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A numerical model of isotropic homogeneous turbulence with helical forcing is investigated. The resulting flow, which is essentially the prototype of the α 2 dynamo of mean-field dynamo theory, produces strong dynamo action with an additional large scale field on the scale of the box (at wavenumber k = 1; forcing is at k = 5). This large scale field is(More)
Key words Sun: magnetic fields – magnetohydrodynamics (MHD) We use direct numerical simulations of forced MHD turbulence with a forcing function that produces two different signs of kinetic helicity in the upper and lower parts of the domain. We show that the mean flux of magnetic helicity from the small-scale field between the two parts of the domain can(More)
Reaction-diffusion equations based on a poly-merization model are solved to simulate the spreading of hypothetic left and right handed life forms on the Earth's surface. The equations exhibit front-like behavior as is familiar from the theory of the spreading of epidemics. It is shown that the relevant time scale for achieving global homochirality is not,(More)
Evidence for non-Fickian diffusion of a passive scalar is presented using direct simulations of homogeneous isotropic turbulence. The results compare favorably with an explicitly time-dependent closure model based on the tau approximation. In the numerical experiments three different cases are considered: ͑i͒ zero mean concentration with finite initial(More)
Several one and two dimensional mean field models are analyzed where the effects of current helicity fluxes and boundaries are included within the framework of the dynamical quenching model. In contrast to the case with periodic boundary conditions, the final saturation energy of the mean field decreases inversely proportional to the magnetic Reynolds(More)
We present a numerical model of an accretion disc with mean-field dynamo action that develops a fast pressure-driven outflow within a cone near the rotation axis and a slower centrifugally driven outflow in the outer parts of the disc. The fast outflow in the cone is confined by the azimuthal field which is produced by the dynamo in the disc and advected to(More)
Axisymmetric mean eld dynamo models in spherical shells are shown to be capable of producing temporally intermittent behaviour. This is of potential importance since (i) it is, as far as we are aware, the rst time such a behaviour has been produced internally by a mean eld dynamo model in a spherical shell, without requiring any additional assumptions or(More)