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Numerical bifurcation and stability analysis of variational gradient-damage models for phase-field fracture
No full textInternational audienc
Adaptive Step-size Iterative Equalization for Underwater Communication
No full textInternational audienceThis paper presents a fully adaptive Minimum Mean Square Error (MMSE) iterative equalization with a joint phase estimation, using various adaptive step-sizes scheme. To meet the requirement of fast convergence and low MSE over time-varying channels, we propose an original self-optimized algorithm whose step-sizes are updated adaptively and assisted by soft-information provided by the channel decoder in an iterative manner. Simulation results show that our proposal achieves better performance over various multipath time-varying channels, compared to the conventional equalizer using a fixed step-size
Strain rate effects on the thermomechanical behavior of glass/polyester composite joints
No full textInternational audienceFor several decades, composite materials have been used in different applications due to their multiple advantages. It has become necessary to understand the dynamic behavior of these materials under critical loads. In-plane (IP) and out-of-plane (OP) dynamic compression tests were investigated on a cubic specimen of composite joints under low to high strain rates using the Split Hopkinson Pressure Bars (SHPB) technique. The specimens consist of two adherents (glass/polyester composite) assembled by an adhesive with different thicknesses (1 and 2 mm). During the experimental tests, the high-speed camera was used to check the damage history and the failure mechanisms on adhesively bonded composite joints. The sample surface temperatures were monitored using an infrared camera (IR). For bonding of two composite substrates, it can be noted that the thickness of the adhesive has a significant effect on the dynamic behavior and the kinetics of the damage. It has been concluded that the damage was localized at the level of the layers in the case of in-plane loading and the level of the adhesive zone in the case of out-of-plane loading. The thermomechanical behavior of cubic specimens of adhesively bonded joints subjected to dynamic compression has been studied. The results underline the sensitivity of the dynamic behavior of the adhesively bonded joints to the strain rate, the loading direction and the appearance of heat dissipation linked to the increase in temperature following the initiation of damage. This rise of temperature can dangerously approach the glass transition temperature of the matrix
Synthesis of 2-phosphonoheterocycles via base-promoted 5-endo cyclization
No full textInternational audienceHerein, a synthesis of 2-phosphonodihydrofurans and 2-phosphonodihydropyrroles via 5-endo cyclization of O-and N-propargylated compounds is described. The reaction is promoted by potassium tert-butoxide and allows a fast access to interesting heterocycles which were easily converted into 2-arylated pyrroles under acidic conditions
Integrated water vapour content retrievals from ship-borne GNSS receivers during EUREC4A
No full textInternational audienceIn the framework of the EUREC4A campaign, integrated water vapour (IWV) contents were retrieved over the open Tropical Atlantic Ocean using Global Navigation Satellite System (GNSS) data acquired from three research vessels : R/V Atalante, R/V Maria S. Merian, and R/V Meteor. This study describes the GNSS processing method and compares the GNSS IWV retrievals with IWV estimates from the ECMWF fifth ReAnalysis (ERA5), from the MODIS infra-red products, and from terrestrial GNSS stations located along the tracks of the ships. The ship-borne GNSS IWVs retrievals from R/V Atalante and R/V Meteor compare well with ERA5, with small biases (-1.62 kg/m2 for R/V Atalante and +0.65 kg/m2 for R/V Meteor) and a RMS difference about ~2.3 kg/m2. The results for the R/V Maria S. Merian are found  to be of poorer quality, with RMS difference of about 6 kg/m2 which are very likely due to the location of the GNSS antenna on this R/V prone to multipath effects. The comparisons with ground-based GNSS data confirm these results. The comparisons of all three R/V IWV retrievals with MODIS infra-red product show large RMS differences of 5-7 kg/m2, reflecting the enhanced uncertainties of this satellite product in the tropics. These ship-borne IWV retrievals are intended to be used for the description and understanding of meteorological phenomena that occurred during the campaign, east of Barbados, Guyana and northern Brazil
How To Measure Competitive Intensity?
No full textInternational audienceIn this research, we analyse the internal structure of competitive intensity on the basis of competitive dynamics. We propose a measure of competitive intensity based on two dimensions: strategic and tactical. This two-dimensional design makes it possible to gain a better understanding of the competitive battle, allowing managers to improve operations and the allocation of resources, according to both dimensions. It also provides a better understanding of the relationship between competitive intensity and other variables
Tracing Evolution of Angle-Wavelength Spectrum along the 40-m Postfilament in Corridor Air
No full textInternational audiencePostfilamentation channel resulting from filamentation of freely propagating 744-nm, 5-mJ, 110-fs pulse in the corridor air is examined experimentally and in simulations. The longitudinal extension of postfilament was determined to be 55–95 m from the compressor output. Using single-shot angle-wavelength spectra measurements, we observed a series of red-shifted maxima in the spectrum, localized on the beam axis with the divergence below 0.5 mrad. In the range 55–70 m, the number of maxima and their red-shift increase with the distance reaching 1 μm, while the pulse duration measured by the autocorrelation technique is approximately constant. Further on, for distances larger than 70 m and up to 95 m, the propagation is characterized by the suppressed beam divergence and unchanged pulse spectrum. The pulse duration increases due to the normal air dispersion
Une organisation sans but lucratif peut-elle perdre sa légitimité en sortant d’un groupe stratégique ? Le cas de France Business School
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Towards Teachable Autonomous Agents
No full textAutonomous discovery and direct instruction are two extreme sources of learning in children, but educational sciences have shown that intermediate approaches such as assisted discovery or guided play resulted in better acquisition of skills. When turning to Artificial Intelligence, the above dichotomy can be translated into the distinction between autonomous agents, which learn in isolation from their own signals, and interactive learning agents which can be taught by social partners but generally lack autonomy. In between should stand teachable autonomous agents: agents that learn from both internal and teaching signals to benefit from the higher efficiency of assisted discovery processes. Designing such agents could result in progress in two ways. First, very concretely, it would offer a way to non-expert users in the real world to drive the learning behavior of agents towards their expectations. Second, more fundamentally, it might be a key step to endow agents with the necessary capabilities to reach general intelligence. The purpose of this paper is to elucidate the key obstacles standing in the way towards the design of such agents. We proceed in four steps. First, we build on a seminal work of Bruner to extract relevant features of the assisted discovery processes happening between a child and a tutor. Second, we highlight how current research on intrinsically motivated agents is paving the way towards teachable and autonomous agents. In particular, we focus on autotelic agents, i.e. agents equipped with forms of intrinsic motivations that enable them to represent, self-generate and pursue their own goals. We argue that such autotelic capabilities from the learner side are key in the discovery process. Third, we adopt a social learning perspective on the interaction between a tutor and a learner to highlight some components that are currently missing to these agents before they can be taught by ordinary people using natural pedagogy. Finally, we provide a list of specific research questions that emerge from the perspective of extending these agents with assisted learning capabilities
Localisation et contrôle sûrs d’un capteur tracté
No full textThe oceans’ exploration becomes more and more reachable, especially thanks to robotics progress. Applications for underwater robots are plentiful. In this thesis, we particularly focus on the search of wrecks, as the Cordelière, which sank in the Bay of Brest (France) in 1512. The proposed robotic system consists of towing a magnetometer likely to detect the ferromagnetic materials of the wreck. The sensor cannot be directly embedded because it is sensitive to the perturbations from the robot. This is why it is deported. Two issues are studied to approach this system. The first one is linked to the control of the magnetometer’s position, whereas we can only act on the towing robot. A feedback linearization method is used to design a controller. Then, this controller is validated under some state constraints by using tools from interval analysis. The second issue relates to underwater localization in a reliable manner. Ways to approach uncertainties and outliers gathered by acoustic sensors are studied. The interval analysis allows to obtain first results, and the fuzzy logic completes the approach by giving more suppleness in the prioritization of the constraints. Finally, some expérimentations are presented with different robots, and especially the localization of a ROV in a pool.L’exploration des océans devient de plus en plus accessible, notamment grâce aux avancées en robotique. Les applications pour les robots sous-marins sont nombreuses. Dans cette thèse, on s’intéresse particulièrement à la recherche d’épaves, telle que celle de La Cordelière, qui a coulé dans la Rade de Brest en 1512. Le système robotique proposé consiste à tracter un magnétomètre susceptible de détecter les matériaux ferromagnétiques de l’épave. Le capteur ne peut pas être directement embarqué car il est sensible aux perturbations du robot. C’est pourquoi il est déporté. Deux problématiques sont alors étudiées pour appréhender ce système. La première est liée au contrôle de la position du magnétomètre alors que l’on ne peut agir que sur le robot tractant. Une méthode de linéarisation par bouclage est alors utilisée pour construire un contrôleur. Ce contrôleur est ensuite validé sous certaines contraintes d’état en utilisant des outils d’analyse par intervalles. La seconde problématique concerne la localisation sous l’eau de manière fiable. Sont alors étudiés des moyens d’appréhender les incertitudes et les données aberrantes collectées par un capteur acoustique. L’analyse par intervalles permet d’obtenir des premiers résultats, et la logique floue vient compléter l’approche en donnant plus de souplesse dans la priorisation des contraintes. Finalement, des expérimentations sont présentées avec différents robots, et notamment la localisation d’un ROV dans une piscine