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Non-Gaussian noise without memory in active matter Fodor, Etienne ; ; et al in Physical Review. E. (2018), 98(6), Modeling the dynamics of an individual active particle invariably involves an isotropic noisy self-propulsion component, in the form of run-and-tumble motion or variations around it. This nonequilibrium ... [more ▼] Modeling the dynamics of an individual active particle invariably involves an isotropic noisy self-propulsion component, in the form of run-and-tumble motion or variations around it. This nonequilibrium source of noise is neither white-there is persistence-nor Gaussian. While emerging collective behavior in active matter has hitherto been attributed to the persistent ingredient, we focus on the non-Gaussian ingredient of self-propulsion. We show that by itself, that is, without invoking any memory effect, it is able to generate particle accumulation close to boundaries and effective attraction between otherwise repulsive particles, a mechanism which generically leads to motility-induced phase separation in active matter. [less ▲] Detailed reference viewed: 28 (3 UL)Spatial Fluctuations at Vertices of Epithelial Layers: Quantification of Regulation by Rho Pathway Fodor, Etienne ; ; et al in BIOPHYSICAL JOURNAL (2018), 114(4), 939-946 In living matter, shape fluctuations induced by acto-myosin are usually studied in vitro via reconstituted gels, whose properties are controlled by changing the concentrations of actin, myosin, and cross ... [more ▼] In living matter, shape fluctuations induced by acto-myosin are usually studied in vitro via reconstituted gels, whose properties are controlled by changing the concentrations of actin, myosin, and cross-linkers. Such an approach deliberately avoids consideration of the complexity of biochemical signaling inherent to living systems. Acto-myosin activity inside living cells is mainly regulated by the Rho signaling pathway which is composed of multiple layers of coupled activators and inhibitors. Here, we investigate how such a pathway controls the dynamics of confluent epithelial tissues by tracking the displacements of the junction points between cells. Using a phenomenological model to analyze the vertex fluctuations, we rationalize the effects of different Rho signaling targets on the emergent tissue activity by quantifying the effective diffusion coefficient, and the persistence time and length of the fluctuations. Our results reveal an unanticipated correlation between layers of activation/inhibition and spatial fluctuations within tissues. Overall, this work connects regulation via biochemical signaling with mesoscopic spatial fluctuations, with potential application to the study of structural rearrangements in epithelial tissues. [less ▲] Detailed reference viewed: 31 (1 UL)Entropy Production in Field Theories without Time-Reversal Symmetry: Quantifying the Non-Equilibrium Character of Active Matter ; Fodor, Etienne ; et al in PHYSICAL REVIEW X (2017), 7(2), Active-matter systems operate far from equilibrium because of the continuous energy injection at the scale of constituent particles. At larger scales, described by coarse-grained models, the global ... [more ▼] Active-matter systems operate far from equilibrium because of the continuous energy injection at the scale of constituent particles. At larger scales, described by coarse-grained models, the global entropy production rate S quantifies the probability ratio of forward and reversed dynamics and hence the importance of irreversibility at such scales: It vanishes whenever the coarse-grained dynamics of the active system reduces to that of an effective equilibrium model. We evaluate S for a class of scalar stochastic field theories describing the coarse-grained density of self-propelled particles without alignment interactions, capturing such key phenomena as motility-induced phase separation. We show how the entropy production can be decomposed locally (in real space) or spectrally (in Fourier space), allowing detailed examination of the spatial structure and correlations that underly departures from equilibrium. For phase-separated systems, the local entropy production is concentrated mainly on interfaces, with a bulk contribution that tends to zero in the weak-noise limit. In homogeneous states, we find a generalized Harada-Sasa relation that directly expresses the entropy production in terms of the wave-vector-dependent deviation from the fluctuation-dissipation relation between response functions and correlators. We discuss extensions to the case where the particle density is coupled to a momentum-conserving solvent and to situations where the particle current, rather than the density, should be chosen as the dynamical field. We expect the new conceptual tools developed here to be broadly useful in the context of active matter allowing one to distinguish when and where activity plays an essential role in the dynamics. [less ▲] Detailed reference viewed: 58 (0 UL)Active cage model of glassy dynamics Fodor, Etienne ; ; et al in Physical Review. E. (2016), 94(1), We build up a phenomenological picture in terms of the effective dynamics of a tracer confined in a cage experiencing random hops to capture some characteristics of glassy systems. This minimal ... [more ▼] We build up a phenomenological picture in terms of the effective dynamics of a tracer confined in a cage experiencing random hops to capture some characteristics of glassy systems. This minimal description exhibits scale invariance properties for the small-displacement distribution that echo experimental observations. We predict the existence of exponential tails as a crossover between two Gaussian regimes. Moreover, we demonstrate that the onset of glassy behavior is controlled only by two dimensionless numbers: the number of hops occurring during the relaxation of the particle within a local cage and the ratio of the hopping length to the cage size. [less ▲] Detailed reference viewed: 67 (1 UL)Generalized Langevin equation with hydrodynamic backflow: Equilibrium properties Fodor, Etienne ; ; et al in Physica A. Statistical Mechanics and its Applications (2015), 422 We review equilibrium properties for the dynamics of a single particle evolving in a visco-elastic medium under the effect of hydrodynamic backflow which includes added mass and Basset force. Arbitrary ... [more ▼] We review equilibrium properties for the dynamics of a single particle evolving in a visco-elastic medium under the effect of hydrodynamic backflow which includes added mass and Basset force. Arbitrary equilibrium forces acting upon the particle are also included. We discuss the derivation of the explicit expression for the thermal noise correlation function that is consistent with the fluctuation dissipation theorem. We rely on general time-reversal arguments that apply irrespective of the external potential acting on the particle, but also allow one to retrieve existing results derived for free particles and particles in a harmonic trap. Some consequences for the analysis and interpretation of single-particle tracking experiments are briefly discussed. (C) 2014 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 46 (1 UL) |
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