We study experimentally and theoretically the evolution of two-dimensional patterns in the Rayleigh—Taylor instability of a thin layer of viscous fluid spread on a solid surface. Various kinds of patterns of different symmetries are observed, with possible transition between patterns, the preferred symmetries being the axial and hexagonal ones. Starting from the lubrication hypothesis, we derive the nonlinear evolution equation of the interface, and the amplitude equation of its Fourier components. The evolution laws of the different patterns are calculated at order two or three, the preferred symmetries being related to the non-invariance of the system by amplitude reflection. We also discuss qualitatively the dripping at final stage of the instability.
The relaxation towards thermal equilibrium of a magnetic polaron bound at an impurity located near the interface of a quantum well structure is calculated. The relaxation is induced by the exchange interaction between the localized spins in the polaron and the randomly aligned localized spins in the barrier. Relaxation of the polaron occurs at two different rates. Fast relaxation Is associated with an lntravalley relaxation while slow relaxation describes the flip-flop motion of the whole polaron.
We report calculations of the binding energy of magnetic polarons bound to acceptor impurities in the Cd1−xMnxTe barriers of CdTe/Cd1−xMnxTe quantum wells. We show the occurrence of a transition between a quantum well polaron state and a bulklike polaron state when the temperature varies.
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