Worms in Electroconvection of Nematic Liquid Crystals
Experimentally localized traveling-wave structures in the form of
"worms" have been observed by M. Dennin, G. Ahlers and D.S.
Cannell (PRL 77 (1996) 2475). Below are two top views, one showing a single long worm and the other
showing a number of snapshots of larger parts of the system.
Since the bifurcation to the extended traveling waves is
supercritical the usual Ginzburg-Landau equations are not sufficient
to describe these localized waves below threshold. An extension
similar to that used for binary-mixture convection explains the
localization mechanism and gives qualitatively similar solutions (H.
Riecke and G.D. Granzow, Phys. Rev. Lett. 81 (1998) 333).
In larger systems a number of these worms can appear and exhibit a
typical distance in the y-direction.
Through the interaction with an additional mode the supercritical
traveling waves become localozed in worms.
Movies of worm
evolution:
Steady
worm (700Kb). The height indicates the strength of the additional
field that is responsible for the localization of the wave. The color
map gives the wave as it would be seen in the experiment.
Start
from small random initial conditions (400kB) without dispersion.
Color and height indicate the strength of the additional field C.
Laterally the additional field C suppresses convection (blue
color indicates negative values of C). The wave character is
as in the movie of the steady worm.
2d
("top view") of the same run starting from random
initial condition.
Unsteady
worm (520Kb) due to dispersion. Smaller
version (300Kb).
Research supported by DOE and NSF.
May 30, 1999
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