The measurement of frequency-dependent viscoelastic moduli is of paramount importance in many fields, from material science to biology, and is typically accomplished in bulk materials using commercial rheometers. The trend towards miniaturization in the biotechnology, manufacturing and chemical processing industries has motivated the extension of viscoelastic measurements to microscopic objects with well-defined shape and size such as droplets, vesicles, microcapsules, or even single cells. Due to the reduced size of the samples, this extension requires novel mechanical techniques to control stress and strain, and novel strategies to disentangle bulk rheology from the contribution of interfaces. In addition, it faces the challenge of sampling highly heterogeneous populations such as those typical of biological samples. To this end, we developed a microfluidic technique to measure the rheology of cells and droplets flowing through narrow channels. Named Rheofluidics, this technique combines the high throughput of microfluidics with the versatility of traditional rheological probes. Like a stress-controlled rheometer, Rheofluidics measures the time-dependent deformation of droplets subject to a well-defined hydrodynamic stress, controlled by the shape of the microfluidic channel in which the droplets are flowing. To validate this approach and to demonstrate the power of Rheofluidics, we use it to study the linear and nonlinear rheology of oil droplets, hydrogel beads and lipid vesicles, extracting their viscoelastic properties with a throughput more than LF00 times higher than that of standard rheology.

We study the geometry of alpha' corrections to D-brane superpotentials using open-closed string duality. More specifically, we use F-Theory to study the contribution of D-branes in type IIB string theory wrapped on holomorphic cycles of a Calabi-Yau manifold to the superpotential, including the leading order alpha' corrections. We argue that mirror symmetry of the F-theoretic Calabi-Yau fourfold suggests that on the mirror dual type IIA side, some alpha' corrections of D-branes wrapped on special Lagrangian 3-cycles are topological and given by gravitational Chern-Simons invariants.

Processes such as embryogenesis, tissue repair, and cancer metastasis rely on the movement of large groups of cells through changes in group morphogenesis or collective migration. These processes involve both molecular and mechanical interactions between cells and their environment. Several efforts have been made to model such interactions [1]. In this presentation, I will demonstrate how studying tissue dynamics through a coarse-grain approach, considering tissues as active polar fluids, helps us understand their physical properties. We will examine two specific examples: first, the case of Neural Crest cell colonies, which migrate during embryogenesis to form head tissue, and how proliferation in these colonies affects their migration [2,3]; second, the case of mouse embryos changing their morphology to spread and attach to the substrate, and how the mother's age can influence this process [4]. [1] R. Alert and X. Trepat. Physical models of collective cell migration. Ann. Rev. 11: 77-LF1 (2020) [2] E.H. Barriga, K. Franze, et al. Tissue stiffening coordinates morphogenesis by triggering collective cell migration in vivo. Nature 554: 523-527 (2018) [3] C.L. Marchant, A.N. Malmi-Kakkada, et al. Cell clusters softening triggers collective cell migration in vivo. Nat. Mat. 21: CR14-CR23 (2022) [4] C. Pérez-González, R. Alert, et al. Active wetting of epithelial tissues. Nat. Phys. 15: 79-88 (2019)

Relations between quantum field theories and vertex operator algebras (VOAs) have proven ubiquitous. I will discuss one such instance, where VOAs arise on the boundary of topologically twisted 3d supersymmetric quantum field theories. These VOAs are defined from twisted non-Abelian quiver gauge theories by restricting to the boundary sector and performing a BRST reduction. The quiver description plays a key role, with parallels between the geometry of the associated quiver variety and structures of the corresponding VOA. There are two interconnected perspectives here: i) physically, BRST closed operators allow to construct an explicit homomorphism from affine W-algebras into the H-twist VOAs of particular quiver gauge theories, while ii) mathematically, the VOAs are defined as a chiralization of an extended quiver variety. The latter point of view is particularly powerful as it allows to implement a reduction procedure for the quiver diagrams, which translates to free-field realisations when lifted to the VOAs.

Potentiel candidat CNRS de l'équipe NMAT

Berglund Hubsch are Calabi-Yau of chain and loop types. We investigate the case when they are defined in the same weighted projective space. We show that they are deformation of each other. We also show that their mirrors are the same manifold for the 79 “Good” cases but not for the 77 “Bad” cases.

During my PhD at MSC (Paris), I investigated capillary flows of suspensions — systems where micrometric particles interact with dynamic free interfaces, such as in droplet spreading or thin film destabilization under their own weight. The suspension obtained upon the addition of the particles can in some cases follow the laws of simple fluids. In other cases, these laws require adjustments or, sometimes, entirely new dynamics emerge, where dissipation, capillarity, and extreme confinement play a key role. Next, I will present two projects from my postdoctoral work at the James Franck Institute (Chicago). The first explores the addition of solid particles to an acoustically levitated droplet, where the shape and stability result from the competition between acoustic pressure, gravity, capillarity, and particle confinement. The second project delves into the phenomenon of shear thickening in colloidal suspensions and investigates how the addition of granular particles affects the suspension’s rheology. Finally, I will present several project ideas for a potential application to the CNRS at the Laboratoire Charles Coulomb. My research would focus on two main axes. The first would investigate marine microplastics, aiming to refine the understanding and modeling of ballast effects caused by biofouling and clay aggregation on their surfaces. The second would focus on soil contamination by microplastics and nanoplastics, with particular attention to their diffusion, fragmentation, and impact on the mechanical and biological properties of soils.

Carbon nanostructures as functional and sustainable device components