The Raman coupling function in amorphous silica and the nature of the long-wavelength excitations in disordered systemsA. Fontana, R. Dell'Anna, M. Montagna, F. Rossi, G. Viliani, G. Ruocco, M. Sampoli, U. Buchenau and A. WischnewskiEurophys. Lett., 47 1 (1999) 56-62DOI: https://doi.org/10.1209/epl/i1999-00351-x