University of Ruse — Prof. Angel Smrikarov University of Ruse - Assoc. Prof. Em. Stoyanka Smrikarova University of Ruse — Assoc. Prof. Tsvetelina Harakchiyska University of Ruse — Prof. Tsvetozar Georgiev University of Ruse — Mr. Vladimir Dochev University of Ruse — Prof. Tzvetomir Vassilev University of Ruse — Dr. Yordan Kalmukov