Éditeur(s) : Gauthier-Villars
Résumé : The three main sources of organic matter in oceanic basins are marine plankton, terrestrial higher plants and undifferentiated residual organic matter which has been highly degraded in subaerial environments. The time and areal distribution of marine organic matter is mainly controlled by the conditions of preservation. In deep oceans accumulation occurs mainly in confined anoxic basins, and also in open ocean, where local conditions generate a surplus of supply over bacterial degradation. Moderately degraded terrestrial organic matter is derived from land plants and carried away by rivers and currents. It is mainly deposited in sediments of the river fans. Residual organic matter has been highly degraded in subaerial conditions prior to transportation, and may consist of contemporaneous and/or recycled material. It cannot be degraded any more and may be spread over wide areas, regardless of the local environments.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1981

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00246/35680/34188.pdf
http://archimer.ifremer.fr/doc/00246/35680/

Éditeur(s) : Société Nationale de Protection de la Nature
Résumé : Monitoring of French Polynesia coral reefs and their recent development.-French Polynesia, consisting of 118 islands in the centre of the Pacific Ocean, has more than 15 000 km(2) of reefs and lagoons managed by the local government. Tourism and pearl culture are the two main economic resources of the country. Polynesian coral reefs are extremely diverse and are among those for which we have thorough knowledge. The exploitation of local resources has been recorded for multiple decades and includes : coral materials, fishing, harvest and export of mother-of-pearl molluscs, pearl production, and ornamental fish. All over the country, many monitoring programmes have been launched to measure the health of reefs and the natural and anthropogenic perturbations that they suffer : hurricanes and seismic events, water quality, health of benthic and fish communities, pearl oyster pathology and radiobiology. These data, collected over the last few decades, allowed to define the relative importance of natural and anthropogenic degradation on reefs and lagoons, and to explain the present status of reefs at different spatial scales. Devastating hurricanes are rare (1903-1906, 1982-1983 and occasionally at other times), but they may annihilate outer slope coral communities on some islands. Bleaching events with considerable coral mortality at different geographical scales occurred mainly in 1991, 1994 and 2003. Outbreaks of Acanthaster destroyed numerous reefs (lagoons and outer slopes) from 1978-1982 and a new demographic wave began in 2006 at many Society islands. Eutrophication events only occurred occasionally and only in some lagoons. Whereas natural catastrophic events degrade the coral reef ecosystem across many islands, at the archipelago or even regional scale, anthropogenic degradation is limited to a few Society Islands, occurring rarely on atolls and not at all on those (one third) which are uninhabited. The main causes of reef degradation in some areas of Tahiti and Moorea include the embankment of fringing zones, coral mining, overfishing, absence of urban sewage treatment and the development of leisure and tourism activities. Because of its large geographical extent, one may conclude that major reef degradation in French Polynesia is caused by catastrophic natural events. On the other hand, anthropogenic degradation is more localized. Unfortunately, the synergistic effects of these causes of degradation prevent reefs from recovering. Optimum coral cover on French Polynesian outer reef slopes is between 50-60%. After a major destructive impact (hurricane, bleaching, Acanthaster) a reef is reduced to less than 10% coral cover, however if no more major disturbance events occur a reef will recover in about 12 years. Most of the 15 000 km(2) of reefs and lagoons in French Polynesia are in good health, and along with their neighbouring reefs in East and Central Pacific they are considered as the least degraded reefs worldwide and at a low risk of becoming degraded in the few next decades. However, we are more and more anxious about the future of reefs in the world particularly because present simulations predict that major impacts of climate change would include : elevation of sea surface temperatures, increase in the strength of hurricanes and acidification of seawater which will affect the formation of coral structures.
La Polynésie française, 118 îles au coeur du Pacifique, possède une surface de plus de 15 000 km2 de récifs et lagons gérés par le gouvernement polynésien. Le tourisme et la perliculture représentent les deux ressources économiques majeures du Pays. Les formations récifales très diversifiées sont parmi les mieux connues. Plusieurs suivis d'exploitation des ressources sont opérationnels depuis des décennies : granulats coralliens, pêche pour l'alimentation, collecte et exportation de mollusques nacriers, production de perles, poissons d'ornement. À l'échelle du Pays de très nombreux programmes de surveillance de l'état des récifs et des perturbations qu'ils subissent, naturelles et anthropiques, ont été mis en place : perturbations cycloniques et sismiques, qualité des eaux, état de santé des peuplements benthiques et ichtyologiques, pathologie des nacres, radiobiologie. Toutes ces données recueillies au fi l des décennies ont permis d'établir l'importance relative des dégradations naturelles et anthropiques sur les récifs et lagons polynésiens et d'expliquer leur état de santé actuel en considérant différentes échelles spatiales. Les périodes cycloniques dévastatrices pour les récifs sont rares (1903-1906, 1982-1983 et épisodiquement) mais les cyclones ont parfois anéanti les communautés coralliennes de pentes externes dans certaines îles. Les blanchissements suivis de mortalités importantes à des échelles spatiales diverses, ont été surtout ceux de 1991, 1994 et 2003. Les explosions démographiques d'Acanthaster ont détruit de nombreux récifs (lagons et pentes externes) en 1978-1982 et une nouvelle pullulation s'amplifie depuis 2006 dans plusieurs îles de la Société. Les crises dystrophiques n'ont perturbé qu'épisodiquement certains lagons. [...]
Revue d'Ecologie de la Terre et de la Vie (0249-7395) (Société Nationale de Protection de la Nature), 2008 , Vol. 63 , N. 1-2 , P. 145-177

Droits : 2008 Société Nationale de Protection de la Nature
http://archimer.ifremer.fr/doc/2008/publication-4558.pdf
http://archimer.ifremer.fr/doc/00000/4558/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Well-dispersed iron oxide nanoparticles supported onto graphene oxide sheets (i.e. GO-Fe3O4 nanocomposite) were synthesised and used as heterogeneous Fenton-like catalyst for the degradation of Acid Orange 7 dye (AO7). The reaction was systematically investigated under various experimental conditions such as nanocomposite dosage, pH, temperature, oxidant and dye concentrations. Best results showed a fast 80% degradation in ∼20 min, whilst ∼98% of AO7 was successfully removed after 180 min of reaction time. The degradation kinetics of AO7 was most influenced by pH and temperature, and can be described by a pseudo-first-order reaction following the Langmuir-Hinshelwood mechanism. Analysis of the spent nanocomposite suggested that the phase of iron oxide nanoparticles remained unchanged whilst minor pore volume losses occurred via carbon deposition and/or re-stacking of GO sheets. © 2014 Elsevier Ltd.
ISSN: 2213-3437

hal-01683206
https://hal.univ-antilles.fr/hal-01683206
DOI : 10.1016/j.jece.2014.08.001

Éditeur(s) : HAL CCSD American Physical Society
Résumé : International audience
This is the first of two papers investigating the mechanical response of cemented granular materials by means of contact dynamics simulations. In this paper, a two-dimensional polydisperse sample with high-void ratio is constructed and then sheared in a simple shear numerical device at different confinement levels. We study the macroscopic response of the material in terms of mean and deviatoric stresses and strains. We show that the introduction of a local force scale, i.e., the tensile strength of the cemented bonds, causes the material to behave in a rigid-plastic fashion, so that a yield surface can be easily determined. This yield surface has a concave-down shape in the mean: deviatoric stress plane and it approaches a straight line, i.e., a Coulomb strength envelope, in the limit of a very dense granular material. Beyond yielding, the cemented structure gradually degrades until the material eventually behaves as a cohesionless granular material. Strain localization is also investigated, showing that the strains concentrate in a shear band whose thickness increases with the confining stress. The void ratio inside the shear band at the steady state is shown to be a material property that depends only on contact parameters.
ISSN: 1539-3755

hal-00523453
https://hal.archives-ouvertes.fr/hal-00523453
DOI : 10.1103/PhysRevE.82.011303

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : French Polynesia started it's Fish Aggregating Device programme in June 1981 with the positioning of the first buoy offshore of the main island of Tahiti. Since then, 251 structures have been installed throughout the 5 archipelagoes of this French overseas territory. The shape and size of the devices have evolved 8 times over this period, however, a single model has not yet been adopted. Trials are currently underway using lighter structures similar to those found in the Indian Ocean. The anchoring lines have progressively been modified through better knowledge of material and product availability, as well as better understanding of environmental constraints. The programme is entirely financed by the territorial government and managed by the public sector. This ongoing technical assistance, aimed towards the local small-scale coastal fishery, is considered an important factor to maintaining this activity alive. Up until 1997, this economical support policy of outer island populations far from the metropolis central town, along with incidental fishing methods around FADs, have given mitigated results without nevertheless putting into cause this programme. The use of 'drifting handlines' retained at the surface by small indicator floats are one of the contributing factors to the degradation of the anchor lines. It is now commonly accepted that a new fishing strategy must be adopted so that professional coastal fishermen become more aware with regards to an expensive work tool due to local bathymetric conditions, so that fishing effort is increased through the development of better adapted fishing techniques, and finally so that community spirit rules over individualism.Original Abstract: Le programme d'ancrage de DCP en Polynesie francaise a vu le jour en juin 1981 avec l'implantation d'un premier dispositif au large des cotes de Tahiti. Depuis cette date, ce sont 251 structures qui ont ete installees dans les cinq archipels de ce pays d'outre-mer. La forme et la taille des bouees ont evolue huit fois sans etre definitivement arretees a un seul modele et des essais sur des structures legeres de type " Ocean Indien " sont en cours. Les lignes d'ancrage ont fait l'objet de modifications progressives en raison de meilleures connaissances des produits ainsi que des contraintes du milieu environnant. Ce programme est finance en totalite par le territoire de la Polynesie francaise et gere par le secteur public. Il s'adresse a la pecherie artisanale et cotiere qui considere depuis de nombreuses annees cette assistance technique comme un atout indispensable au maintien de son activite. La politique d'engagement de ce soutien economique jusqu'en 1997 aupres des populations d'iles et atolls tres eloignes de la capitale ainsi que l'incidence de la technique de peche la plus repandue autour des DCP ont abouti a des resultats mitiges sans pour autant remettre en cause ce programme. En effet, les lignes a main derivantes et retenues en surface par une petite bouee temoin sont un des principaux facteurs de degradation des lignes d'ancrage. Il est desormais reconnu par tous les intervenants qu'une nouvelle strategie doit etre deployee afin que les pecheurs cotiers professionnels soient mieux responsabilises face a un outil de travail onereux en raison de la bathymetrie environnante, pour que l'effort de peche soit accru par l'utilisation de techniques de peche mieux adaptees, et enfin que l'esprit communautaire prime sur l'individualisme.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15292/12649.pdf
http://archimer.ifremer.fr/doc/00042/15292/

Éditeur(s) : HAL CCSD Elsevier
Résumé : Une approche par datations multiples a été menée sur les dépôts de sédiments de crue retrouvés dans les gorges du Gardon (Languedoc). Le plomb-210, le césium-137 et l’analyse géochimique des sédiments contaminés par les mines ont été utilisés pour reconstruire l’histoire des dépôts de crue. Cette approche a été combinée avec l’historique des crues du Gardon depuis 1890 pour affiner l’approche géochronologique. Au niveau de la cavité GG et de la terrasse GE les analyses ont permis d’illustrer les mécanismes d’érosion-redéposition pouvant perturber les séquences de sédiments. Les enregistrements des dépôts de sédiments de crue sont complets sur la terrasse GE située à 10 m au-dessus du lit mineur à partir de 1958, et incomplets auparavant. Sur la période 1880-1958, 25 crues ont eu un débit suffisant (>1450 m3/s) pour recouvrir la terrasse, alors que l’on recense seulement 5 à 6 crues depuis 1958 (pour un débit de submersion supérieur à 1700 m3/s). L’augmentation progressive du débit de submersion et la fréquence moindre d’inondation de la terrasse ont pu permettre sur la période récente la stabilisation de la couche de surface par la végétation et limiter l’érosion lors de crues importantes. Les enregistrements semblent complets dans la cavité GG située à 15 m au-dessus du lit mineur. La fréquence moindre de submersion à ce niveau plus élevé peut expliquer une meilleure stabilisation des dépôts de crue, rendus moins vulnérables à l’érosion. La datation au radiocarbone a été testée même si elle ne permet pas de dater avec précision les dépôts de crue des derniers siècles. Sur la terrasse GE, 80% des dates au carbone 14 sur charbon de bois sont beaucoup trop vieilles par rapport aux autres techniques de datation, ce qui peut s’expliquer par une remobilisation/déstockage de charbons de bois anciens. Les datations radiocarbone sur graines donnent de meilleurs résultats, car issues d’une production annuelle, plus facilement décomposable et moins sujette à des dépôts intermédiaires. Au final, il apparaît que la technique de datation par radiocarbone sur des charbons de bois retrouvés dans les séquences sédimentaires n’est pas fiable, alors qu’elle est la plus pratiquée en paléo-hydrologie. L’utilisation combinée du plomb-210, du césium-137, de l’analyse géochimique des sédiments et des informations sur les crues historiques a permis de discriminer et de dater les différents dépôts de crue de ce dernier siècle dans la cavité GG et la terrasse GE. / A multidating approach was carried out on slackwater flood deposits, preserved in valley side rock cave and terrace, of the Gardon River in Languedoc, southeast France. Lead-210, caesium-137, and geochemical analysis of mining-contaminated slackwater flood sediments have been used to reconstruct the history of these flood deposits. These age controls were combined with the continuous record of Gardon flow since 1890, and the combined records were then used to assign ages to slackwater deposits. The stratigraphic records of terrace GE and cave GG were excellent examples to illustrate the effects of erosion/preservation in a context of a progressively self-censoring, vertically accreting sequence. The sedimentary flood record of the terrace GE located at 10 m above the channel bed is complete for years post-1958 but incomplete before. During the 78-year period 1880-1958, 25 floods of a sufficient magnitude (> 1450 m3/s) have covered the terrace. Since 1958, however, the frequency of inundation of the deposits has been lower:only 5 or 6 floods in 52 years have been large enough to exceed the necessary threshold discharge (> 1700 m3/s). The progressive increase of threshold discharge and the reduced frequency of inundation at the terrace could allow stabilisation of the vegetation cover and improved protection against erosion from subsequent large magnitude flood events. The sedimentary flood record seems complete for cave GG located at 15 m above the channel bed. Here, the low frequency of events would have enabled a high degree of stabilisation of the sedimentary flood record, rendering the deposits less susceptible to erosion. Radiocarbon dating are used in this study and compared to the other dating techniques.Eighty percent of radiocarbon dates on charcoals were considerably older than those obtained by the other techniques in the terrace. On the other hand, radiocarbon dating on seeds provided better results. This discrepancy between radiocarbon dates on charcoal and seeds is explained by the nature of the dated material (permanent wood vs. annual production and resistance to degradation process). Finally, we showed in this study that although the most common dating technique used in paleoflood hydrology is radiocarbon dating, usually on charcoal preserved within slackwater flood sediments, this method did not permitus to define a coherent age model. Only the combined use of lead-210, caesium-137, and geochemical analysis of mining-contaminated sediments with the instrumental flood record can be applied to discriminate and date the recent slackwater deposits of the terrace GE and cave GG.
ISSN: 0169-555X

hal-01059669
https://hal.archives-ouvertes.fr/hal-01059669
https://hal.archives-ouvertes.fr/hal-01059669/document
https://hal.archives-ouvertes.fr/hal-01059669/file/ly2014-pub00040953.pdf
IRSTEA : PUB00040953

Éditeur(s) : HAL CCSD Springer International Publishing
Résumé : The intensive farming practices that have been developed over the past 60 years are based mainly on the use of chemical inputs such as fertilisers and pesticides, mechanical tillage and monoculture. The limitations of these methods are now clear: long-term degradation of soil fertility, impacts on the environment and human health, high consumption of fossil fuels, low efficiency of inputs and threats to food security in a context of climate change. Would farming practices that rely on the activation of ecological processes be an alternative to achieve a balance between high productivity and environmental preservation? While many studies suggest a positive relationship between soil biodiversity and ecosystem services, there is considerable debate on the form such agricultural systems should take. This study reviewed the state of current knowledge and identified aspects requiring further research to achieve the aim of sustainable intensification of agriculture. The following major points emerged: 1) Most studies focused on the evaluation of individual practices. However, changes in farmers’ cropping practices to take advantage of soil biodiversity services would need to manage not only the interactions between various practices but also the trade-off between the technical and socio economic constraints of cropping systems. Advances in agricultural system design approaches may help to ensure appropriate trade-offs. 2) More attention should be given to drawing on knowledge from different sources: laboratory studies focusing on the ecological functions of soil biodiversity, experimental surveys on farmers’ fields to rank the farming practices and processes to be included in site-specific models, and on- station experiments to test hypotheses and acquire additional reference material. 3) Whereas advances in technical and scientific knowledge provide an increasing number of relevant indicators for characterizing biodiversity and ecological functions, studies are rarely targeted at the development of indicators that are accessible to farmers or their technical advisors. The lack of indicators accessible to grassroots players for evaluating the impacts of their decisions on soil biodiversity remains a serious obstacle to the development of innovative agro-ecological systems.
Sustainable Agriculture Reviews 14

ISBN : 978-3-319-06015-6
hal-01268743
https://hal.archives-ouvertes.fr/hal-01268743
DOI : 10.1007/978-3-319-06016-3_5
PRODINRA : 270786

Éditeur(s) : Université de la Rochelle
Résumé : In order to better understand the functioning of the Brouage intertidal mudflat (Marennes- Oléron Basin, France), its carbon-based trophic web has been modelled and analyzed. The foodweb building is based on the 4 step method of Inverse Analysis: 1) conceive an a priori model as the graph of compartments (nodes) between which exist fluxes of material (vertices). These vertices are the unknowns for the problem; 2) gather all the existing knowledge about the ecosystem and translate it into linear equations and inequalities involving the fluxes; 3) complete this set of data by common knowledge on the behaviour of the compartments and translate it into inequalities, 4) solve the obtained linear system under the parsimony principle to find a unique solution vector. The food-web analysis is based on. The first purpose of this work was a methodological one: inverse analysis method has been adapted to consider the seasonal and spatial variability of the temperate ecosystem: two seasons have been coupled in the computation and the area has been divided into three geographical zones along a cross-shore gradient. Hence, two types of physical exchanges are involved: the benthicpelagic ones and the advection ones. Statistical results can also be obtained by coupling Monte Carlo methods to Inverse Analysis. To study the obtained networks, new indices based on Markov Chains take delay into account in describing integrative transfers of material between compartments. This lets emerge the systems' properties that are not obvious at first sight and emphasizes the role of peculiar components. The second purpose was to apply such methods to the Brouage mudflat ecosystem in order to better understand its functioning. As the knowledge and methods evolve, various food webs were computed and analyzed with the help such indices and existing ones. Sensitivity analyses allow to point at the most crucial lacks of knowledge, which can orientate future field research. New data would improve the quality of the model in two ways: one the one hand, they would validate or invalidate the outcomes and on the other hand, they would give useful information to better constrain some of the black boxes and most uncertain fluxes, especially the advection and vertical flows. The main results of the study show a strongly seasonal system in which benthic and pelagic components are linked with intensity. The system is driven by its high local benthic primary production, but also depends on imports from the basin. Each of the 3 geographic zones has a peculiar functioning. The central zone corresponds to the classical description of European intertidal mudflats: very productive, it can feed the other regions. It is a production zone. The upper part is less productive but is fed by the middle one via the water column and can be exploited by shorebirds. It is a degradation zone (material is transformed for less qualitative). The lower part strongly depends on the basin imports for its functioning, as the cultivated bivalves act as a pump for pelagic material of which a great part is deposited under the cultivation structures (oyster racks or mussels "bouchots"). It is a transformation zone.
Un double objectif (méthodologique et appliqué) a été visé par une modélisation du réseau trophique de la vasière de Brouage (Bassin de Marennes Oléron, France) à l'aide de l'analyse inverse, et son étude à l'aide de l'analyse des réseaux. L'Analyse Inverse permet en effet de reconstruire l'ensemble du réseau à partir de données éparses, le problème du manque de données étant récurrent en Ecologie. Au plan méthodologique, l'analyse inverse a été adaptée à la prise en compte des caractères saisonnier et spatialement hétérogène d'un écosystème tempéré de zone intertidale : deux saisons ont ainsi été couplées et la vasière a été considérée le long d'un transect perpendiculaire au rivage et divisé en trois zones spatiales. Deux types de flux physiques interviennent donc : les flux verticaux de dépôt et remise en suspension, et les flux d'advection via la colonne d'eau. Des pistes d'amélioration et de nouvelles méthodes sont proposées. Un résultat sous forme statistique peut être obtenu en couplant l'utilisation de méthodes de Monte Carlo à l'analyse inverse pour la construction des réseaux trophiques. Les moyens d'étude des modèles ont été enrichis par la mise au point d'indices issus de la construction de chaînes de Markov et prenant en compte le caractère temporel des transferts de matière entre compartiments. Enfin, la transformation mathématique du modèle statique pour une étude dynamique de la stabilité de l'équilibre décrit est abordée. Plusieurs modèles ont été construits au cours de l'évolution des méthodes et de l'acquisition de connaissances sur le site. Des méthodes d'analyses existantes et d'autres mises au point dans le cadre de cet ouvrage ont été appliquées aux réseaux obtenus afin de faire émerger les propriétés du fonctionnement de la vasière et de souligner le rôle de certains compartiments. Des analyses de sensibilité permettent d'évaluer la robustesse des résultats et d'orienter les recherches futures en mettant en évidence les manques les plus cruciaux. Des données supplémentaires, notamment concernant les foraminifères benthiques, le zooplancton ou les mouvements verticaux du microphytobenthos permettront de fournir de meilleures contraintes et de valider (ou non) les résultats obtenus. Les principaux résultats montrent un système au fort caractère saisonnier dont les compartiments benthiques et pélagiques sont très liés. La production primaire benthique locale est un moteur important, mais qui ne suffirait pas à suppléer l'indispensable importation de matériel détritique. Le découpage de la vasière en trois zones fait apparaître les particularités de chacune. La zone centrale correspond à la description classique des « vasières intertidales européennes » : très productive, elle peut alimenter les autres régions. C'est une zone de production et d'exportation. La partie supérieure est moins productive et reçoit de la matière de la zone de milieu d'estran via la colonne d'eau. Sa production secondaire peut alors être exploitée par les limicoles, nombreux en hiver. C'est une zone de dégradation et d'exportation. Le bas d'estran dépend fortement des importations extérieures, « pompées » par les bivalves cultivés qui sont ainsi directement responsables d'une forte sédimentation sous les structures mytilicoles et ostréicoles. C'est une zone de transformation.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2005/these-2260.pdf
http://archimer.ifremer.fr/doc/00000/2260/

Éditeur(s) : HAL CCSD Lavoisier
Résumé : International audience
Afin de réduire la consommation d'énergie électrique liée à l'utilisation intense de la climatisation dans les logements des régions tropicales de la Caraïbe, des matériaux composites fibres végétales/ciment ont été préparés en vue d'être utilisés dans le domaine de la construction. Les fibres de dictame (Maranta arundinacée), résidus de l'extraction de la farine de dictame, sont étudiées. Dans cet article, une première partie sera consacrée à la détermination des dimensions des particules et de la composition chimique des fibres de dictame brutes, à l'étude des évolutions structurales et de texture des fibres après leur pyrolyse (200 - 700°C). Puis le travail sur la prise des composites fibres de dictame/ciment sera mené. En particulier, l'influence de paramètres tels que la teneur en fibres, la teneur en eau et la température de pyrolyse des fibres de dictame sera abordée. Par ailleurs les chaleurs dégagées lors de la dégradation thermique des composites sont également déterminées.
ISSN: 1169-7954

hal-00809828
https://hal.univ-antilles.fr/hal-00809828
DOI : 10.3166/rcma.17.327-350

Éditeur(s) : HAL CCSD
Résumé : The geological storage of CO 2 is considered as one of the solutions to the problem of global warming. The most possible scenarios of geological behavior of soil in the long term conditions has to be precisely defined to avoid catastrophic damages in the future. Chemical properties of saline water in the aquifer after the CO 2 injection becomes more acidic with time. Therefore, chemical degradation of rock occurs, which leads to modifications of its mechanical properties (chemo-mechanical coupling) [1]. In this paper an incremental model of chemo-mechanical coupling using homogenization approach (asymptotic expansion method [2,3]) is proposed. The paper is focused on the numerical computations for the X-ray tomography image of carbonate rock microstructure [4]. The chemical degradation of the microstructure is obtained as a homogeneous dissolution in each direction (Fig.1. – Fig.2.) For every porosity state numerical computations to obtain full, orthotropic elasticity tensor are performed. Therefore, the degradations functions for all components of the rigidity tensor were defined (Fig.3.). Moreover, results of numerical calculations of diffusion, tortuosity and permeability tensors are presented [5,6]. The link between geometrical properties and mechanical and transport parameters are discussed. The numerical analysis of the carbonate rock sample in long term conditions shows the increase of porosity and associated mechanical weakening of the rock. Moreover, the increase of diffusion, tortuosity and permeability tensors elements with time were observed. Finally, the solution of the one-dimensional macroscopic problem of soil settlement due to chemical dissolution of rock at constant load is presented. The method is universal, in the sense that the non-dimensional time scale is used.
ALERT Workshop 2013
Aussois, France

hal-01103175
https://hal.archives-ouvertes.fr/hal-01103175

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The paper is motivated by the long term safety analysis of the CO 2 geological storage. We present a methodology for the assessment of the ge-omechanical impact of progressive rock dissolution. The method is based on the use of X-ray tomography and the numerical dissolution technique. The influence of evolution of the microstructure on the macroscopic properties of the rock is analysed by using periodic homogenization method. The numerical computations show progressive degradation of all components of the stiffness (orthotropic) tensor. Moreover, the evolution of associated mass transfer properties (as tortuosity and conductivity tensors), by using the periodic homogenization method, is also calculated. The correlation between the mechanical parameters and the transfer properties during the dissolution pro-cess is presented. The results show that the highest increase of the hydraulic conductivity (in direction Y) is not associated with the highest decrease of Young modulus in this direction. Moreover, the highest decrease of Young modulus (in the direction X) is not associated with percolation in this direction. Finally, an incremental law to calculate settlement, in case of a rock with evolving microstructure, is proposed. The solution of the macroscopic settlement problem under constant stress and drained conditions showed that the geomechanical effects of the rock dissolution are rather limited.
ISSN: 0363-9061

hal-01104204
https://hal.archives-ouvertes.fr/hal-01104204
https://hal.archives-ouvertes.fr/hal-01104204/document
https://hal.archives-ouvertes.fr/hal-01104204/file/Numerical_computations_rock_dissolution_Wojtacki_al_2014.pdf
DOI : 10.1002/nag.2316

Éditeur(s) : HAL CCSD
Résumé : International audience
The carbon capture and storage is considered as one of the solutions of reducing the effects of global warming. It consists in injecting large quantities of CO 2 in supercritical form directly into deeply located geological formations. One of the methods involves sequestration in the carbonate sedimentary rocks (sandstones and limestones) which are considered as a promising solution. The morphology of the pore network and solid skeleton defines important macroscopic prop-erties of the rock (permeability, stiffness). Modelling at micro scale of random heterogeneous materials (porous media) should be based on morphological and statistical characterisation 1,2 of the investigated microstructure. The work is focused on a reconstruction method by grains deposit 3 , for various range of pa-rameters, to obtain equivalent model of natural rock samples (oolitic limestone and fontainebleau sandstone). Generated samples satisfy morphological and statistical informations 4 which were obtained by 3D image analysis of X-ray tomography of the natural rock samples. For validation of the modelling numerical computations of mechanical and transfer properties are also provided.
14th European Mechanics of Materials Conference - EMMC14
Gothembourg, Sweden

hal-01103163
https://hal.archives-ouvertes.fr/hal-01103163

Éditeur(s) : Gauthier-Villars
Résumé : The analysis of humic compounds by elemental analysis, PY-GC-MS and HPLC techniques permitted determination of the origin of organic inputs, essentially terrestrial, and the effects of environmental conditions in the deposits along a north-south transect through the Rhone delta, from the river mouth to the open sea. In the prodelta the sedimentation of fine particles enriches the sediments in organic matter. The humic compound contents were relatively low in sediments, perhaps due to a rapid burying of organic matter which leads to anoxic conditions. In sediments fulvic acids are more abundant than humic acids. Elemental analysis indicated that fulvic acids were enriched in hydrogen and nitrogen as compared to humic acids. Furthermore, H/C and N/C ratios increased in the fulvic and humic acids towards the open sea, related to a more marine character. Pyrolysis analysis showed some differences between the chemical composition of fulvic acids which correspond to low molecular weights enriched in carbohydrates, and that of humic acids, high molecular weight compounds which are enriched in phenols and aromatic hydrocarbons. The pyrolysis-derived phenols were abundant near the river mouth, decreasing towards the open sea as nitrogen-containing-compounds increased. Near the river mouth, the abundance of phenolic aldehydes demonstrated by HPLC emphasized the existence of fresh organic matter. On the other hand, off the mouth, an increase in phenolic acids could indicate a more degraded organic material. The fractionation of humic acids in various classes of molecular weight species using ultrafiltration (Amicon membranes) and their analysis showed that, close to the river mouth, the large proportion of the high molecular weight humic compounds observed was enriched in phenols and carbohydrates, probably inherited from the terrestrial ligno-cellulosic complex. This process seemed to be superimposed on the increase of molecular weights which is usually observed as the environment becomes purely marine. These humic compounds would derived either from organic matter from terrestrial soils swept along by the river flow, after deposition on its bed or, more probably, from high molecular weight compounds which, associated with the mineral phase, flocculated when reaching the fluvio-marine front. Generally, the low molecular weight fractions were enriched in hydrogen and nitrogen. Near the river mouth, nitrogen-containing compounds were concentrated in the low molecular weight classes which correspond to organic molecules regarded as humic precursors. Off the mouth, they were incorporated into the high molecular weight complexes, certainly of marine origin.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 1 , P. 61-74

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00101/21187/18804.pdf
http://archimer.ifremer.fr/doc/00101/21187/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Four fibers from banana-trees (leaf, trunk) and coconut-tree (husk, fabric) were examined before their incorporation in cementitious matrices, in order to prepare insulating material for construction. Their botanical compositions have been determined following a method described previously. Thermal degradation of these fibers were studied between 200 and 700 °C under nitrogen gas flow. Temperature of pyrolysis was the experimental parameter investigated. The solid residues obtained were analyzed by classical elemental analysis, Fourier Transform Infra Red (FTIR) spectroscopy and were observed by Scanning Electron Microscopy (SEM). This study has shown (1) the relation between botanical, chemical composition with both localization of fibers in the tree and type of tree; (2) the rapid and preferential decomposition of banana fibers with increasing temperature of pyrolysis and (3) the rough samples are made of hollow fibers.
ISSN: 0960-8524

hal-00809780
https://hal.univ-antilles.fr/hal-00809780
DOI : 10.1016/j.biortech.2005.11.030

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The present work is concerned with the study of the tribological properties of various fluorinated carbon phases obtained at room temperature and then post-treated under fluorine atmosphere at different temperatures. The tribological tests evidence good intrinsic properties for all the compounds (friction coefficient in the range 0.07-0.09). Differences appear after few cycles. Friction measurements after 100 cycles and complementary Raman analyses of the tribofilm remaining in the wear scar point out that long term tribologic properties of the fluorinated compounds strongly depend on the evolution undergone by the materials under friction. The release of HF molecules, the loss of fluorine and partial rebuilding of graphitic phases are at the origin of the degradation of the friction properties. The good properties of the compounds post-treated at temperature in the range 150-300 °C are attributed to the chemical and structural stability of these compounds under friction.
ISSN: 0022-3697

hal-00756133
https://hal.archives-ouvertes.fr/hal-00756133
https://hal.archives-ouvertes.fr/hal-00756133/document
https://hal.archives-ouvertes.fr/hal-00756133/file/Delbe_6346.pdf
DOI : 10.1016/j.jpcs.2006.01.084

Éditeur(s) : HAL CCSD
Résumé : International audience
Abstract View references (38)This work presents a facile, scalable method for the fabrication of graphene oxide-iron oxide (GO-Fe3O4) nanocomposites produced by co-precipitation of iron ions onto the GO surfaces in basic aqueous media. FTIR and XRD characterisation suggests that Fe3O4 was chemically anchored to the GO sheets, possibly via the carboxyl and hydroxyl groups. Small GO loadings of 0.5 and 1 wt% were not sufficient to alter the Fe3O4 structures. However, increasing the GO loading to 5 and 10 wt% resulted in significant loss in pore volume, thus suggesting the lamellar GO sheets decorated with Fe3O4 were assembling into GO-Fe3O4 nanocomposite stacks. It was found that the GO-Fe3O4 nanocomposites had an enhanced catalytic activity in the heterogeneous Fenton-like oxidation of Acid Orange 7 (AO7) compared to pure GO flat sheets and Fe3O4 nanoparticles. Interestingly, the GO-Fe3O4 nanocomposite with 5 wt% loading ratio exhibited the best catalytic activity with 76% degradation of AO7 dye observed within 90 min of reaction. This was attributed to the synergistic effect of GO by enriching the adsorbed AO7 molecules onto the nanocomposite to be further oxidised in the vicinities of active sites. This finding suggests the promising employment of GO-Fe3O4 nanocomposites in removing organic dyes from polluted water by heterogeneous Fenton-like reaction. © 2014 by American Scientific Publishers.
SCIENCE OF ADVANCED MATERIALS

hal-01683207
https://hal.univ-antilles.fr/hal-01683207
DOI : 10.1166/sam.2014.1812

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Thermogravimetric results on the thermal degradation of isolated components extracted from shells of tropical fruit stones and seeds allowed us to establish the dependence of the yield of char obtained by high-temperature pyrolysis (600-900 °C) of lignocellulosic raw materials on the content of components in precursors...
ISSN: 1387-1811

hal-00809743
https://hal.univ-antilles.fr/hal-00809743
DOI : 10.1016/S1387-1811(03)00288-9

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : Ce numéro de la Revue Études Caribéennes s’intéresse aux liens qui unissent et opposent l’activité touristique et les ressources naturelles, particulièrement dans les pays du Sud. Dans un contexte de médiatisation accrue des enjeux liés à la biodiversité et aux menaces qui pèsent sur elle, le tourisme – et particulièrement l’écotourisme – est souvent présenté comme un moyen de concilier la conservation et le développement. Les autorités locales, malgré l’existence d’un cadre réglementaire propre à l’environnement, ne disposent souvent pas de moyens suffisants (humains, matériels et financiers) pour gérer la croissance de la fréquentation des aires protégées et ses effets potentiels sur l’environnement naturel et humain. En réponse à cette problématique, les institutions financières internationales et les organismes associés proposent aux pays du Sud de trouver un équilibre entre une fréquentation de masse et une fréquentation de bas volume afin de développer « un tourisme de haute qualité ». Même si cela était possible, quels critères peuvent être utilisés pour « cesser » le développement d’un pôle ou d’une région touristique ? L’évolution géographique « naturelle » du tourisme – c’est-à-dire essentiellement basée sur la mise en tourisme de la nature et sur l’accessibilité de ces ressources – pose déjà des problèmes politiques et économiques importants. Les gouvernements (central, régional ou local) sont difficilement en mesure de réaliser un arbitrage de long terme dans ce contexte qui permettrait l’adéquation entre le développement touristique et la préservation des espaces naturels. La relation entre le tourisme et les ressources naturelles s’articule souvent autour de deux objectifs spécifiques, soient : développer un produit à moindre impact, mais aux dépenses élevées et viser un volume de visiteurs qui contribue aux profits économiques, mais qui amène le moins de dégradation écologique/sociale possible. Cette position résume à elle seule à la fois la complexité et les multiples paradoxes dans lesquels s’insère la mise en tourisme de la nature. Les dynamiques sociales et l’extension de l’appropriation privative des espaces naturels et agricoles posent la problématique des modes de gestion des ressources communes et de leur pérennité, particulièrement dans les pays du Sud. Dans ce contexte, les objectifs, les ressources et les stratégies des principaux acteurs concernés sont difficilement conciliables et le système de relation qu’il induit n’est pas nécessairement en phase avec les finalités poursuivies. This edition of Revue Etudes Caribéennes focuses on the links that unite and oppose tourism and natural resources, specifically in southern countries. In a context of increased media coverage of issues related to biodiversity (including threats to it), tourism – particularly ecotourism – is often presented as a mean to reconcile conservation and development. Local authorities, despite the existence of a specific environmental regulatory framework, often have insufficient resources (human, material, financial) to manage the increase of visits to protected areas, and the potential impact of these visits on natural and human environments. In response to this problem, international financial institutions and associated organizations offer to try to find a balance between mass attendance and low volume attendance in order to develop "high quality tourism" in southern countries. Even if this were possible, what criteria can be used to "stop" the development of a tourist site or region for environmental reasons? The “natural” geographic evolution of tourism – in other words, essentially based on the development of nature tourism and accessibility of these resources – already causes huge political and economic problems. Governments (central, regional or local) are hardly able to arbitrate over the long term in a context that would allow finding a balance between tourism development and preservation of natural areas. The relationship between tourism and natural resources often revolves around two specific objectives: to develop a product with less impact, but at high cost and a target volume of visitors that contributes to economic profits, but that causes the least ecological / social degradation possible. This position epitomizes both the complexity and the many paradoxes of nature tourism development. Social interactions and the expansion of private appropriation of natural and agricultural areas highlight the challenges of managing common resources and their sustainability, especially in the southern countries. In this context, development objectives, natural resources and the strategies of key stakeholders are difficult to reconcile, and the relationship between leading actors do not always correspond with these objectives. Esta edición de “Revue Études Caribéennes” se interesa a los lazos que unen y separan la actividad turística y los recursos naturales, particularmente en los países del sur. En un contexto de mediatización en alza sobre los objetivos ligados a la biodiversidad y a las amenazas que pesan sobre ella, el turismo – y particularmente el ecoturismo – está a menudo presentado como un medio de conciliar la conservación y el desarrollo. Las autoridades locales, pese a la existencia de un cuadro propio de reglamentación al medio ambiente, no disponen habitualmente de suficientes medios (humanos, materiales y financieros) para controlar el aumento de visitas en las áreas protegidas y sus efectos potenciales sobre el ambiente natural y humano. En respuesta a esta problemática, las instituciones financieras internacionales y los organismos asociados proponen a los países del sur encontrar un equilibrio entre la frecuentación de masas y una frecuentación de bajo volumen con el objetivo de desarrollar “un turismo de alta calidad”. Incluso si fuese posible, ¿qué criterios podrían ser utilizados para “cesar” el desarrollo de un centro o una región turística? La evolución geográfica “natural” del turismo – esencialmente basada en el desarrollo del turismo de la naturaleza y el acceso de sus recursos – crean problemas políticos y económicos enormes. Los gobiernos (central, regional o local) tienen dificultades para realizar un arbitraje a largo plazo en este contexto que permitiría la adecuación entre el desarrollo turístico y la preservación de los espacios naturales. La relación entre el turismo y los recursos naturales se articula a menudo alrededor de dos objetivos específicos, sean: desarrollar un producto con mínimo impacto, pero con gastos elevados y aspirar a un volumen de visitantes que contribuya a las ganancias económicas, pero que traiga la menor degradación ecológica/social posible. Esta posición resume la complejidad y las múltiples paradojas en las cuales se encaja la puesta del turismo en la naturaleza. Las dinámicas sociales y la extensión de la apropiación privativa de los espacios naturales y agrícolas plantean una problemática en los modos de gestión de los recursos comunes y de su perennidad, particularmente en los países del sur. En este contexto, los objetivos, los recursos y las estrategias de los principales actores concernidos son difícilmente conciliables y el sistema de relación que induce no es necesariamente en la misma fase con los objetivos perseguidos.

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.7884
http://journals.openedition.org/etudescaribeennes/7884

Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : International audience
This paper presents the effects of chemical and thermal treatments on the strength of vegetable fibers that were being considered as reinforcements in cementitious matrix composites for affordable housing. These include vegetable fibers extracted from banana trunks and sugar cane residues. The results suggested that pyrolysis increased the fiber strength, at least by a factor three. Acid attack generally degraded the strengths, while alkali attack had only a limited effect. Pyrolyzed banana leaves, coconut coir, and coconut sheaths fibers were also tested. The implications of the results were discussed for the development of strong cementitious matrix composites.
ISSN: 1042-6914

hal-00809827
https://hal.univ-antilles.fr/hal-00809827
DOI : 10.1080/10426910601063386

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Abstract View references (45)Graphene oxide-iron oxide (GO-Fe3O4) nanocomposites were synthesised by co-precipitating iron salts onto GO sheets in basic solution. The results showed that formation of two distinct structures was dependent upon the GO loading. The first structure corresponds to a low GO loading up to 10wt%, associated with the beneficial intercalation of GO within Fe3O4nanoparticles and resulting in higher surface area up to 409m2g-1. High GO loading beyond 10 wt% led to the aggregation of Fe3O4 nanoparticles and the undesirable stacking of GO sheets. The presence of strong interfacial interactions (Fe-O-C bonds) between both components at low GO loading lead to 20% higher degradation of Acid Orange 7 than the Fe3O4 nanoparticles in heterogeneous Fenton-like reaction. This behaviour was attributed to synergistic structural and functional effect of the combined GO and Fe3O4 nanoparticles.
ISSN: 2045-2322

hal-01683208
https://hal.univ-antilles.fr/hal-01683208
DOI : 10.1038/srep04594