Intérêts et signification écophysiologique de l'estimation de la biomasse et de l'activité photosynthétique de diverses fractions de taille phytoplanctonique en milieu lacustre eutrophe

L'évolution saisonnière de la biomasse phytoplanctonique (estimée par les biovolumes après dénombrements cellulaires et par le dosage de la chlorophylle a), de la production primaire et des coefficients d'activité (P/"BComptage" et P/"BChlorophylle") a été étudiée, par classes de taille, de mars à novembre 1985 dans un lac eutrophe (lac d'Aydat, Massif Central).Il apparaît que la fraction de taille 12-45 µm contribue pour environ 50 % à la biomasse phytoplanctonique totale quelque soit le descripteur de ta biomasse utilisé et pour 65 % à l'activité photosynthétique totale, l'importance quantitative de cette fraction de taille se traduit au niveau des phénomènes d'extinction de la lumière par une relation inverse et hautement significative entre concentrations en chlorophylle a associée à cette classe et les profondeurs de disparition du disque de Secchi (Zs).Si les corrélations linéaires établies entre la production primaire et les rapports surface/volume (S/V) sont significatives au sein de chaque classe, confirmant ainsi l'existence d'une relation directe entre ces 2 paramètres, les valeurs moyennes de P/B de la fraction de taille < 12 µm sont très différentes selon le mode d'expression de la biomasse. L'explication de cette divergence est à rattacher aux divers biais méthodologiques introduits dans les estimations de biomasse retenues dans notre étude. D'une part, la sous estimation de la fraction nanoplanctonique par la technique des dénombrements cellulaires entraîne par voie de conséquence une surestimation des valeurs de P/B"Comptage" attribuées à la fraction < 12 µm. D'autre part, il est reconnu que les teneurs en pigments sont, par unité de volume, supérieures pour la fraction nanoplanctonique que pour les cellules de grande taille. L'adoption d'un facteur unique de conversion entraîne donc une surestimation de ta biomasse de cette fraction.The seasonal distribution of phytoplanktonic biomass (estimated by biovolumes after cell counts and by chlorophyll a concentrations), primary production and primary production to biomass ratios (P/B"Counts" and P/B"Chlorophyll a") was studied by size fractionation in a eutrophic lake (lake Aydat, Massif Central).It appears that the 12-45 µm size fraction contributes about 50 % of the total phytoplanktonic biomass, regardless of what descriptor of the biomass is used and up to 65 % of the total photosynthetic activity. Clearly, the quantitative predominance of this fraction affects the water transparency (Zs) through the highly significant negative correlation obtained between Zs and the 12-45 µm chlorophyll a size fraction.The highly significant linear correlations obtained between the primary production of each fraction and surface to volume ratios (S/V) confirm the direct link between these two parameters. The mean values relative to the P/B of the < 12 µm fraction depend largely on the method used for the biomass estimates. First, the underestimation of the nanoplanktonic fraction by cell counts leads to an over-estimation of the < 12 µm P/B"Counts" fraction. Second, it is well known that chlorophyll a concentrations per unit volume are higher for nanoplankton than for larger cells. Thus, the use of the same biomass conversion factor for all the fractions, overestimates the nanoplankton biomass

Realization of the purely spatial Einstein-Podolsky-Rosen paradox in full-field images of spontaneous parametric down conversion

We demonstrate Einstein-Podolsky-Rosen (EPR) entanglement by detecting purely spatial quantum correlations in the near and far fields of spontaneous parametric down-conversion generated in a type-2 beta barium borate crystal. Full-field imaging is performed in the photon-counting regime with an electron-multiplying CCD camera. The data are used without any postselection, and we obtain a violation of Heisenberg inequalities with inferred quantities taking into account all the biphoton pairs in both the near and far fields by integration on the entire two-dimensional transverse planes. This ensures a rigorous demonstration of the EPR paradox in its original position momentum form

Experimental status of the ππ\pi\pi isoscalar S wave at low energy: f0(600)f_0(600) pole and scattering length

The experimental results obtained in the last few years on kaon decays (K$\to2\pi$ and, above all, Ke4 decays) allow a reliable, model independent determination of low energy $\pi\pi$ scattering in the S0 wave. Using them and, eventually, other sets of data, it is possible to give a precise parametrization of the S0 wave as well as to find the scattering length and effective range parameter. One can also perform an extrapolation to the pole of the "$\sigma$ resonance" [$f_0(600)$]. We obtain the results $$a_0^{(0)}=0.233\pm0.013 M^{-1}_\pi,\quad b_0^{(0)}=0.285\pm0.012 M^{-3}_\pi$$ and, for the $\sigma$ pole, M_\sigma=484\pm17 \mev,\quad\gammav_\sigma/2= 255\pm10 {\rm MeV}.Comment: Plain TeX;4 figures; improved data used; version to appear in Phys. Rev.

La mobilité des adolescents : une pratique socialisée et socialisante

National audienceURL : http://www.metropolitiques.eu/La-mobilite-des-adolescents-une.htm

Protection of the 13 T Nb3Sn Fresca II dipole

The EuCARD project aims on construction of a 19 T hybrid dipole; it will be made of a 6 T HTS dipole associated to a 13 T outsert Nb3Sn dipole [1]. This paper reviews the quench analysis and protection of the 13 T Nb3Sn dipole.Comment: 5 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet, Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva, Switzerlan

Conductivity in organic semiconductors hybridized with the vacuum field

Organic semiconductors have generated considerable interest for their potential for creating inexpensive and flexible devices easily processed on a large scale [1-11]. However technological applications are currently limited by the low mobility of the charge carriers associated with the disorder in these materials [5-8]. Much effort over the past decades has therefore been focused on optimizing the organisation of the material or the devices to improve carrier mobility. Here we take a radically different path to solving this problem, namely by injecting carriers into states that are hybridized to the vacuum electromagnetic field. These are coherent states that can extend over as many as 10^5 molecules and should thereby favour conductivity in such materials. To test this idea, organic semiconductors were strongly coupled to the vacuum electromagnetic field on plasmonic structures to form polaritonic states with large Rabi splittings ca. 0.7 eV. Conductivity experiments show that indeed the current does increase by an order of magnitude at resonance in the coupled state, reflecting mostly a change in field-effect mobility as revealed when the structure is gated in a transistor configuration. A theoretical quantum model is presented that confirms the delocalization of the wave-functions of the hybridized states and the consequences on the conductivity. While this is a proof-of-principle study, in practice conductivity mediated by light-matter hybridized states is easy to implement and we therefore expect that it will be used to improve organic devices. More broadly our findings illustrate the potential of engineering the vacuum electromagnetic environment to modify and to improve properties of materials.Comment: 16 pages, 13 figure

Mesure de l'intensité et de la sélectivité du bronzage zooplanctonique diurne et nocturne sur le peuplement physoplanctonique de la retenue Al Massira (Maroc)

La retenue de barrage Al Massira (Maroc) constitue une pièce maîtresse dans le plan d'aménagement du bassin versant de l'Oum Er Rbia. Elle se situe dans la province de Settat, à 120 km au sud-est de Casablanca. La mesure de l'intensité du broutage zooplanctonique sur le peuplement phytoplanctonique a été réalisée à trois périodes différentes; le 20 mars 1992 d'une part et les 27 et 28 mai 1992 d'autre part, avec respectivement des mesures de jour et de nuit . Pour cela, une analyse de l'évolution des densités phytoplanctoniques au sein d'enceintes immergées in situ à 5 et 15 m pendant 8 heures, en absence (enceintes témoins) et en présence (enceintes expérimentales) de zooplancton, a été réalisée. Les résultats obtenus montrent que:- La technique adoptée est performante dans la mesure où les différences entre les densités algales entre les temps initial et final sont en général significatives dans les deux enceintes. - Conformément aux données de la littérature, le broutage apparaît bien comme sélectif; de nombreuses espèces n'apparaissant pas être consommées. - La sélection effectuée par le zooplancton est principalement basée sur la taille des cellules. Toutefois, à tailles égales, certaines espèces phytoplanctoniques semblent être consommées préférentiellement par les copépodes. - Seules les espèces algales présentant un développement important dans les enceintes témoins sont soumises à la prédation.The Al Massira reservoir, located in the district of Settat 120 km south-east of Casablanca, is of great importance notably at the level of the management of the Oum Er Rbia River-catchment basin.Several grazing experiments were performed to assess the intensity of phytoplankton predation by zooplankton species, on 20 March l992, 27 and 28 May 1992, respectively, over the day and the night. Two enclosures were used and incubated in situ at 5 and 15 m over 8 hours, The first enclosure consisted of a mixture of several phytoplankton and zooplankton species. The second was free of zooplancton.The results clearly demonstrated that the technique used in this work seemed to be effective in that a signifïcant difference between the initial and final numbers of phytoplankton species incubated in the enclosure was detected. In addition, we confirmed several literature reports relative to the selective characteristics of herbivore predation on algae: large phytoplankton (e.g., Peridinium cinctum, Ceratium hirundinellaand Staurastrum pingue) were not affected. The grazing pressure depended on the size of preys and on the exudates released by the physiofogically active small phytoplankton species (e.g., Oocystis crassa, Cyclotella sp.) evolving in the enclosures. Among small preys, only species with high growth rate (estimed in the control flask, e.g., Cosmarium sp. and Tetraedron sp.) were subjected to the zooplankton predation. The copepod nightgrazing was lower than that recorder during the day, probably due to a decrease in their ability to detect preys in the dark.Our result contradict several results obtained by the method of NANEY (1971) according to which grazing increases during the night.Two assumptions may be proposed to explain such a discrepancy:- The zooplankton community of the Al Massira Reservoir was quantitatively dominated by the Calanoid Neolovenula alluaudi.Yet, according to HANEY and HALL (1975), these Copepods showed a slight diel grazing change compared to that of Cladocera. It seemed likely that these temporal variabilities were not statistically significant but rather inherent to the overall internal fluctuation oftlte cell metabolism.- The HANEY (1971) method allows estimation of the water volume per unit time, which transits along the digestive tract of zooplankters. Nevertheless, this technique was mostly performed in markedly stratified natural lakes. From a strictly physiological point of view, and as demonstrated by MC LAREN (1963), organisms which evolved in deep layers (low temperature) became metabolically more active when they reached superficial layers (increased temperature). Clearly, this increase in the cell metabolism abilities is translated into a higher volume of water passing through the digestive tract but not necessarily into an increase in ingested phytoplankton preys. Our results went along with the aforementioned interpretation since we clearly demonstrated an optimal Copepoda-grazing selectivity. However, the selection of preys would not imply a direct relationship between the ingested volume of water and energetic inputs

人格(パースナリティー)理論に就いて

The aim of this study was to evaluate the ability of new rubbery liners, used as a cervical increment, to relieve contraction stress and thereby reduce the formation of cervical gaps in class II composite restorations. The investigated liners were made of polyester-acrylate (PE(1), PE(2) or PE(3)) or silicone-acrylate (S), mixed with UDMA, without (A, B, C, D) or with HEMA (AH, BH, CH, DH). A silanized filler was added to the mixture, DH, to give composites with 20, 40, 60, and 70% (w/w) of filler (DHF20, DHF40, DHF60, DHF70, respectively). The presence and width of cervical gaps were determined using a light microscope. Statistical analysis showed that six of the 12 rubbery liners (AH-DH, DHF20-DHF40) significantly decreased gap formation in comparison with the control group. In addition, the polymerization shrinkage, flow, and strain capacity of these liners were measured and the influence of these factors on gap formation was examined. Two- and three-dimensional regression analyses showed significantly negative linear correlations between gap formation and strain capacity, and between gap formation and flow, and a significantly positive linear correlation between gap formation and shrinkage

Étude préliminaire sur les échanges de phosphore à l'interface eau- sédiment au sein de la retenue d'Al Massira (Maroc)

Les échanges de phosphore à l'interface eau-sédiment ont été étudiés dans la retenue Al Massira. La campagne de prélèvements a été menée pendant la faible oxygénation des eaux profondes au mois d'octobre 1991. Les mesures des échanges de phosphore ont été réalisées in situ en chambre benthique.Les valeurs de pH sont élevées et reflètent clairement l'influence de la nature géologique du bassin versant sur la composition chimique des eaux. Ce bassin versant, formé essentiellement de roches sédimentaires calcaires, est vraisemblablement à l'origine des concentrations élevées en calcium mesurées dans les chambres benthiques.En période de faible oxygénation, on note une augmentation des teneurs en phosphore particulaire dans les eaux surnageantes en raison de la présence de complexes calcium-phosphore, fer-phosphore et manganèse-phosphore. En période d'anoxie, la réduction de ces complexes est accompagnée d'une aug- mentation des teneurs en phosphore.La densité bactérienne et la concentration en phosphore total et notamment en orthophosphates suivent une évolution temporelle comparable. Une fraction non négligeable du phosphore particulaire serait liée aux bactéries.Des mesures drastiques de déphosphatation du tributaire Oum Errbia doivent être prises pour éviter la dissociation des complexes Ca, Fe, Mn-Phosphore et le relargage de phosphore biodisponible.Phosphorus exchange at the sediment-water interface was studied in the Al Massira reservoir. This reservoir, located on the Oum Errbia river, is the most important freshwater resource in Morocco. It provides drinking water to the whole population of Casablanca and contributes to farming and to the functioning of several industrial plants. Our investigations were made in October 1991 and coincided with low oxygen concentrations in the deep layers. The measurements of phosphorus exchange have been made in sitn with a benthic chamber device.The results showed that these exchanges were regulated by a combination ofthe physical chemical variability of the environment and the geological composition of the catchment basin.The pH, which permanently exceeded 7 in Massira, suggests that calcium-bound phosphorus was primarily CaHFO4. Moreover, given the high phosphonrs inputs into the reservoir (570 tonnes. year-1), and despite the fact that, as soon as it reached the reservoir, a large fraction of this element was associated with to calcium, it's likely that the Massira reservoir is subject to eutrophication.In low oxygenated deep layers, we observed an increase in particulate phosphorus concentrations of the overlying water, due to the simultaneous presence of calcium-phosphorus, iron-phosphorus and manganese-phosphorus forms. Under anoxic conditions, the reduction ofthese complexes resulted in an increase of phosphorus concentrations.Bacterial cell numbers and total phosphorus concentratioru showed a comparable temporal behaviour. This would suggest that attached bacteria contributed at least partially to the total particulate phosphoms concentrations.We suggest that a drastic control of phosphorus inputs into the waters must be done through a program of dephosphorylation of tributaries to avoid the dissocation of calcium-, iron-, manganese-bound phosphorus with release upwards of bioavailable phosphorus