The fruit fly larva is a maggot which looks like a dull white cylinder. Within a few days, and without any changes in its genome sequence, it metamorphoses. It gets its sophisticated adult fly shape with wings, legs, antennas, and compound eyes. How do cells migrate, deform, and rearrange to shape a tissue ? To approach step by step the dynamics of this morphogenesis, we will journey from developmental biology to mechanics, from discrete description of cellular material to continuum mechanics quantification, and from experiments to modeling. We will investigate flows within geometries specifically designed to discriminate between models.

Immune cells, particularly lymphocytes, must move, interface with other cell types, extract information from these interactions, and, if necessary, respond rapidly through endocytosis, status changes, proliferation, or cell killing. These critical biological processes rely on cytoskeletal rearrangement, mechanical sensing, and force production. In our research, we use microfluidics and micro-fabricated tools to investigate the forces at cell-cell interfaces and the cellular rearrangements triggered by antigen recognition. Recently, we introduced functionalized oil droplets as a novel antigen-presenting tool in the context of B cells, uncovering an unexpected role of microtubules in limiting F-actin polymerization, which facilitates the formation and maintenance of a distinct immune synapse. Additionally, I will present new applications of these methods, focusing on lymphocyte interactions with the microenvironment of lymph nodes and examining how mechanical factors influence their immune functions.

Propriétés électroniques et magnétiques de graphène Kagomé Alain Rochefort Polytechnique Montréal, Département de génie physique, Montréal, Canada Résumé La formation de polymères Kagomé avec des propriétés qui s’apparentent à celles du graphène a récemment généré de nombreux travaux sur ce type de matériau 2D aux propriétés parfois exotiques telles que des phases topologiques, des structures de bandes plates ainsi que des phases magnétiques liées à la structure des monomères. Dans cette présentation, je montrerai différents exemples de matériaux pouvant être produits par une approche de synthèse de surface (OSS) qui possèdent des propriétés électroniques et magnétiques prometteuses et pour lesquelles nous proposons également différentes approches pour moduler ces propriétés. Je montrerai également comment la symétrie des unités de base du polymère est au centre du contrôle de ces propriétés.

There has been a growing realization that the properties of a material can be modified just by placing it in an optical cavity. The quantum vacuum fields surrounding the material inside the cavity can cause nonintuitive modifications of electronic states through ultrastrong vacuum–matter coupling, producing a vacuum-dressed material with novel properties. Existing theoretical predictions include cavity-enhanced, cavity-induced, and cavity-mediated enhancement of electron–phonon coupling and superconductivity, electron pairing, anomalous Hall effect, ferroelectric phase transitions, quantum spin liquids, and photon condensation. Achieving the so-called ultrastrong coupling (USC) regime is a prerequisite for observing these effects, which arise when the interaction energy becomes a significant fraction of the bare photonic mode and matter excitation frequencies. Most intriguingly, when a material is ultrastrongly coupled with cavity-enhanced vacuum electromagnetic fields, its ground state will contain virtual photons. This nonperturbative virtual driving without external fields can lead to phase transitions in thermal equilibrium. This talk will describe our recent studies of USC phenomena in various solid-state cavity quantum electrodynamics systems in search of such vacuum-induced phases of matter. We utilize the phenomenon of Dicke cooperativity, i.e., many-body enhancement of light–matter interaction, to explore quantum-optical strategies for creating, controlling, and utilizing novel phases in condensed matter enabled by the quantum vacuum.

How well do we understand string theory? As one indicator can be thought of the degree of our understanding of its spectrum. Yet, other than comprising infinitely many physical states of arbitrarily high spin and mass, what does the string spectrum look like? Traditional methodologies can yield its state content on a level-by-level basis, a straightforward procedure which however becomes cumbersome as the level increases. In this seminar, we will discuss a new, covariant and efficient technology with which entire physical trajectories can be excavated. It is based on the observation that the Virasoro constraints in fact encode the generators of a bigger algebra, that is a symplectic algebra, which commutes with the spacetime Lorentz algebra. This enables constructing trajectories deeper inside the spectrum as “clones” of simpler ones, upon suitably dressing the latter, depending on the “depth” of the trajectory we aim to reach.

I will discuss some interesting results on instanton partition functions of Vafa Witten theory on CP^2 with gauge group SU(N). These results can be related to counting of sheaves on CP^2. In 2301.06711 paper we observed the growth of certain mock cusp forms associated with these mock modular forms. Interestingly the growth of these coefficients remain higher than those expected from Deligne bound. In our ongoing work we show that the holomorphic anomaly in theories are associated with these partition functions corresponding to gauge groups of lower ranks.