In this model, a normal outburst corresponds to a period of accelerated mass transfer through the accretion disk that is initiated by a thermal instability. A normal outburst becomes a superoutburst when in addition to being thermally unstable, the disk becomes tidally unstable. The simulations showed that tidal torques remove angular momentum from the disk more efficiently when the disk is tidally unstable. Consequently the disk shrinks, and there is an increased mass flux with a corresponding increase in the disk luminosity. Norman Murray and James Chiang proposed a mechanism for the formation of single peaked emission lines in luminous cataclysmic variables.
Cataclysmic variables consist of a main sequence star orbiting a white dwarf.
The He II 4686 line seen in many eclipsing Nova-like cataclysmics has a radial velocity curve consistent with emission from the accretion disk. Classical disk emission lines are double peaked, yet the He II line in Nova-likes is single peaked. Murray and Chiang show that the presence of shears in the outflowing wind emerging from the disk affects the directions along which line photons escape, suppressing emission from regions of high projected velocity. As a result, the disk emits single peaked lines.