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Publicações

Publicações por SEM

2015

A hybrid path-relinking method for solving two-stage stochastic integer problems

Autores
Amorim, P; Costa, AM; Almada Lobo, B;

Publicação
INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH

Abstract
Path relinking has been used for solving deterministic problems by exploring the neighborhood of elite solutions in an intelligent way. We present an algorithm that combines a mixed-integer linear solver with a truncated path-relinking method in order to solve two-stage stochastic integer problems with complete recourse and first-stage integer variables. This method takes advantage of a possible scenario-based decomposition in an innovative way. Therefore, path relinking is used to combine optimized solutions from different scenarios in order to pursue good stochastic solutions. To assess the computational performance of this method, we use the stochastic lot sizing and scheduling problem dealing with perishable products. In this problem, first-stage decision variables are linked to production sequences and production quantities. After the uncertain demand is unveiled, the second-stage variables decide on the inventory usage. Computational results show a clear advantage of the proposed method when compared to a state-of-the-art mixed-integer linear solver.

2015

Towards a Customer-Driven Value Chain Framework - A Set-Based Oriented Approach

Autores
Bastos, J; Azevedo, A; Avila, P;

Publicação
RISKS AND RESILIENCE OF COLLABORATIVE NETWORKS

Abstract
In today's business, consumers are challenging manufacturers by increasingly demanding low volumes of innovative, fashionable and inexpensive products; adopting high quality standards; responding in smaller intervals of time, and with high configurability and parameterization. This omnipresent scenario poses challenging opportunities for collaborative networked organizations. The present paper addresses the main collaborative business processes tailored for responsiveness and efficient use of knowledge on customized manufacturing environments through a lean-based framework proposal for collaborative networks inspired in the Set-Based Concurrent Engineering (SBCE) methodology. In particular this work describes the ongoing implementation of the proposed concepts through a web-based collaborative portal.

2015

Nonconformity tracking and prioritisation matrix: an approach for selecting nonconformities as a contribution to the field of TQM

Autores
Donauer, M; Pecas, P; Azevedo, AL;

Publicação
PRODUCTION PLANNING & CONTROL

Abstract
Selecting quality improvement projects among a variety of mutually competing ones is characterised by prioritisation. In practice, this is often done by the rule of thumb, following a single attribute criterion or by subjective preferences of individual stakeholders of a project team. An approach to track systematically nonconformities and to identify those critical ones that should be prioritised based on multi-attribute criteria is presented. The approach is introduced and its purpose is explained. After the background of relevant topics is given, the method's importance in research and for practitioners is derived. Steps of the approach are portrayed and an application case of a mature industrial company, integrated in the supply-chain of the automotive industry, is presented. Elements of quality tools and techniques are used as attributes, namely failure mode and effect analysis and Pareto diagram. Results based on industrial data indicate that the use of this approach contributes to support informed and structured prioritisation decisions, which foster a more efficient improvement of future quality-based projects.

2015

iMOOC on Climate Change: Evaluation of a Massive Open Online Learning Pilot Experience

Autores
Rocio, V; Coelho, J; Caeiro, S; Nicolau, P; Teixeira, A;

Publicação
INTERNATIONAL REVIEW OF RESEARCH IN OPEN AND DISTRIBUTED LEARNING

Abstract
MOOCs are a recent phenomenon, although given their impact, they have been subject to a large debate. Several questions have been raised by researchers and educators alike regarding their sustainability, both economically and as an efficient mode of education provision. In this paper we contribute to this discussion by presenting a case study of the MOOC on Lived Experiences of Climate Change, which piloted the iMOOC pedagogical model developed at Universidade Aberta (UAb), the Portugese Distance Learning University. The iMOOC is a hybrid model which incorporates elements from existing MOOCs but adds other features drawn from UAb's experience with online learning and aims at better integrating in the larger context of the institutional pedagogical culture. The iMOOC implied also an integration of platforms - Moodle and Elgg. The pilot course had more than one thousand registrations, and it was the largest MOOC course on Portuguese language delivered so far. We discuss the effort required to design and deliver the course, the technological solution developed, and the results obtained. We registered a moderate effort to create and run the course, ensured by internal staff from the University. The technological solution was a success: an integrated architecture combining well-established, well-tested open software. The completion rate was 3.3%, but the high success of this innovative learning experience was demonstrated by the active involvement of about 50% of the registered participants, that followed the course until the end. Lessons learned from this experience and future research on the field are also discussed.

2015

Hybrid tabu search and a truncated branch-and-bound for the unrelated parallel machine scheduling problem

Autores
Sels, V; Coelho, J; Dias, AM; Vanhoucke, M;

Publicação
COMPUTERS & OPERATIONS RESEARCH

Abstract
We consider the problem of scheduling a number of jobs on a number of unrelated parallel machines in order to minimize the makespan. We develop three heuristic approaches, i.e., a genetic algorithm, a tabu search algorithm and a hybridization of these heuristics with a truncated branch-and-bound procedure. This hybridization is made in order to accelerate the search process to near-optimal solutions. The branch-and-bound procedure will check whether the solutions obtained by the meta-heuristics can be scheduled within a tight upper bound. We compare the performances of these heuristics on a standard dataset available in the literature. Moreover, the influence of the different heuristic parameters is examined as well. The computational experiments reveal that the hybrid heuristics are able to compete with the best known results from the literature.

2015

Assessing Technical and Economic Efficiency of the Artisanal Dredge Fleet in the Portuguese West Coast

Autores
Oliveira, MM; Camanho, AS; Gaspar, MB;

Publicação
OPERATIONAL RESEARCH

Abstract
The bivalve dredge fleet is by far the most extensively studied fleet among the Portuguese artisanal segment. It is considered one of the most important artisanal fisheries, essentially due to the number of fishermen and vessels involved and to the high volume and value of the catches. The present study aimed to explore the efficiency of the dredge fleets that operated in the west coast of Portugal between 2006 and 2012. The methodology was based on the use of data envelopment analysis to assess vessels' efficiency. The inputs considered included the number of days at sea, a biomass stock indicator, and the characteristics of the vessels (power, length and tonnage). The annual fishing quota per vessel was also included in the model as a contextual factor. In the technical efficiency analysis, the outputs were defined by the weight of captures for three different bivalve species. Using data on the prices of each species in the wholesale market, revenue efficiency was also estimated to complement the technical efficiency analysis. The results allowed to gain insights concerning the performance of both Northwest and Southwest fleets, considering both technical and economic aspects of the fishery. It was also possible to identify the benchmark vessels, whose practices should be followed by the other vessels of the fleet.

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