Contamination nitratée des eaux souterraines d'un bassin versant agricole hétérogène 2. Évolution des concentrations dans la nappe

L'usage quasi systématique de fertilisants sur de grandes surfaces a conduit la majorité des aquifères superficiels à un grave niveau de contamination par les nitrates. Des essais de gestion environnementale de cette problématique agricole sont conduits à l'échelle du bassin versant afin d'estimer les flux de nitrates percolant vers la nappe. La présente étude reprend les résultats issus de la modélisation d'un bassin versant dans le but d'appréhender l'évolution de la concentration en nitrates dans les eaux de la nappe. L'importance des conditions hydrogéologiques dans les relations entre zones non saturée et saturée a été mise en évidence par la comparaison des concentrations calculées dans la zone non saturée et observées dans la nappe. En règle générale, les concentrations sont très semblables pour les zones proches des limites amont du bassin, et se différencient de plus en plus vers l'aval du système. Une dilution semble se produire entre les flux percolant des différentes zones non saturées et les flux d'eau et de nitrates s'écoulant dans l'aquifère. Afin de tester cette hypothèse, un modèle de dilution basé sur les flux d'eau et de nitrates dans les zones non saturée et saturée est développé. Appliqué sur l'axe d'écoulement principal du système, le modèle de dilution permet de reproduire adéquatement les concentrations observées dans la nappe à partir de celles calculées dans le sol avec une erreur maximale variant de 1 à 22%. Le couplage d'un modèle environnemental pour la zone racinaire du sol avec un modèle de dilution simple peut permettre le calcul des concentrations en nitrates dans la zone saturée. Toutefois, la prise en compte des conditions hydrogéologiques du système est nécessaire à un calcul de dilution efficace basé sur les valeurs des flux de percolation.Pesticides and nitrates represent the main sources of aquifer contamination in agricultural zones. In many regions, nitrate concentration levels reach and exceed the water quality criteria (50 mg NO3/L). The increasing use of mineral fertilizers (which has doubled during the 20 last years) and the intensive exploitation of the aquifers for crop irrigation (1,1 million ha in France) have led to groundwater contamination by nitrates. The dynamics (long-term persistence) and extensiveness (regional contamination) of this contamination make it a sensitive environmental issue. Comprehensive environmental management is needed in order to limit the increase of the concentration levels and to reduce the extent of the contaminated areas. During the last few years, research has been done in the field of watershed management, from laboratory experiments to field investigations. At the same time, numerous simulation models have been developed at different investigation scales. Banton et al. (1993) developed a model specifically devoted to environmental management. Their model, AgriFlux, is based on a mechanistic approach to the processes, using a stochastic method that takes into account the spatial variability of the parameters. AgriFlux calculates the nitrate concentrations as well as the water fluxes in the unsaturated zone. The concentrations in the unsaturated zone (obtained by modeling or measurement) are generally dissimilar to those observed in the saturated zone (i.e. in the aquifer) because the infiltration water is diluted in the aquifer water. This difference indicates that the concentrations in the unsaturated zone cannot be used to accurately evaluate the actual risk of groundwater contamination. Hydrogeological conditions such as the recharge limits, the flow direction and the flow rate should be incorporated into the evaluation. In this paper, the modeling results obtained previously (Dupuy et al., 1997) with AgriFlux for the La Jannerie watershed are used to determine the concentrations in the aquifer and to compare them with the concentrations measured in the observation wells. This watershed (160 ha) is used exclusively for agriculture. The fractured carbonate strata (Superior Oxfordian) constitute a phreatic aquifer with a vertical extension of about 20 m. First, the temporal evolution of the annual mean concentrations in the aquifer is compared with the evolution of the annual precipitation. The results show that the mean concentrations tend to follow precipitation levels. However, the differences observed at different locations in the watershed cannot be explained by these results. The spatial evolution of the concentrations from the upstream to the downstream part of the aquifer was studied in order to explain the concentration distribution in the watershed. On the main flow line, the concentrations observed from 1985 to 1989 show a decrease from the P7 well (upstream) to the P26 well (downstream). This phenomenon can be attributed to two factors. First, denitrification may occur in the aquifer during flow. However, it is recognized in literature that the denitrification rate is usually low and a long period of time is required to obtain a significant decrease in the nitrate level. The observed attenuation cannot be imputed to this factor alone. The second possible cause is related to the dilution of the nitrates in the water contained in the aquifer.In order to test this hypothesis, a dilution model was elaborated using the watershed division as indicated in Dupuy et al. (1997). In each area, the resulting concentration is obtained by diluting the fluxes of water and nitrate leaching in the unsaturated zone in the fluxes of water and nitrates flowing from the upstream area. The concentrations in the aquifer are calculated from upstream areas to downstream areas for the period between 1985 and 1989. The pattern of the concentration curves obtained in this manner agrees with the trend measured in the different wells. The results clearly show a decrease of the concentration in the aquifer water leached from the unsaturated zone. For the downstream area (well P26), the calculated concentrations are higher than the observed ones. This difference could be due to the fact that the lateral fluxes (flow convergence into the median part) are not taken into account and the concentrations may thus be overestimated. However, the mean resulting error (12%) remains low considering the lack of knowledge of the aquifer characteristics. It is therefore possible to accurately estimate the nitrate concentrations in the saturated zone from the concentrations simulated in the unsaturated zone using a simple dilution model. However, this method is only valid for simple hydrogeological conditions

Orbital Parameter Determination for Wide Stellar Binary Systems in the Age of Gaia

The orbits of binary stars and planets, particularly eccentricities and inclinations, encode the angular momentum within these systems. Within stellar multiple systems, the magnitude and (mis)alignment of angular momentum vectors among stars, disks, and planets probes the complex dynamical processes guiding their formation and evolution. The accuracy of the \textit{Gaia} catalog can be exploited to enable comparison of binary orbits with known planet or disk inclinations without costly long-term astrometric campaigns. We show that \textit{Gaia} astrometry can place meaningful limits on orbital elements in cases with reliable astrometry, and discuss metrics for assessing the reliability of \textit{Gaia} DR2 solutions for orbit fitting. We demonstrate our method by determining orbital elements for three systems (DS Tuc AB, GK/GI Tau, and Kepler-25/KOI-1803) using \textit{Gaia} astrometry alone. We show that DS Tuc AB's orbit is nearly aligned with the orbit of DS Tuc Ab, GK/GI Tau's orbit might be misaligned with their respective protoplanetary disks, and the Kepler-25/KOI-1803 orbit is not aligned with either component's transiting planetary system. We also demonstrate cases where \textit{Gaia} astrometry alone fails to provide useful constraints on orbital elements. To enable broader application of this technique, we introduce the python tool \texttt{lofti\_gaiaDR2} to allow users to easily determine orbital element posteriors.Comment: 18 pages, 10 figures, accepted for publication in Ap

Status of the CTF3 commissioning

The Preliminary Phase of the new CLIC Test Facility CTF3 consists of a low-charge demonstration of the electron bunch train combination process on which the CLIC drive beam generation scheme is based. The principle of the combination relies on the injection of short electron bunches into an isochronous ring using RF deflecting cavities. The commissioning of this facility started in September 2001, with alternating periods of installation work and beam studies. In this paper, we present the status of the facility, the first beam measurements and the next steps towards the completion of the experiment

Human rights and ethical reasoning : capabilities, conventions and spheres of public action

This interdisciplinary article argues that human rights must be understood in terms of opportunities for social participation and that social and economic rights are integral to any discussion of the subject. We offer both a social constructionist and a normative framework for a sociology of human rights which reaches beyond liberal individualism, combining insights from the work of Amartya Sen and from French convention theory. Following Sen, we argue that human rights are founded on the promotion of human capabilities as ethical demands shaped by public reasoning. Using French convention theory, we show how the terms of such deliberation are shaped by different constructions of collectively held values and the compromises reached between them. We conclude by demonstrating how our approach offers a new perspective on spheres of public action and the role these should play in promoting social cohesion, individual capabilities and human rights

Optical thickness and effective radius of Arctic boundary-layer clouds retrieved from airborne nadir and imaging spectrometry

Arctic boundary-layer clouds in the vicinity of Svalbard (78° N, 15° E) were observed with airborne remote sensing and in situ methods. The cloud optical thickness and the droplet effective radius are retrieved from spectral radiance data from the nadir spot (1.5°, 350–2100 nm) and from a nadir-centred image (40°, 400–1000 nm). Two approaches are used for the nadir retrieval, combining the signal from either two or five wavelengths. Two wavelengths are found to be sufficient for an accurate retrieval of the cloud optical thickness, while the retrieval of droplet effective radius is more sensitive to the number of wavelengths. Even with the comparison to in-situ data, it is not possible to definitely answer the question which method is better. This is due to unavoidable time delays between the in-situ measurements and the remote-sensing observations, and to the scarcity of vertical in-situ profiles within the cloud

Rotational Velocities of Individual Components in Very Low Mass Binaries

We present rotational velocities for individual components of 11 very low mass (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s^(–1)), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349–25B and HD 130948C, are rotating at ~30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes ≾3.5 AU, have component v sin i values that differ by greater than 3σ. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary star formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A–BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary star, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A–Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349–25AB and 2MASS 0746+20AB, are also known radio sources

Lucky Imaging Adaptive Optics of the brown dwarf binary GJ569Bab

The potential of combining Adaptive Optics (AO) and Lucky Imaging (LI) to achieve high precision astrometry and differential photometry in the optical is investigated by conducting observations of the close 0\farcs1 brown dwarf binary GJ569Bab. We took 50000 $I$-band images with our LI instrument FastCam attached to NAOMI, the 4.2-m William Herschel Telescope (WHT) AO facility. In order to extract the most of the astrometry and photometry of the GJ569Bab system we have resorted to a PSF fitting technique using the primary star GJ569A as a suitable PSF reference which exhibits an $I$-band magnitude of $7.78\pm0.03$. The AO+LI observations at WHT were able to resolve the binary system GJ569Bab located at 4\farcs 92 \pm 0\farcs05 from GJ569A. We measure a separation of $98.4 \pm 1.1$ mas and $I$-band magnitudes of $13.86 \pm 0.03$ and $14.48 \pm 0.03$ and $I-J$ colors of 2.72$\pm$0.08 and 2.83$\pm$0.08 for the Ba and Bb components, respectively. Our study rules out the presence of any other companion to GJ569A down to magnitude I$\sim$ 17 at distances larger than 1\arcsec. The $I-J$ colors measured are consistent with M8.5-M9 spectral types for the Ba and Bb components. The available dynamical, photometric and spectroscopic data are consistent with a binary system with Ba being slightly (10-20%) more massive than Bb. We obtain new orbital parameters which are in good agreement with those in the literature.Comment: 13 pages, 9 figures, 7 tables, in press in MNRA

Study of mechanical behavior on single use bags welding under gamma irradiation

Since a long time, biopharmaceutical industry utilizes more and more single use plastic bags due to its very easy use (long shelf-lives, mechanical properties), preparation, and storage properties (oxygen and water barriers). These plastic bags are composed of two welded multilayer polymer films. To ensure the function of the closure and the non-contamination from the external environment, welding must answer to several parameters according to norm (“ISO 15747,” 2018) and standard (F02 Committee, n.d.). In this present study, the behavior of weldings on Ethylene Vinyl Acetate (EVA) single use bags under gamma irradiation have been studied. Mechanical tests have been performed at several gamma irradiation doses (from 0 kGy to 270 kGy) and at different location of the bag (Figure 1). The first objective is to study the impact of gamma irradiation dose on the welding mechanical tensile behavior. The second objective is to evaluate the impact of the welding location on the welding tensile properties. Each tensile curve (Figure 2) has been decomposed in 6 characteristic points which were evaluated with Principal Component Analysis (PCA): Ultimate Tensile strength at break (UTS), Ultimate elongation or elongation at break, 1st Yield-Strength (Y1 Strength), 1st Yield-Strain (Y1 Strain), 2nd Yield-Strength (Y2 Strength), 2nd Yield-Strain (Y2 Strain). The study showed that weldings are never impacted during tensile testing: this evaluation reveals that in fine the film cracks before the welding modification. Its function of closure and bag content preservation from external environment is fully achieved whatever the gamma irradiation dose and the welding location. Only the multilayer film on both sides of the welding is altered after 100% elongation strain. The EVA bag showed no degradation up to 115 kGy whereas they become to be altered at 270 kGy. The welding location on EVA bag showed different film mechanical behavior correlated to the polymer film extrusion process orientation. Please click Additional Files below to see the full abstract

A focus on L dwarfs with trigonometric parallaxes

This is an author-created, un-copyedited version of an article published in Publications of the Astronomical Society of the Pacific. Under embargo until 14 May 2019. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1538-3873/aaacc5.We report new parallax measurements for ten L and early T type dwarfs, five of which have no previous published values, using observations over 3 years at the robotic Liverpool Telescope. The resulting parallaxes and proper motions have median errors of 2\,mas and 1.5\,mas/year respectively. Their space motions indicate they are all Galactic disk members. We combined this sample with other objects with astrometry from the Liverpool Telescope and with published literature astrometry to construct a sample of 260 L and early T type dwarfs with measured parallaxes, designated the Astrometry Sample. We study the kinematics of the Astrometry Sample, and derived a solar motion of $(U,V,W)_{\bigodot} = (7.9\pm1.7,13.2\pm1.2,7.2\pm1.0)$\,\kms~ with respect to the local standard of rest, in agreement with recent literature. We derive a kinematic age of 1.5-1.7\,Gyr for the Astrometry Sample assuming the age increases monotonically with the total velocity for a given disk sample. This kinematic age is less than half literature values for other low mass dwarf samples. We believe this difference arises for two reasons (1) the sample is mainly composed of mid to late L dwarfs which are expected to be relatively young and (2) the requirement that objects have a measured parallax biases the sample to the brighter examples which tend to be younger.Peer reviewedFinal Accepted Versio