On the observability of hexagons in modulated Rayleigh-Benard convection.

The prediction of Roppo, Davis and Rosenblat, that hexagons should appear near threshold in a Rayleigh-Benard cell under external modulation of the temperature, is reconsidered with a view to determining the experimental observability of the effect. It is found that in the limit of low modulation amplitude delta considered by Roppo et al., the effects are qualitatively as given by these authors, but quantitatively considerably smaller. The limits of validity of the small-delta expansion are clarified and results of an alternative theory of hexagon effects, valid at arbitrary amplitude delta and frequency omega are briefly summarized. Hexagons will only be observable if large amplitudes can be achieved.