Characterization of juvenile pyroclasts from the Kos Plateau Tuff (Aegean Arc): insights into the eruptive dynamics of a large rhyolitic eruption

Silicic pumices formed during explosive volcanic eruptions are faithful recorders of the state of the magma in the conduit, close to or at the fragmentation level. We have characterized four types of pumices from the non-welded rhyolitic Kos Plateau Tuff, which erupted 161,000years ago in the East Aegean Arc, Greece. The dominant type of pumice (>90vol.%) shows highly elongated tubular vesicles. These tube pumices occur throughout the eruption. Less common pumice types include: (1) "frothy” pumice (highly porous with large, sub-rounded vesicles), which form 5-10vol.% of the coarsest pyroclastic flow deposits, (2) dominantly "microvesicular” and systematically crystal-poor pumices, which are found in early erupted, fine-grained pyroclastic flow units, and are characterized by many small (<50μm in diameter) vesicles and few mm-sized, irregular voids, (3) grey or banded pumices, indicating the interaction between the rhyolite and a more mafic magma, which are found throughout the eruption sequence and display highly irregular bubble shapes. Except for the grey-banded pumices, all three other types are compositionally identical and were generated synchronously as they are found in the same pyroclastic units. They, therefore, record different conditions in the volcanic conduit leading to variable bubble nucleation, growth and coalescence. A total of 74 pumice samples have been characterized using thin section observation, SEM imagery, porosimetry, and permeametry. We show that the four pumice types have distinct total and connected porosity, tortuosity and permeability. Grey-banded pumices show large variations in petrophysical characteristics as a response to mingling of two different magmas. The microvesicular, crystal-poor, pumices have a bimodal bubble size distribution, interpreted as reflecting an early heterogeneous bubble nucleation event followed by homogeneous bubble nucleation close to fragmentation. Finally, the significant differences in porosity, tortuosity and permeability in compositionally identical tube and frothy pumices are the result of variable shear rates in different parts of the conduit. Differential shear rates may be the result of either: (1) pure shear, inducing a vertical progression from frothy to tube and implying a relatively thick fragmentation zone to produce both types of pumices at the same time or (2) localized simple shear, inducing strongly tubular vesicles along the wall and near-spherical bubbles in the centre of the conduit and not necessarily requiring a thick fragmentation zon

Pinus kesiya spread on the endemic Tapia forest: ecological characteristic analysis approach

Biological invasion of alien species is the second major threat to the sustainability of biodiversity within natural forest ecosystems. In Madagascar, the forest vestige of the highlands, Tapia forest which is source of more than 7% of income of the local population, is subject to such invasion. Pinus sp are invading more and more this ecosystem. In relation to this phenomenon, two great theories can be raised to explain the installation of species within a community. In order to understand the method of installation of Pinus species inside the Tapia forest, this study has tried to understand if there are parameters that influence this phenomenon. From a forest inventory on a total area of 3.75 ha, or 0.7% of the total Tapia forest at Arivonimamo II, we collected all ecological data concerning the biophysical, dendrometric and topographic characteristics of the stand. Statistical analyzes such as multi-component analysis and comparison analysis of the environment (invaded and non-invaded) yielded the abundance of Uapaca bojeri (a dominant species in the forest) but also the specific diversity within the stand negatively affects the existence of Pinus. This means that the smaller the number of individuals and fewer species, the easier Pinus is to install. As a result, we concluded that the environmental characteristics influence the distribution of exotic species such as Pinus sp within a forest ecosystem such as the Tapia forest

Energy absorption capacity of composite thin-wall circular tubes under axial crushing with different trigger initiations

The purpose of this study is to evaluate and compare the ability of various composite structures to dissipate the energy generated during a crash. To this end, circular composite tubes were tested in compression in order to identify their behavior and determine their absorbing capabilities using the specific energy absorption (energy absorbed per unit weight). Several composite tubular structures with different materials and architectures were tested, including hybrid composition of carbon-aramid and hybrid configuration of 0/90 UD with woven or braided fabric. Several inventive and experimental trigger systems have been tested to try and enhance the absorption capabilities of the tested structures. Specific energy absorption values up to 140 kJ.kg−1 were obtained, achieving better than most instances from the literature, reaching around 80 kJ.kg−1. Specimens with 0°-oriented fibers coincidental with the direction of compression reached the highest specific energy absorption values while those with no fiber oriented in this direction performed poorly. Moreover, it has consequently been established that in quasi-static loading, a unidirectional laminate oriented at 0° and stabilized by woven plies strongly meets the expectations in terms of energy dissipation. Incidentally, an inner constrained containment is more effective in most cases, reducing the initial peak load without drastically reducing the specific energy absorption value

Effet du pâturage ovin sur les communautés végétales des marais salés de la baie de Somme (France)

The use of domestic animal grazing to manage temperate salt-marsh ecosystems is still debated and requires further field investigations. The effects of sheep grazing on plant community were studied in the salt-marshes of the Bay of Somme (France). We compared vegetation characteristics between two sets of grazed and ungrazed 1m2-plots. We tested for differences in species composition using pair-wise Multi-Response Permutation Procedures (MRPP), used an Indicator Species Analysis (ISA) to distinguish species indicator of grazed and ungrazed areas and described community structures with species rank-abundance curves. Differences in species richness and plant height and biovolume were tested using Mann-Whitney tests. MRPP showed that plant community composition differed significantly between grazed plots, dominated by Puccinellia maritima and Festuca rubra ssp. litoralis, and ungrazed plots, dominated by Halimione portulacoides (T = -60.37; A = 0.10; p < 0.0001). Nine species were indicator of grazed areas and four of ungrazed areas. Grazed communities had higher species richness (3.5 ± 0.2 species.m-2) than ungrazed communities (2.9 ± 0.1 species.m-2; p < 0.001). This significant difference is noteworthy in salt-marsh systems usually characterized by low contrasts of species richness. In grazed plots, vegetation height and biovolume were lower but vegetation cover was higher than in ungrazed plots. According to the identity of the species, plants lost 16.7% to 86.3% of their height under grazing pressure. The species showing the highest decrease in height (> 50%) were mainly pioneer halophytes and grasses. Aster tripolium, Suaeda maritima var. maritima, Halimione portulacoides, Spergularia marina were heavily damaged or browsed and lost more than 90% of their biovolume in grazed area. Through cascading effects, sheep grazing reduces the vegetation height, controls the identity of dominant species, relaxes competitive interaction for light between species and, finally, positively influences plant species richness. We thus recommend a moderate and extensive sheep grazing to manage European salt-marshes dominated by few highly competitive plant species. Finally, we categorized species according to their height loss percentage under grazing and their indicator value from ISA to provide a field tool to help the shepherds to estimate the impact of grazing on salt-marsh plantsL'utilisation du pâturage par les animaux domestiques pour gérer les écosystèmes des marais salés est toujours débattue et demande plus d'investigations de terrain. L'effet du pâturage sur les communautés végétales a été étudié dans des marais salés de la Baie de Somme (France). Nous avons comparé les caractéristiques de la végétation entre deux lots de relevés pâturés et non pâturés. Les différences de composition spécifique ont été évaluées par des tests de permutations multiples (Multi-Response Permutation Procédures; MRPP). Nous avons utilisé une analyse des espèces indicatrices (ISA) pour identifier les espèces caractéristiques des zones pâturées et non pâturées et des courbes rangs-abondances pour décrire les structures des communautés. Les différences de richesse en espèces, de hauteur et de biovolume des plantes ont été évaluées par des tests de Mann-Whitney. Les MRPP ont montré que les compositions des communautés pâturées, dominées par Puccinellia maritima et Festuca rubra ssp. litoralis, et non pâturées, dominées par Halimione portulacoides, diffèrent significativement (T = ―60,37; A = 0,10; p < 0,0001). Neuf espèces sont indicatrices des zones pâturées et quatre des zones non pâturées. Les communautés pâturées présentent une richesse spécifique plus élevée (3,5 ± 0,2 espèces.m-2) que celles non pâturées (2,9 ± 0,1 espèces.m-2; p < 0.001). Cette différence est notable dans des systèmes habituellement caractérisés par de faibles contrastes de richesse. Dans les relevés pâturés, la hauteur et le biovolume de végétation sont plus faibles et le recouvrement de la végétation plus élevé que dans les relevés non pâturés. Selon l'identité des espèces, les plantes perdent de 16,7 à 86,3% de leur hauteur sous pâturage ovin. Les espèces montrant la plus importante perte de hauteur (> 50%) sont principalement des halophytes pionnières et des Poacées. Aster tripolium, Suaeda maritima var. maritima, Halimione portulacoides, Spergularia marina sont particulièrement sensibles au pâturage et perdent plus de 90% de leur biovolume en présence des moutons. À travers des effets en cascade, le pâturage ovin réduit la hauteur de végétation, contrôle l'identité des espèces dominantes, limite les interactions compétitives pour la lumière entre espèces et, finalement, augmente la richesse spécifique. Nous recommandons donc un pâturage modéré et extensif pour la gestion des marais salés européens occupés par quelques espèces très dominantes. Finalement, nous avons classé les espèces selon leur degré d'abroutissement et leur valeur indicatrice de pâturage (ISA) pour fournir aux bergers un outil de terrain leur permettant d'évaluer l'impact des moutons sur les plantes des marais salés

Changes in urine composition after trauma facilitate bacterial growth.

International audienceUNLABELLED: ABSTRACT: BACKGROUND: Critically ill patients including trauma patients are at high risk of urinary tract infection (UTI). The composition of urine in trauma patients may be modified due to inflammation, systemic stress, rhabdomyolysis, life support treatment and/or urinary catheter insertion. METHODS: Prospective, single-centre, observational study conducted in patients with severe trauma and without a history of UTIs or recent antibiotic treatment. The 24-hour urine samples were collected on the first and the fifth days and the growth of Escherichia coli in urine from patients and healthy volunteers was compared. Biochemical and hormonal modifications in urine that could potentially influence bacterial growth were explored. RESULTS: Growth of E. coli in urine from trauma patients was significantly higher on days 1 and 5 than in urine of healthy volunteers. Several significant modifications of urine composition could explain these findings. On days 1 and 5, trauma patients had an increase in glycosuria, in urine iron concentration, and in the concentrations of several amino acids compared to healthy volunteers. On day 1, the urinary osmotic pressure was significantly lower than for healthy volunteers. CONCLUSION: We showed that urine of trauma patients facilitated growth of E. coli when compared to urine from healthy volunteers. This effect was present in the first 24 hours and until at least the fifth day after trauma. This phenomenon may be involved in the pathophysiology of UTIs in trauma patients. Further studies are required to define the exact causes of such modifications

Benchmark of wrinkling formulae and methods for pre-sizing of aircraft lightweight sandwich structures

Sandwich structures are widely used in many industrial applications and especially in light aviation. The local buckling phenomenon named “wrinkling” is one of the primary causes of compressive failure of such structures. Its calculation is a difficult practical problem since this phenomenon cannot be captured by the GFEM (Global Finite Element Model) classically used for aircraft structure sizing. Therefore, pre‐sizing involves the use of a wrinkling model, which can be found in the literature. In practice, such models are used with high safety factors by the industry. This paper proposes an evaluation of analytical wrinkling formulas in an industrial setting. Realistic applications involve a framework (3D stress state, orthotropy, skin asymmetry) far from the assumptions on which most of the analytical formulations are based. The case study is a sandwich composite beam subjected to uniaxial compressive load. Limitations and assumptions of the analytical wrinkling models studied are quantified and a discussion on the relevance of using simple formulas for the design of sandwich structured composites is developed