Effects of crosslinking on the Properties of Soybean Protein-Based Composites

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明胶水凝胶增强策略

明胶水凝胶增强策略Gelatin or agar-agar are commonly used as gelling agents in various food and pharmaceutical products. They are widely used due to their ability to form gels that provide texture, stability, and holding properties. However, there are certain scenarios where the gel strength of these gelling agents needs to be enhanced for specific applications.明胶或琼脂通常用作各种食品和药品中的凝胶剂。

由于它们能够形成提供质地、稳定性和保持性能的凝胶，因此它们被广泛使用。

然而，在特定应用中，这些凝胶剂的凝胶强度需要增强。

One of the strategies to enhance the gel strength of gelatin or agar-agar is to increase the concentration of the gelling agent in the formulation. By increasing the concentration, more cross-linking can occur, resulting in a stronger gel structure. However, this approach may also lead to changes in the sensory attributes and functional properties of the final product.增强明胶或琼脂的凝胶强度的策略之一是增加配方中凝胶剂的浓度。

组织行为学文章英文版

An Examination of the Relationship Among Structure,Trust,and Conﬂict Management Styles in Virtual TeamsXiaojing Liu,Richard J.Magjuka,and Seung-hee Lee I n today’s competitive environment,successful organizations that are able to utilize advanced information technology to establish a dynamic form to adapt to the ever-changing landscape and customer requirements always gain a competitive advantage in global competition (Porter &Lilly,1996).The virtual team has become one of the building blocks of a successful organization.In this article,a virtual team is deﬁned as ‘‘a group of people with complementary competencies executing simul-taneous,collaborative work processes through elec-tronic media without regard to geographic location’’(Chinowsky &Rojas,2003,p.98).Virtual teams can offer a range of beneﬁts toorganizations,among them encouraging constructive dialogue and knowledge,nurturing a community of workers,triggering deeper processing of content through interaction,and offering ﬂexible adaptation to complex tasks (Duarte &Snyder,1999;Conrad &Donaldson,2004;Palloff &Pratt,2005;Lee,Bonk,Magjuka,Su,&Liu,2006).However,a virtual team can also face challenges and issues that must beaddressed for a successful team operation.Fromexisting telework research,Workman,Kahnweiler,and Bommer (2001)summarize three attributes of virtual environments that are barriers to successful virtual collaboration:elevated ambiguity,increased isolation,and a less-structured environment.For example,in virtual environments lack of informal interactions,the constraints of dispersed asynchronous communication context,and limited capabilities of transmittingsocial &2008International Society for Performance ImprovementThe emergence of new technolo-gies has made it increasingly easy for distributed collaboration in both edu-cational and noneducational settings.Although the effectiveness in tradi-tional settings of the dynamics of small group work has been widely researched,there is limited researchthat offers evidence on how teams can work effectively in a virtual environment.The purpose of this study is to examine the relationship among team structure,trust,andconﬂict management style,in addi-tion to their impact on teamwork effectiveness in a virtual environment.An experimental design was used toassess the effects of structure on team performance.Forty-four groups,di-vided into hierarchical and nonhier-archical groups,worked on an online simulation project in an online MBAcourse.The results suggest that team structure is strongly associated with team performance,whereas trust and a collaboration conﬂict manage-ment style contribute to teamworksatisfaction.cues may render an environment that is low in social presence and interactivity.Such an environment can create difﬁculties for effective communication and collaboration (Montoya-Weiss,Massey,&Song,2001).Thus it has been suggested that virtual teams may have to make extra efforts in communication and collaboration for a successful operation.Walther (1996)suggests that in some instances a level of interaction that surpasses face-to-face interaction could occur thanks to strong involvement,intense relationships,and reciprocation.Although the effectiveness of small group work in traditional settings has beenwidely researched,there is still limited researchwith evidence concerning how teams can work effectively in a virtual environment.In particular,there is a lack of research on linking the social,task,and technological dimensions to the entry,process,and outcome variables of the teamwork process (Carabajal,LaPointe,&Gunawardena,2003)in a virtual environment.Existing theory about team-work processes may not be transferable to a virtual setting because introduction of media technology may have changed or altered the dynamics of thegroup process.For example,conﬂict in a virtualteam may persist longer without being noticed (Grifﬁth,Mannix,&Neale,2003),or trust development—which is generally regarded as a prerequisite for developing shared commitment—may be undermined from the lack of a personal human touch (Crossman &Lee-Kelley,2004).The purpose of this study is to add to the existing knowledge about virtual teamwork by examining the roles of team structure,trust,and conﬂict variables in the effectiveness of virtual teamwork.This study intends to answer several research questions:(1)Would there be signiﬁcant differences in team performance or satisfaction if virtual teams were structured differently?(2)Are there any signiﬁcant relationships between trust and virtual team performance or satisfaction?(3)Are there any signiﬁcant relationships between team conﬂict management styles and virtual team performance or satisfaction?Literature ReviewTeam StructureIn this article,team structure refers to the division of a team’s work environment into subtasks assigned to individual members or subteams.Such division can dictate the distribution of information and responsi-bilities of each team member.In teamwork,two types of structures were usually studied to understand their effects on team performance (Moon et al.,2004;Urban,Bowers,Monday,&Morgan,1995).Hierarchical structure refers to those structures in which team members have specialized roles or hold information and capabilities that are unique toExisting theory about teamwork processes may not be transferable to a virtual setting because introduction of media technology may have changed or altered the dynamics of the group process.each other.Such division of roles results in high interdependency among team participants.Nonhierarchical structure refers to those structures in which team members have nonspecialized roles and have fewer interdependencies in accomplishing a common team goal(Urban et al., 1995).In general,team structure deﬁnes the nature and patterns of relationships and the division of work among individuals in groups(Wong &Burton,2000).Studies that examine the relationship between team structure and team performance in organization settings revealed diversiﬁed results. Researchers,for instance,have proposed that a high degree of group division can reinforce individual accountability,and therefore it can prevent participants from slacking off or freeloading,which commonly impairs group performance in a virtual environment(Lin&Hui,1999; Pugh et al.,1963;Lin,Yang,Arya,Huang,&Li,2005).In a study that compared the problem-solving performance in two types of structure,the group with hierarchical structure indicated higher perceptions of intersubjectivity—that is,a‘‘shared collective understanding’’—and deep processing in group learning during the initial weeks of activity.Over time,however,these levels equalized across group structures(Rose,2004). In another study,Joung and Keller(2004)evaluated two types of structure during online group debate.The results suggested that the group with hierarchical structure demonstrated greater use of critical thinking skills and revealed more critical and dynamic interaction patterns than the nonhierarchical group.Nevertheless,some studies also suggested that nonhierarchical structure seemed to have outperformed hierarchical structure(Urban et al.,1995;Bowers,Urban,&Morgan,1992;Kleinman&Serfaty,1989). For example,Urban et al.(1995)studied teams in the context of military training and found that those with nonhierarchical structures were associated with superior performance compared to hierarchical structures when working under a high workload.Team structures were associated with patterns of communication structures.The teams with hierarchical structures tended to rely on question-and-answer sequences to elicit information and resources more than nonhierarchical teams did.This communication pattern of hierarchical teams was less effective than that of nonhierarchical teams,which,because of their similar roles,could communicate more clearly or were able to anticipate each other’s needs rather than waiting on the others to ask for information.The contradictory results of the relationship between structure and performance in the extant literature may have reﬂected the effect of structure under different task environments.Structural contingency theory posits that no structure is better across teams in organizational settings.However,hierarchical structures may work better than nonhierarchical structures in less complex environments,while nonhier-archical structures may work better than hierarchical structures in complex environments(Moon et al.,2004).Research indicates that therules of structural contingency theory are equally applicable in a virtual organization whose members are bounded by a common goal and who ground their work in communications through information technology (Moon et al.,2004;Burns&Stalker,1961).In an unstable or dynamic environment,nonhierarchical,or informal, structure is argued to be an effective way of organizing virtual teams because it allowsﬂexibility for workers to communicate according to the changing demands of the task(Burns&Stalker,1961;Hinds&McGrath, 2006).Virtual environments are generally regarded to be associated with added complexity and uncertainty,though this is not always the case.In their study,Hinds and McGrath(2006)found that in a distributed virtual team environment,dividing tasks in a nonhierarchical,independent way (for example,reducing task interdependences between work sites)reduces the need for frequent communication and therefore minimizes the waiting time and miscommunications that are due to the nature of delayed feedback in virtual communications.In this study,following Hinds and McGrath’s study(2006)and Urban et al.(1995),we hypothesize that in virtual groups that engage in complex problem-solving tasks(such as ill-deﬁned problems with no clear-cut answers),teams with nonhierarchical structures may be able to communicate more efﬁciently(by minimizing waiting time)and more effectively(thanks to their shared knowledge, which allows them to anticipate each other’s needs and explain information more thoroughly).Hypothesis1.Nonhierarchical structures outperform hierarchical structures on their virtual team performance in complex task environments.TrustIn this article,trust is deﬁned as‘‘an emergent state comprising team member intentions to accept vulnerability based on positive expectations of the intentions or behavior of another’’(Rousseau,Sitkin,Burt,& Camerer,1998,p.395).The positive effect of trust on team outcomes is widely documented.For instance,trust can enhance collaboration among team members and reduce the cost of team operations by eliminating extra effort needed to monitor team members(Serva&Fuller,2004).In addition,studies have consistently found that trust can have an inﬂuence on team effectiveness by way of its impact on team processes such as problem solving,decision making,and communication(Kifﬁn-Petersen, 2004).For example,Zand(1972,as cited in Kifﬁn-Petersen,2004)found that teams with high trust demonstrated creative and diversiﬁed patterns of behavior that improved the team’s problem solving.In contrast,low-trust teams showed a defensive pattern of behaviors that interfered with informationﬂow within the team,thus negatively affecting the quality of problem ck of trust has proven to negatively inﬂuence team members’satisfaction with teamwork and their willingness to continue to work with the team(Golembiewski&McConkie,1975).A workrelationship characterized by trust tends to enhance open communication and collaboration,reconcile conﬂict,and increase commitment to a team (Smith&Barclay,1997).Although some claim that working in virtual teams can produce additional challenges owing to the absence of social cues that can transfer interpersonal affections,including trust,research actually suggests that such absence does not necessarily hinder development of trust in virtual teams but may merely prolong the process of trust building(Walther, 1996;Henttonen&Blomqvist,2005).Studies also suggest that trust can play the same important roles in the functioning of virtual teams as in traditional teams(Morris,Marshall,&Kelleyrainer,2002;Henttonen& Blomqvist,2005).A synthesis of existing research suggests that development of trust is associated with continuous interactions and communications and repeated interpersonal exchange(Wilson,Straus,&McEvily,2006;Crossman&Lee-Kelley,2004).As in traditional teams,social communications(greetings, exchanges of personal information)can play an important role in developing trust in virtual teams(Henttonen&Blomqvist,2005). Contemporary theory of‘‘swift trust’’(Jarvenpaa&Leidner,1999)posits that highly active,proactive,and enthusiastic actions can strengthen trust.Compared to nonhierarchical structures,we hypothesize that a hierarchically structured team whose members possess more specialized roles may have to engage in more frequent reciprocal information exchange and take a more active role in seeking information and providing responses to others;this is due to high interdependence among team members(Moon et al.,2004).Such actions may in fact expose team members to more communication and interactions and therefore foster the development of trust.Hypothesis2a.Trust will be positively associated with virtual team performance.Hypothesis2b.Trust will be positively associated with virtual team satisfaction.Hypothesis2c.Hierarchical teams have a higher level of trust than nonhierarchical teams.Conﬂict ManagementConﬂict is an inevitable part of working in teams.In general,conﬂict refers to differences or discrepancies in team members’ideas,opinions,or ways of doing things.Modern organizational theories no longer view conﬂict as a negative sign of organizational issues but tend to regard it as an intrinsic component in organizational dynamics(Medina,Munduate, Dorado,Martı´nez,&Cisneros,2004).A moderate amount of conﬂict is argued to be‘‘essential for attaining and maintaining an optimum level of organizational effectiveness’’(Rahim&Bonoma,1979,p.1325).Whether conﬂict can be used for effective performance relies on strategic conﬂict-handling styles.It has been suggested that how conﬂict is handled is more important to the success of teams than the conﬂict itself (Paul,Seetharaman,Samarah,&Mykytyn,2004).According to Rahim (1992)and Montoya-Weiss et al.(2001),there are various ways to manage conﬂict in a team:avoidance,accommodation,competition,collaboration, and compromise.An avoidance approach to conﬂict management is characterized by evasiveness and failure to directly address conﬂicting viewpoints.An accommodation conﬂict management style reﬂects obligations to others.A competition conﬂict management style is deﬁned as pursuit of one’s own interest without careful regard for others,while a collaboration management style attempts to identify and achieve outcomes for mutual beneﬁt.A compromise management style is characterized byﬁnding mutually accepted solutions through negotiating differences.Past small group research indicates that more cooperative conﬂict management styles are more likely to be associated with positive individual and team outcomes than less cooperative conﬂict management styles(Lin,2003;Paul et al.,2004).The same positive effects were also found in virtual teams.A study that examined a culturally diverse group supported by a groupware system concluded that the groups that lean toward a higher level of collaboration style of conﬂict management perceived higher quality in decision making.Integration of diverse views resulted in integrative decisions and thus improved group agreement (Paul et al.,2004).A competition management style is traditionally viewed as having a negative effect on team performance in that it can result in less social integration and team cohesion(Montoya-Weiss et al.,2001;Cohen &Bailey,1997).Montoya-Weiss et al.(2001)propose that conﬂict theory developed in face-to-face settings may not be fully applicable to asynchronous teams, owing to fundamental differences(communication protocols,reduced social presence,or media richness)in a virtual environment.For example, competition conﬂict management behaviors of a team member may not be conspicuous to other members of the team in an asynchronous virtual environment,and the negative effects may be mitigated in asynchronous virtual teams(Tan,Watson,Clapper,&McLean,1998).In fact,it is possible that competitive behaviors such as aggressive emotions or competitive dominance may not be interpreted as such,but rather be viewed as a means of achieving efﬁciency and effectiveness in a lean,asynchronous commu-nication environment(Montoya-Weiss et al.,2001;Lin,2003).Hypothesis3a.A collaboration conﬂict management style in virtual teams is positively associated with team performance.Hypothesis3b.A collaboration conﬂict management style in virtual teams is positively associated with virtual team satisfaction.Hypothesis3c.A collaboration conﬂict management style in virtual teams is positively associated with trust.Hypothesis3d.A competition conﬂict management style in virtual teams is not associated with virtual team performance.Hypothesis3e.A competition conﬂict management style in virtual teams is not associated with virtual team satisfaction. Research MethodologyResearch SettingThe present study was conducted in an online MBA program at a large midwestern university.The participants were enrolled in a capstone management course.Subjects were separated into project groups of four to six people to work on an online simulation project.Each team was asked to adopt the view of a senior manager responsible for running a business venture,assuming responsibility for a$100million company in the electronic sensor manufacturing industry.The simulations required management teams to evaluate situations and make decisions to stimulate their company’s growth.Teams set a strategy and applied strategic concepts and techniques in forming and implementing a business plan, and they were asked to integrate theﬁrm’s production,marketing,human resources,research and development,ﬁnancial,and pricing plans.The project lasted four weeks.InstrumentsThe22-item questionnaire contained three dimensions:trust,conﬂict management resolution,and teamwork satisfaction.Trust measured subjects’perceptions of trust between themselves and their teammates.Trust scales(10items)were adapted from Jarvenpaa and Leidner(1999)and Mayer,Davis,and Schoorman(1995).Sample items included‘‘I really wish I had a good way to oversee the work of other team members on the project’’and‘‘Overall,the people in my group are very trustworthy.’’Cronbach’s alpha for the trust dimension was.851.Conﬂict management resolution measured scores on two types of strategy used by a subject when working in a team:competition conﬂict management(ﬁve items)and collaboration conﬂict management(three items).Scales of conﬂict management solutions were adapted from previous research(Montoya-Weiss et al.,2001;Paul et al.,2004).Theﬁve items of the collaboration approach to conﬂict management measured the degree of team members’attempts to identify and achieve outcomes that integrated the interests of all parties involved.A sample item for the collaboration conﬂict management approach scale is‘‘Team members seek a resolution that will be good for all of us.’’Subjects were asked to rate on a5-point scale(15strongly agree,55strongly disagree)the degree to which team members agreed with theﬁve statements.For the competition approach to conﬂict management,there are three items measuring the degree to which the conﬂict was a win-lose situation and how each team member might pursue his or her own interest withoutregard for others(such as‘‘Team members treat conﬂict as a win-lose contest’’).The coefﬁcient alphas for the collaboration and competition scales were.826and.806,respectively.Both variables were used as continuous variables in this article.Aggregating individual scores of conﬂict management styles to the team level is logically justiﬁed because the question items were designed to measure the characteristics of the work team(Alper,Tjosvold,&Law, 2000).In addition,the James,Demaree,and Wolf TWG(J)procedure (1984)was used to estimate the interrater reliability of members within each team for the variables of competition and collaboration management conﬂict styles.The median TWG(J)for the two variables across the44 teams were.96,and.90respectively.Both are above.70,which is considered the indicator of sufﬁcient agreement within a group.These test results indicated that the ratings of group members are reasonably homogeneous and can be aggregated to the group level.Teamwork satisfaction included four items that measured subjects’degree of satisfaction with the teamwork process(‘‘Looking back on the whole course,I am satisﬁed with our teamwork project’’),team output(‘‘I think I learned many meaningful lessons throughout team projects’’), overall value(‘‘Overall,I believe that the whole teamwork process of our team is valuable to driving us toward team goals’’),and team decision-making quality(‘‘Overall,I believe that our team came up with the best solution as we expected’’).Team performance was measured by theﬁnal proﬁt score from team simulations.This score presented an objective measure of team performance,reﬂecting the ability of the team to use knowledge and skills learned from the curriculum to make judicious decisions for their simulated industry.Two kinds of team structure were used in the study:hierarchical and nonhierarchical.Teams that used hierarchical structure divided the individual work on the basis of the functionality of the company. Each member was responsible for one specialized area of the company, such as research and development,marketing,product development,ﬁnance,and so forth.Under this structure,each team member had a specialized role and needed to coordinate closely with other divisions to make a decision associated with a product.In a nonhier-archical structure,each team member was responsible for one product.Each member had to assume responsibility for all areas associated with that product.Under this structure,team members could make relatively independent decisions without consulting others but had to coordinate with others on the strategic goals of the company.Teams were randomly assigned to the two types of structure.Each team was asked to follow the instruction protocol of the structure assigned.The members of hierarchical teams were required to take specialized functional roles while those of nonhierarchical teams were asked to take a broader range of similar roles that covered several areas of a product.A dummy variable was used to code the structure;1referred tohierarchical structure,and0was used to refer to nonhierarchical structure.Data CollectionData were collected from all208members of44teams.Six teams’datawere later dropped from the study because the team did not followinstructions closely in structuring their teams.Seventeen teams usedhierarchical structure,while21used nonhierarchical structure.The22-item questionnaire that measured trust,conﬂict management resolution,and teamwork satisfaction was administrated during the midterm of thecourse.The return rate of the questionnaires was about95%.FindingsTable1shows correlations of all the variables measured ormanipulated in this experiment.As indicated in the table,team structurewas negatively correlated with team performance(r5À.323,p o.05).The nonhierarchical structure was associated with higher team performance.The trust level of the group was positively correlated with the collaboration conﬂict management style(r5.754,p o.01)and negativelyassociated with the competition conﬂict management style(r5À.561,p o.01).In addition,the level of trust had a positive relationship withteam satisfaction(r5.561,p o.01).The competition management stylewas negatively correlated with the collaboration management style(r5À.581,p o.01).In ourﬁrst hypothesis(H1),we proposed that a nonhierarchicalstructure would outperform a hierarchical structure in a virtual workingteam;the data supported this hypothesis.Table2contains the ANOVAresults that measured whether groups differed signiﬁcantly in their performance and other variables measured.The results revealed that the1M123451.Structure.5512.Trust 4.11.01713.Collaboration conﬂict4.28.129.754(ÃÃ)1management1.72.081À.561(ÃÃ)À.581(ÃÃ)1petition conﬂictmanagement5.Team performance$9,339À.323(Ã).216.195.00116.Team satisfaction 4.15À.057.561(ÃÃ).664(ÃÃ)À.310(Ã).493(ÃÃ)Ãp o0.05.ÃÃp o0.01.nonhierarchically structured groups had signiﬁcantly better performance than hierarchical groups (F 53.88,p o 0.05),thus supporting H1.Hierarchical regression analyses (Table 2)were conducted to examine the effect of structure,trust,and conﬂict management variables on team performance,as well as satisfaction with teamwork.The results demonstrated a statistically signiﬁcant effect of structure on team performance.The team structure variable accounted for an appreciable amount of total variance (R 25.105).However,structure did not have a signiﬁcant effect on overall team satisfaction.Our second hypothesis (H2a and H2b)focused on the relationship between trust and team effectiveness:performance and satisfaction.Table 3shows that there is no direct effect of trust on team performance.Although this result did not support H2a,it did show a statistically signiﬁcant effect of trust on team satisfaction (R 25.394),and trust accounted for a considerable amount of variance,thus supporting hypothesis H2b.From the correlation analysis (Table 1),a higher level of trust was associated with a collaboration conﬂict management style.This suggested that teams with a high level of trust and whose members placed high conﬁdence in their teammates’abilities and behaviors tended to lean toward a more collaborative approach to solving conﬂicts.Table 2suggests that the two groups did not differ signiﬁcantly in terms of trust level,conﬂict management styles,or team satisfaction.Therefore,H2c was not supported.Table 3indicated a signiﬁcant effect of the collaboration conﬂict management style on team satisfaction (R 25.227)but no signiﬁcant effect on team performance.Thus H3a was refuted,and H3b was supported.According to Table 1correlation results,the trust level of the group was positively correlated with its collaboration conﬂict manage-ment style (r 5.754,p o .01).This result supported by H3c.Table 3showed that the competition conﬂict management style had no signiﬁcant effect on either team performance or satisfaction,supporting H3d and H3e.Although a correlation analysis showed negative2Mean (SD )Dependent VariableHierarchical Group Nonhierarchical Group F ,df Signiﬁcance Level Trust4.134 4.142.011,1.917Collaboration conﬂict management4.268 4.351.661,1.440Competition conﬂict management1.646 1.69.237,1.629Team performance$10,971$7,498 4.204,1.048ÃTeam satisfaction4.15 4.12.115,1.736Ãp o 0.05.relationships between a competition conﬂict management style and team satisfaction,the regression analysis did not show a signiﬁcant effect. Discussion and ConclusionThere are several importantﬁndings of this study worthy of further discussion and investigation.StructureThe results of this study indicated a signiﬁcant effect of team structure on team performance.In the present study,the teams with a non-hierarchical structure outperformed those with a hierarchical structure,a ﬁnding consistent with Urban et al.(1995).Interpretation of thisﬁnding should not exclude considerations of the task environment.The teams worked in an asynchronous online environment,which is commonly believed to bring a higher degree of vagueness,complexity,and lack of structure(Workman,Kahnweiler,&Bommer,2001)into virtual team-work process than face-to-face settings.These attributes may increase the degree of difﬁculty of communication in virtual teamwork.For hierarchically structured teams,each person held a specialized role,and extensive communication was needed for team members to make decisions and maintain routine operations of the team in order to achieve the goal of accomplishing a complex task such as running a simulated industry.Effective communication may be disrupted by possible misunderstandings and disputes stemming from a lack of visual cues in asynchronous virtual teaming environments.Thus it was possible that team members had to spend extra resources on maintenance of the team’s daily communications that may not add to team performance.However, in nonhierarchical teams,each person had a higher degree of autonomy 3Team Performance Team SatisfactionR2b R2b Structure.105ÃÀ.042Ã.003À.149 Trust.046.030.394ÃÃ.105 Collaboration conﬂict management.049.431.227ÃÃ.709ÃÃCompetition conﬂict management.057.282.000À.009 R2Total.257.624F 2.837Ã13.742**df4,334,33Ãp o0.05.ÃÃp o0.01.。

丙烯酸乳液的交联反应

Progress in Polymer Science 36 (2011) 191–217Contents lists available at ScienceDirectProgress in PolymerSciencej o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /p p o l y s ciChemical reactions of polymer crosslinking and post-crosslinking at room and medium temperatureGuillaume Tillet ∗,Bernard Boutevin,Bruno Ameduri ∗Ingénierie &Architectures Macromoléculaires,Institut Charles Gerhardt,UMR 5253,ENSCM 34296Montpellier Cedex,Francea r t i c l e i n f o Article history:Received 1February 2010Received in revised form 29July 2010Accepted 19August 2010Available online 21 September 2010Keywords:CrosslinkingPost-crosslinking PolymerFunctional groupsa b s t r a c tThis review focuses on various strategies that enable the crosslinking and post-crosslinking of polymers,excluding crosslinking obtained by radiation (e.g.,X-ray,UV,etc.)and that at high temperature.The review is divided into two main parts:systems enabling crosslinking at room temperature and those for which crosslinking occurs at intermediate temperatures (<150◦C).In the ﬁrst part,various key functional groups can be used,such as (i)carboxylic acid involving reactions with compounds that bear carbodiimide or aziridine functions;(ii)acetoacetyl groups (with isocyanate,activated alkenes,aldehyde,amine functions);(iii)reactions involving activated amines with carbonyl functions (aldehydes,ketones,etc.);(iv)species bearing acetals as pH-sensitive crosslinking agents since they are stable in basic medium but they can self react under acidic conditions;(v)acrylamide functions which are able to self-crosslink;(vi)crosslinking agents able to react with water (such as species that bear a poly(alkoxy)silane for sol–gel process)and derivatives containing isocyanate functions and (vii)systems that require oxygen,for example polymers bear-ing double bonds,boranes for generating hydroperoxides and acetylenic functions which undergo acetylenic coupling.The second series of systems,used at higher temperatures (yet below 150◦C)involving the following key functions:(i)carboxylic acid that react with oxazoline,or epoxide function where speciﬁc catalysts are necessary;(ii)alcohols react-ing with protected urethanes,azlactones and methylol amide (for coating applications);(iii)azetidines (obtained from a cyclic amine onto an activated double bond)which self-crosslink;(iv)reversible Diels–Alder reaction (such as furane/bismaleimide reaction),and (v)Huisgen reactions between azido and triple bond.Various examples are presented,along with a discussion of their properties and applica-tions.© 2010 Elsevier Ltd. All rights reserved.Contents 1.Introduction (192)2.Crosslinking and post-crosslinking.................................................................................................1932.1.Crosslinking at room temperature..........................................................................................1932.1.1.Carboxylic acid ....................................................................................................193∗Corresponding authors at:Ecole Nationale Supérieure de Chimie de Montpellier,Ingénierie &Architectures Macromoléculaires,8Rue de l’Ecole Normale,34296Montpellier Cedex 5,France.E-mail addresses:guillaume.tillet@enscm.fr (G.Tillet),bruno.ameduri@enscm.fr (B.Ameduri).0079-6700/$–see front matter © 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.progpolymsci.2010.08.003192G.Tillet et al./Progress in Polymer Science36 (2011) 191–2172.1.2.Aceto acetyl function[24–31] (194)2.1.3.Amines[32–40] (196)2.1.4.Acetal function[41–45] (198)2.1.5.Acrylamide derivative[46–50] (199)2.1.6.Other crosslinking moieties (199)2.1.7.Conclusion (205)2.2.Crosslinking at intermediate temperatures (205)2.2.1.Carboxylic acid function (206)2.2.2.Alcohol function[138–139] (207)2.2.3.Azetidine functions[166–169] (210)2.2.4.Diels–Alder reactions[170–176] (210)2.2.5.1,3-Dipolar cycloaddition and“click chemistry”reaction[177–187] (213)2.2.6.Conclusion (213)3.Conclusion (213)References (213)1.IntroductionImprovement of the thermal,mechanical,physico-chemical properties of polymers is a crucial challenge in both synthesis(by the insertion of a key function)and the quest for new search applications.Hence,researchers are in a scientiﬁc,economical and environmental context in which both modiﬁcation and improvement of known polymers are preferred rather than the synthesis of poly-mers from new monomers.The properties of a polymeric material depend on its chemical nature,but,for a given polymer type,they also depend on their molecular weight and the functions borne by the polymer chain.In addition to the overall properties,the mechanical properties which are regarded as the most important features of a material are of particular interest.In this context,polymeric mate-rials can be conveniently divided into two main categories, dependent on their molecular weight:-Those with a molecular weight higher than about 105g mol−1;this value is not a strict limit since it depends on materials and on the intermolecular interactions which occur in these materials;-Those which have low molecular weights,lower than 104g mol−1,often in the range of2–3.103g mol−1.According to the category,it is may be essential to carry out either crosslinking or post-crosslinking.Indeed,poly-mer materials in the lower molecular-weight range often require a crosslinking step to obtain satisfactory mechani-cal properties.It is useful to recall the deﬁnitions and differences between crosslinking and post-crosslinking,the main dif-ference arising from the way the material is processed. To obtain aﬁnal material in one step,either a very high molecular-weight material or a directly crosslinkable oligomer has to be used to fulﬁll the targeted prop-erties.The preparation of an easily processed material requires the synthesis of an easily stored material possess-ing intermediate properties.If the desired performance is not reached,a further step to a post-crosslinking may be required,even though that theﬁrst step may have yielded a pre-crosslinked material.These statements concern all materials but they can be especially relevant for coatings since they must be deposited while they have no(or at most a few)crosslinks,to be crosslinked after they have been applied.Since theﬁelds of applications are various and numer-ous,crosslinking or post-crosslinking reactions have been intensively studied for a long time,and continue to this date.Studies to tune polymerization and crosslinking have as objectives methods to control when and at which rate both these steps take place,and how they can occur either separately or simultaneously.Different types of crosslinkings are possible:(i)covalent crosslinking(which is regarded as the moststable),(ii)ionic bonds,and(iii)physical crosslinking(via Van der Waals,hydrogen bonds or other interactions).One of the most important parameters is,of course, the functionality of the reagents(oligomers and diluents) since crosslinked polymers are usually produced when this functionality is higher than two(even slightly so).Reactive groups are often introduced into the polymeric chains in the case of post-crosslinking.The reactivity and reaction rate of these groups can be controlled by different means: (i)temperature,(ii)radiation,(iii)external reactants(such as moisture,O2,H2O,etc.), (iv)processing.The objective of this review is to provide basic informa-tion to understand the phenomena of crosslinking,without claiming to be exhaustive in that very wideﬁeld.The focus is on some basic chemical reactions involving sim-ple reactants,such as water or oxygen,but also some more complex reactants bearing key or speciﬁc functions.Vari-ous crosslinking and post-crosslinking processes have been excluded,such as those involving radiation,e.g.,ultravio-let beams,which are commonly used to harden coatings (paints,varnishes,etc.),or␥-rays,electron beams,ozone, X-rays,etc.;many reviews have already been published on these methods[1–4].G.Tillet et al./Progress in Polymer Science36 (2011) 191–217193NomenclatureAAEM acetoacetoxyethyl methacrylateAA acrylic acidATRP atom transfer radical polymerizationBH blocking agentCHA N-cyclohexylazetidineDBN1,5-diazabicyclo(4.3.0)non-5-eneDBU1,8-diazabicyclo(5.4.0)undec-7-eneEPA Environmental Protection AgencyGMA glycidyl methacrylateHEA2-hydroxyethyl acrylateHighlink®AG acrylamidoglycolic acid monohydrate Highlink®DMH N-(2,2 -hydroxy-1-dimethoxyethyl)acrylamideHMM hexamethylol melamineHPBd hydrogenated polybutadieneIBMA isobutoxymethylacrylamideIPDI isophorone diisocyanateMAA methacrylic acidMAAMA N-(2,2-dimethoxyethyl)methacrylamideMAGME N-(methoxy methyl acetate)acrylamideMMA methyl methacrylateNMA N-methylolacrylamidePAEK polyaryletherketonePCL polycaprolactonePDMS polydimethyl siloxanePEO polyethylene oxidePEs polyesterPFCB perﬂuorocyclobutanePHEMA polyhydroxyethyl methacrylatePMDETA pentamethyldiethylene triaminePMMA polymethyl methacrylatePMVE perﬂuoromethyl vinyletherPS polystyrenePTFE polytetraﬂuoroethylenePTMO polytetramethylene oxidePVAc polyvinyl acetateR F perﬂuoroalkylREACH registration,evaluation,authorisation andrestriction of chemicalsTEOS tetraethoxysilaneTGIC triglycidyl isocyanurateTMEDA tetramethylethylenediamineTMG tetramethylguanidineTMI®m-isopropenyl-␣,␣-dimethylbenzylisocyanateVDF vinylideneﬂuoride2.Crosslinking and post-crosslinkingFor simplicity,the discussion of crosslinking and post-crosslinking reactions in the following is categorized by types of chemical functions,and discussed successively in two cases,according to the temperature range of the dif-ferent reactions:(i)room temperature,(ii)intermediate temperature below150◦C.2.1.Crosslinking at room temperatureCrosslinking reactions at room temperature are inter-esting for various reasons,such as network development in a heating-sensitive system or to gain energy savings. Several of these are discussed in the following.2.1.1.Carboxylic acidTwo main intermediates are considered as crosslinking agents in this type:carbodiimides(the most common used) and aziridines.2.1.1.1.Carbodiimides[5–18].The use of carbodiimide as a crosslinker agent has been known since the late1960’s[5], though deeper investigations started in1980’s[6,7].The general reaction involves the condensation of a carbodi-imide reactant with a carboxylic acid,leading to an acetyl urea,as shown in Fig.1.Such a condensation does not require any catalyst and this represents an advantage.However,in the presence of moisture,this reaction also competes with the classic reac-tivity of carbodiimides,which are able to trap water and consequently generate anhydride acid and urea,as shown in Fig.1.Nevertheless,by adapting appropriate catalysis and reaction conditions,the reaction is directed towards the synthesis of N-acyl urea.In this way,Taylor and Basset [8]have shown that the N-acyl urea/anhydride acid ratio increased on increasing the solvent polarity,the temper-ature,or even pouring a base into the reaction mixture. Moreover,their studies also reported that above150◦C,N-acyl urea structure is not stable and this limits their uses to crosslinkers efﬁcient at the lower temperature correspond-ing to most coatings.According to Campbell and Smeltz’s investigation[9], carbodiimides can be prepared from isocyanates in the presence of a catalyst such as phospholene oxide at 140–150◦C(Fig.2).Other methods have also been described and are reported in the literature[5,10].Studies on crosslinking have reported[11]that multi-functional carbodiimides are good crosslinking agents at low temperature in theﬁeld of emulsions.Hence,emul-sion mixtures containing acrylic acid and multifunctional carbodiimides lead to paintﬁlms endowed with excellent properties(tensile properties and solvent resistance).Sev-eral patents[12–14]claim that carbodiimide agents can also be utilized in the fabrication ofﬁlms.This crosslinking method is also interesting because it can be used for in vivo conditions.Indeed,collagen matrices have been crosslinked to prevent their rapid degradation and to improve their mechanical properties.Several publi-cations[15–18]describe the crosslinking of collagen by the reaction of a carbodiimide with carboxyl groups of aspartic and glutamic acid residues of the matrix.2.1.1.2.Aziridines[19–23].Theﬁrst paper that reports aziridine as crosslinking agent was published in the early 1970’s[19].Roesler and Danielmeier[20]published a review on the reaction of aziridine with carboxylic acids,194G.Tillet et al./Progress in Polymer Science36 (2011) 191–217Fig.1.Formation of acetyl urea compounds by condensation of a carbodiimide with a carboxylic acid and the side reaction in presence ofwater.Fig.2.Synthesis of a carbodiimide from isocyanate.which spontaneously lead to an amino ester at room tem-perature,as shown in Fig.3.Polyaziridines used as crosslinkers can be obtained by the Michael reaction (Fig.4),such as the addition of amine onto activated unsaturated groups (e.g.,acrylics)[21].Fig.5shows a triaziridine that is soluble in several polar solvents including water,as described by Pollano and Resins [21].This triazine has been used to improve the mechanical properties (lower elongation,higher strength-ening)and the chemical resistance of various coatings,including wood varnishes [20]for interior applications.Fig.6illustrates the crosslinking of carboxylic acid ter-minated polymer with a triaziridine compounds,reported by Liu et al.[22].This reaction does not require any catalyst,and is car-ried out at room temperature,but its reaction rate is slower than that of the reaction involving carbodiimides.However,the reaction rate may be increased by the use of Cr(III)car-boxylate as a catalyst [23].Indeed,while it took one day in the absence of any catalyst,the reaction rate was reduced to 1min in presence of catalyst.Two drawbacks were observed:-As for their homologue carbodiimides,their poor water stability led to inactive amino alcohol.Nevertheless,thisFig.5.Structure of trimethylolpropane tris(2-methyl-1-aziridine propi-onate).limitation can be overcome by adding the polyaziridine crosslinker prior to the processing of the oligomer.-Aziridine compounds are irritant,toxic and mutagen.2.1.2.Aceto acetyl function [24–31]The aceto acetyl function (Fig.7)is a relatively new function,offering interesting potential for wide chem-ical activity.This reactivity is partly due to keto-enol tautomerism (75%ketone/25%enol)presented in Fig.7.Indeed,the insertion of the aceto acetyl functionality in a polymer reduces both the viscosity and the glass transition temperature [24].The other part of the reactivity,show in Fig.8,arises from the metal chelation (with copper,silver,nickel,etc.)by bisketones [25,26].This reaction is quite interesting since it is able to enhance adhesion to metal.Aceto acetyl derivatives can react with various groups,such (i)as isocyanates,(ii)activated alkenes,(iii)aldehydes,and (iv)amines,listed in the following:(i)IsocyanatesThe active methylene group of acetoacetyl function can react with an isocyanate at room temperature like in the reaction of isocyanates with hydroxyls,as shown in Fig.9.Del Rector et al.[24]have noted that this reac-tion occurred but with a lower reaction rate than that involving alcohols.In this case,a lower reaction rateisFig.3.Reaction between an aziridine and a carboxylic acid leading to an aminoester.Fig.4.Synthesis of polyaziridine by “Michael addition”between an amine and an acrylic alkene.G.Tillet et al./Progress in Polymer Science 36 (2011) 191–217195Fig.6.Crosslinking example of a polymer bearing carboxylic acid functions with atriaziridine.Fig.7.Keto–enol tautomerism:chemical equilibrium between keto and enolforms.Fig.8.Chelating of bisketone by copper acetate.a beneﬁt since it allows better control of the crosslink-ing,and also favors convenient conditions to process the ﬁnal product.(ii)Activated alkenes (“Michael addition”)A reaction between the methylene group and an electron deﬁcient alkene can occur under strong basic conditions.This reaction,reported by Clemens and Del Rector [27],is described in Fig.10.These authors used strong bases (p K a >12),such as 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU),1,5-diazabicyclo(4.3.0)non-5-ene (DBN)and tetramethyl-guanidine (TMG),listed in Table 1.Indeed,the p K aofFig.9.Reaction between an isocyanate and an aceto acetyl compounds.196G.Tillet et al./Progress in Polymer Science36 (2011) 191–217Fig.10.“Michael addition”between an aceto acetyl compounds and an activatedalkene.Fig.11.Formation of a linkage between two acetylacetonate groups by reaction with formaldehyde.Table 1Various bases involved in the reaction between acetoacetyl derivatives and acrylates (according to Clemens and Del rector [27]).StructureAcronymp K aNHC NN CH 3CH 3H 3C CH 3TMG13.6NN DBN 12.7NN DBU 12.5such an acetylacetonate derivative linked to the acidic protons of methylene between both ketone functions is estimated to 12which explains the need to use such strong bases.(iii)Aldehydes and more especially formaldehyde.Similarly,acetyl acetonate has also been used efﬁ-ciently with formaldehyde to lead to a short link between two aceto acetyl groups,as shown in Fig.11:(iv)AminesBy contrast,Fig.12illustrates the reaction of amines with the hydroxyl group of the aceto acetyl enolic form.In this way,Mori et al.[28]synthesized “honeymoon-type”adhesives for wood products by crosslinking of acetoacetylated poly(vinyl alcohol)with diamines (these are adhesives consisting of two components,opposite com-ponents being applied to opposite adherends,the two brought together to form a joint).They propose the mech-anism in Fig.13for this crosslinking.Other reactions may occur when acetyl acetonates are involved (in particular for reactions using melamines),butthese reactions do not occur at room temperature,and in this case various examples are reported in Section 2.2.It may be noted that the acetoacetoxyethyl methacrylate (AAEM)monomer,the structure of which is given in Fig.14,has been marketed and is used in many ﬁelds,such as with acrylic latexes.The aceto acetamide function may also be used [29,30]because it should be less sensitive to hydrolysis which is an important feature as well during the polymerization reaction as for its storage [31].2.1.3.Amines [32–40]As amines exhibit high nucleophily,several reactions may occur at room temperature.In addition to the acetyl acetonates reported in Fig.15,aldehydes and ketones [32]are also featured reactants,and imine groups are also pro-duced in this way.This reaction is acido-catalyzed,and it has been found that ﬁve days are required to reach satisfactory properties of polyurethanes bearing two carbonyl groups.Among amines,some hydrazine derivatives are able to react with ketones,as shown in Fig.16.The introduction of ketone groups in the resin has been achieved thanks to the use of the N-(1,1-dimethyl-3-oxobutyl)acrylamide as shown in Fig.17.This reaction,discovered 40years ago,has mainly been used in the ﬁeld of crosslinking chemistry by Mestach and co-workers [33,34]in waterborne acrylic dispersions appli-cations.The second reaction involves amines reacting with epoxides.Several reactions have been published on this is well-known reaction [35–37].Fig.18illustrates the crosslinking between an amine terminated polysiloxane and polysiloxane bearing an epoxide.The epoxy/amine system has been developed for latex by Geurts [38].In that case,the materials are separated into two different phases,called “the two in one system”.The main difﬁculty consists in incorporating aminegroups inFig.12.Reactions between enolic form of aceto acetyl with an amine.G.Tillet et al./Progress in Polymer Science 36 (2011) 191–217197Fig.13.Crosslinking of poly(vinyl alcohol)bearing aceto acetylated groups with a diamine.acrylic latexes.It is easy to insert epoxide groups thanks to the glycidyl methacrylate monomer (GMA).However,the use of GMA for latex synthesis raises a limitation (espe-cially for pre-crosslinking)due to the instability of that monomer in aqueous medium.Therefore,O’Brien et al.[39]used the episulﬁde,equivalent of an epoxide,synthesized as shown in Fig.19.The episulﬁde is more stable towards water,hence limiting pre-crosslinking.The crosslinking of episulﬁdes in the presence of piper-azine is slower than that occurring in the presence of the oxygen containing derivative,and the best conditions of crosslinking are for 30min at 65◦C.However,storage sta-bility is not much improved.This amine has been used for the hardening of both episulﬁde and epoxide because it is water soluble,and thus it can migrate into the particles.Geurts [38]has reported an extensive and remark-able investigation of the synthesis of methacrylateaminoFig.15.Preparation of imines by reaction between an amine and a car-boxylic group.monomers.The same group also prepared the correspond-ing salts of this amine.The best results were obtained when n =5;for lower n a chemical rearrangement occurs (leading to amine),while for higher n,the monomer exhibits so high surfactant properties to enable suitable processing.This system led to interesting results but Geurts noted the presence of an unavoidable Michael reaction in the course of latex synthesis that contains this amine,as shown in Fig.20.Fig.14.Acetoacetoxyethyl methacrylate (AAEM)monomer bearing acetylacetonate group.198G.Tillet et al./Progress in Polymer Science36 (2011) 191–217Fig.16.Reaction of a hydrazine derivative with a polymer bearing ketones groups.The preceding reports the use of primary amines,but extensive researches also deal with the efﬁciency of ter-tiary amines and their reactivity with epoxides.Van de Ven et al.[40]have compared the reactivity of model epoxide molecules in the presence of water,tertiary amine,acid and alcohol,noting that,at room temperature,both the quater-nization reaction and the direct polymerization of epoxide mainly occurred,in contrast to the acid/epoxide reaction, which requiresheat.Fig.17.Structure of N-(1,1-dimethyl-3-oxobutyl)acrylamide.2.1.4.Acetal function[41–45]The acetal function represents the protected form of an aldehyde group and this protects the aldehyde function from amines.However,for lower pH values,the aldehyde is regenerated and the reaction with amine can lead to the corresponding imines.In this case,the driving force is the pH variation.Fig.21displays both reactions.Pichot’s group[41]was one of theﬁrst team that used this concept involving monomers with acetal groups to trap amino-acid,and this strategy was applied in theﬁeld of Life Science.Another French team[42]used this concept in the ﬁeld of acrylic coatings.Further progress was developed by Charleux’s group[42]and also claimed in a patent deposited by Elf Atochem[43].The development of latex for paints,able to undergo further reaction at room temperature during theﬁlm form-ing step,but remaining chemically stable during the latex synthesis and its storage,is obviously very delicate.That balance requires the use of protected chemical groups in the latex,which are deprotected during theﬁlm forming, and hence become reactive.Such a concept also occurs for acetal functions which are stable and inert in basic media[44].However these functions undergo hydrolysis in acid medium to lead to self-reactive aldehyde functions at room temperature.Fig.22displays this concept from N-(2,2-dimethoxyethyl)methacrylamide(MAAMA). Fig.18.Reaction between an epoxy and an amine often used to crosslink epoxyresins.Fig.19.Synthesis of thiirane from anepoxy.Fig.20.“Michael reaction”between an amine and a methacrylate amino monomer.G.Tillet et al./Progress in Polymer Science 36 (2011) 191–217199Fig.21.Protection reaction of an aldehyde by alcohol,reaction between an aldehyde and anamine.Fig.22.Structure of N-(2,2-dimethoxyethyl)methacrylamide (MAAMA).Such a reaction is possible,and studies with model com-pounds have shown that the dimerization of the amido group with aldehyde leads to the cyclic structure shown in Fig.23.This explains the crosslinking obtained thanks to this kind of latex,but this latter must be prepared under basic medium and it has to be acidiﬁed during the ﬁlm forming to carry out the hydrolysis of acetal into aldehyde.In fact,the acetal function is interesting because it acts as a pH-responsive crosslinking agent as Li et al.[45]have shown.2.1.5.Acrylamide derivative [46–50]Acrylamide and aldehyde derivatives have been well-known for decades because they are able to self-crosslink at high temperatures.The chemical reaction arises from the self-condensation of the alcohol function [46]on the acrylamide monomer,as found in urea/formaldehyde or melamine/formaldehyde resins.Likewise,monomers bearing these groups have been synthesized for incorpo-ration in latexes,such as N-methylolacrylamide (NMA),isobutoxymethylacrylamide (IBMA),acrylamidoglycolic acid monohydrate (Highlink ®AG)or N-(2,2 -hydroxy-1-dimethoxyethyl)acrylamide (Highlink ®DMH),illustrated in Fig.24.In addition to the above monomers,many others are commercially available or synthesized.The use of a catalyst enables one to decrease the self-reaction temperature to room temperature,but post-curing is often necessary.These catalysts are either AlCl 3or strong organic acids such as paratoluene sulfonic acid or orthophosphonic acid [47].However,several side reactions are also involved,leading to the formation of formalde-hyde by-products,as shown in Fig.25,which is undesirable because of itstoxicity.Fig.23.Cyclic structure after the dimerization of an amido group with an aldehyde.Monomers such as N-(methoxy methyl acetate)acrylamide (MAGME)have been copolymerized with monomers containing hydroxyl groups,such as 2-hydroxyethyl acrylate (HEA),to obtain self-crosslinkable latexes [48].Indeed,Fig.26shows the presence of three potential crosslinking sites borne by the monomer,includ-ing NH,CH and OMe.Such a chemistry is promising and undergoes a fast development [49,50].2.1.6.Other crosslinking moietiesThis section describes a peculiar process that allows a post-crosslinking process at room temperature.However,it requires the participation of a chemical agent (and from neither thermal nor photochemical effects).Typically,the use of oxygen and water are reported below.2.1.6.1.Water [51–100].2.1.6.1.1.Sol–gel reactions.The chemical reactions of the sol–gel process were reported almost four decades ago [51],but this technique has gained increasing interest.The sol–gel process makes it possible to produce at low tem-perature networks with high purity and high homogeneity.Although many studies have been carried out on sol–gel processes involving organic compounds,a few investiga-tions involve polymers to lead to hybrid materials for which organic and inorganic phases coexist.Furthermore,some multicomponent systems which cannot be made by con-ventional methods due to crystallization can be produced in a sol–gel process [52].Although shrinkage and fracture during the curing process limit the widespread applica-tions of these techniques,much success has been achieved in producing monolithic solids by controlling the diffu-sion rate of volatile components in the system [53].Two methods exist to obtain organic/inorganic materials.The ﬁrst method is based on a mixture of a metal alkoxide [such as Si(OR)4,Ti(OR)4,Zr(OR)4,Al(OR)3]and a polymer.For example,Blanchard et al.[54]reported an extensive study on the hydrolysis and condensation reaction of dif-ferent metal alkoxides M(OR)n (where M represents Si,Ti,Zr atoms,etc.and OR is an alkoxy group).Then,the metal alkoxide undergoes a hydrolysis reaction followed by a polycondensation to form a three-dimensional network containing the polymer.The hydrolysis and polycondensa-tion reactions are described in Fig.27.The resulting materials,initially called “ceramers”by Wilkes et al.[55],should reﬂect some of the proper-ties of the sol–gel glass and the incorporated polymeric reactant.However,the completion of the hydrolysis reac-tion depends upon the amounts of water and acid added to the system.Because of the nature of that process,。

苯丙乳液应用性能的影响因素

第28卷第1期2014年1月材料研究学报CHINESE JOURNAL OF MATERIALS RESEARCH V ol.28No.1January 2014苯丙乳液应用性能的影响因素许利1贾丽洲1易红玲1林珩1徐建2,3傅乐峰2,3郑柏存11.华东理工大学体育新材料研发中心上海2002372.上海三瑞高分子有限公司上海2002323.上海建筑外加剂工程技术研究中心上海200232摘要以苯乙烯(St)、丙烯酸异辛酯(2-EHA)为主要单体采用预乳化半连续种子乳液聚合工艺合成了苯丙乳液。

用激光粒度仪测试了乳胶粒粒径大小及粒度分布,用差示扫描量热法(DSC)测试了共聚物的玻璃化转变温度,用流变仪测量了乳液的流变性能,研究了单体配比、交联剂用量以及乳化剂用量对乳胶粒粒径、乳液的稳定性、流变性、粘结性能的影响。

结果表明:合成的苯丙乳液为假塑型流体;乳液的粘度随着2-EHA/St 配比、交联剂用量和乳化剂用量的增加而升高;乳液的稳定性随着乳化剂用量的增大而提高,随着交联剂用量的增大而降低;乳液胶膜的粘结性随着交联剂用量以及2-EHA/St 配比的增大而增强;乳胶粒的粒径随着乳化剂用量的增加而变小,随着交联剂用量的增加而变大。

关键词有机高分子材料,苯丙乳液,聚合,流变学,粒径分布,玻璃化转变温度分类号TQ433,TB324文章编号1005-3093(2014)01-0075-06Factors Influencing Styrene-Acrylic EmulsionApplication PerformanceXU Li 1JIA Lizhou 1YI Hongling 1LIN Heng 1XU JIAN 2,3FU Lefeng 2,3ZHENG Baicun 1*1.Advanced Sports Material R &D Center,East China University of Science and Technology,Shanghai 2002372.Shanghai Sunrise Chemical Corporation Limited,Shanghai 2002323.Shanghai Engineering Research Center of Center of Construction Admixtures,Shanghai 200232Manuscript received June 28,2013;in revised form September 24,2013.*To whom correspondence should be addressed,Tel:(021)64251146,E-mail:****************.cnABSTRACT The styrene-acrylic emulsion was synthesized by pre-emulsified semi-continuous seededemulsion polymerization,with styrene (St)and 2-ethylhexyl acrylate (2-EHA)as main monomers.The par-ticle size distributions were characterized by laser particle size analyzer,the glass transition temperatureswere measured by DSC,and the rheological behaviors were analyzed by rheometer.The effects of mono-mer-proportion,the amount of cross-linking agent and emulsifiers on particle sizes,emulsion stabilities,rheological behaviors and bonding properties were investigated.The results show that styrene-acrylicemulsion is a pseudoplastic fluid,and the viscosity enhanced with the increase of the ratio of 2-EHA/St,the amount of cross-linking agent or emulsifiers.The emulsions stabilize with the increment of emulsifi-ers,while destabilize with the increment of cross-linking agent.The shear bond strength enhances withthe increment of cross-linking agent or the ratio of 2-EHA/St.The particle size of emulsions decreaseswith the increment of emulsifiers,while increases with the increment of cross-linking agent.KEY WORDS organic polymer materials,styrene-acrylic emulsion,polymerization,rheology,particlesize distribution,glass transition temperature近年来人造草坪行业蓬勃发展,每年的增长率都在20%-25%。

Investigations of the effects of glyoxal cross-linking

Investigations of the effects of glyoxal cross-linking on the structure and properties of chitosan ﬁberQing Yang a,b ,Fengdong Dou b ,Borun Liang a,b ,Qing Shen a,b,*a State Key Laboratory for Modiﬁcation of Chemical Fibers and Polymer Materials,1882W.Yan An Rd.,Shanghai 200051,People’s Republic of China bDepartment of Polymer Material and Engineering,College of Material Science and Engineering,Donghua University,1882W.Yan An Rd.,Shanghai200051,People’s Republic of ChinaReceived 6November 2004;revised 22April 2005;accepted 30April 2005Available online 25July 2005AbstractThe effect of glyoxal cross-linking on the structure and properties of chitosan ﬁber has been studied using different techniques.Swelling results showed that the cross-linking process can be described by a formula such as:S Z 79.24K 5.05C C 0.24C 2(S ,swelling degree;C ,glyoxal concentration).WAXD indicated that the cross-linking affects on the chitosan ﬁbers at reducing of its crystallinity,e.g.from 34.7to 27.2%for this case prepared ﬁparing to uncross-linked chitosan ﬁber,DSC and polarizing microscopy further indicated that the change of the crystal structure for cross-linked chitosan ﬁber is exactly affecting to the thermal properties.Additionally,SEM photographs showed that the cross-linking seems to play a role to smooth the surface of ﬁber due to the surface of original chitosan ﬁber observed roughly.q 2005Elsevier Ltd.All rights reserved.Keywords:Chitosan ﬁber;Glyoxal;Cross-linking;Structure;Property1.IntroductionChitosan ﬁber was early developed by Austin and Brine (1981)and Peniston and Johnson (1977).With respect to the bio-properties of chitosan (Adusumilli &Bolton,1991;AlAngary,AlHelw,AlDardiri,&Mahrous,1998;Aly 1998;Elcin,Dixit,&Gitnick,1998;Kifune,Yamaguchi,&Tanae,1987;Mattiolibelmonte et al.,1995;Naseema,Padayatti,&Paulose,1995;Richardson,Kolbe,&Duncan,1999;Su et al.,1999),it was noted that chitosan ﬁber has been further fabricated to other medical products (Malette &Quigley,1985;Tsurutani,Kifune,&Nakamura,1993).However,it is generally known that this bio-ﬁber has visible shortages in its dimension unstably and mechanical proper-ties weakly as comparing to other natural polymeric ﬁbers.Hence,it was observed that several researchers have tried toapply different reagents to cross-link chitosan ﬁber to improve the tenacity (Knaul,Hudson,&Creber,1999;Lee,Park,&Choi,2004;Suye &Mizusawa,1999).Recently,we have also prepared a chitosan ﬁber and studied of the use of glyoxal as a reagent to cross-link obtained ﬁber obtained positive results (Yang,Dou,Liang,&Shen,2005).Of that case,though the cross-linking related mechanism has been principally known to be due to the occurrence of acetalization and Schiff base reaction (Yang et al.,2005),it was clearly known and proposed that further studies of the inﬂuence of cross-linking on the changes of the crystal structure for chitosan ﬁber is required in coming studies.This is because that the chitosan is considerable to be easily crystallized with respect to its regular and rigid molecular chain,and strong polarity (Ogawa,Yui,&Okuyama,2004).Following previous study (Yang et al.,2005),the aim of this paper is thus proposed to investigate the effects of cross-linking on the crystal structure of chitosan ﬁber,the effect of swelling degree on the tenacity of chitosan ﬁber and the effect of cross-linking on the surface of chitosan ﬁber.In addition to previously used FTIR (Yang et al.,2005),experimentally,several other methodologies were employed in this case,e.g.wide-angle X-ray diffraction,WAXD,differential scanning calorimeter,DSC,polarizing microscopy and scanning electron microscope,SEM.Carbohydrate Polymers 61(2005)393–398/locate/carbpol0144-8617/$-see front matter q 2005Elsevier Ltd.All rights reserved.doi:10.1016/j.carbpol.2005.04.017*Corresponding author.Address:Department of Polymer Material and Engineering,College of Material Science and Engineering,Donghua University,1882W.Yan An Rd.,Shanghai 200051,People’s Republic of China.Tel.:C 862162373311;fax:C 862162193062.E-mail addresses:sqing@ (Q.Shen),sqing@ (Q.Shen).2.Experimental2.1.ChitosanﬁberThe samples of both cross-linked and uncross-linked chitosanﬁbers were prepared as the same as previously described by means of the wet spinning technique(Yang et al.,2005).Brieﬂy,commercial chitosan powder with known viscosity,e.g.of about625mPa S and degree of deacetylation, e.g.91.2%,respectively,was used as received.The reagent used for cross-linking was analytic glyoxal.2.2.SwellingIn order to understand the swelling behavior for cross-linked chitosanﬁber,the diameter ofﬁber before and after soaking in a5%(v/v)acetic acid solution for24h,258C, respectively,were taken as a measure by means of an optical microscope and Eq.(1)Sð%ÞZð1K D0=D SÞ100%(1) where S and D represent the swelling degree andﬁber diameter,respectively;the subscripts,e.g.0and S,represent the diameter ofﬁber pre-and after swelling,respectively.2.3.Fiber analysis and characterizationThe WAXD curves were recorded by Rigaku D-MAX-B type wide-angle X-ray Diffractometer using Ni-ﬁltrated Cu–K radiation at35kV and40mA with a scanning rate of 68C/min.The crystallinity of the chitosanﬁber sample was estimated based on literature(Mo,Zhou,&Sun,1993) suggested formula(2)f c Z ðx2x1I cðxÞd x=ðx2x1IðxÞd x(2)where:f c the crystallinity of chitosanﬁber,I(x)the gross diffraction intensity of chitosanﬁber,I c(x)the diffraction intensity from crystal part of chitosanﬁber,andx2q value.DSC thermogram of chitosanﬁber was obtained using a Mettler Differential Scanning Calorimeter,DSC822e, with a heating rate of58C/min under nitrogen stream condition.The polarizing microscope of the chitosanﬁber was recorded using a BX51Polarizing Microscope(Japan)with a hot stage at different temperatures.In this case,the rate for temperature heating was pre-set at about68C/min and each photo was recorded by an online camera with a shift of about10s.The SEM photographics of the chitosanﬁbers were obtained using a JSM-5600LV Scanning Electron Microscope.3.Results and discussion3.1.Effect of glyoxal cross-linking on the degree of swelling for chitosanﬁberThe effect of cross-linking on the degree of swelling was showed in Fig.1.Observed that the increase of the glyoxal concentration is visible to decrease the swelling degree indicating that the cross-linking reaction is exactly taken place as previous found(Yang et al.,2005).Since Fig.1 showed swelling behavior has been found in good agreement with Uragami and Takigawa(1990),meanwhile to support our previous conclusions(Yang et al.,2005),it is evidently that this case adopted method for description of the cross-linking is capable.According to Fig.1,it is therefore conﬁrmed that the cross-linking process is capable for enhancement of the tenacity for chitosanﬁber.Additionally,Fig.1presented swelling behavior suggests that the use of glyoxal as a reagent to cross-link chitosanﬁber may follow a regulation such as:S Z79.24K5.05C C0.24C2.Of which,S and C represents the swelling degree and the concentration of glyoxal,respectively.3.2.Inﬂuence of cross-linking on the crystal structure of chitosanﬁbersBecause chitosan has two crystal types,e.g.a and b,both belong to the monoclinic system in resulting of molecular chain in regular,rigid,polar and crystallization(Ogawa et al.,2004),and such properties further causing chitosan ﬁber to have different cell parameters(Jiang,2001;0123456789 505560657075Swellingdegree(%)Glyoxal concentration (V/V %)Fig.1.Inﬂuence of the glyoxal concentration on the swelling degree for cross-linking of chitosanﬁber.Q.Yang et al./Carbohydrate Polymers61(2005)393–398 394Urbanczyk &Lippsymonowicz,1994),it is principally considered that those crystal structure of chitosan ﬁber might be inﬂuenced by employed cross-linking reaction.Therefore,to understand the inﬂuence of cross-linking on the structure of chitosan ﬁber is expected.A comparison of the X-ray diffraction spectra for chitosan ﬁbers before and after cross-linking with glyoxal was thus presented in Fig.2.Clearly,two intense diffraction peaks were visibly located at 11.1and 20.38,respectively,for original sample to indicate that these are typical characteristics for chitosan ﬁber.Moreover,according to Jiang (2001),it is further known that these two intense peaks in relation to the a crystal of chitosan.Taking this in mind to characterize the cross-linked chitosan ﬁber (Fig.2),hence these two peaks visibly reduced or shifted for cross-linked chitosan ﬁber would be considered that the crystal structure of cross-linked chitosan ﬁber might be changed from a to b type (Jiang,2001).Obviously,this ﬁnding is important for understanding the mechanism of cross-linking for chitosan ﬁber.Because Jiang (2001)has found that the b type crystal structure for chitosan ﬁber may cause its thermal stability decreasing due to such crystal molecules comprise more amorphous structure than that of a crystal molecules,and the acting forces among b crystal molecules weaker than that of a crystal molecules,it was re-considered that this case found crystal behavior for cross-linked chitosan ﬁber seems to be a good explanation for supporting our previous conclusion that the cross-linking process with glyoxal caused the occurrences of the Schiff base reaction and acetalization (Yang et al.,2005).Based on Eq.(2),the crystal structure change for chitosan ﬁber was also known quantitatively,i.e.the cross-linking seems to reduce the crystal component for this ﬁber from 34.7to 27.2%.In fact,the formation of the imperfect b -crystal was ascribed to the deterioration of the crystallization for chitosan after cross-linking is in good agreement with Monteiro and Airoldi (1999)and Uragami,Matsuda,Okuno,and Miyata (1994).Since the appearance of b -crystal for chitosan ﬁber should inﬂuence on the thermal properties (Jiang,2001),DSC was performed and a comparison of two chitosan ﬁbers pre-and after cross-linking was presented in Fig.3.Of which,the dehydration phenomenon was initially observed for two samples,e.g.at about 758C for uncross-linked and at about 788C for cross-linked chitosan ﬁber,respectively.Probably,these cross-linking induced phenomena are due to the hydroxyls of chitosan ﬁber that resulted in hydrogen bonds in connection with the molecules of water (Jiang,2001).Assuming this is correct,therefore,the visible shift,e.g.38C,for cross-linked chitosan ﬁber that was higher than that of uncross-linked sample might be taken as an indication for understanding the network resulted in chitosan ﬁber and probably due to the embedding of moisture.Since Fig.3further presented two small endothermic peaks consistency at 162or 1638C,respect-ively,for chitosan ﬁbers pre-and after cross-linking,and both seem to be related to the ﬁnding of Ahn,Choi,and Cho (2001)and Ko,Jo,Lee,and Kim (1997).It was further known that the chitosan ﬁber may keep its a -crystal structure at this temperature.In other words,this suggests that the crystal change for chitosan ﬁber may need a more high temperature, e.g.at least higher than 1628C.Obviously,this relationship between the crystal structure and thermal property for chitosan ﬁber is important.According to Fig.3,the evidence for resulting of the b -crystal structure for chitosan ﬁber relating to the temperature seems to be visible because the curve for cross-linked ﬁber has been found obviously raised after 1628C in comparison with uncross-linked sample.How-ever,the detailed temperature seems to be impossible from Fig.3indicating other techniques required.The decompose temperature for both chitosan ﬁbers was observed at about 2948C for uncross-linked sample and about 2798C for cross-linked sample.With respect to above mentioned difference between two chitosan ﬁbers,clearly,this indicated that the cross-linking process would reduce5101520253035I n t e n s i t y2θUncross-linked Cross-linked Crystallinity:34.7%Crystallinity:27.2%11.1˚20.3˚11.6˚22.3˚Fig.2.A comparison of X-ray diffraction diagrams for chitosan ﬁber cross-linked and uncross-linked.255075100125150175200225250275300325T emperature (˚C)Fig.3.A comparison of DSC curves for chitosan ﬁber cross-linked and uncross-linked.Q.Yang et al./Carbohydrate Polymers 61(2005)393–398395Q.Yang et al./Carbohydrate Polymers61(2005)393–398396Fig.4.Polarizing microscopy of chitosanﬁber cross-linked and uncross-linked.A,uncross-linked;B,cross-linked.the degree of crystallization for chitosan ﬁber to support the ﬁnding from literature (Jiang,2001).In addition to the use of DSC,the change of the crystal structure for chitosan ﬁber by cross-linking was furthermore investigated by application of a hot stage polarizing microscope.Relying on observed light intensities,the thermal phenomena for two chitosan ﬁber samples obtained from polarizing microscope was compared in Fig.4.Due to the light intensity observed stronger for uncross-linked ﬁber and weaker for cross-linked sample,it is clearly that the cross-linking is indeed to reduce the thermal properties for chitosan ﬁber.Additionally,since the light intensity observed strongly for uncross-linked chitosan ﬁber corresponding to a tempera-ture range,e.g.from 30to 2308C,then gradually darken until disappeared at a temperature of about 2818C,meanwhile the disappearance of light intensity for cross-linked chitosan ﬁber to be at about 2308C (Fig.4),it indicates that the original chitosan ﬁber may start melting since 2308C and decompos-ing since 2818C,while for cross-linked sample these two temperatures changed.In principal,this means that chitosan ﬁber changes its a -crystal structure to b -crystal structure during the melting process.The inﬂuence of cross-linking on the surface of chitosan ﬁber was investigated by SEM.Fig.5indicated that the cross-linking might play a role to coat the surface of chitosan ﬁber due to the uncross-linked sample presented rough surface,e.g.with a lot of visible grooves,while the surface of cross-linked sample is obviously in smooth.Since the same phenomenon was also observed by Hirano et al.(1999),it is known that one may apply the cross-linking technique to modify the surface of chitosan ﬁber to ﬁt different requests in coming application cases.4.ConclusionFollowing the studies previously (Yang et al.,2005),this paper further studied the chitosan ﬁber after cross-linking with glyoxal using different methods,e.g.swelling,WAXD,DSC,SEM and polarizing microscope.Results showed that the cross-linking reaction may cause chitosan ﬁber to change its crystal structure from a -to b -type meanwhile to reduce the degree of crystallization,and this change might be corresponding to the melt temperature.Therefore,the inﬂuence from cross-linking on thermal properties of chitosan ﬁber is visible.Based on SEM,it was known that the cross-linking process may also smooth the surface for chitosan ﬁber.ReferencesAdusumilli,P.S.,&Bolton,S.M.(1991).Evaluation of chitosan citratecomplexes as matrices for controlled release formulations using a 3(2)full factorial design.Drug Development and Industrial Pharmacy ,17,1931–1945.Ahn,J.S.,Choi,H.K.,&Cho,C.S.(2001).A novel mucoadhesivepolymer prepared by template polymerization of acrylic acid in the presence of chitosan.Biomaterials ,22,923–928.AlAngary,A.A.,AlHelw,A.A.M.,AlDardiri,M.M.,&Mahrous,G.M.(1998).Release and bioavailability of diclofenac sodium from low molecular weight chitosan microspheres treated with Japan and carnauba wax.Pharmazeutische Industrie ,60,629–634.Aly,A.S.(1998).Self-dissolving chitosan,I-preparation,characterizationand evaluation for drug delivery system.Angewandte Makromolekulare Chemie ,259,13–18.Austin,P.R.,&Brine,C.J.(1981).Chitin powder and process for making Patent 4,286,087.Elcin,Y.M.,Dixit,V.,&Gitnick,G.(1998).Hepatocyte attachmenton biodegradable modiﬁed chitosan membranes:In vitro evaluation for the 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Modeling the Effect of Cross-Language Ambiguity on Human Syntax Acquisition

1The STL is an acquisition model in the principles and parameters paradigm. The results presented here are not intended to forward an argument for or against the model, or for t h a t matter, for or against the principles and parameters paradigm. Rather, the results axe presented to point out (the possibly not-so- earthshattering observation) t h a t the acquisition mechanism c a n be extremely sensitive to ambiguity.
1
Principles and P a r a m e t e r s
Chomsky (1981) (and elsewhere) has proposed that all natural languages share the same innate universal principles (Universal Grammar - - UG) and differ only with respect to the settings of a finite number of parameters. The syntactic component of a grammar in the principles and parameters (henceforth P&P) framework, is simply a collection of parameter values - - one value per parameter. (Standardly, two values are available per parameter.) The set of human

山东省济南市2023-2024学年高二下学期7月期末英语试题

山东省济南市2023-2024学年高二下学期7月期末英语试题一、阅读理解The Half Price Books summer reading program, called Summer Reading Camp, gives out free Half Price Books gift cards to kids who read for at least 300 minutes during the months of June and July. This program is for kids from preschool to 14 years of age, in 8th grade or under. There’s also a limit of one reading log(日志) per month for each child. How to Get Free Gift Cards from the Half Price Books Summer Reading ProgramVisit Summer Reading Camp and register. As the summer program gets closer, you'll receive more information in your email.Each day your child reads during June and July, have them write the number of minutes they’ve read on that day on the calendar. The goal is to read for at least 15 minutes each day of the week. At the end of each week, kids can add up their week’s total minutes and have a grown-up sign it. After the child has read at least 300 minutes, fill out their name, age, and total minutes, as well as your name, email, and location information. Cut out the completed part of the form and bring it to your local Half Price Books to get your reward. Encouraging Y our Child through the Half Price Books Summer Reading ProgramWhen your kids are finished with a week, a month, or the whole program, you can fill out a Best Reader Award to keep them encouraged about their progress.As for what your child reads this summer, Half Price Books has put together a list of staff picks by grade level, best alphabet books, 40 books every child should read, and 21 books to start the baby's library.1．Who can attend Summer Reading Camp?A．A 4-month baby.B．A 15-year-old girl.C．A primary school boy D．A college graduate2．How can daily reading be guaranteed in this program?A．By cutting out the forms.B．By submitting reading logs.C．By filling out total reading minutes D．By keeping records on the calendar. 3．What can parents do to encourage their children to read?A．Present a reading award.B．Buy recommended books.C．Give suggestions on reading D．Share post-reading feedback.Matthew Weihmuller, despite being blind from birth, earned his master’s degree in music at Florida State University. He also tours with a band that shows elements of jazz and rock. Additionally, he is a composer, using specialized music technology for the blind. He frequently engages as a speaker, having been a guest lecturer at John Hopkins University.While explaining his shift from performance to teaching, Weihmuller said, “All great performers teach, and it’s the only way to pass along this craft, especially about jazz music. I found that teaching became more my calling than performing. I wanted to make a difference, and that was really important to me.”Innovatively, Weihmuller uses a unique teaching method to enhance communication among jazz students. When practising a play, he turns off the lights, removes the visualelements and forces students to rely more on their other senses. They have to feel their instrument with their fingers and hands. Weihmuller’s own blindness has fueled his mastery of other senses, particularly crucial in playing jazz. “You have to turn your disadvantage into an advantage. Where there is a will, there is a way.” Weihmuller said.Reflecting on his early struggles with sheet music, Weihmuller recalled the challenge of obtaining braille(盲文) music, which was not as accessible then as it is today. To overcome this obstacle, he had to create his own braille music, a process that continued through his college years.Weihmuller has a strong desire to influence his students with value of perseverance and musical progression. His ultimate goal is to inspire others facing challenges and disabilities. He added, “I do hope that when they leave my classroom, they’re not only better musicians but also better people.”4．What can we learn about Weihmuller from Paragraph 1?A．He has multiple roles.B．He owns a music band.C．He complains of his disability.D．He gives talks worldwide.5．What drives Weihmuller to turn to music teaching?A．The duty to help performers.B．The strong desire to succeed.C．The will to pass down music.D．The aim to gain independence.6．Why did Weihmuller turn off lights in his music class?A．To reduce students’ anxiety.B．To train physical abilities.C．To teach students better.D．To test learning results.7．Which of the following can best describe Weihmuller?A．Outgoing and caring.B．Courageous and honest.C．Creative and determined.D．Knowledgeable and patient.Most people think that weeds are something to be pulled up and thrown away. Now, purslane(马齿苋) may be the key to creating drought resistant crops in a world that is getting warmer.Scientists at Yale University found that purslane can create a new form of photosynthesis(光合作用) that allows this weed to endure drought conditions. “This is a very rare ‘super plant’ —one that could be potentially useful in crop engineering.” said Edwards, a professor of ecology and evolutionary biology.Purslane actually enhances its photosynthesis efficiency to match the high levels found in plants like corn, which enables it to maintain productivity under high temperatures. On the other hand, this plant employs a special way of photosynthesis. It stores carbon dioxide at night and uses it during the day, which makes it remarkably resistant to heat. The uniqueness of purslane lies in these two characteristics. Yale team conducted an analysis of the genes in the leaves of the plant and found that they are totally integrated and operate in the same cells. Understanding how this works could allow scientists to engineer main crops like corn to resist long-lasting droughts.Growing across the US, purslane has small round leaves, and red, yellow, or pink flowers. You can plant it in your garden just about anywhere. With its sour-salty taste, it is a healthy food rich in vitamins, minerals, and Omega-3s. You can enjoy it raw in salads or cooked as a dish.“In terms of engineering the plant into a crop like corn, there is still a lot of work to do before that could become a reality,” Edwards said in the news release. Finding and growing new food crops that can survive the effects of climate change is a win-win for a planet that is getting hotter and drier. Who knew this common weed could be the key?8．What makes purslane a “super plant” according to Paragraph 2?A．Its unique taste and color.B．Its ability to grow anywhere.C．Its high capacity in storing water.D．Its uncommon way of photosynthesis. 9．What is the advantage of purslane’s storing carbon dioxide at night?A．Increasing its productivity.B．Helping it to resist drought.C．Allowing it to grow faster.D．Reducing its need for sunlight.10．What can we learn about purslane as food?A．It is rich in nutrition.B．It is not widely accepted.C．It is not suitable in salads.D．It is mainly cooked as a dish.11．What is the main purpose of the text?A．To promote the planting of purslane.B．To warn readers of the danger of the weed.C．To describe different types of photosynthesis.D．To show purslane’s potential in crop engineering.A cohort is a group of people who share a particular characteristic. Typically, the shared characteristic is a life event that took place in a particular time period, like birth or high school graduation. Cohorts often consist of people who have experienced significant life events in the same period, such as starting college the same year or experiencing a natural disaster.The impact of the characteristics of a cohort on the results of a research study is called a cohort effect. Cohort effects influence research results because the shared experiences of a cohort can impact research results. Once a research was done to see how easily people learned to play a mobile game featuring AI. The participants ranged from 20 to 80 years old. The finding showed that compared with the younger participants, the older participants had much more difficulty in learning how to play the game. However, the research finding could also be the result of cohort effects in that older participants would have far less exposure to mobile devices than younger participants, making it more difficult for them to learn how to play the new game. Thus, it is important to take cohort effects into account in research.Cohort effects are a particular issue in studies that use cross-sectional (横断面) methods. In cross-sectional studies, researchers collect and compare data from participants in two or more age-related cohorts at a single point in time. Cross-sectional studies are more efficient but morelikely to be affected by cohort effects.Meanwhile, longitudinal (纵向) studies which collect data from the same participants over time, can better guard against cohort effects. These studies observe changes directly, and eliminate cohort effect concerns. However, they are costly and time-consuming.In conclusion, understanding cohort effects is crucial for interpreting research findings accurately. While longitudinal studies offer a solution, their practical limitations leave cross sectional studies as the more common but potentially cohort-influenced method.12．What does a cohort typically feature?A．The same gender.B．The identical college.C．Some consistent ideal.D．Some shared experience.13．How does the author explain cohort effects in Paragraph 2?A．By conducting a research.B．By presenting an example.C．By proposing a suggestion.D．By playing a mobile game.14．What does the underlined word “eliminate” in Paragraph 4 probably mean?A．Remove.B．Consider.C．Raise.D．Increase. 15．What is the text mainly about?A．Ways to improve cohort-influenced researches.B．The development of science research methods.C．The impact of cohort effects on research findings.D．Copmarisons of cross-sectional and longitudinal methods.It’s believed that health and happiness are two basics that make up a good life. And the two turn out to be more closely related than we might think. The question of whether one causes the other or if the two are correlated is difficult to figure out. 16It’s difficult to distinguish the relationship between health and happiness. 17 Does dealing with a chronic (慢性的) illness consistently worsen mood? Researchers try to answer these questions, but the relationship will always be challenging to say for certain.Happiness is associated with a series of physical health benefits, such as lower blood pressure, reduced risk of heart disease, a stronger immune (免疫的) system, and even a longer life. Positive emotions are also linked to good health in older adults and a reduced risk of injury inyoung adults. 18 People who report feeling a stronger sense of happiness and well-being live longer, on average, than those who report weaker feelings, and the effect exists for both men and women.19 Some research suggests that when people take better care of themselves, they come to feel happier. Some research suggests that people who are healthier just have a more positive attitude to life and the world. Still another research suggests that an essential factor such as genetics or personality contributes to both.Exercise stimulates the body to produce certain chemicals such as hormones (荷尔蒙).20 Exercise also shifts our focus away from current concerns and damaging self-talk and leads us to spend time outside or with others.A．Do certain foods boost happiness?B．Does a happy person also have better health?C．Meanwhile, happiness is related with a longer life.D．However, there’s no doubt that a strong connection exists.E．The exercise we do and the diseases we face all play a role.F．There are various theories for why health may lead to happiness.G．These chemicals are responsible for the feeling of a “runner’s high”.二、完形填空Alicia, a black girl, fell in love with dance when she was three years old. But she didn’t realize her 21 could help her achieve her career until she led a new training program in the Juilliard School.Over the years, she has been training hard and seizing every 22 to participate in professional dance competitions and her fame 23 gradually. She even won an 24 offered by the Dance Theatre of Harlem at 17. Although she had always been 25 as the odd girl because of her color, she felt it all right. Her bright career also 26 her performances in well-known dance theaters. Unluckily, she was injured during a training, but she kept going. However, the injuries 27 forced her to leave the stage, turning her focus on art education.Consistent with the creative philosophy of Juilliard School, Alicia got 28 by theschool. She has been buried in dance teaching since then. After she was appointed to be in charge, she became the first youngest woman of color to 29 the novel dance program. From then on, she has 30 herself to shaking up what is taught and how to make art dance more creative and colorful than ever.Alicia now requires students to 31 hip-hop and West African dance courses, which allows them to have more 32 to choose techniques that interest them. They are encouraged to come as they are, and that even 33 to what they wear to class. “I want them to be as free and 34 as they can. I hope that they have 35 in their careers and therefore they can make it to the end.” she said with a broad smile.21．A．courage B．dream C．passion D．confidence 22．A．motive B．action C．duty D．chance 23．A．continued B．spread C．declined D．changed 24．A．experience B．investment C．award D．occupation 25．A．respected B．appointed C．treated D．promoted 26．A．saw B．made C．kept D．affected 27．A．immediately B．exactly C．frequently D．eventually 28．A．rewarded B．accepted C．refused D．punished 29．A．head B．praise C．support D．judge 30．A．adapted B．helped C．applied D．resigned 31．A．open B．improve C．explain D．take 32．A．freedom B．energy C．intelligence D．time 33．A．extends B．sticks C．refers D．contributes 34．A．humorous B．enthusiastic C．modest D．generous 35．A．trouble B．success C．memory D．perseverance三、语法填空阅读下面材料，在空白处填入适当的内容(1个单词)或括号内单词的正确形式。

混合效应英语

混合效应英语Mixed Effects EnglishThe world of language is a complex and multifaceted one, where the interplay of various factors can give rise to fascinating phenomena. One such phenomenon is the concept of "mixed effects," which refers to the blending of linguistic elements from different sources or backgrounds. In the realm of English, this concept has become increasingly relevant, as the language continues to evolve and adapt to the ever-changing global landscape.At the heart of mixed effects English lies the notion of linguistic diversity. As the world becomes more interconnected, the exchange of ideas, cultures, and traditions has led to a rich tapestry of linguistic influences. English, in particular, has been at the forefront of this linguistic melting pot, absorbing and incorporating elements from a wide range of languages and dialects.One of the most prominent examples of mixed effects English can be found in the realm of vocabulary. The English language has a long and storied history, with roots tracing back to the Germanic tribes that settled in Britain centuries ago. Over time, however, English hasbeen enriched by the influx of words and expressions from other languages, such as French, Latin, Greek, and even indigenous languages from around the world.This linguistic cross-pollination has resulted in a remarkably diverse lexicon, where words from different origins coexist and often blend seamlessly. For instance, the word "restaurant" is derived from the French language, while "algebra" has its roots in Arabic. Yet, both of these words have become integral parts of the English vocabulary, seamlessly integrated into the language.Moreover, the influence of mixed effects can be observed in the evolution of English grammar and syntax. As the language has spread across the globe, it has adapted to the linguistic structures and conventions of the regions it has encountered. This has led to the emergence of regional variations and dialects, each with its own unique grammatical patterns and idiomatic expressions.For example, the use of "y'all" in certain parts of the United States, or the inclusion of specific grammatical structures in Indian English, are reflections of the mixed effects that have shaped the language. These variations, rather than being seen as deviations from a "pure" form of English, should be celebrated as the natural consequences of the language's adaptability and resilience.Beyond the realms of vocabulary and grammar, mixed effects English can also be observed in the realm of pronunciation and accent. As English has spread across the globe, it has been influenced by the phonological systems of the local languages. This has resulted in a rich tapestry of accents, each with its own unique characteristics and nuances.From the melodic tones of Indian English to the distinctive rhythms of Caribbean English, these accents are not merely variations but rather expressions of the cultural and linguistic diversity that has shaped the language. They serve as a testament to the adaptability and resilience of English, as it continues to evolve and thrive in diverse contexts.The phenomenon of mixed effects English is not limited to the linguistic realm alone. It also has profound social and cultural implications. As the language has become a global lingua franca, it has facilitated cross-cultural communication and exchange, enabling individuals from diverse backgrounds to connect and share ideas.In this context, mixed effects English has become a powerful tool for cultural expression and identity. Individuals and communities have embraced the language, infusing it with their own cultural elements and creating unique forms of expression. This has led to the emergence of vibrant literary traditions, music, and art that blend thelinguistic and cultural influences of different regions.Moreover, the recognition and acceptance of mixed effects English have important implications for language education and policy. Rather than insisting on a singular, "correct" form of English, educators and policymakers should embrace the diversity of the language and encourage students to develop their linguistic skills in a way that reflects their cultural and regional identities.By doing so, they can foster a more inclusive and equitable language learning environment, where students are empowered to express themselves authentically and confidently, regardless of their linguistic background.In conclusion, the phenomenon of mixed effects English is a testament to the inherent dynamism and adaptability of language. As the world becomes increasingly interconnected, the blending of linguistic elements from diverse sources has become an integral part of the evolution of English. This process has enriched the language, fostered cross-cultural communication, and challenged traditional notions of linguistic purity.By embracing the diversity and complexity of mixed effects English, we can gain a deeper appreciation for the power of language to reflect and shape the human experience. It is a testament to theresilience and creativity of the human spirit, as we continue to navigate the ever-changing landscape of global communication and cultural exchange.。

东华大学材料学专业英语翻译高分子方向

Graft copolymerization is an efficient method to modify polymers .Various vinyl monomers have been investigated to graft onto starch ,and the starch graft copolymers have been used as flocculating agents , superabsorbents,ion exchanges and matrix or filler of thermo plastics. In this paper,mo dified starch paste by grafting with butylacrylate(BA) is firstly investigated as rubber-reinforcing filler. Three types of natural rubber(NR)/starch composites are prepared . Properties and morphology of these composites and corresponding starch powders are examined .The observed reinforcement effect of modified starch powder on NR/starch composites is interpreted.NO20this exploratory investigation examined the structural mechanism accounting for the enhanced compressive properties of heat-treated Kevlar-29 fibers . A novel theory was set forth that hydrogen-bond disruption and concurrent misorientation of crystallites may account for the observed augmentation of compressive properties. To examine the said theory ,as-received Kevlar-29 fibers were characterized by themogravimetric analysis and differential scanning calorimetry in an effort to determine if crosslinking and/or hydrogen disruption was responsible for the improved behavior in compression.NO21to prevent the loss of fiber strength , ultrahigh-molecular-weight polyethylene (UHMWPE) fibers were treated with an ultraviolet radiation technique combined with a corana-discharge treatment .the physical and chemical changes in the fiber surface were examined with scanning electron microscopy and Fourier transform infrared/attenuated total reflectance .the gel contents of the fibers were measured by a standard device .the mechanical properties of the treated fibers and the interfacial adhesion properties of UHMWPE-fiber-reinforced vinyl ester resin composites were investigated with tensile testing .NO22bicomponent fiber were wet-spun from soybean protein and poly(vinyl alcohol). the protein core of spun bicomponent fiber was brittle .our effort was then to study the soybean protein solution ,with the aim of trying to understand the cause for fiber brittleness and to determine the optimum solution conditions for fiber spinning . the effectsof alkali ,urea ,and sodium sulfite on the viscosity of the soybean protein solution were examined. the hydrolytic stability of the soybean protein solution was examined at various pH values at two temperatures .NO13a novel natural polymer blend ,namely ,a semi-interpenetrating polymer network (semi-IPN)composed of crosslinked chitosan with glutaraldehyde and silk fibroin was prepared .the FTIR spectra of the semi-IPN manifested that the chitosan and silk fibroin had a strong hydrogen-bond interaction and formed an interpolymer complex . the semi-IPN showed good pH sensitivity and ion sensitivity, and could also act as an "artificial muscle" because its swelling-shrinking behavior exhibited a fine reversibility.a number of papers have been published on the structure of PAN using X-ray diffraction ,infrared spectroscopy ,nuclear resonance ,and molecular simulations .based on the scattering pattern ,PAN is considered either orthorhombic with 3D,or hexagonal with 2D order . it has been proposed that hexagonal packing ,of PAN chains in dry samples becomes orthorhombic due to co-crystallization of PAN with polar solvent molecules .in this study ,we use in still XRD measurements, and draw upon these earlier publication ,to understand the deformation process on microscopic scale in PAN and its nanocompositeNO15new organic-inorganic hybrids based on PS/TiO2 hybrid membranes were prepared by sol-gel and phase inversion process. the membranes were characterized in terms of morphology, structure ,hydrophlicity, UF ,performance and thermal stability .the results showed that macrovoids were nearly suppressed with formation of sponge like membrane structure .the TiO2 particles were uniformly dispersed in membrane . the nanodispersed morganic network formed after sol-gel process and the strong interaction between inorganic network and polymeric chains led to the improvement of porosity and thermal stability.NO16polymers carrying a hydrolyzable ester function and bactericidal quaternary ammonium salts were successfully synthesized in two steps . the first one was the modification of hydroxyl functions of poly(vinyl alcohol) by chloroacetic anhydride . the structure of synthesized polymers was confirmed by infrared ,1H-,and 13C- nuclear magnetic resonance .the kinetic results were consistent with a 1-order reaction ,and the activation energy in the case of total modification was found to be 16.8(J/Mol) . the second step was the quaternization of the pendant chlorine atom with a long alkyl chain or aromatic tertiary amines.NO17blending homopolymers with block copolymers has been proved to be another interesting approach to modify the morphology of the block copolymer self-assembly. by blending homopolymer of identical chemical structure with one block in the copolymer , the dimension of the domains in the final phase separation has been adjusted , by changing either the volume fraction or the molecular weight of the homopolymer .at low volume fraction of the block copolymers , the structure formation is analogous to micelle formation of surfactant molecules in solutions, and the interfacial tension between the copolymer and the homopolymer is a critical factor.NO18differential scanning calorimetry and dynamic mechanical zhermal analysis techniques have been used to characterize different Kevlar/epoxy composites. tetra-functional aliphatic amine and anhydride/diglycidyl epoxy have been used as matrix and different quantities of continuous Kevlar fibers as reinforcement .Kevlar fibers had different effects on curing kinetics and final thermal properties depending on epoxy matrix type . a significant decrease in the glass transition temperature(Tg)was observed as Kevlar content increased when anhydride matrix was used .NO10the electrostatic spinning technique was used to produce ultrafine polyamide-6 fibers. the effects of solution conditions on the morphological appearance and the average diameter of as-spun fibers were investigated by optical scanning and scanning electron ,microscopy techniques . it was shown that the solution properties (i.e. viscosity , surface tension and conductivity) were important factors characterizing the morphology of the fibers obtained .among these three properties ,solution viscosity was found to have the greatest effect . solutions with high enough viscosities were necessary to produce fibers without beads.NO11ternary blend fibers (TBFs) ,based on melt blends of poly(ethylene 2,6-naphthalate) , poly(ethylene terephthalate ), and a thermotropic liquid-crystal polymer (TLCP), were prepared by a process of melt blending and spinning to achieve high performance fibers . the reinforcement effect of the polymer matrix by the TLCP component the fibrillar structure with TLCP fibrils of high aspect ratios and the development of more ordered and perfect crystalline structures by an annealing process resulted in the improvement of the tensile strength and modulus for the TBFs .NO12an amphiphilic AB block copolymer composed of poly(N-isopropylacrylamide) as a hydrophilic segment and poly (10-undecenoic acid) as a hydrophobic segment was synthesized . the lower critical solution temperature (LCST) of the copolymer was 30.8 ..,as determined by the turbidity method . the block copolymer forms micells in an aqueous medium. transmission electron microscopy images showed that these nanoparticles were regularly spherical in shap . the micelle size determined by size analysis was around 160 nm .NO7this work examines the PBT/PET sheath/core conjugated fiber with reference to melt spinning, fiber properties and thermal bonding . regarding the rheological behaviors in the conjugated spinning , PET and PBT show the smallest difference between their melt -viscosity at temperatures of 290 and 260 respectively , which has been thought to represent optimal spinning conditions . the effect of processing parameters on the crystallinity of core material-PET was observed and listed . in order of importance , these factors are the draw ratio, the heat-set temperature , and the drawing temperature.NO8thermoresponsive shape memory fibers were prepared by melt spinning form a polyester polyol-based polyurethane shape memory polymer and were subjected to different postspinning operations to modify their structure . the effect of drawing and heatsetting operations on the shape memory behavior , mechanical properties , and structure of the fibers was studied . in contrast to the as-spun fibers , which were found to show permanent shape , the drawn and heat-set fibers showed significantly higher stresses and complete recovery.NO9the dry-jet-wet spinning process was employed to spin poly(lactic acid) fiber by the phase inversion technique using chloroform and methanol as solvent and nonsolvent ,respectively , for PLA . the as-spun fiber was subjected to two-stage hot drawing to study the effect of various process parameters , such as take-up speed ,drawing temperature , and heat-setting temperature on the fiber structural propertics . the take-up speed speed had a pronounced influence on the maximum draw ratio of the fiber . the optimum drawing temperature was observed to be 90 to get a fiber with the tenacity of 0.6 GPa for the draw ratio of 8 .NO1the purpose of this work is to examine zhe changes in thermal properties and zhe crystallization behavior of polyamide 6(PA6) when filled with multi-walled carbon nanotubes (MWCNT). the composites were produced by melt mixing starting from an industrial available masterbatch containing as produced MWCNT . the focus of this article is a detailed discussion of results obtained by differential scanning calorimetry (DSC) ,X-ray ,diffraction (XRD) dynamic mechanical thermal analysis (DMTA), and water sorption . the influence of CNT on zhe thermal transitions (glass transition temperature ,melting ,and crystallization) of PA6 is investigated .NO2the effects of nucleating agents (NAs) on fracture toughness of injection-molded isotactic poly(propylene)/ethylene-diene terpolymer (PP/EPDM) were studied in this work . compared with PP/EPDM blends without any NA,EP/EPDM/NA blends show very small and homo geneous PP sphernlites . as we expected ,PP/EPDM blends nucleated with B-phase NA(TMB-5) present not only a significant enhancement in toughness but also a promotion of brittle-ductile transition . however ,the addition of A-phase NA(DMDBS) has no apparent affect on the toughness of the blends . the impact-fractured surface morphologies of such samples were analyzed via scanning electronic microscope(SEM).NO3solutions of poly(ethylene-co-vinyl alcohol) or EVOH ,ranging in composition from 56 to 71 wt% vinyl alcohol ,can be readily electrospun at room temperature from solutions in 70% 2-propanol/water . the solutions are prepared at 80 and allowed to cool to room temperature .interestingly, the solutions are not stable at room temperature and eventually the polymer precipitates after several hours . however prior to precipitation , electrospinning is extensive and rapid ,allowing coverage of fibers on various substrates . fiber diameters of ca. 0.2-8.0 um were obtained depending upon the solution concentration .NO4the use of macromonomers is a convenient method for preparing branched polymers . however graft copolymers obtained by conventional radical copolymerization of macromonomers often exhibit poorly controlled molecular weights and high polydispersities as well as large compositional heterogeneities from chain-to-chain . in contrast , the development of "living"/controlled radical polymerization has facilitated the precise synthesis of well-defined polymers with lowpolydispersities in addition to enabling synthetic chemists to prepare polymers with novel and complex architectures .NO5the thermal and electrical conductivities in nanocomposites of single ,walled carbon nanotubes (SWNT) and polyethylene (PE) are investigated in terms of SWNT loading the degree of PE crystallinity , and the PE alignment . isotropic SWNT/PE nanocomposites show a significant increase in thermal conductivity with increasing SWNT loading , having 1.8 and 3.5 W/m K at a SWNT volume fraction of ———0.2 in low-density PE(LDPE) and high-density PE (HDPE), respectively . this increase suggests a reduction of the interfacial thermal resistance . oriented SWNT/HDPE nanocomposites exhibit higher thermal conductivities , which are attributed primarily to the aligned PE matrix .NO6we previously discovered that isotropic monomer solution show birefringence due to its anisotropic structure after gelation in the presence of a small amount of rod-like polyelectrolyte. here ,we focus on what mechanism is responsible for the formation of anisotropic structure during gelation .various optical measurements are perfected to elucidate the structure change during gelation . it is found that the existence of a large-size structure in monomer solution with the rod-like polyelectrolyte is essentially important to induce birefringence during gelation .。

The Effect of Native Language on Internet Usage

The Effect of Native Language on Internet UsageNeil Gandal (Tel Aviv University)Carl Shapiro (University of California at Berkeley)September 2001ABSTRACTIn this paper, we empirically explore the relationship between native language and use of the Internet. The ultimate economic and social questions we explore are: (1) how native language affects use of the Internet, both in total and by type of Web site; (2) whether English is likely to retain its “first-mover advantage” on the Web in terms of the language employed by Web sites; and (3) whether the Internet ultimately will accelerate the movement to English as a global language.Our goal is to distinguish between the following two hypotheses: (A) The Internet will remain disproportionately in English and will, over time, cause more people to learn English as second language and thus solidify the role of English as a global language. This outcome will prevail even though there are more native Chinese and Spanish speakers than there are native English speakers. (B) As the Internet matures, it will more accurately reflect the native languages spoken around the world (perhaps weighted by purchasing power) and will not promote English as a global language.English’s “early lead” on the web is more likely to persist if those who are not native English speakers frequently access the large number of English language web sites that are currently available. In that case, many existing web sites will have little incentive to develop non-English versions of their sites, and new sites will tend to gravitate towards English. The key empirical question, therefore, is whether individuals whose native language is not English use the Web, or certain types of Web sites, less than do native English speakers. In order to examine this issue empirically, we employ a unique data set on Internet use at the individual level in Canada from Media Metrix. Canada provides an ideal setting to examine this issue because English is one of the two official languages. Our preliminary results suggest that English web sites are not a barrier to Internet use for French-speaking Quebecois. These results are consistent with the scenario in which the Internet will promote English as a global language.Language TPRC.doc, 9/5/01 10:31 PM, Page 1 of 11. Introduction: Network Effects, First-Mover Advantages, and LanguageIn recent years, English has become the de facto standard for business and academic communication and has to some degree attained the status of a global language. English is the official language of the Asian trade group ASEAN and the official language of the European Central Bank, despite the fact that the bank is in (Frankfort) Germany and neither the U.K. nor Ireland are members of the European Monetary Union.1 Several public schools in Zurich, Switzerland are now teaching some of the elementary school subjects in English. This is occurring in a country where there are four official languages --French, German, Italian, and Romansch. In a recent European Union survey, 70 percent agreed with the notion that everybody should speak English.2In this paper , we examine how native language affects Internet use. The goal is to determine whether the Internet is likely to remain disproportionately English and thus whether the Internet will accelerate the movement to English as a global language.Currently there is much more Internet content available in English than in other languages. A recent estimate by Global Reach indicates that nearly 70 percent of all Internet content is currently in English. Japanese and German follow with approximately 6 percent each.3 The Internet certainly is an effective instrument for circulating English around the world.On the other hand, it is quite possible that several languages will have a large critical mass of Internet content, so that English’s role as a global language will diminish: Although 44 percent of current Web users (March 2001) are native English speakers,4 web use is currently growing faster among non-native English speakers. Indeed, it is estimated that by 2003, only 29 percent of all Internet users will be native English speakers. Additionally because of low transaction1 Wallraff, B., What Global Language, Atlantic Monthly, November 2000, p.53-66.2 Daley, S., “In Europe, Some Fear National Languages are Endangered,” NY Times, 4/16/01.3 See /globstats/refs.php3.4 Source: See Global Reach at /globstats/. Following English, 9.0 percent of all Internet users are native Chinese speakers, while 8.6 percent are Japanese, and 6.1 percent are German.Language TPRC.doc, 9/5/01 10:31 PM, Page 2 of 2costs, the Internet is ideal for bringing together members of small groups like speakers of Frisian, which is spoken by approximately 500,000 people throughout the world.Concern that national languages are becoming endangered might lead policy makers to require websites to be in the domestic national language. France already has many laws in place that protect the French language. Quebec requires all websites in that province be available in French. In Brazil, which has the largest Internet industry in South America, a bill was recently introduced that would prohibit the introduction and use of foreign words.5Additionally, another standards war is already brewing on Internet domain names, which until quite recently exclusively used romance language alphabets. Currently two groups, Verisign Inc. and China’s Internet Authority now issue Chinese language domain names using two incompatible systems. This means that in order two operate in both cyber-spaces, businesses would have to register with both authorities.6 Pindar Wong, the former vice president of the Internet Corporation for Assigned Names and Numbers (ICANN), the global body that governs the Internet indicated that the two incompatible systems risk “Balkanization of the Internet, dividing the Internet up into islands of connectivity.”7A key determinant of whether the Internet will move towards Balkanization (critical mass of content in many languages) or standardization is whether the “first-mover advantage” (of significant web content in English) will encourage non-English speakers to use English language web sites. In such a case, existing content providers would have little incentive to offer non-English versions of their sites, and new sites would have a strong incentive to provide their content in English. Such a first mover advantage may lead to a “bandwagon” because there are network effects in language: learning a second language is more valuable, the more widely that language is used.A network effect exists when the value that consumers place on a particular product increases as the total number of consumers who use identical or compatible goods increases. In the case of5 NY Times, 5/14/01, “English is Spoken Here…Too Much, Some Say,” by Larry Rohter.6 Wall Street Journal, 11/30/2000, “Will Language Wars Balkanize the Web”, by Gren Manuel and Leslie Chang.Language TPRC.doc, 9/5/01 10:31 PM, Page 3 of 3an actual (or physical) network, such as the telephone or email network, the value of the network depends on the total number of subscribers who have access to the network. Since languages are in part communication technologies, the value of a language network increases in the number of speakers and users of that language. Languages are perfect substitutes, but they are incompatible in the sense that two individuals can talk with each other only if they both speak the same language.8 Languages, as a type of communications networks, clearly are subject to strong direct network effects.In the case of virtual networks, that are not linked physically, a network effect arises from positive feedback from complementary goods.9 The positive feedback mechanism works as follows: the value of the base product (such as a DVD players) is enhanced as the variety of (compatible) complementary products (content available on DVD disc) increases; hence consumers will be more likely to purchase a base product with many compatible complementary products. The variety of complementary products, in turn, will depend on the total number of consumers that purchase the base product. As the number of consumers that purchase the base product increases, there is a greater demand for compatible complementary products. This increases the profitability of supplying complementary products. Since there are typically fixed or sunk entry costs, production of the complementary products is characterized by increasing returns to scale. So, more complementary products will be produced or developed for a base product with a large share of the market. This further enhances the value of the base product, causing positive feedback in the system: an increase in the sales of the base product leads to more compatible complementary products, which further increases (the value of and) sales of the base product. See Chou and Shy (1990) and Church and Gandal (1992).Languages are also subject to such indirect or virtual network effects. The value of speaking English increases as the number of English language web sites (or other content, such as books,7 Ibid.8 Of course, when there is no common language, people can still communicate in non verbal ways, such as gestures, expressions, etc.9 Examples of virtual networks in which the value of the “base” product increases as the variety of complementary products increases include computer operating systems, videocassette recorders (VCRs), compact disc players (CD-players), and Digital Versatile Disc players (DVD-players).Language TPRC.doc, 9/5/01 10:31 PM, Page 4 of 4magazines, or movies) increases. This will lead to an increase in the number of non-English speakers learning English in order to have access to the English language web sites, since individuals who speak English will have more web sites to use. This in turn will lead to an increase in the number of English language web sites.Markets in which there are network effects are often characterized by tipping: once a system has gained an initial lead, there is a snowball effect. Katz and Shapiro (1994, p. 105) note that positive feedback means that there is a “natural tendency towards de facto standardization.” Hence it is possible that the first-mover advantage of English may result in English remaining the dominant language on the web, while other languages will end up serving niche markets. This could occur even though there are more native Chinese and Spanish speakers than there are native English speakers. The outcome will depend, in large part, on the strength of the virtual network effect: Does the large number of English language web sites encourage non English speakers to learn English so that they can access them?10The use of language on the Internet can fruitfully be viewed as a co-adoption process.11 Here “adoption” means use of a particular language; we are thus thinking of language training and use as comparable to technology adoption decisions that have been extensively studied. The operator of a web site “adopts” a language by offering its site in that language. Likewise, an individual “adopts” a language by learning that language.More specifically, focusing on the decisions made by web sites and users, we can examine the dynamics of language adoption over three time frames. In the short-term (day to day), individuals decide – based in part on their language skills and in part on the available offerings in different languages – which web sites to visit, how long to stay at these sites, and whether to engage in commercial transactions. These decisions determine actual Internet usage by different10 In the case of language, translation is an ex-post substitute for compatibility. If translation utilities worked well, the issue of language would likely be less important. Given the subtleties involved in language, translation by artificial intelligence is in its infancy and currently works quite poorly.11 Co-adoption processes are common when virtual network effects are present. For example, when there were two rival incompatible formats for 56k modems, Internet Service Providers and consumers selected modem formats, each influenced by the other group’s decisions. This same dynamic arises as well in various server-clientLanguage TPRC.doc, 9/5/01 10:31 PM, Page 5 of 5individuals and groups (such as the group of native French speakers). In the medium term (over a period of several months to a year or two), operators of web sites decide which language to use for their site, and whether to offer their sites in multiple languages (if permitted this choice by their local governments). These decisions are driven in large part by the amount of traffic that a site expects to attract in one language or another, plus the incremental traffic that a site expects to attract by offering its content in multiple languages. Over the long term (more than one to two years), individuals (and their parents and teachers) make decisions about which languages to learn. This decisions are driven in part by the desire to access certain content, as well as the desire to communicate directly with others speaking other languages.In subsequent research, we will to develop a simple theoretical model that captures these three inter-related decisions (visiting web sites, creating content in different languages, and learning languages) that take place continually but over different time frames. We believe that this theoretical treatment, building on the literature on technology adoption and network effects, will support the following general line of reasoning: if in the short term non-native English speakers routinely and extensively use English-language sites, the incentives over the medium term for web sites to make their content available in other languages is reduced, and as a result the incentive over the long term for individuals to learn English as a second language is enhanced, all of which would support the prediction that the Internet will promote English as a global language. On the other hand, if non-native speakers use the Web less, or conduct fewer transactions over the Web than their native-English counterparts (adjusting for other factors such as income and education), web sites will have stronger incentives to offer sites in languages other than English, and English’s first-mover advantage on the Web is more likely to dissipate.In this paper, we explore this issue empirically. To that end, we have obtained a unique data set on Internet use at the individual level in Canada from Media Metrix. Why Canada? Canada provides an ideal setting to examine this issue because English is one of the two official languages. French is, of course, the other official language of Canada.12 If French speakers arearchitectures, and influenced the battle between the Netscape Navigator and Microsoft Internet Explorer browsers,as well as the adoption and use of Sun’s Java.12 Indeed, many of the studies in the economics of language focus on Canada in general, and Quebec in particular. See Grin and Vaillancourt (1997).Language TPRC.doc, 9/5/01 10:31 PM, Page 6 of 6likely to use English content sites where there are few substitutes in French, this suggests that the “first mover advantage” is important and that English may indeed remain the global standard on the Internet.The attractiveness of beginning with a single country (and a single region within a country) is that there is typically greater heterogeneity across countries than within a single country.13 Hence in this paper, we focus primarily on Canada and Quebec. But the techniques discussed are applicable to other regions of the world.14Our preliminary results suggest that in most categories, native French speakers in Quebec are not less likely than native English speakers to use the Internet. There are some slight differences in Internet use patterns: native French-speaking Quebecois are somewhat more likely than their English counterparts to use government sites, while English speaking Quebecois are somewhat more likely to spend time at search sites.We also find that there are some differences in the percent of time spent at English language websites between native French and native English speakers. The differences between the groups in this dimension are less significant for the youngest users (age less than 15) and for the next youngest group of users (ages 15 to 24). This is despite the fact that the youngest native French speakers in Quebec are the least likely to have knowledge of English.While these results are quite preliminary, they suggest that language is much less of a barrier for younger users. These results are consistent with the scenario in which non-native English speakers extensively use English-language sites, the incentives for web sites to make their content available in other languages is reduced, the incentive for individuals to learn English as a second language is enhanced, and that the Internet will promote English as a global language.13 For example, in some countries, local phone calls are metered, while in other countries (such as the U.S. and Canada), there is a fixed monthly charge for local service. Additionally, Internet access speed might differ widelyby country. It can be difficult to find data on and control for these variables.14 At a later stage, we envision examining data from many other countries. There is some casual evidence that the most popular online destinations in Mexico originate in the U.S. and do not target Spanish Speakers. See Heft, D. “Who Rules the Internet in Mexico? Why It’s America, The Standard, June 12, 2001, at/article/0,1902,27096,00.html.Language TPRC.doc, 9/5/01 10:31 PM, Page 7 of 7Our work complements and make use of the growing literature on the economics of language. Grin and Vaillancourt (1997) provide an overview of the literature; a nice survey is provided by Grin (1996). The major research area within this field is the empirical relationship between earnings and language attributes. Two recent papers are Chiswick and Miller (1999), and Zavodny (2000). Grin (1990) and Church and King (1993) examine rational language choice and public policy toward bilingualism using theoretical models. Rauch (1999) shows that common language facilitates international trade in differentiated products. Freund and Weinhold (2000) find that increased access to the Internet increases trade flows among developed countries. To the best of our knowledge, there is no work on the relationship between Internet use and language, which is the focus of this study.The data are described in Section 2. In Section 3, we describe the empirical methodology. Our preliminary results and conclusions are provided in Section 4.2. DataThe project employs a unique data set on Internet use at the individual level in Canada, which comes from Media Metrix, the industry leader in the measurement of Internet use. The data include information on demographics of the user such as income, education, family size, province, etc. Additionally, and this is key for the study, the mother tongue of the user – English or French – is known.The data on Internet use is very detailed. Complete click-stream data are available for the December 2000 period. These data include a separate entry for each URL that is visited, and include the URL domain, as well as the number of active seconds spent at each URL location.15Data were not collected on the language of the web site. Hence, a computer (spider) program was written to check out the language of each URL domain. Although, there were more than 4 million URL full pages, there are “only” approximately 100,000 unique URL domains; an15 Data on total time is available as well. If a user does not enter a key for 60 seconds, the active time count is halted. Hence for less than sixty seconds at a web site, active time is equal to total time. For time spent on a page beyond 60 seconds, active time is less than total time.Language TPRC.doc, 9/5/01 10:31 PM, Page 8 of 8example of a URL domain is and an example of a URL full page is /classifieds/rentals/. Of course, many of the URL domains contain some “interior” pages that are in one language and some interior pages that are in other languages. We employed a crude version of this program for the purposes of obtaining preliminary results.16In order to obtain preliminary results, we employed the “basic” spider program on the approximately 40,000 unique URLs for Quebec. Hence, by this method, we are able to assign a language to websites.We also consider it important to categorize the “type” of website accessed, so we can understand in greater detail how different types of Internet usage are influenced by language . Media Metrix did this categorization for approximately 2/3 of the observations, but this only accounted for 25% of the websites. Research assistants classified a large portion of the remaining websites in Quebec, so that nearly 90 percent of all observations in Quebec have been categorized. Further research assistance will be needed to classify the remaining unclassified web sites from Quebec (and the rest of Canada). Using the Media Metrix descriptions of the categories, we use the following categories: (1) Retail, Business, Finance; (2) Entertainment, News, Sports, Technology; (3) Education; (4) Search/Portals/Directories; (5) Services (Careers, Community, Hobbies, ISPs, Mailboxes, Storage); (6) Government; (7) Adult.The following variables are available for the study:• Active Time – This is the total time (in seconds) that the user was active in each of the seven categories described above.16 Our preliminary spider program classified all unique URL domains that have ASCII characters above 192 (this includes all characters with accents marks such as “é” and “û”) as French. If such characters were not present, the website was characterized as English. Although, this is a fairly crude mechanism, it probably works reasonably well as a first cut, since most of the URL domains in the data set are in either English or French. Of course, precision demands that we employ a more sophisticated spider program or perhaps a program based on standard language identification schemes. See Grefenstette (1995) for an overview. A more sophisticated spider program will eventually have to characterize all of the approximately one million unique URL full pages.Language TPRC.doc, 9/5/01 10:31 PM, Page 9 of 9• Other Time – This is the total active time (in seconds) that the user was active in all other categories17• Age – Age of the user• Gender – A dummy variable that takes on the value 1 if the user is female and 0 if the user is male.• Language – A dummy variable that takes on the value 1 if French is the mother tongue of the user and 0 if English is the mother tongue of the user.• Size – Equal to the number of members of the household, up to a maximum of five. All households with 5 or more members have size equal to five.• Income – The variable takes on the value 1 if the household income is less than $24,000,2 if household income is between $25,000 and $40,000,3 if household income isbetween $40,000 and $60,000, 4 if household income is between $60,000 and $75,000, 5 if household income is between $75,000 and $100,000, and 6 if household incomeexceeds $100,000.• Kids – This is a dummy variable equal to 1 if there are children under age 18 in the household.• Education – The variable takes on the value 1 if the individual has completed middle school or less, 2 if the individual has attended but not completed high school, 3 if theindividual has completed high school, 4 if the individual has attended but not completed college or university, 5 if the individual has an undergraduate degree from a college oruniversity, 6 if the individual has done some post graduate work, but does not have apost-graduate degree, and 7 if the individual has a post-graduate degree.17 As mentioned above approximately 33 percent of the active time has not yet been categorized. These data are included when computing “Other Time.”Language TPRC.doc, 9/5/01 10:31 PM, Page 10 of 10• Pereng – This variable is defined to be the percent of the active time that was spent on websites whose content is in English out of the total active time spent at websites whose content is either English or French.183. MethodologyAre there differences in Internet use between native French and native English speakers? We initially focus on Quebec. The reason for doing so is that there may be significant differences among provinces on variables for which we have no control, such as speed of Internet service. Hence, it makes sense to look at Quebec, which is the only province in Canada with significant proportions of native speakers of both English and French in the Media Metrix sample. According to Statistics Canada, there are 602,865 native English speakers in Quebec and5,728,290 native French speakers in the province. There are 50,585 people who are both native French and English speakers. Approximately 15 percent of our Quebec sample are native English speakers.The first step is to determine whether native language affects Internet use, where Internet use is defined to be active time spent on the Internet, regardless if the active time is spent on French language or English Language websites. We look at this by category, using the seven categories defined above. The next step involves examining what factors determine the percent of the time that each user spends at English language websites. Initially, we examine this by age group.4. Preliminary Results and ConclusionsDescriptive and summary statistics for the Quebec data are contained in Tables 1-3. Table 1 provides summary statistics for all the variables used in the analysis. The table shows overall, English speakers spent approximately 35 percent more time on the Internet. Table 1 also shows that, on average, native English speaking Quebecois accessed English content websites 87 percent of the time, while native French speaking Quebecois accessed English content websites18 The spider program could classify not all websites. This is due primarily to the following reasons: (i) the unclassified websites were services that required the user to enter his/her personal ID or information, (ii) the website Language TPRC.doc, 9/5/01 10:31 PM, Page 11 of 1164 percent of the time. This already suggests that Quebecois are using the web intensively in English.19Table 2 delineates active time by category. Overall, users spend 36 percent of their active time at search/portal sites, followed by services (21 percent of active time) and retail/business (18 percent of active time). Users spend less than two percent on average at government and educational sites combined.Table 3 breaks down the active time by age category and shows that there are significant differences among age groups. In the under 15 age group, native French speakers spent approximately 66 percent more time on the Internet than native English speakers, while in the 25-44 age group, native English speakers spent approximately 77 percent more time on the Internet than native French speakers.20In order to examine whether the differences in Active Time vary across categories, Table 4 presents preliminary ordinary least squares (OLS) regression results with Active Time in seconds as the dependent variable. Table 4 shows that native French-speaking Quebecois are somewhat more likely than their English counterparts to use government sites, while English speaking Quebecois are somewhat more likely to spend time at search sites.21 There is virtually no difference between native French and English speakers in the other categories.22 These preliminary results suggest that in most categories, native French speakers in Quebec are not less likely than native English speakers to use the Internet.23Table 5 examines what factors determine the percent of the time spent at English language websites. Table 5, which reports ordinary least squares (OLS) regressions, shows that language is much less of a barrier for the youngest users (age less than 15) and for the next youngest groupredirected the user more than four times.19 There was little difference in this measure among the various age groups.20 The age group classification was chosen to match the data from Statistics Canada. See table 6.21 The differences are significant at (approximately) the 90 percent level of confidence.22 English speakers spent significantly more active time than French speakers in the adult category.23 These results are still quite preliminary because 10% of the active time data for Quebec has not yet been categorized.Language TPRC.doc, 9/5/01 10:31 PM, Page 12 of 12。

聚酯树脂与异氰酸酯固化剂

聚酯树脂与异氰酸酯固化剂Polyester resin and isocyanate curing agent are commonly used materials in the field of coatings and adhesives. The combination of these two components results in a chemical reaction known as polyurethane formation, which offers a wide range of applications due to its versatile properties. In this discussion, we will explore the problem of using polyester resin and isocyanate curing agent, considering various perspectives such as chemistry, applications, advantages, challenges, and safety concerns.From a chemical perspective, the combination of polyester resin and isocyanate curing agent leads to the formation of a polyurethane network. Polyester resin, which is derived from the reaction between a dicarboxylic acid and a diol, provides the backbone for the polyurethane structure. On the other hand, isocyanate curing agents, such as toluene diisocyanate (TDI) or methylene diphenyl diisocyanate (MDI), contain reactive isocyanate groups that readily react with the hydroxyl groups of the polyesterresin. This reaction, known as an addition polymerization, results in the formation of strong covalent bonds, leading to the crosslinking of the polymer chains and the formation of a three-dimensional network.The combination of polyester resin and isocyanate curing agent offers a wide range of applications. One of the most common applications is in the field of coatings, where polyurethane coatings are known for their excellent durability, chemical resistance, and weatherability. These coatings are widely used in automotive, aerospace, and industrial applications. Additionally, the adhesive properties of polyurethane make it suitable for bonding various substrates, including metals, plastics, and composites. The versatility of polyurethane formulations allows for customization of properties such as flexibility, hardness, and adhesion strength, making it suitable for a wide range of applications.Despite the numerous advantages, there are also challenges associated with using polyester resin and isocyanate curing agents. One significant challenge is thepotential health hazards associated with isocyanates. Isocyanates are known respiratory and skin sensitizers, and exposure to these chemicals should be minimized. Proper personal protective equipment, ventilation systems, and safety protocols should be implemented to ensure the safety of workers. Additionally, the reactivity of isocyanates requires careful handling and storage to prevent premature curing or degradation of the materials. The pot life, or the time available for application, can be limited, and proper mixing ratios and curing conditions should be followed to achieve optimal results.In conclusion, the combination of polyester resin and isocyanate curing agent offers a wide range of applications in the field of coatings and adhesives. The chemical reaction between these two components leads to the formation of a polyurethane network, providing excellent properties such as durability, chemical resistance, and adhesion. However, it is essential to consider the challenges associated with the use of isocyanates,including potential health hazards and the need for proper handling and storage. By understanding the chemistry,applications, advantages, challenges, and safety concerns of using polyester resin and isocyanate curing agent, one can make informed decisions regarding their use in various industries.。

The_Importance_of_Linking_Words_and_Their_Usages_连

The Importance of Linking Words and Their Usages连词的重要性和连词的运用河南郑州市惠济区实验小学张艺文Linking words, also known as transition words or connectors, play a crucial role in writing and speaking. They serve as bridges that connect ideas, sentences, and paragraphs, making the overall communication clearer, more coherent, and easier to understand.When you write, you can use linking words to show how two ideas go together. Linking words can make your writing stronger. For example, without linking words, this passage is choppy and hard to understand:Mary had a terrible morning. She woke up late. She’d forgotten to set the alarm clock. She got dressed quickly. She still missed the school bus. She barely made it to school on time. She got to class. She saw her lunchwas missing.However, with linking words,this passage is easier to read andunderstand:Mary had a terrible morning.She woke up late because she’d forgotten to set the alarm clock. Even though she got dressed quickly, she still missed the school bus. She barely made it to school on time. After she got to class, she saw her lunch was missing.I. The importance of linking wordsThe importance of linking words canbe summarized into the following points:1. Enhance coherenceL i n k i n g w o r d s h e l p e s t a b l i s hlogical connections between sentencesand paragraphs. They ensure that theinformation flows smoothly and thatthe reader or listener can easily follow the train of thought. Without proper linking words, the text may appear disjointed and confusing.2. Improve readabilityBy providing clear connections between ideas, linking words make the text more readable. They allow readers to navigate through the content effortlessly, making it easier for them to grasp the intended message.3. Highlight relationshipsLinking words can indicate various relationships between ideas, such as cause and effect, comparison, contrast, addition, time sequence, and conclusion. They help writers convey their thoughts more precisely and help readers understand the relationships between different concepts.4. Add complexity and depthSophisticated linking words can add complexity and depth to writing. They enable writers to convey nuanced meanings and express complex relationships between ideas, enhancing the overall quality of the content.5. Improve academic writingIn academic writing, linking words are essential for presenting arguments, supporting evidence, and building a coherent essay or research paper. Proper use of linking words can strengthen the structure and flow of academic work, making it more persuasive and compelling.6. Enhance speaking skillsIn oral communication, linking words help speakers organize their thoughts and present information in a structured manner. They allow speakers to express ideas clearly, maintain coherence,and engage the audience effectively.7. Encourage critical thinkingEffective use of linking words encourages writers and speakers to think critically about the connections between ideas. It prompts them to consider the best way to present their thoughts and strengthen their arguments.In conclusion, linking words are essential tools for effective communication in both writing and speaking. They provide the glue that holds ideas together, making the content coherent, readable, and easy to follow. By using linking words appropriately, writers and speakers can convey their messages with clarity, precision, and impact.II. The usages of the linking wordsHere are some common linking words and their usages with examples:1. AdditionLinking words: and, also, besides, furthermore, moreover, in addition, similarly. Example:She loves to read books, and she enjoys watching movies as well.2. ContrastLinking words: but, however, nevertheless, on the other hand, whereas, although, even though. Example:He studied hard; nevertheless, he failed the exam.3. Cause and effectLinking words: because, since, as a result, consequently, therefore, thus. Example:The weather was bad, so the picnic was canceled.4. Time sequenceLinking words: first, next, then, after that, finally, meanwhile, during. Example:First, we went to the zoo, and next, we visited the museum.5. Example and illustrationLinking words: for example, for instance, such as, like. Example:She enjoys outdoor activities, such as hiking and biking.6. ConclusionLinking words: in conclusion, to sum up, overall, all in all. Example:In conclusion, the project was a great success.7. ComparisonLinking words: similarly, likewise, in the same way, compared to, just as. Example:She sings beautifully; likewise, her sister has a melodious voice.8. EmphasisLinking words: indeed, in fact, certainly, surely, of course. Example:It was a difficult task, indeed.9. ConditionLinking words: if, unless, provided that, in case. Example:If it rains, we’ll stay indoors.Remember that the proper use of linking words can greatly enhance the coherence and flowof your writing or speaking. It’sessential to choose the appropriatelinking word depending on thecontext and the relationship youwant to convey between the ideas.。

氨基固化剂英语

氨基固化剂英语Title: Amine Curing Agents in Epoxy CoatingsAmine curing agents are widely used in the formulation of epoxy coatings due to their ability to provide excellent adhesion, chemical resistance, and mechanical properties. These curing agents play a crucial role in the crosslinking of epoxy resins, leading to the formation of a durable and protective coating.There are several types of amine curing agents available, each with its own unique characteristics and applications. One common type is the aliphatic amine curing agents, which are known for their fast cure response and excellent resistance to weathering and UV exposure. These curing agents are often used in outdoor applications such as marine coatings, automotive finishes, and industrial maintenance coatings.Another type of amine curing agents is the cycloaliphatic amines, which offer improved chemical resistance and thermal stability compared to aliphatic amines. These curing agentsare commonly used in demanding environments such as chemical processing plants, oil and gas facilities, and foodprocessing equipment.Aromatic amine curing agents, on the other hand, areknown for their high performance in harsh chemical environments and elevated temperatures. These curing agentsare often used in high-build epoxy coatings for storage tanks, pipelines, and industrial flooring where resistance to aggressive chemicals and abrasion is critical.In addition to the type of amine curing agent, the curing mechanism also plays a significant role in the performance of epoxy coatings. Amine curing agents can be classified as primary, secondary, or tertiary amines based on theirreactivity with epoxy resins. Primary amines are the mostreactive and typically used for fast-cure applications, while secondary and tertiary amines are often employed for their longer pot life and improved flexibility.The choice of the right amine curing agent is critical in achieving the desired performance properties of epoxy coatings. Factors such as cure speed, film hardness, chemical resistance, and flexibility need to be carefully considered when selecting the appropriate curing agent for a specific application.Amine curing agents are typically used in combination with epoxy resins and other additives to formulate a complete coating system. The ratio of epoxy resin to curing agent, as well as the formulation of the coating, can significantly impact the final properties of the cured film. Proper mixing and application procedures are also essential to ensure the full potential of the amine curing agent is realized.In conclusion, amine curing agents are essential components in the formulation of high-performance epoxy coatings. Their unique characteristics and curing mechanisms make them suitable for a wide range of applications, from decorative finishes to protective coatings in harsh environments. Understanding the different types of amine curing agents and their impact on coating performance is crucial for formulators and end-users to achieve the desired results.。

联结的重要性英语作文

联结的重要性英语作文The Importance of Connection。

In today's fast-paced and interconnected world, the importance of connection cannot be overstated. Whether it's through social media, face-to-face interactions, or professional networking, the ability to connect with others is essential for personal and professional success. In this essay, we will explore the various ways in which connection is important and how it can positively impact our lives.First and foremost, connection is crucial for building and maintaining relationships. In our personal lives, having strong connections with friends and family members provides us with a support system that can help us navigate life's challenges. These connections also bring us joy and fulfillment, as we are able to share our experiences and create lasting memories with those we care about. Additionally, strong connections in the workplace can lead to better collaboration, increased productivity, and a morepositive work environment. When we are able to connect with our colleagues and build strong professional relationships, we are more likely to succeed in our careers and feel satisfied with our work.Furthermore, connection plays a key role in our mental and emotional well-being. Studies have shown that people who have strong social connections are happier, healthier, and live longer lives. This is because having a support system can help us manage stress, overcome adversity, and maintain a positive outlook on life. When we feel connected to others, we are more likely to seek help when we need it and to offer support to those in need. This sense of belonging and community can have a profound impact on our overall happiness and sense of fulfillment.In addition to its personal and emotional benefits, connection is also important for professional growth and success. In today's competitive job market, the ability to network and build connections with others is essential for advancing our careers. Whether it's through attending industry events, joining professional organizations, orsimply reaching out to colleagues, making connections with others can open doors to new opportunities and help us stay informed about industry trends and developments. Furthermore, having a strong professional network can provide us with valuable advice, mentorship, and potential job leads, all of which can contribute to our long-term success in our chosen field.Finally, connection is important for fostering understanding and empathy among people from different backgrounds and cultures. In a world that is increasingly diverse and interconnected, the ability to connect with others who may have different perspectives and experiences is essential for building a more inclusive and harmonious society. When we are able to connect with others and truly listen to their stories and experiences, we are better able to understand and appreciate the richness of human diversity. This, in turn, can lead to greater empathy, cooperation, and a more peaceful coexistence among people from all walks of life.In conclusion, the importance of connection cannot beoverstated. Whether it's for building and maintaining relationships, promoting mental and emotional well-being, advancing our careers, or fostering understanding and empathy, the ability to connect with others is essential for personal and professional success. By recognizing the importance of connection and actively seeking to build and maintain meaningful connections with others, we can enrich our lives and contribute to a more connected and compassionate world.。

同伴效应介绍英文作文

同伴效应介绍英文作文英文：The peer effect, also known as the social influence, refers to the impact that peers have on each other's attitudes, behaviors, and beliefs. It is a powerful force that can shape our decisions, even when we are not aware of it.For example, imagine a group of friends who all smoke cigarettes. Even if one member wants to quit, the pressure from the group may make it difficult for them to do so. On the other hand, if the group is made up of non-smokers, the same person may find it easier to quit because of the support and encouragement from their peers.The peer effect can also be seen in academic settings. If a student is surrounded by peers who are motivated and hardworking, they may be more likely to adopt those same traits. Conversely, if the majority of their peers aredisengaged or uninterested in school, the student may be more likely to follow suit.中文：同伴效应，也称为社会影响，指的是同伴对彼此的态度、行为和信仰所产生的影响。

阿司匹林载药淀粉微球吸附性能的研究

阿司匹林载药淀粉微球吸附性能的研究杨黎燕;尤静【期刊名称】《化工科技》【年(卷),期】2013(021)003【摘要】以可溶性淀粉为原料,研究了淀粉微球在反相悬浮体系中对阿司匹林的吸附作用.探讨了交联剂用量、引发剂用量、反应时间及搅拌速度对微球药物吸附量的影响,并考察其体外释放情况.结果表明:当交联剂用量为12 g/L,引发剂用量为3 g/L时,60℃下中速搅拌2.0h,淀粉微球对阿司匹林有较大吸附作用.在酸性条件下,阿司匹林淀粉微球在8h内有较好释放,交联剂用量对释药速率有较大影响.%Aspirin Crosslinked Starch Microspheres (Asp-CSMs) were synthesized with soluble starch as material by reversed phrase suspension method.The effects of reaction time,crosslinking agent dosage and initiator dosage on the adsorption quantity,and the stirring speed were discussed.And the release of Asp-CSMs in vitro was investigated.The results showed that the proper synthesis conditions were that:reaction time,crosslinking agent dosage and initiator dosage,and the stirring speed respectively was 2 h,12 g/L,3 g/L,moderate speed.Vitro release of the drug showed that Asp-CSMs had satisfactory releasing within 8 h under acidic condition.The dosage of crosslinking agent had greater effect to drug releasing rate.【总页数】4页(P27-29,62)【作者】杨黎燕;尤静【作者单位】西安医学院药学院,陕西西安710021;西安医学院药学院,陕西西安710021【正文语种】中文【中图分类】O636.1+2【相关文献】1.交联共聚淀粉微球对阿司匹林吸附性能的研究 [J], 姚少芳2.载药淀粉微球的反相乳液法合成及吸附性能研究 [J], 赵新法;李仲谨;蔡京荣;肖浩江;余丽丽;朱雷3.交联共聚淀粉微球对阿司匹林吸附性能的研究 [J], 姚少芳;赵新法4.阿司匹林载药淀粉微球吸附热力学和释药动力学的研究 [J], 杨黎燕;尤静;余丽丽5.淀粉微球吸附阿司匹林性能的研究进展 [J], 刘佳;张胜飞;白雪;问娟娟因版权原因，仅展示原文概要，查看原文内容请购买。

双向因果固定效应

双向因果固定效应下载温馨提示:该文档是我店铺精心编制而成，希望大家下载以后，能够帮助大家解决实际的问题。

文档下载后可定制随意修改，请根据实际需要进行相应的调整和使用，谢谢!并且，本店铺为大家提供各种各样类型的实用资料，如教育随笔、日记赏析、句子摘抄、古诗大全、经典美文、话题作文、工作总结、词语解析、文案摘录、其他资料等等，如想了解不同资料格式和写法，敬请关注!Download tips: This document is carefully compiled by theeditor. I hope that after you download them,they can help yousolve practical problems. The document can be customized andmodified after downloading,please adjust and use it according toactual needs, thank you!In addition, our shop provides you with various types ofpractical materials,such as educational essays, diaryappreciation,sentence excerpts,ancient poems,classic articles,topic composition,work summary,word parsing,copy excerpts,other materials and so on,want to know different data formats andwriting methods,please pay attention!标题：双向因果关系与固定效应模型：理论与应用一、引言在社会科学、经济学以及许多其他研究领域中，双向因果关系和固定效应模型是理解和分析复杂现象的重要工具。

油漆专业英语

Title: Paint Professional EnglishBase Coat: The initial layer of paint applied to a surface, which provides the foundation for subsequent coats.Blistering: The formation of bubbles or pimples on the painted surface, often caused the expansion of trapped air or moisture.Catalyst: A substance that speeds up a chemical reaction, often used in paint to help it dry or harden.Chalking: The process which the paint film gradually loses its pigments, resulting in a powdery surface.Enamel: A type of paint that dries to a hard, glossy finish, typically used for wood and metal surfaces.Film Formation: The process which the paint dries and forms a continuous, solid layer on the surface.Gloss: The measure of a paint's reflectivity; high gloss finishes are shiny, while low gloss finishes are more matte.Opacity: A term describing how well a paint obscures the surface beneath it; paints with high opacity provide better coverage.Primer: A preparatory coating applied to surfaces before painting to improve adhesion and increase the life of the finish.Sheen: The degree of light reflectance from a painted surface, ranging from flat (no sheen) to high gloss.Solvent: A liquid used to thin paint or clean equipment, which evaporates during the drying process.Tint: The act of adding color to a paint base to achievea specific hue or shade.Title: Paint Professional EnglishViscosity: The thickness or resistance to flow of a paint, which can affect application and the final appearance of the coat.Drying Time: The period it takes for paint to transition from a liquid to a solid state, which can vary depending onthe type of paint and environmental conditions.Fade Resistance: The ability of paint to retain itsoriginal color when exposed to sunlight or other UV light sources over time.Peeling: The lifting or flaking of the paint film fromthe substrate, often due to poor adhesion or underlyingsurface issues.Stain Resistance: The paint's capacity to resistabsorbing and showing stains from spills, dirt, or other contaminants.TouchUp: The process of applying a small amount of paint to cover a blemish or repair a damaged area withoutrepainting the entire surface.Undercoating: A coating applied before the final paint layer to provide additional protection, smoothness, or to enhance the appearance of the topcoat.VOCs (Volatile Organic Compounds): Chemicals found in many paints that can evaporate into the air and contribute to environmental and health issues; low or zero VOC paints are increasingly popular.Aggregate: Finely ground materials added to paint for texture, such as sand in an antislip floor paint.Conversion Coating: A type of coating that chemically alters the surface of a material to improve adhesion and corrosion resistance before painting.Eggshell Finish: A paint finish with a low sheen, smoother than flat but not as glossy as semigloss, often used in living spaces for a subtle reflective quality.Flake: Small, thin pieces of material, often metallic, used in coatings to create a decorative or protective finish.Marbling: A decorative painting technique that mimics the appearance of marble, often used in fine art and faux finishing.Pigment: The solid particles suspended in a vehicle or binder that gives paint its color; different pigments can affect the paint's durability and appearance.Roller Marks: The visible lines or patterns left on a painted surface the nap of a roller, which can be minimized with proper technique and roller selection.Sagging: The downward flow of paint after application, which can lead to an uneven finish, often due to applying the paint too thickly.Wet Edge: The freshly painted area of a surface that must be maintained to ensure a seamless, uniform appearance when applying additional coats or adjacent areas.Title: Paint Professional EnglishChemical Resistance: The ability of a paint film to withstand exposure to various chemicals without degrading, which is crucial in industrial and laboratory settings.Grain Filling: The process of applying a filler to openpored surfaces like wood to create a smooth base for painting, enhancing the final appearance and durability.Matte Finish: A nonreflective, flat finish that absorbs light and is often used in areas where minimizing visual distractions is desired.Overbrushing: A painting technique where a brush is used to apply paint in a way that leaves a slightly textured, brushed appearance, adding depth and character to the surface.Sealer: A type of coating applied to porous surfaces to prevent the absorption of subsequent coats of paint, ensuring even coverage and extending the life of the paint job.Spattering: The fine mist of paint droplets that canoccur during application, often a result of using improper techniques or tools.Tint Base: The base color of a paint to which tinting colors are added to achieve a desired shade or hue.UV Resistance: The paint's ability to withstand the damaging effects of ultraviolet light, which can cause fading and degradation over time.ZincRich Primer: A type of primer that contains a high percentage of zinc, used to protect steel and other metals from corrosion providing a sacrificial layer.Aggregatebroadcasting: The process of throwing or scattering sand, quartz, or other small particles onto wet paint to create a textured surface, often for antislip purposes.CrossLinking: A chemical reaction that occurs when the paint dries, creating a network of strong bonds within thepaint film, which enhances its durability and resistance to wear.Dry Film Thickness: The thickness of the paint after it has dried and cured, which is an important specification for achieving the desired performance and longevity of the coating.Inkjet Printing on Paint: An advanced technique that allows for the direct printing of images or patterns onto painted surfaces, offering customization and unique design possibilities.Latex Paint: A waterbased paint that uses latex oracrylic as the binder, known for its ease of application,fast drying time, and low odor.Masking: The process of covering areas that should not be painted with tape or other materials to create clean, sharp lines and prevent paint from getting onto unintended surfaces.SolventBased Paint: A type of paint that uses a solvent, such as turpentine or mineral spirits, as the thinner, known for its strong odor and slow drying time but often preferred for its durability and finish.。

光环效应英文作文

光环效应英文作文1. The halo effect is a fascinating phenomenon that affects our perceptions and judgments of others. It refers to the tendency to attribute positive qualities or traits to a person based on their overall impression or a single positive characteristic. It's like wearing rose-colored glasses when we see someone, making them appear better than they actually are.2. You know when you meet someone for the first time and they have this magnetic charm that instantly draws you in? That's the halo effect at work. We tend to assume that if someone is physically attractive, they must also be intelligent, kind, and successful. It's like we automatically give them a free pass to all the positive qualities we associate with beauty.3. But here's the thing, the halo effect doesn't just apply to physical appearance. It can also extend to other aspects of a person's life. For example, if someone issuccessful in their career, we might assume that they are also trustworthy, competent, and good in other areas of their life. It's like their success creates this halo around them, making us believe that they can do no wrong.4. The halo effect can have both positive and negative consequences. On one hand, it can lead to admiration and respect for someone who possesses positive qualities. It can also create opportunities and open doors for them, simply because of the positive halo that surrounds them. But on the other hand, it can blind us to their flaws and prevent us from seeing them as they truly are.5. Have you ever been in a situation where you thought someone was amazing based on their reputation, only to be disappointed when you got to know them better? That's the halo effect playing tricks on you. It's like we build up this image of perfection in our minds, and when reality doesn't match up, it can be quite a shock.6. It's important to be aware of the halo effect and not let it cloud our judgment. We need to look beyond thesurface and dig deeper to truly understand a person. Just because someone has a halo doesn't mean they are without flaws. We should strive to see people for who they are, rather than who we want them to be.7. So, the next time you meet someone who seems too good to be true, take a step back and question your assumptions. Don't let the halo effect deceive you. Remember that everyone has their strengths and weaknesses, and it's only by seeing the whole picture that we can form a more accurate judgment.。