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Cumulative air density depletion during high repetition rate filamentation of femtosecond laser pulses: Application to electric discharge triggering
No full textInternational audienceWe study the influence of the laser repetition rate on the generation of low-density channels of air left in the path of femtosecond laser filament. At high repetition rates, we observe the formation of a permanent millimeter-wide low-density channel that exceeds the depth and width of the transient depletion due to a single filament. We also show that this permanent cumulative effect decreases the breakdown voltage between two electrodes and can alter the path of the discharge. By comparing this effect in air and in pure nitrogen, we show that an accumulation of O−2 ions contributes to the reduction in the breakdown voltage
Modeling of the processes of ionization and excitation of nitrogen molecules by short and intense laser pulses
No full textInternational audienceWe present a model describing ionization and excitation of nitrogen molecules by a strong and short laser pulse. In difference to previous publications, both processes are considered within the same formalism of density matrix. We account for the dependence of the dipole moment on the vibrational quantum number and for a large number of excited levels. Populations of the excited levels depend significantly on the laser intensity, wavelength, polarization and pulse duration
La gamification de la société. Vers un régime du jeu ?
No full textInternational audienceLes champs applicatifs de la gamification ou la transposition d’éléments de jeu à des contextes de non-jeu sont aujourd’hui multiples. Ils s’étendent à la santé, l’éducation, le travail, les médias, etc., qui sont désormais concernés par des pratiques gamifiées. Or, les sciences humaines et sociales critiquent et analysent encore bien trop peu ces pratiques. Les recherches conduites sur la gamification portent le plus souvent sur des objets et n’abordent pas la gamification dans sa dimension logique. Considérant que le jeu en tant que modèle et référent, chargé de valeur sociale, mérite d’être interrogé au-delà de ses objets d’application, La gamification de la société propose de rassembler plusieurs textes, observations et critiques qui interrogent l’influence que le jeu et ses «mécaniques » ont sur le social. Les recherches empiriques présentes dans cet ouvrage (pratiques de designers, petite enfance, action politique, quantified self, etc.) sondent en outre différents contextes nationaux – Norvège, Belgique, États-Unis, France, etc. –, restituant cette logique dans sa dimension globalisée
Ma thèse en 180 secondes. Quand la science devient spectacle
No full textInternational audienceÀ quoi sert le concours « Ma thèse en 180 secondes » ? l’encontre des avis iconiques tranchés, cet ouvrage – fruit d’une enquête sociologique au long cours – rend compte de l’installation rapide, dans le champ de l’enseignement supérieur et de la recherche, d’un dispositif compétitif encourageant les doctorants à présenter leurs travaux de manière ludique.Ce faisant, « Ma thèse en 180 secondes » transforme le rapport de ces futurs professionnels de la recherche aux règles du métier scientifique, en favorisant à la fois l’incorporation de dispositions à la promesse et les « ficelles du métier » de la communication. Ce « geste promettant » illustre alors les effets dans le travail et la formation scientifique de l’organisation néolibérale des sciences sur projet. Mais là où le show « fan et sexy » l’emporte, que reste-t-il de l’éthique du travail
Transflower: probabilistic autoregressive dance generation with multimodal attention
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Grounding Spatio-Temporal Language with Transformers
No full textInternational audienceLanguage is an interface to the outside world. In order for embodied agents to use it, language must be grounded in other, sensorimotor modalities. While there is an extended literature studying how machines can learn grounded language, the topic of how to learn spatio-temporal linguistic concepts is still largely uncharted. To make progress in this direction, we here introduce a novel spatio-temporal language grounding task where the goal is to learn the meaning of spatio-temporal descriptions of behavioral traces of an embodied agent. This is achieved by training a truth function that predicts if a description matches a given history of observations. The descriptions involve time-extended predicates in past and present tense as well as spatio-temporal references to objects in the scene. To study the role of architectural biases in this task, we train several models including multimodal Transformer architectures; the latter implement different attention computations between words and objects across space and time. We test models on two classes of generalization: 1) generalization to randomly held-out sentences; 2) generalization to grammar primitives. We observe that maintaining object identity in the attention computation of our Transformers is instrumental to achieving good performance on generalization overall, and that summarizing object traces in a single token has little influence on performance. We then discuss how this opens new perspectives for language-guided autonomous embodied agents. We also release our code under open-source license as well as pretrained models and datasets to encourage the wider community to build upon and extend our work in the future
Guaranteed Identification of Viscous Friction for a Nonlinear Inverted Pendulum Through Interval Analysis and Set Inversion
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Validated Trajectory Tracking using Flatness
No full textInternational audienceThe problem of a safe trajectory tracking is addressed in this paper. It consists in using the results of a validated path planner providing a set of safe trajectories to produce the set of controls to apply to remain inside this set of planned trajectories while avoiding static obstacles. This computation is performed using the differential flatness of many dynamical systems. The method is illustrated in the case of the Dubins car
Shock wave refraction patterns at a slow–fast gas–gas interface at superknock relevant conditions
No full textInternational audienceShock wave refraction theory and high-resolution numerical simulations were employed to predict the refraction pattern under super-knock relevant conditions at slow-fast gas-gas interfaces which are characterized by a higher acoustic impedance in the incident phase than in the transmitted phase. First, our theoretical and computational methodologies were validated against results from the literature for planar shock-planar oblique interface interactions. Second, our framework was applied to planar shock-/cylindrical shock-cylindrical interface interactions. The theoretical regime diagram agrees well with the numerical predictions for the former configuration whereas significant discrepancies were observed for the latter. Numerical results show the formation of temperature and pressure peaks as the refraction structure transits from a Free Precursor Refraction to a Twin von Neumann Refraction. This change in thermodynamic state can induce a significant reduction in ignition delaytime, potentially leading to detonation onset