1. G. N. Shah, H. Razdan, G. L. Bhat, and G. M. Ali, Nature (London) 313, 773 (1985).
2. L. S. Bratolyubova-Tsulukidze, E. A. Grachev, O. R. Grigoryan, V. E. Kunitsyn, B. M. Kuzhevskij, D. S. Lysakov, O. Yu. Nechaev, and M. E. Usanova, Adv. Space Res. 34, 1815 (2004).
3. A. Chilingarian, A. Daryan, K. Arakelyan, A. Hovhannisyan, B. Mailyan, L. Melkumyan, G. Hovsepyan, S. Chilingaryan, A. Reymers, and L. Vanyan, Phys. Rev. D: Part., Fields, Gravitation, Cosmol. 82, 043009 (2010).
4. A. Chilingarian, N. Bostanjyan, and L. Vanyan, Phys. Rev. D: Part., Fields, Gravitation, Cosmol. 85, 085017 (2012).
5. A. Chilingaryan, N. Bostanjyan, T. Karapetyan, and L. Vanyan, in Proceedings of the Cosmic Ray Summer School, Nor Amberd International Conference Center, Nor Amberd, Armenia, June, 2012, Ed. by A. Chilingaryan (Nor Amberd, 2012); A. Chilingarian, N. Bostanjyan, and L. Vanyan, Phys. Rev. D: Part., Fields, Gravitation, Cosmol. 85, 085017 (2012).