1. Informetrics Research Group, Ton Duc Thang University, Ho Chi Minh City, Vietnam
2. Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Vietnam
3. St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia
4. Central Astronomical Observatory at Pulkovo of RAS, Pulkovskoye Chaussee 65/1, 196140 St. Petersburg, Russia
5. Sternberg Astronomical Institute of the Lomonosov Moscow State University, University Avenue 13, Moscow 119234, Russia
6. Department of Physics & Astronomy, University of California Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095-1547, USA
7. Special Astrophysical Observatory, Russian Academy of Sciences, 369167 Nizhnij Arkhyz, Russia
8. Department of Astronomy, University of Texas at Austin, 2515 Speedway, Mail Stop C1400, Austin, TX 78712, USA