Sur un acte prétendu faux de Bérenger Ier, roi d’Italie, pour Saint-Martin de Tours

La confirmation par Bérenger Ier des biens italiens de Saint-Martin de Tours a été considérée comme un faux par la critique moderne. Le présent article propose de réviser cette appréciation. Le diplôme de Bérenger a vraisemblablement été préparé à Saint-Martin : il n’est donc pas authentique, mais c’est aussi le cas de nombreux autres actes royaux en faveur de cette abbaye, que l’on n’a pas classés comme faux. Ce diplôme doit être daté de 916, et non pas de 896 comme on le pensait généralement. Cette nouvelle datation permet d’écarter les critiques que l’on avait formulées sur le contenu de l’acte. Celui-ci fournit d’utiles indications sur la situation de détresse des régions de la Loire, vers 915, face aux Normands, et sur le rôle politique joué à ce moment par le comte Robert, abbé de Saint-Martin.Baccou Philippe. Sur un acte prétendu faux de Bérenger Ier, roi d’Italie, pour Saint-Martin de Tours. In: Mélanges de l'École française de Rome. Moyen-Age, tome 115, n°2. 2003. pp. 711-725

Simulation Results, Post-Processing Experimentations and Comparisons Results for Navigation, Homing and Multiple Vehicles Operations with a New Positioning Method Using one Transponder

International audienceHoming and navigation capabilities are essential for many autonomous underwater vehicle (AUV) applications. This paper presents both problems with respect to a single beacon and an extension of the method for multiple AUV operation using relative location. The difficulties of this approach are due to the fact that a single range measurement does not completely constrain the beacon's position in the vehicle frame. In order to triangulate his position, the AUV needs to maneuver while measuring its displacements between ranges. In addition, range measurements are noisy and sometimes spurious, speed bias and underwater currents affect dead-reckoning measurements. All operation need to have the same beginning. An initialization phase is necessary to obtain an initial estimate of the vehicle's location with respect to a fixed or moving beacon. These initial estimates are refined during the actual displacement towards the beacon by means of a Kalman filter. Two kinds of navigation are used so as to maximize the information matrix and to maintain an accurate absolute position. We also present post-processing results in comparison with LBL navigation and mission experimentation post-processing treatment. And then we applied our method for two vehicles operation

Homing and Navigation Using one Transponder for AUV, Post-Processing Comparisons Results with Long Base-Line Navigation

International audienc

Navigation et positionnement sur une balise d'engins sous-marins autonomes

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Enhancing Bottom Tracking for AUVs by using Sound Diffraction

International audienceIn this paper, we present a method of seabed detection based on the use of a single electro-acoustic transducer (sounder). This method uses both acoustic diffraction and bottom backscattering coefficients. Firstly, we present the acoustic sensor and its geometry. When dimensions of the aperture of the transducer are not very large in comparison with the sound wavelength, diffraction must be taken into account in the estimation of beam geometry. We determine the beam geometry by application of the Huygens-Fresnel principle. We explain how the shape and dimensions of its aperture will influence the diffraction of the acoustic beam (diffraction patterns are presented). We also detail the bottom backscattering properties and their influence on the backscattered acoustic energy of main and secondary beams. In the second part, we introduce a new method aiming to extract seabed features from the received acoustic echo. This method is based on the shape of the received acoustic echo and aims to work out the seabed slope. In the last part, we present results obtained during simulations and during experimentations conducted in the open sea

Using Sound Diffraction to Determine the Seabed Slope

International audienceNavigation of autonomous underwater vehicles (A.U.V.) in very shallow waters implies acoustic detection. In single beam sonar systems, sound emitted by ultrasonic transducers is diffracted and secondary lobes appear. Considering the sea bottom's backscattering properties, secondary lobes can be used to enhance knowledge of seabed features such as slope, and marked variations. In this paper, we firstly consider characteristics of electro-acoustic transducers and study the resulting acoustic diffraction. Then, we introduce a new method aiming to extract seabed features from the received acoustic echo. Thus single beam sonar systems can be used for bottom tracking purposes. We present the results of our simulations and experimental validation

Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment

Since the Fukushima accident, Japanese scientists have been intensively monitoring ambient radiations in the highly contaminated territories situated within 80 km of the nuclear site. The surveys that were conducted through mainly carborne, airborne and in situ gamma-ray measurement devices, enabled to efficiently characterize the spatial distribution and temporal evolution of air dose rates induced by Caesium-134 and Caesium-137 in the terrestrial systems. These measurements revealed that radiation levels decreased at rates greater than expected from physical decay in 2011-2012 (up to a factor of 2), and dependent on the type of environment (i.e. urban, agricultural or forest). Unlike carborne measurements that may have been strongly influenced by the depuration of road surfaces, no obvious reason can be invoked for airborne measurements, especially above forests that are known to efficiently retain and recycle radiocaesium. The purpose of our research project is to develop a comprehensive understanding of the data acquired by Japanese, and identify the environmental mechanisms or factors that may explain such decays. The methodology relies on the use of a process-based and spatially-distributed dynamic model that predicts radiocaesium transfer and associated air dose rates inside/above a terrestrial environment (e.g., forests, croplands, meadows, bare soils and urban areas). Despite the lack of site-specific data, our numerical study predicts decrease rates that are globally consistent with both aerial and in situ observations. The simulation at a flying altitude of 200 m indicated that ambient radiation levels decreased over the first 12 months by about 45% over dense urban areas, 15% above evergreen coniferous forests and between 2 and 12% above agricultural lands, owing to environmental processes that are identified and discussed. In particular, we demonstrate that the decrease over evergreen coniferous regions might be due the combined effects of canopy depuration (through biological and physical mechanisms) and the shielding of gamma rays emitted from the forest floor by vegetation. Our study finally suggests that airborne surveys might have not reflected dose rates at ground level in forest systems, which were predicted to slightly increase by 5 to 10% during the same period of time

Modelling the dynamics of ambient dose rates induced by radiocaesium in the Fukushima terrestrial environment

International audienceSince the Fukushima accident, Japanese scientists have been intensively monitoring ambient radiations in the highly contaminated territories situated within 80 km of the nuclear site. The surveys that were conducted through mainly carborne, airborne and in situ gamma-ray measurement devices, enabled to efficiently characterize the spatial distribution and temporal evolution of air dose rates induced by Caesium-134 and Caesium-137 in the terrestrial systems. These measurements revealed that radiation levels decreased at rates greater than expected from physical decay in 2011-2012 (up to a factor of 2), and dependent on the type of environment (i.e. urban, agricultural or forest). Unlike carborne measurements that may have been strongly influenced by the depuration of road surfaces, no obvious reason can be invoked for airborne measurements, especially above forests that are known to efficiently retain and recycle radiocaesium.The purpose of our research project is to develop a comprehensive understanding of the data acquired by Japanese, and identify the environmental mechanisms or factors that may explain such decays. The methodology relies on the use of a process-based and spatially-distributed dynamic model that predicts radiocaesium transfer and associated air dose rates inside/above a terrestrial environment (e.g., forests, croplands, meadows, bare soils and urban areas).Despite the lack of site-specific data, our numerical study predicts decrease rates that are globally consistent with both aerial and in situ observations. The simulation at a flying altitude of 200 m indicated that ambient radiation levels decreased over the first 12 months by about 45% over dense urban areas, 15% above evergreen coniferous forests and between 2 and 12% above agricultural lands, owing to environmental processes that are identified and discussed. In particular, we demonstrate that the decrease over evergreen coniferous regions might be due the combined effects of canopy depuration (through biological and physical mechanisms) and the shielding of gamma rays emitted from the forest floor by vegetation. Our study finally suggests that airborne surveys might have not reflected dose rates at ground level in forest systems, which were predicted to slightly increase by 5 to 10% during the same period of time

Development of a systematic approach for quantification of thermal hydraulic code model input uncertainty

International audienceUncertainty analysis (UA) is a key element in nuclear power plant (NPP) deterministic safety analysis usingbest-estimate thermal hydraulic codes and best estimate plus uncertainty (BEPU) methodologies. If forwarduncertainty propagation methods have now become mature for industrial applications, the inputuncertainties quantification (IUQ) on the physical models still requires further investigations. TheOECD/NEA PREMIUM project attempted to benchmark the available IUQ methods, but observed a stronguser-effect due to lack of best practices guidance. The SAPIUM project has been proposed towards theconstruction of a clear and shared systematic approach for input uncertainty quantification as it is alreadyaddressed in industries and R&D for related topics. The main outcome of the project is a first “goodpractices” document that can be exploited for safety study in order to reach consensus among experts onrecommended practices as well as to identify remaining open issues for further developments. This paperpresents the systematic approach that consists in five elements in a step by step approach to perform ameaningful model input uncertainty quantification & validation, the key issues to be addressed for eachstep as well as some “good practice guidelines” recommendations and open issues on the tools and methods to be used for each step

Development of a systematic approach for quantification of thermal hydraulic code model input uncertainty

International audienceUncertainty analysis (UA) is a key element in nuclear power plant (NPP) deterministic safety analysis usingbest-estimate thermal hydraulic codes and best estimate plus uncertainty (BEPU) methodologies. If forwarduncertainty propagation methods have now become mature for industrial applications, the inputuncertainties quantification (IUQ) on the physical models still requires further investigations. TheOECD/NEA PREMIUM project attempted to benchmark the available IUQ methods, but observed a stronguser-effect due to lack of best practices guidance. The SAPIUM project has been proposed towards theconstruction of a clear and shared systematic approach for input uncertainty quantification as it is alreadyaddressed in industries and R&D for related topics. The main outcome of the project is a first “goodpractices” document that can be exploited for safety study in order to reach consensus among experts onrecommended practices as well as to identify remaining open issues for further developments. This paperpresents the systematic approach that consists in five elements in a step by step approach to perform ameaningful model input uncertainty quantification & validation, the key issues to be addressed for eachstep as well as some “good practice guidelines” recommendations and open issues on the tools and methods to be used for each step