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Aldina Correia, João Matias, Pedro Mestre and Carlos Serodio

Derivative-free nonlinear optimization filter simplex

The filter method is a technique for solving nonlinear programming problems. The filter algorithm has two phases in each iteration. The first one reduces a measure of infeasibility, while in the second the objective function value is reduced. In real optimization problems, usually the objective function is not differentiable or its derivatives are unknown. In these cases it becomes essential to use optimization methods where the calculation of the derivatives or the verification of their existence is not necessary: direct search methods or derivative-free methods are examples of such techniques. In this work we present a new direct search method, based on simplex methods, for general constrained optimization that combines the features of simplex and filter methods. This method neither computes nor approximates derivatives, penalty constants or Lagrange multipliers.

Open access

Nuno Ricardo Pombo Marques, João Carlos De Oliveira Matias, Raquel Dos Reis Baptista Teixeira and Francisco Miguel Ribeiro Proença Brojo

This article provides technical details concerning the development and implementation of Hazard Analysis Critical Control Points (HACCP) in one of the largest bakeries of Cova da Beira - Portugal. A generic HACCP plan in accordance with legal requirements was made through a detailed audit and analysis of data collected in the company. It was verifi ed by overview of the HACCP system implemented in the bakery, that there was no reduction in quality of the fi nal product during the manufacturing process and the implementation of the requirements was particularly strong, having been instrumental the total commitment and sense of responsibility of all workers.

Open access

Fernando P.S. Rocha, Hugo Louro, Ricardo Matias, João Brito and Aldo M. Costa

Abstract

Our aim was to verify the concurrent validity of a maximal taekwondo specific test (TST) to predict VO2max through an explanatory model. Seventeen elite male taekwondo athletes (age: 17.59 ± 4.34 years; body height: 1.72 ± 6.5 m; body mass: 61.3 ± 8.7 kg) performed two graded maximal exercise tests on different days: a 20 m multistage shuttle run test (SRT) and an incremental TST. We recorded test time, VO2max, ventilation, a heart rate and time to exhaustion. Significant differences were found between observed and estimated VO2max values [F (2, 16) = 5.77, p < 0.01]; post-hoc subgroup analysis revealed the existence of significant differences (p = 0.04) between the estimated VO2max value in the SRT and the observed value recorded in the TST (58.4 ± 6.4 ml/kg/min and 52.6 ± 5.2 ml/kg/min, respectively). Our analysis also revealed a moderate correlation between both testing protocols regarding VO2max (r = 0.70; p = 0.005), test time (r = 0.77; p = 0.02) and ventilation (r = 0.69; p = 0.03). There was no proportional bias in the mean difference (t = -1.04; p = 0.313), and there was a level of agreement between both tests. An equation/model was used to estimate VO2max during the TST based on the mean heart rate, test time, body height and mass, which explained 74.3% of the observed VO2max variability. A moderate correlation was found between the observed and predicted VO2max values in the taekwondo TST (r = 0.74, p = 0.001). Our results suggest that an incremental specific test estimates VO2max of elite taekwondo athletes with acceptable concurrent validity.

Open access

Tatiana Miraldes, Susana Garrido Azevedo, Fernando Bigares Charrua-Santos, Luís António F. Mendes and João Carlos Oliveira Matias

Abstract

This paper aims to study the influence of Information Technologies on the competitiveness of companies/supply chains. That is, it intends to analyse if the adoption of Information Technologies contributes to improve costs, time and customer service. To attain this objective a case study and content analysis methodology is used. Results indicate that there is a positive relation between the adoption of technologies, namely RFID, A.R. and the competitiveness of companies/supply chains. By the use of these technologies it is possible to improve several processes across the supply chain, as well as the reduction of costs related to labor, improvement in inventories and management of transport channels as well as an improvement on customer service. The improvement of these indicators has as consequence a gain in competitiveness allowing the companies to respond to the market needs in a differentiated way increasing by this way the customers’ satisfaction. As the information technologies have been considered very important for businesses it is crucial to improve our understanding on the main advantages associates with them and their contribution for competitiveness improvement of companies and supply chains, so this paper represents an important contribution for academics and professionals in this field.

Open access

Anna Kokkevi, Eleftheria Kanavou, Clive Richardson, Anastasios Fotiou, Sonia Papadopoulou, Karin Monshouwer, Joao Matias and Deborah Olszewski

Abstract

Aim – Previous studies of the association between polydrug use and other risk behaviours have generally been limited to specific substances and a small number of behaviours. The aim of this study is to obtain better insight into polydrug use (comprising legal and illegal substances: tobacco, alcohol, tranquillisers/sedatives, cannabis, and other illegal drugs) and its association with co-occurring problem behaviours drawn from various broad domains (sexual, aggressive, delinquent, school achievement, relationships) among European adolescents. METHODS – Data were obtained from 101,401 16-year-old students from 35 European countries participating in the 2011 ESPAD survey. Associations between polydrug use and other problem behaviours were examined by multinomial and binary logistic regression analyses. RESULTS – Tranquillisers/sedatives appeared among the commonest combinations in the polydrug use pattern, especially for females. A strong trend was found between levels of involvement with polydrug use and other problem behaviours for both genders. The highest associations with polydrug use were for problems with the police, risky sexual behaviour and skipping school. Gender differences showed higher prevalences among boys than girls of problem behaviours of aggressive, antisocial type, while girls prevailed over boys in relationship problems. CONCLUSION – An incremental relationship exists between the level of involvement with polydrug use and the co-occurrence of problem behaviours. Preventative interventions should consider the misuse of tranquillisers/sedatives within the context of polydrug use by adolescents and expand their target groups towards multiple problem behaviours.