\Bibitem{Mak83} \by E.~G.~Maksimov \paper Phonons: theory and experiments \jour UFN \yr 1983 \vol 139 \issue 3 \pages 556--557 \mathnet{http://mi.mathnet.ru/ufn8627} \crossref{https://doi.org/10.3367/UFNr.0139.198303j.0556}