We determine the basic phase diagram of the fish school model derived from data by Gautrais et al (2012 PLoS Comput. Biol. 8 e1002678), exploring its parameter space beyond the parameter values determined experimentally on groups of barred flagtails (Kuhlia mugil) swimming in a shallow tank. A modified model is studied alongside the original one, in which an additional frontal preference is introduced in the stimulus/response function to account for the angular weighting of interactions. Our study, mostly limited to groups of moderate size (in the order of 100 individuals), focused not only on the transition to schooling induced by increasing the swimming speed, but also on the conditions under which a school can exhibit milling dynamics and the corresponding behavioural transitions. We show the existence of a transition region between milling and schooling, in which the school exhibits multistability and intermittence between schooling and milling for the same combination of 7
We show that "dry" active nematics, e.g. collections of shaken elongated granular particles, exhibit large-scale spatiotemporal chaos made of interacting dense, ordered, band-like structures in a parameter region including the linear onset of nematic order. These results are obtained from the study of the relatively simple and well-known (deterministic) hydrodynamic equations describing these systems in a dilute limit, and of a self-propelled particle Vicsek-like model for this class of active matter. In this last case, revisiting the status of the strong fluctuations and long-range correlations now considered as landmarks of orientationally-ordered active phases, we show that the giant number fluctuations observed in the chaotic phase are a trivial consequence of density segregation. However anomalous density fluctuations are present in the homogeneous quasi-ordered nematic phase and characterized by a non-trivial scaling exponent.PACS numbers: 05.65.+b, 45.70.Vn, 87.18.Gh Many of the recent studies on active suspensions and active gels have reported the existence of instabilities leading to spontaneous flows [1][2][3][4]. At the nonlinear level, the term "bacterial turbulence" has been used to describe the fast, collective but chaotic motion of swimmers evolving in what remains a very low Reynolds number, inertialess, world [5][6][7][8]. In remarkable in vitro experiments on actomyosin motility assays, the fluid in which filaments and motors evolve seems to play a key role in the emergence of local order leading in turn to erratic large-scale flows [9]. Other actomyosin systems, like the active nematics suspensions studied by Dogic et al., display spontaneous large-scale dynamics mediated by the nucleation and motion of topological defects [10][11][12][13].In contrast, most of the recent studies of "dry" active matter (where the fluid in which active particles move can be safely neglected), have not reported widespread occurence of large-scale chaos or turbulence [14]. Following the seminal papers of Vicsek et al. [15] and Toner and Tu [16], a lot of attention has been paid to the nature of the onset of orientational order/collective motion and to the existence of generic long-range correlations and anomalous fluctuations in spatially-homogeneous ordered phases [17,18,21]. The existence of long-wavelength instabilities of homogeneous ordered states leading, in dilute systems, to some phase separation between highdensity high-order structures (bands, waves) is now recognized as a generic feature [18][19][20][22][23][24][25][26][27][28][29], but the stability and large-scale dynamics of these structures remain largely unknown.In this Letter, we show that large-scale spatiotemporal chaos arises generically in dry active nematics. We first demonstrate that the solutions of the relatively simple and well-known (deterministic) hydrodynamic equations describing these systems are chaotic in a region of parameter space including the linear onset of nematic order. We show in particular that the nonlinear ordered band...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.