Fig. 3.

The density of states (DOS) of a silica aerogel synthesized by hydrolysis of tetramethoxysilane without the addition of ammonia to the reaetion water. The open circles are TOF measurements at 160 K using 8 Å incident neutrons. The dotted curve indieates the DOS that fits neutron spin-eeho data. The solid line is a fit to neutron backscattering data and is extrapolated as shown by the dashes throughout the high-frequency fracton region. The dashed lines indicate the asymptotic phonon as well as the independent bend and stretch eontributions [12].