Caractérisation d'une entaille dans un milieu homogène par une approche asymptotique

Dans cette étude, une méthodologie de calcul du facteur d'intensité de contraintes a été développée. La particularité de cette méthode consiste en la détermination par un calcul itératif par éléments finis de l'ordre de la singularité qui sera intégré dans la formulation de MARTIN L et al. et dans celle de G. GROSS et MENDELSON pour déterminer ce facteur d'intensité de contraintes. Les résultats obtenus par cette approche ont été validés par la littérature (LEGUILON D)

Depletion of abscisic acid levels in roots of flooded Carrizo citrange (Poncirus trifoliata L. Raf. x Citrus sinensis L. Osb.) plants is a stress-specific response associated to the differential expression of PYR/PYL/RCAR receptors

[EN] Soil flooding reduces root abscisic acid (ABA) levels in citrus, conversely to what happens under drought. Despite this reduction, microarray analyses suggested the existence of a residual ABA signaling in roots of flooded Carrizo citrange seedlings. The comparison of ABA metabolism and signaling in roots of flooded and water stressed plants of Carrizo citrange revealed that the hormone depletion was linked to the upregulation of CsAOG, involved in ABA glycosyl ester (ABAGE) synthesis, and to a moderate induction of catabolism (CsCYP707A, an ABA 8'-hydroxylase) and buildup of dehydrophaseic acid (DPA). Drought strongly induced both ABA biosynthesis and catabolism (CsNCED1, 9-cis-neoxanthin epoxycarotenoid dioxygenase 1, and CsCYP707A) rendering a significant hormone accumulation. In roots of flooded plants, restoration of control ABA levels after stress release was associated to the upregulation of CsBGLU18 (an ABA beta-glycosidase) that cleaves ABAGE. Transcriptional profile of ABA receptor genes revealed a different induction in response to soil flooding (CsPYL5) or drought (CsPYL8). These two receptor genes along with CsPYL1 were cloned and expressed in a heterologous system. Recombinant CsPYL5 inhibited Delta NHAB1 activity in vitro at lower ABA concentrations than CsPYL8 or CsPYL1, suggesting its better performance under soil flooding conditions. Both stress conditions induced ABA-responsive genes CsABI5 and CsDREB2A similarly, suggesting the occurrence of ABA signaling in roots of flooded citrus seedlings. The impact of reduced ABA levels in flooded roots on CsPYL5 expression along with its higher hormone affinity reinforce the role of this ABA receptor under soil-flooding conditions and explain the expression of certain ABA-responsive genes.This work was supported by Ministerio de Economia y Competitividad (MINECO), Fondo Europeo de Desarrollo Regional (FEDER) and Universitat Jaume I through grants No. AGL201676574-R, UJI-B2016-23/UJI-B2016-24 to A.G-C. and V.A. and MINECO, FEDER and Consejo Superior de Investigaciones Cientificas (CSIC) through grant BIO2014-52537-R to P.L.R. S.I.Z. and M.M. were supported by predoctoral grants from Universitat Jaume I and Generalitat Valenciana, respectively. M.G.G. was recipient of a "JAE-DOC" contract from the CSIC. 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The Cys-Arg/N-end rule pathway is a general sensor of abiotic stress in flowering plants

Abiotic stresses impact negatively on plant growth, profoundly affecting yield and quality of crops. Although much is known about plant responses, very little is understood at the molecular level about the initial sensing of environmental stress. In plants, hypoxia (low oxygen, which occurs during flooding) is directly sensed by the Cys-Arg/N-end rule pathway of ubiquitin-mediated proteolysis, through oxygen-dependent degradation of group VII Ethylene Response Factor transcription factors (ERFVIIs) via amino-terminal (Nt-) cysteine [1, 2]. Using Arabidopsis (Arabidopsis thaliana) and barley (Hordeum vulgare), we show that the pathway regulates plant responses to multiple abiotic stresses. In Arabidopsis, genetic analyses revealed that response to these stresses is controlled by N-end rule regulation of ERFVII function. Oxygen sensing via the Cys-Arg/N-end rule in higher eukaryotes is linked through a single mechanism to nitric oxide (NO) sensing [3, 4]. In plants, the major mechanism of NO synthesis is via NITRATE REDUCTASE (NR), an enzyme of nitrogen assimilation [5]. Here, we identify a negative relationship between NR activity and NO levels and stabilization of an artificial Nt-Cys substrate and ERFVII function in response to environmental changes. Furthermore, we show that ERFVIIs enhance abiotic stress responses via physical and genetic interactions with the chromatin-remodeling ATPase BRAHMA. We propose that plants sense multiple abiotic stresses through the Cys-Arg/N-end rule pathway either directly (via oxygen sensing) or indirectly (via NO sensing downstream of NR activity). This single mechanism can therefore integrate environment and response to enhance plant survival

Coupling the Leidenfrost effect and elastic deformations to power sustained bouncing

The Leidenfrost effect occurs when an object near a hot surface vaporizes rapidly enough to lift itself up and hover. Although well-understood for liquids and stiff sublimable solids, nothing is known about the effect with materials whose stiffness lies between these extremes. Here we introduce a new phenomenon that occurs with vaporizable soft solids: the elastic Leidenfrost effect. By dropping hydrogel spheres onto hot surfaces we find that, rather than hovering, they energetically bounce several times their diameter for minutes at a time. With high-speed video during a single impact, we uncover high-frequency microscopic gap dynamics at the sphere-substrate interface. We show how these otherwise-hidden agitations constitute work cycles that harvest mechanical energy from the vapour and sustain the bouncing. Our findings unleash a powerful and widely applicable strategy for injecting mechanical energy into soft materials, with relevance to fields ranging from soft robotics and metamaterials to microfluidics and active matter

Directorium divini cultus ad Cathedralis Ecclesiae Minoriccensis : eiusque Dioecesis usum

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A Simple Model to Describe the Average Propagation Energy of a Brittle Crack Running Along a Porous Interface

International audienceA simple 'Cavity Affected Zone' model is proposed to describe the influence of the interfacial pore fraction on the average interfacial crack propagation energy in a brittle porous interface. It is based on the assumption that each cavity is surrounded by a perturbed interface zone along which the fracture energy is locally different from its reference value in a perfect plain and planar interface. Consequently, when the interface pore fraction is increased, a two-step sequence of regimes is predicted for the measurable overall interfacial fracture energy. This simple but flexible description is found to be consistent with two different recent examples of experimental adhesion measurements. It is expected to be helpful in analysing detailed mechanisms of crack growth and practical adhesion in porous or patterned brittle solid/solid interfaces. (C) Koninklijke Brill NV, Leiden, 201