Multi-mechanism modeling of amorphous polymers

International audienceThe paper is devoted to a multi-mechanism (MM) model for the mechanical behavior of amorphous glassy polymers. A finite strain formulation through updated Lagrangian formalisms is used. In the proposed phenomenological model, three mechanisms are respectively associated to three physical regimes of plastic deformation. The model was successful in describing the stress-strain behavior of glassy polymers for different strain rates and range of temperatures. The description of the three regions observed in the monotonic stress-strain curves is obtained through a coupling matrix between the isotropic hardening variables. A modular strategy based on the determination of the material parameters in three steps is proposed

WSN for Event Detection Applications: Deployment, Routing, and Data Mapping Using AI

In the 20th century, computers were senseless brains, but today, thanks to sensor networks, they can feel things for themselves. This major trend has given rise to many wireless sensor networks with the ability to sense the environment, deliver findings and process those data appropriately. Within this trend, this chapter outlines deployment and routing strategies as well as data handling practices. For convenience, the most encompassing application to consider is that of event detection

PEPTIDES EXTRACTED FROM ARTEMISIA HERBA ALBA HAVE ANTIMICROBIAL ACTIVITY AGAINST FOODBORNE PATHOGENIC GRAM-POSITIVE BACTERIA

Background: Artemisia herba alba, classified into the family of Asteraceae, is an aromatic herb that is traditionally used as a purgative and anti-pyretic folk medicine by rural people of south Tunisia. This study reports the first identification of antimicrobial peptides from this medicinal plant that inhibited the growth of several food-borne pathogenic bacteria. Materials and methods: The extraction and purification of peptidic agents from Artemisia herba alba, have been performed using precipitation by ammonium sulfate of a phosphate buffer crude extract obtained from the plant leaves, followed by reverse-phase HPLC on a C18 column. The mass of the peptides was estimated by SDS-PAGE electrophoresis, followed by a gel overlay assay and ultra-filtration through a 5 kDa cut-off membrane. Fractions from every purification steps were sampled and assayed for activity towards different food-borne bacterial strains pathogenic and non pathogenic to humans. Results: The phosphate buffer crude extract, as well as its ammonium sulfate precipitate, designated AS-P, inhibited the growth of Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus sensu stricto and the new approved species Bacillus cytotoxicus. AS-P MICs (minimum inhibitory concentrations) ranged from 0.241 to 3.8 mg/ml proteins for L. monocytogenes and B. cereus sensu stricto (strains ATCC10987 and IP5832), respectively. The bioactive AS-P molecules were stable up to 10 minutes heating at 120°C and they resisted organic solvent effects. Antimicrobial activity of A. herba alba AS-P decreased to 40 and 60% after proteolytic treatment with trypsin and proteinase K, respectively, suggesting peptides being responsible for the A. herba alba AS-P activity. The mass of antibacterial A. herba alba peptides was estimated below 5 kDa. Two AS-P fractions, eluted at 40 and 37% acetonitrile, showed antibacterial activity when assayed against L. monocytogenes. Conclusion: A. herba alba could make a new source of novel natural anti-infective agents that could be used in food bio-preservation as natural additives or in human infectious disease treatments against multi-drug resistant pathogens

Offspring born to influenza A virus infected pregnant mice have increased susceptibility to viral and bacterial infections in early life

Influenza during pregnancy can affect the health of offspring in later life, among which neurocognitive disorders are among the best described. Here, we investigate whether maternal influenza infection has adverse effects on immune responses in offspring. We establish a two-hit mouse model to study the effect of maternal influenza A virus infection (first hit) on vulnerability of offspring to heterologous infections (second hit) in later life. Offspring born to influenza A virus infected mothers are stunted in growth and more vulnerable to heterologous infections (influenza B virus and MRSA) than those born to PBS- or poly(I:C)-treated mothers. Enhanced vulnerability to infection in neonates is associated with reduced haematopoetic development and immune responses. In particular, alveolar macrophages of offspring exposed to maternal influenza have reduced capacity to clear second hit pathogens. This impaired pathogen clearance is partially reversed by adoptive transfer of alveolar macrophages from healthy offspring born to uninfected dams. These findings suggest that maternal influenza infection may impair immune ontogeny and increase susceptibility to early life infections of offspring

Lung emphysema and impaired macrophage elastase clearance in mucolipin 3 deficient mice

Lung emphysema and chronic bronchitis are the two most common causes of chronic obstructive pulmonary disease. Excess macrophage elastase MMP-12, which is predominantly secreted from alveolar macrophages, is known to mediate the development of lung injury and emphysema. Here, we discovered the endolysosomal cation channel mucolipin 3 (TRPML3) as a regulator of MMP-12 reuptake from broncho-alveolar fluid, driving in two independently generated Trpml3-/- mouse models enlarged lung injury, which is further exacerbated after elastase or tobacco smoke treatment. Mechanistically, using a Trpml3IRES-Cre/eR26-τGFP reporter mouse model, transcriptomics, and endolysosomal patch-clamp experiments, we show that in the lung TRPML3 is almost exclusively expressed in alveolar macrophages, where its loss leads to defects in early endosomal trafficking and endocytosis of MMP-12. Our findings suggest that TRPML3 represents a key regulator of MMP-12 clearance by alveolar macrophages and may serve as therapeutic target for emphysema and chronic obstructive pulmonary disease

Comportements colloïdaux dans des films minces de cristaux liquides

The confinement of colloidal particles in thin liquid films is typically accompanied with interfacial deformations which give rise to long-range capillary forces, attractive in most of the cases. In simple fluids, these capillary forces compete mostly with electrostatic interactions. In thin complex fluid films such as a liquid crystal, other long-range interactions related to bulk distortions of the surrounding fluid appear. The presence of a nematic order drastically changed the long-range interactions between particles via an original elasto-capillarity coupling.In nematic films much thicker than the particles’ size, a particle gives rise to elastic multipoles formed by the particle and nearby topological defects. In thin nematic films with hybrid anchoring conditions at free surfaces, capillary effects strongly modify the behaviour of the elastic dipoles. For a certain range of film thickness values, two new interesting patterns emerged around isolated particles: the giant dipole and the “butterfly” texture. In the giant dipole, a micron-sized sphere is accompanied by a point defect located at a distance up to several hundreds microns. The situation is quite different in the “butterfly” texture: the particle still produces an accompanying defect in its close neighbourhood, but a π-wall is formed on the opposite side. Using spatially resolved retardation and easy-axis maps, we analysed quantitatively and separately the 2D interfaces deformation and the nematic textures. Both behaviours are due to the same axisymmetric capillary deformation of the thin film around the beads but with different boundary conditions for the polar 2D c-director. Using numerical simulations, we were able to reproduce the patterns found in the films. Although capillary interactions between inclusions in a thin film are always attractive, these new spontaneous organizations in thin nematic films offer new ways to self-assemble complex colloidal systems in 2D.Le confinement des microparticules dans un film mince de fluide isotrope est généralement accompagné d’une déformation des interfaces qui donne naissance à de fortes interactions capillaires entre colloïdes, de nature attractive dans la plupart des cas. La situation devient différente lorsqu’il s’agit d’un film mince de fluide complexe à l’exemple du cristal liquide nématique. Nos études ont été alors consacrées au cas des colloïdes piégés dans un film nématique mince étalé sur un liquide isotrope. Lorsque l’épaisseur du film nématique devient inférieure à la taille des colloïdes, l’apparition d’effets capillaires engendre deux nouvelles géométries élastiques autour des particules : Le dipôle élastique géant et la texture « papillon ». La particule dans le cas du dipôle géant est accompagnée de son contre-défaut localisé à une distance qui dépasse 100 fois sa taille. La texture « papillon » est cependant caractérisée par la présence du défaut topologique qui reste très proche de la particule d’un côté et d’une paroi π de l’autre côté. En exploitant les cartes du vecteur directeur bidimensionnel c et de la mesure du retard optique, nous avons analysé quantitativement et séparément la déformation capillaire et les textures élastiques du nématique. Dans les deux géométries observées, la déformation capillaire axisymétrique tend à imposer une orientation radiale au vecteur c autour des colloïdes mais avec des conditions topologiques différentes. En utilisant des simulations numériques nous avons retrouvé les textures élasto-capillaires observées expérimentalement. Finalement, nous avons montré que les distorsions élastiques autour des colloïdes piégés entrainent des forces élastiques à grande distance qui entrent en compétition avec les forces capillaires pour modifier l’auto-organisation des colloïdes aux interface du film nématique mince

Pathological study of Tunisian isolates of Erwinia amylovora and search for apoplastic signals inducing virulence genes

Erwinia amylovora est une bactérie responsable de la maladie du feu bactérien dont les hôtes appartiennent à la sous famille des rosacées, comme le pommier, le poirier et le cognassier. En 2012, E. amylovora a été identifiée en Tunisie, notamment dans le nord où les conditions climatiques sont favorables pour le développement rapide de cette pathologie. La première partie de ma thèse a consisté à isoler et identifier des souches d’E. amylovora à partir du Nord de la Tunisie. La sélection de vingt isolats a été réalisée en se basant sur l’aspect morphologique des colonies, par des méthodes biochimiques et moléculaires grâce à des PCRs en utilisant un ensemble d’amorces chromosomiques et plasmidiques spécifiques d’E. amylovora afin d’étudier la variabilité des souches isolées par rapport aux souches précédemment décrites isolées dans d’autres pays. En parallèle, j’ai testé le degré de pathogénicité de ces isolats en faisant des tests de pouvoir pathogène, de mobilité et de capacité de production de biofilms. La deuxième partie de ma thèse porte sur l’impact de l’azote (N) sur l’interaction E. amylovora - A. thaliana. Mon équipe a montré qu’un faible apport en nitrate réduit la résistance d’A. thaliana à E. amylovora et favorise l’expression in planta des gènes de virulence hrp. L’apoplasme, un des lieux d’infection primaire d’E. amylovora, permet l’échange de métabolites entre la plante et la bactérie, dont certains peuvent être des répresseurs ou des inducteurs des gènes de virulence bactériens. J’ai montré, in vitro, que le liquide apoplastique (AWF) extrait de feuilles d’A. thaliana cultivées en limitation de N (AWF2) induit plus fortement les gènes hrp d’E. amylovora que l’AWF de plantes cultivées à fort N (AWF10). L’analyse métabolomique par GC-MS de l’AWF2 et de l’AWF10 m’a permis d’identifier 114 métabolites primaires dont 102 sont plus accumulés dans l’AWF10 et seulement 12 sont plus accumulés dans l’AWF2. Parmi ces métabolites j’ai identifié des métabolites inducteurs des gènes hrp, comme l’acide linolénique et l’acide cyanurique et des répresseurs comme le citrate et le GABA. Suite à l’infection, 92 métabolites ont été identifiés dans l’AWF. Cependant, le contenu de l’AWF2 est plus sensible à l’infection que l’AWF10 après 6H d’infection. En conclusion, j’'ai montré qu’en condition de limitation en azote, le contenu métabolique de l’apoplasme de la feuille est modifié et de ce fait affecte la capacité d’E. amylovora à induire ses facteurs de virulence au cours des premières étapes de l’infection.Erwinia amylovora, the causal agent of fire blight. This pathogen, belongs to the Enterobacteriacea family. In 2012, this pathogen was identified from the north of Tunisia, where climatic conditions are favorable for the rapid development of this pathology. The first part of my thesis consisted in isolating and identifying strains of E. amylovora from different samples. The selection of twenty isolates was carried out based on the morphological aspect of the colonies, by biochemical and molecular methods thanks to PCRs using a set of chromosomal and plasmid primers specific to E. amylovora in order to study the variability of the isolated strains in comparison with previously described strains isolated in other countries. In parallel, I tested the degree of pathogenicity of these isolates by performing tests of pathogenicity, mobility and biofilm production capacity.The second part of my thesis deals with the impact of nitrogen (N) on the E. amylovora - A. thaliana interaction. Recently, my team has shown that low nitrate supply reduces the resistance of A. thaliana to E. amylovora and promotes the expression of hrp virulence genes in planta. Since the apoplast is the site of primary infection and exchange of molecules between the plant and the bacteria, some of which may be repressors or inducers of bacterial virulence genes. Based on this information, I showed in vitro that the apoplastic fluid (AWF) of A. thaliana grown under N limitation (AWF2) strongly induces hrp genes compared to that of plants grown under high N (AWF10). Metabolomic analyses of AWF allowed me to identify 114 primary metabolites, 102 of which are more accumulated in AWF10 and only 12 are more accumulated in AWF2. Among these metabolites I identified several metabolites that induce hrp gene expression, such as linolenic acid and cyanuric acid, and several hrp repressors such as citrate and GABA. Furthermore, I found that AWF2 content is more sensitive to infection by E. amylovora than AWF10. In conclusion, I have shown that N supply to plants affects the apoplastic content and thus affects the ability of E. amylovora to induce its virulence factors during the early stages of infection