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An experimental researcher whose joint study tracked the Brownian motion of ellipsoidal particles. Their nonspherical shape makes motion along the long axis differ from motion across it. Following both position and orientation with video microscopy reveals how particle geometry changes random motion even in an otherwise uniform liquid.^[ref]

An experimental condensed matter physicist who coauthored measurements of anisotropic Brownian motion. An ellipsoidal probe couples translational observations to its changing orientation, so the measured diffusion depends on the time scale and reference frame. Following a single nonspherical particle makes this geometric effect experimentally visible.^[ref]

In 2006, Yilong Han and colleagues dispersed plastic ellipsoids in water inside a thin glass cell, using a very dilute suspension to limit particle interactions. A camera on an optical microscope recorded 30 frames per second. Image analysis extracted centre positions and long-axis angles, with reported angular resolution about $1^{\circ }$. Their shape supplied the observable axis. Reflected interference colours calibrated cell thickness; nearly constant particle interference colour checked vertical wandering. One tracked particle had dimensions $2.4\times 0.3\times 0.3\mu \mathrm{m}$ in an $846\mathrm{nm}$ gap. Angular displacement variance grew linearly with lag; displacement resolved along the particle's axes and in the laboratory showed how turning washes out translational anisotropy. These are observations of confined particles: walls alter drag, and slight out-of-plane tumbling affected positional resolution. They do not establish the bulk sphere formula. The paper's Figure 1A–B shows simulations; Figure 1F shows a measured trajectory.^[ref]

For interpreting such images, the director distinction is essential: identical ends give an angle modulo $\pi$. A continuously unwrapped trace can follow small successive turns, but it does not make the ends physically distinguishable. The invariant planar axis autocorrelation is $⟨\cos (2\Delta \varphi )⟩$, and its decay determines $D_r$ through $e^{-4D_{r}t}$. Separately measuring position and rigid body orientation is what makes the connection between translational anisotropy and loss of angular memory experimentally accessible.

A researcher whose joint work measured the Brownian motion of an ellipsoid using both a laboratory frame and a frame that rotates with the particle. The two descriptions expose different displacement statistics. This provides an experimental example of why a random trajectory must be analyzed with its changing orientation, rather than position alone.^[ref]

A researcher whose team investigated the coupling of rotational diffusion and translational diffusion in a freely moving ellipsoid. At short times the particle remembers its orientation, while at longer times rotation averages over directions. The experiment shows how the timescale of observation changes the apparent symmetry of Brownian motion.^[ref]

A theoretical condensed matter physicist who coauthored analysis of Brownian motion of an ellipsoid. The study relates different diffusion rates along the particle's axes to rotational motion, explaining why laboratory-frame displacement statistics evolve with observation time. It connects microscopic anisotropy to the stochastic motion measured in a colloidal experiment.^[ref]

An experimental physicist who coauthored direct measurements of Brownian motion of an ellipsoid. Tracking both position and orientation showed how diffusion along the particle's long and short axes differs, and how rotational diffusion changes what a laboratory-frame observer sees. The example exposes geometry hidden by the spherical-particle approximation.^[ref]