Approche continue de la rupture du bois en grands déplacements

La rupture du bois est la conséquence de mécanismes complexes à l’échelle de la microstructure de ce matériau fortement anisotrope. De par son anatomie particulière, le bois exhibe un comportement post-rupture dépendant du type de sollicitation. En compression, une certaine forme de ductilité peut être observée tandis qu’en traction, la rupture est fragile. Ajouté à cela, la direction du chargement (parallèle ou perpendiculaire au grain) introduit une grande spécificité des modes de rupture qu’il est difficile de rassembler à travers un critère unique. Dans la présente étude, on modélisera la rupture du bois en traction ou compression parallèle au fil par une approche continue de la fissuration et le recours à un critère multi-surface de plasticité. L’approche sera formulée dans le cadre des grandes transformations et implémentée dans un code de calcul éléments finis. Le cas du flambement, associant sollicitations de compression et de traction dans une poutre possédant une imperfection initiale, sera étudié afin de vérifier les prédictions du modèle

Characterization of mechanical behavior of nanocrystalline layer induced by SMAT using micro-pillar compression technique coupled with finite element analysis

Micro-pillar compression tests were used to study the mechanical behavior of a stainless steel that has undergone SMAT (Surface Mechanical Attrition Treatment). Micro-pillars were machined using a Focused Ion Beam (FIB) on the cross-section of a SMATed specimen at different distances from the treated surface. These micro-pillars were thus located in different areas more or less affected by the SMAT. They were then compressed with a flat head mounted on a nanoindenter to obtain loading-displacement curves. These compression tests can give information on the mechanical gradient present from the top surface down to the bulk material after SMAT: a superficial nanocrystalline layer (from 10 to 50 micrometers thick and composed of grains with a diameter ranging from 10 to 50 nm) is indeed generated as well as a transition layer (between 200 and 300 micrometers thick and characterized by a grain size gradient from the nanometer to the micrometer scale as the distance from the surface increases) just below the nanocrystalline layer. These compression tests coupled with finite element analysis (FEA) can provide precious information at the mesoscopic scale on the mechanical behavior of the different layers present in the SMATed steel. FEA was used to study the effect of experimental parameters including taper angle (the angle between the tangent of wall and the axis of pillar), aspect ratio (the ratio of height and diameter of the pillar), and misalignment between the pillar axis and the compression direction. Based on the results of FEA, the constitutive behavior in the form of stress-strain curve was identified for the different layers beneath the treated surface including the nanocrystalline layer. According to the obtained stress-strain curves, the mechanical strength of the stainless steel is significantly improved after SMAT

Numerical simulations of impacts during Surface Mechanical Attrition Treatment using crystal plasticity model in finite element method

Surface Mechanical Attrition Treatment (SMAT) is a process, which transforms the top surface layer of materials from coarse grains to nano-sized grains by severe plastic deformation. SMAT is based on multidirectional mechanical impacts between shot and the surface of material. As the strain rate is high and the accumulated plastic strain is large, a great number of defects such as dislocations and deformation twins can be generated at the top surface, which progressively lead to the formation of a nanostructured layer. Simultaneously, high compressive residual stresses may be introduced in the SMAT affected layer. This nanostructured layer coupled with compressive residual stresses induced by SMAT allow to significantly improve the mechanical properties of materials. Due to excellent mechanical properties of SMATed materials, it is necessary and useful to investigate the SMAT process both experimentally and numerically in order to obtain a better understanding and a better control of the process. Experimental studies, extensively performed previously and recorded in the literature, have shown that the mechanical properties of SMATed materials are highly influenced by the microstructure such as grain size and work hardening. From a modeling perspective, it would be highly beneficial to establish accurate numerical models of SMAT in order to consider the influence of the different parameters of this process at the different scales. In this work, a crystal plasticity model introduced in finite element analysis, taking into account the microstructure, was used to investigate the plastic activity due to the impacts between shot and the surface of material. To do this, the shape-controllable 3D Voronoï geometries as well as meshes were first generated using Neper software. A phenomenological crystal plasticity model implemented through user-defined ABAQUS subroutines was used in this work to perform numerical simulations. A number of parameters are studied such as shot size, impact velocity, incident angle, etc. The influences of these different parameters on slip systems and stress fields were analyzed. The first results demonstrated the interests of numerical simulations for this specific process

Ein Modell für verantwortungsvolles Handeln in der IT-Organisation

In der Betriebswirtschaft ist verantwortungsvolles Handeln, repräsentiert durch Konzepte wie Corporate Social Responsibility (CSR), Corporate Citizenship (CC) oder Nachhaltigkeit/Sustainability, eine in Forschung und Praxis breit diskutierte Thematik. Eine umfassende Übertragung der Problematik auf das IT-Management hat jenseits von isolierten Einzelthemen wie „Green IT“ etc. jedoch noch nicht stattgefunden. In diesem Beitrag wird deshalb ein Modell vorgestellt, welches auf der einen Seite einen ganzheitlichen Rahmen für verantwortungsvolles Handeln in der IT-Organisation eröffnet, und auf der anderen Seite Stellschrauben für die aktive, verantwortungsvolle Beeinflussung des Wettbewerbsumfelds aufzeigt. Konkretisiert wird das aufgezeigte Modell anhand verschiedener Maßnahmenfelder zur Umsetzung verantwortungsvollen Handelns

Rosiglitazone Restores Endothelial Dysfunction in a Rat Model of Metabolic Syndrome through PPARγ- and PPARδ-Dependent Phosphorylation of Akt and eNOS

Vascular endothelial dysfunction has been demonstrated in metabolic syndrome (MS). Chronic administration of rosiglitazone ameliorates endothelial dysfunction through PPARγ-mediated metabolic improvements. Recently, studies suggested that single dose of rosiglitazone also has direct vascular effects, but the mechanisms remain uncertain. Here we established a diet-induced rat model of MS. The impaired vasorelaxation in MS rats was improved by incubating arteries with rosiglitazone for one hour. Importantly, this effect was blocked by either inhibition of PPARγ or PPARδ. In cultured endothelial cells, acute treatment with rosiglitazone increased the phosphorylation of Akt and eNOS and the production of NO. These effects were also abolished by inhibition of PPARγ, PPARδ, or PI3K. In conclusion, rosiglitazone improved endothelial function through both PPARγ- and PPARδ-mediated phosphorylation of Akt and eNOS, which might help to reconsider the complex effects and clinical applications of rosiglitazone

Analysis of Flavor Characteristics and Characteristic Components of White Tea Made from Oolong Tea Cultivars

In order to investigate the differences in flavor quality between white tea made from Oolong tea cultivars and traditional white tea, white teas made from eight Oolong tea cultivars such as Zimeigui and Fuding Dahao white tea as a control were analyzed by sensory evaluation, biochemical assays and multivariate statistical analysis. The results showed that the appearance and infusion color of Oolong white tea were darker, while the taste and aroma were better than those of traditional white tea. The biochemical analysis revealed that the differences in conductivity, pH, and the contents of soluble sugars, free amino acids, gallocatechin gallate (GCG) and epigallocatechin gallate (EGCG) were important factors causing the differences in taste between traditional white tea and white tea made from Oolong tea cultivars. Volatile composition analysis showed that trans-2-nonenal, cis-3-nonen-1-ol, methyl palmitate, linalool, methyl linoleate, cedrol, geranyl formate, phenethyl alcohol, nerolidol, methyl salicylate, dibutyl phthalate and phytone were the key differential aroma components contributing to the difference in aroma between Oolong and traditional white tea. Findings from this study will provide a theoretical reference for flavor diversification of white tea

EL SILENCIO EN EL MONSTRUO DEL MANZANARES

Este trabajo estudia la función del silencio en la novela El monstruo del Manzanares, novela corta incluida en la colección La mojiganga del gusto (1641) de Andrés Sanz del Castillo. Esta novela posee constantes alusiones al silencio, las cuales, sumadas a la ausencia de diálogos que reproduzcan las voces de los personajes, nos llevan a considerar, más allá todavía, que el silencio configura un tema en sí mismo dentro de El monstruo de Manzanares y determina notoriamente el sentido final de la novela

Relationship between biofilm formation and antibiotic resistance of Klebsiella pneumoniae and updates on antibiofilm therapeutic strategies

Klebsiella pneumoniae is a Gram-negative bacterium within the Enterobacteriaceae family that can cause multiple systemic infections, such as respiratory, blood, liver abscesses and urinary systems. Antibiotic resistance is a global health threat and K. pneumoniae warrants special attention due to its resistance to most modern day antibiotics. Biofilm formation is a critical obstruction that enhances the antibiotic resistance of K. pneumoniae. However, knowledge on the molecular mechanisms of biofilm formation and its relation with antibiotic resistance in K. pneumoniae is limited. Understanding the molecular mechanisms of biofilm formation and its correlation with antibiotic resistance is crucial for providing insight for the design of new drugs to control and treat biofilm-related infections. In this review, we summarize recent advances in genes contributing to the biofilm formation of K. pneumoniae, new progress on the relationship between biofilm formation and antibiotic resistance, and new therapeutic strategies targeting biofilms. Finally, we discuss future research directions that target biofilm formation and antibiotic resistance of this priority pathogen

Genomic monitoring of SARS-CoV-2 uncovers an Nsp1 deletion variant that modulates type I interferon response

The SARS-CoV-2 virus, the causative agent of COVID-19, is undergoing constant mutation. Here, we utilized an integrative approach combining epidemiology, virus genome sequencing, clinical phenotyping, and experimental validation to locate mutations of clinical importance. We identified 35 recurrent variants, some of which are associated with clinical phenotypes related to severity. One variant, containing a deletion in the Nsp1-coding region (D500-532), was found in more than 20% of our sequenced samples and associates with higher RT-PCR cycle thresholds and lower serum IFN-beta levels of infected patients. Deletion variants in this locus were found in 37 countries worldwide, and viruses isolated from clinical samples or engineered by reverse genetics with related deletions in Nsp1 also induce lower IFN-beta responses in infected Calu-3 cells. Taken together, our virologic surveillance characterizes recurrent genetic diversity and identified mutations in Nsp1 of biological and clinical importance, which collectively may aid molecular diagnostics and drug design.Peer reviewe

Modélisation de la fragilisation dynamique d'un matériau polycristallin sous traction monotone

International audiencePour analyser les conditions de la fragilisation aux joints de grains dans un alliage de cuivre et simuler le processus de fissuration, nous présentons un modèle de fissuration intergranulaire dépendante du temps, qui intègre les points suivants : (i) la plasticité cristalline, (ii) la diffusion des impuretés assistée par contrainte hydrostatique, et (iii) la dégradation de la résistance des joints de grains liée à la couverture de l'impureté. Les premiers résultats des expériences numériques sont présentés