1. Andronikashvili Institute of Physics, 6 Tamarashvili Street, Tbilisi 0177, Georgia
2. Javakhishvili Tbilisi State University, 3 Chavchavadze Avenue, Tbilisi 0128, Georgia
3. California State University, 2345 E. San Ramon Avenue, M/S MH37, Fresno 93740, USA