PACS:92.60.Bh, 92.60.hv, 43.10.Eg (all) DOI:10.1070/PU1964v006n04ABEH003581 URL: https://ufn.ru/en/articles/1964/4/a/ Citation: Polubarinova-Kochina P Ya "Aleksandr Aleksandrovich Fridman (on the seventy-fifth anniversary of his birth)" Sov. Phys. Usp.6 467–472 (1964)