  In these proceedings we present recent efforts to understand the energetics
of magnetohydrodynamic (MHD) turbulence driven by the magneto-rotational
instability (MRI). These studies are carried out in the local (shearing box)
approximation using the Athena simulation code. Athena is a higher order
Godunov algorithm based on the piecewise parabolic method (PPM), the corner
transport upwind (CTU) integration algorithm, and the constrained transport
(CT) algorithm for evolving the magnetic field. This algorithm is particularly
suited for these studies owing to the conservation properties of a Godunov
scheme and the particular implementation of the shearing box source terms used
here. We present a variety of calculations which may be compared directly to
previously published results and discuss them in some detail. The only
significant discrepancy found between the results presented here and in the
published literature involves the turbulent heating rate. We observe the
presence of recurrent channel solutions in calculations involving a mean
vertical magnetic field and the associated time lag between the energy
injection and thermalization rate. We also present the results of a shearing
box calculation which includes an optically thin radiative term with a cooling
rate selected to match the turbulent heating rate. Some properties which we
find uniformly present in all of the calculations presented here are
compressible fluctuations, spiral waves and weak shocks. It is found that these
compressible modes dominate the temporal fluctuations in the probability
distribution functions for most of the thermodynamic variables; only the
specific entropy is relatively immune to their effects.
