Statut  Confirmé 
Série  WORKCONF 
Domaines  condmat.disnn 
Date  Jeudi 23 Mars 2017 
Heure  12:30 
Institut  LPTM 
Salle  Auditorium MIR Neuville sur Oise (IEA/UCP) 
Nom de l'orateur  Torcini 
Prenom de l'orateur  Alessandro 
Addresse email de l'orateur  
Institution de l'orateur  LPTM Cergy 
Titre  Synchronization: a general phenomenon in complex systems 
Résumé  In this talk I will try to give an overview of recent achievements in the field of complexity. The science of complexity is a new and extremely transdisciplinary field of research. Many definitions have been given so far and yet the concept has resisted categorization, but, nevertheless becomes more and more attractive for many researchers in different fields. One of the points of agreement among the scientists is that complex systems are those composed of a large number of interacting elements, so that the collective behaviour of those elements goes far beyond the simple sum of the individual behaviours [1]. In the last twenty years, one of the most studied collective behaviours has been spontaneous synchronization in networks of elements with simple dynamics, e.g., oscillators [2]. Synchronization occurs in physical/biological systems over a wide range of spatial/temporal scales, e.g., in electrochemical oscillators, laser arrays, animal flocking, pedestrians on footbridges, etc [3]. Besides the synchronous firings of cardiac cells required to keep the heart beating, synchrony is required for technological applications, e.g., in electrical powergrids, the generators must lock to the grid frequency [4]. Synchrony also has undesirable effects, e.g., in brain circuits, it can be related to epilepsy. Interactions among identical units can even lead to more complex collective behaviours, e.g., in fully coupled systems, to quasiperiodic and chaotic evolutions [5], while the presence of nonlocal coupling can induce the emergence of new states with broken symmetry, termed ”Chimera States”, where synchronized and desynchronized populations coexist [6]. Chimera states have been reported in experiments in optoelectronic devices, mechanical oscillator networks and electronic delayed oscillators [7]. An extremely powerful exact method recently developed is the OttAntonsen Ansatz [8], which allows to rewrite the dynamics of fullycoupled networks of phase oscillators in terms of few collective variables. The success of the approach has led to hundreds of recent publications in applied mathematics and physics. A recent application [9] to spiking neural networks has opened up the perspective to apply this method to computational neuroscience and to derive exact models able to describe at a macroscopic level the dynamics of a neural population. 
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