Collisions between pulses of traveling-wave convection

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Abstract
The first nonlinear state of traveling-wave convection in binary fluids with moderate negative separation ratio in a narrow geometry consists of ‘‘pulses’’: localized patches of convection whose spatial shape is fixed, and that drift at a velocity that depends on the local Rayleigh number. I present the results of two kinds of experiments on traveling-wave pulses. First, I study the behavior of pulses as they drift past narrow, fixed peaks in Rayleigh number. The pulses are sensitive to the Rayleigh number in a spatial domain that extends far ahead of the main body of the pulse. Second, I study collisions between pairs of counterpropagating pulses as a function of the velocity with which they approach one another. At high approach velocity, only one pulse survives the collision. At low approach velocity, a persistent double-peaked structure is formed. Under certain circumstances, this structure can be interpreted as a weakly bound state of two pulses.