title: Scale-dependent colocalization in a population of gyrotactic swimmers.
abstract: We study the small scale clustering of gyrotactic swimmers transported by a turbulent flow, when the intrinsic variability of the swimming parameters within the population is considered. By means of extensive numerical simulations, we find that the variety of the population introduces a characteristic scale R^{*} in its spatial distribution. At scales smaller than R^{*} the swimmers are homogeneously distributed, while at larger scales an inhomogeneous distribution is observed with a fractal dimension close to what observed for a monodisperse population characterized by mean parameters. The scale R^{*} depends on the dispersion of the population and it is found to scale linearly with the standard deviation both for a bimodal and for a Gaussian distribution. Our numerical results, which extend recent findings for a monodisperse population, indicate that in principle it is possible to observe small scale, fractal clustering in a laboratory experiment with gyrotactic cells.
authors.affiliation: Department of Physics and INFN, Università di Torino, via P. Giuria 1, I-10125 Torino, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Borgnino
authors.affiliation: Department of Physics and INFN, Università di Torino, via P. Giuria 1, I-10125 Torino, Italy.
authors.forename: F
authors.initials: F
authors.lastname: De Lillo
authors.affiliation: Department of Physics and INFN, Università di Torino, via P. Giuria 1, I-10125 Torino, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Boffetta