Cascades of shocks in Active Galactic Nuclei and their radiation
  We discuss accretion flows on massive black holes in which different elements of the flow (clumps) have velocities that may differ substantially. We estimate the consequence of collisions between these clumps as they come close to the central object and calculate the resulting radiation. We show that this radiation is similar to that observed in the optical to X-ray spectral domain in Seyfert galaxies and quasars. We also show that the large scale accretion is likely to be clumpy when arriving in the active region and that the clumps keep their identity between collisions. 
T. J.-L. Courvoisier and M. Turler