, 和聚类算法已经在使用,试图解决这一问题,本文提出一种基于多代理聚类算法控制交通信号灯。

在我们的方法中,聚类算法与道路使用者的价值函数是用来确定每个交通灯的最优决策的,这项决定是基于所有道路使用者站在交通路口累积投票,通过估计每辆车的好处(或收益)来确定绿灯时间增益值与总时间是有差异的,它希望在它往返的时候等待,如果灯是红色,或者灯是绿色。等待,直到车辆到达目的地,通过有聚类算法的基础设施,最后经过监测车的监测。

我们对自己的聚类算法模型和其它使用绿灯模拟器的系统做了比较。绿灯模拟器是一个交通模拟器,监控交通流量统计,如平均等待时间,并测试不同的交通灯控制器。结果表明,在拥挤的交通条件下,聚类控制器性能优于其它所有测试的非自适应控制器,我们也测试理论上的平均等待时间,用以选择车辆通过市区的道路,并表明,道路使用者采用合作学习的方法可避免交通瓶颈。

本文安排如下:第2部分叙述如何建立交通模型,预测交通情况和控制交通。第3部分是就相关问题得出结论。第4部分说明了现在正在进一步研究的事实,并介绍了我们的新思想。

The times is a automation times nowadays,traffic light waits for much the industey equipment to go hand in hand with the computer under the control of.Therefore,a good traffic light controls system,will give road aspect such as being crowded,controlling against rules to give a technical improvement.With the fact that the large-scale integrated circuit and the computer art promptne develop,as well as artificial intelligence broad in the field of control technique applies,intelligence equipment has had very big development,the main current being that modern science and technology develops direction.The main body of a book is designed having introduccd a intelligence traffic light systematically.The function being intelligence traffic light navar’s turn to be able to come true has:The croing carries out supervisory control on four main traffic of some downtown area;Every croing has the fixed duty period,charges centrefor being able to change it’s period and in depending on a road when being crowded;The motro vehicle breaking rules and regulations to the croing is able to take a photo immediately,abstracts and the vehicle shop sign.Within world range ,one uses the microelectronics technology,the computer and the technology communicating by letter are a guide’s,centering on IT and IT industry information revolution is in the ascendant.But,how,computer art applies more effective union and there is an effect’s brought it’s effect into play with reality is the most popular topic of scientific community,is also that computer applications is hit by the unparalleled active field nowadays.The main body of a book is applied up mainly from slicing machine’s only realizing intellectualized administration of croroads traffic light,use operation in controlling the vehicular traffic regularity.Transportation research has the goal to optimize transportation flow of people and goods.As the number of road users constantly increases, and resources provided by current infras-tructures are limited, intelligent control of traffic will become a very important iue in thefuture.However, some limitations to the usage of intelligent tra?c control exist.Avoidingtraffic jams for example is thought to be beneficial to both environment and economy, butimproved traffic-flow may also lead to an increase in demand [Levinson, 2003].There are several models for traffic simulation.In our research we focus on microscopicmodels that model the behavior of individual vehicles, and thereby can simulate dynam-ics of groups of vehicles.Research has shown that such models yield realistic behavior[Nagel and Schreckenberg, 1992, Wahle and Schreckenberg, 2001].Cars in urban traffic can experience long travel times due to inefficient traffic light con-trol.Optimal control of traffic lights using sophisticated sensors and intelligent optimizationalgorithms might therefore bevery beneficial.Optimization of traffic light switching increasesroad capacity and traffic flow, and can prevent tra?c congestions.Traffic light control is acomplex optimization problem and several intelligent algorithms, such as fuzzy logic, evo-lutionary algorithms, and reinforcement learning (RL) have already been used in attemptsto solve it.In this paper we describe a model-based, multi-agent reinforcement learningalgorithm for controlling traffic lights.In our approach, reinforcement learning [Sutton and Barto, 1998, Kaelbling et al., 1996]with road-user-based value functions [Wiering, 2000] is used to determine optimal decisionsfor each traffic light.The decision is based on a cumulative vote of all road users standingfor a traffic junction, where each car votes using its estimated advantage (or gain) of settingits light to green.The gain-value is the difference between the total time it expects to waitduring the rest of its trip if the light for which it is currently standing is red, and if it is green.The waiting time until cars arrive at their destination is estimated by monitoring cars flowingthrough the infrastructure and using reinforcement learning (RL) algorithms.We compare the performance of our model-based RL method to that of other controllersusing the Green Light District simulator (GLD).GLD is a traffic simulator that allows usto design arbitrary infrastructures and traffic patterns, monitor traffic flow statistics such asaverage waiting times, and test different traffic light controllers.The experimental resulthow that in crowded traffic, the RL controllers outperform all other tested non-adaptivecontrollers.We also test the use of the learned average waiting times for choosing routes of cars through the city (co-learning), and show that by using co-learning road users can avoidbottlenecks.

第16篇:外文翻译

中原工学院毕业设计(论文)译文

超声测距系统设计

原文出处:传感器文摘 布拉福德:1993年第13页

摘要:超声测距系统技校在工业场车辆导航水声工程等领域都具有了广泛的应用价值,目前已应用于物理测量,机器人自动导航以及空气中与水下的目标探测、识别定位等场合,因此,深入研究超声的探测理论和方法具有重要的实践意义,为了进一步提高测量的精确度,满足工程人员对测量精度测距量程和测距仪使用的要求,本文研制了一套基于单片机的使拱式超声测距系统。 关键词:超声波 测距仪 单片机

1、前言

随着科技的发展,人们生活水平的提高,城市发展建设加快,城市给排水系统也有较大发展,其状况不断改善,但是,由于历史原因合成时间性的许多不可预见因素,城市给排水系统,特别是排水系统往往落后于城市建设,因此,经常出现开挖已经建设好的建筑设施来改造排水系统的现象。城市污水给人们带来的困扰,因此箱的排污疏通对大城市给排水系统污水理,人们生活舒适显得非常重要。而设计研制箱涵排水疏通移动机器人的自动控制系统,保证机器人在箱涵中自由排污疏通,是箱涵排水系统疏通机器人的设计研制的核心部分,控制系统核心部分就是超声波测仪的研制。因此,设计好的超声波测距仪就显得非常重要了。

1.

1课题背景

随着经济的发展与汽车科学技术的进步,公路交通呈现出行驶高速化、车流密集化和驾驶员非职业化的趋势。同时,随着汽车工业的飞速发展,汽车的产量和保有量都在急剧增加。但公路发展、交通管理却相对落后,导致了交通事故与日剧增,城市里尤其突出。智能交通系统ITS是目前世界上交通运输科学技术的前沿技术,它在充分发挥现有基础设施的潜力,提高运输效率,保障交通安全,缓解交通赌塞,改善城市环境等方面的卓越效能,已得到各国政府的广泛关注。中国政府也高度重视智能交通系统的研究开发与推广应用。汽车防撞系统作为ITS 发展的一个基础,它的成功与否对整个系统有着很大的作用。从传统上说,汽车的安全可以分为两个主要研究方向:一是主动式安全技术,即防止事故的发生,该种方式是目前汽车安全研究的最终目的;二是被动式安全技术,即事故发生后的乘员保护。目前汽车安全领域被动安全研究较多,主要从安全气囊、ABS(防抱死系统)和悬架等方面着手,以保证驾乘人员的安全。从经济性和安全性两方面来说,

中原工学院毕业设计(论文)译文

这些被动安全措施是在事故发生时刻对车辆和人员进行保护,有很大的局限性,因而车辆的主动安全研究尤为重要,引出了本文研究的基于单片机的超声波测距系统。这个系统是一种可向司机预先发出视听语音信号的探测装置。它安装在汽车上,能探测企图接近车身的行人、车辆或周围障碍物;能向司机及乘员提前发出即将发生撞车危险的信号,促使司机采取应急措施来应付特殊险情,避免损失。

1.2 课题设计的意义

随着现代社会工业化程的发展,汽车这一交通工具正为越来越多的人所用,但是随之而来的问题也显而易见,那就是随着车辆的增多,交通事故的频繁发生,由此导致的人员伤亡和财产损失数目惊人。对于公路交通事故的分析表明,80%以上的车祸事由于驾驶员反应不及所引起的,超过65%的车辆相撞属于追尾相撞,其余则属于侧面相撞。奔驰汽车公司对各类交通事故的研究表明:若驾驶员能够提早1S 意识到有事故危险并采取相应的正确措施,则绝大多数的交通事故都可以避免。因此,大力研究开发如汽车防撞装置等主动式汽车辅助安全装置,减少驾驶员的负担和判断错误,对于提高交通安全将起到重要的作用。显然,此类产品的研究开发具有极大的实现意义和广阔的应用前景。

1.

3超声波测距在汽车上应用的介绍

超声波倒车测距仪( 俗称电子眼)是汽车倒车防撞安全辅助装置,能以声音或者更为直观的数字形式动态显示周围障碍物的情况。其较早的产品是用蜂鸣器报警,蜂鸣声越急,表示车辆离障碍物越近。后继的产品可以显示车后障碍物离车体的距离。其大多数产品探测范围在0.4~1.5m,有的产品能达到0.35~2.5m,并有距离显示、声响报警、区域警示和方位指示,有些产品还具备开机自检功能。目前市场上还出现了具有语音报警功能的产品。这些产品存在的主要问题是测量盲区大,报警滞后,未考虑汽车制动时的惯性因素,使驾驶者制动滞后,抗干扰能力不强,误报也较多。汽车防撞雷达之所以能实现防撞报警功能,主要有超声波这把无形尺子, 它测量最近障碍物的距离, 并告诉给车主。其实超声测距原理简单: 它发射超声波并接收反射回波, 通过单片机计数器获得两者时间差t, 利用公式S=Ct/2计算距离, 其中S为汽车与障碍物之间的距离, C为声波在介质中的传播速度。

本文介绍的超声测距系统共有2只超声波换能器(俗称探头),分别布置在汽车的后左、后右2个位置上。能检测前进和倒车方向障碍物距离, 通过后视镜内置的

中原工学院毕业设计(论文)译文

显示单元显示距离和方位, 发出一定的声响, 起到提示和警戒的作用。系统采用一片STC89C52单片机对两路超声波信号进行循环采集。超声波是指频率高于20HHZ的机械波。为了以超声波作为检测手段,必须产生超生波和接收超声波。完成这种功能的装置就是超声波传感器,习惯上称为超声波换能器或超声波探头。超声波传感器有发送器和接收器,但一个超声波传感器也可具有发送和接收声波的双重作用。超声波传感器是利用压电效应的原理将电能和超声波相互转化,即在发射超声波的时候,将电能转换,发射超声波;而在收到回波的时候,则将超声振动转换成电信号。超声波测距的原理一般采用渡越时间法。首先测出超声波从发射到遇到障碍物返回所经历的时间,再乘以超声波的速度就得到二倍的声源与障碍物之间的距离 。测量距离的方法有很多种,短距离的可以用尺,远距离的有激光测距等,超声波测距适用于高精度的中长距离测量。因为超声波在标准空气中的传播速度为331.45米/秒,由单片机负责计时,单片机使用12.0M晶振,所以此系统的测量精度理论上可以达到毫米级。由于超声波指向性强,能量消耗缓慢,在介质中传播距离远,因而超声波可以用于距离的测量。利用超声波检测距离,设计比较方便,计算处理也较简单,并且在测量精度方面也能达到要求。超声波发生器可以分为两类:一类是用电气方式产生超声波,一类是用机械方式产生超声波。本设计属于近距离测量,可以采用常用的压电式超声波换能器来实现触发单元。

利用超声波测距的工作,就可以根据测量发射波与反射波之间的时间间隔,从而达到测量距离的作用。其主要有三种测距方法:

(1)相位检测法,相位检测法虽然精度高,但检测范围有限;

(2)声波幅值检测法,声波幅值检测法易受反射波的影响;

(3)渡越时间检测法,渡越时间检测法的工作方式简单,直观,在硬件控制和软件设计上都非常容易实现。其原理为:检测从发射传感器发射超声波,经气体介质传播到接收传感器的时间,这个时间就是渡越时间。本设计的超声波测距就是使用了渡越时间检测法。在移动车辆中应用的超声波传感器,是利用超声波在空气中的定向传播和固体反射特性(纵波),通过接收自身发射的超声波反射信号,根据超声波发出及回波接收的时间差和传播速度,计算传播距离,从而得到障碍物到车辆的距离。

中原工学院毕业设计(论文)译文

2 超声波测距原理

2.1 压电式超声波发生器原理

压电式超声波发生器实际上是利用压电晶体的谐振来工作的。超声波发生器内部结构,它有两个压电晶片和一个共振板。当它的两极外加脉冲信号,其频率等于压电晶片的固有振荡频率时,压电晶片将会发生共振,并带动共振板振动,便产生超声波。反之,如果两极板间未加电压,当共振板接收到超声波时,将压迫压电晶片做振动,将机械能转换为电信号,这是它就成为超声波接收器了。

测量脉冲到达时间的传统方法是以拥有固定参数的接收信号开端为基础的。这个信号恰恰选于噪音水平之上,然而脉冲到达时间被定义为脉冲信号刚好超过界限的第一时刻。一个物体的脉冲强度很大程度上取决于这个物体的自然属性尺寸还有它与传感器的距离。进一步说,从脉冲起始点到刚好超过界限之间的时间段随着脉冲的强度而改变。结果,一种错误便出现了——两个拥有不同强度的脉冲在不同时间超过界限却在同一时刻到达。强度较强的脉冲会比强度较弱的脉冲超过界限的时间早点,因此我们会认为强度较强的脉冲属于较近的物体。

2.2 超声波测距原理

超声波发射器向某一方向发射超声波,在发射时刻的同时开始计时,超声波在空气中传播,途中碰到障碍物就立即返回来,超声波接收器收到反射波就立即停止计时。超声波在空气中的传播速度为340m/s,根据计时器记录的时间t,就可以计算出发射点距离障碍物的距离(s),即:s=340t/2

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3、超声波测距系统的电路设计

系统的特点是利用单片机控制超声波的发射和超声波自发射至接受往返时间的计时,单片机选用C51,经济易用,且片内有4K的ROM,便于编程。电路的原理如图1所示。

图1 电路原理图

中原工学院毕业设计(论文)译文

3.1 40kHz脉冲的产生与超声波发射

测距系统中的超声波传感器采用UCM40的压电陶瓷,它的工作电压是40kHz的脉冲信号,这由单片机执行下面的程序来产生。 puzel:mov 14h,#12h

here: cp1.0;

nop;

nop;

nop;

djnz 14h,here;

Ret

前方测距电路的输出端接单片机P1.0端口,单片机执行上面的程序后,在P1.0端口输出一个40khz的脉冲信号,经过三极管T放大,驱动超声波发射头UCM40T,发出40khz的脉冲超声波,且持续发射200ms。右侧合作侧测距电路的输入端分别接P1.1和P1.2端口,工作原理和前方测距电路相同。

超声波发射持续200ms 输出40kHz方波

3.2 超声波的接收与处理

接收头采用与发射头配对的UCM40R,将超声波调制脉冲变为电压信号,经运算放大器ic1a和ic1b两级放大后加至IC2,。IC2是带有锁定环的音频译码集成块LM567,内部压控振荡器的中心频率f0=1/1.1R8C3,电容C4决定其带宽。调节R8在发射的载频上,则LM567输入信号大于25mv,输出端8脚由5由高电平跃变为低电平,作为中断请求信号,送至单片机处理。

前方测距电路的输出端接至单片机INT0端口,中断优先级最高,左、右测距电路的输出通过与门IC3A的输出接单片机的INT1端口,同时单片机P1.3和P1.4接到IC3A的输入端,中断源的识别由程序查询来处理,中断优先级为先右后左。部分源程序如下: receive1:push psw

push acc

clr ex1;关中断源1

jnb p1.1,right;P1.1引脚为0,转至右侧距电路中断服务程序

jnb p1.2,left;P1.2 引脚为0,转至左测距中断电路服务程序 returne:SETB EX1;

开外部中断1

pop acc

中原工学院毕业设计(论文)译文

pop psw

reti right:

...;

右测距电路中断服务程序入口

ajmp return

left:

...;

左测距电路中断服务程序入口

ajmp return

3.3 计算超声波传播时间

在启动发射电路的同时启动单片机内部的定时器T0,利用定时器的计数功能,记录超声波发射的时间和受到反射波的时间。当收到超声波反射波时,接受电路输出端产生一个负跳变,在INT0或INT1端产生一个中断请求信号,单片机响应外部中断请求,执行外部中断服务子程序,读取时间差,计算距离。其部分源程序如下:

RECEIVEO: PUSH PSW

PUSH ACC CLR EX0;

关外部中断0 读取时间值

MOV R7,TH0; MOV R6,TL0 CLR C MOV A,R6 SUBB A,#0BBH; MOV 31H,A; MOV A,R7 SUBB A,#3CH MOV 30H,A SETB EX0; POP ACC

POP PSW

RETI 对于一个平坦的目标,测量距离包括两个阶段:粗糙的测量和精细的测量。 第一步:脉冲的传送产生一种简单的超声波

第二步:根据公式改变回波放大器的获得量直到回拨被检测到。 第三步:检测两种回波的振幅与过零时间。

计算时间值 存储结果

开外部中断0

中原工学院毕业设计(论文)译文

第四步:设置回波放大器的所得规格输出,假定是3v。通过脉冲的周期设置下一个脉冲。根据第二部的数据设定时间窗。

第五步:发射两窜脉冲产生干扰波。测量过零时间与回波振幅。如果逆向发生在回波中,决定要不通过在低气压插入振幅。

第六步:通过公式计算距离y。

中原工学院毕业设计(论文)译文

4、超声波测距系统的软件设计

软件分为俩部分,主程序和中断服务程序。主程序完成初始化工作、各路超声波发射和接收顺序的控制。定时中断服务子程序完成三方向超声波的轮流发射,外部中断服务子程序主要完成时间值的读取、距离计算、结果的输出等工作。

中原工学院毕业设计(论文)译文

5、结论

对所要求测量范围30cm-200cm内的平面物体做了多次测量发现,其最大误差为1.5cm,且重复性好。可见基于单片机设计的超声波测距系统具有硬件结构简单、工作可靠、测量误差小等特点。因此,它不仅可用于移动机器人,还可以用在其他检测系统中。

思考:至于为什么不用接收管做放大电路,因为放大倍数搞不好,集成放大电路,还带自动电平增益控制,放大倍数为76db,中心频率是38k到40k,刚好是超声波传感器的谐振频率。

中原工学院毕业设计(论文)译文

参考文献

1.Fox,J.D.,Khuri-Yakub,B.T.and Kino,G.S.,\"High Frequency Acoustic Wave Measurement in Air\",in Proceedings of IEEE 1983 Ultrasonic Symposium,October 31-2 November,1983,Atlanta,GA,pp.581-4.2.Martin Abreu,J.M.,Ceres,R.And Freire,T.,\"Ultrasonic Ranging: Envelope Analysis Gives Improved Accuracy\",Sensor Review, Vol.12 No.1,1992,pp.17-21.3.Parrilla,, M., Anaya,J.J and Fritsch C.,‖Digital Signal Proceing Techniques for High Accuracy Ultrasonic Range Measurement:,IEEE Transactions: Instrumentation and Measurement.Vol.40 No.4, August 1991,pp.750-63.4.Canali, C., Cicco, G.D., Mortem, B., Prudenziati, M., and Taron, A., ―A Temperature Compensated Ultrasonic Sensor Operating in Air for Distance and Proxinmity Measurement‖, IEEE Trasaction on Industry Electronics, Vol, IE-29 No.4,1982, pp.336-41.5.Martin, J.M., Ceres, R., Calderon, L and Freire, T., ‖Ultrasonic Ranging Gets Themal Correction‖, Sensor Review, Vol, 9 No.3, 1989,pp.153-5.

中原工学院毕业设计(论文)译文

Ultrasonic ranging system design Publication title: Sensor Review.Bradford:1993.Vol.13 ABSTRACT: Ultrasonic ranging technology has wide using worth in many field, such as the industrial locale, vehicle navigation and sonar engineering.Now it has been used in level measurement, self-guided autonomous vehicles, fieldwork robots automotive navigation, air and underwater target detection, identification ,location and so on.So there is an important practicing meaning to learn the ranging theory and ways deeply.To improve the precision of the ultrasonic ranging system in hand, satisfy the request of the engineering personal for the precision,the bound and the usage, a portable ultrasonic ranging system based on the single chip proceor was developed.Keywords: Ultrasound r, Ranging System, Single Chip Proceor

1.Introductive With the development of science and technology, the improvement of people’s standard of living, speeding up the development and construction of the city.Urban drainage system have greatly developed their situation is constantly improving.However, due to historical reasons many unpredictable factors in the synthesis of her time, the city drainage system.In particular drainage system often lags behind urban construction.Therefore, there are often good building excavation has been building facilities to upgrade the drainage system phenomenon.It brought to the city sewage, and it is clear to the city sewage and drainage culvert in the sewage treatment system.Confort is very important to people’s lives.Mobile robots designed to clear the drainage culvert and the automatic control system Free sewage culvert clear guarantee robot, the robot is designed to clear the culvert sewage to the core.Control System is the core component of the development of ultrasonic range finder.Therefore, it is very important to design a good ultrasonic range finder.

1.1 subject background

With the development of economy and car scientific and technological progre, highway traffic presents driving fast pace, traffic dense is changed and the driver not profeional trend.At the same time, along with the rapid development of auto industry, automobile yield and quantities are increased dramatically.But road development,

中原工学院毕业设计(论文)译文

transportation management is relatively backward, leading to a large number of traffic accidents in some cities, especially prominent.Intelligent transportation system in the world, ITS transportation science and technology of advanced technology, ITS exerting existing infrastructure of potential, enhance the transport efficiency, safeguard traffic safety and ease traffic wager plug, improving urban environment aspects of outstanding performance, has received the governments of widespread concern.The Chinese government is also highly intelligent transportation system of the development and popularization applications.The automotive anti-collision system as ITS development of a base, ITS succe to the whole system has a very significant role.Traditionally, auto safety said can be divided into two main research direction: first,it is active safety technology, including the prevention of accidents, the way is now automotive safety research ultimate purpose;second, it is paive safety technique, namely the occupant protection after the accident.Now automotive safety field paive safety more research, mainly from the airbag, ABS (antilock brakes) and suspension from the aspects such as to ensure safety of personnel rides.From the economic and safety two ways, these paive safety measures is the accident of vehicle and personnel moments protection, with great limitations, thus vehicle active safety research is particularly important, leads to a of this study is based on single chip ultrasonic ranging system.This system is a kind of can advance to the driver iued audio-visual speech signal detection devices.It is installed in cars that can detect trying to approach the body of a car pedestrians and vehicles or around obstacles, Can send to the driver and crew imminent danger ahead of the signal, prompting a crash drivers take emergency measures to cope with special danger, avoid the lo.

1.2 question design significance

Along with the development of modern society industrialization proce, car this traffic tools are used for more and more people, but any problem has obvious that along with the increase in vehicles, traffic accident, which led to the frequent occurrence of casualties and property loes number astonishing.For highway traffic accident analysis showed that more than 80% of the accident due to the driver reaction inferior things, caused more than 65% of vehicle collision, the rest belongs to tracing cauda collided belongs to the side collision.Mercedes-benz Automobile Company for all kinds of traffic accident research shows that: if the driver can early 1S are aware

中原工学院毕业设计(论文)译文

that a accident risk and take the appropriate corrective measures, the overwhelming majority of traffic accidents can be avoided.Therefore, vigorously research and development as the automotive anti-collision device etc active car auxiliary safe device, reduce the burden and misjudgments drivers to improve the traffic safety will play an important role.Obviously, this kind of product research and development has great realize meaning and broad application prospects.

1.3 Ultrasonic ranging in automotive applications introduced

Ultrasonic back-draft rangefinder (known as electron optics) automotive anti-collision reversing device, can safe adjunct to sound or more intuitive digital form the dynamic display of around obstacles.Its earlier products is to use buzzer alarm, hum more anxious, and says vehicles from obstructions closer.Subsequent product can display the car from the body after the obstacles distance.Most of its products detection range in 0.4 ~ 1.5 m, some product can achieve 0.35 ~ 2.5 m, and have distance display, sound alarm, area-warning and azimuth instructions, some products also has the boot self-checking function.Still appeared on the market at present with voice alarm function of products.These products are the main problem is big, alarm measuring blind area lags behind, without considering the automobile braking inertial factors and make drivers brake lag, the anti-interference ability is not strong, mitatement or more.The automotive anti-collision radar is able to realize impact-proof alarm functions, basically have ultrasonic this intangible ruler, it recently obstacles distance measurement, and told to the owner.Actually ultrasonic range-finding principle simple: it emit ultrasonic echo, and receive reflected by microcontroller counter obtain both lag using formula S = t, Ct / 2 calculating distances, including S for cars and obstacles, C for the distance between the sound wave propagation in the medium speed.

This paper introduces the ultrasonic ranging system only have 2 ultrasonic transducer (known as probe) respectively, decorate in cars left and right after after 2 position.Capable of detecting forward and reverse direction obstacle distance, the rearview mirror built-in display element display distance and direction, iued must be sound, plays the role of hints and alert.System USES a STC89C52 SCM two way ultrasonic signal cyclicly acquisition.Ultrasonic refers to the 20HHZ wave frequency is over.In order to use the ultrasonic detection means, must generate as ultrasonic wave and receiving damnation.Complete the functions of the device is called the

中原工学院毕业设计(论文)译文

ultrasonic sensor, habit, ultrasonic transducer or ultrasonic probe.Ultrasonic sensors have both transmitters and receivers, but a ultrasonic sensors can also has the sending and receiving the sound waves of the dual role.Ultrasonic sensors is using the principle of piezoelectric effect and ultrasonic energy conversion, be in namely emit ultrasonic, energy conversion, launch ultrasonic, And in the stockades, received echo ultrasonic vibration into electrical signal.Ultrasonic ranging principle generally USES the time method for the croing.First measured ultrasonic from the launch to meet obstacles returns experience of time, again multiply ultrasonic speed of get twice the distance between the sound source and obstacles.Measuring distance a variety of ways, short can use ruler, long-range laser displacement etc, are suitable for high accuracy of ultrasonic ranging in long distance measurement.Because of ultrasound in standard air of propagation speed 331.45 meters per second, by single-chip microcomputer is responsible for timing, SCM use 12.0 M crystals, so the system of measurement precision theory can achieve mm level.Because of ultrasonic directivity strong, energy consumption is slow, in a medium transmiion distance, thus ultrasonic can be used for distance measurement.Using ultrasonic detection distance, the design is more convenient, computing procese also relatively simple, and the measurement precision can also meet the requirements.Ultrasonic generator can be divided into two kinds: one kind is to use electrical means producing ultrasonic, one kind is with mechanical approach to producing ultrasonic.This design belongs to nearly distance measurement, can use commonly used the piezoelectric ultrasonic transducer to achieve trigger unit.

Using ultrasonic ranging work, can according to measuring launch reflection wave wave and the time interval between the measured distance, so as to achieve the effect.It mainly have three ranging methods:

(1) phase aay, phase aays high precision, but detection though limited range,

(2) sound amplitude aay, acoustic amplitude aay vulnerable reflection wave influence;

(3) ferrying more time aay, croing the time aay way of working is simple, intuitive, in hardware control and software design are very easy to implement.Its principle is: from the launch emit ultrasonic detection sensor, the gas medium spread to receive sensor of time, this time is croing the more time.This design is the use of ultrasonic ranging the croing the time aay.In the mobile vehicles of the application 15

中原工学院毕业设计(论文)译文

of ultrasonic sensor is the use of ultrasound in air of directional spread and solid reflective characteristics (p-wave) and by receiving their launch ultrasonic reflecting signal, according to the ultrasonic iued and echo receiving the Windows and propagation speed, calculate transmiion distance, thus obtains the obstacles to vehicle distance.

中原工学院毕业设计(论文)译文

2.A principle of ultrasonic distance measurement

2.1 the principle of piezoelectric ultrasonic generator

Piezoelectric ultrasonic generator is the use of piezoelectric crystal resonators to work.Ultrasonic generator, the internal structure as shown, it has two piezoelectric chip and a resonance plate.When it’s two plus pulse signal, the frequency equal to the intrinsic piezoelectric oscillation frequency chip, the chip will happen piezoelectric resonance, and promote the development of plate vibration resonance, ultrasound is generated.Conversely, if the two are not inter-electrode voltage, when the board received ultrasonic resonance, it will be for vibration suppreion, then it becomes the ultrasonic receiver.The traditional way to determine the moment of the echo’s arrival is based on thresholding the received signal with a fixed reference.The threshold is chosen well above the noise level, whereas the moment of arrival of an echo is defined as the first moment the echo signal surpaes that threshold.The intensity of an echo reflecting from an object strongly depends on the object’s nature, size and distance from the sensor.Further, the time interval from the echo’s starting point to the moment when it surpaes the threshold changes with the different intensities arriving exactly at the same tome will surpa the threshold at different moments.The stronger one will surpa the threshold earlier than the weaker, so it will be considered as belonging to a nearer object.

2.2 The principle of ultrasonic distance measurement Ultrasonic transmitter in a direction to launch ultrasound, in the moment to launch the beginning of time at the same time, the spread of ultrasound in the air, obstracles on his way to return immediately, the ultrasonic reflected wave wave received by the reveiver immediately stop the clock.Ultrasonic in the air as the propagation velocity of 340m/s, according to the timer records the time t, we can calculate the distance between the launch distance barrier(s), that is:s=340t/2

中原工学院毕业设计(论文)译文

3.Ultrasonic Ranging System for the Second Circuit Design

System is characterized by single-chip microcomputer to control the use of ultrasonic transmitter and ultrasonic receiver since the launch from time to time, single-chip selection of 8751,economic-to –use, and the chip has 4K of ROM, to facilitate programming.Circuit schematic diagram shown in Figure 1.

Figure 1 circuit principle diagram

中原工学院毕业设计(论文)译文

3.1 40 kHz ultrasonic pulse generated with the launch

Ranging system using the ultrasonic sensor of piezoelectric sensors UCM40, its operating voltage of the pulse signal is 40kHz, which by the single-chip implementation of the following procedures to generate.Puzel:mov 14h,# 12h; ultrasonic firing continued 200ms here:cpl pl.0; output 40 kHz square wave

nop;

nop; nop; djnz 14h, here; ret Ranging in front of single-chip termination circuit P1.0 input port, single chip implementation of the above procedure, the P1.0 port in a 40kHz pulze output signal, after amplification transistor T, the drive to launch the first ultrasonic UCM40T, iued 40kHz ultrasonic pulse, and the continued launch of 200ms.Ranging the right and the left side of the circuit, respectively, then input port P1.1 and P1.2, the working principle and circuit in front of the same location.

3.2 Reception and proceing of ultrasonic

Used to receive the first launch of the first pair UCM40R, the ultrasonic pulse modulation signal into an alternating voltage, the op-amp amplification IC1A and after polarization IC1B to IC2.IC2 is locked loop with audio decoder chip LM567, internal voltage-controlled oscillator center frequency of f0=1/1.1R8C3, capacitor C4 determine their target bandwidth.R8-conditioning in the launch of the carrier frequency on the LM567 input signal is greater than 25Mv, the output from the high jump 8 feet into a low-level, as interrupt request signals to the single-chip proceing.Ranging in front of single-chip termination circuit port INT0 interrupt the highest priority, right or left location of the output circuit with output gete IC3A acce INT1 port single-chip, while single-chip P1.3 and P1.4 received input IC3A, interrupted by the proce to identify the source code is as follows: receivel:

push psw

push ace

中原工学院毕业设计(论文)译文

cir ex1: related external interrupt 1

jnb p1.1, right; P1.1 pin to 0, ranging from right to interrupt service rountine circuit

jnb p1.2, left; P1.2 pin to 0, to the left ranging circuit

interrupt service routine return:SETB EX1;open external interrupt 1

pop

acc pop

psw reti right:…; right location entrance circuit interrupt service rountine

Ajmp Return left:…; left Ranging entrance circuit interrupt service rountine

Ajmp Return

3.3 The calculation of ultrasonic propagation time

When you start firing at the same time start the single-chip circuitry within the timer T0, the use of timer counting function records the time and the launch of ultrasonic reflected wave received time when you receive the ultrasonic reflected wave, the receiver circuit outputs a negative jump in the end of INT0 or INT1 interrupt request generates a signal, single-chip microcomputer in response to external interrupt request, the implementation of the external interrupt service subroutine, read the time difference, calculating the distance.Some of its source is as follows: RECEIVE0: PUSH PSW PUSH ACC CLR EX0; related external interrupt 0 MOV R7, TH0; read the time value MOV R6, TL0 CLR C MOV A, R6 SUBB A,#0BBH; calculate the tome difference MOV 31H, A; storage results MOV A, R7 SUBB A,#3CH

中原工学院毕业设计(论文)译文

MOV 30H,A SETB EX0; open external interrupt 0 POP ACC POP PAW RETI For a flat target, a distance measurement consists of two phases: a coarse measurement and, a fine measurement: Step 1: Transmiion of one pulse train to produce a simple ultrasonic

Wave.Step 2: Changing the gain of both echo amplifiers according to equation,

until the echo is detected.Step 3:detection of te amplitudes anf zero-croing times of both echoes.Step 4:setting the gains of both echo amplifiers to normalize the output at, say 3 volts.Setting the period of the next pulses according to the: period of echoes.Setting the time window according to the data of step 2.Step 5:sending two pulse trains to produce an interfered wave.Testing the zero-croing in the echo,detemine to otherwise calculate to by interpolation using the amplitudes near the trough. Derive t sub ml and t sub m2.Step6: Calculation of the distance y using equation.

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中原工学院毕业设计(论文)译文

4.The ultrasonic ranging system software design

Software is divided into two parts, the main program and interrupt service routine.Completion of the work of the main program is initialized, each sequence of ultrasonic transmitting and receiving control.

Tnterrupt service routines from time to complete three of the rotation direction of ultrasonic launch, the main external interrupt service subroutine to resd the value of completion time, distance calculation, the results of the output and so on.

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中原工学院毕业设计(论文)译文

5.Conclusions

Required measuring range of 30cm~200cm objects inside the plane to do a number of measurements found that the maximum error is 0.5cm, and good reproducibility.Single-chip design can be seen on the ultrasonic ranging system has a hardware structure is simple, reliable, small features such as measurement error.Therefore, it can be used not only for mobile robot can be used in other detection systems.Thoughts: As for why the receiver do not have the transistor amplifier circuit, because the magnification well, integrated amplifier, but also with automatic gain control level, magnification to 76dB, the center frequency is 38k to 40k, is exactly resonant ultrasonic sensors frequency.

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中原工学院毕业设计(论文)译文

REFERENCES 1.Fox,J.D.,Khuri-Yakub, B.T.and Kino, G.S., ‖High Frequency Acoustic Wave Measurement in Air‖, in Proceedings of IEEE 1983 Ultrasonic Symposium, October 31-2 November, 1983, Atlanta, GA, pp.581-4.2.Martin Abreu,J.M.,Ceres,R.and Freire, T.,‖Ultrasonic Ranging: Envelope Analysis Gives Improved Accuracy‖, Sensor Review, Vol.12No.1,1992, pp.17-21.3.Parrilla,, M., Anaya,J.J and Fritsch C.,‖Digital Signal Proceing Techniques for High Accuracy Ultrasonic Range Measurement:,IEEE Transactions: Instrumentation and Measurement.Vol.40 No.4, August 1991,pp.750-63.4.Canali, C., Cicco, G.D., Mortem, B., Prudenziati, M., and Taron, A., ―A Temperature Compensated Ultrasonic Sensor Operating in Air for Distance and Proxinmity Measurement‖, IEEE Trasaction on Industry Electronics, Vol, IE-29 No.4,1982, pp.336-41.5.Martin, J.M., Ceres, R., Calderon, L and Freire, T., ‖Ultrasonic Ranging Gets Themal Correction‖, Sensor Review, Vol, 9 No.3, 1989,pp.153-5.

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第17篇:外文文献

计算机科学课程96(2016)4281.40%)与x方向坐标(0.008 - 0.141%)的百分比差异显著高。与此同时,中心的y方向和主要部分左侧的坐标的百分比差异均高于右侧。结果表明,在主要部件的中心位置和主要部件的左侧,特别是y方向的坐标,需要对所有类型的装配空间进行明显的大调整。这些结果与表1校准的结果相对应,在标准对象的左侧区域发现了最大误差。

使用LabVIEW,我们获得了友好的用户界面程序,帮助用户跟踪装配过程的状态。该程序显示捕获的图像、装配空间、调整后的坐标(x、y)、装配空间的方向,以及IAI协议B的命令,如图10和图11所示。

通过图像处理器,系统可以正确识别和识别装配空间的形状和方向。机器人可以拾取对应于装配空间的正确装配部件。在我们使用转换因子校准程序后,我们发现机器人可以移动到正确的装配位置。如图12所示,机器人可以将组装部分正确地放置到主体部分(100%),从而提高了装配过程的效率。这种自动装配系统需要提高系统的灵活性。该系统可以很好地应用于图像处理器的黑色部分,以检测装配空间、形状和装配空间的方向。然而,这个系统可能与发光的部分不兼容,这些发光的部分可能会给照相机反射出生动的光。在这种情况下,它可能会导致图像处理器的一些误差,从而检测出装配空间的形状和正确方向。这进一步的改进被认为是团队未来的工作。

本文提出了柔性自动化装配系统与机器视觉系统相结合的主要原型。在机器视觉系统的图像处理中,所捕获的图像是指定装配部件的正确目标位置的主要关注点。我们需要进行图像校准,以获得用于机器人拾取和放置过程的装配空间的正确坐标。在主要部件的中心位置和主要部件的左侧,特别是y方向上的坐标,需要对所有类型的装配空间进行大的调整。最后,我们得到了可靠的柔性自动化装配系统,能够正确地检测和识别装配空间的形状和定位,从而实现了SCARA的完美选择和放置过程。该样机预计将被开发用于复杂的产品模型和复杂的生产线,这将是我们未来的挑战工作。

第18篇:网络营销外文翻译

E---MARKETING

(From:E--Marketing by Judy Strau,Adel El--Ansary,Raymond Frost---3rd ed.1999 by Pearson Education pp .G4-G25.)

As the growth of Googel.com shows, some marketing principles never change.Markets always welcome an innovative new product, even in a crowded field of competitors ,as long as it provides customer value.Also,Google`s succe shows that customers trust good brands and that well-crafted marketing mix strategies can be effective in helping newcomers enter crowded markets.Neverthele, organizations are scrambling to determine how they can use information technology profitably and to understand what technology means for their busine strategies.Marketers want to know which of their time-ested concepts will be enhanced by the Internet, databases,wirele mobile devices, and other technologies.The rapid growth of the Internet and subsequent bursting of the dot-com bubble has marketers wondering,\"What next?\" This article attempts to answer these questions through careful and systematic examination of succeful e-mar-keting strategies in light of proven traditional marketing practices.(Sales Promotion;E--Marketing;Internet;Strategic Planning )

1.What is E--Marketing E--Marketing is the application of a broad range of information technologies for: Transforming marketing strategies to create more customer value through more effective segmentation ,and positioning strategies;More efficiently planning and executing the conception, distribution promotion,and pricing of goods,services,and ideas;andCreating exchanges that satisfy individual consumer and organizational customers` objectives.This definition sounds a lot like the definition of traditional marketing.Another way to view it is that e-marketing is the result of information technology applied to traditional marketing.E-marketing affects traditional marketing in two ways.First,it increases efficiency in traditional marketing strategies.The transformation results in new busine models that add customer value and/or increase company profitability.

2.Environment,Strategy,and Performance (ESP) E-Marketing flows form the organization `s overall e-busine strategies and selected busine environment,where legal,technological,competitive,marketrelated, and other environmental, factors external to the firm create both opportunities and threats.Organizations perform SWOT analyses to discover what strengths and weaknees they have to deploy against threats and opportunities.This SWOT analysis leads into e-busine and e-marketing strategy.Firms, select e-busine strategies and e-busine models, and then marketers formulate strategy and create e-marketing plans that will help the firm accomplish its overall goals.The final step is to determine the succe of the strategies and plans by measuring results.Performance metrics are specific measures designed to evaluate the effectivene and efficiency of the e-busine and e-marketing operations.this is so important in today` s e-busine climate that media reports seem to be full of references to ROI and other measures of succe for e-busine strategies and tactics featured in the model.The esp model might just as easily depict a brick-and-mortar busine proce -by removing a few \"e `s\" this underscores the idea that e-businees are built on sound practices and proven procees but with important e-transformations and emarketing practices, as discued in this book.This chapter examines the environmental factors in the ESP model, whereas Chapter 4 and Chapter 5 explore these important factors in more depth.Chapter 2 delves into the strategy area, and Chapter 3 discues the e-marketing planning proce.The marketing environment is ever change, providing plenty of opportunities to develop new products, new markets, and new media to communicate whit customers, plus new channels to reach busine partners.At the same time, the environment poses! Competitive, economic , and other threats.This section introduces three key environmental factors that affect e-marketing : legal, technological, and marketrelated factors.Current and pending legislation can greatly influence e-marketing strategies.Chief among these are laws concerning privacy, digital property, expreion, and fraud.Privacy is difficult to legislate, yet it is critically important to consumers who routinely yield personal information over the Internet.One hot iue involves opt-out e-mail.This occurs when users must uncheck a Web page box to avoid being put on a few users read the Web page carefully enough to notice the opo-out box.Digital property problems began in the Web` s early days and continue to puzzle firms and legislators alike.In a medium where content is freely distributed, it can be freely ripped off-not a good thing for the content authors.Spam, offensive content , and other forms of personal expreion conflict whit user rights and thus, from an ongoing discuion among legislaer needs? Finally , new technology brings new opportunities for fraud.Although regulatory agencies are working hard to prevent fraud, enforcement is difficult in a networked world.Technological developments are altering the composition of Internet audiences as well as the quality of material that can be delivered to them.For example, about 20% of the U.S.Population enjoys high-bandwidth connections-primarily cable modems and DSL lines--that enable delivery of multimedia content.Some Web sites are beginning to create three forms of content :a high-- speed multimedia form, a standard PC offering, and a handheld format for wirele devices such as cell phones.The prolofera-tion of wirele devices creates a new set of design challenges as firms try to squeeze content onto tinier screens.Also important are technology concerns in developing countries.As communication infrastructures improve and more people use handheld devices ,new geographic markets develop.Further ,e-marketing is evolving through software advances.For instance, technologies that target consumers according to their online behavior are becoming increasingly sophisticated.Incorporating these technologies into Web site design can give a firm a distinct competitive advantage.

3.E-Busine Markets Sergio Zyman, formerly chief marketing officer of Coca-cola ,has been quoted as saying, marketing is supposed to sell stuff.One way information technology helps sell stuff if they don’t` identify appropriate markets.Exhibit 1—5 highlights three important markets that both sell and buy to each other: businees, consumers, and governments.Although this book focuses on the B2C markets are where most busine activity occurs.The busine market is huge because a higher proportion of firms are connected to the Internet than consumers, especially in developing countries.Much of the B2B online activity is transparent to consumers because it involves proprietary networks that allow information and database sharing .Consider FedEx, the package delivery firm.This company maintains mation .Its customers can schedule a package pick-up using the Web site, track the package using a PC or handheld Palm Pilot, and pay the shipping bill online.Sometimes the shipping order is automatically triggered when a mail notification of its delivery progre to the retailer.The Internet is a global market with opportunities existing in unimagined locations, which is why e-marketers must understand consumers in potential geographic segments.For example, with an annual average income of US$300, Vietnamese citizens who opt to spend 28% of their salary on online services do not have much purchasing power.Further, there are waiting lists for automobiles in Vietnam, so an online branding campaign might be a waste of resources .Conversely, Iceland and Denmark are two of the most wired countries in the world with over 60% Internet penetration.Also, consumers in many countries pay by the minute for local phone acce.This is a tremendous deterrent to the kind of casual surfing practiced by Internet users in developed nations.In addition, the infrastructure in some countries does not support high-speed modems.Content delivered to these countries may, therefore, have to be light on bandwidth.Chapters 15 and 16 look at global Internet markets in more detail.

4.Strategic Planning Amazon, like every other marketer on and off the Web, uses strategic planning to get ready for a profitable and sustainable busine future.Strategic planning is the “managerial proce of developing and maintaining a viable fit between the organization`s objectives”, Two key elements of strategic planning are the preparation of a SWOT analysis and the establishment of strategic objectives.the SWOT analysis examines the company` s internal strengths and weaknees with respect to the environment and the competition and looks at external opportunities and threats.Opportunities may help to define a target market or identify new product opportunities, while threats are areas of exposure. In a parallel fashion, marketing strategy becomes e-marketing strategy when marketers use digital technology to implement the strategy.Strategic e-marketing is the design of marketing strategy that capitalizes on the organization’s electronic or information technology capabilities to reach specified objectives.In eence, strategic e-marketing is where technology strategy and marketing strategy wed to form the organization’s e-marketing strategy.

Regardle of whether a customer buys from the stone, the catalog, or the Web site, or whether contact is made by phone, in person, through e-mail, or by postal mail, employees can acce the computerized database for up-to-date account activity and information when dealing with customers.

Most strategic plans explain the rationale for the chosen objectives and strategies.This is especially true for a single e-busine project trying to win its share of corporate resources and top-management support.

5.What`s Next Regardle of the current disillusionment with e-busine,many solid succees exist today and exciting new growth areas will soon emerge, For-Tune magazine has identified seven trends that will help businees move forward into e-marketing during the next few years: Integrating IT software.Twenty-six percent of companies will spend money to integrate all the pieces of corporate technology, such as linking front-end customer service software with back-end order fulfillment system.Boom in Web services.Web services will more deeply into finding universal standards for Internet-related software.Microsoft’s dot-net and Sun’s Java are two competing architectures, for example.Collaboration software.This allows employees, advisors, consultants, and other team members to work on projects while in different geographic locations.For example, ”Napster for Marketers” is peer-to-peer software that one consulting firm uses to collaborate on marketing plans with ad agencies, designers, and others.Dealing with too much date.Better customer relationship management software is helping firms reinforce customer loyalty by analyzing the mountain of data about previous behavior to suggest new products.For example, a flight attendant would be able to ask if a paenger wants coffee with sugar instead of the usual, ”What do you want to drink?”data security.Techies are spending lots of time and money trying to protect data from hackers and viruses.Wirele is here to stay.Technologies such ah 802.11 and Bluetooth use shortrange signals to link a variety of computing and handheld devices in homes, offices, and retail stores.growth in portable computing.Inexpensive computer storage and small machines will aid people who want to work at home, in the car or train, or virtually anywhere.Devices such as IBM’s 9-ounce Metapad hold 5 gigabytes of data and will change the way people work.

网络营销

Google.com的成长发展说明一些营销原理从来不曾变化,对于一项创新产品,只要它能为顾客提供价值,即使已有众多竞争者,市场也总是乐于接受的。Google的成功表明顾客信任的号品牌好的营销组合战略可以有效的帮助新顾客进入纷繁复杂的市场,然而,企业组织纷纷确定如何更好的利用信息技术获得效益收益,确定技术对企业战略而言意味着什么,市场营销人员需要只奥因特网,数据库,无线移动设备及其他技术能提升哪些经过长时期实践检验的营销理念,面对飞速发展的因特网及其后爆发的com经济泡沫,市场营销人员总会问:“接下来会是什么?”我们将试图依照传统营销惯例,通过对成功的网络营销战略进行详细而系统的说明。

1什么是网络营销

网络营销通过对信息技术的广泛应用,达到以下目标:第一,通过更为有效的市场细分、目标定位、差异化、渠道策略等方式,转换营销战略,为顾客创造更大价值;第二对网络营销理念、分销策略、促销策略、产品价格、服务及创意等进行更为有效的规划和实施;第三,创造满足个人和组织客户需求的交易。

这个定义听上去与传统营销的定义非常类似。从另一个方面,可以把网络营销看做是信息技术应用于传统营销的结果,网络营销从以下两方面营销传统营销:首先网络营销提高了传统营销的效率;其次网络营销技术的应用使得很多营销战略发生变化。这种改变带来了新的业务模式,使顾客价值得以提升,并能提供公司收益。

2环境、战略和实施

网络营销源于企业电子业务的总体战略以及企业所选择的业务模式,从企业所选择的业务环境开始,法律、技术、竞争、市场及其他企业外部环境因素在为企业创造机会的同时,也带来了威胁。面对这些机会和威胁,企业通过SWOT分析来发现自己的优势和劣势,并制定出电子业务和网络营销战略。公司选择适合自己的电子业务和模式,营销人员对战略进行阐述,并制定出网络营销计划,帮助公司实现其总体目标,最后要通过评估结果确定战略计划是否成功,功能规阵是对电子业务和网络营销的实施效果和效率进行评估的具体方法,站在当前的电子业务时代,媒体报道是评价指标似乎都是ROI及功能矩阵模型中强调的电子业务战略战术的其他成功评论方法,此时,功能矩阵尤显重要。

如果去点一些电子,ESP模型描述的就是砖块加砂浆的业务流程。这一点更 加强调了电子业务是建立在合理的流程和丰富的实践基础之上的,但重要的是发生了电子化转变和网络营销实践,这将进一进行步讨论。

主要将对EPS模型中的环境因素进行讨论说明,其中的重要因素将在技术杠杆和道德和法律问题做进一步阐述。下一节将深入分析战略内容,之后将讨论网络营销计划的制定。

营销环境始终处于不断变化的状态,公司有大量的机会通过开发新产新市场、新媒介与客户沟通,通过开拓新的渠道与商业伙伴合作。同时,环境的变化也会形成竞争,带来经济户其他方面的压力。下面主要将法律、环境因素等。

网路营销会受到现有法律和正在制定的法律的重大影响,其中主要涉及保密性、数字所有权、表述形式和欺诈方面的法律,保密性方面的立法比较困难,但这对于英特网传输个人信息的消费者又十分重要电子邮件的选择退出功能就是一个麻烦问题,用户必须点击网页上的选择退出复选框才能避免被加入该公司的邮件列表,一些立法者认为,供公司这样做不合法,因为很少有客户注意阅读时的选择退出,因特网产生的早期就出现了数字所有权问题,现在这个问题仍然使企业和立法者感到困惑。在能够自由发布的内容的媒介上,内容也能被自由的删除这对于作者来说不是一件好事。垃圾邮件攻击性内容以及其他违背用户权利的表述形式成为立法者只能跪在探讨对的问题。政府如何在此之间保持平衡,最后,心技术的产生也带来了心得欺诈机会。虽然管理机构一直在努力防止欺诈,但是难以在网络世界实施。技术的发展不仅改变了网络受众的组成成分而且使传递到用户的信息质量发生变化。例如,20%的美国人喜欢高宽带连接,主要通过电缆调节器和数字技术 接入因特网,她主要是传递信息媒体,一些WEB网站已经开始介入新形式的信息内容“高速多媒体信息,标准PC产品信息和用于移动电话等无线设备的掌上产品信息。无线设备应用的扩大还带来了新的设计上的挑战:公司试图将信息内容压缩到微小的屏幕中,技术的重要性与国家的发展息息相关。网络营销是通过网络技术的提高而发展的。例如,根据在线确定目标客户已变得越来越复杂,如能将这些结合到WEB得站点中,将会给公司带来明显的竞争优势。

3电子商务市场

可口可乐公司全球经销总监瑟尔资奥斯曼测曾说过:营销就是要把东西卖出去信息技术有助于销售的一种途径是:在交易前后,使公司与潜在客户、客户

合作伙伴及供应链成员之间的联系更加便利,但如果营销者没有进行恰当市场定位,即使有新技术也无法帮助销售商品。相互间存在买卖关系的三方:企业消费者和政府。尽管是以B2C为重点,涵盖B2B,但大多电子商务活动将出现 B2G,C2C商场中。

由于公司链到因特网的你离高于消费者,因此,企业市场更为庞大,这一点在发展中国家尤为明显。由于许多现在交易包含明显共享信息和数据库转悠网络,因此消费者是透明的。美国联邦快递公司拥有一个商业客户货运数据和账务的庞大信息库。消费者可以在WEB站点上制定包裹,利用PC等掌上电脑跟踪包裹,有时消费者在联邦快递消费购买时,可以自动产生订单,随后公司通过邮件通知零售商,告知货运进展情况。

因特网是一个全球性的市场,在许多未知领域存在大量机会,这也是众多网络营销商想要掌握潜在地域细分客户的原因,例如在越南,城市年均收入300美元,按28%的薪水用于在线服务计算,购买力不高,而且,越南人都在排队等待购买汽车,因此在线品牌战略很可能是一种资源浪费,与之相反,冰岛和丹麦属于世界上网络连通最发达的国家,连接因特网的比例超过60%,而许多国家的消费者还在按分钟向网络支付话费,这对于偶尔上网冲浪的发达地区客户是一个巨大的障碍,此外,一些国家的基础设施尚不能支付高度调节器,因此发送到这些国家的信息只能少量的利宽带。

4战略规划

战略规划是在组织的目标技术资源以及不断变化的市场机会之间发展并维护一个可行方式的管理过程,战略规划的两个基本要素是准备SWOT分析和建立战略目标。Swot分析根据公司所处的环境和竞争程度审查了企业内部的有事和劣势,并且看到了 企业外部的机会和威胁,机会可以帮助企业明确市场定位或验证新产品的时机,而威胁是暴露出来的部分。

类似的,当营销人员利用数字技术实施战略时,营销战略就变成了网络营销战略。

战略网络营销是营销战略的设计,它利用组织的电子或信息技术能力来实现特定的目标。从本质上来说,战略网络营销是技术战略和营销战略的结合。

无论客户是从商场、目录栏还是网页购买商品,还是通过电话、面谈、电子邮件或者邮政信件完成联络,雇员处理客户需求时可以进入计算机数据库得到及时更新的账户活动和信息。

大多数的战略计划解释了被选定的目标和战略的合理性。这些对师徒赢得公司资源共享和高级管理层支持的独立电子业务项目来说尤为适用。

5 下一步的趋势

《财富》杂志列出了未来纪念的7个发展趋势,将有助于企业步入网络营销: 集成IT软件。26%的公司将投资对公司全部技术进行集成,如把前端客户服务软件和后端订单处理系统连接起来。

Web服务繁荣。Web服务将有更深入的发展,为因特网相关软件建立通用标准。例如,微软公司的.net和太阳微系统公司的Java就是两个互相竞争的基础构架。

协同软件。使用协同软件,公司的员工、顾问和项目团队的其他成员能够实现在不同的地理区域协同工作。例如“Napster for marketers”是一个对等网络软件,咨询公司使用此软件和广告代理商,设计人员及其他相关人员协作制定营销计划。

大量数据处理。好的客户关系管理软件通过分析用户以前的购买行为向其推荐新的产品,帮助企业提高用户的忠诚度。例如,空中服务员根据乘客以前乘机的偏好记录,可以直接询问他是否需要加糖的咖啡,而不是通常的“您需要什么”。数据安全。技术人员花费了大量时间和资金设法保护数据受到来自黑客和病毒的威胁。无线技术。802.11和蓝牙等技术使用近程信号,把家里、办公司和零售店的多种计算和处理设备连接在一起。

便携式计算的增长。价格低廉的计算机储存设备和小型及其,帮助人们实现在家中、汽车里、火车上,乃至任何地方办公。例如IBM的小型Metapad卡片式电脑仅重9盎司,却能储存5G数据。设备将改变人们的工作方式。

第19篇:外文翻译 英文

Valuing the Warranty Ceiling Clause onNew Mexico Highway 44Using a Binomial Lattice Model

Abstract:

In 1998 the New Mexico State Highway and Transportation Department (NMSHTD) agreed to pay $60 million for a 20-year pavement warranty on their Route 44 project (NM 44, now US 550).The warranty includes a ceiling clause that caps total expenditures at $110 million.As the first long-term highway warranty in the United States, the transaction set a controversial precedent that parties interested in innovative highway contracting, including other state department of transportations (DOTs), the USDOT, sureties, and contractors, view as a test case for evaluating pricing and cost-effectivene.An interim audit report published by the State of\' New Mexico [Abbey (2004).Rep.to the Legislative Finance Committee, State Highway and Transportation Department.Santa Fe.N.M.]provides invaluable fiscal projections and challenges the cost effectivene of the $60 million expenditure.This paper presents an independent analysis of the effectivene of the warranty clauses.Based upon NMSHTD data, the analysis contends that $60 million was a fair cost of the 20-year pavement warranty at the time of acceptance if the expenditure ceiling is not considered.Furthermore.this paper argues that the ceiling on expenditure can be valuable.Using the real options approach, the paper evaluates the warranty ceiling clause on NM 44 and some policy suggestions are discued.

Introduction:

State Departments of Transportation (DOT) turned increasingly proactive when awarding large highway pavement contracts as a result of the United States Federal Highway Administration\'s (FHwA) Special Experimental Projects (SEPs).SEP No.14, implemented in 1990, opened the door for innovative contracting methods including lane rental, cost-plus-time bidding, design.build techniques, and warranty clauses.The warranty clauses hold contractors liable for reparationfor performance failures within a warranty period that typically extends from 5 to 7 years.

Though New Mexico was not among the original eight states that initiated the use of warranties under SEP No.14.they have since evaluated the option of warranty contracting and succe-fully applied it to the New Mexico State Route 44 Project (nowU.S.550),

which traverses 118 mi (190 km) from 1-25 at San Ysidro northwest to Bloomfield, near the Four Corners area.When considering the prospect of infiltrating the northwest corner ofNew Mexico, New Mexico State Highway and TransportationDepartment (NMSHTD) [renamed New Mexico Deparunent of

Transportation (NMDOT) in 2003], determined that the future maintenance and rehabilitation costs of the upgraded 118 mi of roadway would total about $16,000/lane-mi/year over a service life of 20 years (May et al.2003) totaling just over $15I million.Additionally, they determined that the roadbed and surface upgrades would take almost 27 years to complete using normal contracting methods.In an effort to keep the highway in good condition for the long term, NMSHTD purchased a 20-year warranty agreement from MesaPDC who in turn guaranteed the pavement performance during the warranty period.Thc\' NM 44 warranty broke new ground in both length and cost.Itwas the first long-term highway warranty in the United States and.,at $62 million, the most expensive.Since conception, its economics and applicability to other projects has been a subject of debate.Moreover, the two ceiling clauses in the warranty agreement that limit cumulative traffic volume and maintenance expenditures have been neither examined nor evaluated.In this paper we addre the cost effectivene of the warranty clauses in the NM 44 project.

1 Warranty Provisions for NM 44

Two primary participants, NMSHTD and Mesa Project Development Contractor (PDC), a division of Wichita, Kan.-based Koch Performance Roads, Inc., cooperated on the NM 44 project.The NMSHTD laid out design criteria, performance requirements, and oversight procedures, and estimated a life-cycle cost to establish the overall present value of the expected maintenance during the 20-year warranty period.Through team building and open communications, NMSHTD was able to monitor performance without responsibility for performance, while Mesa PDC was able to gain insight into the development and award proce along with the limitations and constraints that had to be addreed.

To carry a long-term warranty agreement, a profeional services contract was introduced.Basic items included delineation of responsibilities and appropriate protocol for repairs, costing, and reimbursement.The final price on the warranty was comprised of $60 million for a 2pavement warranty and, $2 million for a 10-year structures warranty to cover bridges, drainage, erosion, etc.for a total of $62 million in warranty liability.Mesa

PDC also agreed to a 3.5% inflationary risk on future maintenance costs.Based on these numbers, the warranty pricing was $6,400/lane mi/year, a 60% reduction as compared to the initial evaluation ( Mav et al.2003).Additionally, the warranty duration was limited by three ceiling clauses: (1) 20 years of service life: (2) 4,000,000 equivalent single axle loads (ESALs); and (3) $114 million in total expenditures, of which $1 l0 million is the ceiling for the pavement warranty and $4 million is the ceiling for the structure warranty.Thus, in return for $62 million.Mesa PDC agreed to provide up to $114 million in repairs over a period of 20 years or 4 million ESALs.To ensure the fiscal liability was met.the warranty was also backed by a performance bond.

The parties established what constitutes warranted pavement defects based on objective criteria such as smoothne, rutting, transverse crack spacing, crack width, potholes, depreions.bleeding, raveling,and delaminations.Because the warranty provider shoulders the risks aociated with performance, they have a strong incentive to aure quality in the design, composition, and construction of the pavement.The parties also developed plans to monitor performance and perform both preventative and routine maintenance to ensure the highway’s health.

2 Discounted Cash Flow Analysis

In a recent interim report of the NM 44 warranty audit, the state of New Mexico challenged the cost effectivene of the $62 million warranty (Abbey 2004).This interim report and its predeceor (Abbey 1999) provide invaluable cost projections on the NM 44 project and the aociated warranty.Using these data we conducted our own cost analysis based on the information available to the NMSHTD when they made the warranty decision in 1998.So for this analysis,all warrafity benefits and costs incurred during the construction and warranty period were discounted back to the decision time in 1998, and all costs ,and payments were aumed to fall at the end of the year.Additionally, we considered only the pavement warranty which is valued at $60 million and explains 96.8% of the total warranty cost.Ignoring the structures warranty, which is valued at only $2 million, reduces ambiguity without any significant impact on the results.Farthermore.Abbey (2004) estimates that the structures warranty will expire before the end of the 10-year warranty period, while the pavement warranty probably will remain in effect for the entire 20-year term.

3 Discuion and Policy Suggestions

Due to the ceiling clause, the price of the warranty provisions in the NM 44 project

does not reflect the real cost to the NMSHTD.The ceiling clause, valued at 4.8 million/year 1998 dollar as calculated, represents additional revenue to Mesa besides the $62 million warranty payment from NMSHTD.By declaring the ceiling clause, Mesa PDC in fact eliminates unfavorable risk while keeping profitable uncertainty.What Mesa gains is what NMSHTD loses since this is a zero-sum game.The actual cost for the warranty provision in the NM 44 project goes up to 57.3 million/year 1998 dollar.The hurdle rate of a viable warranty provision falls to 4% (Fig.6).Considering that the NMSHTD had to borrow at a higher interest rate to finance the NM 44 project .the warranty provision is not justified because of the high cost of the ceiling clause.

It is suggested that the state highway agencies carefully evaluate the ceiling clauses when requiring warranty services in selling infrastructure projects.A twofold analysis needs to be conducted so a better decision can be made.First, one must realize that the ceiling clause may be costly.The model developed in this paper is a handy approach to evaluate the ceiling clause value.Second state agencies should better determine a favorable ceiling when including ceiling clauses in the warranty.A sensitivity analysis indicates that the value of the ceiling clause is elastic to the determined ceiling.A 10% increase of the ceiling in the NM 44 warranty provisions would reduce the option price of the ceiling clause by 30%.Therefore, careful selection for a ceiling can significantly reduce the impact of the ceiling clause.

The ceiling clause, in eence, is a call option that provides flexibility to switch a decision after more information is available through locking in risks while leaving the favorable uncertainties open.The real option concept provides powerful tools not only for contractors, but also state agencies ceiling clauses or other trigger points in uncertain cash flows.One potential application of the real option concept in warranty contracting is to delay the warranty decision until the end of construction when more performance information is available (Cui et al.2004).Then future maintenance savings could be estimated more accurately, and a better decision can be made on whether to purchase a warranty.

Acknowledgments:

The writers gratefully acknowledge the support for this research provided by the University Transportation Center for Alabama(UTCA) and the Alabama Contractors\' Fees Fund.

Reforance:

1)Warranty Provisions for NM 44Qingbin Cui1; Philip Johnson2; Aaron Quick3; and Makarand Hastak

2)Journal of Construction Engineering and Management,January 2008,Volume 134.Number 1, 10--17

第20篇:毕业论文外文翻译

齿轮和轴的介绍

摘 要:在传统机械和现代机械中齿轮和轴的重要地位是不可动摇的。齿轮和轴主要 安装在主轴箱来传递力的方向。通过加工制造它们可以分为许多的型号,分别用于许 多的场合。所以我们对齿轮和轴的了解和认识必须是多层次多方位的。 关键词:齿轮;轴 关键词 在直齿圆柱齿轮的受力分析中,是假定各力作用在单一平面的。我们将研究作用 力具有三维坐标的齿轮。因此,在斜齿轮的情况下,其齿向是不平行于回转轴线的。 而在锥齿轮的情况中各回转轴线互相不平行。像我们要讨论的那样,尚有其他道理需 要学习,掌握。 斜齿轮用于传递平行轴之间的运动。倾斜角度每个齿轮都一样,但一个必须右旋 斜齿,而另一个必须是左旋斜齿。齿的形状是一溅开线螺旋面。如果一张被剪成平行 四边形(矩形)的纸张包围在齿轮圆柱体上,纸上印出齿的角刃边就变成斜线。如果 我展开这张纸,在血角刃边上的每一个点就发生一渐开线曲线。 直齿圆柱齿轮轮齿的初始接触处是跨过整个齿面而伸展开来的线。斜齿轮轮齿的 初始接触是一点,当齿进入更多的啮合时,它就变成线。在直齿圆柱齿轮中,接触是平行于回转轴线的。在斜齿轮中,该先是跨过齿面的对角线。它是齿轮逐渐进行啮合 并平稳的从一个齿到另一个齿传递运动, 那样就使斜齿轮具有高速重载下平稳传递运 动的能力。斜齿轮使轴的轴承承受径向和轴向力。当轴向推力变的大了或由于别的原 因而产生某些影响时,那就可以使用人字齿轮。双斜齿轮(人字齿轮)是与反向的并 排地装在同一轴上的两个斜齿轮等效。他们产生相反的轴向推力作用,这样就消除了 轴向推力。当两个或更多个单向齿斜齿轮被在同一轴上时,齿轮的齿向应作选择,以 便产生最小的轴向推力。 交错轴斜齿轮或螺旋齿轮,他们是轴中心线既不相交也不平行。交错轴斜齿轮的 齿彼此之间发生点接触,它随着齿轮的磨合而变成线接触。因此他们只能传递小的载 荷和主要用于仪器设备中,而且肯定不能推荐在动力传动中使用。交错轴斜齿轮与斜 齿轮之间在被安装后互相捏合之前是没有任何区别的。它们是以同样的方法进行制 造。一对相啮合的交错轴斜齿轮通常具有同样的齿向,即左旋主动齿轮跟右旋从动齿 轮相啮合。在交错轴斜齿设计中,当该齿的斜角相等时所产生滑移速度最小。然而当

该齿的斜角不相等时, 如果两个齿轮具有相同齿向的话, 大斜角齿轮应用作主动齿轮。 蜗轮与交错轴斜齿轮相似。小齿轮即蜗杆具有较小的齿数,通常是一到四齿,由 于它们完全缠绕在节圆柱上,因此它们被称为螺纹齿。与其相配的齿轮叫做蜗轮,蜗 轮不是真正的斜齿轮。 蜗杆和蜗轮通常是用于向垂直相交轴之间的传动提供大的角速 度减速比。蜗轮不是斜齿轮,因为其齿顶面做成中凹形状以适配蜗杆曲率,目的是要 形成线接触而不是点接触。然而蜗杆蜗轮传动机构中存在齿间有较大滑移速度的缺 点,正像交错轴斜齿轮那样。 蜗杆蜗轮机构有单包围和双包围机构。单包围机构就是蜗轮包裹着蜗杆的一种机 构。 当然, 如果每个构件各自局部地包围着对方的蜗轮机构就是双包围蜗轮蜗杆机构。 着两者之间的重要区别是,在双包围蜗轮组的轮齿间有面接触,而在单包围的蜗轮组 的轮齿间有线接触。一个装置中的蜗杆和蜗轮正像交错轴斜齿轮那样具有相同的齿 向,但是其斜齿齿角的角度是极不相同的。蜗杆上的齿斜角度通常很大,而蜗轮上的 则极小,因此习惯常规定蜗杆的导角,那就是蜗杆齿斜角的余角;也规定了蜗轮上的 齿斜角,该两角之和就等于 90 度的轴线交角。 当齿轮要用来传递相交轴之间的运动时,就需要某种形式的锥齿轮。虽然锥齿轮 通常制造成能构成 90 度轴交角,但它们也可产生任何角度的轴交角。轮齿可以铸出, 铣制或滚切加工。仅就滚齿而言就可达一级精度。在典型的锥齿轮安装中,其中一个 锥齿轮常常装于支承的外侧。 这意味着轴的挠曲情况更加明显而使在轮齿接触上具有 更大的影响。 另外一个难题,发生在难于预示锥齿轮轮齿上的应力,实际上是由于齿轮被加工 成锥状造成的。 直齿锥齿轮易于设计且制造简单,如果他们安装的精密而确定,在运转中会产生 良好效果。然而在直齿圆柱齿轮情况下,在节线速度较高时,他们将发出噪音。在这 些

情况下,螺旋锥齿轮比直齿轮能产生平稳的多的啮合作用,因此碰到高速运转的场 合那是很有用的。 当在汽车的各种不同用途中, 有一个带偏心轴的类似锥齿轮的机构, 那是常常所希望的。这样的齿轮机构叫做准双曲面齿轮机构,因为它们的节面是双曲 回转面。 这种齿轮之间的轮齿作用是沿着一根直线上产生滚动与滑动相结合的运动并 和蜗轮蜗杆的轮齿作用有着更多的共同之处。 轴是一种转动或静止的杆件。通常有圆形横截面。在轴上安装像齿轮,皮带轮, 飞轮,曲柄,链轮和其他动力传递零件。轴能够承受弯曲,拉伸,压缩或扭转载荷,

这些力相结合时,人们期望找到静强度和疲劳强度作为设计的重要依据。因为单根轴 可以承受静压力,变应力和交变应力,所有的应力作用都是同时发生的。 “轴”这个词包含着多种含义,例如心轴和主轴。心轴也是轴,既可以旋转也可 以静止的轴,但不承受扭转载荷。短的转动轴常常被称为主轴。 当轴的弯曲或扭转变形必需被限制于很小的范围内时,其尺寸应根据变形来确 定,然后进行应力分析。因此,如若轴要做得有足够的刚度以致挠曲不太大,那么合 应力符合安全要求那是完全可能的。但决不意味着设计者要保证;它们是安全的,轴 几乎总是要进行计算的,知道它们是处在可以接受的允许的极限以内。因之,设计者 无论何时,动力传递零件,如齿轮或皮带轮都应该设置在靠近支持轴承附近。这就减 低了弯矩,因而减小变形和弯曲应力。 虽然来自 M.H.G 方法在设计轴中难于应用,但它可能用来准确预示实际失效。这 样, 它是一个检验已经设计好了的轴的或者发现具体轴在运转中发生损坏原因的好方 法。进而有着大量的关于设计的问题,其中由于别的考虑例如刚度考虑,尺寸已得到 较好的限制。 设计者去查找关于圆角尺寸、热处理、表面光洁度和是否要进行喷丸处理等资料, 那真正的唯一的需要是实现所要求的寿命和可靠性。 由于他们的功能相似,将离合器和制动器一起处理。简化摩擦离合器或制动器的 动力学表达式中,各自以角速度 w1 和 w2 运动的两个转动惯量 I1 和 I2,在制动器情 况下其中之一可能是零,由于接上离合器或制动器而最终要导致同样的速度。因为两 个构件开始以不同速度运转而使打滑发生了,并且在作用过程中能量散失,结果导致 温升。在分析这些装置的性能时,我们应注意到作用力,传递的扭矩,散失的能量和 温升。所传递的扭矩关系到作用力,摩擦系数和离合器或制动器的几何状况。这是一 个静力学问题。这个问题将必须对每个几何机构形状分别进行研究。然而温升与能量 损失有关,研究温升可能与制动器或离合器的类型无关。因为几何形状的重要性是散 热表面。各种各样的离合器和制动器可作如下分类: 1.轮缘式内膨胀制冻块; 2.轮缘式外接触制动块; 3.条带式; 4.盘型或轴向式; 5.圆锥型;

6.混合式。 分析摩擦离合器和制动器的各种形式都应用一般的同样的程序, 下面的步骤是必 需的: 1.假定或确定摩擦表面上压力分布; 2.找出最大压力和任一点处压力之间的关系; 3.应用静平衡条件去找寻(a)作用力; (b)扭矩;(c)支反力。 混合式离合器包括几个类型,例如强制接触离合器、超载释放保护离合器、超越 离合器、磁液离合器等等。 强制接触离合器由一个变位杆和两个夹爪组成。各种强制接触离合器之间最大的 区别与夹爪的设计有关。为了在结合过程中给变换作用予较长时间周期,夹爪可以是 棘轮式的,螺旋型或齿型的。有时使用许多齿或夹爪。他们可能在圆周面上加工齿, 以便他们以圆柱周向配合来结合或者在配合元件的端面上加工齿来结合。 虽然强制离合器不像摩擦接触离合器用的那么广泛,但它们确实有很重要的运 用。离合器需要同步操作。 有些装置例如线性驱动装置或电机操作螺杆驱动器必须运行到一定的限度然后 停顿下来。为着这些用途就需要超载释放保护离合器。这些离合器通常用弹簧加载, 以使得在达到预定的力矩时释放。当到达超载点时听到的“喀嚓”声就被认定为是所 希望的信号声。 超越离合器

或连轴器允许机器的被动构件“空转”或“超越” ,因为主动驱动件 停顿了或者因为另一个动力源使被动构件增加了速度。 这种离合器通常使用装在外套 筒和内轴件之间的滚子或滚珠。该内轴件,在它的周边加工了数个平面。驱动作用是 靠在套筒和平面之间契入的滚子来获得。 因此该离合器与具有一定数量齿的棘轮棘爪 机构等效。 磁液离合器或制动器相对来说是一个新的发展,它们具有两平行的磁极板。这些 磁极板之间有磁粉混合物润滑。电磁线圈被装入磁路中的某处。借助激励该线圈,磁 液混合物的剪切强度可被精确的控制。 这样从充分滑移到完全锁住的任何状态都可以 获得。

GEAR AND SHAFT INTRODUCTION

Abstract: The important position of the wheel gear and shaft can't falter in

traditional machine and modern machines.The wheel gear and shafts mainly install the direction that delivers the dint at the principal axis box.The paing to proce to make them can is divided into many model numbers, useding for many situations respectively.So we must be the multilayers to the understanding of the wheel gear and shaft in many ways .

Key words: Wheel gear;Shaft

In the force analysis of spur gears, the forces are aumed to act in a single plane.We shall study gears in which the forces have three dimensions.The reason for this, in the case of helical gears, is that the teeth are not parallel to the axis of rotation.And in the case of bevel gears, the rotational axes are not parallel to each other.There are also other reasons, as we shall learn.Helical gears are used to transmit motion between parallel shafts.The helix angle is the same on each gear, but one gear must have a right-hand helix and the other a left-hand helix.The shape of the tooth is an involute helicoid.If a piece of paper cut in the shape of a parallelogram is wrapped around a cylinder, the angular edge of the paper becomes a helix.If we unwind this paper, each point on the angular edge generates an involute curve.The surface obtained when every point on the edge generates an involute is called an involute helicoid.The initial contact of spur-gear teeth is a line extending all the way acro the face of the tooth.The initial contact of helical gear teeth is a point, which changes into a line as the teeth come into more engagement.In spur gears the line of contact is parallel to the axis of the rotation; in helical gears, the line is diagonal acro the face of the tooth.It is this gradual of the teeth and the smooth transfer of load from one tooth to another, which give helical gears the ability to transmit heavy loads at high

speeds.Helical gears subject the shaft bearings to both radial and thrust loads.When the thrust loads become high or are objectionable for other reasons, it may be desirable to use double helical gears.A double helical gear (herringbone) is equivalent to two helical gears of opposite hand, mounted side by side on the same shaft.They develop opposite thrust reactions and thus cancel out the thrust load.When two or more single helical gears are mounted on the same shaft, the hand of the gears should be selected so as to produce the minimum thrust load.Croed-helical, or spiral, gears are those in which the shaft centerlines are neither parallel nor intersecting.The teeth of croed-helical fears have point contact with each other, which changes to line contact as the gears wear in.For this reason they will carry out very small loads and are mainly for instrumental applications, and are definitely not recommended for use in the transmiion of power.There is on difference between a croed helical gear and a helical gear until they are mounted in mesh with each other.They are manufactured in the same way.A pair of meshed croed helical gears usually have the same hand; that is ,a right-hand driver goes with a

right-hand driven.In the design of croed-helical gears, the minimum sliding velocity is obtained when the helix angle are equal.However, when the helix angle are not equal, the gear with the larger helix angle should be used as the driver if both gears have the same hand.Worm gears are similar to croed helical gears.The pinion or worm has a small number of teeth, usually one to four, and since they completely wrap around the pitch cylinder they are called threads.Its mating gear is called a worm gear, which is not a true helical gear.A worm and worm gear are used to provide a high angular-velocity reduction between nonintersecting shafts which are usually at right angle.The worm gear is not a helical gear because its face is made concave to fit the curvature of the worm in order to provide line contact instead of point contact.However, a disadvantage of worm gearing is the high sliding velocities acro the teeth, the same as with croed

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helical gears.Worm gearing are either single or double enveloping.A single-enveloping gearing is one in which the gear wraps around or partially encloses the worm..A gearing in which each element partially encloses the other is, of course, a double-enveloping worm gearing.The important difference between the two is that area contact exists between the teeth of double-enveloping gears while only line contact between those of single-enveloping gears.The worm and worm gear of a set have the same hand of helix as for croed helical gears, but the helix angles are usually quite different.The helix angle on the worm is generally quite large, and that on the gear very small.Because of this, it is usual to specify the lead angle on the worm, which is the complement of the worm helix angle, and the helix angle on the gear; the two angles are equal for a 90-deg.Shaft angle.When gears are to be used to transmit motion between intersecting shaft, some of bevel gear is required.Although bevel gear are usually made for a shaft angle of 90 deg.They may be produced for almost any shaft angle.The teeth may be cast, milled, or generated.Only the generated teeth may be claed as accurate.In a typical bevel gear mounting, one of the gear is often mounted outboard of the bearing.This means that shaft deflection can be more pronounced and have a greater effect on the contact of teeth.Another difficulty, which occurs in predicting the stre in bevel-gear teeth, is the fact the teeth are tapered.Straight bevel gears are easy to design and simple to manufacture and give very good results in service if they are mounted accurately and positively.As in the case of squr gears, however, they become noisy at higher values of the pitch-line velocity.In these cases it is often good design practice to go to the spiral bevel gear, which is the bevel counterpart of the helical gear.As in the case of helical gears, spiral bevel gears give a much smoother tooth action than straight bevel gears, and hence are useful where high speed are encountered.

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It is frequently desirable, as in the case of automotive differential applications, to have gearing similar to bevel gears but with the shaft offset.Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution.The tooth action between such gears is a combination of rolling and sliding along a straight line and has much in common with that of worm gears.A shaft is a rotating or stationary member, usually of circular cro section, having mounted upon it such elementsas gears, pulleys, flywheels, cranks, sprockets, and other power-transmiion elements.Shaft may be subjected to bending, tension, compreion, or torsional loads, acting singly or in combination with one another.When they are combined, one may expect to find both static and fatigue strength to be important design considerations, since a

single shaft may be subjected to static strees, completely reversed, and repeated strees, all acting at the same time.The word “shaft” covers numerous variations, such as axles and spindles.Anaxle is a shaft, wither stationary or rotating, nor subjected to torsion load.A shirt rotating shaft is often called a spindle.When either the lateral or the torsional deflection of a shaft must be held to close limits, the shaft must be sized on the basis of deflection before analyzing the strees.The reason for this is that, if the shaft is made stiff enough so that the deflection is not too large, it is probable that the resulting strees will be safe.But by no means should the designer aume that they are safe; it is almost always neceary to calculate them so that he knows they are within acceptable limits.Whenever poible, the power-transmiion elements, such as gears or pullets, should be located close to the supporting bearings, This reduces the bending moment, and hence the deflection and bending stre.Although the von Mises-Hencky-Goodman method is difficult to use in design of shaft, it probably comes closest to predicting actual failure.Thus it is a good way of checking a shaft that has already been designed or of discovering

8

why a particular shaft has failed in service.Furthermore, there are a considerable number of shaft-design problems in which the dimension are pretty well limited by other considerations, such as rigidity, and it is only neceary for the designer to discover something about the fillet sizes, heat-treatment, and surface finish and whether or not shot peening is neceary in order to achieve the required life and reliability.Because of the similarity of their functions, clutches and brakes are treated together.In a simplified dynamic representation of a friction clutch, or brake, two inertias I1 and I2 traveling at the respective angular velocities W1 and W2, one of which may be zero in the case of brake, are to be brought to the same speed by engaging the clutch or brake.Slippage occurs because the two elements are running at different speeds and energy is diipated during actuation, resulting in a temperature rise.In analyzing the performance of these devices we shall be interested in the actuating force, the torque transmitted, the energy lo and the temperature rise.The torque transmitted is related to the actuating force, the coefficient of friction, and the geometry of the clutch or brake.This is problem in static, which will have to be studied separately for eath geometric configuration.However, temperature rise is related to energy lo and can be studied without regard to the type of brake or clutch because the geometry of interest is the heat-diipating surfaces.The various types of clutches and brakes may be claified as fllows:

1.Rim type with internally expanding shoes 2.Rim type with externally contracting shoes 3.Band type 4.Disk or axial type 5.Cone type 6.Miscellaneous type The analysis of all type of friction clutches and brakes use the same general procedure.The following step are neceary:

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1.Aume or determine the distribution of preure on the frictional surfaces.2.Find a relation between the maximum preure and the preure at any point 3.Apply the condition of statical equilibrium to find (a) the actuating force, (b) the torque, and (c) the support reactions.Miscellaneous clutches include several types, such as the

positive-contact clutches, overload-release clutches, overrunning clutches, magnetic fluid clutches, and others.A positive-contact clutch consists of a shift lever and two jaws.The greatest differences between the various types of positive clutches are concerned with the design of the jaws.To provide a longer period of time for shift action during engagement, the jaws may be ratchet-shaped, or gear-tooth-shaped.Sometimes a great many teeth or jaws are used, and they may be cut either circumferentially, so that they engage by cylindrical mating, or on the faces of

the mating elements.Although positive clutches are not used to the extent of the frictional-contact type, they do have important applications where

synchronous operation is required.Devices such as linear drives or motor-operated screw drivers must run to definite limit and then come to a stop.An overload-release type of clutch is required for these applications.These clutches are usually spring-loaded so as to release at a predetermined toque.The clicking sound which is heard when the overload point is reached is considered to be a desirable signal.An overrunning clutch or coupling permits the driven member of a machine to “freewheel” or “overrun” because the driver is stopped or because another source of power increase the speed of the driven.This type of clutch usually uses rollers or balls mounted between an outer sleeve and an inner member having flats machined around the periphery.Driving action is obtained by wedging the rollers between the sleeve and the flats.The clutch is

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therefore equivalent to a pawl and ratchet with an infinite number of teeth.Magnetic fluid clutch or brake is a relatively new development which has two parallel magnetic plates.Between these plates is a lubricated magnetic powder mixture.An electromagnetic coil is inserted somewhere in the magnetic circuit.By varying the excitation to this coil, the shearing strength of the magnetic fluid mixture may be accurately controlled.Thus any condition from a full slip to a frozen lockup may be obtained.

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