The spatio-temporal dynamics of neutral genetic diversity

International audienceThe notions of pulled and pushed solutions of reaction-dispersal equations introduced by Garnier et al. (2012) and Roques et al. (2012) are based on a decomposition of the solutions into several components. In the framework of population dynamics, this decomposition is related to the spatio-temporal evolution of the genetic structure of a population. The pulled solutions describe a rapid erosion of neutral genetic diversity, while the pushed solutions are associated with a maintenance of diversity. This paper is a survey of the most recent applications of these notions to several standard models of population dynamics, including reaction-diffusion equations and systems and integro-differential equations. We describe several counterintuitive results, where unfavorable factors for the persistence and spreading of a population tend to promote diversity in this population. In particular, we show that the Allee effect, the existence of a competitor species, as well as the presence of climate constraints are factors which can promote diversity during a colonization. We also show that long distance dispersal events lead to a higher diversity, whereas the existence of a nonreproductive juvenile stage does not affect the neutral diversity in a range-expanding population

Etude de l'anisotropie d'endommagement de l'alliage d'aluminium 6061-T6

National audienceL'alliage d'aluminium 6061-T6 est retenu pour la fabrication du caisson-coeur du réacteur expérimental Jules Horowitz. Une étude de caractérisation des propriétés mécaniques en traction montre que le matériau présente une anisotropie marquée de l'allongement total liée à l'anisotropie d'endommagement. Afin d'expliquer ce phénomène, le lien entre la microstructure et le comportement mécanique est proposé dans ce travail. Une quantification des précipités grossiers qui sont à l'origine des mécanismes d'endommagement a été réalisée par analyse d'images. Une étude du comportement mécanique des précipités et de la matrice par micro-indentation montre une différence marquée de comportement entre les phases. Afin de confirmer le rôle des précipités grossiers dans les mécanismes d'endommagement, des essais de traction MEB in-situ ont été effectués. Les précipités Mg2Si et les intermétalliques s'endommagent progressivement durant tous ces essais. En outre, une analyse post mortem après déformation par tomographie X a montré une anisotropie de répartition de cavités. Un scénario d'endommagement de coalescence anisotrope intégrant l'alignement des précipités induit par le procédé de mise en forme semble expliquer l'anisotropie d'endommagement en traction

Latest Altimetry-Based Sea Ice Freeboard and Volume Inter-Annual Variability in the Antarctic over 2003–2020

The relatively stable conditions of the sea ice cover in the Antarctic, observed for almost 40 years, seem to be changing recently. Therefore, it is essential to provide sea ice thickness (SIT) and volume (SIV) estimates in order to anticipate potential multi-scale changes in the Antarctic sea ice. For that purpose, the main objectives of this work are: (1) to assess a new sea ice freeboard, thickness and volume altimetry dataset over 2003–2020 and (2) to identify first order impacts of the sea ice recent conditions. To produce these series, we use a neuronal network to calibrate Envisat radar freeboards onto CryoSat-2 (CS2). This method addresses the impacts of surface roughness on Low Resolution Mode (LRM) measurements. During the 2011 common flight period, we found a mean deviation between Envisat and CryoSat-2 radar freeboards by about 0.5 cm. Using the Advanced Microwave Scanning Radiometer (AMSR) and the dual-frequency Altimetric Snow Depth (ASD) data, our solutions are compared with the Upward looking sonar (ULS) draft data, some in-situ measurement of the SIMBA campaign, the total freeboards of 6 Operation Ice Bridge (OIB) missions and ICESat-2 total freeboards. Over 2003–2020, the global mean radar freeboard decreased by about −14% per decade and the SIT and SIV by about −10% per decade (considering a snow depth climatology). This is marked by a slight increase through 2015, which is directly followed by a strong decrease in 2016. Thereafter, freeboards generally remained low and even continued to decrease in some regions such as the Weddell sea. Considering the 2013–2020 period, for which the ASD data are available, radar freeboards and SIT decreased by about −40% per decade. The SIV decreased by about −60% per decade. After 2016, the low SIT values contrast with the sea ice extent that has rather increased again, reaching near-average values in winter 2020. The regional analysis underlines that such thinning (from 2016) occurs in all regions except the Amundsen-Bellingshausen sea sector. Meanwhile, we observed a reversal of the main regional trends from 2016, which may be the signature of significant ongoing changes in the Antarctic sea ice

Quantitative Anisotropic Damage Mechanism in a Forged Aluminum Alloy Studied by Synchrotron Tomography and Finite Element Simulations

International audienceA highly anisotropic toughness behavior has been revealed on a forged AA6061 aluminum alloy by toughness tests with CT specimens. e toughness values with specimens loaded on the longitudinal direction are larger than that loaded on the transverse direction due to the anisotropic shape and distribution of coarse precipitates induced by the morphological anisotropy of grains during forging process. Synchrotron radiation computed tomography analysis on as-received material and arrested cracks revealed different fracture modes for the two loading configurations. e damage mechanism has been validated by finite element simulations based on the Gurson-Tvergaard-Needleman micromechanical damage model with different sets of damage parameters for the two loading configurations obtained from quantitative void volume fraction analysis on SRCT data, in situ SEM experiments, and SRCT microstructural analysis

Zn speciation in the organic horizon of a contaminated soil by micro X-ray fluorescence, micro and powder EXAFS spectroscopy and isotopic dilution.

Soils which have been acutely contaminated by heavy-metals show distinct characteristics, such as colonization by metal-tolerant plant species and topsoil enrichment in weakly degraded plant debris because biodegradation processes are strongly inhibited by contamination. Such an organic topsoil, located downwind of an active zinc smelter and extremely rich in Zn (~ 2%, dry weight), was investigated by X-ray diffraction (XRD), synchrotron-based X-ray microfluorescence (μSXRF), and powder and micro extended X-ray absorption fine structure (EXAFS) spectroscopy for Zn speciation, and by isotopic dilution for Zn lability. EXAFS spectra recorded on size fractions and on selected spots of thin sections were analyzed by principal component analysis (PCA) and linear combination fits (LCFs). Although Zn primary minerals (franklinite, sphalerite and willemite) are still present (~ 15% of total Zn) in the bulk soil, Zn was found to be predominantly speciated as Zn-organic matter complexes (~ 45%), outer-sphere complexes (~ 20%), Zn-sorbed phosphate (~ 10%) and Znsorbed iron oxyhydroxides (~ 10%). The bioaccumulated Zn fraction is likely complexed to soil organic matter after the plants' death. The proportion of labile Zn ranges from 54 to 92%, depending on the soil fraction, in agreement with the high proportion of organically-bound Zn. Despite its marked lability, Zn seems to be retained in the topsoil thanks to the huge content of organic matter, which confers to this horizon a high sorption capacity. The speciation of Zn in this organic soil horizon is compared with that found in other types of soils

Resveratrol Improves Survival, Hemodynamics and Energetics in a Rat Model of Hypertension Leading to Heart Failure

Heart failure (HF) is characterized by contractile dysfunction associated with altered energy metabolism. This study was aimed at determining whether resveratrol, a polyphenol known to activate energy metabolism, could be beneficial as a metabolic therapy of HF. Survival, ventricular and vascular function as well as cardiac and skeletal muscle energy metabolism were assessed in a hypertensive model of HF, the Dahl salt-sensitive rat fed with a high-salt diet (HS-NT). Resveratrol (18 mg/kg/day; HS-RSV) was given for 8 weeks after hypertension and cardiac hypertrophy were established (which occurred 3 weeks after salt addition). Resveratrol treatment improved survival (64% in HS-RSV versus 15% in HS-NT, p<0.001), and prevented the 25% reduction in body weight in HS-NT (P<0.001). Moreover, RSV counteracted the development of cardiac dysfunction (fractional shortening −34% in HS-NT) as evaluated by echocardiography, which occurred without regression of hypertension or hypertrophy. Moreover, aortic endothelial dysfunction present in HS-NT was prevented in resveratrol-treated rats. Resveratrol treatment tended to preserve mitochondrial mass and biogenesis and completely protected mitochondrial fatty acid oxidation and PPARα (peroxisome proliferator-activated receptor α) expression. We conclude that resveratrol treatment exerts beneficial protective effects on survival, endothelium–dependent smooth muscle relaxation and cardiac contractile and mitochondrial function, suggesting that resveratrol or metabolic activators could be a relevant therapy in hypertension-induced HF

Quelle articulation entre les pôles de compétitivité et les tissus productifs régionaux ?: Une mise en perspective de quatre pôles en Provence-Alpes-Côte d'Azur

L'objectif de ce travail de recherche était de mettre en lumière les conditions de mise en œuvre et les bénéfices attendus de quatre pôles de compétitivité de la région PACA (Solutions communicantes sécurisées ; Mer, sécurité et sûreté, Développement durable ; Fruits et légumes ; Parfums, arômes, senteurs, saveurs). Le questionnement e a été décliné suivant deux axes : 1/ quelle est la capacité réelle de ces dispositifs à produire, diffuser et utiliser des ressources scientifiques et techniques ? Les pôles de compétitivité ont en charge de produire de nouvelles ressources dans des tissus productifs préexistants. Comment s'articulent ces nouvelles ressources avec celles déjà existantes ? Sont-elles susceptibles de se féconder mutuellement ? Mais dans le même temps, n'y a-t-il pas des risques de polarisation de l'activité et de ce fait, des risques d'exclusion ? 2/ quelle est la capacité réelle du nouveau dispositif à susciter et installer durablement la coopération nécessaire à la création des ressources attendues

Non Destructive Evaluation of Containment Walls in Nuclear Power Plants

Two functions are regularly tested on the containment walls in order to anticipate a possible accident. The first is mechanical to resist at a possible internal over-pressure and the second is to prevent leakage. The reference accident LLOCA (Large Loss of Coolant Accident) is the rupture of a pipe in the primary circuit of a nuclear plant. In this case, the pressure and temperature can reach 5 bar and 180°C in 20 seconds. The national project ‘Non-destructive testing of the containment structures of nuclear plants’ aims at studying the non-destructive techniques capable to evaluate the concrete properties and its damaging or progression of cracks. This 4-year-project is segmented into two parts. The first consists in developing and selecting the most relevant NDEs (Non Destructive Evaluations) in the laboratory to reach these goals. These evaluations are developed in conditions representing the real conditions of the stresses generated during ten-yearly visits of the plants or those related to an accident. The second part consists in applying the selected techniques to two containment structures under pressure. The first (technique) is proposed by the ONERA (National Office for Aerospace Studies and Research of France) and the second is a mock-up of a containment wall on a 1/3 scale made by EDF (Electricity of France) within the VeRCoRs program. Communication bears on the part of the project that concerns the damaging and cracking follow-up. The tests are done in bending on 3 or 4 points in order to study the cracks’ generation, their propagation, as well as their opening and closing. The mostly ultrasonic techniques developed concern linear or non-linear acoustic: acoustic emission [1], LOCADIFF (Locating with diffuse ultrasound) [2], energy diffusion, surface waves velocity and attenuation, DAET (Dynamic Acousto-Elasticity Testing) [3]. The data contribute to providing the mapping of the parameters searched for, either in volume, in surface or globally. Image correlation is an important additional asset to validate the coherence of the data. The spatial normalization of the data allows proposing algorithms on the combination of the experimental data. The tests results are presented and they show the capacity and the limits of the evaluation of the volume, surface or global data. A data fusion procedure is associated with these results