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2. M.I. Rabinovich and A.L. Fabrikant, “Nonlinear Waves in Nonequilibrial Media,” Izv. Vuzov: Radiofiz., 19, 721–766 (1976).
3. P.A. Sturrock, “In what sense do slow waves carry negative energy?,” J. Appl. Phys., 31, 2052–2056 (1976).
4. J.R. Pierce, Almost All About Waves [Russian translation], Mir, Moscow (1976), Chs.3–4.
5. M.V. Nezlin, “Waves with negative energy and anomalous Doppler effects,” UFN, 120, 481–495 (1976).