Models of Accretion Disks
  An accretion flow onto a supermassive black hole is the primary process
powering quasars. However, a geometry of this flow is not well constrained.
Both global MHD simulations and observations suggest that there are several
emission components present in the nucleus: an accretion disk, hot plasma
(corona or sphere) with electrons scattering the optical and UV photons, and an
outflow (wind/jet). The relative location and size of these emission
components, as well as their "interplay" affect the emerging quasar spectrum. I
review briefly standard accretion disk models and the recent progress, point
out discrepancies between the predicted and observed spectra and discuss some
issues in fitting these models to the broad-band spectral energy distribution
of quasars. I present examples of models fitted simultaneously to the
optical-UV-X-ray data and possible constraints on the parameters.
