Portail HAL du Collège de France
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Interview “La mythologie tibétaine a deux panthéons”, propos recueillis par Bertrand Audouy
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Evidence for a sub-Jovian planet in the young TWA 7 disk
No full textInternational audiencePlanets are thought to form from dust and gas in protoplanetary disks, with debris disks being the remnants of planet formation. Aged a few million up to a few billion years, debris disks have lost their primordial gas, and their dust is produced by steady-state collisions between larger, rocky bodies1,2. Tens of debris disks, with sizes of tens, sometimes hundreds, of astronomical units have been resolved with high-spatial-resolution, high-contrast imagers at optical and near-infrared or (sub)millimetre interferometers3,4. They commonly show cavities, ring-like structures and gaps, which are often regarded as indirect signatures of the presence of planets that gravitationally interact with unseen planetesimals2,5. However, no planet responsible for these features has been detected yet, probably because of the limited sensitivity (typically 2–10 MJ) of high-contrast imaging instruments (see, for example, refs. 6,7,8,9) before the James Webb Space Telescope. Here we have used the unprecedented sensitivity of the James Webb Space Telescope’s Mid-Infrared Instrument10,11 in the thermal infrared to search for such planets in the disk of the approximately 6.4-Myr-old star TWA 7. With its pole-on orientation, this three-ring debris disk is indeed ideally suited for such a detection. We unambiguously detected a source 1.5 arcsec from the star, which is best interpreted as a cold, sub-Jupiter-mass planet. Its estimated mass (about 0.3 MJ) and position (about 52 au, de-projected) can thoroughly account for the main disk structures
Euclid. I. Overview of the Euclid mission
No full textInternational audienceThe current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance
Unpacking the complexities of consciousness: Theories and reflections
No full textInternational audienceAs the field of consciousness science matures, the research agenda has expanded from an initial focus on the neural correlates of consciousness, to developing and testing theories of consciousness. Several theories have been put forward, each aiming to elucidate the relationship between consciousness and brain function. However, there is an ongoing, intense debate regarding whether these theories examine the same phenomenon. And, despite ongoing research efforts, it seems like the field has so far failed to converge around any single theory, and instead exhibits significant polarization. To advance this discussion, proponents of five prominent theories of consciousness-Global Neuronal Workspace Theory (GNWT), Higher-Order Theories (HOT), Integrated Information Theory (IIT), Recurrent Processing Theory (RPT), and Predictive Processing (PP)-engaged in a public debate in 2022, as part of the annual meeting of the Association for the Scientific Study of Consciousness (ASSC). They were invited to clarify the explananda of their theories, articulate the core mechanisms underpinning the corresponding explanations, and outline their foundational premises. This was followed by an open discussion that delved into the testability of these theories, potential evidence that could refute them, and areas of consensus and disagreement. Most importantly, the debate demonstrated that at this stage, there is more controversy than agreement between the theories, pertaining to the most basic questions of what consciousness is, how to identify conscious states, and what is required from any theory of consciousness. Addressing these core questions is crucial for advancing the field towards a deeper understanding and comparison of competing theories
ADM, BMS, and some puzzling interconnections
No full textInternational audienceThe precise connection between the ADM and BMS formalisms is still far from being fully understood. It leads superficially to some puzzles whose resolution can provide new interesting physical insights. One example concerns the claimed local-in-angle conservation of energy in a gravitational scattering process, whose physical meaning I will try to clarify in an explicit example. As my main topic, I will sketch my own understanding of how a recent saga on the definition of angular momentum, its loss, and its radiation, appears to have found its way to a happy ending by appealing to some non-trivial connections between ADM and BMS quantities in asymptotically flat and stationary spacetimes
Plaques-boucles méditerranéennes de style cloisonné en Septimanie et la question d’un atelier « royal ».
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Des steppes à la ville. Stratégies d’appropriation des espaces dans les microcosmes urbains de Mongolie-Intérieure
No full textInternational audienceLes politiques entreprises par le gouvernement chinois depuis plusieurs décennies pour développer ses territoires périphériques jugés économiquement défavorisés ont entraîné une l’urbanisation graduelle des steppes de Mongolie-Intérieure, la transformation durable des modes de vie et de nouvelles migrations des éleveurs nomades vers la ville. Si cette transition urbaine génère incertitude et confusion, elle offre également de nouvelles opportunités aux éleveurs désireux d’expérimenter des pratiques socio-économiques diverses dans des espaces urbains en constante mutation. Le but de cette proposition est d’explorer la façon dont les populations minoritaires de Mongolie-Intérieure mettent à profit divers modes d’appropriation de microcosmes urbains en mobilisant des stratégies individuelles et/ou collectives
Representations of God and Humanity in Sirach
No full textInternational audienceThe starting point of this chapter is the question of whether, despite the diversity of ancient textual witnesses to the book of Sirach and its inherent disparities, it is possible to provide some elements of synthesis regarding the representations of God and humanity in Sirach. However, the explanation of differences between textual forms must be weighed against the book as a whole and the tradition it carries. The chapter will also attempt to identify the singularity of Sirach in relation to the trend of instructional literature in which it is embedded, but also in relation to other writings from the Second Temple period
On a conjecture of Marton
No full textInternational audienceWe prove a conjecture of K. Marton, widely known as the polynomial Freiman--Ruzsa conjecture, in characteristic 2. The argument extends to odd characteristic, with details to follow in a subsequent paper