117634 research outputs found

    Mapping and interpretation of Sinlap crater on Titan using Cassini VIMS and RADAR data

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    International audienceOnly a few impact craters have been unambiguously detected on Titan by the Cassini- Huygens mission. Among these, Sinlap is the only one that has been observed both by the RADAR and VIMS instruments. This paper describes observations at centimeter and infrared wavelengths which provide complementary information about the composition, 45 topography, and surface roughness. Several units appear in VIMS false color composites of band ratios in the Sinlap area, suggesting compositional heterogeneities. A bright pixel possibly related to a central peak does not show significant spectral variations, indicating either that the impact site was vertically homogeneous, or that this area has been recovered by homogeneous deposits. Both 50 VIMS ratio images and dielectric constant measurements suggest the presence of an area enriched in water ice around the main ejecta blanket. Since the Ku-band SAR may see subsurface structures at the meter scale, the difference between infrared and SAR observations can be explained by the presence of a thin layer transparent to the radar. An analogy with terrestrial craters in Libya supports this interpretation. Finally, a tentative model describes the geological 55 history of this area prior, during, and after the impact. It involves mainly the creation of ballistic ejecta and an expanding plume of vapor triggered by the impact, followed by the redeposition of icy spherules recondensed from this vapor plume blown downwind. Subsequent evolution is then driven by erosional processes and aeolian deposition

    Synthesis and characterization of La2NiO4+δ coatings deposited by reactive magnetron sputtering using plasma emission monitoring

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    International audienceThis work focuses on the structural and electrical characterization of La-Ni-O coatings deposited by reactive magnetron sputtering using Plasma Emission Monitoring (PEM) which allows high deposition rate. The optimal regulation setpoint for lanthanumdeposition is determined and then the current dissipated on the nickel target is adjusted to obtain the convenient La/Ni ratio to achieve the K2NiF4 structure. After an appropriate annealing treatment, all coatings exhibit crystalline structures that depend on the La/Ni ratio. Some cracks appear on samples deposited on alumina substrates depending to the argon flow rate and influence their electrical behavior

    Design of a novel long-range inflatable robotic arm: Manufacturing and numerical evaluation of the joints and actuation

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    International audienceThe aim of this paper is to present the design of a new long-range robotic arm based on an inflatable structure. Inflatable robotics has potential for improved large payload-to-weight ratios, safe collision, and inspection in areas inaccessible to human beings as in nuclear plants. The robot presented here is intended to operate inspection or maintenance missions in critical installation taking care to not collide with its environment. It is made with innovative inflatable joints and an original actuation system. Prototypes of this inflatable manipulator were constructed using two different manufacturing procedures. Using LS-DYNA nonlinear dynamic finite element modeling we have numerically analyzed the specific geometry and dynamical behavior of the resulting joints. The simulations have given insight into understanding the joint bending process and have revealed guidance for optimizing the conception

    Pseudomonas aeruginosa prise en flagrant délit de casse ! Pseudomonas aeruginosa caught in the act !

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    International audienceDes armes qui attaquent le génome eucaryote de façon encore mystérieuse Pseudomonas aeruginosa est une bactérie pathogène opportuniste infectant principalement les individus aux défenses immunitaires affaiblies, les patients ayant une rupture de leurs barrières cutanées (chirurgie, brûlures,...) ou subissant un geste invasif (pose d'une sonde, d'un cathéter) [1]. D'autres sujets sont particulièrement à risque, ainsi 80% des personnes atteintes de mucoviscidose sont chroniquement infectées par cette bactérie. Les infections à P. aeruginosa sont le plus souvent contractées en milieu hospitalier et elles demeurent un défi pour le corps médical en raison de la multi-résistance des souches aux antibiotiques [2]. La pathogénicité liée aux infections aiguës ou chroniques à P. aeruginosa est multifactorielle [3]. L'un des systèmes de virulence majeurs associé aux infections aiguës est le système de sécrétion de type 3 (SST3) [4]. Il est constitué d'une aiguille creuse érigée à la surface de la bactérie qui s'insère dans la membrane plasmique de la cellule hôte et permet l'injection de toxines bactériennes (ExoY, ExoT et ExoS ou ExoU) dans le cytoplasme de la cellule infectée. Nous avons recherché les dommages potentiels causés par P. aeruginosa au patrimoine génétique de la cellule hôte. Pour la première fois, nos travaux montrent que le SST3 est associé à des cassures double-brin de l'ADN, lésions très dangereuses pour le génome, et à une réaction de la cellule hôte qui va tenter de réparer les dégâts [5]

    The sinelaw gap probability, Painlevé 5, and asymptotic expansion by the topological recursion

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    International audienceThe goal of this paper is to rederive the connection between the Painlev'e 5 integrable system and the universal eigenvalues correlation functions of double-scaled Hermitian matrix models, through the topological recursion method. More specifically we prove, to all orders, that the WKB asymptotic expansions of the τ-function as well as of determinantal formulas arising from the Painlev'e 5 Lax pair are identical to the large N double scaling asymptotic expansions of the partition function and correlation functions of any Hermitian matrix model around a regular point in the bulk. In other words, we rederive the "sine-law" universal bulk asymptotic of large random matrices and provide an alternative perturbative proof of universality in the bulk with only algebraic methods. Eventually we exhibit the first orders of the series expansion up to O\left(N^{-5}\right

    Near-band edge optical properties of exfoliated h-BN layers.

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    Luminescence properties of h-BN are governed, in the energy range 5.5 { 6 eV, by strong Frenkel-type excitonic e ects, highly sensitive to structural defects [1-3]. Nowadays, BN meets a growing interest for graphene engineering. It is therefore highly desirable to better know optical and electronic properties of thin layers, in correlation with their structural properties. We carry out optical and structural characterizations of this material by combining CL at 4K in the UV range and TEM. Thin layers are obtained by mechanically exfoliating powders and single crystals and reported on SiO2 substrates for AFM thickness measurements, and then on TEM grids. As for the reference bulk, excitonic emission consists of two series of lines called S and D. Thanks to the CL and TEM imaging capabilities, emission related to D lines, is found to be localized on defects, identi ed as grain boundaries. Their energies are found to be upshifted as the number of layers decreases, indicating a perturbation in the exciton localization, which will be discussed

    Achievable Rate Regions for Two-Way Relay Channel using Nested Lattice coding

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    International audienceThis paper studies Gaussian Two-Way Relay Channel where two communication nodes exchange messages with each other via a relay. It is assumed that all nodes operate in half duplex mode without any direct link between the communication nodes. A compress-and-forward relaying strategy using nested lattice codes is first proposed. Then, the proposed scheme is improved by performing a layered coding: a common layer is decoded by both receivers and a refinement layer is recovered only by the receiver which has the best channel conditions. The achievable rates of the new scheme are characterized and are shown to be higher than those provided by the decode-and-forward stra

    Timescales for electron quasi-linear diffusion by parallel and oblique lower-band chorus waves

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    International audience[1] The loss of relativistic electrons from the Earth's radiation belts can be described in terms of the quasi-linear pitch angle diffusion by cyclotron-resonant waves, provided that their frequency spectrum is broad enough. Chorus waves at large wave-normal angles with respect to the magnetic field are often present in CLUSTER and THEMIS measurements in the outer belt at moderate to high latitudes. An approximate analytical formulation of diffusion coefficients has been derived in the low-frequency limit, leading to a simplified analytical expression of diffusion coefficients and lifetimes for energetic trapped electrons. Large values of the wave-normal angles between the Gendrin and resonance angles are shown to induce important increases in diffusion, thereby strongly reducing the particle lifetimes (by almost two orders of magnitude). The analytical diffusion coefficients and lifetimes obtained here are found to be in a good agreement with full numerical calculations based on CLUSTER chorus waves measurements in the outer belt for electron energies ranging from 100 keV to 2 MeV. Such very oblique chorus waves could contribute to a predominantly perpendicular anisotropy of the global equatorial electron population on the dayside and to a relative isotropization at low energy under disturbed conditions. It is also suggested that they might play a significant role in pulsating auroras

    Convex relaxations of penalties for sparse correlated variables with bounded total variation

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    International audienceWe study the problem of statistical estimation with a signal known to be sparse, spatially contiguous, and containing many highly correlated variables. We take inspiration from the recently introduced k-support norm, which has been successfully applied to sparse prediction problems with correlated features, but lacks any explicit structural constraints commonly found in machine learning and image processing. We address this problem by incorporating a total variation penalty in the k-support framework. We introduce the (k, s) support total variation norm as the tightest convex relaxation of the intersection of a set of sparsity and total variation constraints. We show that this norm leads to an intractable combinatorial graph optimization problem, which we prove to be NP-hard. We then introduce a tractable relaxation with approximation guarantees that scale well for grid structured graphs. We devise several first-order optimization strategies for statistical parameter estimation with the described penalty. We demonstrate the effectiveness of this penalty on classification in the low-sample regime, classification with M/EEG neuroimaging data, and image recovery with synthetic and real data background subtracted image recovery tasks. We extensively analyse the application of our penalty on the complex task of identifying predictive regions from low-sample high-dimensional fMRI brain data, we show that our method is particularly useful compared to existing methods in terms of accuracy, interpretability, and stability

    Electroluminescence efficiencies of erbium in silicon-based hosts

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    International audienceWe report on room-temperature 1.5 lm electroluminescence from trivalent erbium (Er3þ) ionsembedded in three different CMOS-compatible silicon-based hosts: SiO2, Si3N4, and SiNx. We showthat although the insertion of either nitrogen or excess silicon helps enhance electrical conductionand reduce the onset voltage for electroluminescence, it drastically decreases the external quantumefficiency of Er3þ ions from 2% in SiO2 to 0.001% and 0.0004% in SiNx and Si3N4, respectively.Furthermore, we present strong evidence that hot carrier injection is significantly more efficient thandefect-assisted conduction for the electrical excitation of Er3þ ions. These results suggest strategiesto optimize the engineering of on-chip electrically excited silicon-based nanophotonic light sources


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