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Bifurcation to worms in electroconvection Urs Bisang and Guenter Ahlers
 

Summary: Bifurcation to worms in electroconvection
Urs Bisang and Guenter Ahlers
Department of Physics and Center for Nonlinear Science, University of California at Santa Barbara, Santa Barbara, California 93106
Received 25 February 1999
The primary bifurcation to electroconvection of the liquid crystal 4-ethyl-2-fluoro-4 -
2- trans-4-pentylcyclohexyl ethyl -biphenyl I52 with planar alignment leads to localized structures of con-
vection rolls known as ``worms'' when the conductivity of the fluid is relatively small. Worms coexist with the
conduction state. They have a unique small width in the direction perpendicular to the director and a varying,
usually much greater, length parallel to the director. Previous experiments had not determined whether the
bifurcation to worms is supercritical or subcritical. We estimated the voltage Vc corresponding to the stability
limit of the conduction state by measuring the mean-square amplitude of the thermally induced fluctuations
below onset and extrapolating to Vc . We found that worms appear already well below Vc . Thus the bifurca-
tion is subcritical. Measurements of the lifetime of the conduction state below Vc gave information about the
voltage Vs corresponding to the saddle node below which no worms form. We measured Vc and s Vs
2
/Vc
2
1 as a function of the conductance for a cell of thickness 24 m and found for our sample that s
approaches zero from negative values near 1.2 10 8 1
m 1

  

Source: Ahlers, Guenter - Department of Physics, University of California at Santa Barbara

 

Collections: Physics