Vortex-front propagation in Rayleigh-Bénard convection

We present experimental measurements of the velocity of a convective vortex front propagating into an unstable conductive state in a Rayleigh-Bénard system for the wide range of ε (ε≡ΔT/Δ${\mathrm{T}}_{\mathrm{c}}$-1) between 4×${10}^{\mathrm{-}4}$ and 2.5×${10}^{\mathrm{-}1}$. The results are found to be in excellent quantitatitve agreement with the theoretical predictions following from an amplitude equation, exhibiting a sharp selection mechanism in the propagation velocity. Wave-number selection by this dynamical mechanism is also studied.