Rui Guimarães

Setting the length of the planning horizon in the vehicle replacement problem

In some formulations of the vehicle replacement problem, in particular those leading to repair limit type models, the alternative policies are evaluated and compared over a fixed planning horizon. Although it has been widely recognised that the optimal policies derived under these formulations depend critically on the length of the horizon, no method has been presented so far to set appropriately this parameter. In this paper, the authors describe a method which overcomes this shortcoming. Once the best policy has been derived from a given finite horizon with length H, such a policy is repeated indefinitely over time and an equivalent annual rent is computed. The parametrisation of H leads to the definition of an annual rent function with a sequence of nearly equidistant local minima. It is suggested that in practice the second local minimum of this function leads to an adequate choice of the parameter H. The method can be applied both to stochastic and deterministic cost modelling situations. The method was tested using both real data from large samples of different types of passenger vehicles and artificially generated data.

OR in Portugal: Past achievements and current perspectives

Abstract This paper reviews some of the most important aspects of the recent history of OR in Portugal, namely the key role played by academics, the position of OR in the curricula of Portuguese universities, successful applications in industry and the development of APDIO, the Portuguese OR Society. After discussing some negative aspects of the current stage of development of OR in our country, the review ends with a suggestion for a new line of action considered essential in order to ensure a favourable evolution of OR in Portugal.

Simulation-optimisation: The method and its application in the analysis of grain terminal operations

Abstract Simulation-optimisation is presented as a method for solving complex decision problems. It consists of coupling a simulation model with a search method. The paper describes a case study where the method was applied in the analysis of grain terminal operations. A considerable computational effort is required in its application. This becomes critical when the evaluation of the objective function or any of the problem constraint functions is directly associated with the occurrence of ‘rare events’. The case study illustrates how these difficulties can be overcome by a careful exploitation of the particular structure of the problem under analysis.

Purchasing Maize Futures Under a Deadline: Testing and Risk-Yield Evaluation of a Price-Trend Buying Policy

A purchasing rule based on short-term forecasts derived from Taylor’s price-trend model was developed in previous research, for the scenario described as ‘purchasing under a deadline’. Such a rule, when applied to the purchasing of maize futures, was shown to lead to purchasing costs significantly lower than the average market price.

[Reuse of Clinical Records for Scientific Research: Legal Issues Related to the Authorization of the Holders and Anonymisation].

* Co-primeiros autores. 1. Department of Public Health, Forensic Sciences and Medical Education. Faculty of Medicine. University of Porto. Porto. Portugal. 2. MEDCIDS Community Medicine, Health Information and Decision Department. Faculty of Medicine. University of Porto. Porto. Portugal. 3. Hospital Centre São João. Porto. Portugal. 4. Department of Sciences. Institute of Research and Advanced Training in Health Sciences and Technologies. Institute of Health Sciences. Gandra. Portugal. 5. UCIBIO-REQUIMTE Laboratory of Toxicology. Department of Biological Sciences. Faculty of Pharmacy. University of Porto. Porto. Portugal.  Autor correspondente: Ricardo Jorge Dinis-Oliveira. ricardinis@sapo.pt Recebido: 27 de dezembro de 2017 Aceite: 07 de maio de 2018 | Copyright

The NATO Advanced Research Workshop on “A Reappraisal of the Efficiency of Financial Markets”

Thirty one papers were presented at the Nato workshop on the efficiency of financial markets held at Sesimbra in April 1988. This overview paper by the workshop directors summarises the workshop papers and offers suggestions for further research.