Spirals and Spiral Defect Chaos
Dynamics and Selection of Giant Spirals
Spiral patterns are found in many pattern-forming systems. Famous examples include cardiac arrhythmias of the heart, the aggregation of starving slime mold amoebae, and the Belousov-Zhabotinsky chemical reaction. Many of these systems can be classified as excitable media in which the core of the spiral, like a pacemaker, selects the temporal and spatial evolution of the outward travelling spiral waves. We conducted a detailed experimental study of a driven, dissipative system in which the formation of spirals can be attributed to a qualitatively different mechanism acting far away from the spiral's core. In particular, we show for Rayleigh-Bénard convection of a small Prandtl number fluid that the rotation of giant, multi-armed spirals can be captured using concepts based on nonlinear phase equations. These concepts should be universal and preliminary evidence indicates that similar reasoning may also apply to the spiral pattern formation in vibrating granular layers and in gas discharges.The results are summarized in our PRL paper. The figure shows a shadowgraph image of the six convection cells used in the experiment Dark corresponds to warm up-flow, while light corresponds to cold down-flow. The cells used in the analysis are numbered from 1 to 4. Cell 3 contains a "PanAm" pattern and cell 2 contains Spiral Defect Chaos.
MPEG of image above.
Four-armed Spiral evolution movies
Bistability and Competition of Spatiotemporal Chaotic and Fixed Point Attractors
Movies: SDC at eps=0.8 ( 6.75 MB) frames taken 10 minutes appart.
Spiral Defect Chaos Simulations
A MPEG movie (6.5 MB) from simulations of the full fluid dynamics equations done on the IBM SP of the Cornell Theory Center. The movie displays the evolution of a pattern over the time of 3500 tv, corresponding to 2.5 h experiment.