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Microstructural characterization of copper corrosion

in aqueous and soil environments

A.Srivastava,R.Balasubramaniam *

Department of Materials and Metallurgical Engineering,Indian Institute of Technology,Kanpur 208016,India

Received 22March 2005;received in revised form 12April 2005;accepted 15April 2005

Abstract

Scanning electron microscopy has been used to investigate the surface films on pure copper after exposure to different aqueous and soil environments,containing chloride,sulfide and ammonium salts.The morphology of the films formed on copper surface in aqueous and soil environments was different for the same amount of pollutants.The surface films formed in soil environments were not homogenous in contrast to the films formed in aqueous environments.The damaging effect of chloride ions and the benign role of sulfide ions were revealed in both the environments.Local compositional analysis confirmed that the surface films formed on copper consisted predominantly of copper and oxygen.D 2005Elsevier Inc.All rights reserved.

Keywords:Copper;Corrosion;Soil;Surface film;Characterization

1.Introduction

When one considers the existence of human beings on this planet,one of the earliest metals intelligently used for practical applications is copper [1].Copper is one of the most frequently encountered metals in our society.Copper eventually forms a thin layer of cor-rosion,generally brownish-green or greenish-blue in color.This layer is called patina [2].Once the patina is established it tends to be extremely stable and become a permanent part of the copper object.Changes in

patina,which can occur under some conditions,may be detrimental for the base metal.Copper corrosion products are known to have a protective effect against corrosion.However,a different behavior could be obtained in presence of pollutants (chloride,sulfide,etc.).This can be due to corrosion products morphol-ogy and degree of crystallization,rather than their phase composition [3].

Cuprite (Cu 2O)is known to play a decisive role in the protectiveness of corrosion layers on copper [3].In aqueous media,hydrated oxides of copper have also been reported to form over underlying Cu 2O film [4].A low degree of hydration has been found to give much better stability than that of fully hydrated metal oxide in flowing conditions.North et al.[5]found that

*Corresponding author.

E-mail address:bala@iitk.ac.in (R.Balasubramaniam).

Materials Characterization 55(2005)127–

135

the film on copper exposed to3.4%NaCl consisted of Cu2O with traces of Cu2(OH)3CL on top of Cu2O at longer immersion times.Kruger[6]showed that Cu2O is the only corrosion product for shorter immersion times and for longer duration CuO forms over under-lying Cu2O film as second component of the film.The CuO is in fact formed by precipitation from supersat-urated solution at the film/solution interface.Popple-well et al.[7]found that film formed on90–10Cu–Ni in air saturated3.4%NaCl solution possessed a du-plex structure consisting of Cu2O phase underlying the Cu2(OH)3CL layer.Bianchi et al.[8]have shown that for a theoretical system with Cu,Cu2O,CuCl, CuO and Cu2(OH)3CL solid phases,Cu2O is a stable phase for pH ranging from5to14.Whereas, Cu2(OH)3CL is a stable phase in acidic range and CuO in alkaline range while,CuCl is a stable phase in acidic range[8].It is quite likely that any of these phases or their combination may be stable under field or experimental conditions.Ammonia and ammonium salts enhance general attack by dissolving and com-plexing with the copper ion[9].When copper is exposed to aqueous ammonia,then corrosion takes place by two processes.The first process is the for-mation of an oxide film and the second being the attack of ammonium ions on the oxide to form a soluble product.The deleterious effect of sulfide ions on the behavior of copper and its alloys has been reported by many investigators[10,11].Most data indicate acceleration of corrosion of Cu–Ni alloys in sulfide polluted natural water,and similar effects were observed in synthetic seawater and aqueous solution of sodium chloride[11].According to Syrett[12],sulfide interferes with the normal growth of the protective oxide film that forms on the surface of Cu–Ni alloys when exposed to sea-water.Normally a thick black layer of scales is formed on copper surface when exposed to sulfide polluted environment.

Copper and copper-based alloys find applications in structural,architectural,marine,and the electronics industry.Another important use of copper is for can-isters used in underground storage of high-level nu-clear waste.The possibility of disposing of nuclear waste in copper containers buried deep underground has been investigated[13].An underground waste vault would be located at a depth of500to1000m (1640–3280ft)embedded in a bentonite clay envi-ronment in stable bedrock.At these depths,the envi-ronment differs in several respects from that nearer the surface.Most of the earlier studies regarding corro-sion of copper are related to marine environments and the atmosphere.Limited literature is available concerning the corrosion of copper in soil environ-ments.The current research work is an attempt to study the copper surface film evolution and their morphology in soil and compare the same with the film obtained in aqueous environments.

2.Experimental

Rectangular specimens of area1cm?1cm were cut from a3mm thick pure copper sheet.All the surfaces of the specimens were mechanically polished using fine emery paper(starting from grit number320 to800,ANSI)and then degreased using acetone before being used for each immersion experiment. The environments used in the present study are tabu-lated in Table1.Two different kinds of environments, aqueous and soil were used.The soil environments are abbreviated as S1through S4and the aqueous solu-tions are abbreviated from A1to A4.In the prepara-tion of aqueous solutions,300ml of distilled water was used while for soil environments,300g of dried soil was utilized.The additives to soil and aqueous solutions were added according to the composition presented in Table1.The salts NH4Cl and Na2S were added to understand their role as pollutants.

Bentonite clay was used to simulate soil environ-ments.Its characteristics were first understood.The chloride content was determined by titrating it against AgNO3[14].Two grams of solid clay sample was Table1

Test environments

Environment Abbreviation 3.5wt.%NaCl+100ppm Na2S+water A1

100ppm Na2S+water A2

1000ppm NH4Cl+water A3

3.5wt.%NaCl+1000ppm NH4Cl+water A4

3.5wt.%NaCl+20wt.%water+100ppm

Na2S+dry soil

100ppm Na2S+20wt.%water+dry soil S2

1000ppm NH4Cl+20wt.%water+dry soil S3

3.5wt.%NaCl+20wt.%water+1000ppm

NH4Cl+dry soil

A.Srivastava,R.Balasubramaniam/Materials Characterization55(2005)127–135 128

dissolved in 100ml distilled water.After 3h of stirring it was filtered and the filtrate was later titrated against an AgNO 3solution with a K 2CrO 4indicator [15].The amount of filtrate used in titration was a measure of chloride content present in the bentonite clay.The chloride content was determined to be 3540ppm.The moisture content of the soil was determined by drying 10g of soil in a crucible for 8h at 1108C in a microwave oven.Weight loss measurements were determined at intermediate times (Fig.1).After 2h,the weight loss of the dried soil was almost constant,indicating that after 2h the loosely bound water content present in the soil could be mostly removed.Therefore,it was decided to dry the soil for 2h at 1108C in further experiments.A laser scattering particle analyzer (Fritsch Particle Sizer Analysette 22)was used for analyzing the particle size of the bentonite clay.Most of the particles were less than 20A m,while the average particle size was 3.54A m.Soil environ-ments were prepared by adding the constituents and then mixing the soil thoroughly.Homogeneous mix-ing of soil could not be perfectly obtained due to agglomeration of soil particles.

All the immersion experiments were performed in 500ml capacity beakers.The beaker outlets were sealed with Teflon tape in order to prevent evapora-tion of moisture during the course of immersion experiments.A total of eight different beakers were used simultaneously to expose the specimens.The time of total exposure was 432h in different aqueous

and soil environments.The variation in temperature (20–258C)was minimum during the period in which the experiments were performed.Following exposure,the specimens were analyzed in a scanning electron microscope (SEM)FEI Quanta 200equipped with the EDAX (compositional analysis)facility.The surfaces of copper specimens,exposed in soil environments were cleaned by a light air blast to remove soil particles from the surface.Surface microstructures were obtained at different locations in the samples.Spot analysis was also performed to understand the composition of different features on the surface.SEM helped in understanding the physical nature of the surface films and surface.

3.Results and discussion 3.1.Aqueous solutions

The surface obtained after immersion in aqueous solution A1(3.5wt.%NaCl +100ppm Na 2S+water)did not present a smooth appearance.The entire sur-face was covered with very small agglomerated cop-per oxide particles (Fig.2),but at some locations islands of chlorides are found on the surface.The presence of a surface layer could be distinguished.There were several locations where the surface layer was cracked and broken (Fig.3).The porous nature of the surface layer could be discerned by the breakages present in the layer.The structure inside the location where the layer had peeled off was observed at higher magnification (Fig.4).A fine needle-like structure was observed at these locations (Fig.4).EDAX anal-ysis of these fine needle indicated that they were Cu 2O.This indicates that at any local break in the film,Cu 2O forms with time.The needle-like morphol-ogy indicates the nature of the Cu 2O when it first nucleates and grows.

The surface film formed on copper in aqueous solution A2(100ppm Na 2S+water)was blackish-brown in color as seen with the naked eye.Part of the surface film has been disturbed and the underneath exposed metal can be noticed from where the layer has peeled off,Fig 5.The surface layer in this sample was relatively thin,and at several locations the edges of the scale were folded up (Fig.6).The edges do not touch the base metal.It appears that the surface

layer

Fig.1.Weight loss measured as a function of time during drying of 10g of soil at 1108C.

A.Srivastava,R.Balasubramaniam /Materials Characterization 55(2005)127–135129

had slowly lost contact with the base metal and after that,it peeled off from the surface.The film does not appear to be protective,as it is not adherent to the surface.Cracks in the scale (Fig.6)also indicate the non-protective nature of the film.Most of the surface film from the middle of the sample was peeled off.Therefore,throughout the sample,the surface layer was present only in form of patches (Fig.5).

The surface film obtained after immersion in aque-ous solution A3(1000ppm NH 4Cl +water)was brownish-yellow in color as seen by the naked eye.Breakages were noted in the surface layer (Fig.7).This film was thicker than the film obtained in solution A2and moreover did not appear to peel off from the surface.At locations where the surface film had been removed,the underlying grain boundaries were

etched

Fig.4.SEM magnified view of the broken surface layer obtained after immersion in aqueous solution

A1.

Fig.5.SEM micrograph of copper surface obtained after immersion in aqueous solution A2,showing a region of the surface,from where the layer has peeled

off.

Fig.3.SEM micrograph of copper surface obtained after immersion in aqueous solution A1,showing that the surface layer is cracked at some

places.Fig.2.SEM micrograph of copper surface obtained after immersion in aqueous solution A1,showing agglomerated particles.A.Srivastava,R.Balasubramaniam /Materials Characterization 55(2005)127–135

130

by the corrosive solution(Fig.8).The attack occurred

at certain preferential crystallographic directions.

The surface obtained after immersion in aqueous solution A4(3.5wt.%NaCl+1000ppm NH4Cl+ water)was relatively rough and it appeared to have been attacked severely by the corrosive solution(Fig.

9).The uneven surface appeared to be due to non-uniform rate of attack.There were locations that were more deeply attacked than the adjoining region(Fig.

9).The microstructure is indicative of the layer growth by a precipitation process.Cracks are also visible in the layer.

On comparing the surface films obtained in aque-ous solutions,it was found that wherever chloride

ion Fig.7.A typical SEM micrograph of copper surface obtained after

immersion in aqueous solution

A3.

Fig.8.SEM micrograph of copper surface obtained after immersion

in aqueous solution A3,showing that at locations where the surface

film had been removed the underlying grain boundaries were etched

by the corrosive

solution.

Fig.9.SEM micrograph of copper surface obtained after immersion

in aqueous solution A4,showing the severe attack by the corrosive

solution.

Fig.6.SEM micrograph of copper surface obtained after immersion

in aqueous solution A2,showing the portion of the layer that was

peeling off.

A.Srivastava,R.Balasubramaniam/Materials Characterization55(2005)127–135131

was present in the aqueous environment(as in A1),it resulted in breakage of the surface layer(Fig.3)after 432h of immersion.When there was no Clà(as in A2)or when present in very low concentration(as in A3)the surface layer was thin and moreover not adherent to substrate in aqueous solutions(Fig.5). Moreover,the penetration during corrosive attack was not deep in absence of chloride in aqueous solutions. The damaging effect of chloride ions has been exten-sively reported in the literature.The chloride ions will affect the properties and stability of the surface films. It can rapidly reduce the stability of the oxide layer (Cu2O and CuO)on the copper surface[17].By incorporation of CuCl d islands T in the surface Cu2O film,defects are created,which are believed to be initiation points for pitting.Substitution of monova-lent Clàions for divalent O2àin the Cu2O lattice enhances the semi conducting properties of the sur-face film.The Cu2O film formed in Clàsolutions may,therefore,support O2reduction and the anodic

Cu dissolution and,therefore,be less protective than Cu2O films formed in the absence of Clà[13].

3.2.Soil environments

The surface of the metal exposed in the soil condi-tion S1(3.5wt.%NaCl+20wt.%water+100ppm Na2S+dry soil)appeared bluish-green in color,in patches,on the surface.At some places,the surface was brown.Some particles were present on the surface that appeared to have been nucleated on the surface (Fig.10).The surface was not homogeneous(Fig.10). It appears that an oxide layer precipitated in form of agglomerated particles(Fig.11).Fig.12suggests

that Fig.10.SEM micrograph of copper surface obtained after immer-

sion in soil environment S1,showing nucleated oxide particles.The

surface was not

homogeneous.

Fig.11.SEM micrograph of copper surface obtained after immer-

sion in soil environment S1,showing that copper oxide layer was

composed of nucleated

particles.

Fig.12.SEM micrograph of copper surface obtained after immer-

sion in soil environment S1,suggested that small nucleated particles

constitute a surface layer,which was not broken,although cracks

were present in the layer.

A.Srivastava,R.Balasubramaniam/Materials Characterization55(2005)127–135

132

these particles constitute a surface layer,which was not broken,although cracks were present in the layer.Also at some places on the surface,the porous nature of the film could be discerned.

The surface obtained in soil S2(100ppm Na2S+20wt.%water+dry soil)after432h of im-mersion appeared blackish-brown in color.A surface layer could be easily distinguished in Fig.13.It appeared to peel off from the surface.The attack took place along some preferred orientation within the grains.The surface layer was composed of copper oxide particles nucleating and agglomerating on the surface(Fig.14),which was later confirmed by EDAX.In between the agglomerated particles,pores were present(Fig.14).

The surface layer obtained after immersion in soil environment S3(1000ppm NH4Cl+20wt.%water+ dry soil)was found to be detached at some places and the underlying metal was exposed in these areas(Fig.

15).EDAX results confirmed that the underlying

metal was pure copper.Attack had occurred on some preferred crystallographic directions in the metal and also grain boundaries were etched(Fig.15).

Some bright locations were observed on the sur-face obtained after immersion in soil environment S4 (3.5wt.%NaCl+20wt.%water+1000ppm NH4Cl+dry soil).They were the locations from where the layer was peeling off(Fig.16).EDAX analysis at the bright location on the scale(Fig.16) confirmed that it was copper oxide.Moreover,the detached scale was cracked and the cracks propagated in certain preferred directions(Fig.17).The structure at the interface between the bright and dull regions is shown in Fig.18.Some fibrous structure(visible

at Fig.13.SEM micrograph of copper surface obtained after immer-

sion in soil environment S2.The surface layer appeared to peel off

from the

surface.

Fig.14.SEM micrograph of copper surface obtained after immersion

in soil environment S2,showing that the surface layer was composed

of copper oxide nucleating and agglomerating on the

surface.

Fig.15.SEM micrograph of copper surface obtained after immer-

sion in soil environment S3,shows a location where the underlying

metal has been exposed.

A.Srivastava,R.Balasubramaniam/Materials Characterization55(2005)127–135133

bottom right corner of Fig.18)appeared to be incor-porated into the detached layer.This fibrous structure was copper oxide,confirmed by EDAX analysis.The microstructures obtained after 432h of immer-sion in soil environments have suggested that the morphology of the oxide layers was not similar in all the soil environments.The surface film obtained in soil S2was not thick as compared to soil condition S1

(Figs.12and 13).Moreover the oxide particles were cracked in soil S1(Fig.12).

The corrosive attack in the soil environments was not homogeneous as found in aqueous solutions.The damaging effect of chloride ions was more pronounced in aqueous solutions than in soil environments.On increasing the relative humidity,the corrosion effects had been increased significantly for copper in presence of NaCl [16].Similarly accelerated corrosion effects in aqueous solutions containing NaCl could be explained due to the aqueous nature of the environments.The surface obtained after 432h of immersion in aqueous solution A1was more cracked and brittle as compared to surface obtained from soil S1.On comparing micro-structures of aqueous solution A1and soil S1,it was found that morphology of the film breakdown in aque-ous solutions was different than in soil (Figs.3and 12).The needle-type structure formed in the breakage of the surface film obtained from solution A1(Fig.4)was not found in surface film obtained from soil environment S1.On comparing the surface films obtained from aqueous solution A2and soil environment S2,it was found that in both cases the surface layer partly peeled off from the surface (Figs.5and 13).The microstruc-ture presented in Fig.13shows that corrosive attack took place along some preferred orientations on the surface obtained from soil S2,whereas it was not noticed in case of solution A2.The nature of the

surface

Fig.16.A typical SEM micrograph of copper surface obtained after immersion in soil environment

S4.

Fig.17.SEM micrograph of copper surface obtained after immer-sion in soil environment S4.Copper oxide scale was peeling off and cracks were present on the

scale.

Fig.18.SEM micrograph of copper surface obtained after immer-sion in soil environment S4.Fibrous structure was visible at bottom right corner that appeared to be incorporated into the detached layer.

A.Srivastava,R.Balasubramaniam /Materials Characterization 55(2005)127–135

134

films obtained after immersion in aqueous solution A3 and soil S3was almost similar and no specific differ-ence could be noticed(Figs.8and15).The surface films obtained after432h of immersion in solution A4 and corresponding soil S4did not reveal a similar morphology.The surface film formed in soil S4 appeared to peel off(Fig.16)and was cracked along some preferred directions(Fig.17).The whole surface was relatively rough and the surface appeared to have been attacked severely by the corrosive solution in solution A4(Fig.9).

The phases present in the copper corrosion pro-ducts depend on the atmosphere and exposure condi-tions,so that,their composition[3]and morphology can be different in different environments.The corro-sion rates for copper alloys can be very dependent on the morphology of the corrosion products on the copper surface.Corrosion products of the same com-position(Cu2O)could give higher corrosion rates when they do not dry out than when they do[3]. Cuprite is generally the corrosion product first formed regardless of the exposure conditions,so that it is always present on the copper surface[3].In the present study the morphology of the surface film formed on copper in aqueous and soil environments were found to be different.Different morphology may result in different corrosion rates.In all the environ-ments,the compositional analysis at the surface revealed that copper and oxygen were the major con-stituents present on the surface film.

4.Conclusions

Surface films formed on copper after432h of im-mersion in soil and aqueous environments have been investigated by scanning electron microscopy.Chloride, sulfide and ammonium ions were added in the environ-ments as pollutants.The damaging role of chloride ions and the relatively less severe effect of sulfide ions could be discerned from the SEM analysis.The morphology of the films in aqueous solutions and soil environments was different.On comparing the surface films obtained in aqueous solutions,it was found that wherever chlor-ides ion were present in the aqueous environment,it resulted in breakage of the surface layer after432h of immersion.When there was no Clàor when present in very low concentration,the surface layer was thin and not adherent to substrate in aqueous solutions.The penetration during corrosive attack was not deep in absence of chloride in aqueous solutions. References

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利用固定化过氧化氢酶回收纺织品漂染的废水 Silgia A. Costa1, Tzanko Tzanov1, Filipa Carneiro1, Georg M. Gübitz2 &Artur Cavaco-Paulo1,? 1纺织工程系, 米尼奥大学, 4810吉马尔, 葡萄牙 2环境生物技术系, 格拉茨技术大学, 8010格拉茨, 奥地利 ?作者联系方式(Fax: +351 253 510293; E-mail: artur@det.uminho.pt) 关键词：过氧化氢酶的固定化，酶稳定，过氧化氢，纺织印染摘要过氧化氢酶固定在氧化铝载体上并用戊二醛交联，在再循环塔反应器和CSTR反应器中研究贮存稳定性，温度和pH值对酶的活性。固定化酶的在的活性维持在44％，pH值11（30?C），对照组是活性为90％，pH值7（80?C），过氧化氢酶固定化的半衰期时间被提高到2小时（pH12，60?C）。用过氧化氢漂白织物后，洗涤过程中的残留水被固定化酶处理，可以用于再次印染时，记录实验数据。 1 序言由于新的法规的出台，从生态经济的角度来看（Dickinson1984年），对于纺织行业中存在的成本和剩余水域的污染问题，必须给予更多的关注。过氧化氢是一种漂白剂，广泛应用于工业纺织工艺（Spiro & Griffith1997年）。在去除H2O2时，会消耗大量的水和能源（Weck 1991, St?hr & Petry 1995），以避免对氧气敏感的染料（Jensen 2000）产生后续问题。过氧化氢酶可用于降低过氧化氢的含量（Vasudevan & Thakur 1994, Emerson et al. 1996），从而减少水分消耗或方便回收印染洗涤液。过氧化氢酶的使用主要问题出在漂白时温度和清洗液碱度过高。以前，我们试图通过筛选新的嗜热嗜碱的微生物（Paar et al. 2001）或使用不同的酶稳定剂（Costa et al. 2001）来解决此问题。但是染料与蛋白质之间的潜在相互作用（Tzanov et al. 2001a, b）表明，可溶性过氧化氢酶的使用是不恰当的。固定化过氧化氢酶的使用还有一种选择(Costa et al. 2001, Amar et al. 2000)。在这项研究中，我们对氧化铝进行共价固定并使用戊二醛作为交联剂，这种方法在商业中得到验证。本项研究的目的就是探讨过氧化氢酶的固定化动力学，及其稳定性和工艺条件，这将使我们能够应用此系统，以处理可能被用于清洗染色的反复使用的酒。 2 材料和方法 2.1 酶 Terminox（EC1.11.1.6），50L以上，由AQUITEX- Maia提供，葡萄牙产。 2.2 过氧化氢酶的固定化取Al2O3颗粒或薄片（Aldrich），直径分别为3和7毫米，在45摄氏度下，先经浓度4%的γ-氨丙基三乙氧基硅烷(Sigma)烷基化，再放入丙酮中浸泡24小时。用蒸馏水洗涤硅烷化载体后，放入浓度为2％戊二醛水溶液中室温下浸泡2小时（Aldrich），重复清洗一次并在60?C下干燥1小时。取五克的烷基化载体，室温24?C下浸泡在25毫升粗酶制剂中（Costa et al. 2001）。得出，每克Al2O3

英文文献及翻译(计算机专业)

NET-BASED TASK MANAGEMENT SYSTEM Hector Garcia-Molina, Jeffrey D. Ullman, Jennifer Wisdom ABSTRACT In net-based collaborative design environment, design resources become more and more varied and complex. Besides com mon in formatio n man ageme nt systems, desig n resources can be orga ni zed in connection with desig n activities. A set of activities and resources linked by logic relations can form a task. A task has at least one objective and can be broken down into smaller ones. So a design project can be separated in to many subtasks formi ng a hierarchical structure. Task Management System (TMS) is designed to break down these tasks and assig n certa in resources to its task no des. As a result of decompositi on. al1 desig n resources and activities could be man aged via this system. KEY WORDS : Collaborative Design, Task Management System (TMS), Task Decompositi on, In formati on Man ageme nt System 1 Introduction Along with the rapid upgrade of request for adva need desig n methods, more and more desig n tool appeared to support new desig n methods and forms. Desig n in a web en vir onment with multi-part ners being invo Ived requires a more powerful and efficie nt man ageme nt system .Desig n part ners can be located everywhere over the n et with their own organizations. They could be mutually independent experts or teams of tens of employees. This article discussesa task man ageme nt system (TMS) which man ages desig n activities and resources by break ing dow n desig n objectives and re-orga nizing desig n resources in conn ecti on with the activities. Compari ng with com mon information management systems (IMS) like product data management system and docume nt man ageme nt system, TMS can man age the whole desig n process. It has two tiers which make it much more flexible in structure. The lower tier con sists of traditi onal com mon IMSS and the upper one fulfills logic activity management through controlling a tree-like structure, allocating design resources and

建筑外文文献及翻译论文资料

外文原文 Study on Human Resource Allocation in Multi-Project Based on the Priority and the Cost of Projects Lin Jingjing , Zhou Guohua SchoolofEconomics and management, Southwest Jiao tong University ,610031 ,China Abstract----This paper put forward the affecting factors of project’s priority. which is introduced into a multi-objective optimization model for human resource allocation in multi-project environment . The objectives of the model were the minimum cost loss due to the delay of the time limit of the projects and the minimum delay of the project with the highest priority .Then a Genetic Algorithm to solve the model was introduced. Finally, a numerical example was used to testify the feasibility of the model and the algorithm. Index Terms—Genetic Algorithm, Human Resource Allocation, Multi-project’s project’s priority . 1.INTRODUCTION More and more enterprises are facing the challenge of multi-project management, which has been the focus among researches on project management. In multi-project environment ,the share are competition of resources such as capital , time and human resources often occur .Therefore , it’s critical to schedule projects in order to satisfy the different resource demands and to shorten the projects’duration time with resources constrained ,as in [1].For many enterprises ,the human resources are the most precious asset .So enterprises should reasonably and effectively allocate each resource , especially the human resource ,in order to shorten the time and cost of projects and to increase the benefits .Some literatures have

外文文献(市场营销策略)

Marketing Strategy Market Segmentation and Target Strategy A market consists of people or organizations with wants,money to spend,and the willingness to spend it.However,within most markets the buyer' needs are not identical.Therefore,a single marketing program starts with identifying the differences that exist within a market,a process called market segmentation, and deciding which segments will be pursued ads target markets. Marketing segmentation enables a company to make more efficient use of its marketing resources.Also,it allows a small company to compete effectively by concentrating on one or two segments.The apparent drawback of market segmentation is that it will result in higher production and marketing costs than a one-product,mass-market strategy.However, if the market is correctly segmented,the better fit with customers' needs will actually result in greater efficiency. The three alternative strategies for selecting a target market are market aggregation,single segment,and multiple segment.Market-aggregation strategy involves using one marketing mix to reach a mass,undifferentiated market.With a single-segment strategy, a company still uses only one marketing mix,but it is directed at only one segment of the total market.A multiple-segment strategy entails selecting two or more segments and developing a separate marketing mix to reach segment. Positioning the Product Management's ability to bring attention to a product and to differentiate it in a favorable way from similar products goes a long way toward determining that product's revenues.Thus management needs to engage in positioning,which means developing the image that a product projects in relation to competitive products and to the firm's other products. Marketing executives can choose from a variety of positioning strategies.Sometimes they decide to use more than one for a particular product.Here are several major positioning strategies:

英文文献及中文翻译

毕业设计说明书英文文献及中文翻译学院：专 2011年6月电子与计算机科学技术软件工程

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商业建筑外文文献翻译)

Commercial Buildings Abstract: A guide and general reference on electrical design for commercial buildings is provided. It covers load characteristics; voltage considerations; power sources and distribution apparatus; controllers; services, vaults, and electrical equipment rooms; wiring systems; systems protection and coordination; lighting; electric space conditioning; transportation; communication systems planning; facility automation; expansion, modernization, and rehabilitation; special requirements by occupancy; and electrical energy management. Although directed to the power oriented engineer with limited commercial building experience, it can be an aid to all engineers responsible for the electrical design of commercial buildings. This recommended practice is not intended to be a complete handbook; however, it can direct the engineer to texts, periodicals, and references for commercial buildings and act as a guide through the myriad of codes, standards, and practices published by the IEEE, other professional associations, and governmental bodies. Keywords: Commercial buildings, electric power systems, load characteristics 1. Introduction 1.1 Scope This recommended practice will probably be of greatest value to the power oriented engineer with limited commercial building experience. It can also be an aid to all engineers responsible for the electrical design of commercial buildings. However, it is not intended as a replacement for the many excellent engineering texts and handbooks commonly in use, nor is it detailed enough to be a design manual. It should be considered a guide and general reference on electrical design for commercial buildings. 1.2 Commercial Buildings The term “commercial, residential, and institutional buildings”as used in this chapter, encompasses all buildings other than industrial buildings and private dwellings. It includes office and apartment buildings, hotels, schools, and churches, marine, air, railway, and bus terminals, department stores, retail shops, governmental buildings, hospitals, nursing homes, mental and correctional institutions, theaters, sports arenas, and other buildings serving the public directly. Buildings, or parts of buildings, within industrial complexes, which are used as offices or medical facilities or for similar nonindustrial purposes, fall within the scope of this recommended practice. Today’s commercial buildings, because of their increasing size and complexity, have become more and more dependent upon adequate and reliable electric systems. One can better understand the complex nature of modern commercial buildings by examining the systems, equipment, and facilities listed in 1.2.1. 1.2.2 Electrical Design Elements In spite of the wide variety of commercial, residential, and institutional buildings, some electrical design elements are common to all. These elements, listed below, will be discussed generally in this section and in detail in the remaining sections of this recommended practice. The principal design elements considered in the design of the power, lighting, and auxiliary systems include: 1) Magnitudes, quality, characteristics, demand, and coincidence or diversity of loads and load factors 2) Service, distribution, and utilization voltages and voltage regulation 3) Flexibility and provisions for expansion

市场营销英文文献

市场营销英文文献 Innovation Is a Good Way to Maintain Market Presence The Jumbo-Koter venture is a good example of the development of a successful new product by solving a consumer problem. The Wooster Brush Company identified the difficulty that painters were having because their minirollers were sticking after a few uses. The new Jumbo-Koter mini-rollers solved that problem by using a smooth-turning cage frame. Wooster Brush further improved these mini-rollers by using high-quality fabrics from its highly successful nine-inch rollers. Finally, by not extending fabric over the end of the new mini-rollers, Jumbo-Koter enabled the painter to get into tighter spaces than with traditional mini-rollers. This also prevented paint from spinning off onto another surface. One lesson to be learned from the Jumbo-Koter program is that innovationis a good way for a company to maintain its presence in the marketplace. The Wooster Brush Company has made a notable effort to continue to innovate, developing truly beneficial products in a very stodgy, old-fashioned business for many years. The Jumbo-Koter product line is a good example of this. This continuous innovation has enabled the company to compete successfully without participating in industry price wars. At the time of this writing, the Wooster Brush Company was in the process of developing additional new products to meet the paint application needs of its customers. Summary Marketing Plan for: Wooster Jumbo-Koter TM Wooster Brush Company MARKETING PLAN SUMMARY BACKGROUND. Many painters have problems with their mini-rollers. Because these rollers are smaller than traditional rollers, they are great for getting paint into