1. Full Professor, Dept. of Mathematics and Applications, Univ. of Naples “Federico II,” via Claudio 21, 80125 Naples, Italy.
2. Associate Professor, Dept. of Civil and Mechanical Engineering, Univ. of Cassino and the Southern Lazio, via Di Biasio 43, 03043 Cassino, Italy.
3. Assistant Professor, Dept. of Mathematics and Applications, Univ. of Naples “Federico II,” via Claudio 21, 80125 Naples, Italy (corresponding author).
4. Dept. of Mathematics and Applications, Univ. of Naples “Federico II,” via Claudio 21, 80125 Naples, Italy.
5. Full Professor, Dept. of Civil, Architectural and Environmental Engineering, Univ. of Naples “Federico II,” via Claudio 21, 80125 Naples, Italy.