V.N. Biktashev, “Drift of a reverberator in an active medium due
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in Nonlinear Waves II.  Dynamics and evolution, pp. 87–96, 
    
eds A.V. Gaponov-Grekhov, M.I. Rabinovich
    and J. Engelbrecht, Springer, Berlin, ISSN 978-3-642-74366-5,
    1989 (English version).