Ductile to brittle transition concept on fracture behavior of poly(vinylidene fluoride) / poly(methyl methacrylate) blends

International audienceThe fracture behavior of blends of poly(ninylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) was investigated by gradually increasing the PVDF content. The study focuses on semi-crystalline blends. The trends of net stress versus crack opening displacement curves were analyzed. From these plots, two fracture energies were defined: the fracture energy to crack initiation corresponding to the area under the curve up to the maximum net stress and the fracture energy to crack propagation considering the last part of the curve where the load continuously decreases. Fracture surface inspections confirmed typical semi-crystalline polymer features. Critical values of the degree of crystallinity corresponding to brittle to ductile transition were determined, depending on the selected fracture energ

Récits sur l’origine des langues : enromancier Babel

Cette étude, qui porte sur le récit de la Tour de Babel, s’intéresse aux premières traductions de ce texte (douzième et treizième siècles). Après avoir mis en évidence les principales caractéristiques de l’exégèse de ce passage, elle se concentre sur une traduction originale : la Genèse d’Evrat (fin du xiie siècle). Comment ce texte construit-il la valeur du français alors que l’interprétation commune du récit babélien participe de la mise en place d’une hiérarchie linguistique 

Collectif, Le beau et la beauté au Moyen Âge

Cet ouvrage, issu d’un colloque qui s’est tenu en novembre 2011 dans le cadre de l’Institut d’études médiévales de l’Institut catholique de Paris, s’intéresse au concept de beauté au Moyen Âge : reprenant et prolongeant selon diverses modalités les réflexions qu’Olivier Boulnois a proposées dans un article important (« La beauté d’avant l’art : d’Umberto Eco à saint Thomas d’Aquin, et retour », dans Le Souci du passage. Mélanges offerts à Jean Greisch, P. Capelle-Dumont, G. Hébert et M.-D. Po..

Le Perlesvaus et l’ornementation

Le Perlesvaus, a-t-on dit, est un roman « sauvage » qui développe « une véritable poétique de la cruauté, fondée sur des images obsédantes […] et des fantasmes barbares ». Toutefois, dans le même temps et à la faveur d’une surprenante « dualité de tons » qui a elle aussi été soulignée, le roman se distingue par le soin qu’il accorde à l’ornementation des objets et des décors. C’est de cette thématique que nous voudrions partir : le fait qu’un Haut Livre se caractérise par sa prolifération déc..

Conserved Meiotic Machinery in Glomus spp., a Putatively Ancient Asexual Fungal Lineage

Arbuscular mycorrhizal fungi (AMF) represent an ecologically important and evolutionarily intriguing group of symbionts of land plants, currently thought to have propagated clonally for over 500 Myr. AMF produce multinucleate spores and may exchange nuclei through anastomosis, but meiosis has never been observed in this group. A provocative alternative for their successful and long asexual evolutionary history is that these organisms may have cryptic sex, allowing them to recombine alleles and compensate for deleterious mutations. This is partly supported by reports of recombination among some of their natural populations. We explored this hypothesis by searching for some of the primary tools for a sustainable sexual cycle—the genes whose products are required for proper completion of meiotic recombination in yeast—in the genomes of four AMF and compared them with homologs of representative ascomycete, basidiomycete, chytridiomycete, and zygomycete fungi. Our investigation used molecular and bioinformatic tools to identify homologs of 51 meiotic genes, including seven meiosis-specific genes and other “core meiotic genes” conserved in the genomes of the AMF Glomus diaphanum (MUCL 43196), Glomus irregulare (DAOM-197198), Glomus clarum (DAOM 234281), and Glomus cerebriforme (DAOM 227022). Homology of AMF meiosis-specific genes was verified by phylogenetic analyses with representative fungi, animals (Mus, Hydra), and a choanoflagellate (Monosiga). Together, these results indicate that these supposedly ancient asexual fungi may be capable of undergoing a conventional meiosis; a hypothesis that is consistent with previous reports of recombination within and across some of their populations

+1 Frameshifting as a Novel Mechanism to Generate a Cryptic Cytotoxic T Lymphocyte Epitope Derived from Human Interleukin 10

Recent data indicate that some cytotoxic T cells (CTLs) recognize so-called cryptic epitopes, encoded by nonprimary open reading frame (ORF) sequences or other nonclassical expression pathways. We describe here a novel mechanism leading to generation of a cryptic CTL epitope. We isolated from the synovial fluid of a patient suffering from a Reiter's syndrome an autoreactive T cell clone that recognized cellular IL-10 in the HLA-B*2705 context. The minimal IL-10 sequence corresponding to nucleotides 379–408 was shown to activate this clone, upon cotransfection into COS cells with the DNA encoding HLA-B*2705, but the synthetic peptide deduced from this sequence did not stimulate the clone. Using a site-directed mutagenesis approach, we found that this clone recognized a transframe epitope generated by an internal +1 frameshifting in the IL-10 sequence and so derived partly from ORF1, partly from ORF2. We defined that +1 frameshifting was induced by a specific heptamer sequence. These observations illustrate the variety of mechanisms leading to generation of cryptic epitopes and suggest that frameshifting in normal cellular genes may be more common than expected

Influence of chemosynthetic substrates availability on symbiont densities, carbon assimilation and transfer in the dual symbiotic vent mussel <I>Bathymodiolus azoricus</I>

International audienceHigh densities of mussels of the genus Bathymodiolus are present at hydrothermal vents of the Mid-Atlantic Ridge. It was already proposed that the chemistry at vent sites would affect their sulphide- and methane-oxidizing endosymbionts' abundance. In this study, we confirmed the latter assumption using fluorescence in situ hybridization on Bathymodiolus azoricus specimens maintained in a controlled laboratory environment at atmospheric pressure with one, both or none of the chemical substrates. A high level of symbiosis plasticity was observed, methane-oxidizers occupying between 4 and 39% of total bacterial area and both symbionts developing accordingly to the presence or absence of their substrates. Using H13CO3- in the presence of sulphide, 13CH4 or 13CH3OH, we monitored carbon assimilation by the endosymbionts and its translocation to symbiont-free mussel tissues. Although no significant carbon assimilation could be evidenced with methanol, carbon was incorporated from methane and sulphide-oxidized inorganic carbon at rates 3 to 10 times slower in the host muscle tissue than in the symbiont-containing gill tissue. Both symbionts thus contribute actively to B. azoricus nutrition and adapt to the availability of their substrates. Further experiments with varying substrate concentrations using the same set-up should provide useful tools to study and even model the effects of changes in hydrothermal fluids on B. azoricus' chemosynthetic nutrition

Easy Access to a Cyclic Key Intermediate for the Synthesis of Trisporic Acids and Related Compounds

The synthesis of a cyclohexane skeleton possessing different oxygenated functional groups at C–3, C–8 and C–9, and a D1,6-double bond has been accomplished in 10 steps with an overall 17% yield. This compound is a key intermediate for access to a wide range of compounds of the bioactive trisporoid family. The synthetic sequence consists of the preparation of a properly functionalized epoxygeraniol derivative, and its subsequent stereoselective cyclization mediated by Ti(III). This last step implies a domino process that starts with a homolytic epoxide opening followed by a radical cyclization and regioselective elimination. This concerted process gives access to the cyclohexane moiety with stereochemical control of five of its six carbon atoms.This project was supported by the Spanish Ministry of Economy and Competitiveness (project CTQ2010-16818-BQ)

Expression of DC-SIGN and DC-SIGNR on human sinusoidal endothelium: a role for capturing hepatitis C virus particles.

Hepatic sinusoidal endothelial cells are unique among endothelial cells in their ability to internalize and process a diverse range of antigens. DC-SIGNR, a type 2 C-type lectin expressed on liver sinusoids, has been shown to bind with high affinity to hepatitis C virus (HCV) E2 glycoprotein. DC-SIGN is a closely related homologue reported to be expressed only on dendritic cells and a subset of macrophages and has similar binding affinity to HCV E2 glycoprotein. These receptors function as adhesion and antigen presentation molecules. We report distinct patterns of DC-SIGNR and DC-SIGN expression in human liver tissue and show for the first time that both C-type lectins are expressed on sinusoidal endothelial cells. We confirmed that these receptors are functional by demonstrating their ability to bind HCV E2 glycoproteins. Although these lectins on primary sinusoidal cells support HCV E2 binding, they are unable to support HCV entry. These data support a model where DC-SIGN and DC-SIGNR on sinusoidal endothelium provide a mechanism for high affinity binding of circulating HCV within the liver sinusoids allowing subsequent transfer of the virus to underlying hepatocytes, in a manner analogous to DC-SIGN presentation of human immunodeficiency virus on dendritic cells