Images of Localized Structures


Another interesting phenomenon unique to nonlinear systems is the formation of localized structures of convection known as pulses. These examples were obtained in an annulus filled with a mixture of ethanol and water and heated from below. The convection rolls form at one end of the pulse, travel through it, and disappear at the other end. The pulses are surrounded by non-convecting fluid.

From J.J. Niemela, G. Ahlers, and D.S. Cannell, Phys. Rev. Lett. 64, 1365 (1990).





In two-dimensional systems pulses can form as well. Here the rolls form at the right, travel through the pulse, and leave it at the left. Again, the pulse is completely surrounded by non-convecting fluid. This experiment was done also in an ethanol-water mixture.

From K. Lerman, E. Bodenschatz, D.S. Cannell, and G. Ahlers, Phys. Rev. Lett. 70, 3572 (1993).





In a container of circular cross section filled with ethanol-water the localization can also be in the radial direction, with the convection confined near the perimeter. In this example the rolls travel in the clockwise direction.

From K. Lerman, G. Ahlers, and D.S. Cannell, Phys. Rev. E 53, R2041 (1996).





A traveling wall mode occurs also under very different circumstances, namely in a horizontal layer of fluid heated from below and rotated about a vertical axis. This example is for a hydrogen-xenon mixture with a Prandtl number of 0.18 and a dimensionless rotation frequency of 400; but the phenomenon occurs as well in pure fluids. Here the wall mode travels in the clockwise direction.

From K.M.S. Bajaj, W. Pesch, and G. Ahlers, to be published.





Localized structures occur also in electro-convection. But here the degree of localization differs in the two directions because of the anisotropy of this system. Because of their strange appearance, these structures have become known as worms.

From M. Dennin, G. Ahlers, and D.S. Cannell, Phys. Rev. Lett. 77, 2475 (1996).





Here are some more examples of worms.

From M. Dennin, G. Ahlers, and D.S. Cannell, Phys. Rev. Lett. 77, 2475 (1996).





Home - About us - News - Members - Alumni - Pattern Formation - Critical Phenomena - Recent Publications - Collaborators
Quantum Institute - Physics Department - UC Santa Barbara