Biogels formed through the self-association of polysaccharide coils, collagen, actin filaments or attractive globular proteins play a major role in biochemistry and microbiology, biological networks and cell mechanics as well as in food science. Their mechanical properties are the physical basis of biomechanics and morphogenesis. These biomaterials all behave as elastic solids under small deformations but display remarkable non-linear behaviour generally featuring stress- or strain-stiffening and fractures prior to irreversible rupture.

Here we explore the mechanical behaviour of a model protein gel (acid-set sodium caseinate, i.e. "yoghurt") under stress : either constant shear stress that drives it to irreversible rupture; or swelling-induced compressive stress that causes wrinkling of a thin sheet of gel. The former emphasises the similarity between biogels and brittle solids, in excellent agreement with recent fiber-bundle models that include damage accumulation on elastic fibers. The latter highlights the soft nature of biogels, in particular their porosity and the influence of the solvent.

Different from the large scale where bulk forces prevail, at small scales, fluid-structure interactions are dominated by surface forces. For example, even if the fluid is at rest, small sized flexible structures can be deformed by the action of surface tension forces.

As an example of this type of interactions, I will present an experimental study of the out of plane buckling of a flexible annulus floating on a bath of water and submitted to a a difference in surface tension between its inner and outer edges. Based on standard buckling theory, scaling laws for the buckling threshold of the annulus, as well as for the wave length and radial extension of the wrinkles are presented.

As a brief introduction, I will present a general view of my past and recent research on the fluid-structure interaction domaine, as well as some future perspectives.

I will show how the usual Loop Quantum Gravity phase space can be deformed to characterize hyperbolic discrete geometries and thus be a candidate to describe the discretization of SU(2) BF theory with a (negative) cosmological constant. The quantization of this model will then give at the kinematical level, an Hilbert space spanned by spin networks built on Uq(su(2)) (with q real). I will also build an Hamiltonian constraint and show that the Turaev-Viro amplitude with q real is a solution of the quantum Hamiltonian. This model is therefore a natural candidate to describe 3D loop quantum gravity with a (negative) cosmological constant.

In this talk I will review the most relevant results obtained in arXiv:1411.7623.
In particular, I will focus on the possibility to use the gamma-ray data collected by the Fermi Large Area Telescope as a probe to investigate non-standard properties of cosmic-ray diffusion in the Milky Way galaxy. The seminar, although technical in various aspects, is addressed to a broad audience.

Phospholipids (PLs) with polyunsaturated acyl chains are extremely abundant in a few
specialized cellular organelles such as synaptic vesicles and photoreceptor discs, but their
effect on membrane properties is poorly understood. Here, we found that polyunsaturated
PLs increased the ability of dynamin and endophilin to deform and vesiculate synthetic
membranes. When cells incorporated polyunsaturated fatty acids into PLs, the plasma
membrane became more amenable to deformation by a pulling force and the rate of
endocytosis was accelerated, in particular, under conditions in which cholesterol was
limiting. Molecular dynamics simulations and biochemical measurements indicated that
polyunsaturated PLs adapted their conformation to membrane curvature. Thus, by
reducing the energetic cost of membrane bending and fission, polyunsaturated PLs may
help to support rapid endocytosis.

Briefly, i will introduce before the role of a confinement on cytoskéleton self-organization (phD project).

Temperley-Lieb algebras are rank-one quotients of the famous Hecke algebras and known in the theory of invariants as the Schur-Weyl duals to the Lusztig's specialization of the quantum group U_q sl(2). The TL algebras appear in a transfer-matrix formulation of statistical lattice models, like XXZ and super-symmetric spin-chains. At q roots of unity, the lattice models enjoy an interesting property that taking the continuum limit gives a logarithmic conformal field theory, which is a non-rational CFT based on non-semisimple Virasoro representations. Taking these limits in a rigorous way is usually poorly understood. In the talk, I will present an explicit inductive system construction for finite TL algebras at a root of unity that gives the Virasoro in the limit. On the abstract grounds, I will also discuss my recent result on a connection between finite TL algebras and the deformed Virasoro algebra at roots of unity cases.

I introduce a novel class of soft structures that exhibit elastic instabilities. I use them
as a building block to create soft mechanical metamaterials with
highly nonlinear and novel properties, such as negative elasticity, elastic memory and programmability.
Combining fabrication via 3D printing, experiments, numerical simulations and theory,
I fabricate and investigate the physics of 1D (beams), 2D (holey sheets) and 3D (cubes) systems.
On these examples, I will show that nonlinearity is the main ingredient to understand and design these
exotic mechanical responses.

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

I will explain how to compute the Hilbert series that
counts chiral operators parametrising the Coulomb branch of the
moduli space of 3d N=4 supersymmetric field theories. The formula has
applications to physics, such as to the study of infrared dualities
in three dimensions and of backgrounds with eight supercharges, as
well as to mathematics, where it provides a new way to characterise
hyperKähler cones as algebraic varieties. I will then show how the
Coulomb branch of certain 3d N=4 generalised quiver gauge theories
can be used to compute the Hilbert series of the moduli space
of k G-instantons, for any simple Lie group G.
The construction is alternative to the ADHM construction
that is only available for classical groups G.