We have developed a process for creating liquid-core capsules having a thin hydrogel shell that can enclose either oil or aqueous media. The shell results from the gelling of an alginate solution (a natural polymer that turns into gel in presence of divalent cations) after a co-extrusion step. The encapsulation of an aqueous medium within a hydrogel envelope is not as straightforward since all phases are potentially miscible. I will show how mixing can be circumvented by playing with bulk and interfacial physicochemical properties of the various fluids. Then, I will present the features of the hydrogel membrane in terms of permeability and mechanical properties. Flow of a concentrated dispersion of capsules, where friction between objects can be tuned, will also be reported. Finally, I will discuss the use of such objects, especially in biotechnology. Indeed, the possibility to encapsulate cells into such a reservoir having a semi-permeable membrane opens the way to screen cell growth in various three-dimensional environments.

Le graphène est un cristal bidimensionnel (monoplan) de carbone dont l'empilement constitue le graphite. Il suscite un engouement considérable à la fois dans la recherche académique et dans le monde industriel. Ce sont principalement les propriétés électroniques exceptionnelles et uniques de ce matériau, dont la maîtrise reste un défi, qui expliquent cet intérêt mondial. Dans cet exposé, je décrirai les avancées récentes autour du graphène et des hétérostructures graphène/h-BN.

Amorphous materials as diverse as foams, emulsions, colloidal suspensions and granular media can jam into a solid-like disordered state. In this state each particle has a certain equilibrium position and can vibrate around it.

I show how to decompose the dynamical matrix M into the form M = AA^T. This representation allows to apply the random matrix theory and estimate the vibrational density of states. The resulting vibrational density of states is approximately constant over a wide frequency range which is determined mostly by the ratio of the number of degrees of freedom and the total number of contacts in the system. The results are in a good agreement with numerical experiments performed by various authors.

Examples for single cell volume and density measurements and elastography of cellular aggregates. Cell volume is a fundamental parameter for understanding cell cycle progression and regulation. I will describe a micro-fabricated system to accurately measure the volume of individual cells, adherent or not, over several cell division cycles. By following single cells through several division cycles, we found signatures of different cell size homeostasis mechanisms in different cell lines. Surprisingly, cells in mitosis exhibit a significant volume increase associated with a drop in cell density that could generate strong pushing forces.

On a multicellular level, tumors are subjected to external stress generated by their own growth in a confined environment and their surrounding tissues. Using full field optical coherence tomography, we measure spatially and temporally the strain inside spheroids after applying an isotropic osmo-mechanical pressure. The results show that spheroids do not behave as homogeneous viscoelastic spheres as they overreact to the applied stress. We finally estimate viscoelastic parameters of spheroids at the macro-scale.

"Thé au cube" est la pause café scientifique de l'axe PTh. L'orateur y expose de manière interactive et accessible aux théoriciens non-spécialistes, ses intérêts scientifiques du moment. N'oubliez pas de ramener vos tasses et autres mugs préférés.

Il sera démontré que, par l’action combinée du potentiel de confinement des électrons bidimensionnels dans le plan (xy) et du champ magnétique appliqué perpendiculaire à ce plan (force de Lorentz), un accepteur ionisé, donc répulsif pour un électron, peut localiser un ou deux électrons 2D de conduction. Le confinement des électrons de conduction autour de l’ion accepteur a pour résultat la création d’états discrets au dessus des états libres de Landau. Seront alors évoquées les conséquences observées sur les propriétés physiques d’un gaz 2D d’électrons sous champ magnétique quantifiant (domaine de l’effet Hall quantique).

In this talk, I will give a modern introduction to the challenges of studying black hole physics, both form bottom-up and top-down perspectives. As a top-down example, I will discuss a simple construction of gauged supergravity theories with spontaneously broken supersymmetry in Minkowski vacua with light charged matter in the low energy spectrum; one in which the microscopic entropy of black holes can still be counted reliably. I will also point out how such a simple idea naturally provides a stringy realization of the $\rho$ algebras of Schwimmer-Seiberg. Additionally, I will point out how this leads to a generalization of the AdS_3/CFT_2 correspondence; to one with twisted boundary conditions. Finally, I will briefly mention some work in progress on a bottom-up approach to black hole horizon dynamics.