  We perform global three-dimensional simulations of accretion disks
integrating the compressible, non-viscous, but diffusive MHD equations. The
disk is supposed to be isothermal. We make use of the ZEUS-3D code integrating
the MHD equations and added magnetic diffusivity. We measure the efficiency of
the angular-momentum transport. Various model simulations delivered transport
parameters of alpha_SS=0.01 to 0.05 which are consistent with several local
numerical investigations. Two of the models reach a highly turbulent state at
which alpha_SS is of the order of 0.1. After a certain stage of saturating of
the turbulence, Reynolds stress is found to be negative (inward transport) in
many of the models, whereas Maxwell stresses dominate and deliver a positive
(outward) total transport. Several of the models yield strongly fluctuating
Reynolds stresses, while Maxwell stresses are smooth and always transport
outwards.
  Dynamo action is found in the accretion disk simulations. A positive
dynamo-alpha is indicated in the northern hemisphere of the most prominent run,
coming along with negative kinetic and current helicities (all having the
opposite sign on the southern side). The dipolar structure of the magnetic
field is maintained throughout the simulations, although indication for a decay
of antisymmetry is found. The simulations covered relatively thick disks, and
results of thin-disk dynamo models showing quadrupolar fields may not be
compatible with the results presented here.
