Dresden 2006 – wissenschaftliches Programm

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SYSS: Structure Formation and Self-Organization in non-equilibrium Systems

SYSS 3: Structure Formation and Self-Organization in non-equilibrium Systems - Poster

SYSS 3.6: Poster

Donnerstag, 30. März 2006, 16:00–18:00, P1

Excitation symmetries and existence of subharmonic response of electroconvection patterns — •Jana Heuer and Ralf Stannarius — Institut für experimentelle Physik, Otto-von-Guericke-Universität Magdeburg

In electrohydrodynamic convection (EHC), surprising fundamentally new phenomena are still discovered, that contribute to general understanding of pattern dynamics in spatially extended dissipative systems. The excitation of this system with sine or square waves of period T leads to convection structures in which the dynamic variables (charge density, director and velocity fields) perform T-periodic oscillations. Non-conventional wave forms like sawtooth excitation can lead to patterns with T-periodic as well as T-antiperiodic (subharmonic) dynamics. We consider different classes of excitation wave forms E(t): such with antisymmetry in the two half periods, E(t) = −E(t+T/2), such with time inversion symmetry, E(t) = E(−t), and dichotomous wave forms (two alternating values, E₁, E₂) and discuss their influence on the pattern dynamics. From the Floquet analysis of linear differential equations that describe the system near threshold, we show analytically that each of these conditions inhibits subharmonic dynamics at onset. Numerical and experimental support of these predictions is provided.

By some generalization, other dynamic systems can be characterized by equally simple ODEs. Therefore we propose general conclusions about the relations between the time symmetry of the excitation field and the dynamic response of the system.