1. Institute of Electronics, Bulgarian Academy of Sciences, Tzarigradsko Chaussee 72, 1784 Sofia, Bulgaria
2. Department of Joining and Welding Technology, Brandenburg University of Technology, Platz der Deutschen Einheit 1, 03046 Cottbus, Germany
3. Institute of Metal Science, Equipment and Technologies with Center for Hydro- and Aerodynamics, Bulgarian Academy of Sciences, 67 Shipchenski Prohod Blvd., 1574 Sofia, Bulgaria
4. Department of Mathematics, Informatics and Natural Sciences, Technical University of Gabrovo, 4 Hadzhi Dimitar Str., 5300 Gabrovo, Bulgaria