  We measure the turbulent resistivity in the nonlinear regime of the MRI, and
evaluate the turbulent magnetic Prandtl number. We perform a set of numerical
simulations with the Eulerian finite volume codes Athena and Ramses in the
framework of the shearing box model. We consider models including explicit
dissipation coefficients and magnetic field topologies such that the net
magnetic flux threading the box in both the vertical and azimuthal directions
vanishes. We first demonstrate good agreement between the two codes by
comparing the properties of the turbulent states in simulations having
identical microscopic diffusion coefficients (viscosity and resistivity). We
find the properties of the turbulence do not change when the box size is
increased in the radial direction, provided it is elongated in the azimuthal
direction. To measure the turbulent resistivity in the disk, we impose a fixed
electromotive force on the flow and measure the amplitude of the saturated
magnetic field that results. We obtain a turbulent resistivity that is in rough
agreement with mean field theories like the Second Order Smoothing
Approximation. The numerical value translates into a turbulent magnetic Prandtl
number Pm_t of order unity. Pm_t appears to be an increasing function of the
forcing we impose. It also becomes smaller as the box size is increased in the
radial direction, in good agreement with previous results obtained in very
large boxes. Our results are in general agreement with other recently published
papers studying the same problem but using different methodology. Thus, our
conclusion that Pm_t is of order unity appears robust.
