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