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Detection of triboelectric discharges during dust events on Mars
No full textInternational audienceLightning is among the most energetic manifestation of electrical activity in planetary atmospheres, with documented observations not only on Earth but also on Saturn and Jupiter. On Mars, the existence of electrical activity has long been suspected but never directly demonstrated. The dusty atmosphere of Mars undergoes aeolian processes, ranging from wind-blown dust and sand, metre-to-hundred-metre-sized dust devils to thousand-kilometre-scale dust storms, which, in Earth’s deserts, can become electrified through triboelectric charging. For this reason, electric fields have been predicted to build up on Mars, but with no measurement of Martian atmospheric electrical activity so far. Here we report in situ detections of triboelectric discharges, identified by their electrical and acoustic signatures captured by the SuperCam microphone aboard the Perseverance rover. Fifty-five events have been detected over two Martian years, usually associated with dust devils and dust storm convective fronts. These serendipitous observations demonstrate that Martian electric fields can reach the breakdown threshold of the near-surface atmosphere of Mars, predicted to be on the order of several tens of kV m−1. Such electrical activity could affect dust dynamics and potentially fuel a reactive electrochemical environment enhancing the oxidizing capacity of the atmosphere, with consequences for the preservation of organic molecules. This in situ evidence may have implications for surface chemistry, habitability and human exploration
Dépasser la « ville créative », vraiment ?
No full textInternational audienceDans le cadre de la séance "Quel quartier culturel après la ville créative ?" du cycle de séminaires de la MSH Paris Nord "Art, culture et création dans la fabrique des territoires", cette communication a pour objectif de discuter du modèle de la "ville créative" néolibérale pour en montrer les réalités, les limites et ouvrir le débat sur son possible dépassement. Les cas des quartiers culturels du M50 à Shanghai et du canal de l'Ourcq dans le Nord-Est parisien sont mobilisés pour illustrer empiriquement les enjeux globaux de ce modèle urbain circulant à l'échelle internationale
Auto-ethnographing the work of “men in the shadows”: social distances and research practices among video protection operators
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Activity Unmasks Chirality in Liquid-Crystalline Matter
No full textInternational audienceActive matter theories naturally describe the mechanics of living systems. As biological matter is overwhelmingly chiral, an understanding of the implications of chirality for the mechanics and statistical mechanics of active materials is a priority. This article examines active, chiral materials from a liquid-crystal physicist's point of view, extracting general features of broken-symmetry-ordered phases of such systems without reference to microscopic details. Crucially, this demonstrates that activity allows chirality to affect the hydrodynamics of broken-symmetry phases in contrast to passive liquid crystals, in which chirality induces the formation of a range of spatially periodic structures whose large-scale mechanics have no signatures of broken parity symmetry. In active systems, chirality leads to the formation of phases that break time translation symmetry, which is impossible in equilibrium, and the existence of new kinds of elastic force densities in translation symmetry-broken states
ALMA-JELLY. I. High Resolution CO(2–1) Observations of Ongoing Ram Pressure Stripping in NGC 4858 Reveal Asymmetrical Gas Tail Formation and Fallback
No full textInternational audienceAbstract We present new CO(2–1) observations (resolution ∼1″ = 460 pc) of the Coma cluster jellyfish galaxy NGC 4858 obtained from the ALMA-JELLY large program. Analyzing this data alongside complimentary Subaru H α and Hubble Space Telescope (F600LP / F350LP) observations, we find numerous structural and kinematic features indicative of the effects from strong, inclined ram pressure, including an asymmetric inner gas tail. We estimate a highly inclined disk-wind angle of ϕ DW = 7 5 − 27 + 10 . By subtracting a simple circular velocity model, we find (1): gas clumps that are being accelerated by ram pressure, and (2): signatures of gas clumps that had been previously pushed out of the disk but are now falling inward. We also discuss head-tail morphologies in star complexes within the stellar disk that appear to be ram pressure stripping (RPS)-influenced. Lastly, we compare this galaxy to state-of-the-art galaxy “wind tunnel” simulations. We find that this galaxy is one of the best nearby examples of strong and inclined ram pressure gas stripping, and of gas that is perturbed by ram pressure but not fully stripped and falls back. We emphasize the importance of torques due to ram pressure in highly inclined interactions, which help drive gas inward on the side rotating against the wind, contributing to the formation of asymmetric inner RPS tails
Du hacking à la scène : conception d’un dispositif performatif art/science entre cyborg et voix chantée
No full textInternational audienceThis paper examines the design of a performative research device that takes the cyborg imaginary as a research question, investigating the dynamics of the human/non-human boundary through an interdisciplinary combination of robotic body augmentation, artificial intelligence, and the singing voice. First, we discuss the exploratory strategies implemented as part of the research-creation methodology, targeting Do-It-Yourself approaches as enabler of functional redefinitions. Then we look at how these strategies relate to two issues raised by cyborg imaginaries: as a robot-human interface involving the entire self, how does the vocal gesture of the singer help unframing the experience of a prosthesis? And then, how does the unpredictable nature of a robot empowered by an AI algorithm help foiling the perception of the boundaries between human, animal, and machine?Cet article propose d’examiner la conception d’un dispositif de recherche performative prenant l’imaginaire cyborg comme question de recherche et interrogeant, à partir d’un agencement interdisciplinaire convoquant robotique embarquée, intelligence artificielle et voix chantée, la dynamique de la frontière humain/non-humain. Sont tout d’abord discutées les stratégies exploratoires mises en œuvre dans le cadre de la méthodologie de recherche-création, en particulier les approches Do-It-Yourself en tant que génératrices d’opérations de redéfinitions fonctionnelles. Une seconde partie propose d’articuler ces stratégies avec deux problématiques soulevées par l’imaginaire cyborg : en tant que modalité d’interface robot-humain engageant l’intégralité de soi, comment le geste vocal chanté contribue-t-il à décadrer l’expérience de la prothèse ? Comment le caractère imprévisible d’un robot autonomisé par un algorithme d’intelligence artificielle concourt-il à déjouer la perception des frontières entre humain, animal et machine
Distribution des biais des algorithmes de régression pseudo-linéaire en identification récursive
No full textThis paper presents a detailed analysis of the asymptotic bias distribution of recursive identification schemes based on Pseudo-Linear Regression. As shown in a previous paper, the criterion asymptotically minimized is the variance of an unmeasurable signal (called the equivalent prediction error) when the system to be identified is in the model set. We prove that this is still approximately true if the true system is not in the model set provided that the bias (which necessarily occurs) remains small
Quasi-monoenergetic multi-GeV electron acceleration in a plasma waveguide
No full textInternational audienceLaser-plasma accelerators present a promising alternative to conventional accelerators. To fully exploit the extreme amplitudes of the plasma fields and produce high-quality beams, precise control over electron injection into the accelerating structure is required, along with effective laser pulse guiding to extend the acceleration length. Recent studies have demonstrated efficient guiding and acceleration using hydrodynamic optically field-ionized (OFI) plasma channels. This guiding technique has also been combined with controlled electron injection to produce high-quality electron beams at the GeV level using a 50 TW laser. The present work extends these results to higher laser energies, demonstrating the generation of quasi-monoenergetic electron beams with peak energies exceeding 2 GeV, for a PW-class laser
The effect of cognitive load on linguistic fluency, lexical production, and emotional polarity: An exploratory study on self-directed French
No full textInternational audienceCognitive load refers to the mental resources available in working memory, which can vary due to, e.g., the inherent complexity of a task. Studies have investigated the effect of a higher cognitive demand on speech, either on fluency, lexical use or linguistic display of emotions. Fewer have investigated all these parameters jointly, and most focus on English. Here we manipulate working memory load with an image-depiction task with or without access to the image and investigate whether cognitive load impacts speech production in French, i.e., correlates with both fluency metrics (number of word tokens and lemmas, lemma-token ratio, counts and rates of filled pauses, interruptions and repetitions) and/or with lexical metrics (use of words from a given lexical field or with a given connotation). Our results show that, compared to their peers in the low cognitive load condition (with access to the image), speakers under high cognitive load (who describe the image from memory) indeed tend to use more disfluencies but show little differences in the use of specific vocabulary or in emotional words. Although the absence of lexical differences may be due to inherent language- or task-specific differences, the confirmation that an increase in cognitive load implies an increase in disfluency indicates that at least this one parameter is a cross-linguistic indicator of speech production under high cognitive load