1. Department of Physics “Gh. Asachi” Technical University, Iasi 700050, Romania
2. Department of Civil Engineering, University of Thessaly, 383 34 Volos, Greece
3. Department of Mathematics, Jadavpur University, Kolkata 700 032, West Bengal, India
4. School of Applied Mathematics and Physical Sciences, National Technical University of Athens, 157 80 Athens, Greece
5. Department of Mathematics, Amity University, Kolkata 700135, India
6. Department of Physics, University of Trieste, 34127 Trieste, Italy