Portail HAL Ensta
Not a member yet
11080 research outputs found
Sort by
Self-probed ptychography from semiconductor high-harmonic generation
No full textInternational audienceWe demonstrate a method to image an object using a self-probing approach based on semiconductor high-harmonic generation. On the one hand, ptychography enables high-resolution imaging from the coherent light diffracted by an object. On the other hand, high-harmonic generation from crystals is emerging as a new source of extreme-ultraviolet ultrafast coherent light. We combine these two techniques by performing ptychography measurements with nanopatterned crystals serving as the object as well as the generation medium of the harmonics. We demonstrate that this strong field in situ approach can provide structural information about an object. With the future developments of crystal high harmonics as a compact short-wavelength light source, our demonstration can be an innovative approach for nanoscale imaging of photonic and electronic devices in research and industry
Techniques for accelerating branch-and-bound algorithms dedicated to sparse optimization
No full textInternational audienceWe propose two acceleration techniques for sparse optimization (the minimization of a cardinality-penalized least-squares function) with branch-and-bound algorithms. Convex duality is applied to the relaxation problems at each node of the search tree, allowing one to early prune suboptimal nodes thanks to the computation of valid dual bounds. Then, screening methods are implemented during each node evaluation, which reduce the problem size by fixing variables to their optimal value. Numerical experiments study the efficiency of such techniques as a function of the problem difficulty
Curiosité, apprentissage et numérique : Que dit la recherche ?
No full textArticle de vulgarisation destiné pour la rubrique "Que dit la recherche" du réseau canopé. Il présente les travaux menées pour investiguer l'utilisation des technologies éducatives pour concevoir des entraînements d'apprentissage dirigés par la curiosité pour les enfants
Learning deep morphological networks with neural architecture search
No full textInternational audienc
Experimental investigations about complex non-relaxing fatigue loads for carbon-black filled natural rubber
No full textInternational audienceThis paper presents an extensive test campaign and analysis to better understand the fatigue behavior and the mechanisms at stake for natural rubber under complex non-relaxing loads. This database includes relaxing uniaxial tests under tension and torsion, relaxing and non-relaxing tension tests for 3 temperatures, relaxing multiaxial tension-torsion proportional tests, and non-relaxing tension-torsion multiaxial sequenced tests for different temperatures. The tests are conducted on hourglass-shaped natural rubber specimens, loaded by coupled and aligned tension and torsion actuators. Various strain ratios, uniaxial and biaxial loading sequences and critical plane orientation histories over a loading cycle are achieved. A total of 240 specimens were tested. Different temperatures are imposed to affect reinforcement and provide a comparison to previous results on crystallization. Furthermore, finite element analyses (FEA) are performed to determine first the respective local mechanical state in the specimens and then to infer the crack orientation predicted from a critical plane approach based on the maximum principal strain. Finally, the results are carefully analyzed based on three indicators: the relative improvement on fatigue lifetime, the cracks features (roughness and branching, from optical and SEM observations) and their comparison to the crack orientation predicted using the critical plane approach
Titanium-catalysed transformations of alkynes into complex molecular architectures
No full textInternational audienc
Exploring space for robot mistakes in child robot interactions
No full textInternational audienceAbstract Understanding the impact of robot errors in child-robot-interactions (CRI) is critical, as current technological systems are still limited and may randomly present a variety of mistakes during interactions with children. In this study we manipulate a task-based error of a NAO robot during a semi-autonomous computational thinking task implemented with the Cozmo robot. Data from 72 children aged 7–10 were analysed regarding their attitudes towards NAO (social trust, competency trust, liking, and perceived agency), their behaviour towards the robot (self-disclosure, following recommendations), as well as their task performance. We did not find quantitative effects of the robot’s error on children’s self-reported attitudes, behaviour, or task performance. Age was also not significantly related to either social attitudes or behaviours towards NAO, although there were some age-related differences in task performance. Potential reasons behind the lack of statistical effects and limitations of the study with regards to the manipulation of robot errors are discussed and insights into the design of future CRI studies provided
Flow Conditions‐Controlled Divergent Oxidative Cyclization of Reticuline‐Type Alkaloids to Aporphine and Morphinandienone Natural Products
No full textInternational audienceDescribed herein is a divergent continuous-flow approach for the biomimetic oxidative cyclization of reticuline-type alkaloids to aporphine and morphinandienone natural products using hypervalent iodine(III) reagents. The methodologies developed in this work were based on the detailed knowledge of the reaction mechanisms in order to develop robust and original experimental conditions toward the selective synthesis of either aporphine or morphinandienone natural products. In this frame, we exploited the ability of HFIP to stabilize radical cation intermediates and to activate hypervalent iodine(III) oxidants for the flow synthesis of aporphine natural products such as glaucine, rogersine and nantenine. On the other hand, we established that PhI(OAc)(OTf), prepared by action of TMSOTf on PhI(OAc)2, was a powerful oxidant for the synthesis of morphinandienone natural products such as sebiferine and amurine. Also described in this contribution, the very first structure-reactivity relationship to assess the current limits of such oxidative flow processes
Procédé de configuration d'un circuit logique programmable, circuit logique programmable et dispositif pour implémenter le procédé
No full textL’invention concerne un procédé de configuration d’un circuit logique programmable à partir d’un flux binaire de configuration, le circuit logique programmable comprenant une entrée de configuration de circuit pour le chargement du flux binaire de configuration et une pluralité de modules logiques programmables comprenant chacun une entrée de module et une sortie de module, le procédé comprenant : - définir un vecteur de méta-configuration comprenant une succession de champs de sélection d’une source de configuration de module parmi une pluralité de sources de configuration de module, - segmenter le flux binaire de configuration en une pluralité de segments binaires de configuration, - charger ledit vecteur de configuration dans un registre de méta-configuration du circuit logique programmable, puis, - charger respectivement lesdits segments binaires de configuration dans lesdits modules logiques programmables selon les valeurs desdits champs dudit vecteur de méta-configuration