The turbulent diffusion eta(T) of a large-scale magnetic field B-0 is numerically studied in two-dimensional magnetohydrodynamic turbulence with an imposed shear flow. We demonstrate that a shear flow plays a dual role, quenching transport through shear destruction and enhancing it via resonance. Specifically without resonance eta(T)proportional to B-0(-4) with no shear (rms shearing rate=Omega=0) and eta(T)proportional to Omega(-2.7) for B-0=0, while with resonance eta(T)proportional to B-0(-2)proportional to Omega(-2). These results indicate that the absence of resonance is responsible for the most catastrophic reductions in transport
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