Hybrid multi-grids simulations of Ganymede's magnetosphere

International audienceThe Jovian satellite Ganymede is the biggest moon of our solar system. One of the main motivation of our interest for this moon is its own intrinsic magnetic field, which has been discovered during the Galileo mission (Kivelson et al. 1996). The magnetic field of Ganymede directly interacts with the corotating jovian plasma, leading to the formation of a mini-magnetosphere which is embedded in the giant magnetosphere of Jupiter. This is the only known case of interaction between two planetary magnetospheres.In the frame of the European space mission JUICE (Jupiter Icy moon Exploration), we investigate this unique interaction with a 3D parallel multi-species hybrid model. This model is based on the CAM-CL algorithm (Matthews 1994) and has been used to study the ionized environments of Titan, Mars and Mercury. In the hybrid formalism, ions are kinetically treated whereas electrons are considered as a zero-inertial fluid to ensure the quasi-neutrality of the plasma. The temporal evolution of the electromagnetic fields is calculated solving Maxwell's equations. The jovian magnetospheric plasma is described as being composed of oxygen and proton ions. The magnetic field of Ganymede, which includes dipolar and induced components (Kivelson et al, 2002), is distorted by its interaction with the Jovian plasma and formed the Alfvén wings. The planetary plasma is described as being composed of O+, with a scale height equal to 125 km. The description of the exosphere is provided by the 3D multi-species collisional exospheric/atmospheric model of Leblanc et al, (2015) and Turc et al. (2014). The ionization of this neutral exosphere by charge exchanges, by electronic impacts, and by reaction with solar photons contributes to the production of planetary plasma. In this model, calculations are performed on a cartesian simulation grid which is refined (down to ~120 km of spatial resolution) at Ganymede, using a multi-grids approach (Leclercq et al., submitted, 2015). Results are compared with Galileo observations obtained during the G1, G2 and G8 flybys

Sodium recycling at Europa: what do we learn from the sodium cloud variability ?

International audienceWe study the ejection of sodium atoms from Europa's surface by both magnetospheric ion and electron sputtering and desorption stimulated by UV solar photons. The depletion of the surface by ejection and its enrichment by redeposition of sodium atoms are described. The redistribution of sodium atoms at the surface induced by photo-stimulated desorption from the dayside and by sputtering ejection from the trailing hemisphere cannot explain the observed variation of the Na emission brightness. However, a transient increase of the sputtering rate due to a plasma injection may explain such an increase. The relationship between the sodium surface content and the sodium exosphere are also discussed

L'enjeu de la taxation et le débat démocratique dans la Province du Canada, 1841-1856

Au milieu du XIXe siècle, la Province du Canada obtient progressivement une plus grande autonomie financière que ce soit en raison des revendications des responsables coloniaux ou par des changements dans la politique impériale. Ces changements arrivent au moment où s’instaure un nouveau mode de gouvernance politique, ce qui entraîne de nombreux débats sur la position que l’État doit occuper. La place de la taxation est centrale dans ces préoccupations puisqu’elle révèle des enjeux à dimension démocratique et de gouvernance. Ce mémoire propose d’explorer sous l’angle de la rationalisation de la pensée étatique, en analysant les débats parlementaires de la Province du Canada entre 1841 et 1856. La rationalisation permet la création de catégories et la normalisation du droit, ce qui entraîne l’universalisation des mesures fiscales. Elle s’observe à travers la mise en place d’une logique de l’utilisateur-payeur pour les services publics et un déclin des critères moraux pour justifier la taxation.In the mid-nineteenth century, the Province of Canada gradually gained greater financial independence, as the result both of colonial demands and changes in broader imperial policy. These changes occurred at a time when the role of the state itself was changing, raising debates about the position it should occupy. Taxation was central to these concerns, since it brought up issues concerning both democracy and governance. This thesis explores the debate on taxation from the perspective of the rationalization of thinking about the state. It focuses on the parliamentary debates of the Province of Canada between 1841 and 1856. Rationalization led to the creation of categories and the standardization of law, which in turn resulted in the universalization of fiscal measures. This can be seen through the introduction of the user-pay principle for public services and the decline in recourse to moral criteria to justify taxation

Improved Modelling of hydraulic works including run-of-the-river dam in TELEMAC

Hydrodynamic

A global hybrid model for Mercury's interaction with the solar wind: Case study of the dipole representation

International audienceThe interaction of the solar wind (SW) with the magnetic field of Mercury is investigated by means of a three dimensional parallelized multispecies hybrid model. A comparison between two mathematical representations of Mercury's intrinsic magnetic field is studied. The first model is an Offset Dipole (OD) having the offset and dipolar moment reported by Anderson et al. (2011). The second model is a combination of a Dipole and a Quadrupole (DQ), the total field is fitted to the offset dipolar field, for northern latitudes greater than 50°. Simulations reproduce the features which characterize Mercury's interaction with the SW, encompassing the Bow Shock (BS), the magnetosheath, the magnetotail, the "cusps" region and the neutral current sheet. Global hybrid simulations of the Hermean magnetosphere run for the OD and DQ models demonstrate that the southern parts of the magnetospheres produced by the OD and DQ models differ greatly in topology and volume meanwhile their northern parts-are quite similar. In particular the DQ model exhibits a dome of closed field lines around the south pole in contrast to the OD. Without further information on the intrinsic magnetic field of the planet in the southern region which should be provided by BepiColombo after year 2020, we can only speculate on the influence of the different magnetic topologies on the magnetospheric dynamics

Propagation of Transient Perturbations into a Planet's Exosphere: Molecular Kinetic Simulations

The upper atmospheres of Mars and Titan, as well as those on many other planetary bodies, exhibit significant density variations vs. altitude that are interpreted as gravity waves. Such data is then used to extract vertical temperature profiles, even when such perturbations propagate through the transition region from a collision dominated regime and into a planet's exosphere. Since the temperature profile is critical for describing the upper atmospheric heating and evolution, we use molecular kinetic simulations to describe transient perturbations in a Mars-like upper atmosphere. We show that the standard methods for extracting the temperature profile can fail dramatically so that molecular kinetic simulations, calibrated to observed density profiles, are needed in this region of a planet's atmosphere

Rapid identification and quantification of Campylobacter coli and Campylobacter jejuni by real-time PCR in pure cultures and in complex samples

<p>Abstract</p> <p>Background</p> <p><it>Campylobacter </it>spp., especially <it>Campylobacter jejuni </it>(<it>C. jejuni</it>) and <it>Campylobacter coli </it>(<it>C. coli</it>), are recognized as the leading human foodborne pathogens in developed countries. Livestock animals carrying <it>Campylobacter </it>pose an important risk for human contamination. Pigs are known to be frequently colonized with <it>Campylobacter</it>, especially <it>C. coli</it>, and to excrete high numbers of this pathogen in their faeces. Molecular tools, notably real-time PCR, provide an effective, rapid, and sensitive alternative to culture-based methods for the detection of <it>C. coli </it>and <it>C. jejuni </it>in various substrates. In order to serve as a diagnostic tool supporting <it>Campylobacter </it>epidemiology, we developed a quantitative real-time PCR method for species-specific detection and quantification of <it>C. coli </it>and <it>C. jejuni </it>directly in faecal, feed, and environmental samples.</p> <p>Results</p> <p>With a sensitivity of 10 genome copies and a linear range of seven to eight orders of magnitude, the <it>C. coli </it>and <it>C. jejuni </it>real-time PCR assays allowed a precise quantification of purified DNA from <it>C. coli </it>and <it>C. jejuni</it>. The assays were highly specific and showed a 6-log-linear dynamic range of quantification with a quantitative detection limit of approximately 2.5 × 10²CFU/g of faeces, 1.3 × 10²CFU/g of feed, and 1.0 × 10³CFU/m²for the environmental samples. Compared to the results obtained by culture, both <it>C. coli </it>and <it>C. jejuni </it>real-time PCR assays exhibited a specificity of 96.2% with a kappa of 0.94 and 0.89 respectively. For faecal samples of experimentally infected pigs, the coefficients of correlation between the <it>C. coli </it>or <it>C. jejuni </it>real-time PCR assay and culture enumeration were R²= 0.90 and R²= 0.93 respectively.</p> <p>Conclusion</p> <p>The <it>C. coli </it>and <it>C. jejuni </it>real-time quantitative PCR assays developed in this study provide a method capable of directly detecting and quantifying <it>C. coli </it>and <it>C. jejuni </it>in faeces, feed, and environmental samples. These assays represent a new diagnostic tool for studying the epidemiology of <it>Campylobacter </it>by, for instance, investigating the carriage and excretion of <it>C. coli </it>and <it>C. jejuni </it>by pigs from conventional herds.</p

PAC-Bayesian Learning of Aggregated Binary Activated Neural Networks with Probabilities over Representations

Considering a probability distribution over parameters is known as an efficient strategy to learn a neural network with non-differentiable activation functions. We study the expectation of a probabilistic neural network as a predictor by itself, focusing on the aggregation of binary activated neural networks with normal distributions over real-valued weights. Our work leverages a recent analysis derived from the PAC-Bayesian framework that derives tight generalization bounds and learning procedures for the expected output value of such an aggregation, which is given by an analytical expression. While the combinatorial nature of the latter has been circumvented by approximations in previous works, we show that the exact computation remains tractable for deep but narrow neural networks, thanks to a dynamic programming approach. This leads us to a peculiar bound minimization learning algorithm for binary activated neural networks, where the forward pass propagates probabilities over representations instead of activation values. A stochastic counterpart that scales to wide architectures is proposed