The structures and the role of an international agency for the control of satellites

Legal questions involved in the liability of a proposed agency which would control internationally owned satellites for monitoring worldwide compliance with arms control agreements are discussed. Difficulties in acquiring the signed consent of all the relevant nations, and guaranteeing satisfactory compliance with the terms of such an agreement are noted. Additional problems to be solved comprise the construction of the ground based facilities and the satellites, the funding for the venture, and the reconciliation of the functions of the proposed agency with the sovereignty of individual states. The agency would gather, treat, and format data for signatories of arms control agreements and provide technical assistance in crisis conditions. It is concluded that the existence and functioning of the agency would reduce the amount of classified information and would consequently reduce the level of international tensions

Finite-Temperature Quasicontinuum: Molecular Dynamics without All the Atoms

Using a combination of statistical mechanics and finite-element interpolation, we develop a coarse-grained (CG) alternative to molecular dynamics (MD) for crystalline solids at constant temperature. The new approach is significantly more efficient than MD and generalizes earlier work on the quasicontinuum method. The method is validated by recovering equilibrium properties of single crystal Ni as a function of temperature. CG dynamical simulations of nanoindentation reveal a strong dependence on temperature of the critical stress to nucleate dislocations under the indenter

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

Cn to ccn relationships and cloud microphysical properties in different air masses at a free tropospheric site

International audienceThe fraction of aerosol particles activated to droplets (CCN) is often derived from semi-empirical relationships that commonly tend to overestimate droplet number concentration leading to major uncertainties in global climate models. One of the difficulties in relating aerosol concentration to cloud microphysics and cloud albedo lies in the necessity of working at a constant liquid water path (LWP), which is very difficult to control. In this study we observed the relationships between aerosol number concentration (NCN), cloud droplet concentration (Nd) and effective radius (Reff), at the Puy de Dôme (France). A total of 20 cloud events were sampled representing a period of more than 250 h of cloud sampling. Samples are classified first according to air mass origins (Modified Marine, Continental and Polluted) and then according to their liquid water content (Thin, Medium and Thick clouds). The CCN fraction of aerosols appears to vary significantly according to the air mass origin. It is maximum for Continental air masses and minimum for Polluted air masses. Surprisingly, the CCN fraction of Modified Marine air masses fraction is lower than the continental air mass and from expected from previous studies. The limited number of activated particles in Modified Marine air masses is most likely the result of the presence of hydrophobic organic compounds. The limited activation effect leads to a 0.5 to 1 µm increase in Reff with respect to an ideal Marine case. This is significant and implies that the dReff/dNCN of low-continental clouds is higher than expected

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

M3Fusion: A Deep Learning Architecture for Multi-{Scale/Modal/Temporal} satellite data fusion

Modern Earth Observation systems provide sensing data at different temporal and spatial resolutions. Among optical sensors, today the Sentinel-2 program supplies high-resolution temporal (every 5 days) and high spatial resolution (10m) images that can be useful to monitor land cover dynamics. On the other hand, Very High Spatial Resolution images (VHSR) are still an essential tool to figure out land cover mapping characterized by fine spatial patterns. Understand how to efficiently leverage these complementary sources of information together to deal with land cover mapping is still challenging. With the aim to tackle land cover mapping through the fusion of multi-temporal High Spatial Resolution and Very High Spatial Resolution satellite images, we propose an End-to-End Deep Learning framework, named M3Fusion, able to leverage simultaneously the temporal knowledge contained in time series data as well as the fine spatial information available in VHSR information. Experiments carried out on the Reunion Island study area asses the quality of our proposal considering both quantitative and qualitative aspects

Core level photoelectron spectroscopy of heterogeneous reactions at liquid-vapor interfaces: Current status, challenges, and prospects

Liquid–vapor interfaces, particularly those between aqueous solutions and air, drive numerous important chemical and physical processes in the atmosphere and in the environment. X-ray photoelectron spectroscopy is an excellent method for the investigation of these interfaces due to its surface sensitivity, elemental and chemical specificity, and the possibility to obtain information on the depth distribution of solute and solvent species in the interfacial region. In this Perspective, we review the progress that was made in this field over the past decades and discuss the challenges that need to be overcome for investigations of heterogeneous reactions at liquid–vapor interfaces under close-torealistic environmental conditions. We close with an outlook on where some of the most exciting and promising developments might lie in this fiel

Precise Dynamical Masses of Directly Imaged Companions from Relative Astrometry, Radial Velocities, and Hipparcos-Gaia DR2 Accelerations

We measure dynamical masses for five objects--three ultracool dwarfs, one low-mass star, and one white dwarf--by fitting orbits to a combination of the Hipparcos-Gaia Catalog of Accelerations, literature radial velocities, and relative astrometry. Our approach provides precise masses without any assumptions about the primary star, even though the observations typically cover only a small fraction of an orbit. We also perform a uniform re-analysis of the host stars' ages. Two of our objects, HD 4747B and HR 7672B, already have precise dynamical masses near the stellar/substellar boundary and are used to validate our approach. For Gl 758B, we obtain a mass of $m=38.1_{-1.5}^{+1.7}$ $M_{Jup}$, the most precise mass measurement of this companion to date. Gl 758B is the coldest brown dwarf with a dynamical mass, and the combination of our low mass and slightly older host-star age resolves its previously noted discrepancy with substellar evolutionary models. HD 68017B, a late-M dwarf, has a mass of $m=0.147\pm 0.003$ $M_\odot$, consistent with stellar theory and previous empirical estimates based on its absolute magnitude. The progenitor of the white dwarf Gl 86B has been debated in the literature, and our dynamical measurement of $m=0.595 \pm 0.010$ $M_\odot$ is consistent with a higher progenitor mass and younger age for this planet-hosting binary system. Overall, these case studies represent only five of the thousands of accelerating systems identified by combining Hipparcos and Gaia. Our analysis could be repeated for many of them to build a large sample of companions with dynamical masses.Comment: 33 pages, 24 figures, 9 tables, AJ accepted with minor revision

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