M.  Zanatta, Baldi, G., Brusa, R. S., Egger, W., Fontana, A., Gilioli, E., Mariazzi, S., Monaco, G., Ravelli, L., and Sacchetti, F., ?Structural Evolution and Medium Range Order in Permanently Densified Vitreous SiO2?, Physical Review Letters, vol. 112, p. 045501, 2014.