Figure 17.2 — Hydrodynamic interactions between trapped colloidal particles Figure 17.2 — Hydrodynamic interactions between trapped colloidal particles. (a) Cross-correlation in the position fluctuations of two trapped colloidal particles for three different particle separations. The lines through the data points are the expected form of the cross-correlation using a theory based on the hydrodynamic coupling described in the text. (b) Pairing of particles driven around the circumference of a ring-shaped vortex beam trap. (c) Hydrodynamic synchronisation of a pair of optically trapped oscillators.Figure (a) is reprinted from Meiners and Quake, Phys. Rev. Lett. 82, 2211–14. Copyright (1999) by the American Physical Society.Figure (b) is reprinted from Sokolov et al., Phys. Rev. Lett. 107, 158302. Copyright (2011) by the American Physical Society.Figure (c) is reprinted from Kotar et al., Proc. Natl. Acad. Sci. U.S.A. 107, 7669–73. Copyright (2010) National Academy of Sciences, U.S.A.