Dresden 2017 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 18: Brownian Motion / Noise (joint session DY/TT)

DY 18.3: Talk

Tuesday, March 21, 2017, 10:30–10:45, ZEU 147

Non-Gaussian Statistics of Tracer Positions in Fluids Stirred by Microswimmers — •Thomas John¹, Levke Ortlieb¹, Philippe Peyla², Salima Rafaï², and Christian Wagner¹ — ¹Experimental physics University of Saarland — ²Laboratoire Interdisciplinaire de Physique, Grenoble

We performed statistical analyses on the measured positions of µm-sized tracer particles in liquids stirred by the microswimmer Chlamydomonas reinhardtii. Various tracer diameters, swimmer concentrations and mean swimmer velocities were examined. The statistical characteristics are compared with predictions from various models. Our observed mean squared displacement of the tracer is linear over more than two order of magnitudes in time. The underlying probability density function (pdf(Δ t)) of the displacements has a Gaussian core from the Brownian motion and non-Gaussian tails from the interactions with the flow field from the swimmers. The pdf shows a transient diffusive scaling behavior at short times. This scaling breaks down at times longer than few seconds. Our results are in very good agreement with the predictions of the microscopic model by Thiffeault, PRE 92 023023(2015).