Torus models for obscuration in type 2 AGN
  We discuss a clumpy model of obscuring dusty tori around AGN. Cloud-cloud collisions lead to an effective viscosity and a geometrically thick accretion disk, which has the required properties of a torus.   Accretion in the combined gravitational potential of central black hole and stellar cluster generates free energy, which is dissipated in collisions, and maintains the thickness of the torus. A quantitative treatment for the torus in the prototypical Seyfert 2 nucleus of NGC 1068 together with a radiative transfer calculation for NIR re-emission from the torus is presented. 
Thomas Beckert, Wolfgang J. Duschl, Bernd Vollmer