Department of Mathematics, University of Aveiro, Campus Universitário de Santiago, Aveiro, Portugal. vera@ua.pt.|Department of Electronics, Telecommunications and Informatics, University of Aveiro, Campus Universitário de Santiago, Aveiro, Portugal. cbastos@ua.pt.|Department of Electronics, Telecommunications and Informatics, University of Aveiro, Campus Universitário de Santiago, Aveiro, Portugal. cbastos@ua.pt.|Department of Medical Sciences and Institute of Biomedicine - iBiMED, University of Aveiro, 3810-193 Aveiro, Portugal, Campus Universitário de Santiago, Aveiro, Portugal. raquelsilva@ua.pt.