1. Faculty of Forest Industry, University of Forestry, Kl. Ohridsky Blvd. 10, 1756 Sofia, Bulgaria
2. Faculty of Hydrotechnics, Civil Engineering and Geodesy, University of Architecture, Hristo Smirnenski Blvd. 1, 1046 Sofia, Bulgaria
3. Faculty of Physics, Sofia University “St. Kliment Ohridski”, J. Bouchier Blvd. 5, 1164 Sofia, Bulgaria