Nanomechanical testing study of the elementary deformation mechanisms in the Ti2AlN and Cr2AlC MAX phases

Abstract: Deformation mechanisms in MAX phases are still not well understood. The complex mechanical behavior of these materials, including mechanical hysteresis, arises both from their crystallography, with a nanolayered structure alternating nitride or carbide layers with metal atoms layers, and from their macroscopic polycrystalline structure, composed of platelets-like grains. In order to distinguish from these two contributions, we focused our study at the sub-micrometer scale, in order to probe the mechanical response of individual grains. Please click Additional Files below to see the full abstract

Deformation twinning in Cr2AlC MAX phase single crystals: A nanomechanical testing study

In a recent study [1], we observed and characterized for the first time deformation twinning in the Ti2AlN MAX phase deformed at high temperature (800°C) by Berkovich nanoindentation. Since plastic deformation in these nanolayered materials was believed to be governed only by basal plane dislocations involved in kink band mechanisms, this result has shed a new light on the mechanical behavior of MAX phases. In order to go further in the understanding of twinning deformation mechanisms in MAX phases, we performed a study in Cr2AlC single crystal, deformed at room temperature by spherical nanoindentation and by micropillar compression tests, in such an orientation that the basal plane was edge on, to inhibit basal dislocations and to promote twinning. Please click Download on the upper right corner to see the full abstract

Hepatitis E : an emerging zoonosis ?

Hepatitis E virus (HEV) causes acute, enterically transmitted hepatitis. It is associated with epidemics in endemic regions and sporadic cases in non-endemic regions. Although the waterborne origin of epidemics is well documented, the origin of sporadic cases is frequently autochthonous and remains unknown. Unlike the other hepatitis viruses, HEV has an animal reservoir. Phylogenetic studies on human and animal strains, and the identification of cases transmitted directly from animal to man strongly suggest that HEV is a zoonotic agent. It is essential to set up a surveillance system of the animal reservoir and of human cases to determine the origin of all autochthonous cases. In addition, potential routes of contaminations must be identified to define preventive measures.Le virus de l'hépatite E (VHE) est responsable d'une hépatite aiguë à transmission entérique. La maladie existe sous formes d'épidémies dans les régions endémiques (Asie, Afrique), et de cas sporadiques dans les régions non endémiques. Alors que l'origine hydrique des épidémies est bien caractérisée, celle des cas sporadiques est fréquemment autochtone et reste inconnue. Le VHE se différencie des autres virus des hépatites par la présence d'un réservoir animal. Des études phylogénétiques sur les souches humaines et animales, ainsi que l'identification de cas de transmission directe de l'animal à l'homme suggèrent fortement que le VHE est un agent zoonotique. Il faudrait mettre en place un système de surveillance du réservoir animal, couplé à un observatoire des cas humains, afin de déterminer l'origine de tous les cas autochtones. Les voies possibles de contamination doivent également être identifiées, afin de définir des mesures de prévention

Transcriptomic analysis of Arabidopsis developing stems: a close-up on cell wall genes

<p>Abstract</p> <p>Background</p> <p>Different strategies (genetics, biochemistry, and proteomics) can be used to study proteins involved in cell biogenesis. The availability of the complete sequences of several plant genomes allowed the development of transcriptomic studies. Although the expression patterns of some <it>Arabidopsis thaliana </it>genes involved in cell wall biogenesis were identified at different physiological stages, detailed microarray analysis of plant cell wall genes has not been performed on any plant tissues. Using transcriptomic and bioinformatic tools, we studied the regulation of cell wall genes in <it>Arabidopsis </it>stems, <it>i.e. </it>genes encoding proteins involved in cell wall biogenesis and genes encoding secreted proteins.</p> <p>Results</p> <p>Transcriptomic analyses of stems were performed at three different developmental stages, <it>i.e.</it>, young stems, intermediate stage, and mature stems. Many genes involved in the synthesis of cell wall components such as polysaccharides and monolignols were identified. A total of 345 genes encoding predicted secreted proteins with moderate or high level of transcripts were analyzed in details. The encoded proteins were distributed into 8 classes, based on the presence of predicted functional domains. Proteins acting on carbohydrates and proteins of unknown function constituted the two most abundant classes. Other proteins were proteases, oxido-reductases, proteins with interacting domains, proteins involved in signalling, and structural proteins. Particularly high levels of expression were established for genes encoding pectin methylesterases, germin-like proteins, arabinogalactan proteins, fasciclin-like arabinogalactan proteins, and structural proteins. Finally, the results of this transcriptomic analyses were compared with those obtained through a cell wall proteomic analysis from the same material. Only a small proportion of genes identified by previous proteomic analyses were identified by transcriptomics. Conversely, only a few proteins encoded by genes having moderate or high level of transcripts were identified by proteomics.</p> <p>Conclusion</p> <p>Analysis of the genes predicted to encode cell wall proteins revealed that about 345 genes had moderate or high levels of transcripts. Among them, we identified many new genes possibly involved in cell wall biogenesis. The discrepancies observed between results of this transcriptomic study and a previous proteomic study on the same material revealed post-transcriptional mechanisms of regulation of expression of genes encoding cell wall proteins.</p

Transcriptomic analysis of Arabidopsis developing stems: a close-up on cell wall genes

<p>Abstract</p> <p>Background</p> <p>Different strategies (genetics, biochemistry, and proteomics) can be used to study proteins involved in cell biogenesis. The availability of the complete sequences of several plant genomes allowed the development of transcriptomic studies. Although the expression patterns of some <it>Arabidopsis thaliana </it>genes involved in cell wall biogenesis were identified at different physiological stages, detailed microarray analysis of plant cell wall genes has not been performed on any plant tissues. Using transcriptomic and bioinformatic tools, we studied the regulation of cell wall genes in <it>Arabidopsis </it>stems, <it>i.e. </it>genes encoding proteins involved in cell wall biogenesis and genes encoding secreted proteins.</p> <p>Results</p> <p>Transcriptomic analyses of stems were performed at three different developmental stages, <it>i.e.</it>, young stems, intermediate stage, and mature stems. Many genes involved in the synthesis of cell wall components such as polysaccharides and monolignols were identified. A total of 345 genes encoding predicted secreted proteins with moderate or high level of transcripts were analyzed in details. The encoded proteins were distributed into 8 classes, based on the presence of predicted functional domains. Proteins acting on carbohydrates and proteins of unknown function constituted the two most abundant classes. Other proteins were proteases, oxido-reductases, proteins with interacting domains, proteins involved in signalling, and structural proteins. Particularly high levels of expression were established for genes encoding pectin methylesterases, germin-like proteins, arabinogalactan proteins, fasciclin-like arabinogalactan proteins, and structural proteins. Finally, the results of this transcriptomic analyses were compared with those obtained through a cell wall proteomic analysis from the same material. Only a small proportion of genes identified by previous proteomic analyses were identified by transcriptomics. Conversely, only a few proteins encoded by genes having moderate or high level of transcripts were identified by proteomics.</p> <p>Conclusion</p> <p>Analysis of the genes predicted to encode cell wall proteins revealed that about 345 genes had moderate or high levels of transcripts. Among them, we identified many new genes possibly involved in cell wall biogenesis. The discrepancies observed between results of this transcriptomic study and a previous proteomic study on the same material revealed post-transcriptional mechanisms of regulation of expression of genes encoding cell wall proteins.</p

Accuracy of hyaluronic acid level for predicting liver fibrosis stages in patients with hepatitis C virus

BACKGROUND: In patients with chronic hepatitis C virus, liver biopsy is the gold standard for assessing liver disease stage; nevertheless, it is prone to complications, some of them serious. Non-invasive methods have been proposed as surrogate markers for liver fibrosis. It was shown that serum hyaluronic acid (HA) level increases with the development for liver fibrosis. The aim of this study was to evaluate the diagnostic value of HA as well as to determine the HA level cut-off for predicting the presence or absence of fibrosis, severe fibrosis, and cirrhosis. RESULTS: 405 patients with chronic hepatitis C were prospectively included with biomarker measurement and liver biopsy done the same day: 151 in the training set (only biopsy lengths of 25 mm or more) and 254 in the validation set. For the discrimination of significant fibrosis, severe fibrosis, and cirrhosis in the training set, the areas under curve (AUCs) were 0.75 ± 0.03, 0.82 ± 0.02, and 0.89 ± 0.03, respectively. Absence of significant fibrosis, severe fibrosis, and cirrhosis can be predicted by HA levels of 16, 25, and 50 μg/l, respectively (with negative predictive values of 82%, 89%, and 100%, in the same order). Presence of significant fibrosis, severe fibrosis, and cirrhosis can be predicted by HA levels of 121, 160, and 237 μg/l, respectively (with positive predictive values of 94%, 100%, and 57%, in the same order). CONCLUSION: In the validation set, HA was accurate in predicting significant fibrosis, severe fibrosis, and cirrhosis with AUCs of 0.73, 0.77, and 0.97, respectively. Moreover, accurate HA level cut-offs were defined for predicting significant fibrosis, severe fibrosis, and cirrhosis. Thus, the study supports that HA level may be clinically useful as a non-invasive marker for liver fibrosis and/or cirrhosis

Investigating ramp wave propagation inside silica glass with laser experiments and molecular simulations

Under elastic shock compression silica glass exhibits a very specific behaviour. A shock propagating inside a material is usually seen as the propagation of a discontinuity. However in silica glass, shocks are unstable and lead to the propagation of a ramp wave where the shock front becomes gradually larger over time. Ramp waves were already reported in the literature, however their origin remain uncertain. This work presents an original study combining laser shock-induced experiments and molecular dynamics simulation aiming to improve the understanding of the mechanisms involved. Experimental ramp waves were directly observed using shadowgraphy technique allowing for an estimation of the head and tail velocities. Molecular dynamics simulations were carried out in order to reproduce ramp waves and to gain insight into the material properties. Ramp waves were observed for both elastic and plastic shockwaves. In the latter case, the plastic waves were preceded by an elastic ramp precursor. The sound speed, related to the material compressibility, was found to decrease with increasing pressure, as observed experimentally for quasi-static hydrostatic loading, thus providing an explanation for the instabilities that lead to the propagation of ramp waves

Possible Zoonotic Transmission of Hepatitis E from Pet Pig to Its Owner

Hepatitis E is transmitted mainly by water or food, but in industrialized countries, all routes of transmission have not been identified. We describe possible zoonotic transmission of hepatitis E virus that involved direct contact between a pet pig and its owner

Zoonotic hepatitis E: animal reservoirs and emerging risks

Hepatitis E virus (HEV) is responsible for enterically-transmitted acute hepatitis in humans with two distinct epidemiological patterns. In endemic regions, large waterborne epidemics with thousands of people affected have been observed, and, in contrast, in non-endemic regions, sporadic cases have been described. Although contaminated water has been well documented as the source of infection in endemic regions, the modes of transmission in non-endemic regions are much less known. HEV is a single-strand, positive-sense RNA virus which is classified in the Hepeviridae family with at least four known main genotypes (1–4) of mammalian HEV and one avian HEV. HEV is unique among the known hepatitis viruses, in which it has an animal reservoir. In contrast to humans, swine and other mammalian animal species infected by HEV generally remain asymptomatic, whereas chickens infected by avian HEV may develop a disease known as Hepatitis-Splenomegaly syndrome. HEV genotypes 1 and 2 are found exclusively in humans while genotypes 3 and 4 are found both in humans and other mammals. Several lines of evidence indicate that, in some cases involving HEV genotypes 3 and 4, animal to human transmissions occur. Furthermore, individuals with direct contact with animals are at higher risk of HEV infection. Cross-species infections with HEV genotypes 3 and 4 have been demonstrated experimentally. However, not all sources of human infections have been identified thus far and in many cases, the origin of HEV infection in humans remains unknown

Characterization of a cinnamoyl-CoA reductase 1 (CCR1) mutant in maize: effects on lignification, fibre development, and global gene expression

Cinnamoyl-CoA reductase (CCR), which catalyses the first committed step of the lignin-specific branch of monolignol biosynthesis, has been extensively characterized in dicot species, but few data are available in monocots. By screening a Mu insertional mutant collection in maize, a mutant in the CCR1 gene was isolated named Zmccr1–. In this mutant, CCR1 gene expression is reduced to 31% of the residual wild-type level. Zmccr1– exhibited enhanced digestibility without compromising plant growth and development. Lignin analysis revealed a slight decrease in lignin content and significant changes in lignin structure. p-Hydroxyphenyl units were strongly decreased and the syringyl/guaiacyl ratio was slightly increased. At the cellular level, alterations in lignin deposition were mainly observed in the walls of the sclerenchymatic fibre cells surrounding the vascular bundles. These cell walls showed little to no staining with phloroglucinol. These histochemical changes were accompanied by an increase in sclerenchyma surface area and an alteration in cell shape. In keeping with this cell type-specific phenotype, transcriptomics performed at an early stage of plant development revealed the down-regulation of genes specifically associated with fibre wall formation. To the present authors’ knowledge, this is the first functional characterization of CCR1 in a grass species