Autori:
1. Svilen Rachev, Technical University of Gabrovo, Department of Physics, Chemistry and Ecology 4 Hadzhy Dimitar str., Bulgaria
2. Hristo Hristov, Technical University of Gabrovo, Department of Physics, Chemistry and Ecology 4 Hadzhy Dimitar str., Bulgaria
3. Georgi Iliev, Bulgaria

Sažetak rada