1. Department of Mathematics and Physics “Ennio De Giorgi”, University of Salento, Via per Arnesano, 73100 Lecce, Italy
2. CNR NANOTEC-Institute of Nanotechnology, Via Monteroni, 73100 Lecce, Italy
3. Institute of Advanced Materials (INAM), Universidad Jaume I, Av. Sos Baynat s/n, 12071 Castelló, Spain
4. Department of Civil, Energy, Environmental and Materials Engineering (DICEAM), Mediterranean University, 89122 Reggio Calabria, Italy
5. Dipartimento di Architettura, Costruzione e Design (ArCoD), Politecnico di Bari, Via Orabona 4, 70125 Bari, Italy
6. State Key Laboratory on Integrated Optoelectronics, College of Electronic Science & Engineering, Jilin University, Changchun 130012, P. R. China
7. Department of Mathematical and Computer Sciences, Physical Sciences and Earth Sciences, University of Messina, 98166 Messina, Italy
8. Department of Applied Mathematics, Campinas State University,13083-859 São Paulo, Brazil