Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We present a 2-D Contact Dynamics discrete element model for simulating initiation and motion of rock avalanches, integrating hillslope geometry, Mohr-Coulomb rock behavior, pore pressure before avalanche triggering, and avalanche trigger. Avalanche motion is modeled as a dense granular flow of dry frictional and cohesive particles. On the basis of granular physics and shear experiments, we review some of the theories for the unexpectedly long runout of rock avalanches. Different causes are evoked, according to the strength (strong or weak) of the slip surface relative to the bulk. "Mechanical fluidization'' and "acoustic fluidization'' theories state that agitation of rock particles reduces frictional strength, increasing runout. Conversely, granular mechanics suggests that, as "shear-strain'' rate increases, granular material becomes more agitated, more dissipative, and more resistant. Another theory states that dynamic fragmentation of clasts creates an isotropic pressure that drives longer runout. In contrast, granular mechanics suggests that fragmentation may induce fluidization and strengthening of the granular material, while particle size reduction (among others) induces weakening of the granular flow and enhances long runout. Runout is also enhanced for column-like rock masses collapsing from steep hillslopes. Long runout may also be linked to thermal weakening mechanisms at the slip surface (e.g., thermal pressurization, and shear melting), which may lower drastically the shear strength. The model is illustrated with a hypothetical example of a rain-triggered avalanche, mobilizing shallowly dipping layers. Several phases are identified, including slope failure, avalanche triggering resulting from slip weakening, and avalanche motion in which rocks are folded and sheared.
ISSN: 0148-0227

hal-00420883
https://hal.archives-ouvertes.fr/hal-00420883
DOI : 10.1029/2008JF001072

Éditeur(s) : Université Montpellier 2 - Sciences et Techniques du Languedoc
Résumé : The work reported here was motivated by the economical importance of the pacific blue shrimp Litopenaeus stylirostris farming where high mortality rates are due to bacterial and viral diseases. It consists in the characterisation of two original peptides, the first members of a new multifunctional family of peptides from peneide shrimps, the stylicines. Those two peptides, named stylicines 1 and 2, are negatively charged (pI < 6.0), and characterised by a proline-rich N-terminal region and a C-terminal region containing 13 cysteine residues. Stylicines are synthesized by heamocytes where they are stored within small cytoplasmic granules. To understand the role of these peptides in the immune response of shrimps to a vibrio infection, their recombinant forms were produced in E. coli BL21 (DE3) plysS, purified and characterised. The two rstylicines display biological anti-proliferative and blood clotting activities. Only rstylicine 1 displays antimicrobial activities: antifungal against Fusarium oxysporum (MIC<2.5μM) and bacteriostatic against Gram (−) bacteria, Vibrio sp. (MIC<80μM). Moreover this peptide displays an LPS-binding activity (dissociation constant (Kd) of 9.6×10−8 M) and agglutinate Vibrio. penaeicida "in vitro". Finally, the presence of sequences coding for modified forms of stylicine 1 in some shrimp’s genome may be in relation with their lower ability to survive infections.
Les travaux présentés dans ce mémoire ont été motivés par l’importance économique de l’élevage de la crevette bleue du pacifique Litopenaeus stylirostris dont les fortes mortalités sont principalement dues au développement de maladies bactériennes et virales. Ils ont consisté en la caractérisation des deux premiers membres d’une famille originale de peptides multifonctionnels présents chez les crevettes pénéides, les stylicines. Ces peptides, nommés stylicines 1 et 2, sont des peptides anioniques (pI < 6.0), formés d’une région amino-terminale riche en résidus de type proline et d’une région carboxyterminale riche de treize résidus cystéines. Ces molécules sont synthétisées et stockées dans de petits granules présents dans le cytoplasme des hémocytes. Pour mieux appréhender leurs rôles dans la réponse immunitaire des crevettes à une infection par des Vibrio, leurs formes recombinantes ont été produites dans E. coli BL21 (DE3) plysS, purifiées et caractérisées. Les deux rstylicines présentent des activités antiproliférative et anticoagulante. Seule la rstylicine1 présente des activités antimicrobiennes : antifongique sur Fusarium oxysporum (CMI<2.5 μM), et antibactérienne (bactériostatique) sur Vibrio sp (CMI<80 μM). Ce peptide est également capable de se lier aux LPS des bactéries à Gram (-) (Kd= 9.6x10-8 M) et d’agglutiner V. penaeicida "in vitro". Enfin, l’existence de gènes codant des formes modifiées de la stylicine1, chez certaines crevettes, pourrait être en relation avec une diminution de la résistante des individus aux infections.

Droits : 2010 The Author, Univ Montpellier 2
http://archimer.ifremer.fr/doc/00024/13558/10612.pdf
http://archimer.ifremer.fr/doc/00024/13558/

Éditeur(s) : HAL CCSD
Résumé : The present PhD thesis is devoted to the numerical simulation and analysis of shear on cohesive granular materials. In the framework of the Contact Dynamics method, we developed a model of cohesive bonding, which mimics cohesion by cementation. This model involves three contact strength parameters (a tensile strength, a coefficient of sliding friction, and a coefficient of rolling friction) as well as a local criterion, which controls the creation and the breaking of cohesive bonds. All contacts are cohesive at the beginning of the numerical simulations, and contact rupture leads to an irreversible loss of tensile strength (debonding). We varied systematically the three contact strength parameters and studied their influence on the shear strength, the dilatancy, and the microstructure of the granular media. Our results show that internal friction and macroscopic tensile strength have different origins at the contact scale. We also find that the microstructure of the granular media, when sheared at the steady state (also known as the `critical state"), is strongly affected by the local coefficients of sliding and rolling friction. In particular, the mechanical role of the weak network changes with these two contact parameters, which results from the formation of a new structure of force transmission. On the other hand, we also applied the same numerical simulation method to the simulation of landslides. We developed a methodology, which takes into account the initial morphology of the hillslope, the strength of geomaterials, and a triggering factor, integrating in the same model the initiation and propagation phases of the landslide. To illustrate this methodology, we applied it to the simulation of a hypothetical example of avalanche triggered by the progressive rise of a water table.
Ce travail de thèse porte sur la modélisation numérique et l'analyse du cisaillement dans les milieux granulaires cohésifs. Dans le cadre de la méthode de la Dynamique des Contacts, nous avons développé un modèle de cohésion qui cherche à imiter la cohésion par cimentation. Ce modèle fait intervenir trois paramètres de résistance au niveau des contacts (une résistance à la traction, un coefficient de frottement de glissement, et un coefficient de frottement de roulement) ainsi qu'un critère de création et de rupture des liens cohésifs. Les contacts sont cohésifs au début des simulations et leur rupture entraîne la perte irréversible de la résistance à la traction. Nous avons fait varier les trois paramètres microscopiques et nous avons étudié leur influence dans la résistance au cisaillement, la dilatance, et la microstructure du milieu. Nos résultats montrent que le frottement interne et l'adhésion macroscopiques ont des origines microscopiques différentes. Nous observons aussi que la microstructure du milieu cisaillé à l'état stationnaire (aussi connu comme ``l'état critique") est fortement affectée par l'angle de frottement et la résistance au roulement au niveau des contacts. En particulier, le rôle mécanique du réseau faible change avec ces deux paramètres microscopiques, ce qui résulte de la formation d'une nouvelle structure de transmission de forces. D'autre part, nous avons appliqué cette méthode de simulation numérique à l'étude d'un processus naturel : les glissements de terrain. Nous avons développé une méthodologie qui tient compte de la morphologie initiale du système, de la résistance des géomatériaux, et d'un mécanisme de déclanchement, ce qui permet d'intégrer dans le même modèle les phases d'initiation et de propagation du glissement. Pour illustrer cette méthodologie, nous l'avons appliquée à la modélisation d'un exemple hypothétique d'avalanche déclenchée par la montée progressive du niveau d'une nappe d'eau.
https://tel.archives-ouvertes.fr/tel-00311303

tel-00311303
https://tel.archives-ouvertes.fr/tel-00311303
https://tel.archives-ouvertes.fr/tel-00311303/document
https://tel.archives-ouvertes.fr/tel-00311303/file/these_estrada.pdf

Éditeur(s) : HAL CCSD
Résumé : International audience
Tsavorite is exclusively hosted in the Neoproterozoic Metamorphic Mozambique Belt (NMMB). The gemstone mines, widespread between Kalalani (Tanzania) and Mgama Ridge (Kenya), define a continuous corridor over a hundred kilometers in length. The tsavorite is hosted by a metasedimentary sequence defined as the Kurase tsavorite-bearing metasediments (Kurase-TB metasediments) that also hosts rubies. These metasediments underwent amphibolite-facies metamorphism and are surrounded by granulitic gneisses that are also of sedimentary origin (the Kurase high-temperature gneisses). All these rocks lie below the Kasigau Group, a unit dominated by granulite-facies metamagmatic rocks.To constrain the timing of events that led to this peculiar occurrence of tsavorite, we have performed geochronological analyses of thin sections and of separated grains of zircon, monazite, and rutile using LA-ICP-MS and ID-TIMS, as well as 40Ar/39Ar of muscovite and phlogopite from various lithologies. The results show that the different terranes were metamorphosed synchronously between 620–580 Ma but under different P-T strain conditions. The Kurase-HT gneisses and the rocks from the Kasigau Group are highly strained and underwent granulite-facies metamorphism with abundant partial melting and emplacement of felsic melts between 620 and 600 Ma. Textural observations also underlined a late regional water flux controlling the occurrence of V-free muscovite and monazite mineralizations at 585 Ma. The latter event can be related to the activity of the Galana shear zone, in the east. The Kurase-TB metasediments escaped strain and partial melting. They record amphibolite-facies conditions with static heating, since initial sedimentary structures were locally preserved. The age of the tsavorite mineralization was inferred at 600 Ma from metamorphic zircon rims and monazite from the closest host-rocks, sampled in the mines. Hence, tsavorite crystallization occurred statically at the end of the metamorphic event, probably when the temperature and the amount of volatiles were at maximum levels.Conversely, the ruby formed by local metasomatism of felsic dikes and isolated ultramafic bodies. The rubies are older and zircons and monazites from a ruby-bearing felsic dike (plumasite) were dated at 615 Ma. Finally, data from rutile and micas indicate a global cooling below 430 °C of the whole region between 510 and 500 Ma.
The Canadian Mineralogist

hal-01616037
https://hal.archives-ouvertes.fr/hal-01616037
https://hal.archives-ouvertes.fr/hal-01616037/document
https://hal.archives-ouvertes.fr/hal-01616037/file/JEM.pdf
DOI : 10.3749/canmin.1700019

Éditeur(s) : Elsevier
Résumé : High P-wave velocities (7.1-7.8 km/s) lower crustal bodies (LCBs) imaged along volcanic margins are commonly interpreted as plume and break-up-related thick mafic underplating. This interpretation is partly challenged in this paper based on new seismic observations and modelling of the outer Voring Basin (Norway). An exceptional strong amplitude reflection, the T Reflection, is particularly well defined below the North Gjallar Ridge (NGR) between 7 and 8 s TWT. The T Reflection is located near the volcanic lava flows emplaced during the NE Atlantic breakup (similar to 55-54 Ma ago) and coincides with the top of the LCB, forming a mid-crustal dome. Based on structural and temporal relationships, we show that the dome clearly influences the structural development of the NGR and predates the continental breakup at least by 10-15 Ma. Using a thermo-kinematical model, we tried also to investigate and quantify the relationships between the extension, LCB and the magmatic production. Modelling suggests that significant Paleocene-Early Eocene magmatism can be produced without any temperature anomaly in the mantle if differential stretching occurs during the break-up initiation. The conclusion of 2D thermo-kinematical parametric analysis is that the magmatic model predicts, either little extension (beta < 2) with no melting or high extension (beta > 5) with significant melting along the outer Voring Basin. We suggest that the continental part of the LCB could not necessarily be breakup-related and so magmatic, as has often been stated previously. It is concluded here that the continental part of the LCB observed beneath the outer Voring Basin may be partly (or fully) attributed to inherited, high-pressure granulite/eclogite lower crustal rocks. The real amount of mafic material emplaced along the outer Voring Basin could be 20-40% less than thought.
Tectonophysics (0040-1951) (Elsevier), 2006 , Vol. 412 , N. 3-4 , P. 255-278

Droits : 2005 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2006/publication-1042.pdf
DOI:10.1016/j.tecto.2005.10.038
http://archimer.ifremer.fr/doc/00000/1042/

Éditeur(s) : HAL CCSD
Résumé : International audience
In this paper, we compare the effect of rolling resistance at the contacts in granular systems composed of disks with the effect of angularity in granular systems composed of regular polygonal particles. For this purpose, we use contact dynamics simulations. By means of a simple shear numerical device, we investigate the mechanical behavior of these materials in the steady state in terms of shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. We find that, based on the energy dissipation associated with relative rotation between two particles in contact, the effect of rolling resistance can explicitly be identified with that of the number of sides in a regular polygonal particle. This finding supports the use of rolling resistance as a shape parameter accounting for particle angularity and shows unambiguously that one of the main influencing factors behind the mechanical behavior of granular systems composed of noncircular particles is the partial hindrance of rotations as a result of angular particle shape.
AIP Conference Proceedings
Sydney, Australia

hal-00842799
https://hal.archives-ouvertes.fr/hal-00842799
https://hal.archives-ouvertes.fr/hal-00842799/document
https://hal.archives-ouvertes.fr/hal-00842799/file/Comparison_effects_rolling_Estrada_al.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
In this study, the cellular organization of the gill that harbors symbiotic bacteria is described in the thyasirid Thyasira falklandica collected from South Shetlands in Antarctic. Sections of the gills revealed that T. falklandica belongs to the gill type 3, as described by Dufour (Biol Bull, 208:200-212, 2005), with an elongated lateral zone along the frontal-abfrontal axis of the gill Wlaments. The ciliated and intermediary zones looked similar to those described in symbionts-bearing bivalves. The lateral zone is more complex in T. falklandica than in other Thyasiridae already described. Such a zone is composed of four different cell types. Bacteriocytes are abundant in the frontal and abfrontal positions, while the middle part of the lateral zone is occupied mostly by numerous granule cells devoid of bacteria. All along the lateral zone, TEM and SEM observations show some ciliated cells, which are regularly interspersed between bacteriocytes and/or granule cells. Such cells, according to the long double ciliary roots of their cilia, should have a sensory function. Intercalary cells, which have never been observed between bacteriocytes, are restricted to the middle part of the lateral zone where their expansions overlap the adjacent granule cells. Bacterial symbionts occur only extracellularly among long microvilli diVerentiated by the bacteriocytes. They are abundant, usually spherical in shape (around 0.7 m length), and covered by the glycocalix from bacteriocyte microvilli. According to TEM views, the empty vesicles located in the periplasmic space should be sulfur storage, as known for other sulfur-oxidizing symbionts.
ISSN: 0720-213X

hal-00755289
https://hal.univ-antilles.fr/hal-00755289
DOI : 10.1007/s00435-007-0034-4

Éditeur(s) : HAL CCSD Cold Spring Harbor Laboratory Press
Résumé : International audience
The genome of male germ cells is actively transcribed during spermatogenesis to produce phase-specific protein-coding mRNAs and a considerable amount of different noncoding RNAs. Ribonucleoprotein (RNP) granule-mediated RNA regulation provides a powerful means to secure the quality and correct expression of the requisite transcripts. Haploid spermatids are characterized by a unique, unusually large cytoplasmic granule, the chromatoid body (CB), which emerges during the switch between the meiotic and post-meiotic phases of spermatogenesis. To better understand the role of the CB in male germ cell differentiation, we isolated CBs from mouse testes and revealed its full RNA and protein composition. We showed that the CB is mainly composed of RNA-binding proteins and other proteins involved RNA regulation. The CB was loaded with RNA, including pachytene piRNAs, a diverse set of mRNAs, and a number of uncharacterized long noncoding transcripts. The CB was demonstrated to accumulate nascent RNA during all the steps of round spermatid differentiation. Our results revealed the CB as a large germ cell-specific RNP platform that is involved in the control of the highly complex transcriptome of haploid male germ cells.
ISSN: 1355-8382

hal-00985894
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00985894
DOI : 10.1261/rna.043729.113
PUBMED : 24554440

Éditeur(s) : HAL CCSD
Résumé : Incipient granulite facies conditions and carnockitization affected metasedimentary formations of northern Nigeria during the early stage of the Late Neo-proterozoic (Pan-African) orogeny. This domain is characterized by recumbent foliations consistent with crustal thickening. Far from the Pan-African plutons, initial Barrovian-type metamorphism (medium temperature) evidenced by kyanite and staurolite inclusions is documented only front garnet cores. This early stage was followed by a temperature increase up to >= 700 C, with decompression coeval with the generation of garnet-cordierite melts and emplacement of garnet granitoid sheets. Hectometric-wide layers of non-retrograded granulites survived conformably within anatexites and S-type garnet-bearing anatectic granites from the Toro area. Temperatures of >= 800 C required for the crystallization of granulites facies rocks at c. 0.7 GPa pressure and coeval dry anatexis, were reached regionally as a result of heat supply from abundant anhydrous monzo-dioritic to noritic magmas injected as metre-wide veins and as stocks and pinions (charnockites, monzodiorites). The available geochronological results suggest a long-lived thermal perturbation (638-585 Ma) in this former continental domain of northern Nigeria rooted by Archaean crust that was later the site of the Jurassic anorogenic magmatism.
Proceedings Of The Geologists Association

hal-00407196
https://hal.archives-ouvertes.fr/hal-00407196
DOI : 10.1016/S0016-7878(07)80046-0

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
This study describes the structure of the digestive gland of Strombus gigas in individuals from Guadeloupe and discusses the function of its cell types and their relationship with intracellular Apicomplexa-like parasites. Three cellular types were found in the epithelium of the blind-ending tubules of the digestive gland according to histological and transmission electron microscopy (TEM) observations; these were: digestive cells, pyramidal crypt cells and vacuolated cells. Columnar digestive cells were characterized by large Alcian blue-positive granules, which have not been previously described in digestive cells of other caenogastropods. Such granules contain large quantities of proteoglycans that are exported to the stomach through the physiological destruction of the digestive cells, which undergo a holocrine secretion. Their cytoplasm appears vacuolar due to lipid extraction by solvents used for tissue preparation. Vacuolated cells also appear to be lipid-storage cells. Small triangular-shaped crypt cells, on the other hand, appear to be metabolically active as suggested by a strong positive in situ hybridization of eukaryotic ribosomes, which was confirmed by their large content of ribosomes and rough endoplasmic reticulum compared to the other cell types. These observations suggest that crypt cells may be immature cells that are involved in the replacement of eliminated digestive cells. However, their spherocrystal inclusions indicate that they may be excretory cells or calcium cells. Large brown inclusions were frequently observed in vacuolated cells; these were identified as parasitic protozoans and were present in the digestive gland of all sampled specimens. These protozoans have previously been described from a queen conch population in the San Andres Archipelago (Colombia). Several life cycle stages of the parasite were identified by scanning electron microscopy and TEM; trophozoites were characterized by their conoid-like structure, sporocysts by their thick walls, and gamonts by their thin walls. These observations suggest that this parasite completes its entire life cycle within the same host and type of tissue. Although previous investigations place this parasite within the Apicomplexa group, further investigations are necessary in order to confirm the identification of the parasite.
ISSN: 0260-1230

hal-00755287
https://hal.univ-antilles.fr/hal-00755287
DOI : 10.1093/mollus/eyn041

Éditeur(s) : HAL CCSD Elsevier
Résumé : In Vietnam, recent studies demonstrated that the Kon Tum Massif was part of the Indosinian mountain system, together with the Truong Son Belt. One sector of the Kon Tum Massif (Song Ba valley) is a granulite facies terrain for which Ar–Ar and U–Pb ages cluster around 245–250 Ma. In the area of Song Bien river, also metamorphosed under granulite facies conditions, Ar–Ar ages of 410 Ma are displayed by biotite. In this study, U–Pb dating of monazite and zircon has been used to understand the reason for these two groups of ages, taking into account the metamorphic mineral assemblages related to granulite facies metamorphism in the two districts. For granulites of Song Ba valley, ages of 245–250 Ma are confirmed from monazites. In the Song Bien district, ages of 465–470 Ma displayed by monazites are interpreted to correspond to the metamorphic climax. Zircons from one of these samples record the age of anatexis that has affected the granulitic rocks. The younger age recorded in the Song Ba valley is considered to reflect high temperature related to charnockitic intrusions emplaced near the end of the Indosinian orogeny, overprinting the earlier formed granulites and resetting the U–Pb and Ar–Ar ages. For the first time, two HT events are dated in the Kon Tum Massif, one occurring during the Ordovician and the other during the Permo-Triassic.
ISSN: 0743-9547

hal-00404975
https://hal.archives-ouvertes.fr/hal-00404975
DOI : 10.1016/j.jseaes.2007.01.005

Éditeur(s) : HAL CCSD Elsevier
Résumé : This paper presents a numerical investigation on the mechanical behavior of cemented granular materials by means of discrete element simulations. In particular, two conceptual elements of this behavior were explored: the yield surfaces and the plastic potentials, as defined in the framework of elastoplastic constitutive models. For this purpose, we implemented a contact model that mimics the mechanical behavior of cemented bonds, we constructed a set of polydisperse samples with different solid fractions, and we tested these samples by means of a biaxial device with four rigid walls. The yield surfaces and plastic potentials were thus obtained and analyzed as functions of the solid fraction of the material, drawing interesting conclusions, confirming previous experimental findings, and, consequently, evidencing the great potential of discrete element simulations in exploring the behavior of real cemented geomaterials.
ISSN: 0266-352X

hal-00853748
https://hal.archives-ouvertes.fr/hal-00853748
DOI : 10.1016/j.compgeo.2012.11.001

Résumé : Depuis maintenant plus de trois ans, l'équipe IFREMER de Martinique travaille à la mise au point technique de l'élevage de l'ombrine subtropicale (Sciaenosp ocellata), dans des conditions intensives. En matière de reproduction, l'équipe IFREMER a engagé dès 1987, une opération de transfert de la technologie Américaine de maturation et ponte grâce au contrôle environnemental de la température et de la phtopériode. Près de 50 millions d'oeufs ont été produits en 1989, à partir de 5 femelles de 5 à 6 kg. En terme d'alevinage, les "résidus d'expérimentation" ont été de 12 000, 18 000, 9 000 et 89 000 alevins sevrés (1 à 2g), respectivement pour les années 1987, 88, 89 et 1990. En 1990, l'objectif principal de démonstration de la faisabilité de la technique d'alevinage en intensif a été atteint avec succès à travers trois élevages "pilotes" successifs aux taux de survie moyen, à 2 grammes, de 14% , 15% et 24%. En expérimentation larvaire, un effort conséquent a été réalisé sur l'approche des besoins nutritionnels de l'espèce. La valeur limite en acides gras essentiels se situerait pour l'ombrine, entre 0,15% et 0,25% de 20:5w3 (en % de poids sec de nauplii) ou entre 0,22% et 0,33% des 2 AGLOPI essentiels: le 20:5w3 et le 22:6w3. En phase de grossissement, les élevages ont permis d'obtenir des poissons de 400 g de poids moyen en 6 à 7 mois en cages flottantes. Le poids initial des alevins est d'environ 2 g pour 2 mois d'âge. L'aliment utilisé est un granulé de type "loup", non spécifique, à 52% de protéines et près de 9% de lipides. Avec cet aliment, les taux de nutrition évoluent de 5, 0-5, 5% en début d'élevage, pour finir à 1,0-1,5% en fin d'élevage (350-500g). Les taux de conversion expérimentaux chez les aquaculteurs, sont compris entre 1,2-2,3. Les charges moyennes des élevages sont de 10 à 15 kg/m3, et la charge maximale enregistrée, de 20-22 kg/m3. La survie moyenne est de 60-70%.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00130/24140/22146.pdf
http://archimer.ifremer.fr/doc/00130/24140/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Digestive tubules of Strombidae are composed by three cell types: digestive cells, vacuolated cells, and crypt cells. The last one is characterized by the presence of intracellular granules identified as spherocrystals. Such structures are known to occur in basophilic cells of gastropod digestive gland, where they are supposed to be involved in the regulation of some minerals and in detoxification. In this study, energy-dispersive X-ray analysis (EDX) and energy filtered transmission electron microscopy (EFTEM) were used to determine the elemental content of spherocrystals in two Strombidae, Strombus gigas and Strombus pugilis. In freshly collected individuals of both species, the following elements were detected: Ca, Fe, Mg, P, and Zn. Aluminum and Mn were also detected in S. gigas. Their presence in spherocrystals indicates that, in Strombidae, spherocrystals are involved in the regulation of minerals and essential trace metals. In order to answer the question ''are spherocrystals involved in nonessential trace metals scavenging?,'' artificial cadmium and lead exposure by both waterborne and dietary pathways was applied to S. pugilis. No evidence of cadmium (Cd(NO3)2) or lead (Pb(NO3)2) provided by food was found in spherocrystals. Cadmium provided in water (Cd(NO3)2 and CdCl2) causes structural modifications of the digestive gland; however, this element was not trapped in spherocrystals. These results suggest that spherocrystals are not involved in detoxification of such nonessential trace metals.
ISSN: 1059-910X

hal-00743762
https://hal.univ-antilles.fr/hal-00743762
DOI : 10.1002/jemt.21073

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) : Edp Sciences S A
Résumé : A study on nitrogenous and phosphorous waste production in European seabass (Dicentrarchus labrax) was carried out in a flow-through land-based farm. The main objectives were (i) to calculate nitrogenous (N) and phosphorous (P) waste production (particulate and dissolved) from in situ measurements for different rearing ponds with specific fish biomasses, fish sizes and flow rates, (ii) to establish nitrogenous and phosphorous waste production budgets, ratios and equations, and (iii) to compare, for the whole farm, in situ measurements to estimate N and P waste production from waste equations. Waste production was manifest by an increase in concentrations of total ammonia nitrogen, total Kjeldhal nitrogen, particulate nitrogen, dissolved phosphorus and total phosphorus concentrations in the outlet water compared to the inlet water for both batches and whole farm. However, no production of nitrite or nitrate was observed. In our budgets, the N and P amounts from biomass gains and wastes were explained by the N and P derived from feed over the range 83.9-105.2 % and 66.5-104.6 % respectively, depending on the fish batch. Values were respectively 103.4 and 87.5 % for the same calculations in the farm. When the whole-farm waste production was calculated from previous equations derived from batches, and then compared with the measured data, the percentages of recovery (estimated by the ratio predicted data/measured data) were 88 and 94 % for total-N and total-P respectively.
L'étude de la production des déchets (azote et phosphore) d'une ferme de production de bars (Dicentrarchus labrax) est réalisée. Cette étude à pour objectif (i) de mesurer in situ la production des déchets azotés et phosphores sous forme particulaire et soluble, pour différents bassins d'élevage présentant des caractéristiques variables en terme de biomasse de poisson, de taille des poissons, de débit de l'eau de renouvellement, (ii) d'établir des équations de production de déchets à partir des données précédemment acquises, (iii) de comparer, pour l'ensemble des rejets au niveau de la ferme, les résultats obtenus par des mesures in situ, d'une part, et à l'aide des équations, d'autre part. La production de déchets se traduit par une augmentation des concentrations de l'azote particulaire, de l'azote ammoniacal, de l'azote organique dissous, ainsi que du phosphore particulaire et dissous. Aucune augmentation des nitrates et nitrites n'est observée. L'établissement des budgets d'azote et de phosphore permettent de rendre compte, selon les bassins, du devenir de 88,2 à 105,2 % de l'azote et de 66,2 à 104,6 % du phosphore introduits dans les bassins sous forme de nourriture en granulés. L'étude des budgets réalisée par les deux méthodes (mesures in situ et utilisation des équations) montre que les budgets établis à l'aide des équations rendent compte respectivement de 88 et 94 % de récupération de l'azote et du phosphore. Ces résultats sont respectivement de 103,4 et 87,5 % lorsqu'ils sont établis par des mesures in situ.
Aquatic Living Resources (0990-7440) (Edp Sciences S A), 1998-07 , Vol. 11 , N. 4 , P. 247-254

Droits : 1998 Published by Elsevier SAS
http://archimer.ifremer.fr/doc/1998/publication-872.pdf
DOI:10.1016/S0990-7440(98)89007-4
http://archimer.ifremer.fr/doc/00000/872/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Larsemann Hills area is part of a reworked early Neoproterozoic metamorphic terrain in southwestern Prydz Bay, East Antarctica. Ultramafic and mafic granulites, whose origins remain controversial, occur as lenses, boudins or layered bodies within the para- and ortho-gneiss in the region. The ultramafic and mafic granulites show spinel-olivine-bearing and two-pyroxene-bearing mineral assemblages recrystallized at 860–900 °C. Their bulk rock analyses indicate an origin as igneous cumulates, with high Mg# (molar MgO/(MgO + FeO)) from 0.73 to 0.84 for ultramafic granulite and from 0.46 to 0.78 for mostly mafic granulite as well as high Cr and Ni contents ([Cr] and [Ni] up to 1826 ppm and 1400 ppm respectively for ultramafic granulite and [Cr] of 1460 ppm for mafic granulite). Trace element patterns show pronounced negative Nb anomalies, suggesting a subduction-related tectonic setting for their precursors, consistent with derivation from arc basalts, also suggested by low TiO2 and K-enrichment in mafic granulites. The ultramafic to mafic granulites may have been formed in a subduction-related continental back-arc basin environment simultaneously with peak metamorphism associated with arc-continent collision during the early Neoproterozoic (990–900 Ma) Rayner orogeny.
ISSN: 0743-9547

hal-01622589
https://hal.archives-ouvertes.fr/hal-01622589
DOI : 10.1016/j.jseaes.2017.06.012

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Garnet growth in high-pressure, mafic garnet granulites formed by dehydration melting of hornblende-gabbronorite protoliths in the Jijal complex (Kohistan palaeo-island arc complex, north Pakistan) was investigated through a microstructural EBSD-SEM and HRTEM study. Composite samples preserve a sharp transition in which the low-pressure precursor is replaced by garnet through a millimetre-sized reaction front. A magmatic foliation in the gabbronorite is defined by mafic-rich layering, with an associated magmatic lineation defined by the shape-preferred orientation (SPO) of mafic clusters composed of orthopyroxene (Opx), clinopyroxene (Cpx), amphibole (Amp) and oxides. The shape of the reaction front is convoluted and oblique to the magmatic layering. Opx, Amp and, to a lesser extent, Cpx show a strong lattice-preferred orientation (LPO) characterized by an alignment of [001] axes parallel to the magmatic lineation in the precursor hornblende-gabbronorite. Product garnet (Grt) also displays a strong LPO. Two of the four < 111 > axes are within the magmatic foliation plane and the density maximum is subparallel to the precursor magmatic lineation. The crystallographic relationship < 111 >(Grt)//[001](Opx,Cpx,Amp) deduced from the LPO was confirmed by TEM observations. The sharp and discontinuous modal and compositional variations observed at the reaction front attest to the kinetic inhibition of prograde solid-state reactions predicted by equilibrium-phase diagrams. The P-T field for the equilibration of Jijal garnet granulites shows that the reaction affinities are 5-10 kJ mol.(-1) for the Grt-in reaction and 0-5 kJ mol.(-1) for the Opx-out reaction. Petrographic and textural observations indicate that garnet first nucleated on amphibole at the rims of mafic clusters; this topotactic replacement resulted in a strong LPO of garnet. Once the amphibole was consumed in the reaction, the parallelism of [001] axes of the mafic-phase reactants favoured the growth of garnet crystals with similar orientations over a pyroxene substrate. These aggregates eventually sintered into single-crystal garnet. In the absence of deformation, the orientation of mafic precursor phases conditioned the nucleation site and the crystallographic orientation of garnet because of topotaxial transformation reactions and homoepitaxial growth of garnet during the formation of high-pressure, mafic garnet-granulite after low-pressure mafic protoliths.
ISSN: 0263-4929

hal-00411323
https://hal.archives-ouvertes.fr/hal-00411323
DOI : 10.1111/J.1525-1314.2008.00789.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We performed torsional deformation experiments on pre-hydrated fine-grained olivine aggregates using an innovative experimental assembly to investigate water weakening in mantle rocks at high shear strains. San Carlos olivine powder was cold-pressed and then hot-pressed under hydrous conditions, producing aggregates with average grain sizes of 7 or 15 μm. Deformation experiments were performed in a high-resolution gas-medium apparatus equipped with a torsional actuator, under a confining pressure of 300 MPa, a temperature of 1200 °C, and constant shear strain rates ranging from 8 × 10−5 to 1.4 × 10−4 s−1. Maximum shear stresses range from 150 to 195 MPa. These values are 30% lower relative to those determined in previous torsion experiments on dry, fined-grained dunites under similar conditions. Textures and microstructures of the starting and deformed specimens were characterized by scanning and transmission electron microscopy. All deformed aggregates exhibit a shape-preferred orientation marking a foliation and lineation, as well as a reduction in mean grain size from 15 μm down to 3-4 μm due to dynamic recrystallization. Olivine crystallographic fabrics developed rapidly (γ < 0.1), but their strength, characterized by the J-index, is low compared to naturally deformed peridotites or to polycrystalline olivine deformed at similar finite shear strains under dry conditions. The crystallographic fabrics are consistent with deformation by a dislocation accommodated creep mechanism with activation of multiple {0 k l}[1 0 0] systems, among which the (0 1 0)[1 0 0] slip system is dominant, and minor participation of the (0 1 0)[0 0 1] slip system. Transmission electron microscopy confirmed the occurrence of dislocations with [1 0 0] and [0 0 1] Burgers vectors in most grains. Analysis of unpolarized infrared spectra indicates that hydrogen concentration in the olivine lattice is below the saturation level of 18 ppm wt H2O, which is similar to those typically observed in spinel-bearing peridotite xenoliths, and also provide evidence for water-rich inter-granular material trapped in pores and grain boundaries. Seismic properties computed from the CPO observations correspond to those most commonly observed in naturally deformed mantle peridotites with fast P-wave propagation and S-wave polarization subparallel to the shear direction. These torsion experiments on fine-grained olivine polycrystals under hydrous conditions indicate that water weakening under lithospheric conditions is linked to various defects with hydrogen in the olivine structure, as well as with water-derived species in grain boundaries or pores.
ISSN: 0031-9201

hal-00745170
https://hal.archives-ouvertes.fr/hal-00745170
DOI : 10.1016/j.pepi.2012.05.001

Éditeur(s) : HAL CCSD American Physical Society
Résumé : International audience
This is the second 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 sheared in a load-controlled simple shear numerical device until the stress state of the sample reaches the yield stress. We first study the stress transmission properties of the granular material in terms of the fabric of different subsets of contacts characterized by the magnitude of their normal forces. This analysis highlights the existence of a peculiar force carrying structure in the cemented material, which is reminiscent of the bimodal stress transmission reported for cohesionless granular media. Then, the evolution of contact forces and torques is investigated trying to identify the micromechanical conditions that trigger macroscopic yielding. It is shown that global failure can be associated to the apparition of a group of particles whose contacts fulfill at least one of the local rupture conditions. In particular, these particles form a large region that percolates through the sample at the moment of failure, evidencing the relationship between macroscopic yielding and the emergence of large-scale correlations in the system.
ISSN: 1539-3755

hal-00523451
https://hal.archives-ouvertes.fr/hal-00523451
DOI : 10.1103/PhysRevE.82.011304