Pskov FilimonovAnatoliyV.Pskov State University, 2 Lenina Sq., Pskov 180000, Russiakafotist@pskgu.ru Read more about Anatoliy V. Filimonov Жучков Константин БорисовичPskov State University, 2 Lenina Sq., Pskov 180000, RussiaZhuchkov.konstantin@rambler.ru Read more about Жучков Константин Борисович