1. Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bontchev St., Bl. 4, 1113 Sofia, Bulgaria
2. Faculty of Dental Medicine, Medical University of Sofia, St. Georgi Sofiiski Blvd., 1431 Sofia, Bulgaria
3. Institute of Metal Science, Equipment and Technologies with Hydro- and Aerodynamics Centre “Acad. A. Balevski”, Bulgarian Academy of Sciences, 67 Shipchenski Prohod Street, 1113 Sofia, Bulgaria
4. Faculty of Chemistry and Pharmacy, Sofia University, 1 James Bourchier Blvd., 1164 Sofia, Bulgaria