Evolution of protoplanetary discs driven by MHD turbulence and turbulence and other agents

After reviewing our current understanding of how the magnetorotational instability (MRI) operates in protoplanetary disks, we present preliminary results on the dynamical evolution of such systems, based on the predicted spatial distribution of viscous torques. One-dimensional, a-disk models are constructed for protoplanetary disks incorporating different values of the a parameter to reflect different agents giving rise to the torques driving disk evolution. We take into account the effects of turbulent viscosity resulting from the MRI, of torques resulting from self-gravity, prescribed in terms of an effective viscosity, and of other agents characterized by a less efficient turbulent viscosity. The resulting disk structure and evolution is drastically different than that predicted by uniform a models or by layered accretion models for protoplanetary disks.