Direct measurement of shear-induced cross-correlations of Brownian motion.
Shear-induced cross-correlations of particle fluctuations perpendicular and along streamlines are investigated experimentally and theoretically. Direct measurements of the Brownian motion of micron-sized beads, held by optical tweezers in a shear-flow cell, show a strong time asymmetry in the cross-correlation, which is caused by the non-normal amplification of fluctuations. Complementary measurements on the single particle probability distribution substantiate this behavior and both results are consistent with a Langevin model. In addition, a shear-induced anticorrelation between orthogonal random displacements of two trapped and hydrodynamically interacting particles is detected, having one or two extrema in time, depending on the positions of the particles.
Ziehl
A
A
Technische Physik, Universität des Saarlandes, 66041 Saarbrücken, Germany.
Bammert
J
J
Holzer
L
L
Wagner
C
C
Zimmermann
W
W