Résumé : Le fluide chaud produit par les forages de la centrale géothermique de Bouillante (Guadeloupe) est enrichi en espèces dissoutes telles que la silice qui peuvent précipiter sous forme de dépôts solides lors de son refroidissement et gêner fortement la production électrique. L’un des principaux objectifs de ce travail de thèse a donc été d’améliorer l’état des connaissances sur les conditions physiques, chimiques et cinétiques de la précipitation de la silice amorphe à Bouillante. Après une étude des caractéristiques physico-chimiques des fluides et des dépôts associés au champ de Bouillante, des expériences sur la cinétique de précipitation de la silice, sur site, pour une large gamme de température (25 - 90°C) et de pH (4 - 12) ont été menées et analysées en détail.Pour l’ensemble de ces expériences, seule la polymérisation (réversible) de la silice dissoute, sous forme de suspensions colloïdales très stables en solution, a été observée. La modélisation des données expérimentales de cinétique montre que la vitesse de polymérisation de la silice suit une loi d’ordre 2 vis-à-vis de la silice dissoute jusqu’à l’équilibre en accord avec une dimérisation de la silice. Par contre, durant l’étape initiale de la réaction, une loi d’ordre 4 semble mieux adaptée, suggérant des réactions de polymérisation plus complexes avec formation de tétramères. La température a un effet limité sur la cinétique de polymérisation de la silice comparé à l’effet du pH qui est beaucoup plus important. L’énergie d’activation de la réaction globale est de 41 - 54 kJ pour des pH compris entre 5 et 8.La caractérisation de la silice précipitée a mis en évidence des différences notables entre la structure poreuse de la silice solide prélevée sur les installations de surface et celle de la silice colloïdale obtenue par polymérisation lors des expériences de cinétique, ce qui semble indiquer que des mécanismes différents interviennent dans ces deux contextes de précipitation de la silice dissoute.Le deuxième objectif de cette thèse était d’évaluer la possibilité de valoriser la silice extraite de l’eau géothermale de Bouillante dans un procédé de traitement des eaux naturelles par adsorption. Pour cela, les propriétés d’adsorption de la silice géothermale brute et fonctionnalisée par le poly(ethylèneimine) (ou PEI) ont été étudiées pour deux polluants : un colorant, le bleu de méthylène et un métal lourd, le plomb. Les résultats obtenus montrent que la silice brute possède une grande capacité d’adsorption vis-à-vis du bleu de méthylène. En outre, la fonctionnalisation de la silice par le PEI permet d’améliorer sa capacité d’adsorption vis-à-vis du plomb en solution, en accord avec un modèle cinétique du pseudo-second ordre suggérant une chimisorption. Le modèle d’isotherme de Redlich-Peterson est également en très bon accord avec les données expérimentales.
The hot geothermal fluid produced by the geothermal power plant of Bouillante (Guadeloupe) contains various dissolved components such as silica that can precipitate as solid deposits during their cooling and cause serious problems on the electricity generation. One of the aim of this study is to improve the understanding on the physical, chemical and kinetics conditions of the amorphous silica precipitation in the Bouillante geothermal field. After a study on the physical and chemical characteristics of the Bouillante fluids and deposits which can form during their exploitation, experiments on the kinetics of silica precipitation, on site, under a large range of temperature (25 – 90°C) and pH (4 – 12) have been carried out and analyzed in detail.During on site kinetics experimentations only dissolved silica polymerization (reversible) as colloidal gel, very stable in solution, was observed. Modeling of the experimental data showed that the kinetics polymerization is characterized by a 2-order kinetic law relative to dissolved silica until the equilibrium that is consistent with silica dimerization. On the other side, the initial stage of the reaction is better characterized by a 4-order kinetic law that suggested more complex polymerization reactions with tetramers formation.Temperature has a little effect on the polymerization kinetics compared with the pH which has an effect more important. The activation energy of silica precipitation calculated between 25 and 90°C, is about 41 - 54 kJ for pH ranging to 5 - 8.The characterization of the silica precipitate reveals significant differences in the porous structure of the silica collected on the surface installations and the one obtained from kinetic experiments that suggests different precipitation mechanisms. The second objective of this thesis was to evaluate the possibility to promote geothermal silica for the treatment of natural waters containing contaminants by adsorption. Adsorption properties of the untreated and functionalized by poly(ethylèneimine) (ou PEI) geothermal silica have been investigated for two pollutants: a colorant, the methylene blue and a heavy metal, the lead.Results showed that untreated silica has a great adsorption capacity concerning the methylene blue. Besides, silica functionalization by the PEI allows improving the adsorption capacity for lead in solution. The adsorption kinetics curves followed a pseudo-second order model consistent with a chimisorption. The isotherm model of Redlich-Peterson fitted well the experimental data.

http://www.theses.fr/2014AGUY0698/document

Éditeur(s) : Gauthier-Villars
Résumé : The Scopoletin-Peroxidase fluorescence decay method has been developed using standard additions and a flow injection manifold for hydrogen peroxide (H2O2) determination in marine waters. The limit of detection of the method was optimized using stored milli-Q water with a minimum of 5 nM (3 sigma). The method was found to be linear from 5 to 700 nM, with an approximate relative standard deviation of 10%. This accuracy was verified on both milli-Q and natural waters running systematically duplicate analysis. The validity and the sensitivity of the technique was studied through the influence of pH, salinity and the dissolved organic matter (DOM) concentration. Standard additions avoided all matrix and experimental interferences, making it possible to use this method under any field conditions and on ''humic-rich'' waters. Additionally, the flow injection manifold improved the accuracy and the runtime of the analytical procedure and simplified the field manipulation.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1995 , Vol. 18 , N. 3 , P. 353-361

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00097/20784/18409.pdf
http://archimer.ifremer.fr/doc/00097/20784/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This manuscript reports on a novel field experiment carried out on a microtidal beach in Camargue, France. For the first time in the field, a comprehensive description of the groundwater dynamics under sandy beach swash zone is presented. A cross-shore network of 15 buried pressure sensors is combined with terrestrial LiDAR measurements to study the swash-groundwater dynamics. The presented data focus on the decay of a moderate storm which allows to monitor the evolution of the groundwater pressure field in response to the retreat of the swash zone. Both horizontal and vertical head gradients are measured within the porous sand soil to estimate the groundwater flow field using Darcy’s law. Time-averaged analysis demonstrates the presence of a rather consistent groundwater circulation pattern under the swash zone, shifting offshore with the swash zone. The main tendency is an offshore directed flow, with infiltration/exfiltration in the upper/lower parts of the swash zone. Time-resolved analysis highlights the typical groundwater response to swash events which consists mainly of an overall infiltration flow during the bed inundation by the swash tongue, a seaward flow during the swash retreat and, for long backwash events, a localized exfiltration flow under the next incoming uprush.
ISSN: 0309-1708

hal-01412450
https://hal.archives-ouvertes.fr/hal-01412450
DOI : 10.1016/j.advwatres.2016.09.009

Éditeur(s) : Elsevier Science Bv
Résumé : Monitoring fish and underwater habitats, particularly in and around marine protected areas (MPAs) requires non-destructive observation methods. This is generally achieved by divers conducting underwater visual censuses (UVC), but video-based techniques are now being used more often to observe underwater macrofauna and habitats. A comparison of these two techniques is relevant with the development of high-definition (HD) video, which constitutes a substantial improvement over previously available video resolutions at limited extra cost. We conducted a paired observation experiment involving both HD video and UVC in an MPA located in the New Caledonian lagoon, which is a highly diversified coral reef ecosystem. We compared three techniques for counting fish along 50 m x 4 m delineated strip transects: UVC and two video techniques in which the diver used either a straight trajectory (I-type transect) or a browsing one (S-type transect). The results showed that the proportion of fish that were not identified up to the species level did not exceed 3.3% in video observations versus 1.7% in UVC. The abundance and species richness were larger in UVC than in videos, and S-type transects detected more individuals and species than I-type transects. The average abundance and species richness observed by UVC were 1094 individuals and 69.7 species per transect respectively. In comparison with UVC. I-type and S-type video transects detected on average 56% and 61% of the abundance and 85% and 77% of the species richness seen by UVC respectively. Our results showed that, in comparison to UVC data recorded in situ, the post field analysis of HD video images provided representative observations of fish abundance and species diversity, although fewer species and individuals were detected. The advantages and shortcomings of each observation technique for monitoring fish assemblages, particularly in an MPA are discussed. HD video appears to be a cost-effective technique in terms of the human resources and time needed for field implementation. Overall, this study suggests that HD video-based techniques constitute an interesting complement to UVC, or an alternative when these cannot be implemented. (C) 2010 Elsevier B.V. All rights reserved.
Fisheries Research (0165-7836) (Elsevier Science Bv), 2011-01 , Vol. 107 , N. 1-3 , P. 84-93

Droits : 2010 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00031/14192/11470.pdf
DOI:10.1016/j.fishres.2010.10.011
http://archimer.ifremer.fr/doc/00031/14192/

Éditeur(s) : HAL CCSD SPRINGER
Résumé : International audience
A key question in evolutionary biology is the reproducibility of adaptation. This question can now be quantitatively analyzed using experimental evolution coupled to whole genome sequencing (WGS). With complete sequence data, one can assess convergence among replicate populations. In turn, convergence reflects the action of natural selection and also the breadth of the field of possible adaptive solutions. That is, it provides insight into how many genetic solutions or adaptive paths may lead to adaptation in a given environment. Convergence is both a property of an adaptive landscape and, reciprocally, a tool to study that landscape. In this chapter we present the links between convergence and the properties of adaptive landscapes with respect to two types of microbial experimental evolution. The first tries to reconstruct a full adaptive landscape using a handful of carefully identified mutations (the reductionist approach), while the second uses WGS of replicate experiments to infer properties of the adaptive landscape. Reductionist approaches have highlighted the importance of epistasis in shaping the adaptive landscape, but have also uncovered a wide diversity of landscape architectures. The WGS approach has uncovered a very high diversity of beneficial mutations that affect a limited set of genes or functions and also suggests some shortcomings of the reductionist approach. We conclude that convergence may be better defined at an integrated level, such as the genic level or even at a phenotypic level, and that integrated mechanistic models derived from systems biology may offer an interesting perspective for the analysis of convergence at all levels.
ECOLOGICAL GENOMICS: ECOLOGY AND THE EVOLUTION OF GENES AND GENOMES

ISBN : 978-94-007-7347-9; 978-94-007-7346-2
hal-01544757
https://hal.archives-ouvertes.fr/hal-01544757
DOI : 10.1007/978-94-007-7347-9__11

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : International audience
Fluid-rock interactions can control earthquake nucleation and the evolution of earthquake sequences. Experimental studies of fault frictional properties in the presence of fluid can provide unique insights into these interactions. We report the first results from experiments performed on cohesive silicate-bearing rocks (microgabbro) in the presence of pressurized pore fluids (H2O, drained conditions) at realistic seismic deformation conditions. The experimental data are compared with those recently obtained from carbonate-bearing rocks (Carrara marble). Contrary to theoretical arguments, and consistent with the interpretation of some field observations, we show that frictional melting of a microgabbro develops in the presence of water. In microgabbro, the initial weakening mechanism (flash melting of the asperities) is delayed in the presence of water; conversely, in calcite marble the weakening mechanism (brittle failure of the asperities) is favored. This opposite behavior highlights the importance of host-rock composition in controlling dynamic (frictional) weakening in the presence of water: cohesive carbonate-bearing rocks are more prone to slip in the presence of water, whereas the presence of water might delay or inhibit the rupture nucleation and propagation in cohesive silicate-bearing rocks.
ISSN: 0091-7613

hal-01054327
https://hal.archives-ouvertes.fr/hal-01054327
DOI : 10.1130/G34916.1

Éditeur(s) : HAL CCSD
Résumé : We present an experimental study of relations between hydraulic properties of clayey rocks and their deformation at bulk and micro scale. The experimentation is based on triaxial deformation of kaolinitic core samples, on permeability measurements, and on several methods of analysis of the microstructure. To produce the samples, remoulded kaolinite material is consolidated by axial loading up to 20 MPa in an oedometric cell. Then, in a triaxial cell, an undrained stress path is applied in order to induce shearing damage in the sample. The permeability of the sample is measured by fluid flow across the sample. Before and after these hydro-mechanical tests, the evolution and the homogeneity of the pore space and moreover the texture of the material are analysed by X-ray tomography, environmental scanning electron microscopy and thermic neutron diffraction. Contrary to expectations, the permeability at the sample scale does not vary significantly, although quite large deformation is reached. The final deformation is heterogeneous, with well-developed shear bands. It appears that the development of compacting and dilating zones generates a heterogeneous permeability field, which results in a negligible variation of the bulk permeability at the sample scale.
International Journal of Rock Mechanics and Mining Science

hal-00496407
https://hal.archives-ouvertes.fr/hal-00496407
DOI : 10.1016/j.ijrmms.2010.04.007

Éditeur(s) : Springer
Résumé : Two recurring syndromes threaten the viability of the shrimp industry in New Caledonia, which represents the second largest export business. The "Syndrome 93" is a cold season disease due to Vibrio penaeicida affecting all shrimp farms, while the "Summer Syndrome" is a geographically restricted vibriosis caused by a virulent lineage of Vibrio nigripulchritudo. Microbiological procedures for diagnosis of these diseases are time-consuming and do not have the ability to discriminate the range of virulence potentials of V. nigripulchritudo. In this study, we developed a multiplex PCR method to simultaneously detect these two bacterial species and allow for pathotype discrimination. The detection limits of this assay, that includes an internal amplification control to eliminate any false-negative results, were determined at 10 pg purified DNA and 200 cfu/ml. After confirming the effectiveness of our method using experimentally infected animals, its accuracy was compared to standard biochemical methods during a field survey using 94 samples collected over 3 years from shrimp farms encountering mortality events. The multiplex PCR showed very high specificity for the detection of V. penaeicida and V. nigripulchritudo (inclusivity and exclusivity 100%) and allowed us to detect the spreading of highly pathogenic isolates of V. nigripulchritudo to a farm adjoining the "Summer Syndrome area." This assay represents a simple, rapid, and cost-effective diagnostic tool for implementing timely risk management decisions but also understanding the seasonal and geographical distribution of these pathogens.
Microbial Ecology (0095-3628) (Springer), 2012-01 , Vol. 63 , N. 1 , P. 127-138

Droits : Springer Science+Business Media, LLC 2011
http://archimer.ifremer.fr/doc/00063/17398/15169.pdf
DOI:10.1007/s00248-011-9951-3
http://archimer.ifremer.fr/doc/00063/17398/

Résumé : Les objectifs de développement de systèmes de culture durables imposent aux acteurs du développement rural une reconception de ces systèmes. Les méthodes de conception actuelles conduisent souvent les chercheurs à être seuls concepteurs alors que parallèlement l'appropriation des innovations dépend fortement de l'implication des autres acteurs. En réponse, des approches participatives sont de plus en plus fréquentes pour pallier à cette difficulté d'appropriation. La méthode développée dans cette thèse -nommée DISCS pour 're-Design and assessment of Innovative Sustainable Cropping Systems' - met en oeuvre un processus de reconception des systèmes de culture par une approche participative tout en développant des outils d'évaluation multicritère. La méthode DISCS s'inscrit dans la lignée de la méthodologie du prototypage mais se différencie par une démarche itérative à trois échelles d'étude (parcelle, exploitation et territoire) afin de s'assurer que les innovations répondent bien aux attentes des acteurs. A chaque étape du processus une évaluation est réalisée à l'aide d'un jeu d'indicateurs. DISCS a été testée sur le système de culture agrumicole en Guadeloupe dans un but de réduire l'utilisation des pesticides. Cinq prototypes de gestion de l'enherbement ont été conçus collectivement puis testés selon les principes d'une approche systémique. Dans cette thèse, nous présentons les premières étapes de reconception du système agrumicole guadeloupéen basée sur la méthode DISCS. Notre travail nous permet de recommander des techniques de gestion de l'enherbement en jeunes vergers d'agrumes répondant aux contraintes actuelles de développement de systèmes de culture durable.
Re-designing sustainable cropping systems has become a major challenge for agricultural researchers and farmers. In most designing methods, researchers are the main, or sometimes the only designers. However, more and more attempts for involving different kinds of stakeholders in participatory approaches have been accounted for. The new method described in this thesis (DISCS for 're-Design and assessment of Innovative Sustainable Cropping Systems') implements a participatory re-designing process. Though founded on the common structure of prototyping methods, this five-step-method differs first by implementing three progress loops, at experimental field, farm then regional scale. Besides, an ongoing progress dynamic is set between research at the experimental station and crop management in farms, in order to ensure that innovative techniques actually match the farmers' expectations. Assessment at each step is performed using a scale-specific set of indicators. The DISCS method was tested on citrus production in Guadeloupe, to develop lower-pesticide sustainable cropping systems. Five weed management prototypes were collectively designed then tested at an experimental station based on the principles of a systematic approach. In this thesis, we present the first stages of citrus cropping system redesigning based on DISCS method. Our work enables us to recommend sustainable weed management techniques for young orchards that correspond to the current constraints facing orchards in Guadeloupe

http://www.theses.fr/2011AGUY0449/document

Éditeur(s) : Université Paris 7 – Denis Diderot
Résumé : Sea surface salinity (SSS) influences numerous oceanic phenomena, for instance surface water ventilation, deep water formation and thermohaline circulation. SSS also controls some ocean-atmosphere coupled processes, such as the intensity of freshwater flux and the penetration of heat flux and turbulence. Salinity is more difficult to measure than temperature from in situ surveys, which results in 20 times less data being currently available. Moreover, sea surface temperature (SST) is routinely estimated from satellites, which is not possible yet for SSS. Two space missions will fill this gap soon: SMOS from the European Space Agency and Aquarius/SAC-D from NASA and CONAE. To contribute to the SMOS project, we propose a method for estimating SSS from current satellite observations and for studying the mechanisms governing its variability. We developed a simplified model of the ocean mixed layer, based on the "slab mixed layer" formulation (Frankignoul et Hasselmann, 1977). This 2D horizontal model is implemented over the global ocean, using a near 100 km resolution, and integrated during a climatological year. Air-sea fluxes are taken from the ECMWF meteorological model (ERA40 reanalysis) and the surface currents are provided by altimeter data (SSALTO-DUACS analysis). The mixed layer depth (MLD) is derived from SST observations, using an original inversion technique. The MLD fields obtained from this inversion are well correlated to in situ estimates. This effective depth represents the air-sea fluxes penetration and ensures consistency between fluxes, les currents and SST. We first validate the simulation through examination of the heat balance in north-eastern Atlantic, by comparing to measurements and models from the POMME experiment. Then we study the salinity balance in the global domain, in terms of its geographical distribution and seasonal evolution. Equilibrium between the various processes appears generally more complex than for temperature. Noteworthy, the role of atmospheric flux is less predominant (22%), while geostrophic advection (33%) and diapycnal mixing (22%) contribute more strongly. Our results indicate this model succeeds in reconstructing SSS variability over most of the oceans. Daily SSS variations are also simulated, whereas they are not represented in current observed data at a global scale. Owing to its simplicity and fast computation, the model will be useful to the SMOS mission. It can help for the measurement calibration/validation and provide a first guess estimate to the sophisticated algorithm required for SSS restitution.
La salinité de surface des océans (SSS) influence de nombreux phénomènes océaniques, parmi lesquels la ventilation des eaux de surface, la formation d'eaux profondes et la circulation thermohaline. Elle détermine aussi certains processus couplés océan-atmosphère, notamment l'intensité du flux d'eau douce, la pénétration du flux de chaleur et de la turbulence. La mesure in situ de salinité est plus compliquée que celle de température, si bien qu'on dispose actuellement de 20 fois moins de données pour cette propriété. De plus, la température de surface (SST) est couramment estimée par satellite, ce qui n'est pas encore le cas de la SSS. Deux missions spatiales vont prochainement combler cette lacune : le satellite SMOS de l'Agence Spatiale Européenne et le satellite Aquarius/SAC-D de la NASA et de la CONAE. En préparation du projet SMOS, nous proposons une méthode pour estimer la SSS à partir des observations satellitaires actuelles et étudier les mécanismes de sa variabilité. Nous avons développé un modèle simplifié de couche mélangée océanique, basé sur la formulation "slab mixed layer" (Frankignoul et Hasselmann, 1977). Ce modèle 2D horizontal est implémenté sur l'océan global, avec une résolution proche de 100 km, et intégré au cours d'une année climatologique. Les flux air-mer proviennent du modèle météorologique ECMWF (réanalyse ERA40) et les courants de surface sont issus de l'altimétrie (analyse SSALTO-DUACS). La profondeur de la couche mélangée (MLD) est dérivée des observations de SST, grâce à une technique d'inversion originale. La MLD obtenue par inversion est bien corrélée aux estimations basées sur des données in situ. Cette profondeur effective représente la pénétration des flux air-mer et assure la cohérence entre les flux, les courants et la SST. La simulation est d'abord validée en examinant le bilan de chaleur dans l'Atlantique Nord-Est, par comparaison aux mesures et aux modèles de l'expérience POMME. Puis le bilan de salinité est étudié dans le domaine global, en termes de distribution géographique et d'évolution saisonnière. L'équilibre entre les différents processus est généralement plus complexe que pour la température. Notamment, le rôle du flux atmosphérique est moins prépondérant (22%), tandis que l'advection géostrophique (33%) et le mélange diapycnal (22%) contribuent fortement. Nos résultats montrent que ce modèle parvient à restituer la variabilité de la SSS sur la majeure partie des océans. Le modèle simule aussi les variations journalières de SSS, qui ne sont pas représentées à l'échelle globale dans les observations actuelles. Grâce à sa simplicité et à sa rapidité, le modèle pourra être utile dans le cadre de SMOS. Il pourra aider à la calibration/validation de la mesure et fournir une estimation a priori pour l'algorithme complexe nécessaire à la restitution de la SSS.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2006/these-2302.pdf
http://archimer.ifremer.fr/doc/00000/2302/

Éditeur(s) : HAL CCSD Institute of Electrical and Electronics Engineers
Résumé : International audience
An effective solution for increasing the exposure uniformity and efficiency of biological samples in in vitro bioelectromagnetic experiments at 60 GHz is proposed by introducing a novel choke ring antenna (CRA). The CRA is optimized to provide a uniform exposure of samples, whose dimensions are equivalent to those of a standard 35-mm Petri dish, positioned close to the antenna aperture, i.e., 10-20 wavelengths. The antenna prototype is fabricated in metallized foam. The realized exposure efficiency of the sample exceeds 55% (if estimated for an exposure uniformity better than - 0.5 dB). To validate the numerical results, the field intensity profiles on the surface of a high-water-content phantom have been experimentally obtained using a high-resolution infrared camera. Compared to the standard open-ended waveguide and horn antennas, typically used for millimeter-wave dosimetry, a twofold advantage of the proposed CRA is demonstrated, namely, the improvement of the exposure efficiency by a factor of 1.5 to 2 with a simultaneous reduction of the exposure distance by a factor of 8-2, respectively, depending on the type of the reference antenna. These advantages make the proposed CRA an excellent candidate for 60-GHz short-range exposure systems for in vitro bioelectromagnetic studies.
ISSN: 0018-9480

hal-00874349
https://hal.archives-ouvertes.fr/hal-00874349
DOI : 10.1109/TMTT.2013.2255619

Éditeur(s) : HAL CCSD Springer
Résumé : International audience
Playbacks are a useful tool for conducting well-controlled and replicated experiments on the effects of anthropogenic noise, particularly for repeated exposures. However, playbacks are unlikely to fully reproduce original sources of anthropogenic noise. Here we examined the sound pressure and particle acceleration of boat noise playbacks in a field experiment and reveal that although there remain recognized limitations, the signal-to-noise ratios of boat playbacks to ambient noise do not exceed those of a real boat. The experimental setup tested is therefore of value for use in experiments on the effects of repeated exposure of aquatic animals to boat noise.
The Effects of Noise on Aquatic Life II

ISBN : 978-1-4939-2980-1 (Print) 978-1-4939-2981-8 (Online)
hal-01270660
https://hal-univ-perp.archives-ouvertes.fr/hal-01270660
DOI : 10.1007/978-1-4939-2981-8_55

Éditeur(s) : HAL CCSD Elsevier
Résumé : We describe, test, and explain the relative effectiveness of six thermal and microwave techniques of absolute palaeointensity determination applied to lava samples from Mount Etna (Sicily) that acquired their thermoremanence (TRM) in a known geomagnetic field. The application of a single alternating field demagnetisation treatment prior to each measurement in a standard Thellier experiment is demonstrated to be beneficial: increasing the quality of the results and making the analysis simpler. A new quasi-perpendicular (QP) method dramatically improves the linearity of Arai plots by reducing or altogether eliminating non-ideal effects due to multidomain (MD) grains. Two broad types of sample were encountered by this study and the QP method is the only one capable of producing accurate measurements from them both. Its ease of use, speed, and increased reliability should allow it to replace standard double heating methods in studies such as these where laboratory alteration can be detected by other means than pTRM checks. The results of experiments performed using a microwave palaeointensity system provide further proof that the microwave (de)magnetisation process is equivalent to conventional thermal excitation. They also demonstrate that microwave experiments are subject to the same risks as conventional experiments when performed on samples containing MD grains. The behaviour of the samples in both the thermal and microwave experiments is in good agreement with a recently proposed model of MD TRM which is based on first-order symmetry of the remagnetisation process.
ISSN: 0012-821X

hal-00407671
https://hal.archives-ouvertes.fr/hal-00407671
DOI : 10.1016/j.epsl.2007.03.016

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Despite the impact of soil millipedes on litter fragmentation in tropical forests, there have been few studies dealing with factors determining their habitat preference in these ecosystems. In a natural secondary dry forest of Guadeloupe on Leptosol, two complementary studies were carried out in order to test the hypothesis that litter N-content strongly influences millipede distribution. Millipede abundance and species richness were described in the field under two tree species, Bursera simaruba and Pisonia subcordata, and were related to the chemical characteristics of their foliage. In addition, a laboratory experiment was done in order to assess millipede feeding preferences regarding the chemical characteristics of leaves from various species. Millipede abundance and species richness were significantly higher under P. subcordata than under B. simaruba, probably due to the higher N content of P. subcordata leaves. Moreover, millipedes fed preferentially on N-rich leaves. The present study confirms that there was a close correlation between the preferred food, its chemical composition and the local distribution of millipede populations.
ISSN: 0178-2762

hal-00495211
https://hal.archives-ouvertes.fr/hal-00495211
https://hal.archives-ouvertes.fr/hal-00495211/document
https://hal.archives-ouvertes.fr/hal-00495211/file/BFSO-D-08-00133-1.pdf
DOI : 10.1007/s00374-008-0321-3

Éditeur(s) : HAL CCSD
Résumé : International audience
Understand the dynamics of the fresh-salt water interface in aquifers is a key issue to comprehend mixing processand to quantity the discharge of nutrients in to coastal areas. In order to go beyond the current knowledge inthis issue an experimental site has been set up at the alluvial aquifer Riera Argentona (Barcelona – Spain). Thesite comprises 16 shallow piezometers installed between 30 and 90 m from the seashore, with depths rangingbetween 15 and 25 meters. The seawater interface is being monitored using several techniques, the combinationof which will help us to understand the spatial and temporal behaviour of the mixing zone and the geochemicalprocesses occurring there. Specially the deepest piezometers are equipped with electrodes in order to performcross-hole electrical resistivity tomography (CHERT). In addition, all piezometers are also equipped with FiberOptic cable to perform distributed temperature measurements. Two single steel armoured fibre optic cable lines ofaround 600m length were installed in all boreholes. The objective is to use the cable both as passive and activetemperature sensor. The first is being done for the continuous monitoring of temperature whereas; the secondprovides a higher temperature resolution used to monitor field experiments.Periodic CHERT measurements are carried out between the piezometer equipped with electrodes, resultingin parallel and perpendicular vertical cross sections of the site resistivity. The position of the fresh-salt waterinterface can be identified due to the resistivity contrast between the saline and fresh water. Preliminary resultsof periodic distributed temperature measurements will be also be used to monitor the position of the mixing zonethanks to the contrast and seasonal temperature changes. Periodic down-hole EC profiles will be used to validatethe method.AcknowledgementsThis work was funded by the projects CGL2013-48869-C2-1 y CGL2013-48869-C2-2-R of the Spanish Government.We would like to thank SIMMAR (Serveis Integrals de Manteniment del Maresme) and the ConsellComarcal del Maresme in the construction of the research site
European Geosciences Union General Assembly 2016
Vienne, Austria

insu-01308757
https://hal-insu.archives-ouvertes.fr/insu-01308757

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We analyze the kinematics of fault tip folding at the front of a fold-and-thrust wedge using a sandbox experiment. The analog model consists of sand layers intercalated with low-friction glass bead layers, deposited in a glass-sided experimental device and with a total thickness h = 4.8 cm. A computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation. Active deformation at the tip of the forward propagating basal décollement is monitored along the cross section with a high-resolution CCD camera, and the displacement field between pairs of images is measured from the optical flow technique. In the early stage, when cumulative shortening is less than about h/10, slip along the décollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium. In this stage of detachment tip folding, horizontal displacements decrease linearly with distance toward the foreland. Vertical displacements reflect a nearly symmetrical mode of folding, with displacements varying linearly between relatively well defined axial surfaces. When the cumulative slip on the décollement exceeds about h/10, deformation tends to localize on a few discrete shear bands at the front of the system, until shortening exceeds h/8 and deformation gets fully localized on a single emergent frontal ramp. The fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system. As long as strain localization is not fully established, the sand layers experience a combination of thickening and horizontal shortening, which induces gradual limb rotation. The observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds, relate finite deformation to incremental folding, and derive shortening rates from deformed geomorphic markers or growth strata.
ISSN: 2169-9313

hal-00138061
https://hal.archives-ouvertes.fr/hal-00138061
https://hal.archives-ouvertes.fr/hal-00138061/document
https://hal.archives-ouvertes.fr/hal-00138061/file/Bernard_et_al-2007-Journalsur Geophysical_Research__Solid_Earth_%281978-2012%29.pdf
DOI : 10.1029/2005JB004149

Éditeur(s) : HAL CCSD
Résumé : The mantle deformation processes that control the thinning and break-up of continental lithosphere remain poorly understood. Our knowledge is restricted to either lithospheric scale thermo-mechanical models --that use experimentally derived flow laws--, geophysical imaging and/or rare xenoliths from active continental rifts, such as the East African Rift System. The originality of this work relies on the study of the two largest outcrops of diamond facies subcontinental lithospheric mantle in the world: the Beni Bousera and Ronda peridotite massifs in N Morocco and S Spain, respectively. The structures and petrologic and metamorphic zoning preserved in these massifs --implying a polybaric and polythermal evolution-- provides a unique opportunity to investigate the thermo-mechanical evolution of thick subcontinental lithospheric mantle in extensional settings. In this thesis we studied the deformation mechanisms in both peridotites and pyroxenites to constrain the modes of exhumation of subcontinental lithospheric mantle from garnet-, to spinel-, and finally, to plagioclase lherzolite facies conditions. We combined field mapping of tectonometamorphic domains and structural mapping of ductile structures, microstructural analysis, crystal preferred orientations (CPO) measurements and conventional thermobarometric calculations and thermodynamic modeling (Perple_X) to unravel the pressure and temperature conditions of deformation. We showed that exhumation from garnet- to spinel lherzolite facies conditions was accommodated by fast shearing --in thermal disequilibrium--along a lithospheric scale transtensional shear zone. In this context, the petrological zoning and the large temperature gradient (ca. 100ºC/km) preserved in the Beni Bousera massif represent the mechanical juxtaposition of progressively deeper and hotter lithospheric levels at depths of ca. 60 km in the latest Oligocene (ca. 25 Ma). Final exhumation from spinel- to plagioclase facies lherzolite and emplacement into the crust is best recorded in the Ronda massif where it occurred by inversion and lithospheric scale folding of the highly attenuated continental lithosphere in a back-arc region, probably in relation with southward slab rollback and subsequent collision with the palaeo-Maghrebien passive margin in the early Miocene (21-23 Ma).
Les processus de déformation contrôlant l'amincissement de la lithosphère continentale sont encore mal contraints. Nos connaissances sont principalement basées sur la modélisation thermomécanique d'extension à l'échelle de la lithosphère--utilisant des lois rhéologiques derivées expérimentalement, l'imagerie géophysique et l'analyse de xénolithes provenant de rift continentaux actifs à ce jour, tels que le Rift Est-Africain. L'originalité de ce travail reside dans l'étude des deux plus grands massifs de péridotites sous-continentales ayant enregistrées des conditions primaires du facies à diamant: les massifs de Beni Bousera au nord du Maroc et de Ronda au sud de l'Espagne, respectivement. Les structures et la zonation petrologique et métamorphique --impliquant une évolution polybarique et polythermique-- préservéees dans ces massifs offrent une opportunité unique pour étudier l'évolution thermo-mécanique du manteau sous-continental dans un contexte extensif. Dans ce travail, nous avons étudié les mécanismes de déformation des péridotites et des pyroxénites afin de contraindre les modes d'exhumation du manteau lithosphérique sous-continental, depuis des conditions du facies des lherzolites à grenat, jusqu'au facies à spinelle et enfin à plagioclase. Nous avons combiné la cartographie des faciès tectono-métamorphiques et des structures ductiles de déformation, l'analyse des microstructures, la mesure d'orientations préférentielles de réseau (OPR), et la géothermobarométrie conventionelle couplée à la modélisation thermodynamique (PerpleX) afin de contraindre les conditions de pression et température de la déformation. Nous avons montré que l'exhumation précoce du facies à grenat au facies à spinelle était accomodée par une faille transtensive affectant le manteau lithosphérique. Dans ce contexte, la zonation tectono-métamorphique et le gradient thermique important (ca. 100ºC/km) préservés à Beni Bousera résultent de la juxtaposition mécanique de domaines lithosphériques initialement équilibrés à différentes pressions et températures, fossilisée à une profondeur de ca. 60 km durant l'Oligocène supérieur (ca. 25 Ma). L'exhumation finale du facies de lherzolite à spinelle au facies à plagioclase et l'emplacement final dans la croûte, mieux enregistrés dans Ronda, se sont produits par inversion et plissement de la section lithosphérique fortement amincie dans un contexte arrière-arc, probablement lors du retrait vers le sud de la lithosphère subduite et la collision de l'arc avec les paléo-marges maghrébines au Miocène inférieur (21-23 Ma).
https://tel.archives-ouvertes.fr/tel-00767700

tel-00767700
https://tel.archives-ouvertes.fr/tel-00767700
https://tel.archives-ouvertes.fr/tel-00767700/document
https://tel.archives-ouvertes.fr/tel-00767700/file/THESE_Frets.pdf

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Losses of corals worldwide emphasize the need to understand what drives reef decline. Stressors such as overfishing and nutrient pollution may reduce resilience of coral reefs by increasing coral–algal competition and reducing coral recruitment, growth and survivorship. Such effects may themselves develop via several mechanisms, including disruption of coral microbiomes. Here we report the results of a 3-year field experiment simulating overfishing and nutrient pollution. These stressors increase turf and macroalgal cover, destabilizing microbiomes, elevating putative pathogen loads, increasing disease more than twofold and increasing mortality up to eightfold. Above-average temperatures exacerbate these effects, further disrupting microbiomes of unhealthy corals and concentrating 80% of mortality in the warmest seasons. Surprisingly, nutrients also increase bacterial opportunism and mortality in corals bitten by parrotfish, turning normal trophic interactions deadly for corals. Thus, overfishing and nutrient pollution impact reefs down to microbial scales, killing corals by sensitizing them to predation, above-average temperatures and bacterial opportunism.
ISSN: 2041-1723

Droits : http://creativecommons.org/licenses/by/
hal-01340547
https://hal-univ-perp.archives-ouvertes.fr/hal-01340547
https://hal-univ-perp.archives-ouvertes.fr/hal-01340547/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01340547/file/ncomms11833.pdf
DOI : 10.1038/ncomms11833

Éditeur(s) : HAL CCSD
Résumé : International audience
The published literature related to distributed parameter systems theoryis quite large, and it is not feasible in a single book to give a detailedreview on the wide historical development of all of it. Our choice of whatto cover was motivated by the following consideration. Since distributedparameter systems evolve in time and space, the research investigationson their analysis and control focus on considering the whole system domainfor any study. We feel strongly that within this research field, animportant consideration was missing; that of considering that the systemmay give raise to prescribed subdomains (regions) where one has toachieve an objective. This is the case of so many applications rangingfrom engineering to life sciences. For that reason, covering classical prerequisitein analysis and control areas, we have devoted the book to theextension of the classical distributed parameter results to regional ones.Students of mathematics do not come into contacts with distributedparameter systems during their classes. They are introduced to themwhen they start research and often they are influenced by the knowledgeand the advice of experimented scientists. This was our case at the verybeginning of these research investigations in the mid 70’s. We would liketo express our special thanks to many of them and mainly late ProfessorAnthony J. Pritchard (University of Warwick, GB) and late Professor J.L. Lions (College de France) who were so encouraging in front of our determinationin driving an academic carrier. We also express our thanksto our co-workers and research students. We wish to acknowledge thefeedback from all those who took courses based on various parts of thisbook.This book may be used by graduate students in mathematics, engineering,physics, and even by students from other fields such as life orenvironmental sciences. This book may also be used as an informationvi Avant-propossource for researchers and education professionals. We assume that thereaders already know the basic concepts of analysis and control of distributedparameter systems.
https://hal.archives-ouvertes.fr/hal-01297261

ISBN : 978-2-35412-140-2
hal-01297261
https://hal.archives-ouvertes.fr/hal-01297261

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Large sand intrusions often exhibit conical morphologies analogous to magmatic intrusions such as saucer-shaped or cup-shaped sills. Whereas some physical processes may be similar, we show with scaled experiments that the formation of conical sand intrusions may be favoured by the pore-pressure gradients prevailing in the host rock before sand injection. Our experiments involve injecting air into a permeable and cohesive analogue material to produce hydraulic fractures while controlling the pore pressure field. We control the state of overpressure in the overburden by applying homogeneous basal pore pressure, and then adding a second local pore pressure field by injecting air via a central injector to initiate hydraulic fractures near the injection point. In experiments involving small vertical effective stresses (small overburden, or high pore fluid overpressure), the fracturing pressure (lambda(fract)) is supralithostatic and two dipping fractures are initiated at the injection point forming a conical structure. From theoretical considerations, we predict that high values of lambda(fract), are due to strong cohesion or high pore fluid overpressure distributed in the overburden. Such conditions are favoured by the pore pressure/stress coupling induced by both pore pressure fields. The dips of cones can be accounted for elastic-stress rotation occurring around the source. Contrary to magmatic chamber models, the aqueous fluid overpressure developed in a parent sandbody (and prevailing before the formation of injectites) may diffuse into the surrounding overburden, thus favouring stress rotation and the formation of inclined sheets far from the parent source. For experiments involving higher vertical effective stresses (thick overburden or low pore fluid overpressure), the fracturing pressure is lower than the lithostatic stress, and a single fracture is opened in mode I which then grows vertically. At a critical depth, the fracture separates into two dilatant branches forming a flat cone. We make use of a P.I.V. (Particle Imaging Velocimetiy) technique to analyse plastic deformation, showing that these inclined fractures are opened in mixed modes. Close to the surface, they change into steep shear bands where fluids can infiltrate. The final morphology of the fracture network is very similar to the common tripartite architecture of various injection complexes, indicating that different mechanisms may be involved in the formation of dykes. Feeder dykes under the sill zones may open as tensile fractures, while overlying dykes may be guided by the deformation induced by the growth of sills. These deformation conditions may also favour the formation of fluid escape structures and pockmarks. (C) 2011 Elsevier B.V. All rights reserved.
ISSN: 0012-821X

hal-00745640
https://hal.archives-ouvertes.fr/hal-00745640
DOI : 10.1016/j.epsl.2011.10.029