**Author details**

Antoni Ivanov\*, Viktor Stoynov, Kliment Angelov, Radostin Stefanov, Dimitar Atamyan, Krasimir Tonchev and Vladimir Poulkov Technical University of Sofia, Sofia, Bulgaria

\*Address all correspondence to: astivanov@tu-sofia.bg

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
