1. Instituto Politécnico de Coimbra, ESAC, Bencanta, Coimbra, Portugal
2. Department of Mathematics, CIDMA - Center for Research and Development in Mathematics in Applications, University of Aveiro, Aveiro, Portugal
3. Department of Mathematics, iBiMED - Institute of Biomedicine, CIDMA -Center for Research and Development in Mathematics and Applications, University of Aveiro, Aveiro, Portugal