Showing papers by "David S. Cannell published in 1993"

Spiral defect chaos in large aspect ratio Rayleigh-Bénard convection.

Abstract: We report experiments on convection patterns in a cylindrical cell with a large aspect ratio. The fluid had a Prandtl number [sigma][approx]1. We observed a chaotic pattern consisting of many rotating spirals and other defects in the parameter range where theory predicts that steady straight rolls should be stable. The correlation length of the pattern decreased rapidly with increasing control parameter so that the size of a correlated area became much smaller than the area of the cell. This suggests that the chaotic behavior is intrinsic to large aspect ratio geometries.

Transient localized states in 2D binary liquid convection.

Abstract: We report an experimental study of the onset of convection in ethanol/water mixtures confined in a circular cell of radial aspect ratio of 11.6. The initial bifurcation was to radial traveling waves; however, the linear state typically gave way to a nonlinear one in which convection alternately focused along one cell diameter and then another roughly perpendicular to the first. After a number of cycles, this state frequently contracted radially to a localized pulse of traveling-wave convection very similar to those observed in 1[ital D] geometries. The pulses we observed either decayed back to pure conduction or grew to fill or nearly fill the cell.

Thermal convection in the presence of a first-order phase change.

Abstract: We report experimental results for convection in a thin horizontal layer of a fluid which is heated from below and which undergoes a first-order phase change. For some parameter ranges the denser layer may be stably stratified above the lighter one, as predicted by Busse and Schubert. Over various parameter ranges we observed hexagonal, inverted-hexagonal, and roll flow. Interesting interactions between two-phase convection and Rayleigh-Benard convection are observed near two codimension-two points.

Spinodal decomposition in a binary fluid.

Abstract: Light scattering has been used to study a mixture of 3-methylpentane and nitroethane undergoing spinodal decomposition. The scattered intensity has been measured in absolute units allowing the first test or theory with no adjustable parameters. The measured structure factor does not evolve according to theory even when the initial fluctuations are taken into account. We believe the reason is that the evolving concentration field causes the sample temperature to change continuously throughout the decomposition process

Thermal convection in a planar nematic liquid crystal with a stabilizing magnetic field

Abstract: We report experimental results for thermal convection in a horizontal layer of a planar nematic liquid crystal [4-[ital n]-pentyl-4[prime]-cyanobiphenyl (5CB)] heated from below in a uniform horizontal magnetic field [bold H]. The threshold for convection and the critical wave-vector components were measured as a function of [ital H]. The convection rolls were oriented with their axes normal (oblique) to the field direction for [ital H][lt][ital H][sub [ital L]1] ([ital H][sub [ital L]1][lt][ital H][lt][ital H][sub [ital L]2]), where [ital H][sub [ital L]1] and [ital H][sub [ital L]2] are the lower and upper Lifshitz fields, respectively. Above [ital H][sub [ital L]2] the orientation was parallel to [bold H]. The dependence of the orientation on [ital H] near [ital H][sub [ital L]1] and [ital H][sub [ital L]2] agrees with theoretical predictions.

Thermal convection in a planar nematic liquid crystal with a stabilizing magnetic field

Abstract: We report experimental results for thermal convection in a horizontal layer of a planar nematic liquid crystal [4-n-pentyl-4'-cyanobiphenyl (5CB)] heated from below in a uniform horizontal magnetic field H. The threshold for convection and the critical wave-vector components were measured as a function of H. The convection rolls were oriented with their axes normal (oblique) to the field direction for H