1. Institute of Metal Science, Equipment and Technologies with Hydro- and Aerodynamics Centre “Acad. A. Balevski”, Bulgarian Academy of Sciences, 67 “Shipchenski Prohod” Blvd., 1574 Sofia, Bulgaria
2. Institute of Mechanics, Bulgarian Academy of Sciences, Acad. Georgi Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria