Excitations nucléaires dans les plasmas : le cas du 84m Rb

This experimental and theoretical work deals with the Nuclear Excitation by Electron Tran-sition (NEET) process which involves a coupling between the nucleus and its electron cloud. In this process, an electron de-excitation can induce a nuclear excitation if the atomic and nuclear transitions are resonant and have the same multipolarity. This process could be observed in a laser created plasma of 84Rb because this nucleus has a low energy transition (around 3 keV) between the isomeric state (Jπ= 6−,T1/2= 20,26m) and theJπ= 5−(T1/2= 9ns) state. To evaluate a NEET excitation rate, the atomic states in plasma must be described and the nuclear transition must be precisely characterised.To describe the atomic states in plasma, a method based on a MCDF (Multi-ConfigurationDirac-Fock) code was developed. This one uses a procedure to select the most probable atomic configurations according to the plasma properties. This method was checked by the interpretation of a X-rays spectrum emitted by a Rb plasma. This plasma was produced by the PHELIXlaser of the GSI laboratory at an intensity of6×1014W/cm2.The energy of the nuclear transition between the states6−and5−was not accurate enough for the NEET rate evaluation. Twoγ-rays spectroscopy experiments were conducted at the ELSA accelerator from CEA/DAM/DIF and at the Tandem accelerator from the Orsay laboratory. The accuracy of the nuclear transition energy was improved of more than one order of magnitude. In this work, the NEET rate was evaluated to predict an experiment. The Rb plasma must have a high temperature (around 400 eV) to obtain a sufficient number of excited isomers and therefore to make possible the detection.Ce travail, à la fois expérimental et théorique, présente l’étude d’un processus d’excitation nucléaire, appelé NEET (Nuclear Excitation by Electron Transition), faisant intervenir un cou-plage entre le noyau et le cortège électronique. Dans celui-ci, une désexcitation électronique peut induire une excitation nucléaire si les transitions nucléaire et atomique sont résonantes et ont la même multipolarité. Le noyau de84Rbest un bon candidat pour mettre en évidence ce processus dans un plasma créé par laser car il possède une transition de basse énergie (environ 3 keV) entre l’état isomérique (Jπ= 6−,T1/2= 20,26min) et l’état Jπ= 5−(T1/2= 9ns). Afin d’évaluer un taux d’excitation par effet NEET, il est nécessaire de décrire les états atomiques dans un plasma et de caractériser précisément la transition nucléaire.Afin d’obtenir une description précise des états atomiques dans un plasma, une méthode de calcul de structure atomique a été développée. Cette méthode est basée sur le code de physique atomique MCDF (Multi-Configuration Dirac-Fock) et emploie une technique de sélection des configurations électroniques les plus probables en tenant compte des propriétés du plasma. Cette méthode de calcul a été validée par l’interprétation d’un spectre X émis par un plasma de Rb produit avec le laser PHELIX du GSI à une intensité de6×1014W/cm2.L’énergie de la transition nucléaire entre les états6−et5−n’était pas connue avec une précision suffisante (∼200eV) pour une évaluation précise du taux d’excitation par effet NEET.Deux expériences de spectroscopie γ ont alors été réalisées auprès des accélérateurs ELSA duCEA/DAM/DIF et Tandem de l’IPN d’Orsay. Elles ont permis d’améliorer de plus d’un ordre de grandeur la précision sur l’énergie de cette transition.A l’issue de ce travail, une évaluation du taux d’excitation par effet NEET dans un plasma a été réalisée afin de dimensionner une expérience. D’après celle-ci, le plasma doit avoir une température suffisamment élevée (de l’ordre de 400 eV) afin d’obtenir un nombre d’isomères excités suffisant pour être détectés

Recuit simulé pour le shape from shading

Nous formalisons le problème du shape from shading dans un cadre bayesien. La fonctionnelle utilisée s'interprète alors comme l'énergie associée à un champ markovien et est minimisée par un recuit simulé. Des premiers résultats sur un relief synthétique montrent les avantages de cette approche par rapport aux approches déterministes classiques

Corrélation spatiale de la phase des images radar

Ce travail traite du comportement spatial de la phase, dans une image radar. Celle-ci apparaît spatialement corrélée (et donc partiellement déterministe) aux résolutions élevées au regard de la longueur d'onde. Nous proposons un modèle statistique de la phase pour expliquer ce phénomène, dont la résolution analytique est exposée dans un cadre restreint. Des simulations viennent étayer ce résultat pour différentes situations du modèle, et sont confrontées à des mesures sur des données réelles

Health and Pleasure in Consumers' Dietary Food Choices: Individual Differences in the Brain's Value System

Taking into account how people value the healthiness and tastiness of food at both the behavioral and brain levels may help to better understand and address overweight and obesity-related issues. Here, we investigate whether brain activity in those areas involved in self-control may increase significantly when individuals with a high body-mass index (BMI) focus their attention on the taste rather than on the health benefits related to healthy food choices. Under such conditions, BMI is positively correlated with both the neural responses to healthy food choices in those brain areas associated with gustation (insula), reward value (orbitofrontal cortex), and self-control (inferior frontal gyrus), and with the percent of healthy food choices. By contrast, when attention is directed towards health benefits, BMI is negatively correlated with neural activity in gustatory and reward-related brain areas (insula, inferior frontal operculum). Taken together, these findings suggest that those individuals with a high BMI do not necessarily have reduced capacities for self-control but that they may be facilitated by external cues that direct their attention toward the tastiness of healthy food. Thus, promoting the taste of healthy food in communication campaigns and/or food packaging may lead to more successful self-control and healthy food behaviors for consumers with a higher BMI, an issue which needs to be further researched

Genomic Species Are Ecological Species as Revealed by Comparative Genomics in Agrobacterium tumefaciens

The definition of bacterial species is based on genomic similarities, giving rise to the operational concept of genomic species, but the reasons of the occurrence of differentiated genomic species remain largely unknown. We used the Agrobacterium tumefaciens species complex and particularly the genomic species presently called genomovar G8, which includes the sequenced strain C58, to test the hypothesis of genomic species having specific ecological adaptations possibly involved in the speciation process. We analyzed the gene repertoire specific to G8 to identify potential adaptive genes. By hybridizing 25 strains of A. tumefaciens on DNA microarrays spanning the C58 genome, we highlighted the presence and absence of genes homologous to C58 in the taxon. We found 196 genes specific to genomovar G8 that were mostly clustered into seven genomic islands on the C58 genome—one on the circular chromosome and six on the linear chromosome—suggesting higher plasticity and a major adaptive role of the latter. Clusters encoded putative functional units, four of which had been verified experimentally. The combination of G8-specific functions defines a hypothetical species primary niche for G8 related to commensal interaction with a host plant. This supports that the G8 ancestor was able to exploit a new ecological niche, maybe initiating ecological isolation and thus speciation. Searching genomic data for synapomorphic traits is a powerful way to describe bacterial species. This procedure allowed us to find such phenotypic traits specific to genomovar G8 and thus propose a Latin binomial, Agrobacterium fabrum, for this bona fide genomic species

Measurement of the production of a W boson in association with a charm quark in pp collisions at √s = 7 TeV with the ATLAS detector

The production of a W boson in association with a single charm quark is studied using 4.6 fb−1 of pp collision data at s√ = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96+0.26−0.30 at Q 2 = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio σ(W + +c¯¯)/σ(W − + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s−s¯¯¯ quark asymmetry

Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS

Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations

Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s√=8 TeV with the ATLAS detector

The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy s√=8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c) of approximately 30

Measurement of χ c1 and χ c2 production with s√ = 7 TeV pp collisions at ATLAS

The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at s√ = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → μ + μ −) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured

Evidence for the Higgs-boson Yukawa coupling to tau leptons with the ATLAS detector

Results of a search for H → τ τ decays are presented, based on the full set of proton-proton collision data recorded by the ATLAS experiment at the LHC during 2011 and 2012. The data correspond to integrated luminosities of 4.5 fb−1 and 20.3 fb−1 at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV respectively. All combinations of leptonic (τ → `νν¯ with ` = e, µ) and hadronic (τ → hadrons ν) tau decays are considered. An excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.5 (3.4) standard deviations. This excess provides evidence for the direct coupling of the recently discovered Higgs boson to fermions. The measured signal strength, normalised to the Standard Model expectation, of µ = 1.43 +0.43 −0.37 is consistent with the predicted Yukawa coupling strength in the Standard Model