We have employed a laser-beam-deflection technique to measure the Soret coefficient of ethanol/water solutions with ethanol weight fractions ranging from 0.02 to 0.39, over the temperature range 10 to 40 °C. This technique also allows precise determination of the mass-diffusion coefficient and of the index of refraction. These results have permitted us to obtain a quantitative understanding of recent experiments on oscillatory traveling-wave convection in binary fluid mixtures.

We describe experiments on convection in binary fluid mixtures in a large-aspect-ratio annular container. In this geometry, the convective rolls align radially and travel azimuthally, providing a model of travelling waves in an extended one-dimensional nonlinear dynamical system. Several different stable non-equilibrium states can be produced in this experiment, and the competition between them leads to a wide variety of steady and time-dependent behaviour. The observed spatiotemporal behaviour may shed light on recent theories of the nature of stable nonlinear travelling-wave convection, the pinning of travelling waves, and the creation of spatiotemporal defects.

We report experiments on weakly nonlinear traveling-wave convection in an annular cell. The evolution of small-amplitude waves consists of the repetitive formation and sudden collapse of spatially localized pulses. This leads to continuously erratic dynamics with no stable saturated state, even near onset, and even when convection begins with a unidirectional, nearly spatially uniform state. Such behavior is reminiscent of simulations of the complex Ginzburg-Landau equation in the limit of strong nonlinear dispersion.PACS numbers: 47.25.Qv, 47.20.Ky, 47.20.Tg Convection in a thin, horizontal layer of a binary fluid mixture which is heated from below has emerged in recent years as an interesting nonequilibrium system for studying the physics of pattern formation. When the temperature difference applied across the layer exceeds a certain threshold, the quiescent state gives way to a state of traveling waves (TW). Above onset, a wide variety of nonlinear TW states can occur. For example, experiments in narrow rectangular cells' have revealed onedimensional TW states in which wave energy ''sloshes'' or ''blinks'' back and forth across the cell. In this geometry, reflections from the end walls of the cell lead to the existence of two counterpropagating wave components, and Cross^ has asserted that the saturating nonlinear interaction between them is responsible for the dynamical behavior. Numerical simulations of a model of this physics, consisting of a system of two coupled Ginzburg-Landau equations for the complex wave amplitudes (CGLE), with real coefficients, exhibit behavior which closely parallels the experimental results."^ In this paper, we report that, when the same experiments are repeated in an annular cell, in which there are no end-wall reflections, completely different dynamical behavior occurs. A small-amplitude, unidirectional wave train exhibits repeated episodes of linear growth, formation of a spatially localized pulse, and sudden collapse. This leads to a continuously erratic state arbitrarily close to onset, even if convection begins with a state of unidirectional TW. The measured parameters of the system are shown to correspond to a limit of strong nonlinear dispersion in the CGLE, and our observations bear a striking resemblance to numerical simulations^ of the CGLE in this limit. Thus we refer to this spatiotemporal behavior as "dispersive chaos." We believe that our results constitute the first experimental observation of this kind of dynamical behavior.We use an improved version of a previously described apparatus."^ The cell is an annular channel formed by a plastic disk and ring which are clamped between a rhodium-plated, mirror-polished copper bottom plate and a sapphire top plate. The cell dimensions are ^=0.301 cm height xl.73^ radial width xgO.l^ mean circumference. Cooling water circulates azimuthally over the top plate, and the bottom plate is heated electrically. The temperature difference applied across the fluid layer, A7, is typically 3.9 K and is regulated with a stability of ...

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