Ignatovich, S. Yu. , V. N. Karazin Kharkiv National university, Svobody sqr., 4, Kharkiv, Ukraine, 61022 Ignatovich, Svetlana, V. N. Karazin Kharkiv National University Ignatovich, Svetlana, V. N. Karazin Kharkiv National University, Svobody sqr., 4, Kharkiv, Ukraine, 61022