1. Institute of Gravitation and Cosmology, RUDN University, ul. Miklukho-Maklaya 6, 117198 Moscow, Russia
2. Research Laboratory of Geometry, Dynamical Systems and Cosmology, University of the Aegean, 83200 Samos, Greece
3. Department of Marine Sciences, University of the Aegean, University Hill, 81100 Mytilene, Greece