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Type Ia supernova feedback effects on globular clusters of different masses
No full textInternational audienceThrough 3D hydrodynamical simulations, we explore the impact of Type Ia supernova (SN) explosions on the star formation history and chemical properties of second-generation (SG) stars in young globular clusters with masses of 10^5-10^6 Msun. We assume that the SG is formed out of the asymptotic giant branch (AGB) ejecta of first-generation stars plus pristine interstellar medium gas which is modelled as a uniform gas moving at a constant velocity towards the cluster. We tested two values for the infalling gas density of 10^(-24) and 10^(23) g/cm^3. Type Ia SNe start to explode together with the release of gas from the most massive AGB stars. Three simulated models are analyzed. In the low-mass and low-density scenario, we find that SNe Ia quench star formation which however restarts when the gas cools down again in between two explosions. SG stars are dominated by a He-rich population (Y>0.33), which is poorly diluted by pristine gas. In the high-mass models, star formation is mildly affected, while the He composition is significantly altered as exploding SNe prevent the accretion of pristine gas and therefore extremely helium-rich stars form. In the high-density model, such weak gas accretion leads to a maximum enhancement in helium mass fraction much larger than the observed one and not correlating with the initial cluster mass as found in models without Type Ia SNe. As for the iron content, small spreads have been found in all models, but the SG is less homogeneous than the FG, at variance with current observations
Nature(s) de la guerre. Ressources, appropriations, expropriations, restitutions dans les Amériques (du XVe siècle à nos jours)
No full textMeasurement of small linear birefringences in chiral photonic devices
No full textInternational audienceWe present a straightforward and accurate method for measuring the birefringence of chiral waveguides. Due to the chiral nature of these devices, the supported modes are elliptical, enabling direct access to their linear birefringence characteristics. Consequently, determining the linear birefringence reduces to measuring the device’s Mueller matrix. This method is particularly effective when the linear birefringence is comparable in magnitude to the circular birefringence (on the order of 10−5). The technique is applied to study the impact of humidity on sol-gel-based chirowaveguides. Four distinct linear birefringence contributions are identified and measured: (1) Opto-geometrical birefringence, resulting from the waveguide geometry and modal TE/TM decomposition; (2) tensile stress-induced birefringence (∼ 10−4), linked to the waveguide fabrication process; (3) compressive stress-induced birefringence, which increases with humidity due to material swelling; and (4) residual diagonal birefringence (∼ 10−6), attributed to slight asymmetries in the rib waveguide cross-section
Ultramafic float rocks at Jezero crater (Mars): excavation of lower crustal rocks or mantle peridotites by impact cratering?
No full textInternational audienceBased on observation and data from meteorites and in situ scientific missions, experiments as well as models, the Martian mantle is assumed to share some compositional and mineralogical affinity with the terrestrial mantle. However, there might be subtle differences like the Martian mantle being more ferroan. Yet, we do not have any direct analysis of a Martian mantle rock to confirm this assumption. NASA’s Perseverance rover found olivine-rich boulder-sized float rocks on the upper Jezero fan (Mars). These boulders have an ultramafic composition and their mineralogy is dominantly composed of Fo73±3 olivine with high-Mg orthopyroxene, Cr-rich Ti-Fe oxides and minor plagioclase and high-Ca pyroxene. Microtextural and petrological analysis reveals that these minerals crystallized at equilibrium. In addition, these boulders are different from all the bedrocks analyzed by Perseverance along its traverse which are crustal igneous rocks and sediments. Comparing our data to Martian meteorites and available Mars bulk silicate models (BSM), we discuss that these boulders could represent primitive melts and/or lower crustal material, and we specifically hypothesize that they could be mantle peridotites. We propose that these putative mantle rocks could have been excavated by the succession of impacts from the shallow mantle or lower crust in the Isidis region where Jezero crater is located. These olivine-rich boulders could thereby constitute the first direct analysis of a Martian mantle rock
Negative Selection Maintains Grossly Altered but Broadly Stable Karyotypes in Metastatic Colorectal Cancer
No full textInternational audienceAbstract Aneuploidy is near-ubiquitous in cancer and contributes to tumor biology. However, the temporal evolutionary dynamics that select for aneuploidy remain uncharacterized. We performed longitudinal genomic analysis of 755 samples from 167 patients with colorectal-derived neoplasias from different stages through metastasis and treatment. Adenomas had few copy number alterations (CNA) and most were subclonal, whereas cancers had many clonal CNAs, suggesting that progression goes through a CNA bottleneck. Individual colorectal cancer glands from the same tumor had similar karyotypes, despite evidence of ongoing instability at the cell level. CNAs in metastatic lesions, after therapy, and in late recurrences were similar to the primary. Mathematical modeling indicated that these data are consistent with the action of negative selection on CNAs that “trap” cancer genomes on a fitness peak characterized by specific CNAs. Hence, progression to colorectal cancer requires traversing a rugged fitness landscape, whereas subsequent CNA evolution is constrained by negative selection. Significance: We profiled 167 long-term responders longitudinally (755 samples), documenting long-term cancer evolution. We found that a genetic bottleneck is required for progression and is associated with dramatic increase in CNAs but decrease in clonal diversity. After initiation, copy number evolution is constrained by negative selection through metastasis and treatment
An intense peak of paraglacial dismantlement of mountain slopes: Insights from dating and volume quantification of rock-slope failure deposits in the Icelandic Westfjords (Dýrafjörður and Önundarfjörður)
No full textInternational audienceParaglacial rock slope failures (RSFs) are prominent processes of landscape evolution in deglaciated terrains, such as the Westfjords of Iceland. This study aims to provide chronological and volumetric data on RSF deposits in the Dýrafjörður and Önundarfjörður fjords, in order to document the magnitude, duration, and geomorphic impact of the intense peak of Early and Middle Holocene paraglacial denudation. By refining the timing of a paraglacial signal, this work contributes to a better understanding of sedimentary production and landscape evolution during the Holocene.A total of 17 RSFs was studied, described and mapped using the Schmidt-hammer exposure-age dating method, calibrated with radiocarbon dating. Surficial block morphometry and volumetric estimates of RSF deposits were derived from field measurements, orthophotography, and high-resolution digital elevation models.RSF ages are concentrated in the Early to Middle Holocene. The vast majority of this activity occurred between 12 and 6 cal. ka BP. During this 6000-year interval, ~83 million m3 of debris were deposited, which accounts for approximately 90% of the total volume (~92.5 M m3) from all 17 RSF sites. This indicates a primary paraglacial adjustment phase characterized by high sediment delivery efficiency. Slope reactivations occurred over periods up to 3400 years, with superimpositions of deposits: these are multi-phased RSFs.Finally, a significant lag of approximately 3000 years is observed between the deglaciation (~10.2 cal. ka BP) and the peak in rock-slope failure activity (8–6 cal. ka BP), which coincides with the Holocene Thermal Maximum climax in Iceland (8.6–5.2 cal. ka BP). The subsequent cessation of major RSFs activity after ~4 cal. ka BP marks the transition to a stable, non-glacial equilibrium
La politique des statistiques internationales du tourisme : Entre exigences financières et préoccupations environnementales
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Code de la Justice pénale des mineurs :Les nouvelles temporalités juridiques et professionnelles
No full textProjet de recherche financé proposant une analyse du nouveaux rythme procédural introduit par le Code de la justice pénale des mineurs au prisme des conditions de travail des professionnel