Boyadzhieva, Vladimira Vasileva http://orcid.org/0000-0002-6780-5810
Stoilov, Nikolay Rumenov http://orcid.org/0000-0001-7183-086X
Stoilov, Rumen Malinov http://orcid.org/0000-0002-6340-9650
Article History
Received: 10 May 2020
Accepted: 31 August 2020
First Online: 15 September 2020
Compliance with ethical standards
: No part of the manuscript including the table and figure were published elsewhere.
: The authors declare non-conflict of interest.
Free to read: This content has been made available to all.