1. Department of Engineering, University of Sannio, Corso Garibaldi 107, 82100 Benevento, Italy
2. Department of Mathematics, University of Salerno, Via Ponte don Melillo Stecca 8, 84084 Fisciano (SA), Italy
3. Department of Economics and Law, University Parthenope of Napoli, Via Generale Parisi 13, 80132 Napoli, Italy
4. Department of Information Engineering, Computer Science and Mathematics, University of l'Aquila, Via Vetoio 67100 L'Aquila, Italy