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
| 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 | Ana-Maria Bratu - LadHyX Geometry-driven jets underlie dispersal of plants and fungi by raindrops Plants and fungi have independently evolved a wide range of reproductive strategies, including the use of wind, insects, fruit-eating animals, and rain to disperse their reproductive units. In some cases, convergent evolution has led to the emergence of similar mechanisms in unrelated organisms. A striking example is the development of specialized cup-shaped structures called splash-cups that store reproductive units. Upon raindrop impact, these structures enable the ejection of the units away from the parent organism, facilitating local colonization. While the role of rain in plant dispersal has been first observed by Brodie [1], and later examined through the lens of fluid mechanics by Amador et al. [2], the underlying mechanisms governing dispersal remain poorly understood. Most existing research on droplet impact has focused on flat surfaces [3], with only limited attention given to complex concave geometries like splash-cups [2, 4]. Dispersal by rain therefore remains understudied despite its biological significance. We investigate how splash-cup structures enable the rain-driven dispersal of reproductive units in diverse organisms. When impacted by raindrops, these structures can redirect the incoming water to form fluid jets that eject the reproductive units away from the parent organism. To study the underlying dynamics, we conducted drop impact experiments on 3D-printed biomimetic cups, varying morphological parameters such as cup diameter and cone angle. Our results reveal two distinct dynamical regimes and their boundaries within the morphological parameter space, as well as two jetting behaviors that we associate with dispersal strategies optimized for different classes of organisms. We thus provide a mechanistic understanding of dispersal by rain and introduce a class of drop impact problems of fundamental interest. [1] H. J. Brodie, “THE SPLASH-CUP DISPERSAI. MECHANISM IN PLANTS’”. [2] G. J. Amador, Y. Yamada, M. McCurley, and D. L. Hu, “Splash-cup plants accelerate raindrops to disperse seeds,” J. R. Soc. Interface, vol. 10, no. 79, p. 20120880, Feb. 2013, doi : 10.1098/rsif.2012.0880. [3] C. Josserand and S. T. Thoroddsen, “Drop Impact on a Solid Surface,” Annu. Rev. Fluid Mech., vol. 48, no.1, pp. 365–391, Jan. 2016, doi : 10.1146/annurev-fluid-122414-034401. [4] M. O. Hassett, M. W. F. Fischer, Z. T. Sugawara, J. Stolze-Rybczynski, and N. P. Money, “Splash and grab : Biomechanics of peridiole ejection and function of the funicular cord in bird’s nest fungi,” Fungal Biol., vol. 117, no. 10, pp. 708–714, Oct. 2013, doi:10.1016/j.funbio.2013.07.008. |
| 4 juin | Eva Kanso - USC |
