Dans le cadre des activités de l'Erasmus Mundus Master in Complex Systems Science, et à l'occasion de la visite de Lev Tsimring au LPMA, un mini-workshop interdisciplinaire est organisé à destination des étudiants du master et d'un public plus large.

Programme des exposés

  • 11:15-12:00 Do plants do Math? The use of simple rules by growing life.
    Stéphane Douady (MSC, Université Paris Diderot)
  • 14:15-15:00 Active matter: a new interdisciplinary emerging field.
    Hugues Chaté (SPHYNX, CEA Saclay)
  • 15:15-16:00 Synchronization of synthetic gene oscillators.
    Lev Tsimring (University of California, San Diego)

Date et localisation

Le mini-workshop aura lieu vendredi 3 avril 2015 au Laboratoire de Probabilités et Modèles Aléatoires, Université Paris Diderot, Bâtiment Sophie Germain, Salle 1009 (1er étage). (Vous trouverez un plan ici.)


Abstracts

  • 11:15-12:00 Do plants do Math? The use of simple rules by growing life.
    Stéphane Douady (MSC, Université Paris Diderot)
    How to explain the Fibonacci series in leaf arrangements? The shape of the leaves? It can be traced to simple rules of growth, trying to optimize locally the packing (of embryonic leaves at the surface of the bud, or of the growing leaf in the volume of the bud). But the geometry of the space in which this growth occurs then imposes some unforeseen consequences.
  • 14:15-15:00 Active matter: a new interdisciplinary emerging field.
    Hugues Chaté (SPHYNX, CEA Saclay)
    Active matter is the vocable used today to group various situations in which particles, agents, spend energy to move. Such situations abound in biology and animal behavior, but they are also rising in computer science and robotics (distributed robotics, swarm intelligence), and increasingly in physics (smart colloids, in vitro assays with molecular mmotors, micro and nano swimmers, etc.). In this context, the toolbox and mindset of statistical physics plays a central role. I will describe how with statistical physics approaches we can hope to uncover and understand the generic if not universal collective properties of active matter.
  • 15:15-16:00 Synchronization of synthetic gene oscillators.
    Lev Tsimring (University of California, San Diego)
    One of the defining characteristics of life is the ability to keep time, which organisms often achieve by using internal genetic “clocks” to govern fundamental cellular behavior. While the gene networks that produce oscillatory expression signals are typically quite elaborate, certain recurring network motifs are often found at the core of these biological clocks. In this lecture I will describe our recent experimental and theoretical work on the oscillatory dynamics of synthetic gene circuits. One common motif which leads to oscillations in many natural biological “clocks” is delayed auto-repression. We designed and constructed synthetic gene circuits based on this design principle, and observed robust and tunable oscillations of gene expression in bacteria. Computational modeling and theoretical analysis show that the key mechanism responsible for oscillations is a small delay in the negative feedback loop. In a strongly nonlinear regime, this time delay leads to long-period oscillations that are characterized by “degrade and fire” dynamics. Using a variant of the same design in which oscillators are coupled chemical signals diffusing through cell membranes, we achieved regimes population-wide synchronization. We also observed an interesting regime of intra-cellular synchronization of two different gene oscillators indirectly coupled by a common degradation enzyme.

Co-organisateurs: Esteban Guevara (IJM, Paris 7), Vivien Lecomte (LPMA, Paris 7), Khashayar Pakdaman (IJM, Paris 7)