The implementation of photosensitive surfactants into various bottom-up designed soft matter systems allows us to place under photocontrol a large variety of properties and functions. At the molecular scale, the photocontrol of nucleic acid (DNA, RNA) higher-structure [1,2] enables the photocontrol of gene expression at both transcription and translation levels, in a sequence-independent and reversible manner [3,4]. This is currently applied for the photocontrol of enzymatic reactions and membrane protein assembly. At a supramolecular level, we use light to break the membrane of giant unilamellar vesicles (GUVs) with high spatial resolution [5]. The GUV response to light is sensitive to membrane fluidity and critically depends on the presence of solid or liquid-ordered lipid domains. At the micro-scale, light-induced changes of wettability allow us to dynamically control using light the generation of micro-droplets in simple microfluidic devices [6]. At a macroscopic scale, a light-controllable Marangoni effect, called chromocapillary effect, is used to manipulate millimeter-sized droplets with high spatio-temporal resolution [7]. References: [1] Chem. Eur. J. 2010, 16, 11890-11896 [2] Soft Matter 2011, 7, 5854-5860 [3] Proc. Natl. Acad. Sci. USA 2009, 106, 12219-12223 [4] Biomacromolecules 2011, 12, 3945-3951 [5] J. Am. Chem. Soc. 2012, doi: 10.1021/ja211664f [6] Lab Chip 2011,11, 2666-2669 [7] Angew. Chem. Int. Ed. 2009, 48, 9281-9284

Conventional computer simulations of biomolecular systems are greatly hampered by the multiple-minima problem，where the simulations tend to get trapped in some of a huge number of local-minimum energy states. In order to overcome this difficulty，we have been advocating the uses of generalized-ensemble algorithms，which are based on non-Boltzmann weight factors. Multicanonical algorithms, simulated tempering, and replica-exchange methods are popular examples of generalized-ensemble algorithms. With these algorithms we can explore a wide range of the conformational space. The advantage of generalized-ensemble algorithms lies in the fact that from only one simulation run， one can obtain accurate estimates of various thermodynamic quantities as functions of temperature and other parameters of the system. In this talk，I will present the latest results of various applications of generalized-ensemble simulations to biomolecular systems. Examples are folding of a small protein, ligand docking, and pressure-induced denaturation.

We will consider the quantification of the invariant sub-algebras of the loop and of the half-loop Lie algebras of sl(2). This quantification use the notion of twist for Manin triples. The Manin triples are usually used in the construction of the quantum loop and half-loop Lie algebra of sl(2). From this construction, we obtain four co-ideal algebras: the q-Onsager and the augmented q-Onsager for the " loop" case and the two twisted Yangians for the "half-loop" case. We will discuss the role of these algebras in the context of quantum integrable models with boundaries and reflection equations. Some open problems about the "Drinfel'd second realisation" of the reflection algebra and the Q baxter operators will be presented.

Le comportement des objets de la physique quantique est dominé par la dualité onde-particule, Cette caractéristique fondamentale est singulière. Parfaitement décrite par la mécanique quantique, elle échappe à notre intuition et elle est habituellement considérée comme sans équivalent possible en physique classique. Nous avons récemment montré qu'une gouttelette, rebondissant sur une surface liquide vibrée, peut se coupler aux ondes de surface qu’elle génère. Elle forme alors un “marcheur” auto-propulsé associant une particule à une onde. Nous présenterons plusieurs expériences visant à comprendre comment, dans ce système classique, une onde étendue et une particule localisée peuvent avoir une dynamique commune. On verra que, de manière inattendue, on retrouve une forme de principe d'incertitude ainsi qu'une forme de quantification des orbites. On montrera que dans ces expériences la structure du champ d'onde contient une mémoire de la trajectoire récente de la particule. C'est cet effet de « mémoire de chemin » qui est responsable des comportements observés. Les limites dans lesquelles ce système macroscopique et dissipatif peut être comparé aux objets quantiques seront discutées.

La dynamique des électrons dans le potentiel périodique d’un réseau cristallin est étudiée. Les différences entre la vitesse instantanée et la vitesse moyenne, l’impulsion et la quasi impulsion d’un électrons sont soulignées. Le modèle simple à deux bandes d’un semi-conducteur est développé et il est démontré quel genre de masse effective de l’électron l’on doit introduire. Les électrons dans le graphène sont alors considérés comme illustration. Un effort dans la présentation est fait pour corriger les malentendus existants dans les manuels de physique du solide.

In tube flow, blood is usually treated as a Newtonian fluid down to diameters of about 200 µm. By means of Dissipative Particle Dynamics (DPD) we investigate the flow of red blood-cell (RBC) suspensions driven through small tubes (diameters 10-150 µm) marking the transition from arterioles and venules to the largest capillary vessels. Previously our DPD suspension model (Fedosov DA, Pan W, Caswell B, Gompper G, and Karniadakis GE, Predicting human blood viscosity in silico, Proc. Nat. Acad. Sci. USA, 108(29):11772-11777(2011)) successfully predicted the measured values of the Couette viscosity (CV) of blood in homogeneous plane shear flow. In tube flow the cross-stream stress gradient induces an inhomogeneous distribution of RBCs. It features a centerline cell density peak, and a cell-free layer (CFL) at the wall whose inner edge is the point of maximum RBC distortion. For a neutrally buoyant suspension the imposed linear shear-stress distribution together with the differentiable velocity distribution allow the calculation of the local viscosity across the section. At constant tube hematocrit (Ht) and after suitable scaling, the viscosity across the section as function of the scaled strain rate is found to be similar; i.e. it becomes essentially independent of size for the larger tubes. From experimental CV values this function is found to be determined by the local Ht and shear rate, i.e. in every cylindrical annulus, dr, the suspension responds to the local shear rate as if it were a plane Couette flow at the local Ht. As the tube size decreases the viscosity departs from the similarity function. Analysis of cell orientation suggests that just beyond the CFL the hematocrit(H) is depleted to the point where cell orientations can approach their CV values. Conservation then requires H to increase towards the center; hence for smaller tubes (<100µm) this crowding hinders the cells from attaining their CV orientations and the viscosity departs from similarity. Hence for the smaller tubes the flow cannot be described in terms of the Couette viscosity, and thus the stress cannot be described as a continuum, even a heterogeneous one.

During my Phd, I studied by analytical methods the glassy dynamics and the thermodynamics of a system of harmonic spheres, a model system interpolating between usual structural glasses and zero-temperature hard-spheres, allowing to study both the glass transition and the jamming transition. I will present results on the dynamics near the glass transition, and in the vicinity of the jamming point at very low, but finite temperature, that clarify the existing theoretical frameworks used to describe those two phenomena.

Purely elastic instabilities are known to occur in flows with curved streamlines of viscoelastic fluids at low Reynolds numbers (Re). They have recently attracted renewed interest as they have been shown to increase mixing in wavy microchannels [1]. The onset of instability has been proposed to be a function of the balance between streamline curvature and hoop normal stresses [2], but the exact form of this relation is scarcely studied, in particularly for channel flow. Here we report the results of a combined experimental and numerical investigation of variation of the instability threshold with the channel curvature. The experimental study is performed for a dilute polymer solution in a wavy microchannel. The channel of width W comprises a series of half loops of radius R which is systematically varied. We have analyzed the critical Weissenberg number (Wic) at which the flow becomes unstable as a function of the geometry of the channel and the properties of the polymer solution. The numerical simulations study the creeping flow limit (Re = 0) for a viscoelastic fluid obeying the upper-convected Maxwell model. Two-dimensional simulations matching the experimental conditions show that above a critical Weissenberg number the flow becomes unsteady. Good qualitative agreement between experiments and simulations is obtained and we show that the instability onset Wic is proportional to the square root of R/W with a small offset when R/W tends towards zero. These results are confirmed by a simple scaling argument following the Pakdel-Mckinley criterion [2]. [1] A. Groisman and V. Steinberg, New J. Phys. 6, 29 (2004). [2] P. Pakdel and G. H. McKinley. Physical Review Letters, 77(12):2459-2462, 1996.

Particle settling is a pervasive process in nature, and centrifugation of insoluble solids is a much versatile industrial separation technique. Sedimentation studies also originated powerful analytical methods such as ultracentrifugation, widely used in the separation of cellular organelles, carbon nanotubes, or graphene. Yet, the results of settling and ultracentrifugation experiments often appear to contradict the very law on which they are based: Archimedes Principle - arguably, the oldest Physical Law. The purpose of my talk is delving at the very roots of the concept of buoyancy by means of a combined experimental and theoretical study on sedimentation profiles in colloidal mixtures. Our analysis shows that the standard Archimedes’ principle is only a limiting approximation, valid for mesoscopic particles settling in a molecular fluid, and we provide a general expression for the actual buoyancy force. This “Generalized Archimedes Principle” accounts for unexpected effects, such as denser particles floating on top of a lighter fluid, which in fact we observe in our experiments. These findings should be highly relevant for the interpretation of many experiments in geophysics, chemical engineering, biology, and medicine, and may provide a tool to devise new ultracentrifuge separation methods sensitive to particle size.