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Vila Real de Santo António, Portugal

Avelino C.P.,UTAD
Optimal Control Applications and Methods | Year: 2010

In this paper, we consider a class of nonlinear optimization problems that arise from the discretization of optimal control problems with bounds on both state and control variables. We are particularly interested in degenerate cases, i.e. when the linear independence constraint qualification is not satisfied. For these problems, we analyse the basic global convergence properties and the numerical behaviour of a multiplier method that updates multipliers corresponding to inequality constraints instead of dealing with multipliers associated with equality constraints. Numerical results obtained for several instances of a discretized optimal control problem governed by a semi-linear elliptic equation are included and indicate that this method is robust on degenerate cases, compared with other nonlinear optimization solvers. Copyright © 2009 John Wiley & Sons, Ltd. Source

Azevedo-Perdicoulis T.P.,UTAD | Jank G.,RWTH Aachen | Lopes dos Santos P.,FEUP
Multidimensional Systems and Signal Processing | Year: 2015

In this paper, the gas dynamics within the pipelines is modelled as a repetitive process with smoothing. Controllability and observability criteria when the system is steered through initial and boundary data, which is achieved by an adequate choice of the homogeneity, are obtained. From the point of view of the technical applications, it seems to make more sense to consider boundary data controls as for instance in the management of high pressure gas networks. Stability criteria suitable computer simulations are also included. © 2015 Springer Science+Business Media New York Source

Pereira F.A.M.,CITAB UTAD | Morais J.J.L.,CITAB UTAD | Dourado N.,CITAB UTAD | De Moura M.F.S.F.,University of Porto | Dias M.I.R.,UTAD
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2011

Fracture energy release rate under mode II loading of bovine cortical bone is determined using a miniaturized testing device of the end loaded split test. The energy release rate is evaluated by means of a data reduction scheme based on specimen compliance, beam theory and crack equivalent concept. Experimental tests were carried out to evaluate the Resistance curve which provides a successful method to characterize fracture behavior of quasi-brittle materials like bone. A numerical analysis including a cohesive damage model was used to validate the procedure. It was demonstrated that the end loaded split test and proposed data reduction scheme provide a valuable solution for mode II fracture characterization of bone. © 2011 Elsevier Ltd. Source

Monzon A.,University of Tras os Montes e Alto Douro | Vaz da Silva S.,Direccao Regional de Florestas do Centro | Manso F.T.,UTAD
Forest Ecology and Management | Year: 2012

The ever growing presence of red deer (Cervus elaphus) in the forest perimeters of the Lousã Mountain area of central Portugal is causing local conflicts among stakeholders who report damage to agriculture and forest. One of the forest perimeter regions (Lousã) has been selected to develop a Portuguese Standard for the Forest Certification System (PEFCC). The aim of this study was to determine whether any real damage or impact caused by red deer had in fact occurred in the area. Four types of forest cover were considered and nine plots (150m 2) were randomly selected within each type. All trees were recorded and the diameter at breast height (dbh) was measured. The characteristics of marks of each rubbed tree were recorded. The amount of foliage browsing was estimated visually as a percentage except in situations of regeneration where the total number of consumed leader or lateral shoots was counted. The shrub layer was scored according to height and cover. Altitude and distance to the nearest village, river or national road were measured in each plot to analyse their influence on the degree of damage. Cluster analysis allowed us to observe a damage pattern across the study plots that separated browsing damage from fraying damage. Pine regeneration type vegetation suffered significant damage by browsing but the percentage of damage due to fraying was not significantly different between forest types. Some species of trees, such as sweet chestnut (Castanea sativa), were more susceptible to fraying damage. In all cases, deer clearly preferred rubbing on the smallest trees.A classification tree where the percentage of rubbed trees was the response variable, showed that diameter at breast height (dbh), distance to national road and the number of trees were primary contributors to probability of damage. We propose that new indicators should be introduced into the certification process and that there is also a need to find a balance between different stakeholders' interests and wildlife. © 2011 Elsevier B.V. Source

Santos E.L.,Federal University of Rio de Janeiro | Novaes J.S.,Federal University of Rio de Janeiro | Reis V.M.,UTAD | Giannella-Neto A.,Federal University of Rio de Janeiro
International Journal of sports Medicine | Year: 2010

The purpose of this work was to apply a simple method for acquisition of power output (PO) during the Wingate Anaerobic Test (WAnT) at a high sampling rate (SR) and to compare the effect of lower SR on the measurements extracted from the PO. 26 male subjects underwent 2 WAnTs on a cycle ergometer. The reference PO was calculated at 30 Hz as a function of the linear velocity, the moment of inertia and the frictional load. The PO was sampled at 0.2, 0.5, 1, 2 and 5 Hz. Both the peak (16.03±2.22 W·kg-1) and mean PO (10.34±1.01 W·kg-1) presented lower relative values when the SR was lower. Peak PO was attenuated by 0.29-42.07% for decreasing sampling rates, resulting in different values for 0.2 and 1 Hz (P<0.001). When the SR was 0.2 Hz, the time to peak was delayed by 53.81% (P<0.001) and the fatigue index was attenuated by 22.12% (P<0.001). In conclusion, due to the differences achieved here and the fact that the peak flywheel frequency is around 2.3 Hz, we strongly recommend that the PO be sampled at 5 Hz instead of 0.2 Hz in order to avoid biased errors and misunderstandings of the WAnT results. © Georg Thieme Verlag KG. Source

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