Crystallization of self-propelled hard-discs : a new scenario

We experimentally study the crystallization of a monolayer of vibrated discs with a built-in polar asymmetry, a model system of active liquids, and contrast it with that of vibrated isotropic discs. Increasing the packing fraction $\phi$, the quasi-continuous crystallization reported for isotropic discs is replaced by a transition, or a crossover towards a "self-melting" crystal. Increasing the packing fraction from the liquid phase, clusters of dense hexagonally-ordered packed discs spontaneously form, melt, split and merge leading to a highly intermittent and heterogeneous dynamics. The resulting steady state cluster size distribution decreases monotonically. For packing fraction larger than $\phi^*$, a few large clusters span the system size and the cluster size distribution becomes non monotonic, the transition being signed by a power-law. The system is however never dynamically arrested. The clusters permanently melt from place to place forming droplets of active liquid which rapidly propagate across the system. This state of affair remains up to the highest possible packing fraction questioning the stability of the crystal for active discs, unless at ordered close packing.Comment: 4 pages, 4 figures, 1 Supp Mat

A complete set of covariants of the four qubit system

We obtain a complete and minimal set of 170 generators for the algebra of SL(2,\C)^{\times 4}-covariants of a binary quadrilinear form. Interpreted in terms of a four qubit system, this describes in particular the algebraic varieties formed by the orbits of local filtering operations in its projective Hilbert space. Also, this sheds some light on the local unitary invariants, and provides all the possible building blocks for the construction of entanglement measures for such a system.Comment: 14 pages, IOP macros; slightly expanded versio

Les effets des formes graphiques sur l'étiquette des bouteilles de vin sur la perception des jeunes consommateurs

L’étiquette faciale des bouteilles de vin est l’un des principaux vecteur de communication permettant au consommateur d’évaluer le produit et notamment ses qualités gustatives. Ces évaluations se font sur la base d’informations écrites mais également graphiques. Force est de constater que la majorité des jeunes consommateurs est non-initiée aux termes techniques du vin et il semble donc pertinent de tenter de les guider grâce aux représentations graphiques présentes sur l’étiquette faciale de la bouteille de vin. Des recherches antérieures menées en psychologie et en études sensorielles mettent en évidence la possibilité d’induire une perception de goût d’un produit alimentaire ou d’une boisson grâce à l’utilisation de représentations graphiques. Nous tentons, au travers de nos recherches, de tester ces effets potentiels sur le vin, un produit perçu comme complexe à appréhender par les jeunes consommateurs non-initiés et de formuler quelques recommandations.

Telescope guide and pointing precision at THEMIS

We present the very basic features—from the observer’s point of view—of the software pack allowing for driving the telescope, the dome, the preslit at the primary focus and the field rotator between the primary and the secondary focus. The original program was developed by C. Veillet as an adaptation for THEMIS of the program used to drive the “Laser-Lune” telescope at the Observatoire of the Cˆote d’Azur (France). Further adaptations were made by the authors to meet observational and technical needs emerged during operation of the THEMIS telescope. When talking about the way observations at THEMIS are affected by the pointing precisionw e clearly have to distinguish betweento different levels: 1) a short-term effect, affecting short-term observing actions such as scans on the solar disk and 2) a long-term level affecting the correct tracking of a target. All short-term effects just depend on the precision of the software interface and we discuss here their origin, the way they are controlled, their value and how they affect scanning procedures. All long-term effects depend on precision of the software interface but also on mechanical and optical alignment accuracy

The cross-modal effects of packaging glossiness on haptic perception

International audienc

ESTIMATING THE STOCK OF GLASS EELS IN AN ESTUARY BY MARK-RECAPTURE EXPERIMENTS USING VITAL DYES

Glass eels (Anguilla anguilla) arriving after the fishing season in the Vilaine estuary (France) were caught by boat and at a trapping ladder located at a blocking dam upstream in the estuary. They were marked with Bismarck brown, rhodamine B or neutral red, and released into the estuary. The effect of marking on behaviour, mortality and recapture differed according to the dye and concentration used. The glass eels also differed in response to marking according to their origin. Estuarine glass eels were clearly desynchronized in their selective tidal stream transport and left the release area after a few tidal cycles. Trapped glass eels were less sensitive to marking. They remained in the release area and were recaptured in larger number both in the trapping ladder and in the estuary. These results supported a model of two behavioral fractions in the estuary: flow-carried migrants and active glass eels with stronger rheotactic behaviour. The proportion of active glass eels in the estuary shifted from none for the two weeks after the fishery closure, to 10% value of the total stock. At the trapping ladder, the migration ended in June each year, while a large stock was still present in the estuary. These observations favour the interpretation of a short duration of the active phase at this site followed by the transition towards a more benthic behavior. The daily efficiency of the trapping ladder was calculated as 4% of the active stock from both stock estimations and average recapture rate. This value was consistent with the low annual efficiency of the trapping ladder, calculated as 30% of the estuarine stock of glass eels that arrived after the fishing season

THEMIS as particle detector: Spectropolarimetry of solar flares

The progressive phases of three solar flares have beenobserv ed with THEMIS in July 2000, using the multiline spectropolarimetric MTR mode. A preliminary analysis of the characteristics of the polarization of the Hα and Hβ lines observed at the beginning of the progressive phase of one of these flares is presented

catena-Poly[[bis(pyridine)­lead(II)]bis(μ-penta­fluoro­benzene­thiol­ato)]

The title compound, [Pb(C6F5S)2(C5H5N)2]n, shows the PbII atom in a ψ-trigonal bipyramidal S2N2 bonding environment. Pyridine N atoms occupy axial sites, while thiol­ate S atoms and a stereochemically active lone pair occupy equatorial sites. Very long inter­molecular Pb⋯S inter­actions [3.618 (4) and 3.614 (4) Å] yield a weakly associated one-dimensional polymeric structure extending parallel to [010]