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外文翻译材料制备机械设计理论中的新趋势和新问题

外文翻译材料制备机械设计理论中的新趋势和新问题
外文翻译材料制备机械设计理论中的新趋势和新问题

郑州航空工业管理学院

英文翻译

2012届机械设计制造及其在自动化专业1006962班级

姓名郝振兴学号100696208

指导教师贺红霞职称教授

二О一二年三月十二日

New Trends and Problems in Material Processing Machine

Design Theory

Abstract :

Based on reviewing the historical background, prospecting for the development trend ,analyzing the complicacy and mechanism and summing up some achievements and experiences in scientific research , several new problems and the possible direction of development in material processing technology and machine are proposed ,such as ,producing new concept materials possessing some specific and extraovdinary properties by means of integrating and coalescing conelative frontier science and technology ;and thereafter a brief discussion is given.

Keywords: interface; extraordinary physical field; procession machine ; function material

1The Time Background of Material Processing Machine In the long span of history of human progress ,many tools ,machines and methods were created and a variety of materials with different properties were processed. Materials and its processing have become one of pillar and driving force of mankind progress. In pace with multi - polar competition in current world and people’s striving perseveringly for happier life ,material function goes beyond unceasingly men’s knowledge and imagination ,for example ,cryptic function material ,semiconductor material ,energy material ,vibration - absorptive material , super - strength aluminum alloy accounting for 70 percent of application of aeronautics and space ,metal foil of 4~5μm ,deep drawing plate with anisotropy below 1 percent ,electronic aluminum foil with micro - orientation up to 95 percent ,heat resisting aluminum alloy with super strong specific strength used in aeronautics ,space and deep sea ,etc. Thus several important development trends with distinct time features in material processing domain are shaped up as follows :

(1) Creating material processing machine with extraordinary physical field for processing material with special texture structures and functions. For example ,applications of thermal energy and mechanical energy are breaking through unceasingly technology limit ,and some non - tradition energy ,such as microwave ,chemical energy , bioenergy , etc. , are introduced into material processing procedure one after another ,so that some material processing machines with extraordinary energy circumstance are produced.

(2) Breaking through traditional physical limits and integrating melting ,solidifying ,plastic deformation and heat treatment to obtain special function of material and cut down expenses[3 ] . For example ,near - net shaping material processing technology , such as fast rolling , spraying deposition ,over - plastic molding , injection molding , high energy beam ,etc ,is applied.

(3) Material processing process is forged ahead in the direction of high speed ,heavy - duty and high accuracy online control ,for instance , the rolling speed goes up to 130 m·s - 1 ,the deformation pressure rises up to 300 MPa ,accuracy of dimension up to 0.1μm ,accuracy of shape up to 0. 1 I ,strength accuracy comes up to 0.1 MPa. For these reasons ,it is necessary for material processing machine design theory to integrate and coalesce ingeniously correlative frontier science and technology to create and produce some new concept material processing machine with following functions.

2Due Functions of New Concept Material Processing Machine

(1) To have the ability to produce and bear extraordinary physical field and transmit extraordinary energy flow with the aim of providing extraordinary physical circumstances necessary for new concept material processing. For example ,high gradient temperature field with the speed of cool - down of work interface which exceeds 104~106 K·s - 1 , line wave and pulse complex exerted in solidifying - deforming area , super - strength contact stress field of material forming interface ,turbulent flow field of molten metal with very big flakiness ratio ,low frequency magnetic field with random frequency ,microwave field for powder metal heating ,ultrasonic field for large volume solidifying ,etc. [4 ] ,are applied.

(2) To have the ability to work in critical state so that high stability and ideal performance of processing machine is ensured under the circumstance of reinforced technological condition and multi - field coupling operation. For example ,chatter suppressing capability of fast ultra - thin rolling under the condition of boundary lubricating state[5 ] ,the capability of self - excited vibration suppressing under the condition of special friction state ,synergism stability and disturbance stability of flexible connecting parallel shaft with multi - driving system ,etc. [4 ] ,are ensured.

(3) To have the ability to accurately control the material processing in order to obtain low loss ,high efficiency and high quality of material processing. For example , super - high accuracy on - line monitor of products form ,on –line monitor and on - line adjustment of products texture and properties ,precision coordination control of multi - procedure , on - line monitor of micro - orientation of metal plastic deformation ,etc. [4 ] ,are ensured. Some products accuracy index may be enumerated as follows : dimensional accuracy coming to 0.1μm , microstructure uniformity to crystal lattice ,strength error to 0.1 MPa ,etc.

[4 ]In short ,only by new concept material processing machine with extraordinary function being designed and made , can special function material be processed.

3Science Problems and Study Contents of Metal Material Processing Machine

Under the Circumstance of Extraordinary Physical Field

In view of these facts and background mentioned above ,several new research topics can be advanced as follows.

3. 1 Coupling Heat Transfer Mechanism of Multi - Phase Interface

Temperature - Stress Field

A brand - new microstructure can be obtained through continuously large deformation and fast solidifying when melting metal is in critical state of liquid solid. At this very moment ,high density heat flow and dynamic heat resistance are present in material processing circumstance .

A basic theory problem of designing this kind of machine is to study mechanism of heat transmittance and energy conversion ,and to establish mathematical model .

3. 2 Friction Constraint Mechanism of Plastic Flow Interface of

Material Processing Machine

The coupling between operation mechanism and workpiece is very complicated because plastic flow is present in processing interface. The interface state , determined by velocity , load thermodynamic process , elasticity of operation mechanism ,plasticity of workpiece ,dynamic behaviour of interface sticking - sliding and partial hydrodynamic lubrication ,etc ,affect and form friction constraints mechanism peculiar to material processing machine ,because these constraints present strong non - linearity ;and under certain circumstances ,the constraints may be destroyed or mismatched instantaneously and thus dynamic instability is resulted in. Thus following problems can be put forward : Mechanism of “spectre chatter”arose from sticking - sliding friction and partial hydrodynamic lubrication in rolling interface , instability condition and mechanism of constraint between smooth surface and rotating body under the circumstance of high speed ,heavy - duty and boundary lubrication , Lubrication film absorption mechanism and physical chemistry behaviour of interface of unceasingly regenerative surface ,the relationship between rheological characteristic and machine operation parameters.

3. 3 Multi - Body Non - Linear Contact Mechanism Under the

Condition of Extra - High Pressure Field

To build the super strength pressure field on large area is one of basic function of material processing machine , and it is also necessary to

form by once large - size structure element (such as spacecraft , intercontinental vehicles ,car and large - scale aeroplane etc) . The ability to build super strong pressure field is one of important feature and the base of independent national defense. Under the circumstance of super strength pressure field ,multi - body strong nonhertz contact and non - linear friction will be produced ,thus local permanent deformation and degrading of element accuracy may be led. New theory foundation of design of machine with super strength pressure field will be furnished through study of multi - body strong non - hertz contact mechanism , multi - body non - linear friction mechanism (such as providing force - displacement mixed solving process of three - dimension multi - body) . 3. 4 Load Distribution Law in Multi - Sliding Pair With Structure

Bias Load

With regard to statically indeterminate structure ,load distribution of constraint point is determined by deformation compatibility condition. However ,concerning some plane large - size statically indeterminate structure with sliding degree of freedom in third dimension ,load distribution can not be determined by deformation compatibility condition. Thus new theory basis will be provided by analyzing of contact behaviour and mechanism of sliding pair (such as creep ,force of friction ,integral deformation compatibility condition ,etc) .

3. 5 Coupling Mechanism and Stability of Multi - Physical Fields in

Material Processing Systems

In the wake of system function becoming more and more diversified , conventional technology limits in material processing machine is being broke through unceasingly ,system structure also becomes increasingly complicated ,and system performance becomes increasingly multi - causal . For example ,any instantaneous state of roller in fast rolling mills is affected by elastic deformation ,plastic flow ,heat transfer process , hydro - dynamic lubrication process ,interface physical chemistry molecular state and so on . In addition ,electromechanical coupling in processing system have already gone beyond conventional concept ,for instance ,some singular point phenomenon (such as micro - variable can be transformed into macro - variable) ,are present ,thus roller operation instability may be led by perturbation[8 ] . Therefore ,this subject will study the interaction mechanism of multi - physical field and the influence on processing system stability and processing material quality started with analysis of micro - state of executive body.

3. 6 Multi - Technology Integration and Coalescence of Accurate

Control

The material processing machine ,which operate under the circumstance of extraordinary physical field ,is a complicated large - scale system ,and some parameters of the system vary on feasible field boundary ;thereby ,to keep under accurate control and adjustment of multi field circumstance ,multi - dimension coordination ,multi - energy conversion , multi - level information transfer ,interface multi - process coupling ,etc. is of much significance. Since a variety of multi - interaction exists in control model ,it is necessary to establish integration framework of coordination work according to decoupling of control model ,so as to accurate control based on the multi - technology integration and coalescence is realized.

3. 7 Quasi - Reality Design and Concurrent Design Based on

Knowledge Innovation Systems

Digitalization and visualization of material processing technology will promote immediately the quality of design, operation and control . Therefore optimization of material processing technology and material processing machine by means of realization of virtual simulation of processing procedure through quasi - reality design and concurrent design is one of our pressing study subjects.

3. 8 Mechanical Behavior of Special Function Materials in the

Extraordinary Physical Field

Many key elements and parts in material processing machine are often under the circumstance of super strong force field ,temperature field ,electronic magnetic field and flow field ,and must have the functions of constructing special physical interface. However ,it is difficult for common single - substance material such as metal ,ceramic polymer ,etc. to have both high index of single property and excellent overall quality. Therefore we need to use certain material with new functions for key position[9 ],for instance ,multi - dimension function gradient material with ultrahigh physical property ,multi - dimension function gradient material with intelligence. For these reasons ,it is necessary to study basic law and mechanism of these kind of function material mentioned above ,for instance ,stress (strain) distribution function ,failure mechanism and design criteria of material under the circumstance of extraordinary physical field ,static (dynamic) stiffness and damping ,digitalization design and visualization design of processing system made of gradient function material ,etc ,so that the general

mechanics law of element which is under the circumstance of extraordinary physical field and made of anisotropy multi - dimension gradient function material is obtained. Nowadays ,material processing science and technology is forging rapidly ahead. A forward - looking study aiming at key technology problem of material processing machine will provide theory and technology reserve for manufacturing science and industry of 21st century.

4 Design experience

Graduation design is we learned in the university of technology and the basic courses, all course all professional class after the. This is we have all of the course of the first in-depth comprehensive review of the total, is also our into social work in front of a theory with the practice of training. Therefore, it is in our four year university life holds an important position. Personally, I hope I can pass the graduation design for your future will be engaged in the work of a light training, to exercise his analysis problem, problem-solving ability, for the future of our motherland in the four construction lay a good foundation.

Turn an eye for four weeks of mechanical manufacturing technology and special jig design will be over, the design of curriculum review around the feeling of life as a process of ascension, and in the curriculum design, we constantly see the teaching material, look at reference see material, meet the problem and not understand we analyzed together or ask the teacher for advice and so on to find a useful to our design of data and material, and then will they become our design such as raw material, through this design we've learned a lot of knowledge, and learn to and familiar with the look-up table and check reference book, also mastered proe and CAD related operations, for parts of the process design had a deep understanding and the understanding of fixture design also has an understanding of and know some basic fixture the specific structure parts, such as flap, drill set, mandrels...... . Through the cooperation and team members make process and fixture that I understand cooperation is very important, division of labor cooperation can work better and faster.

In this course design, the teacher gave us valuable reference opinions, let us know how to complete a course design, how to put your things done, thanks to the teacher carefully counselling. And we have more analysis and problem solving ability. In the process, we found that the most lack is the social practice experience, empty have books theory knowledge, no perceptual cognition, often will likely and actual apart. In general, do this kind of design can make the we will have learned knowledge system related to link, which exposed the deficiencies. Also hope we in the later study can into society, make more social practice, in order to improve their ability to adapt to society.

Reference

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中文译文:

材料制备机械设计理论中的新趋势和新问题

摘要:

在全面综述材料制备机械技术及设备发展动态的基础上,提出了研究领域的几个新问题和发展方向,如通过集成和融合现代相关前沿科学和技术,生产具有超常和特殊性能的新概念材料等,并进行了简要分析和讨论.

关键词:界面;超常物理场;制备机械;功能材料

1 机械材料加工的时代背景

在人类进步的一段长时间范围内,许多工具、机械和方法被提出来;不同的原料用不同的工具来加工。原料及其处理过程已经变成了推动人类进步不可缺的一部份。在当前世界中日益激烈的竞争和人们追求幸福生活的今天,物质的功能已经远远超出了人类现有的并不断增长的知识及想象。例如:神秘原料功能,半导体材料,原料能量有吸力的材料,在航空领域中占有70%份额的强力铝合金4~5um的薄金属片,用各向异性深冲压金属板在1%以下;电子铝箔与强耐热铝合金已经被应用到航空、宇宙及深海领域中,等等;在原料加工加工领域中不同的时间段里,材料重要发展趋势就这样形成了:

(1)在特殊的物理领域里制造原料加工机械,是为了能有特殊的质地结构和辅助性的加工功能。例如:运用热能和机械能能够突破科学技术的极限,将一些不常用的能量,例如:微波、化学能、生物能等等,一个接一个的被引入到材料加工中来,因此一些加工特殊能量原材料的加工设备就被制造出来了。

(2)突破传统的物质限制,将溶化、凝固、造型一体化,然后加热得到具有特殊功能的原料,这样就可以降低加工费用。例如:材料加工整形技术,比如像快速翻滚,喷雾处理、塑胶成型、喷射造型法、高能量射束等等被应用。

(3)原料加工处理正在向高速、重载和高精度在线控制方向上迈进。例如:轧制速度达到130m/s,压力变形已达到300MPa,尺寸精度达到了0.1um,成型精度已达到0.1i;浓度精度已达到0.1MPa。由于这些原因,原料加工机械设备设计理论将科学与技术相关联的领域有机的结合起来设计生产一中新概念材料加工设备是可能的。

2 对于新概念材料加工设备的期望功能

(1)要有能力生产具有特殊物质的领域;能传送那些对于新概念材料加工在特定的物质环境下是非常必要的特殊能流。例如:在高温环境下能使那些高温波或者脉冲以超过104~106K/s的速度冷却下来;将外表面的凝固、变形合成一体,然后在将超强接触面应力重新组合成新的分界面;融化的大金属薄片的湍流;随机的低频率磁场用于金属末加热的微波、用于大量凝固的超声波等等都已经被应用了。

(2)有能力在临界状态下工作,因此高稳定性和理想性能的处理设备是在加强技术条件和室外操作的保证。例如:禁止在润滑状态下边界上的摇晃;在特有的摩擦状态下的抗震能力;有韧性的连接管的合力稳定性和干扰稳定性与轴相比更易驱动系统。

(3)有能力精确的控制原料加工而获得低损耗、高功率、高性能的原料加工。例如:精确的在线监测产品成型;在线监测和在线调整产品品质和器具还有在线控制金属、塑胶成型的程序。产品的精确度指数可以列举如下:宏观上精确度可达到0.1um,微观上的晶状体结构非常均匀,浓度误差在0.1MPa 。简而言之,拥有特别功能的新概念原料加工设备应该被设计和生产出来。这样的话,那些特别性能的原料就能被处理加工了。

3 在特殊的物理领域和环境下金属材料加工设备的问题和

需要学习的内容

由于这些原因和以上提到的背景,如下的一些新的研究主题应该被改进:

3.1 连接传热装置和温度应力场的相界面

当融化金属处于液体和固体的临界状态时通过连续的变形和快速凝固,一种全新的微观结构可以被获得。在这个非常时刻,高浓度的热流和动态的热阻力在材料加工处理中成了主要事项。关于设计这个设备的基本理论问题是要学习核心传动系统合能量转化和建立数学模型。

3.2 材料加工设备表面粘流摩擦力的抑制

操作装置和工件的连接是相当复杂的因为粘流阻挡了加工表面界面态由周转速度、热力学处理工作量、操作装置的弹性、工件的可塑性、滑性界面的动态行为、局部水力的润滑油等等来决定。它们影响着材料加工设备抗摩擦装置的成型。因为它们会会强制其产生很大的非线性,这种强制会在瞬间被损坏或者是失谐,最后会导致动态不稳定性。因此提出了以下的问题:机械装置的噪声可能在晃动的界面引起滑动摩擦、不稳定状态;在高速、重载和边界润滑状态下在光滑表面和旋转式喷灌器之间的装置抑制。润滑油薄膜吸收装置和不断再生的表面的物理化学行为;流变学的特征和操作参数之间的关系。

3.3 在高压场条件下非线性接触式机械装置

在大范围内组建一个超强力压力场是材料加工设备的一个基本功能。当然形成一个大结构的元素也是可能的(例如太空船、大陆洲际间的交通工具、汽车、飞机)。组建一个超强压力场是最重要的特征之一,也是保卫国家独立最基本的装备。在强压力场环境下,接触式和非线性摩擦将会产生;因此将会导致局部的永久的变形和不好的因素。在强压力场下设计过程中,将会涉及到设备的设计新理论,例如:非接触式、非线性摩擦机构。

3.4 负荷分配规律

关于超静定结构,抑制点的负荷分配规律由相容性条件决定。虽然,关于那些大尺寸的、不定的、静止的结构在真实空间中是自由变化的,但负荷分配规律是不能决定相容性条件。因此新的基础理论由分析接触行为和变形装置获得(例如:摩擦力、变形相容性条件,等等)。

3.5 耦合装置和在材料加工系统中物理领域内的稳定性

随着系统的功能越来越多元化;许多限制材料加工进度的传统技术正在不断的被改善;系统结构也逐渐变得越来越复杂,系统性能变得越来越好。例如:钢扎厂的快速瞬间反转受弹性形变、粘流、散热处理、水动力润滑处理的,物理化学分子状态的影响。另外,机电的耦合在处理系统中已经超出了传统的概念;例如,一些奇特的现象(微小的变化可以引起很大的变化)已经出现;因此,滚筒操作的不稳定性可能会导致混乱。所以,这个主题将会在机械装置的物理领域中,在处理系统稳定性的影响和加工助剂质量上被提及和充分关注;

3.6 技术综合和合并精准的控制

在特定的物理条件下进行操作的材料加工设备是一个相当复杂系统,一些系统的参数在领域的边界上也是可以改变的;因此在领域环境下精确的控制与调整,调和尺寸,能量转换,信息传递,界面耦合等等是非常重要的。因为在控制模型中多种交互作用的存在,根据退耦控制模型而建立综合框架是必要的;精确的控制基于综合技术。

3.7 优化的和创新的设计基于创新的知识

材料加工技术能促进产品的设计质量的提高。最优化的材料加工技术和材料加工设备意味着实现实质的仿真通过类似的设计和一致的设计是我们学习的主题。

3.8 在特殊的领域里机械装置的特殊功能和应用

一些重要的元素和部分在材料加工设备中常常在强力场、温度场、电磁场和流场中工作,有建造特别物理界面的功能;虽然对那些普通单一的物质象金属、陶瓷等拥有单一的高指数和卓越的总质量是很困难的。因此我们需要在重要部位采用具有新功能的原料;例如:尺度功能有倾向的材料是想当可贵的。由于这些原因,学习基本法律和以上提到的具有这些功能的机械装置;例如:强调分配功能、破坏机理和在特定领域中的设计标准,静态(动态)的硬度和阻尼,模糊设计和明朗设计处理系统构成了有斜度的材料,等等。

今天,材料加工科学和技术正在快速的向前发展;把学习的目标瞄准材料加工设备的技术问题将会为21世纪的制造业提供技术支持。

4 设计心得

毕业设计是在我们学完了大学的全部基础课、技术基础课以及全部专业课之后进行的。这是我们对所学各课程的一次深入的综合性的总复习,也是我们在走进社会工作岗位前的一次理论联系实际的训练。因此,它在我们四年的大学生活中占有重要的地位。就我个人而言,我希望能通过这次毕业设计对自己未来将从事的工作进行一次适应性训练,从中锻炼自己分析问题,解决问题的能力,为今后参加祖国的“四化”建设打下一个良好的基础。

转眼间4周的机械制造技术和专用夹具的设计就结束了,周围的课程设计审查对生活的感悟作为一个提升的过程,并在课程设计,会不断地看到教材,看参考书看资料,遇到问题却不明白我们一起分析或向老师请教等找到一个有用的与我们的设计数据和资料,然后他们会成为我们的设计为原料,通过这种设计我们学到了很多的知识,学习并熟悉与查表,检查参考书,也掌握了证明和CAD相关的操作,因为部分工艺设计有着深刻的认识和理解的夹具设计也有了一定的了解,知道一些基本的夹具的具体结构部件,如皮瓣,钻套,顶头……。通过合作和团队成员及夹具,使过程中我了解合作是非常重要的,分工合作可以工作更快更好。

在这个课程设计,老师给我们提供了宝贵的参考意见,让我们知道如何完成的课程设计,如何把你的事情,多亏老师的精心辅导。和我们有了更多的分析和解决问题的能力。在这个过程中,我们发现最缺乏的是社会实践经验,空虚有书籍理论知识,没有感性的认知,往往会有可能和实际分开。一般来说,这种设计可以使我们会学会知识体系相关链接,这暴露了不足之处。也希望我们在以后的学习可以进入社会,使更多的社会实践活动,为了提高自己的能力,以适应社会。

参考文献

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[18] 徐家军.汽车减振器CAPP系统的开发与研制[D].湖南省长沙市:中南林学院,2004.

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外文翻译 专业机械设计制造及其自动化学生姓名刘链柱 班级机制111 学号1110101102 指导教师葛友华

外文资料名称: Design and performance evaluation of vacuum cleaners using cyclone technology 外文资料出处:Korean J. Chem. Eng., 23(6), (用外文写) 925-930 (2006) 附件: 1.外文资料翻译译文 2.外文原文

应用旋风技术真空吸尘器的设计和性能介绍 吉尔泰金,洪城铱昌,宰瑾李, 刘链柱译 摘要:旋风型分离器技术用于真空吸尘器 - 轴向进流旋风和切向进气道流旋风有效地收集粉尘和降低压力降已被实验研究。优化设计等因素作为集尘效率,压降,并切成尺寸被粒度对应于分级收集的50%的效率进行了研究。颗粒切成大小降低入口面积,体直径,减小涡取景器直径的旋风。切向入口的双流量气旋具有良好的性能考虑的350毫米汞柱的低压降和为1.5μm的质量中位直径在1米3的流量的截止尺寸。一使用切向入口的双流量旋风吸尘器示出了势是一种有效的方法,用于收集在家庭中产生的粉尘。 摘要及关键词:吸尘器; 粉尘; 旋风分离器 引言 我们这个时代的很大一部分都花在了房子,工作场所,或其他建筑,因此,室内空间应该是既舒适情绪和卫生。但室内空气中含有超过室外空气因气密性的二次污染物,毒物,食品气味。这是通过使用产生在建筑中的新材料和设备。真空吸尘器为代表的家电去除有害物质从地板到地毯所用的商用真空吸尘器房子由纸过滤,预过滤器和排气过滤器通过洁净的空气排放到大气中。虽然真空吸尘器是方便在使用中,吸入压力下降说唱空转成比例地清洗的时间,以及纸过滤器也应定期更换,由于压力下降,气味和细菌通过纸过滤器内的残留粉尘。 图1示出了大气气溶胶的粒度分布通常是双峰形,在粗颗粒(>2.0微米)模式为主要的外部来源,如风吹尘,海盐喷雾,火山,从工厂直接排放和车辆废气排放,以及那些在细颗粒模式包括燃烧或光化学反应。表1显示模式,典型的大气航空的直径和质量浓度溶胶被许多研究者测量。精细模式在0.18?0.36 在5.7到25微米尺寸范围微米尺寸范围。质量浓度为2?205微克,可直接在大气气溶胶和 3.85至36.3μg/m3柴油气溶胶。

管理信息系统外文翻译

管理信息系统外文翻译-标准化文件发布号:(9456-EUATWK-MWUB-WUNN-INNUL-DDQTY-KII

英文文献翻译 二〇年月日

科技文章摘译 Definition of a Management Information System There is no consensus of the definition of the term "management information system". Some writers prefer alternative terminology such as "information processing system", "information and decision system", "organizational information system", or simply "information system" to refer to the computer-based information processing system which supports the operations, management, and decision-making functions of an organization. This text uses “MIS” because it is descriptive and generally understood; it also frequently uses “information system” instead of “MIS” to refer to an organizational information system. A definition of a management information system, as the term is generally understood, is an integrated, user-machine system for providing information to support operations, management, and decision-making functions in an organization. The system utilizes computer hardware and software; manual procedures; models for analysis planning, control and decision making; and a database. The fact that it is an integrated system does not mean that it is a single, monolithic structure; rather, it means that the parts fit into an overall design. The elements of the definition are highlighted below. 1 Computer-based user-machine system Conceptually, management information can exist without computer, but it is the power of the computer which makes MIS feasible. The question is not whether computers should be used in management information system, but the extent to which information use should be computerized. The concept of a user-machine system implies that some tasks are best performed by humans, while others are best done by machine. The user of an MIS is any person responsible for entering input data, instructing the system, or utilizing the information output of the system. For many problems, the user and the computer form a combined system with results obtained through a set of interactions between the computer and the user. User-machine interaction is facilitated by operation in which the user’s input-output device (usually a visual display terminal) is connected to the computer. The computer can be a personal computer serving only one user or a large computer that

引进外资外文翻译资料

河南科技学院新科学院 2013届本科毕业生论文(设计) 英文文献及翻译 Foreign capital inflows and welfare in an economy with imperfect competition 学生姓名:王艳杰 所在院系:经济系 所学专业:国际经济与贸易 导师姓名:侯黎杰 完成时间:2013年4月15日

Foreign capital inflows and welfare in an economy with imperfect competition Abstract:This paper examines the resource allocational and welfare effects of exogenous inflows of foreign capital in a general-equilibrium model with oligopolistic competition and unemployment. Although the welfare impact for the short run is ambiguous and dependent upon the strength of excess profits and scale economies relative to unemployment in manufacturing, in the long run additional inflows of foreign capital always improve national welfare with capital mobility. Hence, attracting foreign capital remains a sound policy for economies characterized by imperfect competition, scale economies,and regional unemployment. Keywords: International capital mobility; Imperfect competition; Welfare 1.Introduction The welfare effects of exogenous inflows of foreign capital in the presence of trade restrictions have been extensively studied. Brecher and Diaz Alejandro (1977) show that when imports are subject to tariffs, an introduction of fo reign capital inflows accentuates the tariff distortion and hence reduces national welfare if the import-competing sector is relatively capital-intensive. In contrast, Dei (1985) shows that when imports are restricted by quotas,foreign capital inflows in the presence of foreign-owned capital always improve welfare by depressing the rental and so lowering the payments to existing foreign-owned capital. Recently, Neary (1981), using a common framework for both tariffs and quotas, obtains more general results of foreign capital inflows; the welfare effect of such inflows depends crucially on whether foreign-owned capital exists initially in the home country. In addition, Khan (1982) and Grinols (1991) have examined the effects of foreign capital inflows for a generalized Harris-Todaro economy under tariff protection. Khan finds that the result by Brecher and Diaz Alejandro is still valid even in the presence of unemployment, whereas Grinols argues that increased foreign capital need not be detrimental to welfare if the opportunity costs of labor are sufficiently low. Noteworthy is that the models used by these authors are all based upon the premise of perfect competition along with constant returns-to-scale technology. Although perfect competition serves as a useful assumption in crystallizing theoretical insights, it nevertheless fails to depict many of the real-world phenomena. The real-world economy is characterized, to a large extent, by imperfect competition and economies of scale. The policy implications of imperfect competition and economies

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