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