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Authors: Florian Thüroff, Christoph Weber, and Erwin Frey
The intriguing and fascinating world of swarming systems motivated scientists to investigate the generic principles underlying the non-equilibrium phase transition from disorder to collective motion. To make progress towards a better understanding of these phenomena, first-principle approaches, based on the interactions between individual particles, have been developed leading to hydrodynamic equations which are consistent with those obtained by symmetry arguments, and whose coefficients are explicitly given in terms of the system's microscopic properties [1,2]. Here, our focus is on the ordering instabilities that occur in non-equilibrium fluids of (self-) propelled rod-like colloids which, microscopically, interact by means of polar collision rules. Starting from a Boltzmann equation, we employ a well-established coarse-graining scheme to derive the hydrodynamic equations governing the rod fluid's motion for large wave lengths. Given the kinetic coefficients in terms of the microscopic parameters, we study the impact of the rods' aspect ratio on the phase behavior and analyze the stability of the various phases. Finally, we compare our approach with other coarse-grained models discussed in the literature. [1] I.S. Aranson and L.S. Tsimring, Phys. Rev. E 71, 050901 (2005) [2] E. Bertin, M. Droz, and G. Gregoire, J. Phys. A: Math. Theor. 42, 445001 (2009). |
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