On the convergence of Magnetorotational turbulence in stratified   isothermal shearing boxes
  We consider the problem of convergence in stratified isothermal shearing boxes with zero net magnetic flux. We present results with the highest resolution to-date--up to 200 grid-point per pressure scale height--that show no clear evidence of convergence. Rather, the Maxwell stresses continue to decrease with increasing resolution. We propose some possible scenarios to explain the lack of convergence based on multi-layer dynamo systems. 
G. Bodo, F. Cattaneo, A. Mignone and P. Rossi
astro-ph.HE astro-ph.SR