Dust covering factor, silicate emission, and star formation in luminous QSOs R. Maiolino, O. Shemmer, M. Imanishi, H. Netzer, E. Oliva, D. Lutz and E. Sturm A&A, 468 3 (2007) 979-992 Published online: 11 April 2007 DOI: 10.1051/0004-6361:20077252