The experiment uses pressurized carbon dioxide gas held at a vertical temperature gradient. The convection patterns formed by the gas are viewed using a shadowgraphic technique. The initial state of straight convective rolls are prepared in a reproducible fashion by rastering a laser across the convective cell, thereby locally driving the flow.
The straight convective rolls are then thermally perturbed locally to study the response of the convective rolls. The dynamics of the system are enhanced by looking at differences of images between the intitial state of straight rolls and the states affected by the perturbation.
The modal structure of the dynamics that evolves from such a perturbation
is extracted using a modification of the Karhunen-Loeve decomposition,
also yielding the growth rates of such modes. Recent theoretical work [1]
suggests Spiral Defect Chaos is driven in large part by such instabilities
.
Talks: March
2001, APS ( Requires Microsoft Internet Explorer )
Movie: perturbation.avi
( 10 MB AVI movie format -24 bit color), perturbation.gif
(1.3 KB Animated GIF - 8bit color)
References: [1] Egolf D A, Melinkov I V, Pesch W, Ecke R E, Nature, 404, 733-736 (2000)
