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Article History

Received: 13 March 2018

Revised: 22 May 2018

Accepted: 1 November 2018

First Online: 3 September 2019

COMPLIANCE WITH ETHICAL STANDARDS

: <i>Conflict of interest.</i> The authors declare no explicit and potential conflicts of interest associated with the publication of this article.

: <i>Statement of compliance with standards of research involving humans as subjects.</i> All studies were performed in accordance with the principles of biomedical ethics set out in the 1964 Declaration of Helsinki and its later amendments and approved by the Ethics Committee of St. Petersburg State University.

: <i>Informed consent.</i> Each study participant provided a signed voluntary written informed consent after explanations of potential risks and benefits as well as the nature of the forthcoming investigations.