Absolute Single Ion Thermometry

We describe and experimentally implement a single-ion local thermometry technique with absolute sensitivity adaptable to all laser-cooled atomic ion species. The technique is based on the velocity-dependent spectral shape of a quasi-dark resonance tailored in a J $\rightarrow$ J transition such that the two driving fields can be derived from the same laser source leading to a negligible relative phase shift. We validated the method and tested its performances in an experiment on a single 88 Sr + ion cooled in a surface radio-frequency trap. We first applied the technique to characterise the heating-rate of the surface trap. We then measured the stationary temperature of the ion as a function of cooling laser detuning in the Doppler regime. The results agree with theoretical calculations, with an absolute error smaller than 100 $\mu$K at 500 $\mu$K, in a temperature range between 0.5 and 3 mK and in the absence of adjustable parameters. This simple-to-implement and reliable method opens the way to fast absolute measurements of single-ion temperatures in future experiments dealing with heat transport in ion chains or thermodynamics at the single-ion level

Strong quantum correlations in four wave mixing in 85^{85}Rb vapor

We study quantum intensity correlations produced using four-wave mixing in a room-temperature rubidium vapor cell. An extensive study of the effect of the various parameters allows us to observe very large amounts of non classical correlations.Comment: 8 pages and 8 figures; work presented at the SPIE Photonics Europe conference (Brussels, 2010

Isotope shifts of natural Sr+ measured by laser fluorescence in a sympathetically cooled Coulomb crystal

We measured by laser spectroscopy the isotope shifts between naturally-occurring even-isotopes of strontium ions for both the 5s\,\,^2S_{1/2}\to 5p\,\,^2P_{1/2} (violet) and the 4d\,\,^2D_{3/2}\to 5p\,\,^2P_{1/2} (infrared) dipole-allowed optical transitions. Fluorescence spectra were taken by simultaneous measurements on a two-component Coulomb crystal in a linear Paul trap containing $10^3$--$10^4$ laser-cooled Sr$^+$ ions. The isotope shifts are extracted from the experimental spectra by fitting the data with the analytical solution of the optical Bloch equations describing a three-level atom in interaction with two laser beams. This technique allowed us to increase the precision with respect to previously reported data obtained by optogalvanic spectroscopy or fast atomic-beam techniques. The results for the 5s\,\,^2S_{1/2}\to 5p\,\,^2P_{1/2} transition are $\nu_{88}-\nu_{84}=+378(4)$ MHz and $\nu_{88}-\nu_{86}=+170(3)$ MHz, in agreement with previously reported measurements. In the case of the previously unexplored 4d\,\,^2D_{3/2}\to 5p\,\,^2P_{1/2} transition we find $\nu_{88}-\nu_{84}=-828(4)$ MHz and $\nu_{88}-\nu_{86}=-402(2)$ MHz. These results provide more data for stringent tests of theoretical calculations of the isotope shifts of alkali-metal-like atoms. Moreover, they simplify the identification and the addressing of Sr$^+$ isotopes for ion frequency standards or quantum-information-processing applications in the case of multi-isotope ion strings.Comment: 19 pages; 5 figures; accepted on Phys. Rev. A (http://pra.aps.org/

A tight Erd\H{o}s-P\'osa function for wheel minors

Let $W_t$ denote the wheel on $t+1$ vertices. We prove that for every integer $t \geq 3$ there is a constant $c=c(t)$ such that for every integer $k\geq 1$ and every graph $G$, either $G$ has $k$ vertex-disjoint subgraphs each containing $W_t$ as minor, or there is a subset $X$ of at most $c k \log k$ vertices such that $G-X$ has no $W_t$ minor. This is best possible, up to the value of $c$. We conjecture that the result remains true more generally if we replace $W_t$ with any fixed planar graph $H$.Comment: 15 pages, 1 figur

Anticipation in the Dial-a-Ride Problem: an introduction to the robustness

International audienceThe Dial-a-Ride Problem (DARP) models an operation research problem related to the on demand transport. This paper introduces one of the fundamental features of this type of transport: the robustness. This paper solves the Dial-a-Ride Problem by integrating a measure of insertion capacity called Insertability. The technique used is a greedy insertion algorithm based on time constraint propagation (time windows, maximum ride time and maximum route time). In the present work, we integrate a new way to measure the impact of each insertion on the other not inserted demands. We propose its calculation, study its behavior, discuss the transition to dynamic context and present a way to make the system more robust

3′ UTR G-quadruplexes regulate miRNA binding

Abstract : MicroRNAs (miRNAs) are small noncoding RNAs that repress the translation of their target genes. It has previously been shown that a target’s availability to miRNA can be affected by its structure. G-quadruplexes (G4) are noncanonical structures adopted by G-rich nucleic acids that have been shown to have multiple biological functions. In this study, whether or not G4 structures’ presence in the 3′ UTRs of mRNAs can hinder miRNA binding was investigated. Putative G4 overlapping with predicted miRNAs’ binding sites was searched for, and 44,294 hits were found in humans. The FADS2 mRNA/mir331-3p pair was selected as a model example. In-line probing and G4-specific fluorescent ligand experiments binding were performed and confirmed the presence of a G4 near the predicted miRNA binding site. Subsequent luciferase assays showed that the presence of the G4 prevents the binding of mir331-3p in cellulo. Together, these results served as proof of concept that a G4 structure present in a 3′ UTR sequence should be taken into consideration when predicting miRNA binding sites

Conception complexe et ingénierie système.

S'il est une tendance admise en matière de dynamique technique de longue période, c'est bien celle de la complication croissante des « objets techniques » [SIM 58] voulus, conçus, produits et utilisés par l'Homme. Pour s'en convaincre, il suffit de procéder à une comparaison facile et de mettre en rapport une plaque de métal - objet banal du XIX° siècle - avec un téléphone portable – objet banal de notre époque - de même dimension et masse. Il ne fait alors aucun doute que celui-ci répond à plus nombreuses fonctions que celle-là. Il permet en effet de communiquer des messages par la voix, l'écrit ou l'image, de photographier, de filmer, de jouer, d'avoir l'heure, de gérer ses rendez-vous, etc., si bien, d'ailleurs, que sa compréhension par l'utilisateur relève de plus en plus du pensum [MOR 07]. Pour assurer toutes ses fonctions, il intègre de nombreux composants, matériels et logiciels, relevant, qui plus est, de domaines techniques et scientifiques éloignés : télécommunications, électronique, énergie, traitement du signal, logiciel enfoui et interface homme-machine, etc. Du fait de cette densité fonctionnelle particulièrement élevée, il ne peut donc pas se comprendre comme un simple composant, mais comme une véritable architecture multiphysique. Il exhibe aussi différents comportements : il répond aux commandes venant de l'utilisateur lorsque celui-ci appuie sur ses touches ou effleure son écran, il cherche les émetteurs les plus proches, il vérifie l'état de la batterie, il vibre ou sonne, etc. Enfin, il est à la fois produit en masse et varié, ce qui suppose un système de production et une chaîne logistique particulièrement compliqués