J. Phys. II France
Volume 5, Numéro 4, April 1995
Page(s) 561 - 572
DOI: 10.1051/jp2:1995149
J. Phys. II France 5 (1995) 561-572

Excitability and Defect-Mediated Turbulence in Nematic Liquid Crustal

T. Frisch and J.M. Gilli

Institut Non Linéaire de Nice, U.M.R 129 C.N.R.S., Université de Nice Sophia - Antipolis, 1361 Route des Lucioles, 06560 Valbonne, France

(Received 22 November 1994, accepted 10 January 1995)

We report the observation of one-arm spiral waves and of turbulence states in a nematic slab subjected to an external forcing. These one-arm spiral waves constitute a close analog to the spiral waves observed in chemical and biological excitable media. Those results were obtained by adding a small vertical magnetic field on the experimental apparatus described in [1], in which double-arm spiral waves were observed in a sample with homeotropic alignment. We also describe a Ginzburg-Landau dynamical model accounting for the main kinds of experimental behavior and patterns obtained. In particular, the experiments and the simulations of this model reveal the appearance of a new instability of the 2 $\pi$ walls which is associated with the spontaneous formation of +1, -1 vortex, with the undoubling of the wavefronts, and which also leads to 2D turbulence.

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