Tracking quasi-classical chaos in ultracold boson gases

We study the dynamics of a ultra-cold boson gas in a lattice submitted to a constant force. We track the route of the system towards chaos created by the many-body-induced nonlinearity and show that relevant information can be extracted from an experimentally accessible quantity, the gas mean position. The threshold nonlinearity for the appearance of chaotic behavior is deduced from KAM arguments and agrees with the value obtained by calculating the associated Lyapunov exponent.Comment: 4 pages, revtex4, submitted to PR

Confining caesium in expanded natural Perlite

We present the potential use of expanded perlite, a metastable amorphous hydrated aluminum silicate, as a permanent medium for the long-term confinement of caesium. A simple loading by mixing an aqueous caesium nitrate solution and expanded perlite at 300K followed by thermal annealing leads to 96% sintering. The formation of pollucite, CsAlSi2O6, a naturally occurring mineral phase, appears as the crystalline phase embedded in a glassy phase. Leaching tests on the resulting glass-ceramics reveal a very low Cs departure of 0.5 mgm−2 day−1. This simple method seems to be a good way to permanently confine caesium issued from recycled nuclear waste

Quantum coherence generated by interference-induced state selectiveness

The relations between quantum coherence and quantum interference are discussed. A general method for generation of quantum coherence through interference-induced state selection is introduced and then applied to `simple' atomic systems under two-photon transitions, with applications in quantum optics and laser cooling.Comment: 17 pages, 7 figures, to be published in Journal of Modern Optics' special issue on quantum interferenc

Microwave heating-induced DC magnetic flux penetration in YBa2_{2}Cu3_{3}O7−δ_{7-\delta} superconducting thin films

The magneto-optical imaging technique is used to visualize the penetration of the magnetic induction in YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ thin films during surface resistance measurements. The in-situ surface resistance measurements were performed at 7 GHz using the dielectric resonator method. When only the microwave magnetic field $H_{rf}$ is applied to the superconductor, no $H_{rf}$-induced vortex penetration is observed, even at high rf power. In contrast, in the presence of a constant magnetic field superimposed on $H_{rf}$ we observe a progression of the flux front as $H_{rf}$ is increased. A local thermometry method based on the measurement of the resonant frequency of the dielectric resonator placed on the YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ thin film shows that the $H_{rf}$--induced flux penetration is due to the increase of the film temperature.Comment: 6 pages, Journal of Applied Physic

The binary fraction of planetary nebula central stars I. A high-precision, I-band excess search

In an attempt to determine how many planetary nebulae derive from binary interactions, we have started a project to measure their unbiased binary fraction. This number, when compared to the binary fraction of the presumed parent population can give a first handle on the origin of planetary nebulae. By detecting 27 bona fide central stars in the I band we have found that 30% of our sample have an I band excess between one and a few sigmas, possibly denoting companions brighter than M3-4V and with separations smaller than approximately 1000 AU. By accounting for the undetectable companions, we determine a de-biased binary fraction of 67-78% for all companions at all separations. We compare this number to a main sequence binary fraction of (50+/-4)% determined for spectral types F6V-G2V, appropriate if the progenitors of today's PN central star population is indeed the F6V-G2V stars. The error on our estimate could be between 10 and 30%. We conclude that the central star binary fraction may be larger than expected from the putative parent population. Using the more sensitive J band of a subset of 11 central stars, the binary fraction is 54% for companions brighter than approximately M5-6V and with separations smaller than about 900 AU. De-biassing this number we obtain a binary fraction of 100-107%. The two numbers should be the same and the discrepancy is likely due to small number statistics. We also present an accurately vetted compilation of observed main sequence star magnitudes, colours and masses, which can serve as a reference for future studies. We also present synthetic colours of hot stars as a function of temperature (20-170kK) and gravity (log g= 6-8) for Solar and PG1159 compositions.Comment: 22 pages, 6 figures, 12 tables, accepted by MNRA

Variabilité de la morphologie chez Fusarium oxysporum f. sp. lycopersici

La variabilité morphologique chez #Fusarium oxysporum f. sp. #lycopersici a été recherchée à deux niveaux : au sein d'une population de conidies provenant du thalle d'un isolat (variabilité interclonale) et au sein d'une population de conidies provenant d'un thalle issu d'un clonage monospore (variabilité interclonale). Enfin, cette variabilité a été étudiée sur des cultures jeunes et âgées. L'ensemble des essais a été réalisé sur deux isolats. Les résultats mettent en évidence l'existence d'une variabilité morphologique importante, mais également des réponses différentes suivant les deux isolats. La variabilité interclonale n'a été observée que chez l'un des isolats et semble être une propriété constitutive de l'isolat. La variabilité interclonale se manifeste chez les deux isolats, mais uniquement au sein d'une population de conidies récoltées sur des thalles âgés. Dans ce dernier cas, on observe une forte augmentation de la fréquence d'apparition d'un morphotype considéré comme sénescent sans, toutefois, que cette forme soit irréversiblement acquise : on note un taux non négligeable de réversion vers des morphotypes considérés comme juvéniles. (Résumé d'auteur