61 research outputs found
ContrÎle de santé vibro-acoustique de l'endommagement des matériaux composites à base polymÚre pour l'aéronautique
The present study investigates the mechanical behavior under static, fatigue, linear and non linear vibration and assesses damage by the acoustic emission method of laminated composite materials (tensile and buckling) and of sandwich composite materials (4 points bending).Ce travail de thĂšse a pour objet dâĂ©tudier le comportement mĂ©canique en statique, en fatigue, en vibration linĂ©aire et non linĂ©aire et dâĂ©valuer et suivre les mĂ©canismes endommagement par Ă©mission acoustique des matĂ©riaux composites stratifiĂ©s et sandwichs. Deux grandes familles de matĂ©riaux composites ont Ă©tĂ© considĂ©rĂ©es dans ce travail: a) descomposites stratifiĂ©s constituĂ©s de fibres de carbone, fibres hybrides (verre/carbone) et fibres de verre avec diffĂ©rentes sĂ©quences dâempilement associĂ©es Ă une rĂ©sine Ă©poxyde, b) des matĂ©riaux sandwichs constituĂ©s de peaux en stratifiĂ©s Ă fibres de verre/rĂ©sine Ă©poxyde et d'une Ăąme en mousse PVC de diffĂ©rentes densitĂ©s. La mise en oeuvre de lâensemble de ces matĂ©riaux est rĂ©alisĂ©e au laboratoire (LAUM).Les composites stratifiĂ©s ont Ă©tĂ© caractĂ©risĂ©s en sollicitations de traction et de flambement en statique et en fatigue. Au cours de ces essais, les signaux dâĂ©mission acoustique sont collectĂ©s dans les diffĂ©rents matĂ©riaux. Les mĂ©canismes dâendommagement de chaque matĂ©riau sont identifiĂ©s, caractĂ©risĂ©s et suivis en utilisant une analyse multivariable(mĂ©thode de coalescence floue) des signaux collectĂ©s. Lâanalyse des rĂ©sultats obtenus a permis de mettre en Ă©vidence lâeffet du type de renfort, la sĂ©quence dâempilement et de lâĂ©paisseur des couches Ă 90° sur le comportement mĂ©canique et sur la dynamique de chaque mĂ©canisme dâendommagement jusquâĂ la rupture des diffĂ©rents stratifiĂ©s. Une analyseexpĂ©rimentale du comportement dynamique des composites stratifiĂ©s de diffĂ©rents renforts fibreux et diffĂ©rentes orientations des plis a Ă©tĂ© menĂ©e dans le cas de vibration en flexion. La rĂ©ponse Ă une excitation par pot vibrant a Ă©tĂ© Ă©tablie et les frĂ©quences de rĂ©sonance et les amortissements ont Ă©tĂ© dĂ©duits et comparĂ©s dans diffĂ©rents composites.Ensuite, une Ă©tude dĂ©taillĂ©e est menĂ©e pour caractĂ©riser le comportement mĂ©canique en statique et en fatigue cyclique des matĂ©riaux sandwichs avec une Ăąme de diffĂ©rentes densitĂ©s.Les essais ont Ă©tĂ© conduits en flexion 4-points sur des poutres de ces matĂ©riaux. Lâanalyse des rĂ©sultats et lâobservation des signaux dâEA obtenus dans ces structures ont permis de dĂ©finir les principales signatures acoustiques des diffĂ©rents modes dâendommagement prĂ©pondĂ©rants dans les peaux et dans lâĂąme du matĂ©riau sandwich. Une Ă©tude de comportement vibratoire linĂ©aire des composites sandwichs aux Ă©tats sains a Ă©tĂ© menĂ©e en flexion.Enfin, une Ă©tude du comportement mĂ©canique en statique, en fatigue cyclique, en vibration linĂ©aire et non linĂ©aire des matĂ©riaux sandwichs endommagĂ©s par des fissures de type cisaillement dans lâĂąme a Ă©tĂ© menĂ©e. Les caractĂ©ristiques statiques sont dĂ©terminĂ©es en fonction de la densitĂ© de fissuration. En fatigue, la rigiditĂ©, lâĂ©nergie dissipĂ©e, lâamortissement et la durĂ©e de vie sont Ă©valuĂ©s Ă partir des donnĂ©es expĂ©rimentales en fonction de la densitĂ© defissures et du nombre de cycles. Ensuite, une Ă©tude expĂ©rimentale du comportement vibratoire linĂ©aire et non-linĂ©aire des composites sandwichs endommagĂ©s a Ă©tĂ© menĂ©e. Elle a permis de mesurer les frĂ©quences propres et les amortissements de ces matĂ©riaux autour de chaque pic de rĂ©sonance en fonction de la densitĂ© de fissuration. Enfin, la mĂ©thode de vibration non linĂ©aire a Ă©tĂ© appliquĂ©e pour caractĂ©riser le comportement des matĂ©riaux sandwichsendommagĂ©s par fissuration. Les paramĂštres non linĂ©aires relatifs au dĂ©calage frĂ©quentiel et Ă lâamortissement sont mesurĂ©s en faisant varier lâamplitude dâexcitation et sont comparĂ©s aux paramĂštres linĂ©aires
Conditions for the Palladium-Catalysed Direct 2-Arylation of 3-Bromobenzo[b]thiophene Tolerant of the Benzothienyl Carbon-Bromine Bond
International audiencePhosphine-free palladium(II) acetate catalyst was found to promote the direct 2-arylation of 3-bromobenzo[b]thiophene without cleavage of the benzothienyl carbon-bromine bond, allowing the synthesis of 2-aryl-3-bromobenzo[b]thiophenes in only one step. The best results were generally obtained using a low loading of the palladium catalyst (0.5 mol%), quite low reaction temps. (80-120 °C) and short reaction times (0.5-2 h). The reaction proceeds with electron-deficient para-, meta- and ortho-substituted aryl bromides and also with heteroaryl bromides. The benzothienyl carbon-bromine bond has been profitably employed for further palladium-catalyzed functionalisations. This strategy allows the straightforward synthesis of 2,3-di(hetero)arylated benzo[b]thiophenes with two different (hetero)aryl units via sequential catalytic arylations
Cohomology of acting on the space of bilinear differential operators on the superspace
We compute the first cohomology of the ortosymplectic Lie superalgebra
on the (1,1)-dimensional real superspace with
coefficients in the superspace of bilinear
differential operators acting on weighted densities. This work is the simplest
superization of a result by Bouarroudj [Cohomology of the vector fields Lie
algebras on acting on bilinear differential operators,
International Journal of Geometric Methods in Modern Physics
(2005), {\bf 2}; N 1, 23-40]
Association of Vascular Endothelial Growth Factor Polymorphisms with Asthma in Tunisian Children
Background: Previous studies demonstrated that the vascular endothelial growth factor (VEGF) was being implicated in the airways inflammation and remodeling process in patients with asthma.Aims: We explored the relationship of three polymorphisms in the VEGF gene with asthma in both case control and family studies.Methods: We Genotyped a total of 210 children with asthma, 224 unrelated controls and 160 parents for the +936 C > T (rs3025039), â634 G > C (rs2010963) and â2549 â2567 del 18 of the VEGF promoter region. The Mutations were identified with polymerase chain reaction followed by restriction fragment length polymorphism (RFLP) analysis for the +936 C > T, and â634 G > C polymorphisms.Results: Of the three polymorphisms studied, a borderline association with asthma was found for the G allele in the â634 G > C polymorphism (p = 0.059). No Statistically significant differences were observed for both +936 C > T, and â2549 â2567 del 18 polymorphisms between asthmatic patients and controls, considering either allelic or genotypic frequencies.The distribution of genotypes according to the severity status revealed a significant differences for the +936 C > T, and â2549 â2567 del 18 polymorphisms. In addition, association was found with the haplotypes inferred by the three polymorphisms and asthma susceptibility.Conclusion: We suggest that VEGF Gene polymorphisms can be implicated in asthma
Passage through a hydropower plant affects the physiological and health status of Atlantic salmon smolts
A Comparative Analysis between Right and Left Congenital Diaphragmatic Hernias
Congenital diaphragmatic hernia (CDH) is a rare congenital anomaly of the diaphragm with an incidence of 1:2000-5000 of live births. This study retrospectively evaluated patients who had been operated on for CDH at our department of Pediatric Surgery between January 2013 and December 2016. The Demographic Data and outcomes of right CDH cases (Group 1) were compared with left CDH cases (Group 2)
Repeated hormonal induction of spermiation affects the stress but not the immune response in pikeperch (Sander lucioperca)
The effect of a daytime 60-min nap opportunity on postural control in highly active individuals
Although napping is commonly used as a strategy to improve numerous physical and cognitive performances, the efficacy of this strategy for improving postural balance has not yet been elucidated. Thus, the aim of this study was to conduct a comprehensive examination of the effect of a 60 min nap opportunity (N60) on different components of postural control. Ten highly active individuals (age = 27 ± 3.5 y, height = 1.75 ± 0.52 m, weight = 66.02 ± 8.63 kg) performed, in a randomized order, two afternoon test sessions following no nap (NN) and N60. Postural balance was assessed using the sensory organisation test (SOT), the unilateral stance test (UST), and the limits of Stability Test performed on NeuroCom(Ÿ) Smart Balance Master. The subjective rating of sleepiness before and after the nap conditions was also assessed. Compared to NN, N60 improved the composite balance score (p 0.05). Overall, a 60 min post lunch nap opportunity may be viable for improving static balance, although further work, involving larger samples and more complex motor activities, is warranted
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