Hexagons and rolls in periodically modulated Rayleigh-Benard convection.

A laterally infinite liquid layer is heated from below in a time-periodic fashion with frequency omega and amplitude delta. A Lorenz-like truncation of the hydrodynamic equations is used to study the pattern competition between hexagons and rolls near threshold. By comparison with the work of Roppo, Davis and Rosenblat it is shown that the truncation becomes exact in the low-frequency limit for stress-free horizontal boundaries. In contrast with Roppo et al. however, we find an unobservably small jump in convection amplitude at the subcritical bifurcation from conduction to hexagonal convection.