https://doi.org/10.1140/epjst/e2015-02456-1
Regular Article
Motion of Euglena gracilis: Active fluctuations and velocity distribution
1 Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA
2 Thaer-Institute, Humboldt Universität zu Berlin, 10099 Berlin, Germany
3 Department of Mathematics, Uppsala University, Box 480, Uppsala 75106, Sweden
4 Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland
5 School of Physics, Complex and Adaptive Systems Lab, University College Dublin, Belfield, Dublin 4, Ireland
6 Department of Physics, Humboldt Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
a e-mail: vladimir.lobaskin@ucd.ie
b e-mail: alsg@physik.hu-berlin.de
Received: 8 April 2015
Revised: 18 May 2015
Published online: 24 July 2015
We study the velocity distribution of unicellular swimming algae Euglena gracilis using optical microscopy and active Brownian particle theory. To characterize a peculiar feature of the experimentally observed distribution at small velocities we use the concept of active fluctuations, which was recently proposed for the description of stochastically self-propelled particles [Romanczuk, P. and Schimansky-Geier, L., Phys. Rev. Lett. 106, 230601 (2011)]. In this concept, the fluctuating forces arise due to internal random performance of the propulsive motor. The fluctuating forces are directed in parallel to the heading direction, in which the propulsion acts. In the theory, we introduce the active motion via the depot model [Schweitzer, et al., Phys. Rev. Lett. 80(23), 5044 (1998)]. We demonstrate that the theoretical predictions based on the depot model with active fluctuations are consistent with the experimentally observed velocity distributions. In addition to the model with additive active noise, we obtain theoretical results for a constant propulsion with multiplicative noise.
© EDP Sciences, Springer-Verlag, 2015
