Costas P. Pappis

A comparative assessment of measures of similarity of fuzzy values

The properties of several measures of similarity of fuzzy values are presented and compared. The measures examined include the measure based on the union and intersection, the one based on the maximum difference and the one based on the differences as well as the sum of corresponding grades of membership. It is shown that several properties are common to all measures. However, some properties do not hold for all of them.

Fuzzy relational equations and the inverse problem

Abstract The inverse problem concerned with fuzzy relations is investigated. The conditions for the existence of a solution are shown and an analytical solution is given. A method for the improvement of the solution is proposed.

Value approximation of fuzzy systems variables

Abstract The notion of approximation of the values of fuzzy variables is discussed. A measure of proximity of fuzzy values is introduced and a definition of approximately equal fuzzy values is given. It is shown that the property of approximation is preserved when the maxmin compositional rule of inference is applied to approximately equal values of fuzzy variables and fuzzy relations. This is not true in the case of the upper bound of the solutions of the ‘inverse problem’.

Scheduling jobs with values exponentially deteriorating over time

Abstract In this paper we study a new type of single machine scheduling problem, where the critical scheduling parameter, that is job value, deteriorates exponentially over time. A heuristic algorithm for finding a sub-optimal solution of the problem and the computer program created for testing the algorithm are presented. The algorithm has been tested in a case of remanufacturing of PCs and it has been shown that it yields near optimal schedules.

Operations research and environmental planning

This paper aims at specifying the contribution of OR to environmental planning. To this purpose a framework for classifying relevant literature is proposed, according to which the literature has been reviewed and discussed with respect to both thematic and methodological aspects. It is shown that during the last few years, OR has extended its scope to include notably environmental applications. Several OR methods and tools are employed either to identify the type and intensity of environmental problems, or to assist environmental planners to effectively cope with these problems. It is illustrated that ORs relationship with environmental planning is dynamic and interactive in the sense that from the complexity of the issues examined stems the need to develop and/or adapt specific methodological tools and thus contributes to the development of both scientific fields.

An environmental analysis of the reverse supply chain of SLI batteries

An environmental analysis of the used starting, lighting and ignition (SLI) batteries sector, based on the logistics involved in the recovery process and the tools available for measuring the environmental impact of such a process, is performed in this paper. The different phases of the reverse supply chain of used batteries are analysed, and the operations and practices involved are related with the impact on the environment, using a life cycle analysis. The analysis is exemplified by using the results of a case study. In addition, the situation in different countries from a legislative point of view is presented. Finally, the results of the analysis are summarised and several important issues arising from the analysis are discussed.

Applying life cycle inventory to reverse supply chains: a case study of lead recovery from batteries

Abstract The increasing demand for efficient management of used products after the end of their life cycle stems from the increasing awareness of modern society about possible threats against the environment. Used starter or lead–acid batteries contain lead up to 65%, which is also valuable after the end of their life cycle. Recycling of lead gives rise to some environmental problems associated with its collection, processing and recycling and, finally, entering the main (forward) supply chain. In this paper, the lead recovery from old batteries is examined using life cycle inventory analysis (LCIA). The reverse supply chain of used starter or lead–acid batteries is outlined and analyzed. A model for this product system is formulated, which is used to identify the lead emissions as well as all the environmental exchanges through materials balance. The proposed model formulation, which is appropriately adapted to the needs of the reverse supply chain, is used as a tool in a LCIA in order to identify those stages in the battery life cycle that give rise to the greatest environmental burdens. A similar analysis is also made for the case of disposal. The model may be used in order to assess all the associated impacts in an in-depth life cycle analysis (LCA). A preliminary comparison between the two end-of-life scenarios in terms of their environmental inputs and outputs is also attempted. Thus, based on several assumptions, an inventory analysis referring to the above chains has been conducted whose results have been summarized in an Inventory table, which produces comprehensive information about each life stage of the examined end-of-life scenarios.

Computer-supported collaborative argumentation and fuzzy similarity measures in mutiple criteria decision making

Abstract Group decision making is usually performed in the presence of conflicting goals and criteria, brought up by spatially dispersed parties with different backgrounds and interests. Recent advances in information technology and computer science may satisfactorily address a variety of related problems, such as communication among the decision makers and efficient elicitation and representation of the domain knowledge. Furthermore, they may significantly automate the decision making process itself. On the other hand, the inherent uncertainty of the problem advocates the use of approximation models, often coming from the fuzzy sets discipline. This paper presents an integrated framework for multiple criteria decision making among groups on the World Wide Web. The agents involved use a fully implemented argumentative discourse system to pursue their criteria and objectives, the aim being the specification of the desired solution to the problem. The system organizes the collective knowledge in a discussion graph with truth maintenance and consistency checking features. Fuzzy similarity measures are then involved in order to assess alternative existing solutions with respect to the desired one. Scope and purpose We view multiple criteria decision making as a collaborative process, where decision makers have to follow a series of communicative actions in order to establish a common belief on the dimensions of the problem. Such dimensions may concern the choice criteria, the existing or desired alternative solutions, or the objective function, to mention some. This paper presents a framework for multiple criteria decision making among groups. Our approach exploits recent advances in information technology and manages to (i) remove the communication impediments among spatially dispersed decision makers, (ii) efficiently represent the domain knowledge, (iii) develop efficient mechanisms to structure and consistently maintain the decision analysis, and (iv) automate the multiple criteria decision making process per se. The framework is based on a fully implemented system, namely H ermes , which enhances decision making by supporting argumentative discourse among decision makers. The system is implemented in Java and runs on the World Wide Web, thus providing relatively inexpensive access to a broad public.

A framework for group decision support systems : Combining AI tools and OR techniques

Abstract Work on the implementation of Group Decision Support Systems has to exploit recent advancements of computer science. Existing frameworks for single-user Decision Support Systems, based on well-established Operations Research methods such as Multicriteria Decision Making techniques, have to be integrated with successful technical developments in electronic communication and computing. Starting from the presentation of the related Operations Research background, this paper proceeds by discussing challenges coming from the areas of Computer-Supported Cooperative Work and Information Systems on the World Wide Web platform. Based on this discussion, a framework for an ‘open’, computer-mediated Group Decision Support System is proposed. The term ‘open’ is related to a platform-independent system, which can efficiently support alternative types of goals and control protocols between its users.

Extended Design Principles for Closed Loop Supply Chains: Optimising Economic, Logistic and Environmental Performance

Closed loop supply chains aim at closing goods flows thereby limiting emission and residual waste, but also providing customer service at low cost. In this paper we study design principles for closed loop supply chains, both from a theoretical perspective and a business case. Obvious improvements can be made by applying traditional ‘forward logistics’ principles. Also new, life cycle driven principles need to be applied. This can be supported by advanced management tools such as LCA and LCC.