We study the radial ionization structure at the surface of an X-ray illuminated accretion disc. We plot the expected iron Kα line energy as a function of the Eddington ratio and of the distance of the emitting matter from the central source, for a non-rotating and a maximally rotating black hole. We compare the predicted disc line energies with those measured in an archival sample of active gal...

We consider the evolution of a warped disc around a Kerr black hole, under conditions such that the warp propagates in a wavelike manner. This occurs when the dimensionless effective viscosity, α, that damps the warp is less than the characteristic angular semi-thickness, H/R, of the disc. We adopt linearized equations that are valid for warps of sufficiently small amplitude in a Newtonian disc...

We study the stability of poloidal magnetic fields anchored in a thin accretion disc. The two-dimensional hydrodynamics in the disc plane is followed by a grid-based numerical simulation including the vertically integrated magnetic forces. The 3–dimensional magnetic field outside the disc is calculated in a potential field approximation from the magnetic flux density distribution in the disc. F...

Unlike most double-disc grinding processes, which use forced workpiece rotation, some processes rely on self-rotation driven by non-uniform shear forces resulting from partial wheel-workpiece coverage. This is poorly understood, with angular frequency remaining unknown despite its importance. paper investigates the kinematics of via analytical modelling moment-equilibrium conditions, derived ex...