Affiliation: | 1. Math and Physics Department, Belgorod State Agricultural Academy, 1 Vavilov St., Maysky, Belgorod, 308503, Russia 2. National Scientific Center “Kharkov Institute of Physics and Technology” NAS of Ukraine, 1 Akademicheskaya, St., Kharkov, 61108, Ukraine 3. Institute of Radiophysics and Electronics NAS of Ukraine, 12 Ac. Proskura St., Kharkov, 310085, Ukraine; e-mail
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