Control of primary productivity and the significance of photosynthetic bacteria in a meromictic kettle lake.

During 1986 planktonic primary production and controlling factors were investigated in a small (A0 = 11.8 · 103 m2, Zmax = 11.5 m) meromictic kettle lake (Mittlerer Buchensee). Annual phytoplankton productivity was estimated to ca 120 gC · m–2 · a–1 (1,42 tC · lake–1 · a–1). The marked thermal stratification of the lake led to irregular vertical distributions of chlorophylla concentrations (Chla) and, to a minor extent, of photosynthesis (Az). Between the depths of 0 to 6 m low Chla concentrations (< 7 mg · m–3) and comparatively high background light attenuation (kw = 0,525 m–1, 77% of total attenuation due to gelbstoff and abioseston) was found. As a consequence, light absorption by algae was low (mean value 17,4%) and self-shading was absent. Because of the small seasonal variation of Chla concentrations, no significant correlation between Chla and areal photosynthesis (A) was observed. Only in early summer (June–July) biomass appears to influence the vertical distribution of photosynthesis on a bigger scale. Around 8 m depth, low-light adapted algae and phototrophic bacteria formed dense layers. Due to low ambient irradiances, the contribution of these organisms to total primary productivity was small. Primary production and incident irradiance were significantly correlated with each other (r2 = 0.68). Although the maximum assimilation number (Popt) showed a clear dependence upon water temperature (Q10 = 2.31), the latter was of minor importance to areal photosynthesis

A three-dimensional model of the human blood-brain barrier to analyse the transport of nanoparticles and astrocyte/endothelial interactions

The aim of this study was to develop a three-dimensional (3D) model of the human blood-brain barrier in vitro, which mimics the cellular architecture of the CNS and could be used to analyse the delivery of nanoparticles to cells of the CNS. The model includes human astrocytes set in a collagen gel, which is overlaid by a monolayer of human brain endothelium (hCMEC/D3 cell line). The model was characterised by transmission electron microscopy (TEM), immunofluorescence microscopy and flow cytometry. A collagenase digestion method could recover the two cell types separately at 92-96% purity. Astrocytes grown in the gel matrix do not divide and they have reduced expression of aquaporin-4 and the endothelin receptor, type B compared to two-dimensional cultures, but maintain their expression of glial fibrillary acidic protein. The effects of conditioned media from these astrocytes on the barrier phenotype of the endothelium was compared with media from astrocytes grown conventionally on a two-dimensional (2D) substratum. Both induce the expression of tight junction proteins zonula occludens-1 and claudin-5 in hCMEC/D3 cells, but there was no difference between the induced expression levels by the two media. The model has been used to assess the transport of glucose-coated 4nm gold nanoparticles and for leukocyte migration. TEM was used to trace and quantitate the movement of the nanoparticles across the endothelium and into the astrocytes. This blood-brain barrier model is very suitable for assessing delivery of nanoparticles and larger biomolecules to cells of the CNS, following transport across the endothelium

A relevant in vitro rat model for the evaluation of blood-brain barrier translocation of nanoparticles

Poly(MePEG2000cyanoacrylate-co-hexadecylcyanoacrylate) (PEG-PHDCA) nanoparticles have demonstrated their capacity to reach the rat central nervous system after intravenous injection. For insight into the transport of colloidal systems across the blood-brain barrier (BBB), we developed a relevant in vitro rat BBB model consisting of a coculture of rat brain endothelial cells (RBECs) and rat astrocytes. The RBECs used in our model displayed and retained structural characteristics of brain endothelial cells, such as expression of P-glycoprotein, occludin and ZO-1, and immunofluorescence studies showed the specific localization of occludin and ZO1. The high values of transendothelial electrical resistance and low permeability coefficients of marker molecules demonstrated the functionality of this model. The comparative passage of polyhexadecylcyanoacrylate and PEG-PHDCA nanoparticles through this model was investigated, showing a higher passage of PEGylated nanoparticles, presumably by endocytosis. This result was confirmed by confocal microscopy. Thanks to a good in vitro/in vivo correlation, this rat BBB model will help in understanding the mechanisms of nanoparticle translocation and in designing new types of colloidal carriers as brain delivery systems

Rapport VI-3 Soutien des étiages et régularisation des débits dans le bassin du Lot. Effets et adaptation des aménagements hydro-électriques existants

Flow disturbances in the Lot basin due to the many hydroelectric schemes called for steps to be taken (a) to increase minimum stream flows, and (b) to reduce daily variations. Increasing the minimum flows required that water stored for this purpose in the upper basin be made available downstream. The possibilities were (a) to release water from existing hydroelectric structures, (b) to create impounding reservoirs, or (c) to combine the two. Optimum solutions were selected by comparing the economic and energy-production effects of releasing water, and by estimating the cost of a new reservoir designed both for energy production and for low water control. Daily fluctuations in flow due to lockage water and to lake-sited plant in the upper basin were reduced by making optimum use of balancing reservoirs, by staggering the peak flows of the Lot and its tributaries, and by building new balancing reservoirs where necessary. To smooth the flow disturbances in the lower reaches caused by low-head hydroelectric plant operated by Electricité de France, factories and other private owners, a co-ordinated water management policy is needed. The policy is being defined with the aid of a mathematical hydrodynamics model which enables power plant operation to be simulated.Dans le bassin du Lot, très équipé au plan hydroélectrique, de nouveaux besoins se sont exprimés concernant le renforcement des étiages et la régularisation des débits fortement modulés par l’exploitation hydro-électrique. L’augmentation des débits d’étiage implique la disponibilité de volumes affectés à cet effet dans le haut bassin. Ils peuvent être obtenus par le déstockage de réservoirs hydroélectriques existants, par la création de nouveaux barrages-réservoirs, ou par une combinaison des deux options. La comparaison et le choix entre ces solutions sont rendus possibles après avoir analysé l’impact énergétique et économique des déstockages et après avoir quantifié l’intérêt d’associer les deux objectifs soutien d’étiage et hydroélectricité dans un nouveau réservoir. Pour réduire les variations journalières de débits dues aux centrales de lacs et d’éclusées du haut bassin, les moyens mis en œuvre consistent en l’utilisation optimum des bassins de compensation, en l’organisation du décalage des débits maximums entre rivière et affluents et si nécessaire, en la création de nouveaux bassins de compensation. Pour atténuer les perturbations de débits sur le cours aval, dues aux usines de basse-chute gérées par divers types d’exploitants (producteurs autonomes, industriels, E.D.F.), il faut définir une gestion coordonnée. La recherche de cette gestion s’appuie sur la conception et l’utilisation d’un modèle mathématique hydrodynamique permettant la simulation de fonctionnement des usines.Lamire J., Sormail Lucien, Cornillon P., Pineau J., Normand D., Megard J. Rapport VI-3 Soutien des étiages et régularisation des débits dans le bassin du Lot. Effets et adaptation des aménagements hydro-électriques existants . In: L'hydrotechnique au service d'une politique de l'eau. Evolution des problèmes de l'eau au cours de la dernière décennie. Compte rendu des XVes journées de l'hydraulique. Toulouse, 5, 6 et 7 septembre 1976. Tome 2, 1979

Influence de frequences spatiales sur l'extraction de cibles

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