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The Normandy region is prone to gravitational movements of various kinds (mudflows, rockfalls, rotational or translational landslides, etc.). The Pays d'Auge, at the contact between the Armorican Massif and the Paris Basin, is particularly concerned by these processes, due to a wide lithological variability and the sensitivity of materials to the presence of water. Many researches have been carried out in hinterland and coastal areas, contributing to the understanding of the landforms and the processes at work.Within the framework of the ANR RICOCHET program, this PhD thesis aims to provide some answers regarding the hazard assessment, both in terms of predisposing and triggering factors. The studied area extends specifically at the coastal and hinterland fringe of the Pays d'Auge, in the lower valley of the Touques river.Using a multidisciplinary approach combining geomorphology, geophysics, hydrogeology and geotechnics, investigations were carried out on three representative sites of landslide phenomena affecting this territory. By using existing data sets, completed by new acquisitions, this work aims to improve the knowledge of the hydromechanical functioning of each major type of landslide considered. The stability of the sites was assessed using numerical models based on finite element (SLOPE/W®) and finite difference (FLAC®) methods. A spatialized assessment of the susceptibility and hazard is then carried out at a larger scale (1:10,000) by the joint use of (1) a physically based model to simulate the triggering probability (ALICE®) and (2) an empirical model for the propagation (Flow-R®). The landslide sensitivity is highlighted with respect to current forcing, and considering the expected influence of climate change. ; La région Normandie est sujette aux mouvements gravitaires de diverses natures (coulées de boues, éboulements, glissements de terrain rotationnels ou translationnels, etc.). Le Pays d’Auge, au contact entre Massif armoricain et Bassin parisien, est particulièrement affecté par ces ...

In the context of climate change, Arctic marine ecosystems are affected by rapid environmental modifications, whose effects on biotic communities are still debated. The sea-ice decline and the increase in freshwater inputs and turbidity are likely to impact Arctic primary producers, with cascade effects on a key-process in those ecosystems: the trophic relationship between primary producers and benthic consumers (generally referred as “pelagic-benthic coupling”). The direct study of such complex interaction is not straightforward in the Arctic. The biological model of filter-feeding bivalves offers the possibility to get around these problems, allowing to study those ecological processes indirectly. Among the advantages of this model, there is first of all the fact that these organisms record in their shell, in the carbonate layers, some dynamics of their environments. The information recorded in such “bioarchives” are interpreted through the methods of sclerochronology and sclerochemistry and relate to a time window corresponding to the organism lifespan (from some years to more than 500 years). Given that these organisms are primary consumers, another advantage of this biological model is that the study of their diet can provide information about the trophic relationship with primary producers. With the methods of trophic ecology, especially fatty acids and stable isotopes, the study of the tissues allows the investigation of sources assimilated at a timescale of weeks/months.The main objective of this thesis is to test the potential of bivalves Astarte moerchi (borealis complex) as a biological model for the study of marine Arctic ecosystems. A coupled approach is used to combine shell analysis by the methods of sclerochronology and sclerochemistry (elemental ratios) and tissue analysis by the methods of trophic ecology (fatty acids, carbon and nitrogen stable isotopes, compound-specific carbon stable isotopes on individual fatty acids). Two living A. moerchi populations have been studied in two fjords ...

Data centers, factories housing thousands of computer servers that work permanently to exchange, store, process data and make it accessible via the Internet. With the digital sector development, their energy consumption, which is largely fossil fuel-based, has grown continuously over the last decade, posing a real threat to the environment. The use of renewable energy is a promising way to limit the ecological footprint of data centers. Nevertheless, the intermittent nature of these sources hinders their integration into a system requiring a high reliability degree. The hybridization of several technologies for green electricity production, coupled with storage devices, is currently an effective solution to this problem. As a result, this research work studies a multi-source system, integrating tidal turbines, photovoltaic panels, batteries and a hydrogen storage system to power an MW-scale data center. The main objective of this thesis is the optimization of a data center power supply, both for isolated sites and grid-connected ones. The first axis of this work is the modeling of the system components using the energetic macroscopic representation (EMR). Energy management strategy based on the frequency separation principle is first adopted to share power between storage devices with different dynamic characteristics. The second axis concerns the optimal sizing of the proposed system, in order to find the best configuration that meets the technical constraints imposed at minimum cost, using particle swarm optimization (PSO) and genetic algorithm (GA). Here, a rules-based energy management technique is used for simplicity and reduced computing time purposes. The last axis focuses on the energy management optimization through GA, taking into account the storage systems degradation in order to reduce their operating costs and extend their lifetime. It should be noted that each axis previously discussed has been the subject of a specific sensitivity analysis, which aims to evaluate the performance of the hybrid ...

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are two families of hydrophobic compounds sharing some similar environmental properties. Previous studies have demonstrated that these compounds could affect fish life-history traits. However, few studies have focused on environmental situations. This thesis is divided into three parts. The first part aimed to evaluate the effects of a realistic mixture of PCBs and PBDEs on the life-history traits of zebrafish. The results showed a slower growth, but to a larger asymptotic length, and delayed spawning probability in exposed fish. In addition, offspring issued from early spawning events of exposed fish exhibited a lower larval survival under starvation condition. The second part aimed to identify, on the basis of a bioenergetic model (DEB), the physiological modes of action (PMoA) of PCBs and PBDEs. Two potential PMoAs have been revealed: the first one was through an increase of the fraction of energy allocated to somatic maintenance and growth and the second one was through an increase of the cost of production of an egg. The third part focused on the population dynamical consequences of the individual life-history effects of PCBs and PBDEs. The results showed a lower abundance, a higher biomass and a higher risk of overexploitation in exposed population compared to control population. The results of this thesis could be a helpful tool for sustainable management of fish stocks that take into account the effects of multiple contaminations that are added to the fishing pressure. ; Les polychlorobiphényles (PCB) et les polybromodiphényléthers (PBDE) sont deux familles de composés hydrophobes partageant certaines propriétés physico-chimiques. Des travaux antérieurs ont montré que ces composés pouvaient affecter les traits d’histoire de vie des poissons. Il s’avère cependant que les études approchant des situations environnementales sont rares. Cette thèse se divise en trois parties. La première partie s’est attachée à évaluer les effets ...

International audience The Reduction of greenhouse gas Emissions due to Deforestation and forest Degradation (REDD) is a mechanism preached in international negotiations for the elaboration of a protocol which is supposed to replace the Kyoto protocol after 2012. In these negotiations, remote sensing is requested to provide solutions to methodological difficulties relating to REDD implementation. It indeed raises the question to know how to measure avoided deforestation and the quantities of greenhouse gas not emitted in the atmosphere thanks to deforestation avoidance. This paper presents knowledge related to this question starting from a review of recent scientific publications in remote sensing of deforestation and forest logging in tropical areas. Bibliographical review shows that measurement of reduction in forest cover is made at several levels (global, regional, national, local) with images provided by various sensors. Countries, like Brazil or India, have national systems of monitoring by remote sensing, which allows a follow-up of deforestation at national level. Remote sensing of forest logging is not current and is still mainly in research, like measurement of greenhouse gas emissions due to land cover and land use changes (deforestation/forest degradation). The paper underlines the great variability of quantifications by remote sensing, with many statistical inaccuracies which forecast a difficult use of remote sensing in the REDD framework. Additional methodological research is needed for an efficient use of remote sensing to support REDD implementation. La Réduction des Emissions de gaz à effet de serre (GES) dues à la Déforestation et à la Dégradation forestière (REDD) est un mécanisme prôné dans les négociations internationales pour l'élaboration du protocole censé remplacer le protocole de Kyoto après 2012. Dans ces négociations, la télédétection est sollicitée pour fournir des solutions aux difficultés méthodologiques relatives à la mise en œuvre de la REDD. Il se pose la question de savoir comment mesurer la déforestation et la dégradation forestière évitées ou réduites, ainsi que les quantités de GES associées à cette déforestation et à cette dégradation forestière évitée ou réduite. Cet article fait le point sur cette question à partir d'une revue des publications scientifiques récentes en télédétection de la déforestation et de l'exploitation forestière dans la zone intertropicale. La recherche bibliographique effectuée montre que la mesure de la diminution du couvert forestier est faite à plusieurs niveaux (global, régional, national, local) grâce aux images fournies par différents capteurs. Des pays, comme le Brésil ou l'Inde, disposent de systèmes nationaux de monitorage par télédétection, ce qui permet un suivi de la déforestation au niveau national. La télédétection de l'exploitation forestière n'est pas courante et relève encore en grande partie de la recherche, tout comme la mesure des émissions de GES en lien avec les changements d'occupation du sol (déforestation/dégradation forestière). L'article rend compte de la grande variabilité des quantifications par télédétection, avec de nombreuses imprécisions statistiques qui augurent d'une difficile utilisation de la télédétection dans l'optique de la REDD, ce qui souligne la nécessité de recherches méthodologiques complémentaires.

Intertidal organisms live in a fluctuating environment. The blue mussel Mytilus edulis is a key species of those ecosystems and are largely use as sentinel species. Global warming associated with anthropization will expose mussels to contaminations together with increased temperatures. In addition, more frequent heatwaves are expected. In this work, mussels were collected at two sites depicting contrasted levels of contamination and thermal exposure in microcosm were conducted. Two acclimation scenarios were set up prior to exposure to an identical acute thermal stress. In order to decipher joint effects of acclimation and contamination on protein homeostasis, gill proteome comparisons were performed. High mortality was observed only for mussels collected at the contaminated site and acclimated to current temperatures. Concerning gill proteome analysis, organisms from the pristine site exhibit high abundance of thermal stress proteins. Proteoforms involved in anaerobic metabolism were also up-regulated. Interestingly, mussels acclimated to the higher temperatures show an enhanced response compare to the one acclimated to current temperatures. Concerning mussels from the contaminated site, the response appears more confusing, excepted for heat stress protein response. This may indicate deleterious effects of combined contamination and heat stress. Therefore, organisms acclimated to higher temperature display improved responses. In conclusion, mussels with a clean life history show better physiological abilities than individuals with contaminated life history. Moreover, organisms prepared to heat stress by higher acclimation temperatures also develop a more effective response. ; Dans un contexte de réchauffement climatique et d'anthropisation, les organismes colonisant les espaces côtiers sont, et seront soumis, à des variations importantes de leur milieu de vie. Parmi ces organismes, la moule bleue Mytilus edulis constitue une espèce clé des écosystèmes intertidaux et est utilisée comme sentinelle. Au cours de ...

The research work presented in this document is a continuation of the GREAH laboratory research activities on the issues of optimal energy management on board of electric and hybrid electric vehicles. Indeed, the coupling of several electrical energy sources with different characteristics causes several issues like energy sources sizing, energy exchange quality and the lifetime of the interconnected elements. In the case of transport applications, the main factors of these problems are based on the high fluctuations in the power required by the propulsion/traction chain; the limited life expectancy of the electrical energy storage elements; the lack of realistic standard mission profile and the need to optimize the electric vehicles energy consumption. The appropriate method for studying the multi-source systems is by using systemic approach. This approach is necessary to establish behavioral models of energies sources and power converters for the development of optimal energy management strategies. The contribution of this thesis is focused on the investigation and the development of energy management strategies considering the electrical energy sources performances and their state of functioning according to the power fluctuations from the propulsion/traction chain, which presents the load in a touristic vehicle. ; Ce sujet s’inscrit dans la continuité des activités de recherche du laboratoire GREAH sur les problématiques de la gestion optimale d’énergie électrique embarqué à bord des véhicules électriques hybrides. En effet, le couplage de plusieurs sources de natures différentes entraîne des problématiques de dimensionnement, de qualité d’énergie et de la durée de vie des éléments interconnectés. Pour les applications de transport par exemple, les principaux facteurs de ces problématiques reposent sur : - les fluctuations de la puissance demandée par la chaîne de propulsion/ traction, la durée de vie limitée des éléments de stockage d’énergie électrique, l’absence de profil de mission standard réaliste et la ...

Since the pioneering work of Brown and Roshko on the effects of density variations within the mixed layer flow, several other theoretical, experimental and numerical studies harnessed to finely investigate this flow. The motivations are of practical order (chemical industry, aerodynamics, combustion. . .) or purely theoretical (the role of coherent structures,secondary instabilities). These studies have focused on, among others, the effects of compressibility and/or variable density. To our knowledge, the effects of viscosity variations in the mixing layer configuration are not discussed in the literature. The objective of this researchis the theoretical and numerical exploration of the variable viscosity temporal mixedlayer flow, especially during its initial phase of development. From a numerical viewpoint, the Navier-Stokes equations are solved in weakly compressible formulation, using the solver CHOC-WAVES, based on WENO scheme. The DNS approach is justified by the absence in the literature of subgrid models that account for the effects of variable viscosity. The transport equations of different mean and fluctuating quantities at a point and each scale (scale-by-scale energy budget) are rewritten in incompressible and variable-viscosity formulation. Additional terms, generated by the spatial and temporal variations of viscosity occur in these equations. These are used as a tool to explore the mixed layer flow and study the development of turbulence in a heterogeneous environment. The simulated viscosity ratios are Rv = [1 − 18]. The numerical results show that the mixing layer thickness δθ growsfaster when the viscosity ratio Rv is high. The vertical gradients of the longitudinal mean velocity are amplified by the viscosity gradients, a gain of almost 60 %, compared to initial values was observed. The production of turbulent kinetic energy is also amplified. The temporal evolution of the velocity fluctuations is accelerated, they are increased to nearly 120 % with respect to the constant viscosity flow. The ...

International audience

In Normandy, the cultivation of soft wheat (Triticum aestivum L) occupies 24% of the regional UAA and holds an importantplace among the vegetable productions. Each year 3.6 Mt are harvested, i.e. 10% of the national total. But a stagnation in yieldshas been observed since the mid-1990s, a sign that Normandy cereal growing is already suffering from climate change.This doctoral thesis in geography and agro-climatology focuses on the consequences of climate change on soft wheat cultivationin Normandy and questions the issues and prospects of the cereal agrosystem. To answer this question, the research chose theCaen Plain as a representative study area for regional cereal growing. Meteorological data from Météo-France stations and theSAFRAN model are used, as well as climate projections extracted from the regional ALADIN-Climat model for 3 RCPscenarios. The data processing is carried out for the historical (1961-2020) and future (2021-2050 and 2071-2100) periods. Themethod is based on agroclimatic and phenoclimatic indicators. Soil surveys are conducted to estimate the water retentioncapacity of the soils in the study area. A field survey is also conducted with farmers and agricultural technicians. Finally,exploratory field measurements highlight the diversity of weather conditions in the plain.The results show the complexity of climate change and illustrate the need for prospective impact studies in climatologyaccording to a systemic, spatial, temoral and multidisciplinary approach to rationally consider the adaptation of agrosystems toclimate change. ; En Normandie, la culture du blé tendre (Triticum aestivum L) occupe 24 % de la SAU régionale et tient une place importanteparmi les productions végétales. Chaque année 3,6 Mt sont moissonnées, soit 10 % du total national. Mais une stagnation desrendements est observée depuis le milieu des années 1990, signe que la céréaliculture normande subit déjà le changementclimatique.Ce travail de thèse de doctorat en géographie et en agro-climatologie s'intéresse aux ...