The Physical Mechanism of Oscillatory and Finite Amplitude Instabilities in Systems with Competing Effects

The onset of convection in a horizontal layer of fluid heated from below, the so-called Rayleigh-Benard instability, has been extensively investigated for a long time 1,2. In recent years there has been considerable interest in the new phenomena that occur in systems in which two competing stability influencing effects with different relaxation times are present. The first example of such systems that was studied in detail is the case of thermal convection in binary mixtures3,4. More recently it has been pointed out that thermal convection in nematic liquid crystals can also be advantageously considered from the same point of view 5. It has been found that under certain conditions both binary mixtures 3,4 and nematic liquid crystals 6,7, when heated from below, show oscillatory and finite amplitude instabilities. In this contribution I will discuss the common physical mechanism underlying these phenomena from the point of view of the energy balance of convective disturbances.