We estimate the Shakura-Sunyaev viscosity parameter alpha for diierent values of the shear/vorticity ratio, =!, using local simulations of dynamo-generated turbulence. We nd that the time average of is approximately proportional to =! (at least for =! < 10). We point out that this result may have important implications for the properties of thick accretion discs, because there ! is small and wo...

The study of cataclysmic variables (CVs), and in particular of the evolution of their accretion discs throughout their different brightness states, has benefited largely from the use of indirect imaging techniques. I report on the latest results obtained from Doppler tomography of CVs concentrating mainly on results published since the 2000 Astrotomography meeting in Brussels. Emphasis is given...

There is a class of dynamos where the eld is caused by a velocity eld which, in turn, is driven by the generated magnetic eld. Numerical three-dimensional simulations of this type of process are reviewed. This process is here discussed in connection with accretion discs, but we point out that similar mechanisms have also been suggested in the context of solar and galactic dynamos. The underlyin...

We estimate the Shakura-Sunyaev viscosity parameter alpha for diierent values of the shear/vorticity ratio, =!, using local simulations of dynamo-generated turbulence. We nd that the time average of is approximately proportional to =! (at least for =! < 10). We point out that this result may have important implications for the properties of thick accretion discs, because there ! is small and wo...

We calculate spectral energy distributions (SEDs) of steady accretion discs at high accretion rates, as appropriate for bright QSOs, under the assumption that the outer parts are heated sufficiently to maintain marginal gravitational stability, presumably by massive stars formed within the disc. The SED is independent of the nature of these auxiliary sources if their inputs are completely therm...

We present a linear analysis of the vertical structure and growth of the magnetorotational instability in weakly ionised, stratified accretion discs. The method includes the effects of the magnetic coupling, the conductivity regime of the fluid and the strength of the magnetic field, which is initially vertical. The conductivity is treated as a tensor and assumed constant with height. The Hall ...

We study protoplanetary disc evolution assuming that angular momentum transport is driven by gravitational instability at large radii, and magnetohydrodynamic (MHD) turbulence in the hot inner regions. At radii of the order of 1 AU such discs develop a magnetically layered structure, with accretion occurring in an ionized surface layer overlying quiescent gas that is too cool to sustain MHD tur...

In this paper, we extend our previous analysis (Lodato & Rice 2004) of the transport properties induced by gravitational instabilities in cooling, gaseous accretion discs to the case where the disc mass is comparable to the central object. In order to do so, we have performed global, three-dimensional smoothed particle hydrodynamics simulations of massive discs. These new simulations show a muc...

I review the observational evidence for spiral structure in the accretion discs of cataclysmic variables (CVs). Doppler tomography is ideally suited to resolve and map such co-rotating patterns and allows a straightforward comparison with theory. The dwarf nova IP Pegasi presents the best studied case, carrying two spiral arms in a wide range of emission lines throughout its outbursts. Both arm...

Recent discoveries have confirmed the existence of a large population of Xray sources fuelled by accretion from the stellar wind of an OB supergiant. Such systems are powerful laboratories to study many aspects of astrophysics. Over the last decades, the physics of accretion in these systems has been the subject of extensive research, mainly through numerical methods. In spite of this effort, l...