The study of plants from a biophysical point of view offers new highlights about plant growth, development and sensing. I will describe a range of experiments, where mechanical measurements combined with modelling help us to unravel interesting plant properties such as cytoskeleton rearrangement under an external force or modification of the seed properties along developmental stages. Among all mechanical parameters, I will focus on the hydrostatic pressure inside plant cells and present a new method to measure it using atomic force microscopy.

In the coming years the LHC will continue the exploration of the TeV scale by measuring the detailed properties of the discovered Higgs boson and by looking for signatures of new physics beyond the Standard Model. I will discuss why a full exploitation of the LHC physics reach requires precise theoretical predictions and simulation tools. I will then explain the basic concepts and approximations upon which these computations are based and review the theoretical developments that in the last decade allowed to improve substantially their accuracy, by including higher-order corrections. Examples of future LHC searches where the above improvements can be relevant to explore (directly or indirectly) BSM signatures will be discussed.

Although the DNA structure in double-helix is robust enough to enable
the preservation of the genetic code, it is sufficiently loose to allow
the formation of denaturation bubbles, i.e. the cooperative opening of a
sequence of consecutive base-pairs, even at physiological temperature.
DNA opening is central in biological mechanisms such as replication,
transcription, repair, or protein binding.

The issue of the nucleation and slow closure mechanisms of non
superhelical stress-induced denaturation bubbles in DNA is tackled using
coarse-grained MetaDynamics and Brownian simulations. A minimal
mesoscopic model is used where the double helix is made of two
interacting bead-spring rotating strands with a prescribed torsional
modulus in the duplex state. We demonstrate that timescales for the
nucleation (resp. closure) of an approximately 10 base-pair bubble, in
agreement with experiments, are associated to the crossing of a
free-energy barrier of 22 k_B T (resp. 13 k_B T) at room temperature T.
MetaDynamics allows us to reconstruct accurately the free-energy
landscape, to show that the free-energy barriers come from the
difference in torsional energy between the bubble and the duplex states,
and thus to highlight the limiting step, a collective twisting, that
controls the nucleation/closure mechanism, and to access opening time
scales on the millisecond range. Contrary to small breathing bubbles,
these more than 4 base-pair bubbles are of biological relevance, for
example when a preexisting state of denaturation is required by specific
DNA-binding proteins.

Thèse de Fernando.

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.

In this seminar I will review a family of models that couple Maxwell equations for the classical description of an electromagnetic field induced by a laser and Bloch equations for the quantum description of matter, which will be of various type, isotropic gases, crystals, quantum boxes. The models are obtained either in the Schrödinger or the Heisenberg picture of quantum mechanics. Various phenomena can be taken into account such as nonlinear effects, Coulomb interaction, electron-phonon interactions… Numerical methods have been developed to show the numerous situations that can be described by these models. They are however very expensive to simulate and a few hints on derived asymptotic models will also be given.