REQUIMTE/DQ, Faculty of Science and Technology, University Nova de Lisboa, Campus de Caparica, 2829-516, Caparica, Portugal.|REQUIMTE/DQ, Faculty of Science and Technology, University Nova de Lisboa, Campus de Caparica, 2829-516, Caparica, Portugal.|REQUIMTE/DQ, Faculty of Science and Technology, University Nova de Lisboa, Campus de Caparica, 2829-516, Caparica, Portugal.|DEQ, Faculty of Engineering, University do Porto, Rua Dr. Roberto Frias s/n, 4200-465, Porto, Portugal.|REQUIMTE/DQ, Faculty of Science and Technology, University Nova de Lisboa, Campus de Caparica, 2829-516, Caparica, Portugal. rmo@fct.unl.pt.