Institution: | 1. Center for Research and Development in Mathematics and Applications, Department of Mathematics,University of Aveiro, 3810-193 Aveiro, Portugal 2. Center for Research and Development in Mathematics and Applications, Department of Mathematics,University of Aveiro, 3810-193 Aveiro, Portugal ;Department of Mathematics, Faculty of Engineering and Natural Sciences, Lusophone University of Humanities and Technologies, 1749-024 Lisbon, Portugal |