1. Department of Biophysics and Radiobiology, Faculty of Biology, Sofia University “St. Kliment Ohridski”, 8 Dragan Tzankov blvd., 1164 Sofia, Bulgaria
2. Department of Genetics, Faculty of Biology, Sofia University “St. Kliment Ohridski”, 8 Dragan Tzankov blvd., 1164 Sofia, Bulgaria
3. Faculty of Mechanical Engineering, Technical University of Sofia, 8 Kl. Ohridski blvd., 1784 Sofia, Bulgaria
4. Georgi Nadjakov Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tsarigradsko Chaussee blvd., 1784 Sofia, Bulgaria