Berlin 2015 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 16: Microswimmers - Part I (joint session DY/ BP/ CPP)
DY 16.2: Talk
Tuesday, March 17, 2015, 09:45–10:00, BH-N 128
Statistics of passive tracers in an active fluid — •Levke Ortlieb1, Matthias Mußler1, Christian Wagner1, Thomas John1, Philippe Peyla2, and Salima Rafaï2 — 1Universität des Saarlandes — 2Université Joseph Fourier - CNRS - LIPHY, Grenoble
In all aqueous suspension on earth there are various microswimmers, e.g. algae. In our experiments we tracked passive polystyrene particles with diameters from 1 to 3µm in suspension with the green alga Chlamydomonas reinhardtii at various concentrations. We used dark field microscopy for observations. The alga has a nearly spherical body of 5 to 10µm diameter and two flagella, which allow it to swims as a puller. We analysed the trajectories of the colloids statistically, in particular, the mean squared displacement and the probability density function (pdf) of position were computed. We found similarities to Brownian motion, as the mean squared displacement is proportional to time, but interestingly also a significant deviation was found: a non gaussian pdf of the tracer particle positions.