Active nematics on a substrate: Giant number fluctuations and long-time tails

By S. Ramaswamy, R. Simha, J. Toner. 2002

273 citations recorded by the source corpus.

We construct the equations of motion for the coupled dynamics of order parameter and concentration for the nematic phase of driven particles on a solid surface, and show that they imply i) giant number fluctuations, with a standard deviation proportional to the mean in dimension d = 2 of primary relevance to experiment, and ii) long-time tails $\sim t^{-d/2}$in the autocorrelation of the particle velocities despite the absence of a hydrodynamic velocity field. Our predictions can be tested in experiments on aggregates of amoeboid cells as well as on layers of agitated granular matter.

Subfields: Biomedical Engineering, Computer Networks and Communications, Condensed Matter Physics

View Paper: https://www.semanticscholar.org/paper/d3254119b124ed0dd13ce03abe1d7236661cd227

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Citations in the corpus

Physics of microswimmers—single particle motion and collective behavior: a review (2014, background): “…point particles has led to numerous analytical (Baskaran and Marchetti, 2009; Bertin et al., 2009; Golestanian, 2009; Peruani et al., 2008; Ramaswamy et al., 2003; Simha and Ramaswamy, 2002; Toner and Tu, 1995; Toner et al., 2005b) as well as computational (Aldana et al., 2007; Chaté et…”
Tuned, driven, and active soft matter (2015, background): “two-dimensional case of active nematics, an exponent ζ = 1 was predicted [407, 408] and later confirmed through simulations [406].”
Active Brownian particles (2012, methodology): “Phenomena like giant number fluctuations, phase separation and clustering phenomena fall into this class and have all been observed in experiments [244,270,298], predicted or reproduced by theoretical analysis and numerical simulations of appropriate models [235,266,278,269,343].”
Topological active matter (2020, background): “Another class of orien-tationally ordered fluids is active nematics 38,39 , which are composed of head–tail symmetrical rod-like entities that exert internally generated stresses on their surroundings and organize in states of orientational order that is apolar.”
Active Matter (2010, unknown): “Fluctuations in active systems are generically large, often deviating qualitatively from the predictions of simple arguments based on the central limit theorem [45] [46] [47] [37].”
Hydrodynamics of soft active matter (2013, methodology): “The unique physics of the self-driven nematic state (Ramaswamy, Simha, and Toner, 2003) enters through active contributions to the current J in the conservation law @t% ¼ !r & J; (24) where J ¼ !”
Minimal model of active colloids highlights the role of mechanical interactions in controlling the emergent behavior of active matter (2015, background): “The q−2 divergence of the structure factor as q → 0 is also the signature of the giant number fluctuations (GNF) predicted and observed ubiquitously in the ordered state of flocking models [48, 49, 50, 3].”