Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Properties of composite materials depend on interatomic phenomena occurring between binder crystals. Experimental information of Atomic Force Microscopy (A.F.M.) is of prime importance; however understanding is helped by molecular modeling. As underlined in Section 1, the present study is able to simulate crystal interfaces in presence of a solution within apertures less than 1 Nanometer at a full atomic scale. Section 2 presents the case study of a gypsum solution between (120) gypsum faces, with related boundary conditions and atomic interactions. Section 3 deals with the mass equilibrium of the solution within interfaces <5 angstrom, using the original Semi Analytical Stochastic Perturbations (SASP) approach. This information becomes in Section 4 the key for explaining the peak of adhesion obtained in A.F.M. around an aperture of 3 A and gives enlightenments on gypsum cohesion. In conclusion, this illustration shows the potentialities of full atomic modeling which could not be attained by any numerical approach at a mesoscopic scale.
ISSN: 0008-8846

hal-00411868
https://hal.archives-ouvertes.fr/hal-00411868
DOI : 10.1016/j.cemconres.2007.09.022

Éditeur(s) : HAL CCSD Elsevier
Résumé : The depth of the oceanic lithosphere–asthenosphere boundary (LAB), as inferred from shear wave velocities, increases with lithospheric age, in agreement with models of cooling oceanic lithosphere. On the other hand, the distribution of radial anisotropy under oceanic plates is almost age-independent. In particular, radial anisotropy shows a maximum positive gradient at a depth of ∼70 km, which, if used as a proxy, indicates an age-independent LAB depth. These contrasting observations have fueled a controversy on the seismological signature of the LAB. To better understand the discrepancy between these observations, we model the development of lattice preferred orientation (LPO) in upper mantle crystal aggregates and predict the seismic anisotropy produced by plate-driven mid-ocean ridge flows. The model accounts for the progressive cooling of the lithosphere with age and can incorporate both diffusion and dislocation creep deformation mechanisms. We find that an age-independent distribution of radial anisotropy is the natural consequence of these simple flows. The depth and strength of anisotropy is further controlled by the deformation regime – dislocation or diffusion creep – experienced by crystals during their ascent towards, and subsequent motion away from, the ridge axis. Comparison to surface wave tomography models yield constraints on rheological parameters such as the activation volume. Although not excluded, additional mechanisms proposed to explain some geophysical signatures of the LAB, such as the presence of partial melt or changes in water content, are not required to explain the radial anisotropy proxy. Our prediction, that the age-independent radial anisotropy proxy marks the transition to flow-induced asthenospheric anisotropy, provides a way to reconcile thermal, mechanical and seismological views of the LAB.
ISSN: 0012-821X

hal-01553243
https://hal.archives-ouvertes.fr/hal-01553243
DOI : 10.1016/j.epsl.2016.12.004

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : We investigated the relationship between habitat association and physiological performance in four congeneric species pairs exhibiting contrasting distributions between seasonally flooded and terra firme habitats in lowland tropical rain forests of French Guiana, including Virola and Iryanthera (Myristicaceae), Symphonia (Clusiaceae), and Eperua (Caesalpiniaceae). We analyzed 10-year data sets of mapped and measured saplings (stems 150 cm in height and <10 cm diameter at breast height [dbh]) and trees (stems 10 cm dbh) across 37.5 ha of permanent plots covering a 300-ha zone, within which seasonally flooded areas (where the water table never descends below 1 m) have been mapped. Additionally, we tested the response of growth, survival, and leaf functional traits of these species to drought and flood stress in a controlled experiment. We tested for habitat preference using a modification of the torus translation method. Strong contrasting associations of the species pairs of Iryanthera, Virola, and Symphonia were observed at the sapling stage, and these associations strengthened for the tree stage. Neither species of Eperua was significantly associated with flooded habitats at the sapling stage, but E. falcata was significantly and positively associated with flooded forests at the tree stage, and trees of E. grandiflora were found almost exclusively in nonflooded habitats. Differential performance provided limited explanatory support for the observed habitat associations, with only congeners of Iryanthera exhibiting divergent sapling survival and tree growth. Seedlings of species associated with flooded forest tended to have higher photosynthetic capacity than their congeners at field capacity. In addition, they tended to have the largest reductions in leaf gas exchange and growth rate in response to experimental drought stress and the least reductions in response to experimental inundation. The corroboration of habitat association with differences in functional traits and, to a lesser extent, measures of performance provides an explanation for the regional coexistence of these species pairs. We suggest that specialization to seasonally flooded habitats may explain patterns of adaptive radiation in many tropical tree genera and thereby provide a substantial contribution to regional tree diversity.
ISSN: 0012-9658

hal-01031746
https://hal.archives-ouvertes.fr/hal-01031746

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Trace metals (Cd, U, Co, Ni, Cu, Ba, Fe, Mn), total organic carbon (TOC) and C and N stable isotope signatures (delta C-313 and delta N-15) were determined in short sediments cores from the inner and outer shelf off Concepcion, Chile (similar to 36 degrees S). The objectives were to establish the effect of environmental conditions on trace metal distributions at two shelf sites, one affected by seasonal oxygenation and the other by permanent low oxygen conditions due to the presence of the oxygen minimum zone (OMZ). We evaluate trace metals as proxies of past changes in primary productivity and the bottom water oxygen regime. Concentrations of pore water sulfides and NH4+ were also measured as indicators of the main diagenetic pathways at each site. Our results for the inner shelf (seasonal suboxia) suggest that the oxidative state of the sediments responds to seasonal pulses of organic matter and that seasonal oxygenation develops during high and low primary productivity in the water column. Here, positive fluxes (to the water column) estimated from pore water concentrations of several elements were observed (Ba, Co, Ni, Fe and Mn). The less reduced environment at this site produces authigenic enrichment of Cu associated with the formation of oxides in the oxic surface sediment layer, and the reduction of U within deeper sediment sections occur consistently with negative estimated pore water fluxes. In the outer shelf sediments (permanent suboxia, OMZ site), negative fluxes (to the sediment) were estimated for all elements, but these sediments showed authigenic enrichments only for Cd, Cu and U. The short oxygenation period during the winter season did not affect the accumulation of these metals on the shelf. The distribution of Cu, Cd and U have been preserved within the sediments and the authigenic accumulation rates estimated showed a decrease from the deep sections of the core to the surface sediments. This could be explained by a gradual decrease in the strength of the OMZ in the last 100 years, in combination with periods of strong oxygenations during El Nino events. (C) 2011 Elsevier Ltd. All rights reserved.
ISSN: 0278-4343

hal-00745672
https://hal.archives-ouvertes.fr/hal-00745672
DOI : 10.1016/j.csr.2011.11.006

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The Ronda peridotite massif in Southern Spain shows a well-defined 'recrystallization' front that separates a large-scale partial melting domain formed at the expense of the continental lithospheric mantle from a 'preserved' lithospheric domain. To investigate the processes allowing a transient lithosphere-asthenosphere boundary to propagate in the lithospheric mantle, we performed a joint petrostructural and geochemical study of an similar to 2.5 km(2) zone extending from the melting front to the mylonites that mark the western limit of the massif. This study emphasizes a feedback between heat transfer, melt percolation, and deformation in the lithospheric mantle. Petrographical observations and geochemical data show that heterogeneous reactive percolation of melts produced in the underlying partial melting domain led to refertilization of lithospheric peridotites up to 1.5 km ahead from the melting front, producing metre-scale layering of fertile and refractory mantle rocks. Within 800 m from the front, pre-existing garnet pyroxenite layers were partially molten and the resulting melts probably contributed to the refertilization process. Detailed structural mapping and analysis of the microstructures and crystal preferred orientations highlight the relations between reactive melt transport and deformation, and the control of the temperature gradient on both processes. Parallelism between the recrystallization front, compositional boundaries, and deformation structures, as well as variations in the deformation intensity of pyroxenes and spinels, suggest syn- to late-tectonic melt transport controlled by both the deformation and the thermal gradient. Variations in the strength of olivine crystal preferred orientations as a function of the modal and chemical composition of the spinel tectonites point to a higher contribution of diffusion to deformation in the most fertile rocks, corroborating the hypothesis that deformation occurred in presence of melt. Finally, the systematic dispersion of olivine [100] and orthopyroxene [001] axes in the foliation plane suggests a dominantly transpressive deformation regime.
ISSN: 0022-3530

hal-00420904
https://hal.archives-ouvertes.fr/hal-00420904
DOI : 10.1093/petrology/egp032

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study reports petrostructural observations in the pargasite and phlogopite-bearing Finero peridotite massif (Italian Western Alps), which suggest that the pervasive foliation in this massif was formed by deformation concomitant with percolation of hydrous Si-rich melts: (1) diffuse contacts, but systematic parallelism between the pyroxenitic layers and the foliation of the peridotite (2) strong shape and crystal preferred orientations (SPO and CPO), but subhedral or interstitial shapes and weak intracrystalline deformation of the hydrous phases, (3) CPO, but interstitial shapes of the pyroxenes, (4) very coarse olivine grain sizes, which are correlated to the olivine abundance, and (5) elongated shapes, but weak intracrystalline deformation, and extremely weak and highly variable CPO of olivine. The pervasive deformation of the Finero peridotite occurred therefore under conditions that allowed coexistence of H2O–CO2-bearing melts, pargasite, and spinel, that is, temperatures of 980–1080 °C and pressures <2 GPa. The petrostructural observations suggest that the presence of hydrous melts results in accommodation of large amounts of deformation by stress-controlled dissolution–precipitation and advective transport of matter by the melts and in fast grain boundary migration in olivine. By consequence, it produces significant rheological weakening. Water contents in olivine are <4 ppm wt., implying limited contribution of hydration of olivine to weakening. In addition, the analysis of protomylonites composing the external domains of the shear zones that overprint the pervasive foliation indicates that the transition to melt-free conditions results in enhanced contribution of dislocation creep to the deformation. The associated increase of the peridotites' strength leads to onset of strain localization. The latter is not correlated to the local abundance in pargasite or phlogopite, implying that crystallization of amphiboles or phlogopite, even at concentrations of 25 vol.%, does not produce rheological weakening in the upper mantle.
ISSN: 0012-821X

hal-01667879
https://hal.archives-ouvertes.fr/hal-01667879
DOI : 10.1016/j.epsl.2017.08.015

Résumé : Cette these porte sur une analyse de politique publique dans un champ d'action internationale, la cooperation au developpement. l'etude s'interesse particulierement au cas de la construction de la politique communautaire de cooperation au developpement, et de son affirmation visa- vis des politiques nationales europeennes. pour ce faire, cette these analyse d'un point de vue qualitatif les ressorts de l'action de l'union europeenne, a la fois pour penser le developpement dans la caraïbe, et pour penser et faire l'europe. de l'autonomisation d'une politique a l'harmonisation des politiques nationales par le bas, c'est une veritable recomposition du systeme d'acteurs qui s'opere. ce renforcement de l'integration europeenne, dans un domaine d'action partage, par le biais d'outils renouveles de l'action publique, dessine alors progressivement les premices et les contours du cadre legislatif qui a ete mis en place par le traite de lisbonne en 2009
This dissertation analyses a public policy in an international field of action: the development cooperation. the study focuses in particular on the emergence of the european community policy of development cooperation and its assertion towards european national policies. using a qualitative methodology, this research aims to improve the understanding of the motivation and the processes at stake within the european union. the field analysis has led to observe both how the development policy in the caribbean ras been thought and built, and how this process may rave an impact on the european integration process itself. from the empowerment of a policy to the harmonisation of national policies, this process carries also consequences on the system of actors, which ras been reconstructed by those changes. as a result, the european integration process has been strengthened in a field where the competence is generally shared between the eu and its member states. bringing out some new or renewed tools of public action, this outlines also some of the signs or provisions of the forthcoming legal and political framework, set up by the 2009 lisbon treaty

http://www.theses.fr/2012AGUY0574/document

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We conducted triaxial compression experiments to investigate the effects of pressure, temperature and strain rate on the rheology of talc rocks. The tests were carried out at T from 25 to 860 degrees C, P from 0.1 to 300 MPa, and <(epsilon) over dot> from 0.3 to 30 x 10-5 s(-1). In addition to being very weak, there are other important differences between the mechanical behavior of talc and that of most other silicates. Deformation at all temperatures up to dehydration was accommodated by a combination of crystal plasticity, frictional sliding, and cataclasis. A transition from localized to distributed deformation occurred at P = 300 MPa and T = 400 degrees C, but this transition is ill-defined as both distributed and localized deformation were observed at P = 300 MPa and T = 600 degrees C. Unlike most silicates, both the coefficient of internal friction and the coefficient of (sliding) friction are very low and nearly equal to each other. Temperature enhances plastic deformation (kinking), and inter- and intra-granular microcracks are observed parallel to the (001) planes at all conditions. Voids are created by delamination along (001) planes at kink-band boundaries. Full crystal plasticity was not achieved under any of the conditions tested, i.e., the von Mises criterion was never satisfied. However, the strength of the aggregates remained much less than the confining pressure. These unusual properties are likely a manifestation of the pronounced mechanical anisotropy of talc at the grain scale. At T >= 750 degrees C dehydration is observed, but only along shear zones. These results suggest that feedbacks between deformation and reaction kinetics could control fluid flow in fault zones. The presence of talc can promote significant weakening and strain localization in the oceanic lithosphere, the subducting plate and the overlying mantle wedge. (c) 2008 Elsevier B.V. All rights reserved.
ISSN: 0012-821X

hal-00492706
https://hal.archives-ouvertes.fr/hal-00492706
DOI : 10.1016/j.epsl.2008.02.004

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We report preliminary results of a seismological experiment, SEISMOTANZ'07, which consisted in the deployment of a local network (35 stations) in the East African Rift System (EARS), North Tanzania, during 6 months in 2007. We compare two earthquake sequences (Gelai and Manyara) occurring respectively in the southern end of the Kenya rift and in the North Tanzanian Divergence (NTD). Only distant of 150 km, their triggering mechanisms are different. None of the sequences depicts typical swarm or mainshock-aftershock patterns. They highlight the change in the magmatic/tectonic nature of the rift where the eastern branch of the EARS enters the Tanzanian craton. The similar shape and long-axis of the elongate sequences emphasize the preferred locus of active strain release along NE-SW discontinuities which probably root at depth into steep Proterozoic shear zones. At Gelai, the deformation is dominated by aseismic process involving slow slip on normal fault and dyke intrusion within the upper crust Calais_et_al_2008. The spatial and temporal earthquake distribution indicates a possible correlation between the Gelai crisis and the eruption of the nearby Oldoinyo Lengai volcano. At Manyara, the sequence is more uncommon, revealing a long-lasting seismic activity deepely rooted (20-35 km depth) possibly related to stress loading transmitted laterally. The yield stress envelope modelled from the depth frequency distribution of earthquakes in the NTD is consistent with the presence of a mafic lower crust and further supports the strength increase of the rifted crust from south Kenya to the NTD.
ISSN: 0899-5362

hal-00420599
https://hal.archives-ouvertes.fr/hal-00420599
DOI : 10.1016/j.jafrearsci.2009.09.005

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Analysis of the microstructures in the km-scale mantle shear zone that separates the northern and the central parts of the Lanzo peridotite massif provides evidence of an evolution in time and space of deformation processes accommodating shearing in the shallow mantle within an extensional setting. This shear zone displays an asymmetric distribution of deformation facies. From south to north, gradual reorientation of the foliation of coarse porphyroclastic plagioclase-bearing peridotites is followed by development of protomylonites, mylonites, and mm-scale ultramylonite bands. A sharp grain size gradient marks the northern boundary. Early deformation under near-solidus conditions in the south is recorded by preservation of weakly deformed interstitial plagioclase and almost random clinopyroxene and plagioclase crystal orientations. Feedback between deformation and melt transport probably led to melt focusing and strain weakening in the shear zone. Overprint of melt-rock reaction microstructures by solid-state deformation and decrease in recrystallized grain size in the protomylonites and mylonites indicate continued deformation under decreasing temperature. Less enriched peridotite compositions and absence of ultramafic dykes or widespread melt-impregnation microstructures north of the shear zone and clinopyroxene and amphibole enrichment in the mylonites and ultramylonites suggest that the shear zone acted as both a thermal barrier and a high-permeability channel for late crystallizing fluids. These observations, together with chemical data indicating faster cooling of central Lanzo relative to the northern body, corroborate that this shear zone is a mantle detachment fault. All deformation facies have crystal preferred orientations consistent with deformation by dislocation creep with dominant activation of the (010)[100] and (100)[001] systems in olivine and orthopyroxene, respectively. Dynamic recrystallization produces dispersion of olivine CPO but not a change of dominant deformation mechanism. Evidence for activation of grain boundary sliding is limited to mm-scale ultramylonite bands, where solid-state reactions produced very fine grained polymineralic aggregates. Except for these latest stages of deformation, strain localization does not result from the microstructural evolution; the grain size decrease is a consequence of the need to deform a rock volume whose strength continuously increases because of decreasing temperature conditions. Strain localization in the intermediate levels thus essentially results from the more localizing behavior of both the deep, partially molten, and shallow parts of this extensional shear zone distribution.
ISSN: 1525-2027

hal-00644844
https://hal.archives-ouvertes.fr/hal-00644844
DOI : 10.1029/2011GC003627

Éditeur(s) : HAL CCSD Elsevier
Résumé : Water molecules play a fundamental role in the physics of slow crack propagation in glasses. It is commonly understood that, during stress-corrosion, water molecules that move in the crack cavity effectively reduce the bond strength at the strained crack tip and, thus, support crack propagation. Yet the details of the environmental condition at the crack tip in moist air are not well determined. In a previous work, we reported direct evidence of the presence of a 100 nm long liquid condensate at the crack tip in fused silica glass during very slow crack propagation (10(-9)-10(-10) m/s). These observations are based on in situ AFM phase imaging techniques applied on DCDC glass specimens in controlled atmosphere. Here, we discuss the physical origin of the AFM phase contrast between the liquid condensate and the glass surface in relation to tip-sample adhesion induced by capillary bridges. We then report new experimental data on the water condensation length increase with relative humidity in the atmosphere. The measured condensation lengths were much larger than what predicted using the Kelvin equation and expected geometry of the crack tip.
ISSN: 0022-3093

hal-00412153
https://hal.archives-ouvertes.fr/hal-00412153
DOI : 10.1016/j.jnoncrysol.2007.06.090

Éditeur(s) : HAL CCSD BMJ Publishing Group
Résumé : International audience
Objective The potential impact of environmental exposure to pyrethroid insecticides on child neurodevelopment has only just started to receive attention despite their widespread use. We investigated the associations between prenatal and childhood exposure to pyrethroid insecticides and behavioural skills in 6-year-olds. Methods The PELAGIE cohort enrolled 3421 pregnant women from Brittany, France between 2002 and 2006. 428 mothers were randomly selected for the study when their children turned 6, and 287 (67%) agreed to participate. Children's behaviour was assessed using the Strengths and Difficulties Questionnaire (SDQ). Three subscales (prosocial behaviour, internalising disorders and externalising disorders) were considered. Five pyrethroid metabolites were measured in maternal and child urine samples collected between 6 and 19 gestational weeks and at 6 years of age, respectively. Logistic regression and reverse-scale Cox regression models were used to estimate the associations between SDQ scores and urinary pyrethroid metabolite concentrations, adjusting for organophosphate metabolite concentrations and potential confounders. Results Increased prenatal cis-3-(2,2-dichlorovinyl)-2,2dimethylcyclopropane carboxylic acid (DCCA) concentrations were associated with internalising difficulties (Cox p value=0.05). For childhood 3phenoxybenzoic acid (PBA) concentrations, a positive association was observed with externalising difficulties (Cox p value=0.04) and high ORs were found for abnormal or borderline social behaviour (OR 2.93, 95% CI 1.27 to 6.78, and OR 1.91, 95% CI 0.80 to 4.57, for the intermediate and highest metabolite categories, respectively). High childhood trans-DCCA concentrations were associated with reduced externalising disorders (Cox p value=0.03). Conclusions The present study suggests that exposure to certain pyrethroids, at environmental levels, may negatively affect neurobehavioral development by 6 years of age.
ISSN: 1351-0711

hal-01519255
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01519255
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01519255/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01519255/file/Behavioural%20disorders%20in%206-year-old%20children_JFViel_HAL.pdf
DOI : 10.1136/oemed-2016-104035

Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : International audience
This work evaluates the influence of three different intensities of refinement of sisal pulp and the effect of accelerated aging cycles on the behavior of composites. Fiber-cements were prepared by the slurry de-watering method and pressing as a crude simulation of the Hatschek process. Mechanical behavior of composites was evaluated by four-point bending test at 28 days, and after 50 and 100 wet/dry cycles. Refinement of pulp and aging have increased the strength and bulk density of composites and decreased the toughness and porosity. The best mechanical performance after aging was achieved for samples with highly refined fibers.
ISSN: 1042-6914

hal-00809817
https://hal.univ-antilles.fr/hal-00809817
DOI : 10.1080/10426910601062065

Éditeur(s) : HAL CCSD
Résumé : International audience
BACKGROUND: Dairy working increases the prevalence of lower airway respiratory diseases, especially COPD and asthma. Epidemiological studies have reported that chronic inhalation of organic dusts released during specific daily tasks could represent a major risk factor for development of these pathologies in dairy workers. Knowledge on size, nature and biological activity of such organic dusts remain however limited. OBJECTIVE: To compare size distribution, microbial composition and cellular effects of dusts liberated by the spreading of straw bedding in five French dairy farms located in Brittany. RESULTS: Mechanized distribution of straw bedding generated a cloud of inhalable dusts in the five dairy farms' barns. Thoracic particles having a 3-7.5µm size constituted 58.9-68.3% of these dusts. Analyses of thoracic dusts by next generation sequencing showed that the microbial dust composition differed between the five French farms, although Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria represent more than 97.5% of the bacterial phyla detected in each sample. Several bacteria genera comprising of human pathogenic species, such as Pseudomonas, Staphylococcus, Thermoactinomyces or Saccharopolyspora were identified. Cladosporium and Alternaria fungal genera, which are potent environmental determinants of respiratory symptoms, were detected in dusts collected in the five farms and their levels reached 15.5-51.1% and 9-24.7% of assignable fungal sequences in each sample, respectively. Finally, all dust samples significantly and strongly increased the expression of the pro-inflammatory TNF-α, IL-1β, IL-6 and IL-8 cytokines at both mRNA and protein levels in human monocyte-derived macrophages. Their effects were dose-dependent and detectable from 1µg/ml. The intensity of the macrophage responses however differed according to the samples. CONCLUSIONS: Our results strengthen the hypothesis that organic dusts released during the distribution of straw bedding are mainly constituted of thoracic particles which are small enough to deposit on lower bronchial epithelium of dairy farmers and induce inflammation.
Environmental Research

hal-01579610
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01579610
DOI : 10.1016/j.envres.2017.07.025
PUBMED : 28735230

Éditeur(s) : HAL CCSD Springer Verlag
Résumé :  
Growth strains were measured in situ in nine trees of three species from a French Guiana tropical rainforest in a clearly active verticality restoration process. The aim was to detect tension wood within the samples. Wood specimens were cut in the vicinity of the growth strain measurements in order to determine the microfibril angle and some mechanical and physical properties. As suspected, tensile growth strain was much higher in tension wood zones, as shown by the slightly higher longitudinal modulus of elasticity. Conversely, tension wood showed reduced compression strength. Longitudinal shrinkage was much higher in tension wood than in opposite wood. Clear relationships between the microfibril angle and longitudinal properties were noted in comparison (i) with those observed in gymnosperm compression wood and (ii) with expected relationships from the organization of wood fibres cell wall structure.
ISSN: 0043-7719

hal-01032114
https://hal.archives-ouvertes.fr/hal-01032114
DOI : 10.1007/s00226-010-0323-9

Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
Background: The Ras/Raf/MEK/ERK signaling pathway is involved in essential cell processes and it is abnormally activated in similar to 30 % of cancers and cognitive disorders. Two ERK isoforms have been described, ERK1 and ERK2; ERK2 being regarded by many as essential due to the embryonic lethality of ERK2 knock-out mice, whereas mice lacking ERK1 are viable and fertile. The controversial question of why we have two ERKs and whether they have differential functions or display functional redundancy has not yet been resolved. Results: To investigate this question we used a novel approach based on comparing the evolution of ERK isoforms' sequences and protein expression across vertebrates. We gathered and cloned erk1 and erk2 coding sequences and we examined protein expression of isoforms in brain extracts in all major clades of vertebrate evolution. For the first time, we measured each isoforms' relative protein level in phylogenetically distant animals using anti-phospho antibodies targeting active ERKs. We demonstrate that squamates (lizards, snakes and geckos), despite having both genes, do not express ERK2 protein whereas other tetrapods either do not express ERK1 protein or have lost the erk1 gene. To demonstrate the unexpected squamates' lack of ERK2 expression, we targeted each ERK isoform in lizard primary fibroblasts by specific siRNA-mediated knockdown. We also found that undetectable expression of ERK2 in lizard is compensated by a greater strength of lizard's erk1 promoter. Finally, phylogenetic analysis revealed that ERK1 amino acids sequences evolve faster than ERK2' s likely due to genomic factors, including a large difference in gene size, rather than from functional differences since amino acids essential for function are kept invariant. Conclusions: ERK isoforms appeared by a single gene duplication at the onset of vertebrate evolution at least 400 Mya. Our results demonstrate that tetrapods can live by expressing either one or both ERK isoforms, supporting the notion that ERK1/2 act interchangeably. Substrate recognition sites and catalytic cleft are nearly invariant in all vertebrate ERKs further suggesting functional redundancy. We suggest that future ERK research should shift towards understanding the role and regulation of total ERK quantity, especially in light of newly described erk2 gene amplification identified in tumors.
ISSN: 1471-2148

hal-01546165
https://hal.archives-ouvertes.fr/hal-01546165
DOI : 10.1186/s12862-015-0450-x

Éditeur(s) : HAL CCSD Station Biologique
Résumé : International audience
Four "morphotypes" of Mytilidae were collected from wood falls in the west Pacific (Vanuatu islands) and in the Bohol sea (Philippines) between 300 and 1800 metre depth. Results from our study demonstrated the existence of extracellular bacteria located between microvilli at the apical surface of the cells all along the lateral zone of the gill filaments in the four mytilid morphotypes analyzed. Based on TEM observations, these Gram-negative bacteria were not methanotrophic due to the lack of concentric stacking of intracellular membranes in their cytoplasm. Based on FISH experiments, these bacteria belong to g-Proteobacteria. These preliminary observations described gill symbiosis-like interactions in metazoan species associated with sunken wood, strengthening the hypothesis that decomposing wood may serve as steps for the introduction of symbiotic Mytilidae to vents and seeps. Phylogenetic analysis of these extracellular bacteria are in progress in our lab in order to compare their 16SrDNA sequences to that of other marine invertebrate symbionts described to date.
ISSN: 0007-9723

hal-00753023
https://hal.univ-antilles.fr/hal-00753023

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The interseismic velocity field provided by geodetic methods is generally interpreted in the framework of a thick elastic lithosphere with a slipping fault at depth. Because lateral variations of lithospheric rheology play a key role in determining the geological strain distribution, I examine the idea that interseismic strain rate variations also occur in response to lateral variations in the elastic thickness of the lithosphere. Using a stress balance principle and some simplifying assumptions, I show using a 1D model that elastic thickness is inversely proportional to strain rate for the simple case of pure strike-slip faulting. Elastic thickness computed on three profiles crossing the San Andreas fault system (SAFS) suggests that the distribution of interseismic strain rate is compatible with a thick elastic lithosphere in the Great Basin-Sierra Nevada province and on the Pacific plate. Conversely, a thin plate with a shallow asthenosphere is needed on the SAFS to explain its high strain rate. A 2.5D Finite Element model of interseismic strain in the Carrizo Plain region in Central California shows how known vertical and horizontal variations of elastic properties refine 1D model predictions. In a case of a multiple fault system, I point out that the interseismic velocity is not causally tied to faults slip rate. Therefore, analysing the velocity field across the SAFS cannot reliably provide faults slip rate distribution as previously claimed. Rather, the apparent correlation between geologic slip rate and interseismic strain may only indicate that the elastic thickness plays a dominant role in controlling fault strength. Finally, I suggest that interseismic geodetic strain could be a new way to infer effective elastic plate thickness on the continents.
ISSN: 0012-821X

hal-00412155
https://hal.archives-ouvertes.fr/hal-00412155
DOI : 10.1016/j.epsl.2008.01.046

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : Ten international laboratories participated in an inter-laboratory comparison of a fossil bone composite with the objective of producing a matrix and structure-matched reference material for studies of the bio-mineralization of ancient fossil bone. We report the major and trace element compositions of the fossil bone composite, using in-situ method as well as various wet chemical digestion techniques. For major element concentrations, the intra-laboratory analytical precision (%RSDr) ranges from 7 to 18%, with higher percentages for Ti and K. The %RSDr are smaller than the inter-laboratory analytical precision (%RSDR; <15-30%). Trace element concentrations vary by similar to 5 orders of magnitude (0.1 mg kg(-1) for Th to 10,000 mg kg(-1) for Ba). The intra-laboratory analytical precision %RSDr varies between 8 and 45%. The reproducibility values (%RSDR) range from 13 to <50%, although extreme value >100% was found for the high field strength elements (Hf, Th, Zr, Nb). The rare earth element (REE) concentrations, which vary over 3 orders of magnitude, have %RSDr and %RSDR values at 8-15% and 20-32%, respectively. However, the REE patterns (which are very important for paleo-environmental, taphonomic and paleo-oceanographic analyses) are much more consistent. These data suggest that the complex and unpredictable nature of the mineralogical and chemical composition of fossil bone makes it difficult to set-up and calibrate analytical instruments using conventional standards, and may result in non-spectral matrix effects. We propose an analytical protocol that can be employed in future inter-laboratory studies to produce a certified fossil bone geochemical standard. (C) 2007 Elsevier B.V. All rights reserved.
ISSN: 0003-2670

hal-00407629
https://hal.archives-ouvertes.fr/hal-00407629
DOI : 10.1016/j.aca.2007.08.015

Éditeur(s) : HAL CCSD American Physical Society
Résumé : International audience
Using contact dynamics simulations, 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. In simple shear conditions, we consider four aspects of the mechanical behavior of these systems in the steady state: shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. Our main finding is 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.
ISSN: 1539-3755

hal-00594891
https://hal.archives-ouvertes.fr/hal-00594891
https://hal.archives-ouvertes.fr/hal-00594891/document
https://hal.archives-ouvertes.fr/hal-00594891/file/Estrada2010ReSubmitV2.pdf
ARXIV : 1105.4418