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-B\'enard system for the wide range of \ensuremath{\epsilon} (\ensuremath{\epsilon}\ensuremath{\equiv}\ensuremath{\Delta}T/\ensuremath{\Delta}${\mathrm{T}}_{\mathrm{c}}$-1) between 4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ and 2.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}1}$. 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.