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Des statues pour mémoire ? Colonialisme et espace public
No full textInternational audienceIn 2020, a worldwide wave of protests targeted statues in the public space honoring personalities involved in colonization and slavery. The contestation of statues, erected to serve as civic models at the heart of the common space that is public space, is certainly not new. This special issue offers a different perspective, based on biographies of colonial statues contested in French public space. These statues convey a vision of the world and the arrangements of social relations forged during the colonial period. We aim to interrogate these colonial legacies, at times indecipherable and as if deactivated, at other times serving as anchor points for contestations, to explore the inscription of plural memories of colonization in the public space.En 2020, une vague mondiale de contestations a visé les statues honorant dans l’espace public des personnalités impliquées dans la colonisation et l’esclavage. La contestation des statues, érigées pour servir de modèles civiques au cœur de l’espace commun qu’est l’espace public, n’est assurément pas nouvelle. Ce dossier ouvre une autre perspective à partir de biographies de statues coloniales contestées dans l’espace public français. Ces statues véhiculent une vision du monde et des agencements des relations sociales forgés à la période coloniale. Ce sont ces legs coloniaux, par moments indéchiffrables et comme désactivés, à d’autres moments servant de point d’ancrage aux contestations, qui seront interrogés pour réfléchir à l’inscription des mémoires plurielles de la colonisation dans l’espace public
Investigating processes affecting wintertime air pollution variability and estimating contributions of power plant emissions relative to the surface in the stratified Arctic boundary layer
No full textInternational audienceThe Arctic is warming rapidly compared to the global average. As Arctic warming continues, urbanisation and industrial activities are predicted to increase, along with complex climate and ecosystem feedbacks. Therefore, local sources of air pollutants are expected to play an increasingly significant role in Arctic environmental changes in the coming years. Poor air quality is already a growing public health issue in Arctic and sub-Arctic cities. During wintertime, stable meteorological conditions and the persistence of strong surface-based temperature inversions suppress the dispersion of pollutants, which accumulate due to enhanced emissions linked to high energy demands. Fairbanks, in central Alaska, is an example of a sub-Arctic city that suffers from acute wintertime pollution episodes. The city’s topography (situated in a basin), strong stratification of the Arctic boundary layer (ABL), and high emissions, primarily from domestic heating at the surface, and power plant stacks aloft, are known to contribute to the problem. However, interactions between vertical stratification of the ABL and dispersal of pollutants from surface and elevated sources are poorly quantified due to a lack of observations and complexities of the ABL structure and dynamics. To address these uncertainties, comprehensive atmospheric composition and meteorological measurements were collected at the surface, and vertical profiles were obtained using a tethered balloon during the international ALPACA (Alaskan Layered Pollution and Chemical Analysis) field campaign in January and February 2022.Here, we explore the contribution of power plants and surface emission sources to pollution concentrations in the Fairbanks region. We use the FLEXPART-Weather Research and Forecasting (WRF) Lagrangian particle dispersion model, driven by meteorological fields from US Environmental Protection Agency (EPA) WRF simulations including data assimilation of meteorological observations, to simulate the evolution of selected emission tracers. Hourly power plant and sector-based surface EPA emissions at 1.3km resolution during ALPACA 2022 are included in the model runs. A novel model parameterisation of power plant plume injection heights accounts for the ABL structure, notably surface-based and elevated temperature inversions. Model results are evaluated against available observations from ALPACA 2022, and sensitivity to, for example, emissions and vertical mixing is explored. The simulation of pollution plume altitudes is significantly improved when ABL stratification is taken into account in the plume rise parameterisation since inversion layers can trap plumes. Variability in modelled surface pollutant concentrations is predominantly driven by meteorology, and the ability of the model to capture surface-based temperature inversions (as low as 10m). A cold-temperature dependence for NOx vehicle emissions, currently missing from the EPA emission inventory, is required to reproduce the magnitude of observed NOx surface concentrations at low temperatures below 0°C and needs to be considered in future emission inventories in the Arctic, and potentially in other wintertime environments. Finally, using the most realistic simulation, we estimate the contribution of power plant emissions to surface pollution in the Fairbanks region, addressing an important policy question. The results indicate preferential areas for downward transport of pollution from aloft and larger contributions to surface pollution under less stable meteorological conditions
Global census of the significance of giant mesopelagic protists to the marine carbon and silicon cycles
No full textInternational audienceThriving in both epipelagic and mesopelagic layers, Rhizaria are biomineralizing protists, mixotrophs or flux-feeders, often reaching gigantic sizes. In situ imaging showed their contribution to oceanic carbon stock, but left their contribution to element cycling unquantified. Here, we compile a global dataset of 167,551 Underwater Vision Profiler 5 Rhizaria images, and apply machine learning models to predict their organic carbon and biogenic silica biomasses in the uppermost 1000 m. We estimate that Rhizaria represent up to 1.7% of mesozooplankton carbon biomass in the top 500 m. Rhizaria biomass, dominated by Phaeodaria, is more than twice as high in the mesopelagic than in the epipelagic layer. Globally, the carbon demand of mesopelagic, flux-feeding Phaeodaria reaches 0.46 Pg C y −1 , representing 3.8 to 9.2% of gravitational carbon export. Furthermore, we show that Rhizaria are a unique source of biogenic silica production in the mesopelagic layer, where no other silicifiers are present. Our global census further highlights the importance of Rhizaria for ocean biogeochemistry
Optimization of thermoelectric parameters for quantum dot-assisted polymer nanocomposite
No full textInternational audienceThe interdependency among thermal conductivity, electrical conductivity, and the Seebeck coefficient acts as a challenge to enhancing thermoelectric (TE) performance. However, thanks to nanotechnology, it is possible to break this interdependency by employing the phonon glass electron crystal (PGEC) approach. The present work aims to decrease the lattice thermal conductivity by inducing nanoflower-like structures in a conducting polymer matrix. Herein, we report the thermoelectric properties of graphene oxide and titanium dioxide (GO–TiO2) quantum dots (QDs) in poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS). The effect of QDs on the thermoelectric performance of the PEDOT:PSS polymeric matrix has been investigated experimentally and then analyzed using several theoretical models. The obtained nanocomposite showed an enhancement in Seebeck coefficient and electrical conductivity while decreasing lattice thermal conductivity. Furthermore, the filler successfully broke the interdependent relationship of thermoelectric parameters due to the existence of energy-filtering phenomena and interfacial thermal resistance
Phenomenology of the Composition of PM2.5 at an Urban Site in Northern France
No full textInternational audienceIn this work, PM2.5 was sampled at Dunkerque, a medium-sized city located in northern France. The mean concentration of PM2.5 during the sampling period was 12.6 ± 9.5 μg·m−3. Samples were analyzed for elemental and organic carbon (EC/OC), water-soluble organic carbon (WSOC), humic-like substances (HULIS-C), water-soluble inorganic ions, and major and trace elements. The origin and the variations of species concentrations were examined using elemental enrichment factors, bivariate polar plot representations, and diagnostic concentration ratios. Secondary inorganic ions were the most abundant species (36% of PM2.5), followed by OC (12.5% of PM2.5). Secondary organic carbon (SOC) concentrations were estimated to account for 52% of OC. A good correlation between SOC and WSOC indicated that secondary formation processes significantly contribute to the WSOC concentrations. HULIS-C also represents almost 50% of WSOC. The determination of diagnostic ratios revealed the influence of anthropogenic emission sources such as integrated steelworks and fuel oil combustion. The clustering of 72 h air masses backward trajectories data evidenced that higher concentrations of PM2.5, OC, and secondary inorganic aerosols were recorded when air masses came from north-eastern Europe and the French continental sector, showing the considerable impact of long-range transport on the air quality in northern France
La mycorhization protège le blé contre la septoriose: analyse transcriptomique de la résistance induite
No full textInternational audienceLa recherche d’alternatives aux produits phytosanitaires, néfastes pour l’environnement et l’être humain, devient prioritaire. En remplacement des fongicides conventionnels, les champignons mycorhiziens à arbuscules (CMA) permettraient de lutter contre les maladies fongiques du blé. Des études ont démontré l’efficacité d’un CMA, Funneliformis mosseae (Fm), à protéger le blé contre l’oïdium et la septoriose, en lien avec l’établissement dans les feuilles d’une résistance induite (MIR pour Mycorrhiza-Induced Resistance). Notre travail vise à caractériser les modifications de l’expression des gènes lors de l’établissement de la MIR dans les feuilles de blé, susceptibles de conduire à la protection contre Zymoseptoria tritici (Zt), agent pathogène responsable de la septoriose. Des feuilles de plants de 3, 4 et 6 semaines, inoculés ou non par Fm, ont été échantillonnées pour étudier l’expression des gènes durant l’établissement de la symbiose racinaire. Puis à 6 semaines, des plantes, mycorhizées ou non par Fm, ont été infectées par Zt ; leur réaction à l’infection a été analysée après 48 heures. A 3 et 4 semaines, 9 gènes, liés au stress abiotique et au métabolisme lipidique, sont sur-exprimés chez les plants mycorhizés. A 6 semaines, 214 gènes, majoritairement liés aux stress biotiques et abiotiques et au métabolisme glucidique, sont sur-exprimés chez les plants mycorhizés. 162 d’entre eux sont également sur-exprimés chez les plants non-mycorhizés et infectés. Par ailleurs,120 gènes sont sous-exprimés chez les plants mycorhizés infectés en comparaison des plants non-mycorhizés et infectés. Enfin, 41 gènes, induits chez des plants mycorhizés non-infectés, sont sous-exprimés chez les plants mycorhizés et infectés. L’analyse fonctionnelle des gènes modulés a été réalisée. Une analyse par RT-qPCR affinera les profils d’expression de gènes modulés par la mycorhization et possiblement impliqués dans la MIR. Leur expression pourra être suivie lors de l’inoculation du blé par d’autres espèces de CMA afin de sélectionner de potentiels marqueurs de la MIR
A Step Test to Evaluate the Susceptibility to Severe High-Altitude Illness in Field Conditions
No full textInternational audienceA laboratory-based hypoxic exercise test, performed on a cycle ergometer, can be used to predict susceptibility to severe high-altitude illness (SHAI) through the calculation of a clinicophysiological SHAI score. Our objective was to design a field-condition test and compare its derived SHAI score and various physiological parameters, such as peripheral oxygen saturation (SpO2), and cardiac and ventilatory responses to hypoxia during exercise (HCRe and HVRe, respectively), to the laboratory test. A group of 43 healthy subjects (15 females and 28 males), with no prior experience at high altitude, performed a hypoxic cycle ergometer test (simulated altitude of 4,800 m) and step tests (20 cm high step) at 3,000, 4,000, and 4,800 m simulated altitudes. According to tested altitudes, differences were observed in O2 desaturation, heart rate, and minute ventilation (p < 0.001), whereas the computed HCRe and HVRe were not different (p = 0.075 and p = 0.203, respectively). From the linear relationships between the step test and SHAI scores, we defined a risk zone, allowing us to evaluate the risk of developing SHAI and take adequate preventive measures in field conditions, from the calculated step test score for the given altitude. The predictive value of this new field test remains to be validated in real high-altitude conditions
Relations taille-poids chez 13 espèces de poissons du Parc National d’Akanda au Gabon, Afrique Centrale
No full textInternational audienceThis study provides the length-weight relationships (LWRs) for 13 fish species belonging to 10 families. Samples were collected in the mangrove area of Akanda National Park (ANP) in Gabon between May 2017 and March 2018 with fishing trammel gillnets (15 m long and 1.10 m high, 100 mm large mesh outer layers, and one 10, 27, and 40 mm small mesh each net). Fish total length and total weight were measured, with the precision of 1 mm and 1 g, respectively. The LWRs parameters for the 13 fish species had not yet been reported in FishBase for Central Africa. Our study provides large size ranges for Monodactylus sebae and Pseudotolithus senegalensis LWRs for Central Africa. The determination coefficient (r²) between total length and total body weight ranged from 0.946 (Pellonula leonensis) to 0.999 (Pseudotolithus senegalensis). Allometric coefficients b varied from 2.9388 for Parachelon grandisquamis to 3.6258 for Pomadasys perotaei. The results of this study establish important baselines on the LWRs of 13 fish species from Central Africa and could be worthy for fisheries scientists and managers to complement further studies of population dynamics in order to improve management decisions in ANP in Gabon.Cette étude fournit les relations taille-poids (RTP) pour 13 espèces de poissons appartenant à 10 familles. Les données ont été collectées dans la zone de mangrove du Parc National d’Akanda (PNA) au Gabon entre mai 2017 et mars 2018. L’échantillonnage a été réalisé à l’aide de filets maillants trémails (15 m de long et 1,10 m de chute, couches extérieures à grandes mailles de 100 mm, et un filet à petites mailles de 10, 27 et 40 mm chacun). La longueur totale et le poids total ont été mesurés pour chaque individu avec une précision de 1 mm et 1 g respectivement. Les paramètres de la relation taille-poids pour les 13 espèces de poissons n’avaient pas encore été rapportés dans FishBase pour l’Afrique Centrale. Notre étude a permis d’obtenir une large gamme de taille pour Monodactylus sebae et pour Pseudotolithus senegalensis pour l’Afrique Centrale. Le coefficient de détermination (r²) entre la longueur totale et le poids total variait de 0,946 (Pellonula leonensis) à 0,999 (Pseudotolithus senegalensis). Le coefficient d’allométrie b variait entre 2,9388 (Parachelon grandisquamis) et 3,6258 (Pomadasys perotaei). Les résultats de cette étude constituent des références importantes sur les RTP de 13 espèces de poissons en Afrique Centrale et devraient aider les scientifiques et les gestionnaires des pêches à compléter leurs études ultérieures sur les populations de poissons afin d’appuyer les décisions de gestion dans le PNA au Gabon
In situ imaging sheds light on particle sinking speeds in the North Atlantic
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THREE-TERM ASYMPTOTIC FORMULA FOR LARGE EIGENVALUES OF THE QUANTUM RABI MODEL WITH A RESONANT BIAS
No full textWe investigate the asymptotic distribution of large eigenvalues of the asymmetric quantum Rabi model with an integer static bias. For this model, we consider a variant of the generalized rotating-wave approximation, corresponding toperturbations of double eigenvalues. Using this idea, we obtain a three-term asymptotic formula for the m-th eigenvalue with the remainder estimate O(m^{−1/2} ln m) when m tends to infinity