ESPCI web site
Séminaire Café (Interne)
Il s’agit d’un exposé assez court (20 min) et assez informel.
Prière aux conférencier·ère·s de ne jamais dépasser 30 min et de vérifier la compatibilité avec le projecteur avant le séminaire.
Les séminaires ont lieu les jeudis après la réunion du laboratoire qui débute à 13h30 dans la bibliothèque du labo sur le campus Jussieu, Barre Cassan, Bât A, 1er étage.
Pour suggérer un titre et envoyer un abstract, contacter 
et 
.
Coffee seminars are supposed to be short and informal presentations (20 min).
Please never last longer than 30 min and check the compatibility of the projector with your computer before the seminar.
Location : Campus Jussieu, Barre Cassan, Bât A, 1er étage
7 quai Saint Bernard
75005 Paris
To suggest a title or send an abstract, please contact and
| 30 avril | Éléonore Duval - Université du Mans, MSC Instabilités paramétriques spatio-temporelles dans un ruban _mou_ Des variations périodiques de la tension d’une corde peuvent générer un mouvement transverse lorsque la fréquence de forçage approche le double de l’une de ses fréquences propres. Ce phénomène, identifié par Melde au XIXe siècle, est analogue à la résonance d’un oscillateur soumis à un forçage paramétrique. On s’intéresse ici à un ruban mou soumis à une modulation de sa tension. Contrairement au cas classique de résonance paramétrique, dominé par un unique mode sous-harmonique à fréquence moitié, l’utilisation d’un matériau très souple induit une modulation simultanément spatiale et temporelle, donnant naissance à une dynamique atypique. L’émergence conjointe de deux composantes sous-harmoniques permet des réponses dont la période dépasse nettement celle de l’excitation. Le régime non linéaire diffère de celui des résonances paramétriques usuelles, et un régime tristable est notamment observé. Un modèle théorique reposant sur un développement en échelles multiples prédit et décrit cette dynamique. L’ensemble met en évidence une forme originale d’instabilité spatio-temporelle dans un système de dimension finie, élargissant le cadre des instabilités paramétriques traditionnelles. |
| 7 mai | Nicolas Harmand - LJP Stress and rheology measurements at the microscale : Droplets as versatile sensors in vivo A recent study, using zebrafish embryos as a model system, showed that the developing eye exerts lateral traction forces on the olfactory placode via the ExtraCellular Matrix (ECM), impacting morphogenetic movements and axon extension within the placode. To tackle this question further and understand how the ECM transmits forces between the two tissues, we are developing self-functionalizing droplets that can display binders on their surface upon injection of the droplet in the embryo. The droplets can be designed to adhere to various components of ECM. By tuning the surface tension, they can be made deformable enough to reveal information about the forces at play, from droplet shape analysis and modeling. During morphogenetic events both mechanical and biochemical signaling can contribute to changes in ECM structure and properties. In order to reach a complete understanding of the role of ECM as force transmitter we need to understand how these properties emerge. For that, we design ferrofluid droplets actuated by an oscillating magnetic field to map the rheological properties of ECM. These two types of mechanical sensors are embedded within the ECM of developing zebrafish embryos which enable us to completely characterize the bio-mechanical phenomena at play during morphogenetic events. Altogether, this approach will bring new mechanistic knowledge on the role of ECM and its mechanical properties during tissue morphogenesis in vivo, with potential implications for ECM-related diseases, tissue engineering and regenerative approaches. |
| 14 mai | Ascension - pas de séminaire café |
| 21 mai | Julien Le Dreff - LadHyX Moving backward to go faster : Diatom-inspired sliding reveals efficient modes of locomotion Across biological scales, from sperm cells to whales, locomotion commonly relies on undulatory gaits, in which traveling deformation waves interact with the surrounding fluid to generate thrust opposite to the direction of wave propagation. In viscous environments, microorganism locomotion is classically understood in terms of undulatory bending of slender filaments such as flagella, with optimal propulsion achieved when the deformation wavelength is comparable to the swimmer length. Inspired by diatom colonies, we identify a fundamentally different swimming mechanism based on sliding between neighboring elements within a chain. We show that sliding between stacked elongated cells generates internal shear that drives propulsion opposite to classical undulatory swimming, while achieving higher speeds and greater energetic efficiency. Remarkably, optimal performance occurs at wavelengths much larger than the chain length and at cell aspect ratios consistent with those observed in natural diatom colonies, suggesting that hydrodynamic efficiency may constitute an evolutionary selective pressure in diatom chains. Together, these results identify sliding as a previously overlooked mode of locomotion in multicellular assemblies. |
| 28 mai | Reda Belbahri - Owkin |
