Vitesses de réaction de dissolution et précipitation au voisinage de l'interface oxydo-réducteur dans un lac méromictique : le lac Pavin (Puy de Dôme, France)

Une étude à l'échelle centimétrique de l'interface redox situé à la limite entre mixolimnion et monimolimnion d'un lac méromictique (le lac Pavin) a permis d'observer très finement l'évolution de la concentration d'un certain nombre d'éléments chimiques. Nous avons choisi de présenter ici des résultats concernant 5 éléments qui présentent des comportements très contrastés : le rubidium, le fer, le baryum, le vanadium et le manganèse. La comparaison avec un élément conservatif, le sodium, montre que Rb est conservatif, que Fe, Ba et V sont précipités et que Mn est dissous dans cette zone.Une modélisation de ces concentrations en vue de préciser à quelle profondeur et avec quelle vitesse se produisent les réactions concernant ces éléments nécessite la détermination des paramètres de transport au voisinage de cet interface.Une représentation analytique des concentrations de sodium permet de calculer le coefficient de diffusion turbulente Kz en fonction de la profondeur. Au voisinage de l'interface redox, ce coefficient est très petit (0,0017m2/jour) et inférieur au coefficient de diffusion thermique moléculaire.Les concentrations des éléments étudiés ont pu être représentés avec précisions par des polynômes en fonction de la concentration en sodium.Cela permet d'estimer les vitesses des réactions de précipitation dissolution en fonction de la profondeur. Le rubidium n'est affecté par aucune réaction. Le fer précipite entre 63 et 65 m, le baryum entre 68 et 72 m tandis que le vanadium précipite à la fois dans ces 2 zones. Le manganèse réagit dans une zone très étroite : il est précipité entre 61,5 et 62 m et dissous entre 62,8 et 63,1 m.Une étude similaire de tous les éléments majeurs (y compris pH et COD) pourrait permettre d'élucider les processus qui conduisent à ces comportements complexes.Lake Pavin, French Massif Central, is the main meromictic lake in France and has been extensively studied from more than 50 years. The upper part (mixolimnion) at a depth of less than about 60 m behaves as an oligotrophic lake and is oxic during the major part of the year. The lower layer (monimolimnion) has a higher salinity and is permanently anoxic. Unlike the top of the mixolimnion, element concentrations in the monimolimnion can be considered at steady state. The boundary between mixolimnion and monimolimnion is a redox interface. At this interface, an important number of both chemical and biochemical reactions occur. This boundary, where element concentrations vary greatly, was studied at the centimeter scale between 58 and 64 m depth. The present paper is focused on five elements showing very different behaviour: rubidium, iron, manganese, vanadium and barium. Sodium was used as a reference element. Sodium and rubidium concentrations had similar patterns: a progressive increase began at 61 m depth and the maximal gradient was located at 63 m. They continue to increase towards the bottom of the lake. Iron concentrations were low (< 1 µmol/L) at a depth less than 62.8 m and increased very sharply below this depth. Manganese concentrations were very low in the mixolimnion(<0.01 µmol/L), exhibited a peak between 62.4 and 63.5 m depth (up to 60 µmol/L at 63 m) and reached a value of about 30 µmol/L at 85 m. Barium concentrations began to increase only at depths greater than 65-67 m. Vanadium concentrations in the mixolimnion were about 14 nmol/L, decreased to a minimum below the detection limit at 62.2 m and then increase drastically (150 nmol/L at 85 m).In order to derive the accurate location of the chemical reactions and an estimation of their rates from the concentration profiles, knowledge of the transport parameters was needed. As advection can be considered to be negligible, the major parameter of interest is the vertical eddy diffusion coefficient Kz. Na is assumed to be unreactive in the studied layer. Its concentrations can be represented by an analytical function      Cmax - Cmin                 Cmax + CminC = ___________ * th [P(z)] + ___________             2                                    2with P(z)=0.0016 * (z-zo)3 - 0.0493 * (z-zo)2 + 0.5735 * (z-zo) - 0.4811This allows the determination of the coefficient Kz.Kz = λ ch2 [P(z)]/ [P'(z)]λ is determined from the value of Kz at 85 m depth previously obtained from an hydrodynamic study of the lake (Aeshbach-Hertig et al., 1999). This coefficient is about 0.1 m2/day at the bottom of the monimolimnion. It is very low at the redox interface (0.0017 m2/day), far below the molecular thermal diffusion coefficient. It increases very sharply at the bottom of the mixolimnion. The Kz profile is in fair agreement with the results obtained from the earlier hydrodynamic study. A quantitative study of the dissolution-precipitation reactions at the center of the lake at depths between 55 and 85 m can then be undertaken. The 55 m limit corresponds to a depth where inputs of fresh water can occur. The 85 m limit is about 7 m above the bottom of the lake. Below this depth important inputs from the pore waters occur which are not taken into account by the present modeling. Concentrations of Rb, Fe, Ba and V can be accurately represented by polynomial functions of the Na concentration. The parameter u=th[P(z)] represents the concentrations of these 4 elements by polynomials :          NX(u) = Σ an * un          0The rate of dissolution-precipitation for each element as a function of depth can be derived.                                       NR = - λ [P'(z)] * ch-2[P(z)] Σ ann(n-1) * thn-2[P(z)]                                        0Rb concentrations are a linear function of the Na ones and therefore rubidium is not reactive. Fe concentrations can be related to sodium concentrations by a parabolic relationship. From this relationship, it can be derived that strong iron precipitation occurs in the 63 - 65 m depth layer. V concentrations are related to sodium ones by a 4th degree polynomial. It can be derived that V deposition occurs at depths of 63-65 m and at 70 m.Ba precipitates around 70 m depth. Mn concentrations are represented by [Mn]=a0 +a1 u + b1 exp[-(z-z°)2/z*2] and the derivation shows that Mn is strongly dissolved between 62.8 and 63 m and precipitated just above. These results are in good agreement with a previous study of particles fluxes derived from sediment trap analysis (Viollier et al, 1997).This study shows the complexity of this interface and more comprehensive studies including all major elements, dissolved organic carbon (DOC) and pH are needed

Morphological classification and structural parameters for early-type galaxies in the Coma cluster

We present the results of an isophotal shape analysis of three samples of galaxies in the Coma cluster. Quantitative morphology, together with structural and photometric parameters, is given for each galaxy. Special emphasis has been placed on the detailed classification of early-type galaxies. The three samples are: i) a sample of 97 early-type galaxies brighter than m$_B$ = 17.00 falling within one degree from the center of the Coma cluster; these galaxies were observed with CCD cameras, mostly in good to excellent resolution conditions; ii) a magnitude complete sample of 107 galaxies of all morphological types down to m$_B$ = 17.00 falling in a circular region of 50 arcmin diameter, slightly offcentered to the North-West of the cluster center; the images for this and the next sample come from digitized photographic plates; iii) a complete comparison sample of 26 galaxies of all morphological types down to m$_R$ = 16.05 (or m$_B$ $\simeq$ 17.5), also in a region of 50 arcmin diameter, but centered 2.6 degrees West of the cluster center. The reliability of our morphological classifications and structural parameters of galaxies, down to the adopted magnitude limits, is assessed by comparing the results on those galaxies for which we had images taken with different instrumentation and/or seeing conditions, and by comparing our results with similar data from other observers.Comment: 22 pages, including 4 figures and 4 tables, uuencoded, gzipped postscrip

Biochemical characterization, molecular cloning and localization of a putative odorant-binding protein in the honey bee Apis mellifera L. (Hymenoptera: Apidea)

AbstractA honey bee antennal water-soluble protein, APS2, was purified and characterized as the first Hymenoptera putative odorant-binding protein. Comparison of its measured Mr (13 695.2±1.6) to that of the corresponding cDNA clone shows it does not undergo any post-translational modification other than a 19-residue signal peptide cleavage and formation of three disulfide bridges. These biochemical features are close to those of Lepidoptera odorant-binding proteins. In situ hybridization experiments demonstrated its specific expression in olfactory areas. Based on its higher expression in the worker than in the drone, ASP2 might be more involved in general odorant than in sex pheromone detection

Phase transitions in social sciences: two-populations mean field theory

A new mean field statistical mechanics model of two interacting groups of spins is introduced and the phase transition studied in terms of their relative size. A jump of the average magnetization is found for large values of the mutual interaction when the relative percentage of the two populations crosses a critical threshold. It is shown how the critical percentage depends on internal interactions and on the initial magnetizations. The model is interpreted as a prototype of resident-immigrant cultural interaction and conclusions from the social sciences perspectives are drawn

The role of potassium channels in Arabidopsis thaliana long distance electrical signalling: AKT2 modulates tissue excitability while GORK shapes action potentials

Fast responses to an external threat depend on the rapid transmission of signals through a plant. Action potentials (APs) are proposed as such signals. Plant APs share similarities with their animal counterparts; they are proposed to depend on the activity of voltage-gated ion channels. Nonetheless, despite their demonstrated role in (a)biotic stress responses, the identities of the associated voltage-gated channels and transporters remain undefined in higher plants. By demonstrating the role of two potassium-selective channels in Arabidopsis thaliana in AP generation and shaping, we show that the plant AP does depend on similar Kv-like transport systems to those of the animal signal. We demonstrate that the outward-rectifying potassium-selective channel GORK limits the AP amplitude and duration, while the weakly-rectifying channel AKT2 affects membrane excitability. By computational modelling of plant APs, we reveal that the GORK activity not only determines the length of an AP but also the steepness of its rise and the maximal amplitude. Thus, outward-rectifying potassium channels contribute to both the repolarisation phase and the initial depolarisation phase of the signal. Additionally, from modelling considerations we provide indications that plant APs might be accompanied by potassium waves, which prime the excitability of the green cable

Flexible n-i-p thin film silicon solar cells on polyimide foils with textured ZnO:Ga back reflector

In thin film silicon solar cells on opaque substrates in n-i-p deposition sequence where the textured transparent conductive oxide (TCO) layer serves as a back reflector, one can independently optimize the morphology of the TCO layer without compromise on transparency and conductivity of this layer and further adjust the electro-optical properties of the back contact by using additional layers on top of the textured TCO. In the present work, we use this strategy to obtain textured back reflectors for solar cells in n-i-p deposition sequence on non-transparent flexible plastic foils. Gallium doped ZnO (ZnO:Ga) films were deposited on polyimide substrates by DC magnetron sputtering at a temperature of 200 °C. A wet-chemical etching step was performed by dipping the ZnO:Ga covered foil into a diluted HCl solution. The textured ZnO:Ga is then coated with a highly reflective Ag/ZnO double layer. On this back reflector, we develop thin film silicon solar cells with a microcrystalline silicon absorber layer. The current density for the cell with the textured ZnO:Ga layer is ~ 23 mA/cm2, 4 mA/cm2 higher than the one without such layer, and a maximum efficiency of 7.5% is obtained for a 1 cm2 cell.Fundação para a Ciência e a Tecnologia (FCT

Photometric structure of the peculiar galaxy ESO 235-G58

We present the near-infrared and optical properties of the peculiar galaxy ESO 235-G58, which resembles a late-type ringed barred spiral seen close to face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk galaxy of relatively low luminosity. We have analyzed the light and color distributions of ESO 235-G58 in the NIR and optical bands and compared them with the typical properties observed for other morphological galaxy types, including polar ring galaxies. Similar properties are observed for ESO 235-G58, polar ring galaxies, and spiral galaxies, which leads us to conclude that this peculiar system is a polar-ring-related galaxy, characterized by a low inclined ring/disk structure, as pointed out by Buta & Crocker in an earlier study, rather than a barred galaxy.Comment: 16 pages, 15 figures, accepted for publication in Astronomy & Astrophysic

Goal-directed fluid management based on pulse pressure variation monitoring during high-risk surgery: a pilot randomized controlled trial

Abstract\ud \ud \ud \ud Introduction\ud \ud Several studies have shown that maximizing stroke volume (or increasing it until a plateau is reached) by volume loading during high-risk surgery may improve post-operative outcome. This goal could be achieved simply by minimizing the variation in arterial pulse pressure (ΔPP) induced by mechanical ventilation. We tested this hypothesis in a prospective, randomized, single-centre study. The primary endpoint was the length of postoperative stay in hospital.\ud \ud \ud \ud Methods\ud \ud Thirty-three patients undergoing high-risk surgery were randomized either to a control group (group C, n = 16) or to an intervention group (group I, n = 17). In group I, ΔPP was continuously monitored during surgery by a multiparameter bedside monitor and minimized to 10% or less by volume loading.\ud \ud \ud \ud Results\ud \ud Both groups were comparable in terms of demographic data, American Society of Anesthesiology score, type, and duration of surgery. During surgery, group I received more fluid than group C (4,618 ± 1,557 versus 1,694 ± 705 ml (mean ± SD), P < 0.0001), and ΔPP decreased from 22 ± 75 to 9 ± 1% (P < 0.05) in group I. The median duration of postoperative stay in hospital (7 versus 17 days, P < 0.01) was lower in group I than in group C. The number of postoperative complications per patient (1.4 ± 2.1 versus 3.9 ± 2.8, P < 0.05), as well as the median duration of mechanical ventilation (1 versus 5 days, P < 0.05) and stay in the intensive care unit (3 versus 9 days, P < 0.01) was also lower in group I.\ud \ud \ud \ud Conclusion\ud \ud Monitoring and minimizing ΔPP by volume loading during high-risk surgery improves postoperative outcome and decreases the length of stay in hospital.\ud \ud \ud \ud Trial registration\ud \ud NCT00479011The authors thank Maria De Amorim (Paris, France) and Julia Fukushima (São Paulo, SP, Brazil) for help in data analysis, Dr Julia Wendon (London, UK) for reviewing the manuscript, and Dixtal (Sao Paulo, SP, Brazil) for providing the software for the automatic calculation of ?PP.The authors thank Maria De Amorim (Paris, France) and Julia Fukushima (São Paulo, SP, Brazil) for help in data analysis, Dr Julia Wendon (London, UK) for reviewing the manuscript, and Dixtal (Sao Paulo, SP, Brazil) for providing the software for the automatic calculation of ?PP

Star formation in the warped outer pseudoring of the spiral galaxy NGC 3642

NGC 3642 was classified as a spiral galaxy with three rings and no bar. We have performed an HI and optical study of this nearly face-on galaxy. We find that the nuclear ring might in fact be part of an inner one-armed spiral, that could be driving nuclear accretion and feeding the central activity in the inner kpc. The inner ring is faint, and the outer ring is a rather ill-defined pseudoring. Furthermore, the size ratio of the rings is such that they cannot be due to a single pattern speed linking them together. The outer pseudoring is peculiar, since it lies in the faint outer parts of the disk, where star formation is still going on at 1.4 times the optical radius. Higher HI column densities are associated with these regions and the atomic gas layer is warped. These perturbations affect only the outer disk, since the kinematics within the main body conforms well to an ordinary differentially rotating disk. We propose here that both nuclear activity and star formation in the warped outer parts might be linked to the fact that NGC 3642 is located in a rich environment, where its close neighbors show clear signs of merging. Our suggestion is that NGC 3642 has captured recently a low-mass, gas-rich dwarf, and star formation was triggered in this infalling external gas that produced also a pronounced warp in the gaseous disk.Comment: Accepted for publication in A&A. Full resolution version available at http://www.iaa.es/~lourdes/3642/H3551.tar.g