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Perturbations in Flocking Systems (PIFS)
Date du début: 1 août 2013, Date de fin: 31 juil. 2017 PROJET  TERMINÉ 

"Flocking, the collective motion displayed by large groups of birds in the absence of a leader, is one of the most spectacular examples of emergent collective behavior in nature. Flocking is not only restricted to birds but can be observed in an extremely wide range of active matter systems – systems composed by “active particles” able to extract and dissipate energy from their surroundings to produce coherent motion -- as diverse as fish schools, vertebrate herds, bacteria colonies, insect swarms and active macromolecules in living cells.While our knowledge of collective motion has greatly advanced in recent years little is known concerning the response of moving groups to perturbations, a question of both theoretical interest (fluctuation-response in out-of-equilibrium physics) and of great ethological importance (biological significance of group response, spatio-temporal mechanisms of information propagation in cases of alert).Protection from external threats is thought to be one of the most important factors in the evolution towards collective behavior, and there is indeed evidence that certain collective properties observed in animal groups cannot be understood in the context of unperturbed theories. Experimental observations in starlings, for instance, have revealed that flocks are much more internally correlated, and thus have a more efficient collective response mechanism than expected from standard unperturbed flocking theories.Our working hypothesis is that certain properties of collectively moving animal groups can only be understood in terms of the system response to localized, dynamical perturbations. We will characterize the response of flocks to such perturbations, devoting particular attention to the role of information transmission from the boundaries to the bulk of a finite system.We will consider finite perturbations, but also the limit of infinitesimal perturbations, which may allow for a deeper theoretical analysis of linear response."