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Les Formulations d'Einstein du Principe de Mach
No full textCette traduction française de l'article « Einstein’s Formulations of Mach’s Principle » de Carl Hoefer, initialement publié en 1995 dans « Mach’s Principle: From Newton’s Bucket to Quantum Gravity » (Birkhäuser), est mise en ligne avec l’accord explicite des ayants droit.Mach's Principle: From Newton's Bucket to Quantum Gravity. The Center for Einstein Studies, Birkhauser Publishers, 1995, edited by Julian B. Barbour and Herbert Pfister., p.6
Optical spectroscopy of blazars for the Cherenkov Telescope Array Observatory- IV
No full textInternational audienceBlazars, including BL Lacs and FSRQs, are the most luminous extragalactic γ-ray sources. They account for about 56% of the sources listed in the recent Fermi-LAT catalog (4FGL-DR4). The optical and UV spectra of BL Lacs are nearly featureless, making it difficult to precisely determine their redshifts. Consequently, nearly half of the γ-ray BL Lacs lack reliable redshift measurements. This poses a major challenge, since redshift is crucial for studying the cosmic evolution of the blazar population and γ-ray propagation studies such as indirect evidence of EBL, placing constraints on IGMF and searches for LIV and ALPs. This paper is the fourth in a series dedicated to determining the redshift of a sample of blazars identified as key targets for future observations with the Cherenkov Telescope Array Observatory (CTAO). We performed Monte Carlo simulations to select γ-ray blazars detected by Fermi-LAT with hard spectra, that lack redshift measurements. These blazars are expected to be detectable by CTAO within 30 hours or less of exposure assuming an average flux state. In this fourth paper, we report the results of detailed spectroscopic observations of 29 blazars using the ESO/VLT, Keck II, and SALT telescopes. Our analysis involved a thorough search for spectral lines in the spectra of each blazar, and when features of the host galaxy were identified, we modeled its properties. We also compared the magnitudes of the targets during the observations to their long-term light curves. In the sample studied, 9 of 29 sources were observed with a high signal-to-noise ratio (S/N > 100), while the remaining 20 were observed with a moderate or low S/N. We successfully determined firm redshifts for 12 blazars, ranging from 0.1636 to 1.1427, and identified two lower limit redshifts at z > 1.0196 and z > 1.4454. The remaining 15 BL Lac objects exhibited featureless spectra
Hydrokinetic Energy Potential in Southern Patagonia: Le Maire Strait site
No full textInternational audienceIn this work, the hydrokinetic energy potential of a new part of the Argentinian coastline is assessed. This site is on the surrounding coast of Isla de los Estados, off the eastern tip of the main island of Tierra del Fuego Province. Located at the southernmost part of Argentina, this site is composed of multiple high energetic locations, subdivided into: Le Maire Strait, exposed coastline East of the Isla de los Estados, and fiords inside this island. Here, only Le Maire Strait is analyzed due to its larger size and relevance: it extends for 30 km between the main island of Tierra del Fuego and the west coast of Isla de los Estados with an average depth of 100 m and plays a crucial role for navigation onto the Drake Passage and Antarctica. This first approach replicates former assessments in the region by means of a numerical 2D (depth-averaged) hydrodynamical model made in Delft3D-FLOW. Results were obtained by a nested modelling strategy that accurately propagates astronomical tidal dynamics from open seas onto the shores without disproportionately increasing computational costs. Since the region presents a strong astronomical tidal dominance, even though it might not be the case for this site, no meteorological tide nor waves were included at this stage. Previous works in the region have shown that Patagonian Estuaries have significant tidal energy potential, which, even though is not top rated worldwide, is still of importance and could be harnessed mostly by small to medium devices, and with some areas for larger turbines. On this site, however, mean current velocities higher than 1 m/s are found in large areas (around 30.000 Ha), with over 200 Ha above 1.5 m/s and high-power density (>1.5 kW/m2). Even though no mean current velocities above 2 m/s were found, Le Maire Strait is probably the site with the largest amounts of available power in Argentina for this kind of renewable energy and might be an ideal site once the technology has matured. Finally, a comparison with Alderney Race (France), which is one of the best sites in the world for hydrokinetic energy is made to bring a wider perspective of the hydrokinetic power available on this site
Halogens in proto-Iceland plume basalts
No full textInternational audienceMelt inclusions in olivine phenocrysts from high 3He/4He proto-Iceland plume (PIP) basalts from Baffin Island and West Greenland have elevated Br/Cl ratios, extending to values significantly above those found in mid-ocean ridge basalt (MORB) and ocean island basalt (OIB). Chlorine isotope compositions are indistinguishable from MORB-source mantle and high Br/Cl occurs in the absence of geochemical indicators for serpentinite, altered oceanic crust or sediment. The highest Br/Cl occurs in melt inclusions from basalts with the highest 3He/4He. The high Br/Cl ratios are at the high end of the range of putative Earth-source meteorites (CI- and CM-type carbonaceous chondrites). The PIP melt inclusion compositions are consistent with the addition of a small volume of halogen-rich, high Br/Cl chondritic material to halogen-depleted, low Br/Cl mantle
Detection of Polar Stratospheric Clouds With IASI
No full textInternational audiencePolar Stratospheric Clouds (PSCs) play a key role in the formation of the Antarctic ozone hole. They contribute to the formation of reactive halogen species (mainly chlorine) and lead to the denitrification and dehydration of the stratosphere, which prevents neutralization of these active chlorine species. PSCs, composed of nitric acid, sulfuric acid, and water, form when temperatures are sufficiently low, i.e., during the winter inside the polar vortex at altitudes between 15 and 25 km. Space-based observations of PSCs are critical for better characterizing their abundance, formation and spatiotemporal variations, as demonstrated by the recent observations from the limb sounders MIPAS and ACE, and the lidar sounder CALIOP. While their measurements offer excellent vertical characterization, they suffer from poor spatial coverage. Here, we report the first IASI observations of the most important and abundant PSCs, type Ia PSCs, which are composed of nitric acid trihydrate (NAT) particles. We analyse in detail a selection of IASI spectra and show the unambiguous presence of the characteristic spectral signature of NAT particles in the infrared. Using a hyperspectral range index (HRI) specifically developed for the South Pole (below 50°S), we further demonstrate that PSCs can be observed systematically in the polar winter and obtain detailed daily detection maps. With respect to the physicochemical mechanisms at play in the Antarctic stratosphere, we show a remarkable consistency between the 2008-2023 timeseries of detected PSCs and the timeseries of temperature and nitric acid. In addition, during the winter months, we manage to show a clear anticorrelation at short time scales between the detection of PSCs and the abundance of nitric acid (or temperature). Interannual variability is also briefly investigated and discussed. Finally, we present the first steps towards the development of a quantitative product. Overall, our results emphasize the remarkable capabilities of nadir hyperspectral sounders to monitor stratospheric polar processes. Further insights on the chemistry at play during the polar night will undoubtedly come with IASI-NG, owing especially to its improved radiometric performances
Deep learning for exoplanet detection and characterization by direct imaging at high contrast
No full textInternational audienceExoplanet imaging is a major challenge in astrophysics due to the need for high angular resolution and high contrast. We present a multi-scale statistical model for the nuisance component corrupting multivariate image series at high contrast. Integrated into a learnable architecture, it leverages the physics of the problem and enables the fusion of multiple observations of the same star in a way that is optimal in terms of detection signal-to-noise ratio. Applied to data from the VLT/SPHERE instrument, the method significantly improves the detection sensitivity and the accuracy of astrometric and photometric estimation
Solar Wind-Induced Sputtering: Investigating Anisotropy in the Angular Distribution of Ejecta using SDTrimSP
No full textInternational audienceSputtering in planetary science occurs as the solar-wind (SW)—a stream of energetic ions emitted from the Sun—impacts an airless body, ejecting atoms from its surface [1,2]. This process alongside micrometeorite impacts, photo-stimulated desorption, and thermal desorption contribute to the formation of planets’ exospheres [3–5]. While various spacecraft can detect exospheric species such as MESSENGER, BepiColombo, LADEE, and CHACE-2, they cannot discern the respective contributions of the mentioned processes and thus a strong theoretical understanding of sputtering is needed to quantify its influence on the exosphere [6–9].The sputtering yield is well-studied. In contrast, the angular distribution of ejecta has been given significantly less attention, its treatment being particularly sparse in cases relevant to planetary science. As such, sputtering models that consider the angular distribution of ejecta often assume isotropy. Here, we present a theoretical study quantifying anisotropy in the angular distribution of ejecta for SW-induced sputtering cases, helping advance the understanding of sputtering’s contribution to exosphere formation. Further, we compare the results to a common experimental case since experiments often employ heavier, higher energy ions to leverage the enhanced mass detection consequent of a greater sputter yield. These experimental results must then be scaled to inform SW-induced sputtering and, as such, unique behaviors occurring for lower mass impactor cases may be overlooked. Finally, following quantification, we consider the relative contributions from four ejecta-types demonstrated in Fig. 1, an approach enabling us to understand the underlying behavior leading to anisotropy differences between the different cases considered
DART-based temporal and spatial retrievals of solar-induced chlorophyll fluorescence quantum efficiency from in-situ and airborne crop observations
No full textInternational audienceRemotely sensed top-of-the-canopy (TOC) SIF is highly impacted by non-physiological structural and environmental factors that are confounding the photosystems' emitted SIF signal. Our proposed method for scaling TOC SIF down to photosystems' (PSI and PSII) level uses a three-dimensional (3D) modeling approach, capable of accounting physically for the main confounding factors, i.e., SIF scattering and reabsorption within a leaf, by canopy structures, and by the soil beneath. Here, we propose a novel SIF downscaling method that separates the structural component from the functional physiological component of TOC SIF signal by using the 3D Discrete Anisotropic Radiative Transfer (DART) model coupled with the leaf-level fluorescence model Fluspect-CX, and estimates the Fluorescence Quantum Efficiency (FQE) at photosystem level. The method was first applied on insitu diurnal measurements acquired at the top of the canopy of an alfalfa crop with a near-distance pointmeasuring FloX system. The retrieved photosystem-level FQE diurnal courses correlated significantly with photosynthetic yield of PSII measured by an active leaf florescence instrument MiniPAM (R = 0.87, R2 = 0.76 before and R = -0.82, R2 = 0.67 after 2.00 pm local time). Diurnal FQE trends of both photosystems jointly were descending from late morning 9.00 am till afternoon 4.00 pm. A slight late-afternoon increase, observed for three days between 4.00 and 7.00 pm, could be attributed to an increase in FQE of PSI that was retrieved separately from PSII. The method was subsequently extended and applied to airborne SIF images acquired with the HyPlant imaging spectrometer over the same alfalfa field. While the input canopy SIF radiance computed by two different methods, i) a spectral fitting method (SFM) and ii) a spectral fitting method neural network (SFMNN), produce broad and irregularly shaped (skewed) histograms (spatial coefficients of variation: CV = 29-35 % and 14-20 %, respectively), the retrieved HyPlant per-pixel FQE estimates formed significantly narrower and regularly bellshaped near-Gaussian histograms (CV = 27-34 % and 14-17 %, respectively). The achieved spatial homogeneity of resulting FQE maps confirms successful removal of the TOC SIF radiance confounding impacts. Since our method is based on direct matching of measured and physically modelled canopy SIF radiance, simulated by 3D radiative transfer, it is versatile and transferable to other canopy architectures, including structurally complex canopies such as forest stands
Development of a Method for Analysing Persistent, Mobile and Toxic Compounds, from Groundwater to Drinking Water, using LC-HRMS
No full textInternational audienceThe growing pressure on water resources is leading to drinking water shortages and increased pollution. Certain persistent, mobile, and toxic (PMT) substances in aquatic environments have intrinsic properties that allow them to remain in the environment, pass through filtration systems, and withstand conventional drinking water treatments. They can accumulate, especially when wastewater is recycled, eventually reaching resources intended for drinking water. Current data on PMT contamination in water resources is limited, raising significant environmental and public health concerns. In this context, this study focuses on analysing PM/PMT substances in groundwater, surface water, and drinking water of 4 locations around the world with a gradient of anthropic pressure on the water resources from no pressure a priori to increasing pressures depending on water treatment and reuse practices. The initial step of this study was to develop a sample preparation protocol and an LC-MS (liquid chromatography-mass spectrometry) method suited to these compounds. A literature review of 480 PM/PMT molecules resulted in the selection of 59 compounds from various categories (pharmaceuticals, pesticides, and REACH-regulated chemicals) for targeted analytical method development keeping in mind that a broader suspect screening approach will be also conducted. To achieve an optimal sample preparation and analysis of PMT substances, five solid-phase extraction (SPE) protocols with different cartridges (Hydrophilic-Lipophilic Balance (HLB), Weak Anion Exchange (WAX), ENVI-Carb™, Mixed-mode Anion Exchange (MAX), and Mixed-mode Cation Exchange (MCX)) were tested on the 59 selected compounds. For LC-MS analysis, four chromatographic columns (Biphenyl, BEHC18, Cortecs T3, and Acclaim Trinity P1) with various mobile phases were also evaluated.Following evaluation, the Acclaim Trinity P1 chromatographic column demonstrated superior performances in terms of retention of polar analytes and sensitivity. Regarding sample preparation, 2 complementary methods were selected: HLB and WAX. The HLB cartridge achieved superior results, delivering higher recoveries and lower matrix effects for 43 compounds. Additionnaly, the WAX cartridge enhanced the extraction of 8 additional compounds that were insufficiently retained by the HLB cartridge. Application of this optimised method on real samples collected in the frame of project revealed the presence of various PM/PMT substances
Seafloor geodesy unveils seismogenesis of large subduction earthquakes in Mexico
No full textInternational audienceBased on measurements of near-trench deformations of the oceanic and overriding plates, in this investigation, we elucidate the tectonic and mechanical processes leading to the M w 7.0 (moment magnitude of 7.0) Acapulco, Mexico, earthquake in 2021. We exploit unprecedented ocean-bottom observations using ultralong-period “tilt mechanical amplifiers,” along with hydrostatic pressure, global navigation satellite system, and satellite interferometric synthetic aperture radar data. The joint inversion of these geodetic data, template-matching seismicity, and repeating earthquakes, revealed the first two shallow slow slip events (SSEs) observed in Mexico. The first one migrated from the trench to the earthquake hypocenter before rupture, and the second one occurred following an M w 7.3 long-term SSE induced by the earthquake. Episodic near-trench oceanic-crust deformations (i.e., tilt transients) associated with shallow and deep synchronous decoupling of the plate interface reveal the occurrence of “slab-pull surges” before three regional earthquakes of magnitude 7 or greater, including the Acapulco event, suggesting that they may serve as rupture precursors observable in subduction zones