Absorbeurs de vibrations hybrides hyperstables

International audienceL'hybridation des systèmes actifs et passifs est une voie en plein essor que ce soit pour l'isolation ou l'amortissement des structures. L'hybridation a pour objectif de combiner le meilleur des approches actives et passives. Les apports principaux sont généralement l'adaptabilité apportée au système passif initial mais également l' amélioration des performances a des couts énergétiques bien inférieurs aux versions purement actives. L'aspect fail-safe du système hybride est également un atout non négligeable dans le cadre des applications embarquées. Cependant certaines difficultés apparaissent lorsque l'on cherchè a coupler contrôle actif et contrôle passif au sein d'un même système mécanique notamment en terme de stabilité. On présente ici une loi de contrôle qui est une évolution du Direct Velocity Feedback appliquée aux absorbeurs de vibrations accordés. Deux pôles et deux zéros sont ajoutés a la loi de contrôle initiale, pour interagir avec la dynamique de la structure. L' intérêt de ces interactions est de modifier le lieu des pôles du système en boucle fermée afin de rendre le système contrôlé hyperstable. Les marges de gain et de phase sont ainsi infinies. L'absorbeur hybride développé dans cette étude est comparé a d'autres approches plus classiques en termes d' atténuation, de consommation et de débattement

Selective drug transport and P-glycoprotein activity in an in vitro blood-brain barrier model

International audienceTo determine whether compounds are able to reach the neural microenvironment, a blood-brain barrier (BBB) co-culture model has been recently developed with bovine brain capillary endothelial cells and newborn rat astrocytes. In this study, the permeability of confluent endothelial cells to various compounds and the functional activity of P-glycoprotein (P-gp), an ATP-dependent pump known to efflux drugs from multidrug-resistant tumoral cells, was assessed. The permeability of the lipophilic compounds imipramine and sulpiride differed in relation to their structure. A good correlation was observed with in vivo brain extraction levels. P-gp activity was estimated by measuring the uptake of [3H]vinblastine by the endothelial cells, with or without verapamil, which is known to reverse drug resistance. Intracellular accumulation of the vinca alkaloid was strongly increased after addition of verapamil, suggesting that P-gp is active in these cells. These results provide further support for the use of the co-culture model of bovine brain endothelial cells and rat astrocytes to screen new centrally active drugs

Fluorescent probes for predicting drug induced cholestasis

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A new mechanism of action for skin whitening agents: binding to the peroxisome proliferator-activated receptor

International audienceSynopsis Octadecenedioic acid is known as a skin whitening agent but its activity is not mediated via a direct inhibition of tyrosinase. Based on the secondary properties of this molecule, such as its anti-inflammatory and anti-ageing effects, we postulated that octadecenedioic acid interacted with the peroxisome proliferator-activated receptor (PPAR) as this nuclear receptor also mediates these effects. Using reporter gene technology, we were indeed able to demonstrate binding of octadecenedioic acid to all three PPAR subtypes, in particular PPARgamma with an EC(50)-value of approx. 1 x 10(-6) m. Binding to PPARgamma of octadecenedioic acid or rosiglitazone, a known pharmaceutical PPARgamma agonist, led to reduced melanogenesis. Subsequently also tyrosinase mRNA (as measured by real-time polymerase chain reaction) and tyrosinase levels (as measured by Western blot) were reduced, suggesting the existence of a complete novel mechanism of skin whitening agents: binding to PPARgamma results in reduced tyrosinase mRNA expression which in turn results in less tyrosinase being formed. This in turn leads to reduced melanogenesis both in vitro and in vivo Because octadecenedioic acid binds not only to PPARgamma but also to PPARalpha and PPARdelta, other efficacies mediated via these receptors may also be expected

Induced lactation in cows and heifers by short-term treatment with steroid hormones

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Ikebana: Ikenobo School [015]

Photograph of hanging scroll and flower arrangementIkenobo school, Kyoto, Japan