Search

International audience; Design floods on the upper Rhine River are a major issue for French-German agreements on flood embankments. As intense river training has modified the Rhine River morphology during the 19th century, with a significant rectification of the river course, some disagreement does exist on the interest and value of including information on historical floods. Some hydrological studies are using discharge series from the 20th century only, arguing that it is not possible to estimate flood discharge correctly during and before the river works of the 19th century. Other studies include a set of large historical floods during the 19th century. Unfortunately, design flood estimates with or without historical information are significantly different. We used two long discharge series in Basel-Switzerland (1808-2018, with a set of historical floods since 1268) and Maxau-Germany (1815-2018). A preliminary analysis allowed crossing different archive sources, correcting data to account for the main river corrections (1714 and 1890), checking the homogeneity of data and assessing the uncertainty of the stage-discharge relationship. We present a comparative study of design floods with several distributions and several series lengths (a few decades to several centuries). A statistical Bayesian framework allows comparing design floods and the corresponding uncertainties.; Les crues de référence du Rhin supérieur constituent un enjeu majeur pour les accords franco-allemands sur les digues de protection contre les inondations. Les travaux de rectification du Rhin au cours du 19ème siècle ont modifié la morphologie du Rhin, ce qui induit un certain désaccord sur l'intérêt des informations sur les crues historiques. Certaines études hydrologiques n'utilisent que les séries de débit du 20ème siècle, arguant qu'il n'est pas possible d'estimer correctement le débit des crues pendant et avant les travaux fluviaux du 19ème siècle. D'autres études incluent une série de grandes inondations historiques au cours du 19ème siècle. Malheureusement, les estimations des crues extrêmes, avec ou sans information historique, sont significativement différentes. Nous avons utilisé deux longues séries de débit à Bâle-Suisse (1808-2018, avec un ensemble de crues historiques depuis 1268) et à Maxau-Allemagne (1815-2018). Une analyse préliminaire a permis de croiser différentes sources d'archives, de corriger les données pour tenir compte des principales corrections des rivières (1714 et 1890), de vérifier l'homogénéité des données et d'évaluer l'incertitude de la relation hauteur-débit. Nous présentons une étude comparative des crues de référence avec plusieurs distributions et plusieurs longueurs de séries (de quelques décennies à plusieurs siècles). Un cadre statistique bayésien permet de comparer les crues de référence et les incertitudes correspondantes.

International audience; Establishing streamflow time series in unstable rivers is challenged by changes in the stage-discharge relation after floods. Then, the field hydrologist must develop a new stage-discharge rating curve using new calibration data but also using some information from previous calibration data and previous rating curves. The process includes a large amount of informal expert knowledge and hydraulic assumptions seldom made explicit. This paper develops a stage-period-discharge (SPD) model based on the physical interpretation of changes in the stage-discharge relation across a series of stability periods defined by known dates and times. Using simple hydraulic equations, the user provides prior knowledge on the controls, their static and varying parameters, and their possible changes. As a single model is used for all the periods, the estimation of all rating curves can be performed in one go: All gaugings hence provide information to estimate the static parameters and the varying parameters for the relevant periods. Bayesian inference is used, providing a natural way to include prior knowledge and to quantify uncertainty. The generality and some key properties of the method are demonstrated through application to two hydrometric stations, differing in hydraulic configuration and in number and type of changes. Specific experiments demonstrate the ability of the SPD model to transfer information across periods. Consequently, rating curves are more precisely estimated than by separately estimating them for each period. The SPD model provides a hydraulically based, transparent, and user-friendly approach to replace manual shift corrections traditionally applied in operational practice, with a quantification of uncertainties.

International audience; The stage-discharge rating curve is subject at many hydrometric stations to sudden changes (shifts) typically caused by morphogenic floods. We propose an original method for estimating shift times using the stage-discharge observations, also known as gaugings. This method is based on a recursive segmentation procedure that accounts for both gaugings and rating curve uncertainties through a Bayesian framework. It starts with the estimation of a baseline rating curve using all available gaugings. Then it computes the residuals between the gaugings and this rating curve with uncertainties. It proceeds with the segmentation of the time series of residuals through a multi-change point Bayesian estimation accounting for residuals uncertainties. Once the first set of shift times is identified, the same procedure is recursively applied to each sub-period through a “top-down” approach searching for all effective shifts. The proposed method is illustrated using the Ardèche River at Meyras in France (a typical hydrometric site subject to river bed degradation) and evaluated using several synthetic data sets for which the true shift times are known. The applications confirm the added value of the recursive segmentation compared with a “single-pass” approach and highlight the importance of properly accounting for uncertainties in the segmented data. The recursive procedure effectively disentangles rating changes from observational and rating curve uncertainties.; La relation hauteur-débit est sujette, pour de nombreuses stations hydrométriques, à des détarages brusques généralement causés par des crues morphogènes. Nous proposons une méthode originale pour estimer les dates de détarage à partir des données de jaugeage. Cette méthode est basée sur une procédure de segmentation récursive bayésienne, qui tient compte des incertitudes liées aux jaugeages et aux courbes de tarage. Elle commence par l'estimation d'une courbe de tarage de base en utilisant tous les jaugeages disponibles. Ensuite, on calcule les résidus entre les jaugeages et cette courbe de tarage avec incertitudes. La segmentation de la série temporelle des résidus est réalisée par une estimation bayésienne des dates de changement, en tenant compte des incertitudes des résidus. Une fois que la première série de détarages est identifiée, la même procédure est appliquée de manière récursive à chaque sous-période par une approche descendante en recherchant tous les détarages effectifs. La méthode proposée est illustrée pour la rivière Ardèche à Meyras en France, site hydrométrique sujet aux changements morphologiques du lit de la rivière. Elle est ensuite évaluée en utilisant plusieurs jeux de données synthétiques pour lesquels les dates de détarages sont connues. Les applications confirment la valeur ajoutée de la segmentation récursive par rapport à une approche "simple sans itération" et soulignent l'importance de bien prendre en compte les incertitudes dans les données segmentées. La procédure récursive permet de trouver efficacement les dates de détarage, en exploitant les incertitudes liées aux jaugeages et au calage de la courbe de tarage.

N-doped TiO2 nanocrystals with high photoactivity in the visible range, were successfully synthesized by hydrothermal method, followed by thermal annealing at different temperatures (350-600 degrees C), in order to allow differential nitrogen diffusion into the TiO2 lattice. Optical and magnetic properties, studied by diffuse reflectance spectroscopy, electron paramagnetic resonance and X-ray photoelectron spectroscopy analysis, revealed that TiO2 was effectively doped. The thermal treatment induces insertion of nitrogen into TiO2 lattice in the form of nitride anion N-, detected as N-center dot by EPR, whose ionic character varies with the temperature of annealing. The amount of N-center dot increases till 450 degrees C, then it decreases. Similar trend was observed for the photomineralization of phenol under visible light irradiation (lambda > 385 nm): the photoactivity of N-doped samples becomes maximum for N-TiO2 annealed at 450 degrees C. The overall results suggest that the efficacy of the catalyst depends on the ability of N- centers to trap photogenerated holes. This effect lowers the rate of electron-hole recombination and allows the N-center dot (N- + h(+)) center acts as strong oxidizing agent. (C) 2009 Elsevier B.V. All rights reserved.

A number of distributed applications require communication services with quality of service (QoS) guarantees. Building global-scale distributed systems with predictable properties is one of the great challenges for computer systems engineering in the new century. Work undertaken within the Internet Engineering Task Force has led to the definition of novel architectural models for the Internet with QoS support. According to these models, the network has to be appropriately configured in order to provide applications with the required performance guarantees. In next-generation networks, enabling applications to interact with the underlying QoS services is of primary importance. Hence, several special-purpose application programming interfaces (APIs) have been defined to let applications negotiate QoS parameters across QoS-capable networks. However, so far, none of these APIs are available in different operating environments. We believe that such features should be embedded in programming environments for distributed applications. In this work we present how we included QoS control features in Tcl, a programming language that has been widely adopted for the development of distributed multimedia applications. Our work has led to the implementation of QTcl, an extended Tcl interpreter that provides programmers with a new set of primitives, in full compliance with the standard SCRAPI programming interface for the RSVP protocol. QTcl in highly portable, in that it enables standard QoS negotiation to be performed in a seamless fashion on the most common operating systems. Copyright © 2003 John Wiley & Sons, Ltd.