A NEUTRON SCATTERING STUDY OF THE DENSITY OF VIBRATIONAL STATES OF FRACTAL SILICA AEROGELS G. CODDENS, R. VACHER, T. WOIGNIER, J. PELOUS and E. COURTENS J. Phys. Colloques, 50 C4 (1989) C4-151-C4-156 DOI: 10.1051/jphyscol:1989424