Stoyanov, Lyubomir
Zhekova, Maya
Stefanov, Aleksander
Stefanov, Ivan
Paulus, Gerhard G.
Dreischuh, Alexander
Funding for this research was provided by:
Projekt DEAL
Article History
Received: 10 August 2020
Accepted: 18 November 2020
First Online: 15 December 2020
Competing interests
: The authors declare no competing interests.