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The Doppler boosted LISA response to gravitational waves
No full textInternational audienceThe future space-based gravitational wave observatory LISA is expected to detect massive black hole binaries (MBHBs) with high signal-to-noise ratios (SNRs), ranging up to thousands. Such high-precision observations require accurate modeling of the detector response. However, current derivations of the response function neglect the motion of the spacecraft during light travel time, omitting velocity-dependent terms of order . In this work, we derive the velocity-dependent corrections to the gravitational wave response. We analyze the contribution of the velocity-terms for MBHBs in the mass range using a modified version of the state-of-the-art response simulator lisagwresponse. We find that corrections introduce residual SNRs up to for the loudest events and fractional differences up to , compared to lisagwresponse. While small, these effects are comparable to current waveform modeling uncertainties and imprint distinctive sky-localization signatures, making them potentially relevant for parameter estimation of high-mass MBHBs and simulation of mock datasets
Nouvelles caractéristiques rostrales et endocrâniennes partagées par Leidyosuchus canadensis et Stangerochampsa mccabei, des Alligatoroidea du Crétacé supérieur du Canada
No full textInternational audienceLes crocodiliens interagissent avec leur environnement principalement via les structures sensorielles contenues dans leur rostre. Ces organismes ont connu une grande variété de morphologie rostrale au cours de leur histoire évolutive, soulignant les liens entre plasticité morphologique, environnement et paramètres écologiques. Deux formations du Crétacé tardif de l’Alberta, Canada, ont permis de mettre au jour des spécimens d’alligatoroïdes considérés comme distants phylogénétiquement (Brochu, 1999) : la Formation Dinosaur Park d’Alberta, Canada (~76.5 à 74.5 Ma) a révélé Leidyosuchus canadensis Lambe, 1907, l’alligatoroïde le plus basal connu, et la Formation Horseshoe Canyon (~73.1 à 68 Ma) a révélé Stangerochampsa mccabei Wu et al., 1996, un globidonte plus dérivé. Ces deux espèces sont respectivement mésorostre et brévirostre. Leurs descriptions et études phylogénétiques sont majoritairement basées sur des caractères externes, masquant le poids des caractères internes et ne prenant pas en compte les caractères reliés à des structures internes. Le tout peut alors biaiser la position phylogénétique de ces espèces.Sur la base de données de scanner médical, nous avons reconstruit en 3D et comparé la morphologie endocrânienne de Leidyosuchus et Stangerochampsa. Nous avons ainsi pu révéler des caractères uniques et partagés par les deux espèces, dont une projection postérieure des cavités neuro-vasculaire du rostre ainsi que des sinus paratympaniques aux caractéristiques pédomorphiques similaires. Ces nouvelles données vont permettre d’asseoir l’importance des caractères internes dans les comparaisons entre espèces. Elles questionnent également les relations phylogénétiques à la base des alligatoroïdes.RéférencesLambe, L. M. (1907). On a new crocodilian genus and species form the Judith River Formation of Alberta. Proceedings and transactions of the Royal Society of Canada, ser3, v1:219-244Wu, X., Brinkman D. B., Russell A. P. (1996). A new alligator from the upper Cretaceous of Canada and the relationships of early Eusuchians. Paleontology, Vol 39, Part 2, pp 351-375, 3 pls.Brochu, C. A. (1999). Phylogenetics, Taxonomy and historical Biogeography of Alligatoroidea. Journal of Vertebrate Paleontology, Vol 19 pp 9-100, (10.1080/02724634.1999.10011201
Through the fog: A complementary optical galaxy classification scheme for intermediate redshifts
No full textInternational audienceContext. Understanding the evolution of galaxies strongly depends on our interpretation of their spectra. In the optical, BPT diagrams have been the main way to distinguish whether the principal excitation mechanism of a galaxy is dominated by star formation (SF) or by an active galactic nucleus (AGN). Although different classification methods exist, they are based on either hard-to-detect or high-energy emission lines. To date, the Balmer lines remain the most consistent way to classify galaxies, but at intermediate redshifts (1.5 < z < 2.5), galaxies are hard to parse in the BPT diagrams (and siblings) because the crucial Hα emission line is out of the range of ground-based optical spectrographs.Aims. In this work, we re-explore a diagram, which we call the OB-I diagram, that compares the equivalent width of Hβ and the emission line flux ratio of [OIII]λ5007/Hβ, and we breathe new life into it as it has the potential to be used for the classification of galaxies at these intermediate redshifts and to ‘clear the fog’ that permeates galaxy classification in the optical rest frame.Methods. We used data from SDSS, LEGA-C, VANDELS, JADES, 3D-HST, and MOSDEF to explore galaxy classifications in the OB-I diagram across a wide range of redshifts (0 < z < 2.7).Results. Our results show that, at z < 0.4, the OB-I diagram clearly separates galaxies between two distinct types: one dominated by an AGN and a second made up of a mixed population of SF galaxies and AGN activity. Comparison with the BPT diagrams and theoretical models shows that this mixed population can be partially separated from a pure SF population with a simple semi-empirical fit. At higher redshifts, we find that half of AGNs identified by other classification schemes are correctly recovered by the OB-I diagram, potentially making this diagram resistant to the cosmic shift that plagues most optical classification schemes, but more research is needed to understand this phenomenon.Conclusions. We find the OB-I diagram, which only requires two emission lines to be implemented, to be a useful tool at separating galaxies that possess a dominating AGN component in their emission from others. This applies not only to the Local Universe, but also seemingly at redshifts near the Cosmic Noon (z ∼ 2), without any need for significant adjustments in our empirical fit
Model and Observation for surface–atmosphere interactions over heterogeneous landscape: MOSAI project
No full textInternational audienceThe land surface impacts the atmosphere from daily to seasonal time scales. An accurate assessment of the land–atmosphere exchanges, and their correct representation in surface schemes, are therefore essential for weather and climate forecasts. However, Earth System and Numerical Weather Prediction models often have large biases in their representation of surface–atmosphere fluxes when compared to observations. The Model and Observation for Surface–Atmosphere Interactions over heterogeneous landscape (MOSAI) project aims at improving modeling and estimating surface fluxes, with a focus on the impact of surface heterogeneity.First of all, a fair evaluation of the simulated land–atmosphere interactions in the models needs dedicated measurements and appropriate methods. Thus, the first MOSAI objective is to establish the uncertainty and representativity of land–atmosphere exchanges measured over a heterogeneous landscape. The second MOSAI objective addresses some simplifications and hypotheses in the coupling between land and atmospheric models, and their impacts on the simulated land–atmosphere exchanges. Then, the third scientific objective is to propose and test observation–model comparison methods that go further than point-to-point, time, or case-study comparisons.The MOSAI strategy leans on permanent surface energy balance stations belonging to research infrastructure and on devoted experimental campaigns in different heterogeneous landscapes. A wide range of models are also involved, from large-eddy simulation to climate models.This article will start with an overview of the impact of heterogeneous surfaces on the atmospheric boundary layer, on the difficulty of measuring surface fluxes over heterogeneous landscape, and on the simplifications of surface–atmosphere interactions over heterogeneous landscape employed by numerical models. Then, the objectives and strategy of the MOSAI project will be presented, illustrated by preliminary results
Sur l'impact des distorsions dans l'imagerie hyperspectrale codée
No full textInternational audienceSingle Disperser Coded Aperture Spectral Snapshot Imagers (SD-CASSI) have been widely used to reduce the data quantity of hyperspectral images (HSI) through coded acquisitions. Based on prior work [1], most SD-CASSI systems include an expensive double-Amici prism as their dispersive element, as it allows for a direct-view and almost no distortions, contrary to systems relying on off-the-shelf single prism. We compared those two types of systems on a reconstruction task and concluded that distortions can be compensated as long as they are known and modeled.Les Single Disperser Coded Aperture Spectral Snapshot Imagers (SD-CASSI) sont très utilisés pour réduire la quantité de données des images hyperspectrales grâce à des acquisitions codées. Sur la base de travaux antérieurs [1], la plupart des systèmes SD-CASSI comprennent un prisme Amici coûteux comme élément dispersif, car il permet d'avoir un système aligné et pratiquement aucune distorsion, contrairement aux systèmes qui utilisent un prisme simple, disponible dans le commerce. Nous avons comparé ces deux types de systèmes pour une tâche de reconstruction et avons conclu que les distorsions peuvent être compensées tant qu'elles sont connues et modélisées
Projections of coral reef carbonate production from a global climate–coral reef coupled model
No full textInternational audienceCoral reefs are under threat due to climate change and ocean acidification. However, large uncertainties remain concerning future carbon dioxide emissions, climate change and the associated impacts on coral reefs. While most previous studies have used climate model outputs to compute future coral reef carbonate production, we use a coral reef carbonate production module embedded in a global carbonclimate model. This enables the simulation of the response of coral reefs to projected changes in physical and chemical conditions at finer temporal resolution. The use of a fastintermediate complexity model also permits the simulation of a large range of possible futures by considering different greenhouse gas concentration scenarios (Shared Socioeconomic Pathways (SSPs)) and different climate sensitivities (hence different levels of warming for a given level of acidification), as well as the possibility of corals adapting their thermal bleaching thresholds. We show that without thermal adaptation, global coral reef carbonate production decreases to less than 25 % of historical values in most scenarios over the 21st century, with limited further declines between 2100 and 2300 irrespective of the climate sensitivity. With thermal adaptation, there is far greater scenario variability in projections of reef carbonate production. Under high-emission scenarios the rate of 21st century declines is attenuated, with some global carbonate production declines delayed until the 22nd century. Under high-mitigation sce-narios, however, global coral reef carbonate production can recover in the 21st and 22nd centuries and thereafter persist at 50 %-90 % of historical values, provided that the climate sensitivity is moderate
Atmospheric Response to Antarctic Coastal Polynyas
No full textInternational audienceAbstract The lack of sea ice in Antarctic coastal polynyas enables strong ocean‐to‐atmosphere heat fluxes and intense sea‐ice production. Although these features are primarily driven by intense offshore winds, their impact on local atmospheric conditions remains poorly understood. This study employs a high‐resolution polar Weather Research and Forecasting model configuration over the Prydz Bay region, East Antarctica, home to two major coastal polynyas: Cape Darnley and Mackenzie Bay polynyas. Sensitivity experiments over three winters (2014–2016) comparing simulations with and without polynyas reveal a marked and spatially confined atmospheric response. Polynya openings induce substantial surface heat release (up to 700 W m −2 ), warming near‐surface air by over 5 K and triggering convection and clouds. This results in a thickening of the atmospheric boundary layer and the development of stronger surface winds (up to 4 m s −1 ) that converge toward a low‐pressure anomaly. A particular emphasis is placed on the mechanisms controlling wind anomalies, using a dedicated wind tendency analysis. This diagnosis highlights that the processes involved depend on location and altitude within the polynya region and involve a balance between vertical mixing, horizontal advection, and pressure gradient forces—vertical mixing acting as the initiating factor. This study provides a novel modeling framework used to isolate the atmospheric response to coastal polynyas, overcoming limitations of previous studies and coarse‐resolution models. It offers new insights into the role of polynyas in modulating regional climate and improving understanding of the processes driving their dynamics
The role of antecedent conditions in translating precipitation events into extreme floods at the catchment scale and in a large-basin context
No full textInternational audienceIn this study, we analyze how precipitation, antecedent conditions, and their spatial patterns and interactions lead to extreme floods in a large catchment. The analysis is based on 10 000 years of continuous simulations from a hydro-meteorological modelling chain for a large catchment, the Aare River basin, Switzerland. To account for different flood-generating processes, we based our work on simulations with hourly time resolution. The hydro-meteorological modelling chain consisted of a stochastic weather generator (GWEX), a bucket-type hydrological model (HBV), and a routing system (RS MINERVE), providing the hydrological basis for flood protection management in the Aare River basin. From the long continuous simulations of runoff, snow, soil moisture, and dynamic storage, we were able to assess which combinations of antecedent conditions and triggering precipitation lead to extreme floods in the sub-basins of the Aare catchment. We found that only about 18 % to 44 % (depending on the sub-catchment) of annual maximum precipitation (AMP) and simulated annual maximum flood (AMF) events occurred simultaneously, highlighting the importance of antecedent conditions for the generation of large floods. For most sub-catchments in the 200–500 km2 range, after return periods greater than 500 years we found only AMF caused by triggering AMP, which is notably higher than the return periods typically used for design floods. Spatial organization within a larger area is complicated. After routing the simulated runoff, we analyzed the important patterns and drivers of extreme flooding at the outlet of the Aare River basin using a random forest. The different return period classes had distinct key predictors and showed specific spatial patterns of antecedent conditions in the sub-catchments, leading to different degrees of extreme flooding. While precipitation and soil moisture conditions from almost all sub-catchments were important for more frequent floods, for rarer events only the conditions in specific sub-catchments were important. Snow conditions were important only from specific sub-catchments and for more frequent events
Caractérisation géoélectrique de l'hydrodynamique et de la distribution dans des sols gelés non saturés
No full textWith the intensification of global climate change, permafrost degradation, which affects hydrological processes, ecosystem integrity, and infrastructure stability. Repeated phase transitions of pore water during freeze-thaw cycles results in frost cracking in frozen porous materials, further accelerating permafrost degradation and potentially exacerbating global climate change. Geo-electrical methods (e.g., Spectral Induced Polarization), as non-destructive techniques with a wide ranges of approaches, are widely used to investigate the pore structure, hydrological, and thermodynamic characteristics of permafrost environments. This thesis comprehensively explores the application of spectral induced polarization in frozen environments through both theoretical modeling and laboratory experiments. The first part of thesis develops new capillary bundle models to describe the effects of surface conduction at different water interfaces, water saturation, salinity, and hysteresis on the electrical conductivity of frozen porous media. A series of laboratory experiments are carried out using an electrical resistance apparatus and the nuclear magnetic resonance method for validating the proposed models. The fitting results show an excellent agreement between the predicted values and the experimental dataset, indicating that the new physically-based models can effectively predict the variation of the electrical conductivity in cold regions. The second part of thesis presents a series of experimental, theoretical, and modeling investigations using spectral induced polarization to characterize the coupled effects of initial water content and clay mineralogy on soil cracking behaviors and complex conductivity under freeze-thaw cycling and desiccation processes. Experimental results show that freeze-thaw cycle significantly influences the morphological and intersection patterns of surface cracks during desiccation. Initial moisture contents and clay mineralogy notably affect the water evaporation and surface crack pattern in clayey soils. Both components of complex conductivity are linearly sensitive to surface crack ratio and gravimetric water content, exhibiting a similar decay behavior with drying time. These findings quantitatively characterize the relationship between geophysical and geological parameters of clayey soils during desiccation, offering new insights and monitoring methods for studying clay slope stability and its interaction with global climate change.Avec l'intensification du changement climatique mondial, la dégradation du pergélisol affecte les processus hydrologiques, l'intégrité des écosystèmes et la stabilité des infrastructures. Les transitions de phase répétées de l'eau interstitielle pendant les cycles de gel-dégel provoquent des fissures par le gel dans les matériaux poreux gelés, ce qui accélère davantage la dégradation du pergélisol et peut potentiellement aggraver le changement climatique global. Les méthodes géoélectriques, telles que la polarisation provoquée spectrale, en tant que techniques non destructives aux multiples approches, sont largement utilisées pour étudier la structure des pores, les caractéristiques hydrologiques et thermodynamiques des environnements gelés. Cette thèse explore de manière approfondie l'application de la polarisation provoquée spectrale dans les milieux gelés à travers des modélisations théoriques et des expériences en laboratoire. La première partie développe de nouveaux modèles de faisceaux capillaires pour décrire les effets de la conduction de surface aux interfaces aqueuses, de la saturation en eau, de la salinité et de l'hystérèse sur la conductivité électrique des milieux poreux gelés. Une série d'expériences en laboratoire ont été réalisées à l'aide d'un dispositif de résistance électrique et de la résonance magnétique nucléaire afin de valider les modèles proposés. Les résultats montrent un excellent accord entre les valeurs prédites et les données expérimentales, indiquant que ces modèles physiques permettent de prédire efficacement les variations de conductivité électrique dans les régions froides. La seconde partie de la thèse présente une série d'études expérimentales, théoriques et de modélisation, utilisant la polarisation provoquée spectrale pour caractériser les effets couplés de la teneur en eau initiale et de la minéralogie de l'argile sur les fissurations du sol et la conductivité complexe lors des processus de gel-dégel et de dessiccation. Les résultats expérimentaux montrent que les cycles de gel-dégel influencent fortement les motifs morphologiques et d'intersection des fissures en surface. L'humidité initiale et la minéralogie de l'argile affectent également l'évaporation de l'eau et la formation des fissures. Les deux composantes de la conductivité complexe sont linéairement sensibles au taux de fissuration et à la teneur en eau pondérale et présentent un comportement de décroissance similaire au fil du temps de séchage
Assessment of the Environmental Significance of Heavy Metals Pollution in Surficial Sediments of South Brittany Waters, France: An Ecological Risk Assessment Approach
No full textInternational audienceDistribution patterns of selected heavy metals content in sediments from the Bay of Quiberon and Gulf of Morbihan were studied to understand the current heavy metals contamination due to urbanization and mariculture activities in the coastal area. Therefore, a survey was conducted and 196 sediments collected were characterized for heavy metals content using Inductively Coupled Plasma -Mass Spectrometry (ICP-MS) after mix acid digestion process.The distribution maps of the concentrations of the heavy metals studied were produced as an isopleth map based on data interpolation by the ArcGIS software application. The association with the adverse effects on aquatic organisms was determined by the classification of the sediment according to the sediment quality guidelines. Therefore, two approaches were employed namely; direct comparison with Sediment Quality Guidelines (SQGs) by USEPA and comparison with other numerical SQGs, threshold effect level/probable effect level, and effect range low /effect range medium. In order to estimate the effect of multiple contaminations of heavy metals, the mean-ERM-quotient was calculated at each sampling point.</div