The liquid-crystalline smectic blue phases

Smectic blue phases (BPSm) are new mesophases of thermotropic liquid crystals, which exhibit a double geometrical frustration: the extension of chirality in three spatial dimensions like the classical blue phases, and helical twist competing with smectic order, as in the TGB phases. The existence of a quasi-long range smectic order in BPSm phases breaks the cubic symmetry of classical blue phases. The symmetries of these new phases have been determined by X-ray scattering and optical polarizing microscopy experiments.Comment: 5pages, 13 figure

Fast Diffusion of Long Guest Rods in a Lamellar Phase of Short Host Particles

We investigate the dynamic behavior of long guest rod-like particles immersed in liquid crystalline phases formed by shorter host rods, tracking both guest and host particles by fluorescence microscopy. Counter-intuitively, we evidence that long rods diffuse faster than short rods forming the one-dimensional ordered smectic-A phase. This results from the larger and non-commensurate size of the guest particles as compared to the wavelength of the energy landscape set by the lamellar stack of liquid slabs. The long guest particles are also shown to be still mobile in the crystalline smectic-B phase, as they generate their own voids in the adjacent layers.Comment: 5 pages, 4 figures, Accepted in Phys. Rev. Let

Elementary edge and screw dislocations visualized at the lattice periodicity level in smectic phase of colloidal rods

We report on the identification and quantitative characterization of elementary edge and screw dislocations in a colloidal smectic phase of tip-labeled rods. Thanks to the micrometer layer spacing, direct visualization of dislocations has been performed at the \textit{smectic periodicity scale} by optical fluorescence microscopy. As a result, the displacement field around an edge dislocation has been experimentally established and compared with the profile predicted by elastic theory. Elementary screw dislocations have been also evidenced, for which the core size as well as the \textit{in situ} handedness have been determined. Self-diffusion experiments performed at the individual particle level reveal for the first time nematic-like or "melted" ordering of the defect core.Comment: 5 pages, 5 figures, accepted in PR

Focus in Ewe

International audience—In this paper, a strides detection algorithm is proposed using inertial sensors worn on the ankle. This innovative approach based on geometric patterns can detect both normal walking strides and atypical strides such as small steps, side steps and backward walking that existing methods struggle to detect. It is also robust in critical situations, when for example the wearer is sitting and moving the ankle, while most algorithms in the literature would wrongly detect strides

Directing liquid crystalline self-organization of rod-like particles through tunable attractive single tips

Dispersions of rodlike colloidal particles exhibit a plethora of liquid crystalline states, including nematic, smectic A, smectic B, and columnar phases. This phase behavior can be explained by presuming the predominance of hard-core volume exclusion between the particles. We show here how the self-organization of rodlike colloids can be controlled by introducing a weak and highly localized directional attractive interaction between one of the ends of the particles. This has been performed by functionalizing the tips of filamentous viruses by means of regioselectively grafting fluorescent dyes onto them, resulting in a hydrophobic patch whose attraction can be tuned by varying the number of bound dye molecules. We show, in agreement with our computer simulations, that increasing the single tip attraction stabilizes the smectic phase at the expense of the nematic phase, leaving all other liquid crystalline phases invariant. For a sufficiently strong tip attraction, the nematic state may be suppressed completely to get a direct isotropic liquid-to-smectic phase transition. Our findings provide insights into the rational design of building blocks for functional structures formed at low densities.Comment: 13 pages, 4 figure

Pathways in education and access to employment: THE CASE OF FRENCH VOCATIONAL TERTIARY TRACKS

22 p.This paper aims to compare the pathways in education and the access to employment of young French graduates from the two principal tertiary short vocational tracks: the Advanced Technical Courses (STS ) and the Technological University Institutes (IUT). The originality of this comparison lies in its re-examination of these educational pathways in the light of individual trajectories onto the labour market, and the perspectives that emerge. Not only course changes, dropouts or academic failures but also successfully completed studies are viewed here as elements in the increasing complexity of training pathways, based on which career guidance upstream and its effect on the transition options from education to employment downstream will be examined. The comparison of pathways during and following higher education revolves around three key questions: - What similarities and differences can be observed between the careers strategies and the academic profiles of students following IUT and STS tracks? - What progress is made by enrolees to these tracks during higher education and what determining factors explain the different structures? - In what ways do these differentiated educational pathways result in more or less effective access into the labour market

La procédure FREQ de SAS. Tests d'indépendance et mesures d'association dans un tableau de contingence

Une première version de ce document fut d'abord publiée en 1992 à l'Université d'Orléans ; il est maintenant épuisé. En 1996 il a été complété et réédité à l'INSEE sous forme d'un document de travail de la Direction des Statistiques Démographiques et Sociales, n° 9603, 78 pages, toujours disponible. En 1997, il fut de nouveau réédité dans la revue MODULAD de Juin 1997 dans une version un peu raccourcie (50 pages). C'est cette version remaniée qui est publiée par la Revue MODULAD dans son numéro 33.This paper presents, in a pedagogical way, the different tests and association measurements available in PROC FREQ of SAS software, distinguishing them according to the nature of the variables in presence: categorical, ordinal-scaled. They are then described with comments and applied to various examples. The probabilistic approach based on odd-ratios and logit model is tackled. In order to point out the possible doubts when using a unique test, a "curiosity" is reported revealing the differences in the results obtained from various standpoints. A history of the exact Fisher test allows the reader to confort his opinion.Ce document présente de manière pédagogique, les divers tests et mesures d'association disponibles dans la procédure FREQ de SAS. Ces tests et mesures sont classés selon le type : nominale, ordinale des variables étudiées, puis ils sont décrits, commentés et appliqués sur des exemples variés. L'approche probabiliste basée sur les odds-ratio et le modèle logit est abordée. Afin de montrer les doutes que l'on doit avoir lors d'un test unique une «curiosité » est rapportée, celle-ci révèle les discordances des résultats selon les points de vue. Un historique sur le test exact de Fisher permet au lecteur de conforter son opinion

Orientational order of carbon nanotube guests in a nematic host suspension of colloidal viral rods

In order to investigate the coupling between the degrees of alignment of elongated particles in binary nematic dispersions, surfactant stabilized single-wall carbon nanotubes (CNTs) have been added to nematic suspensions of colloidal rodlike viruses in aqueous solution.We have independently measured the orientational order parameter of both components of the guest-host system by means of polarized Raman spectroscopy and by optical birefringence, respectively. Our system allows us therefore to probe the regime where the guest particles (CNTs) are shorter and thinner than the fd virus host particles. We show that the degree of order of the CNTs is systematically smaller than that of the fd virus particles for the whole nematic range. These measurements are in good agreement with predictions of an Onsager-type second-viral theory, which explicitly includes the flexibility of the virus particles, and the polydispersity of the CNTs.Comment: 5 pages, 2 figure