Hydromagnetic processes play an important role in many astrophysical systems (e.g. stars, galaxies, accretion discs). This is because the medium is hot enough to be partially or fully ionized. Because of the huge scales involved the medium is usually turbulent, provided there is an instability (shear, convection) facilitating the cascading of energy down to small scales. In turbulence research ...

The predictive power of mean-field theory is emphasized by comparing theory with simulations under controlled conditions. The recently developed test-field method is used to extract turbulent transport coefficients both in the kinematic and the nonlinear or quasi-kinematic cases. A striking example of the quasi-kinematic method is provided by magnetic buoyancy-driven flows that produce an α eff...

Aims. We present global 3DMHD simulations of disks of gas and solids, aiming at developing models that can be used to study various scenarios of planet formation and planet-disk interaction in turbulent accretion disks. A second goal is to demonstrate that Cartesian codes are comparable to cylindrical and spherical ones in handling the magnetohydrodynamics of the disk simulations while offering...

We present a model to explain the origin of local clouds, including the so-called Local Fluff surrounding the solar system. We present observational evidence from ROSAT PSPC data, that manifest the existence of an interaction shell between our local interstellar bubble and the adjacent Loop I superbubble. A linear stability analysis of this compressed interaction shell has been performed. We sh...