Showing papers by "David S. Cannell published in 1998"

Patterns of electroconvection in a nematic liquid crystal

Abstract: We present a survey of pattern formation in electroconvection of the nematic liquid crystal 4-ethyl-2fluoro-4 8-[2-(trans-4-pentylcyclohexyl)-ethyl] biphenyl~I52! as a function of three control parameters: the applied voltage, applied frequency, and electrical conductivity of the sample. The patterns are dominated by oblique-roll states. Over the lower range of conductivity, the initial transition is a supercritical Hopf bifurcation which leads to four degenerate modes: right- and left-traveling zig and zag rolls. For higher values of the conductivity, the primary instability is a subcritical bifurcation to a single set of stationary oblique rolls. The convecting states exhibit a rich variety of patterns as a result of the interactions between the four modes, including states of spatiotemporal chaos and localized states. @S1063-651X~98!08301-9#

The Dynamics of Disorder-Order Transition in Hard Sphere Colloidal Dispersions

Abstract: The Physics of Hard Spheres Experiment (PHaSE) seeks a complete understanding of the entropically driven disorder-order transition in hard sphere colloidal dispersions. The light scattering instrument designed for flight collects Bragg and low angle light scattering in the forward direction via a CCD camera and performs conventional static and dynamic light scattering at 10-160 deg. through fiber optic cables. Here we report on the kinetics of nucleation and growth extracted from time-resolved Bragg images and measurements of the elastic modulus of crystalline phases obtained by monitoring resonant responses to sinusoidal forcing through dynamic light scattering. Preliminary analysis of the former indicates a significant difference from measurements on the ground, while the latter confirms nicely laboratory experiments with the same instrument and predictions from computer simulations.