“…Mizushima et al [38] were the first to attempt a rigorous determination of the behaviour of the system near the bifurcation point, confirming that the dual solutions were due to an imperfect transcritical bifurcation. Petrone et al [39,40], performed a stability analysis of numerically obtained steady-state solutions, and concluded that, in the limit R/1, the imperfect transcritical bifurcation closes into the pitchfork bifurcation typical of the onset of RayleigheBénard convection, leading once again to the threshold value, Ra H;c ¼ 1708. In Fig.…”