Portail HAL du Collège de France
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Ancestralité et autochtonie. Une recherche pluridisciplinaire sur la mémoire des origines
No full textInternational audienceComment la mémoire des origines participe-t-elle à la construction des identités et des territoires ? Cette interrogation, qui traverse les individus et les sociétés dans la longue durée, est abordée dans ce volume en questionnant le rapport aux origines autour de deux formes d’appartenance : l’ancestralité (comme rapport aux origines familiales) et l’autochtonie (comme rapport aux origines géographiques). La problématique de la mémoire des origines, parce qu’elle associe une analyse critique de la notion d’origine et une réflexion sur l’expression spatiale des identités individuelles et collectives, nécessite une approche résolument pluridisciplinaire. L’ouvrage regroupe ainsi les contributions d’historiens spécialistes des différentes périodes, d’archéologues, d’anthropologues, de politistes et de juristes afin de confronter les concepts et les méthodes autour d’un objet partagé. Ce choix a permis de multiplier les contextes d’analyse — avec une attention particulière portée aux enjeux de mémoire liés au fait colonial (antique, moderne et contemporain) — et de confronter différentes manières de faire vivre cette mémoire des origines, à travers des mots, des objets, des lieux
Between foot rot and wolves
No full textInternational audienceAny system of reindeer herding faces two threats, with contrasting consequences: scattering of herds engenders an external threat, from predators and wild reindeer, while excessive concentration of herds gives rise to the internal threat of disease epidemics. Treating one threat invariably exacerbates the other. Based on fieldwork and historic sources, this article studies the balances and techniques used among Tozhu reindeer herders, throughout the transformations of the 20th century resulting from policies of collectivization and privatization. It describes a contrast between a system of cognition involving both humans and reindeer in traditional herding, and a system of division of labor between humans, assisted by complex technologies in rationalized Soviet zootechny
Search for gravitational waves emitted from SN 2023ixf
No full textInternational audienceWe present the results of a search for gravitational-wave transients associated with core-collapse supernova SN 2023ixf, which was observed in the galaxy Messier 101 via optical emission on 2023 May 19th, during the LIGO-Virgo-KAGRA 15th Engineering Run. We define a five-day on-source window during which an accompanying gravitational-wave signal may have occurred. No gravitational waves have been identified in data when at least two gravitational-wave observatories were operating, which covered of this five-day window. We report the search detection efficiency for various possible gravitational-wave emission models. Considering the distance to M101 (6.7 Mpc), we derive constraints on the gravitational-wave emission mechanism of core-collapse supernovae across a broad frequency spectrum, ranging from 50 Hz to 2 kHz where we assume the GW emission occurred when coincident data are available in the on-source window. Considering an ellipsoid model for a rotating proto-neutron star, our search is sensitive to gravitational-wave energy and luminosity for a source emitting at 50 Hz. These constraints are around an order of magnitude more stringent than those obtained so far with gravitational-wave data. The constraint on the ellipticity of the proto-neutron star that is formed is as low as , at frequencies above Hz, surpassing results from SN 2019ejj
Search for continuous gravitational waves from known pulsars in the first part of the fourth LIGO-Virgo-KAGRA observing run
No full textInternational audienceContinuous gravitational waves (CWs) emission from neutron stars carries information about their internal structure and equation of state, and it can provide tests of General Relativity. We present a search for CWs from a set of 45 known pulsars in the first part of the fourth LIGO--Virgo--KAGRA observing run, known as O4a. We conducted a targeted search for each pulsar using three independent analysis methods considering the single-harmonic and the dual-harmonic emission models. We find no evidence of a CW signal in O4a data for both models and set upper limits on the signal amplitude and on the ellipticity, which quantifies the asymmetry in the neutron star mass distribution. For the single-harmonic emission model, 29 targets have the upper limit on the amplitude below the theoretical spin-down limit. The lowest upper limit on the amplitude is for the young energetic pulsar J0537-6910, while the lowest constraint on the ellipticity is for the bright nearby millisecond pulsar J0437-4715. Additionally, for a subset of 16 targets we performed a narrowband search that is more robust regarding the emission model, with no evidence of a signal. We also found no evidence of non-standard polarizations as predicted by the Brans-Dicke theory
The helion charge radius from laser spectroscopy of muonic helium-3 ions
No full textInternational audienceHydrogen-like light muonic ions, in which one negative muon replaces all of the electrons, are extremely sensitive probes of nuclear structure. Using pulsed laser spectroscopy, we have measured three 2S-2P transitions in the muonic helium-3 (μ3He+) ion, an ion formed by a negative muon and bare helium-3 nucleus. This allowed us to extract the Lamb shift, the 2P fine structure splitting, and the 2S-hyperfine splitting in μ3He+. Comparing these measurements with theory, we determined the root-mean-square charge radius of the helion (3He nucleus) to be rh = 1.97007(94) fm, in good agreement with the value from elastic electron scattering but a factor 15 more accurate. Our results represent benchmarks for few-nucleon theories and open the way for precision quantum electrodynamics tests in He atoms and ions
