HAL Université de Savoie
Not a member yet
59053 research outputs found
Sort by
Search for Axion-Like Particles from Nearby Pre-Supernova Stars
No full textInternational audienceAxion-like particles (ALPs) are hypothetical pseudoscalar bosons that arise in many extensions of the Standard Model and are well-motivated dark matter candidates. Nearby massive stars in the late stages of stellar evolution provide a promising environment for enhanced ALP production due to their high core temperatures and densities. We search for a combined signal of ALP-induced hard X-ray and soft -ray emission from 18 nearby pre-supernova stars using the full public 22-year INTEGRAL/SPI dataset, construct individual stellar spectra and link them in a coherent analysis. A maximum-likelihood approach is used to extract fluxes in the 20--2000 keV energy range. Stellar evolution models are employed to obtain the expected spectral shapes of ALP production processes peaking between 50--500 keV, depending on stellar mass and evolutionary stage. We construct a joint likelihood that incorporates uncertainties in stellar parameters to derive combined constraints on the coupling constants and as a function of the ALP mass . The hard X-ray and soft -ray fluxes of all selected stars are consistent with zero within uncertainties. We provide upper limits on the continuum emission and on the 511 keV and 1809 keV line fluxes. The combined upper limit on is GeV (95% C.I.) while the ALP-photon coupling is constrained to GeV (95% C.I.) for eV, depending on the time to core collapse and magnetic field assumptions. Conservative limits of GeV (95% C.I.) are obtained assuming all but one star are in the early He-burning phase. These results rank among the strongest limits on ALP couplings to date and demonstrate the importance of soft -ray observations for probing ALPs and massive star evolution
Holocene climatic changes in the Kerguelen archipelago (South Indian Ocean) based on marine and lacustrine palaeoclimatic archives
No full textInternational audienceClimatic variability in the Southern Hemisphere is largely controlled by the latitudinal position of the Southern Hemisphere Westerly Winds (SHW), whose migration influences precipitation, temperature, and Antarctic upwelling. This study presents the results of analyses of two lacustrine sediment cores from Lake Armor, located on the subantarctic Kerguelen Islands (49 • 15′S, 69 • 10′E), within the SHW belt. Lipid biomarkers (Glycerol Dialkyl Glycerol Tetraethers, n-alkanes, and their hydrogen isotopes) were used to reconstruct mean annual air temperature above freezing (MAF) and humidity conditions. These records are compared with a high-resolution diatom-based summer sea surface temperature (SST) reconstruction from marine core MD11-3353, situated 150 km southwest of Lake Armor. In the late glacial and Early Holocene, our results reveal a period of warm air temperature, comparable to current values and very warm sea surface temperature, 5°C above the current values. Around 9000 cal a BP, an abrupt transition occurred, marked by a cooling of 5°C in SST and 1.5°C in MAF, interpreted as a northward migration of the SHW and associated oceanic fronts. The Mid-to-Late Holocene period is characterized by pronounced MAF variability, including a notably warm interval between 3000 and 2000 cal a BP, when n-alkane dD suggests the prevalence of wetter conditions. Since ~250 cal a BP, a southward migration of the SHW has produced a 2.5°C rise in MAF. Our findings are overall consistent with previous studies from the Indian Ocean, but permit us to go a step further as by comparing SSTs and air temperatures. This suggests that SST is not a reliable predictor of air temperature on the Kerguelen Islands, particularly during the Early Holocene. We hence argue that Kerguelen air temperature is predominantly controlled by the position of westerly winds, as an indicator of reorganisations in air mass trajectories
Exploring the freeze-in mechanism for scotogenic singlet dark matter
No full textInternational audienceWe present an exploratory study of the freeze-in mechanism within a scotogenic framework, where dark matter can either be a scalar singlet or a fermion singlet. Based on a random parameter scan, we show that large portions of the parameter space feature a dark matter relic density in agreement with the limits derived by Planck. Moreover, constraints related to lepton flavour violation are mostly respected within such parameter regions. Our study shows that it will be worth to further investigate the freeze-in mechanism within scotogenic frameworks
Understory plant indicator values poorly perform at monitoring temporal changes in French forest soil chemical properties
No full textInternational audienceUnderstory plant communities are widely used to infer soil conditions through species indicator values (IVs), scores reflecting species’ ecological preferences for factors such as soil acidity, moisture, or nutrient levels. While their reliability to describe soil conditions along spatial gradients is well established, their ability to capture temporal changes in soil chemistry remains largely untested at both temporal and geographical scales. We combined 26 years of vegetation monitoring with two French national soil surveys (1993–1997; 2007–2012) across 102 permanent forest plots to assess the reliability of community soil indices (CSIs) as bioindicators of soil pH, carbon-to-nitrogen ratio (C/N), and extractable phosphorus. CSIs were computed by averaging species IVs for each plot and survey. Temporal dynamics of measured soil properties and CSIs were analyzed using mixed-effects models at the national scale, while local trends were estimated separately for each plot to directly compare measured and vegetation-inferred changes. CSIs showed strong spatial correlations with measured pH and C/N, but weaker relationships for phosphorus. In contrast, no significant coupling was found between temporal changes in CSIs and measured soil parameters, with frequent mismatches in both direction and magnitude at the plot level. Measured soil dynamics were mainly driven by initial edaphic conditions and stand age, whereas CSI dynamics responded primarily to canopy openness and anthropogenic disturbances such tree harvesting. These findings confirm the value of IVs for spatial bioindication but highlight their limited sensitivity for detecting long-term soil changes, especially where soil changes remain modest
Sediment routing and palaeogeographic evolution of the Western Alpine Foreland Basin during the early collisional stage
No full textInternational audienceIn the Western Alpine Foreland Basin (WAFB), Late Eocene and Miocene periods were characterized by longitudinal sediment routing systems: The first one was situated within the turbidite basin during the underfilled phase and exhibited a northward orientation toward the Swiss Basin, whereas the second was located in the Rhône Valley during the overfilled phase and was directed southward toward the Mediterranean Sea. The transition between these two periods occurred during the Oligocene, which corresponds to both the underfilled/ overfilled transition and the early overfilled period. In this study, we provide new fieldwork observations, seismic and well data interpretations, biostratigraphic analyses and a literature synthesis to reconstruct the palaeogeographic and source-to-sink evolution of the WAFB from Priabonian to Aquitanian. The aim is to discuss this reorganisation of sediment routing in relation to the evolution of the Alpine orogenic wedge, as well as the structural inheritance and the suite of geodynamic events that affected southeastern France during the mid-Cenozoic. We divided the WAFB sedimentary formations into four depositional sequences (S1 to S4). During the deposition of the first two sequences (Priabonian to early late Rupelian; ~37.4-28.8 Ma), the WAFB routing system was influenced by the end of the Pyrenean-Provençal orogeny, the European Cenozoic Rifting System (controlling the Rhône Valley s.l.) and the Alpine orogenic wedge (controlling the Alpine foredeep). The very first connection between the Alpine domain and the Rhône Valley is established at ~30 Ma, during the late Rupelian (S2 highstand), controlled by E-W inherited Pyrenean-Provençal structures implying a 'broken foreland'. In the meanwhile, from the Dévoluy Basin and northward, the orogenic wedge controlled a classical, although thin, foreland basin characterized by a northward sediment routing connected to the Northern Alpine Foreland Basin. Most of the S3 sequence (Latest Rupelian to middle Chattian; ~28.8-23.25 Ma) corresponds to a decrease of clastic Alpine inputs throughout SE France caused by a reorganisation of the drainage network related with the exhumation of the southern External Crystalline Massifs. S3 highstand and S4 sequence (late Chattian to Aquitanian; from ~23.25 Ma) correspond to the establishment of a longitudinal sediment routing system in the Rhône Valley, with material flowing southwards toward the Gulf of Lion, and supplied by the Palaeo-Isère to the north and potentially by the Palaeo-Durance to the south. This final stage in the reorganisation of the drainage network is clearly associated with the post-rift phase of the Gulf of Lion, which facilitated the opening of a new sink and the ultimate southward migration of the sedimentary area
A Geometric View on Crossing-Symmetric Dispersion Relations
No full textInternational audienceWe introduce a general framework for constructing dispersion relations using crossing-symmetric variables, leading to infinitely many distinct representations of the 2-to-2 scattering amplitude of identical scalars. Classical formulations such as the Auberson-Khuri crossing-symmetric dispersion relations (CSDRs), the Mahoux-Roy-Wanders relations, and the local CSDR, as well as fixed-t dispersion relations emerge as special cases. Within this setting we re-derive the null constraints from a geometric perspective. Finally, we present, for the first time, an explicit extension of Roy-like equations that remain valid at arbitrarily high energies, relying only on the rigorously established analyticity domain of scattering amplitudes
What is the most suitable medicine ball mass for assessing maximal upper-extremity power in the seated single-arm horizontal push test?
No full textInternational audienceIntroduction. Different medicine ball (MB) masses are used for the unilateral MB push to indirectly determine upper-extremity power. This study aimed to identify the most suitable MB mass for assessing maximal upper-extremity power through the seated single-arm horizontal push test (SSAHPT).Methods. Thirty-four athletes performed the SSAHPT with three different MB masses (1 kg, 3 kg, and 5 kg) and the unilateral ballistic bench press test. For each limb, the SSAHPT distance was determined, and the maximal power (Pmax) and force-velocity profile (SFv) were extracted from the unilateral bench press test.Results. For the 1-kg and 3-kg MB, SSAHPT performance variation was explained by the variations of Pmax and Dominance (R2 = 0.82–0.86), with the effect of Pmax about 5.5 times greater than the effect of Dominance. For the 5-kg MB mass, SSAHPT performance variation was explained by the variations of Pmax, Dominance, and SFv (R2 = 0.85). The effect of Pmax was 5.3 and 1.6 times greater than the effect of Dominance and SFv, respectively.Conclusion. To limit the involvement of the athlete's force-velocity profile in SSAHPT performance with a 5-kg MB mass, it is advisable to use either a 1-kg or 3-kg MB mass when SSAHPT is employed to reflect maximal upper-extremity power
Détection automatique de bruit routier à l'aide de modèles de classification automatique et d'analyse de l'évolution du niveau sonore
No full textInternational audienceNoise management has become a major public health issue over several decades. To initiate protective measures against noise overexposure, it is essential to accurately evaluate annoyance. This involves detecting sound sources, their emission durations and associated sound levels. Among commonly encountered sources, road traffic is a prominent contributor to noise pollution, according to health organisation reports. This paper presents an automatic roadway noise detection system. The proposed method combines event detection and classification through a multi-layer approach. Sound event detection is ensured by distinct units. First, a sliding window enables signal preclassification by identifying specific patterns on its mel-spectrogram. Simultaneously, sound level features are used to detect prominent periods, often marking off sound events. Both units combined and sharpened provide detection of the most relevant sound events over the acoustic signal. Precise classification is issued by an additional AI model, dedicated to recognising roadway noise among various vehicle types. Our system operates in diverse soundscapes while maintaining a high level of roadway noise detection accuracy. It permits an automatic estimation of roadway noise contribution, which corresponds to equivalent sound level when roadway noise prevails. This estimation closely aligns with manual assessments from experts, validating the proposed system relevance
