Plug-in estimation of level sets in a non-compact setting with applications in multivariate risk theory

This paper deals with the problem of estimating the level sets of an unknown distribution function $F$. A plug-in approach is followed. That is, given a consistent estimator $F_n$ of $F$, we estimate the level sets of $F$ by the level sets of $F_n$. In our setting no compactness property is a priori required for the level sets to estimate. We state consistency results with respect to the Hausdorff distance and the volume of the symmetric difference. Our results are motivated by applications in multivariate risk theory. In this sense we also present simulated and real examples which illustrate our theoretical results.Level sets ; Distribution function ; Plug-in estimation ; Hausdorff distance ; Conditional Tail Expectation

Étude du comportement physique et hydrogéochimique d'un dépôt de résidus miniers en pâte dans des conditions de surface = Study of the Physical and Hydrogeochemical behaviour of surface paste disposal

L’industrie minière génère chaque année une importante quantité de rejets solides que l’on peut classer en deux principales catégories : (i) les stériles : fragments de roche de granulométrie assez grossière et (ii) les rejets de concentrateur : minerai très finement broyé dont on a extrait les substances à intérêt économique. Une partie des rejets de concentrateur est retourné sous terre sous forme de remblais miniers (hydraulique ou en pâte) et une autre partie est stockée en surface dans des parcs à résidus. Ces parcs à résidus, souvent ceinturés d’importantes digues, sont des ouvrages difficiles à gérer et coûteux à restaurer; ils sont à la base de nombreuses catastrophes (on dénombre a peu près deux ruptures de digues de parcs à résidus par an dans le monde). Par ailleurs, le principal problème environnemental lié à l’exploitation minière et particulièrement à la gestion des rejets est le drainage minier acide (DMA). Il se produit quand des minéraux sulfureux sont exposés à l’eau et à l’air. L’oxydation libère alors de l’acidité dans le milieu favorisant ainsi la mise en solution de certains contaminants comme des métaux lourds. Les résidus épaissis en pâte sont obtenus en épaississant des rejets de concentrateur jusqu'à la densité voulue (en général plus de 80% par masse de solide), puis en les mélangeant avec de l’eau et un liant. Après le mélange des divers ingrédients, on obtient un matériau ayant la consistance d’une pâte et qui peut être transporté par pompage ou par gravité à l’aide d’un réseau de tuyauterie. Depuis une vingtaine d’années, ils étaient principalement utilisés pour remblayer les chantiers souterrains (remblais miniers en pâte cimentés). Mais, pour remplacer les parcs à résidus « traditionnels » et mieux gérer le DMA certaines exploitations minières utilisent cette méthode pour l’entreposage en surface (dépôt de pâte en surface ou DPS). Le but de ce travail était d’étudier le comportement environnemental de résidus sulfureux stockés en utilisant la méthode des DPS. Plus particulièrement nous avons cherché à améliorer les propriétés de la pâte en ajoutant de faibles quantités de ciment. Pour cela nous avons réalisé des essais en colonnes, nous avons utilisé un model physique instrumenté et utilisé des outils de modélisation numérique. Les résultats montrent principalement que l’ajout de ciment peut fortement améliorer les propriétés environnementales de résidus sulfureux, cependant une mauvaise utilisation du ciment peut avoir l’effet inverse. Des tests en colonnes (préparées avec des résidus très générateurs d’acide contenant 54% de pyrite) ont montré que l’intercalation de couches contenant 2% de ciment entre des couches non cimentées permettait d’améliorer de manière significative le comportement environnemental du dépôt. L’ajout de couches contenant 1% de ciment donnait de plus mauvais résultats que la configuration sans ciment. Ce travail a aussi permis de mettre en évidence l’impact important des différentes discontinuités (fractures de dessiccation, interfaces entre les couches et fracturations secondaires liée à l’attaque sulfatique). Ces différentes discontinuités peuvent créer un réseau d’oxydation et d’infiltration préférentiel favorisant la formation du DMA

Azimuthal anisotropy of Rayleigh-wave phase velocities in the east-central United States

We explore the Rayleigh-wave phase velocity structure of the east-central US in a broad period range (10-200 s). Using a recent implementation of the two-stations method, we first measure interstation dispersion curves of Rayleigh-wave phase velocities along 60 paths. We then invert our collection of dispersion curves for isotropic and azimuthally anisotropic (2Ψ and 4Ψ) phase-velocity maps. The inversion is performed by a damped, smoothed LSQR, and the output model is parametrized on a triangular grid of knots with a 140 km grid spacing. Using the isotropic component of the phase velocity maps to constrain regional variations in shear velocity and Moho-depth, we observe that over the upper-middle crust depth range (z 1 per cent), and the azimuth of the fast-propagation direction is uniform over the entire region and equal to 54°. Our results suggest that azimuthal anisotropy beneath the east-central US is vertically distributed in three distinct layers, with a different geodynamic origin for each of the

Influence of intensive agriculture and geological heterogeneity on the recharge of an arid aquifer system (Saq–Ram, Arabian Peninsula) inferred from GRACE data

This study assesses the detailed water budget of the Saq–Ram Aquifer System (520 000 km2) over the 2002–2019 period using satellite gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions were tested for their local compatibility to compute groundwater storage (GWS) variations in combination with the three soil moisture datasets available from the land surface models (LSMs) of the Global Land Data Assimilation System (GLDAS). Accounting for groundwater pumping, artificial recharge, and natural discharge uniformly distributed over the Saq–Ram domain, the GRACE-derived mass balance calculation for water yields a long-term estimate of the domain-averaged natural recharge of (2.4±1.4) mm yr−1, corresponding to (4.4±2.6) % of the annual average rainfall (AAR). Beyond the regional-scale approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin: chiefly induced by irrigation excess over irrigated surfaces (about 1 % of the domain), artificial recharge corresponds to half of the total recharge of the aquifer. The second source of recharge heterogeneity identified here is natural: volcanic lava deposits (called harrats on the Arabian Peninsula) which cover 8 % of the Saq–Ram aquifer domain but contribute to more than 50 % of the natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge, which has been poorly discussed hitherto. Due to large lag times of the diffuse recharge mechanism, the annual analysis using this GRACE–GLDAS approach in arid domains should be limited to areas where focused recharge is the main mechanism, while long-term analysis is valid regardless of the recharge mechanism. Moreover, it appears that about 15 years of GRACE records are required to obtain a relevant long-term recharge estimate.</p

Attitude Determination from Single-Antenna Carrier-Phase Measurements

A model of carrier phase measurement (as carried out by a satellite navigation receiver) is formulated based on electromagnetic theory. The model shows that the phase of the open-circuit voltage induced in the receiver antenna with respect to a local oscillator (in the receiver) depends on the relative orientation of the receiving and transmitting antennas. The model shows that using a {\it single} receiving antenna, and making carrier phase measurements to seven satellites, the 3-axis attitude of a user platform (in addition to its position and time) can be computed relative to an initial point. This measurement model can also be used to create high-fidelity satellite signal simulators that take into account the effect of platform rotation as well as translation.Comment: 12 pages, and one figure. Published in J. Appl. Phys. vol. 91, No. 7, April 1, 200

“Bridging” Engineering & Art: An Outreach Approach For Middle And High School Students

In this paper describes a novel outreach approach to high school and middle school students to familiarize them with engineering functions and methods. In this approach students participated in a seven-day summer research camp and learned many engineering skills and tools such as CAD solid modeling, finite element analysis, rapid prototyping, mechanical tests, team working, and communication skills under a project-based bridge design research project. The project choice was intended to integrate principles of artistic design, creative use of public spaces, as well as principles of engineering design. End of the program survey results showed a good understanding about the engineering skills and functions and a high degree of satisfaction among participants.

Reef response to sea-level and environmental changes during the last deglaciation: Integrated Ocean Drilling Program Expedition 310, Tahiti Sea Level

The last deglaciation is characterized by a rapid sea-level rise and coeval abrupt environmental changes. The Barbados coral reef record suggests that this period has been punctuated by two brief intervals of accelerated melting (meltwater pulses, MWP), occurring at 14.08-13.61 ka and 11.4-11.1 ka (calendar years before present), that are superimposed on a smooth and continuous rise of sea level. Although their timing, magnitude, and even existence have been debated, those catastrophic sea-level rises are thought to have induced distinct reef drowning events. The reef response to sea-level and environmental changes during the last deglacial sea-level rise at Tahiti is reconstructed based on a chronological, sedimentological, and paleobiological study of cores drilled through the relict reef features on the modern forereef slopes during the Integrated Ocean Drilling Program Expedition 310, complemented by results on previous cores drilled through the Papeete reef. Reefs accreted continuously between 16 and 10 ka, mostly through aggradational processes, at growth rates averaging 10 mm yr-1. No cessation of reef growth, even temporary, has been evidenced during this period at Tahiti. Changes in the composition of coralgal assemblages coincide with abrupt variations in reef growth rates and characterize the response of the upward-growing reef pile to nonmonotonous sea-level rise and coeval environmental changes. The sea-level jump during MWP 1A, 16 ± 2 m of magnitude in ~350 yr, induced the retrogradation of shallow-water coral assemblages, gradual deepening, and incipient reef drowning. The Tahiti reef record does not support the occurrence of an abrupt reef drowning event coinciding with a sea-level pulse of ~15 m, and implies an apparent rise of 40 mm yr-1 during the time interval corresponding to MWP 1B at Barbados. © 2012 Geological Society of America