Nanoparticle Diffusion, Aggregation, and Fractal Growth in Fluid Smectic Membranes

Membranes can be found in many biological systems and the transport and diffusion of inclusions, especially nanoparticles, in such membranes is important in understanding many biological processes. Additionally, the unique two-dimensional (2-D) nature of membranes makes them an ideal system in which to probe the limits of 2-D hydrodynamics. We observe directly the diffusion and aggregation of nanoparticles (buckyballs) embedded in thin, freely-suspended smectic A films of 8CB liquid crystal using reflected light microscopy in order to better understand the hydrodynamics of inclusions in finite, two-dimensional fluids. The growth of buckyball aggregates has been measured using time-lapse video, and is seen to have an effective radius that increases linearly with time. Large buckyball fractals form in the final stage of the aggregation process. The measured fractal dimension of these objects suggests that the aggregation is a diffusion-limited process and yields an approach to characterizing the stickiness of different particles by their final fractal dimension. Measurements of the diffusion of buckyball aggregates at varying stages in the aggregation process yield mobilities that deviate significantly from theoretical predictions for single inclusions. Similar behavior is observed in several high density systems, which suggests that the higher inclusion mobilities may be a result of crowding

Superconducting/magnetic three state nanodevice for memory and reading applications

We present a simple nanodevice that can operate in two modes: i) three-state memory and ii) reading device. The nanodevice is fabricated with an array of ordered triangular-shaped nanomagnets embedded in a superconducting thin film. The input signal is ac current and the output signal is dc voltage. Vortex ratchet effect in combination with out of plane magnetic anisotropy of the nanomagnets is the background physics which governs the nanodevice performance.Comment: 10 pages, 4 figure

Visualizing the geometry of state space in plane Couette flow

Motivated by recent experimental and numerical studies of coherent structures in wall-bounded shear flows, we initiate a systematic exploration of the hierarchy of unstable invariant solutions of the Navier-Stokes equations. We construct a dynamical, 10^5-dimensional state-space representation of plane Couette flow at Re = 400 in a small, periodic cell and offer a new method of visualizing invariant manifolds embedded in such high dimensions. We compute a new equilibrium solution of plane Couette flow and the leading eigenvalues and eigenfunctions of known equilibria at this Reynolds number and cell size. What emerges from global continuations of their unstable manifolds is a surprisingly elegant dynamical-systems visualization of moderate-Reynolds turbulence. The invariant manifolds tessellate the region of state space explored by transiently turbulent dynamics with a rigid web of continuous and discrete symmetry-induced heteroclinic connections.Comment: 32 pages, 13 figures submitted to Journal of Fluid Mechanic