The transition from supercooled liquid to glass is marked by the increase in viscosity as the temperature is lowered. As the stress relaxation time exceeds that of mechanical response measurements, the elastic-like response of the liquid becomes observable and we have a viscoelastic liquid. In this talk we determine the magnitude of the elastic modulus of the viscoelastic liquid (the so called plateau modulus) and its dependence on temperature and system size. We examine the relationship between the plateau modulus of the viscoelastic liquid and that of the low temperature glass.

On présente des expériences de propagation d’ondes à la surface de l’eau dans des contextes de propagation en milieux complexes. La mesure du champ d’élévation de ces ondes de gravité est effectuée à l’aide d’une technique de mesure de Profilométrie par Transformée de Fourier, qui permet une mesure globale et instantanée. Outre leur intérêt propre (propagation océanique, tsunami, vagues scélérates, ...), les ondes à la surface de l’eau présentent une analogie avec la propagation d’ondes acoustiques (équation de Helmholtz) qui motive l’utilisation de concepts développés en électromagnétisme (métamatériaux, cristaux photoniques/photoniques); cependant, dans le cas des ondes à la surface de l’eau, les effets de viscosité, de capillarités (par exemple aux ménisques) peuvent modifier les phénomènes attendus. Des exemples seront donnés: le cloacking par un milieu homogénéisable en couche, l’hyperfocalisation par un réseau de tiges et la résonance d’un réseau périodique d’obstacles. Des études plus spécifiques, concernant le comportement des ondes non linéaires, seront également présentées: turbulence d’ondes de gravité/capillarité, tsunami, retournement temporel des ondes à la surface de l’eau.

La ségrégation de l’ADN chez les bactéries est une étape essentielle du cycle cellulaire qui permet la transmission fidèle du matériel génétique dupliqué de la cellule mère à chacune des deux cellules filles. Ce processus est assuré par des systèmes actifs très efficaces. Ils sont minimalistes et se composent de seulement trois éléments essentiels : un centromère, une protéine de fixation au centromère (ParB) et une protéine qui hydrolyse l’ATP (ParA), considérée comme la protéine motrice de la ségrégation. Le mécanisme moléculaire sous-jacent à ce processus clé du cycle cellulaire est cependant controversé. Il existe deux modèles majeurs pour décrire la ségrégation. Le premier suggère qu’elle est entrainée par une polymérisation de ParA, tandis que le second suggère qu’elle est induite par un mécanisme de réaction-diffusion. Dans les deux modèles, il est considéré que ParB stimule l’hydrolyse de l’ATP par la protéine motrice ParA, lui donnant l’énergie nécessaire pour se déplacer dans la cellule. Nos travaux récents, sur le système de ségrégation du plasmide F d’Escherichia coli par la combinaison d’approche génétique, biochimique et de microscopie, révèlent le rôle de l’hydrolyse de l’ATP dans l’étape précoce de séparation des centromères. Nous cherchons aussi à caractériser l’architecture de l’assemblage nucléo-protéique sur le centromère.

Biology has been an important source of inspiration for physics in the past. One famous example is the Brownian motion of seeds that finally lead to the determination of Avogadro’s number. Another example is the discovery of the first virus, Tabacco Mosaic Virus, that lead the famous paper of Onsager on the isotropic-nematic phase transition, showing that colloidal rods form the most basic system to study the origin of self-assembled structures. In this talk I will first show what can be learned from the dynamical behavior of individual rods about the nature of the equilibrium self-assembly in structure with no ordering, only orientational ordering and 1-, 2- and 3-D positional ordering [1,2]. This is experimentally achieved by tracking rod-like fd viruses with video fluorescence microscopy. The viruses are ideal model systems since they are very slender, monodisperse and can be made with variable stiffness. Dynamic signatures for the different phase transitions are obtained, leading to a reconsideration of the nature of the transitions. Another interesting aspect of colloidal rods is that they are very susceptible to external fields. In shear flow the torque on the rod will cause alignment, while in confinement rods tend to align with the wall. Both effects can drive or frustrate structure formation. In the second part of the talk, I will give several examples of this interplay of rod dispersions with external fields and show pathways to a microscopic understanding of the observed phenomena. Here I will also include experiments on F-actin in shear flow. [1] M. P. Lettinga and E. Grelet. Self-Diffusion of Rodlike Viruses through Smectic Layers. Phy. Rev. Lett. 99, 197802, 2007. [2] S. Naderi E. Pouget, P. Ballesta, P. van der Schoot, M. . Lettinga, and E. Grelet. Fractional hoping-type motion in columnar mesophase of semi-flexible rod-like particles. Phys. Rev. Lett. 2013.

I introduce a new tool, SModelS for decomposing generic SUSY spectra into SMS topologies and testing them against the existing Simplified Model Spectra (SMS) limits from the LHC. While the current implementation focuses on supersymmetry, the tool is in principle applicable to any beyond the Standard Model theory respecting a Z2 symmetry. I will explain the working principle of SModelS, as well as its validation and limitations. I will exemplify the applicability of SMS results to SUSY parameter space and discuss how we can learn more about improving the representation of experimental results in an efficient fashion ( arXiv:1312.4175). As a physics-case example, I will then present the application of SModelS in a study of light neutralino dark matter in the MSSM (arXiv:1308.3735). Here I will discuss the viability of light neutralino DM with mass below 35 GeV consistent with LHC bounds. Higgs search results as well as direct and indirect DM detection constraints are taken into account.

We discuss how the nonequilibrium driving forces introduced by the natural biological activity or by a physical self-propulsion mechanism generically affects the structure, dynamics and phase transitions of particle systems. We use theory and computer simulations to analyse simple models of such active materials, and make connections with experimental studies of self-propelled colloidal systems and biological tissues.

Inspired by the relations with matrix models and gauge theories, we introduce equations in 2d conformal field theory, which are the analogs of the loop equations of matrix models. Solving a conformal field theory then amounts to solving these equations. We solve them for two values of the central charge: c=1 and c=infinity. In the case c=1, the solution is built from a Lax matrix, which is a matrix square root of the energy-momentum tensor. In the case c=infinity, the solution is built from a non-commutative spectral curve, which (via topological recursion) encodes the perturbative expansion of correlation functions. In both cases, we recover the appropriate limit of the Liouville three-point function.

We will present the physics of hydrodynamic waves in stratified fluids and in particular in the ocean. Starting with simple experiments emphasizing the generation of  localized  nonlinear  internal  waves at the interface of layers with different  densities,  we will consider the formation  of  hydrodynamics solitons, also called tsunamis. More sophisticated experiments in a continuously stratified fluid allow to understand the behavior of these waves, often very unusual. We will present in particular interesting nonlinear  effects, such  as  parametric  subharmonic  instabilities or reflection on sloping  boundaries which are among the dominant mechanisms leading to dissipation.

In this talk, I will first make a brief introduction on historical situation about mathematics in Japan. From this one may understand why the Institute of Mathematics for Industry (IMI) was established in Kyushu University. I will present various research and educational activities (mostly PhD programs) in IMI with industry and technology based on fundamental research on mathematics (sometimes/often relation with other science), and explain shortly also some initiatives of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japanese government.