Authors
Ivan Beloev
University of Ruse “Angel Kanchev”, Ruse, Bulgaria
Diyana Kinaneva
University of Ruse “Angel Kanchev”, Ruse, Bulgaria
Georgi Georgiev
University of Ruse “Angel Kanchev”, Ruse, Bulgaria
Plamen Zahariev
University of Ruse “Angel Kanchev”, Ruse, Bulgaria