On couple-stress fluid heated from below in porous medium in hydromagnetics

A layer of electrically conducting couple-stress fluid heated from below in porous medium in presence of magnetic field is considered. For stationary convection, the couple-stress and magnetic field postpone the onset of conv ection whereas the medium permeability hastens the onset of convection. The magnetic field introduces oscillatory modes in the system which were non-e xistent in its absence. A sufficient condition for the non-existence of ove rstability is obtained.