Multiple melting in blends of poly(vinylidene fluoride) with isotactic poly(ethyl methacrylate)

Multiple melting phenomena have been studied in blends of poly(vinylidene fluoride) (PVF₂) with low molar mass isotactic poly(ethyl methacrylate) (it-PEMA). In all blends, as well as in pure PVF₂, a transition (T₁) was observed prior to the main melting point (T₂). T₁ is probably connected with the melting of secondarily-crystallized material. In addition to this, a high temperature melting endotherm (T₃) was observed, which could be ascribed completely to recrystallization of PVF₂. The highest transition (T₄) was caused by melting of the σ form of PVF₂. From Hoffman-Weeks plots—T₂ vs. crystallization temperature, T_c — it could be concluded that no thermody amic depression of the melting point of PVF₂ occurred in the blends. The stabilities of PVF₂ crystallites in the various blends were derived from the slopes of Hoffman-Weeks plots and were in good agreement with lamellar thicknesses found from SAXS measurements.     

Tool support for verifying UML activity diagrams

We describe a tool that supports verification of workflow models specified in UML activity diagrams. The tool translates an activity diagram into an input format for a model checker according to a mathematical semantics. With the model checker, arbitrary propositional requirements can be checked against the input model. If a requirement fails to hold, an error trace is returned by the model checker, which our tool presents by highlighting a corresponding path in the activity diagram. We summarize our formal semantics, discuss the techniques used to reduce an infinite state space to a finite one, and motivate the need for strong fairness constraints to obtain realistic results. We define requirement-preserving rules for state space reduction. Finally, we illustrate the whole approach with a few example verifications.     

Gel-spun polyethylene fibres

The tensile strength of gel-spun polyethylene fibres hot-drawn to the maximum draw ratio depends on the spinning conditions such as spinning speed, spinline draw ratio and spinning temperature. High deformation rates during spinning introduce defects and fibres with poor ultimate properties are produced. These defects are already present before the hot-drawing step and can be detected indirectly by wide-angle X-ray scattering, since they are accompanied by preferential c-axis orientation parallel to the fibre axis and a shish-kebab structure. The introduction of flaws such as chain scission and tight knots can be prevented by avoiding spinline stretching and/or increasing the spinning temperature. This is due to the fact that higher spinning temperatures reduce the span of time in which the chains remain entangled and behave like a real network. Due to their lamellar/shish-kebab structure, the extracted fibres show a mechanical behaviour which to some extent is characteristic of composites.     

Improving the quality of vocational students’ collaboration and knowledge acquisition through instruction and joint reflection

International Journal of Computer-Supported Collaborative Learning - New societal demands call for schools to train students’ collaboration skills. However, research thus far has focused...     

Dynamics of poly(ethylene oxide) chains in water

Dynamic moduli of dilute aqueous solutions of four poly(ethylene oxide) samples were measured as a function of frequency at four temperatures. From the measurements on two quite monodisperse samples the value of the Peterlin parameter was determined using a shifting procedure. A definite decrease in was observed when going from 10°C to 40°C. Polydisperse samples were analysed by treating them as consisting of one monodisperse high-molecular mass fraction which does, and a remaining polydisperse lower-molecular mass fraction which does not contribute to the reduced dynamic moduli.     

Requirements-Level Semantics and Model Checking of Object-Oriented Statecharts

In this paper we define a requirements-level execution semantics for object-oriented statecharts and show how properties of a system specified by these statecharts can be model checked using tool support for model checkers. Our execution semantics is requirements-level because it uses the perfect technology assumption, which abstracts from limitations imposed by an implementation. Statecharts describe object life cycles. Our semantics includes synchronous and asynchronous communication between objects and creation and deletion of objects. Our tool support presents a graphical front-end to model checkers, making these tools usable to people who are not specialists in model checking. The model-checking approach presented in this paper is embedded in an informal but precise method for software requirements and design. We discuss some of our experiences with model checking. Correspondence and offprint requests to: Rik Eshuis, Department of Computer Science, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. Email: eshuis@cs.utwente.nl     

Specification and verification of harmonized business-process collaborations

In the area of business-to-business (B2B) collaboration, original equipment manufacturers (OEMs) are confronted with the problem of spending a considerable time and effort on coordinating suppliers across multiple tiers of their supply chains. By supporting inter-organizational business-process collaborations with service-oriented technology, a scope for more efficient and effective supply-chain coordination is anticipated. This paper defines a formal framework, called eSourcing, for specifying structurally harmonized inter-organizational business-process collaborations. The framework permits verification of harmonized processes before their enactment. Moreover, the framework uses private and public layers to protect competitive knowledge of the individual partners. In the research project CrossWork, the eSourcing framework has been integral for harmonizing on an external level the intra-organizational business processes of a service-consuming and one or many service-providing organizations.     

Internet-Based Support for Process-Oriented Instant Virtual Enterprises

The ever-increasing complexity of contemporary products and services demands business supply chains that ultimately involve a large number of autonomous organizations. Competitive markets require these chains to be highly agile, effective, and efficient, which organizations can achieve by forming dynamic virtual enterprises within supplier networks, called instant virtual enterprises (IVEs). The authors present the CrossWork system, which helps these organizations efficiently create and operate IVEs by providing automated, Internet-based support for the composition, setup, and execution of global business processes. This article uses the automotive domain to illustrate the system's optimal use.     

Understanding Social Cohesion Differences in Common Interest Housing Developments

The worldwide upsurge of common interest housing developments (CIDs) has stirred up debates regarding community development and social cohesion. Critics have argued that CIDs lack social cohesion because people regulate the community via rules and contracts rather than through social relationships and mutual contact. However, some research points at high levels of socialization and friendship in CIDs, facilitated by the homogeneity of the community in terms of socio-economic class and cultural background. This paper takes the uncertainty regarding social cohesion in CIDs as its starting point. On the basis of empirical research in three cases, this paper shows that social cohesion in CIDs varies, and that themes such as golfing or ecological sustainability play an important role in the development of social cohesion. The paper shows how a clear theme facilitates the development of shared symbols and rituals, and provides logical points of social encounter and interaction.