Le trachyte en Auvergne : exploitation, utilisation et diffusion de l’Antiquité à l’époque moderne

L’année 2016 a permis aux chercheurs du PCR de travailler sur l’ensemble des axes définis lors de l’année probatoire. Le levé LiDAR manquant (puy Chopine) a été acquis (fig. 1), permettant ainsi de travailler sur une cartographie fine des zones de carrières de trachyte de la chaîne des Puys. Fig. 1 – Levé LiDAR du volcan Chopine Crédits : CNRS. Les prospections ont révélé des édifices médiévaux, modernes et contemporains, religieux ou civils, utilisant le trachyte dans leur construction. Un ..

Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows

International audienceAn extended version of the hybrid recursive regularized Lattice-Boltzmann model which incorporates external force is developed to simulate humid air flows with phase change mechanisms under the Boussinesq approximation. Mass and momentum conservation equations are solved by a regu-larized lattice Boltzmann approach well suited for high Reynolds number flows, whereas the energy and humidity related equations are solved by a finite volume approach. Two options are investigated to account for cloud formation in atmospheric flow simulations. The first option considers a single conservation equation for total water and an appropriate invariant variable of temperature. In the other approach, liquid and vapor are considered via two separated equations, and phase transition is accounted for via a relaxation procedure. The obtained models are then systematically validated on four well-established benchmark problems including a double diffusive Rayleigh Bénard convection of humid air, 2D and 3D thermal moist rising bubble under convective atmospheric environment as well as a shallow cumulus convection in framework of large-eddy simulation

L'usage des trachytes de la Chaîne des Puys dans l'antiquité

Rapport d'opération archéologique Opération de prospection thématique annuelle Opération archéologique n° 6889 Arrêté n° 2011-130Un relevé 3D LiDAR du centre de la Chaîne des Puys, effectué en mars 2011 (Coordination Centre Régional Auvergnat de l'Information Géographique, CRAIG ; contrôle scientifique P. Labazuy, LMV-OPGC, UBP), a compris spécifiquement la zone du Kilian en haute résolution. Le fichier définitif a été livré au CRAIG au mois d'octobre 2011, suite à quoi il a été possible d'extraire les données intéressant le Kilian. Leur analyse a permis de mettre en évidence la très forte anthropisation du cratère et sa complexité. Elle a, de plus, aidé à la définition des parcours d'investigations géophysiques qui seront effectués en 2012. Une campagne de prospection systématique des dépôts de fouille et dépôts de musées (Musées de la Ville de Clermont, dépôts DRAC, INRAP, Conseil Général du Puy-de-Dôme) a été entreprise afin de repérer tous les trachytes gallo-romains provenant, soit de fouilles et découvertes fortuites anciennes - et conservés dans des collections publiques - soit de fouilles récentes. Plusieurs dizaines d'objets ont ainsi pu être inventoriés. Par suite, des prélèvements systématiques de trachyte ont été effectués, en donnant la priorité à des objets documentés et datables. Des lames minces ont été réalisées et analysées. Les conclusions des analyses confirment que le Kilian a été, de beaucoup, la principale source de trachyte dès la seconde moitié du premier siècle de notre ère, aussi bien dans le secteur du puy de Dôme qu'en Limagne. En outre, de rares éléments témoignent ponctuellement de l'utilisation d'autres trachytes : trachyte du puy de Dôme, du Sarcouy et du Clierzou (ou de l'Aumône). En parallèle, des prélèvements de trachyte sur les sites potentiels d'exploitation (volcans trachytiques), ont été poursuivis de façon à enrichir et affiner notre base de données. Enfin, de nouvelles analyses d'éléments traces non encore pris en compte (séries U et Th) ont montré que ces derniers pouvaient être très discriminants dans la recherche des sources

La police devrait-elle cibler les taudis malfamés ?

Les modèles de police de résolution de problèmes et de police communautaire sont souvent présentés en opposition l’un de l’autre. Le présent article propose l’évaluation d’une intervention policière qui incorporait des ingrédients des deux modèles et qui avait pour objectif de mettre fin au foyer de désordres causés par un immeuble de location de chambres. L’étude, qui utilise les appels 911 faits par les locataires des immeubles d’appartements d’un quartier de Montréal, départage les effets spécifiques d’une police de proximité et d’une police de résolution de problèmes. Les résultats de l’évaluation indiquent qu’un régime de patrouille intensive stimule la fréquence des appels 911 faits par les citoyens et que la stratégie de profiler un taudis de mauvaise réputation pour faire diminuer les désordres dans l’ensemble du quartier n’a pas été, dans le site observé, particulièrement concluante.Problem-oriented and community policing are often contrasted. In this paper we evaluate the impact of a police crackdown that incorporates ingredients of both approaches in an effort to neutralize tenants of a troublesome flophouse. Weekly 911 calls by tenants of all block apartments located in a Montreal neighborhood are analyzed. The evaluation design isolates the specific effects of both ingredients. Findings show that intensive patrol surveillance increases residents’ propensity to report disorders and that the strategy to reduce disorder levels by targeting place managers and other agencies was not particularly successful.Los modelos de policía orientada hacia la resolución de problemas y de policía de proximidad son a menudo presentados como opuestos. Este artículo evalúa una intervención policiaca que incorporó elementos de ambos modelos y cuyo objetivo era poner fin a desórdenes originados a partir de un edificio de habitaciones de alquiler. El estudio analiza las llamadas de emergencia (número 911) realizadas por inquilinos de edificios de apartamentos de un barrio de Montreal y desagrega los efectos específicos de una policía de proximidad y una policía orientada hacia la resolución de problemas. Los resultados de la evaluación indican que la vigilancia intensiva de la policía estimula la frecuencia de llamadas al 911 por parte de los ciudadanos y que la estrategia de vigilar estrechamente un inmueble de mala reputación para hacer disminuir los desórdenes en todo el barrio no fue particularmente concluyente en el sitio observado

Updated Hybrid Lattice-Boltzmann Model for Low-Mach Reactive Flows

International audienc

Reduced-kinetic mechanisms for hydrogen and syngas combustion including autoignition

Reduced chemical-kinetic mechanisms are investigated for hydrogen and syngas combustion to fill the need for simplified chemistry able to describe with accuracy both premixed and diffusion flames and also autoignition, necessitated for instance in computational work that addresses turbulent combustion or the transition from deflagration to detonation. The reduced descriptions incorporate steady-state assumptions for O and OH, which are found to be reasonably accurate for flames but much less accurate for hightemperature autoignition. A detailed description of ignition histories, both above and below the second explosion limit, provides explicit analytic expressions for the ignition time of hydrogen-air mixtures, valid in a wide range of pressure, temperature, and equivalence ratios, and also leads to a correction for the rates of the reduced chemistry that improves accuracy of predicted high-temperature ignition times while keeping the simplification associated with the steady-state assumptions for O and OH. The resulting reduced mechanisms, which consist of three overall steps for hydrogen combustion and one additional CO-oxidation step for syngas combustion, possess reasonable accuracy for most computational purposes, as is demonstrated through extensive validation exercises including comparisons with detailed-chemistry computations and experimental measurements of flame-propagation velocities, extinction strain rates, and ignition times. The three-step mechanism is used also to investigate a turbulent, supersonic, autoignition-stabilized, hydrogenair lifted flame, enabling reduced-chemistry capabilities to be tested in a large scale simulation including turbulence modelling. --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------En esta tesis se aborda el desarrollo de mecanismos cinéticos reducidos para la combustión de hydrógeno y gas de síntesis que sean capaces de describir con precisión tanto llamas de premezcla y difusión como procesos de autoignición. Este tipo de mecanismos multipropósito son necesarios, por ejemplo, para cálculos numéricos de combustión turbulenta o de transiciones de deflagración a detonación. En la reducción de la química se hace uso de las hipótesis de estado estacionario para las especies químicas O y OH. Aunque estas aproximaciones son adecuadas para llamas, se observa que no lo son tanto para el caso de la autoignición a temperaturas por encima de la denominada temperatura de cruce. Mediante el estudio analítico de los procesos de autoignición se deducen expresiones explícitas para el tiempo de ignición de mezclas de hidrógeno y aire para un amplio rango de presiones, temperaturas y composiciones, incluyendo condiciones por encima y por debajo de cruce. Además, el estudio proporciona una corrección para las velocidades de reacción de la química reducida que tiene en cuenta la evolución de O y OH fuera del estado estacionario durante la ignición a alta temperatura, mejorando sensiblemente la capacidad predictiva de la química reducida. Los mecanismos resultantes incluyen tres reacciones globales para la combustión de hidrógeno, a las que hay que añadir una reacción adicional de oxidación de monóxido de carbono para la combustión de gas de síntesis. La validación incluye comparaciones extensivas con cálculos numéricos con química detallada y medidas experimentales de velocidades de propagación de llamas, condiciones críticas de extinción aerodinámica de llamas de difusión y tiempos de ignición, dando resultados satisfactorios. El mecanismo global de tres pasos para la combustión de hidrógeno se utiliza también para investigar llamas turbulentas levitadas en una configuración supersónica con autoignición, lo que permite comprobar la capacidad de la química reducida en una simulación numérica a gran escala incluyendo modelado de la turbulencia

Non-linear modal analysis of structural systems using multi-mode invariant manifolds

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76304/1/AIAA-1994-1672-138.pd

A fast and reliable method for the delineation of tree crown outlines for the computation of crown openness values and other crown parameters

Numerous crown parameters (e.g., leaf area index, diameter, height, volume) can be obtained via the analysis of tree crown photographs. In all cases, parameter values are functions of the position of the crown outline. However, no standardized method to delineate crowns exists. To explore the effect of different outlines on tree crown descriptors, in this case crown openness (CO), and facilitate the adoption of a standard method free of user bias, we developed the program Crown Delineator that automatically delineates any outline around tree crowns following predetermined sensibility settings. We used different outlines to analyze tree CO in contrasting settings: using saplings from four species in young boreal mixedwood forests and medium-sized hybrid poplar trees from a low-density plantation. In both cases, the estimated CO increases when calculated from a looser outline, which had a strong influence on understory available light simulations using a forest simulator. These results demonstrate that the method used to trace crown outlines is an important step in the determination of CO values. We provide a much-needed computer-assisted solution to help standardize this procedure, which can also be used in many other situations in which the delineation of tree crowns is needed (e.g., competition and crown shyness)

Simulation of a supersonic hydrogen-air autoignition-stabilized flame using reduced chemistry

A three-step mechanism for H2-air combustion (Boivin et al., Proc. Comb. Inst. 33, 2010) was recently designed to reproduce both autoignition and flame propagation, essential in lifted flame stabilization. To study the implications of the use of this reduced chemistry in the context of a turbulent flame simulation, this mechanism has been implemented in a compressible explicit code and applied to the simulation of a supersonic lifted co-flowing hydrogen-air flame. Results are compared with experimental measurements (Cheng et al. C&F 1994) and simulations using detailed chemistry, showing that the reduced chemistry is very accurate. A new explicit diagnostic to readily identify autoignition regions in the post-processing of a turbulent hydrogen flame simulation is also proposed, based on variables introduced in the development of the reduced chemical mechanism.This work was supported by the UE Marie Curie ITN MYPLANET, by the Spanish MCINN through projects # ENE2008-06515 and # CSD2010-00010 and by the Comunidad de Madrid through project # S2009/ENE-1597. We acknowledge fruitful discussions on hydrogen chemistrywith Prof. A.L. S´anchez and Prof. F.A. Williams. We also wish to thank Prof. T. S. Cheng and Prof. R. W. Pitz for providing experimental data in electronic form.European Community's Seventh Framework ProgramPublicad

Explicit analytic prediction for hydrogen–oxygen ignition times at temperatures below crossover

This paper addresses homogeneous ignition of hydrogen-oxygen mixtures when the initial conditions of temperature and pressure place the system below the crossover temperature associated with the second explosion limit. A three-step reduced mechanism involving H2, O2, H2O, H2O2 and HO2, derived previously from a skeletal mechanism of eight elementary steps by assuming O, OH and H to follow steady state, is seen to describe accurately the associated thermal explosion. At sufficiently low temperatures, HO2 consumption through HO2 + HO2 → H2O2 + O2 is fast enough to place this intermediate in steady state after a short build-up period, thereby reducing further the chemistry description to the two global steps 2H2 + O2 → 2H2O and 2H2O → H2O2 + H2. The strong temperature sensitivity of the corresponding overall rates enables activation-energy asymptotics to be used in describing the resulting thermal runaway, yielding an explicit expression that predicts with excellent accuracy the ignition time for different conditions of initial temperature, composition, and pressure.This work was supported by the Comunidad de Madrid through project # P2009/ENE-1597. The first two authors also acknowledge support from the EU through the Marie Curie ITN MYPLANET and from the Spanish MCINN through projects # ENE2008-06515 and CSD2010-00011.European Community's Seventh Framework ProgramPublicad