Diffusive modes in Rayleigh-Bénard structures

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Abstract
We present experimental measurements of the dynamical properties of Rayleigh-Bénard convective structures in the case of high Prandtl number fluid and slightly supercritical Rayleigh number. We show that these measurements can be carried out like a phonon study in a crystal. However we demonstrate that, as predicted, the dynamics of phase modes is actually diffusive in Rayleigh-Bénard convection. When possible we determine the associated diffusion coefficient D ∥ or its main characteristic in the case of D⊥ . We find that these results are in agreement with the theoretical predictions