Search

Cities are responsible for more than half of all greenhouse gas emissions. While many cities have committed to emission reduction trajectories, many lack the infrastructure to develop their emissions budgets. The measurement of CO2 plumes from cities by satellite imagery, coupled with atmospheric inversion methods, could allow quantifying direct CO2 emissions from cities, or at least detecting trends in their evolution.OCO-3, with its Snapshot Area Maps (SAMs) mode, is the first instrument to provide 2D (≈80km*80km) images of the total CO2 column at high resolution (≈2km*2km). In particular, these SAMs target atmospheric plumes of CO2 from cities and powerplants, with the goal of quantifying their emissions. Methods to estimate these emissions must be reliable and fast to process all available images (several thousands for OCO-3), whose number will increase with the CO2M and GeoCarb missions. The inversion methods by direct flux calculation (Integrated Mass Enhancement, Cross-Sectional and Source Pixel) or with a Gaussian plume model require little computation time. This thesis aims to evaluate the accuracy of these CO2 plume inversion methods and to study the favorable cases in terms of target and observation condition. This is done in a theoretical framework (atmospheric transport simulations) and by applying the methods to acquired SAMs.We quantify and analyze the different sources of error of these methods in detail using satellite pseudo-images of plumes, first over Paris and then over 31 cities in the world. The error of these methods is mainly due to errors in the estimation of the background concentration (XCO2 concentration that does not come from the city emissions) and in the estimation of the effective wind that carried the plume. We show, with a decision tree learning method, the sensitivity of the error on the emission estimate to the variability of the wind direction in the PBL and to the city's emission budget. The set of pseudo-images for which the emissions are large (>2.1ktCO2/h) and the wind direction variability low (2.1ktCO2/h) et la variabilité de la direction du vent faible (

The popularization of sequencing technologies in the past twenty years led to a high increase of the number of sequenced genomes. The diversity of the newly sequenced reference genomes highlighted the biases of using a single reference, which is not enough to access all the diversity within a species. There are many examples of intraspecific variations within plants, including presence / absence and copy number variations. These variations can have a strong effect on plant phenotypes, as exemplified by the African rice in which the presence of the gene Sub1A is linked to drought tolerance. The concept of pangenome appeared to better integrate these variations within genomics approaches. A pangenome can be built from genes only or from any genomic fragments found within a group, and is useful to compare their distributions between multiple individuals. Depending on the presence rate, many categories of elements can be defined; the main ones are the elements present in all the individuals (part of the ‘core’ genome) and these absent in at least one of them (part of the ‘variable’ genome). Pangenomics still lacks tools, especially for visualization. This is particularly true for eukaryotes (including plants) which have larger and more complex genomes than bacteria. Pangenomes were first built for bacteria, but their related tools cannot properly work on bigger genomes. My PhD investigated the creation of novel visual representations and tools for the visualization of plant pangenomes (and eukaryotes in general).Within this dissertation, I introduce the state of the art of pangenome visualization: I distinguish pan-gene from pangenomes, the latter often being represented by pangenome graphs where each sequence is a node and each observed sequence succession forms an edge; I also identify unspecific, qualifying, positioned, structural and composite visualization tools. The first chapter introduce ten principles for creating a genomic visualization tool, for future biology or bioinformatics scientists interested in datavisualization. The second chapter describes my first pangenome visualization, published in the journal Bioinformatics under the name ‘Panache: a Web Browser-Based Viewer for Linearized Pangenomes’. I detail the visual representation used within Panache and the creation of the resulting web application built in JavaScript, enabling the dynamic exploration of pangenomic data. The third and final chapter details the design of a composite visualization tools for pangenomes, called SaVanache, and enabling the navigation between four view scales. There are four of them: one for global diversity, one for structural variations, one for the presence / absence variations, and one for nucleotide variations. I propose a new approach for the annotation and visual representation of structural variations within a pangenome graph, based on a pivot path within the graph used as a reference coordinate system.; La démocratisation des technologies de séquençage lors des vingt dernières années a entraîné une explosion du nombre de génomes séquencés. La diversité des génomes de référence ainsi disponible a mis en évidence les biais induits par l’utilisation d’une unique référence, qui n’est pas suffisante pour donner accès à la diversité au sein d’une espèce. Chez les plantes, de nombreux exemples de variations intraspécifiques ont été recensés, notamment de la variation en présence / absence ou en nombre de copies de gènes. Ces variations peuvent exercer une forte influence sur le phénotype des plantes, par exemple chez le riz où la présence d’un gène Sub1A est associée à une tolérance à l’inondation. Pour une meilleure intégration de ces variations en génomique, le concept de pangénome s’est progressivement développé. Un pangénome peut être construit aussi bien pour recenser des gènes que pour tous types de fragments génomiques présents au sein d’un groupe, et est utile pour comparer la répartition de ces éléments entre plusieurs individus. Plusieurs catégories d’éléments existent selon le taux de présence ; les deux principales recensent les éléments présents chez tous les individus (les éléments ‘core’) et ceux présents seulement chez certains (les éléments ‘variable’). La pangénomique souffre encore d’un manque d’outils, notamment pour sa visualisation. Ce manque est particulièrement vrai pour les eucaryotes (dont les plantes), aux génomes plus gros et complexes que les bactéries, premier domaine d’application des pangénomes et dont les outils existants ne supportent pas facilement le passage à l’échelle vers des génomes plus volumineux. Mes travaux de thèse ont donc porté sur la création de nouvelles représentations visuelles ainsi que la création d’outils de visualisation utilisables pour la visualisation de pangénomes de plantes, et d’eucaryotes en général.Dans ce manuscrit de thèse, je présente l’état de l’art de la pangénomique : j’y fais la distinction entre la notion de pan-gene atlas et de pangénome, le second étant souvent représenté sous la forme d’un graphe où chaque séquence forme un noeud et chaque succession observée de séquence forme des liens entre ces noeuds ; j’identifie également des outils de visualisation non spécifiques, qualitatifs, positionnés, structuraux, et enfin composites. Le premier chapitre recueille dix conseils pour créer un outil de visualisation de données génomiques, à l’attention de futurs chercheu·r·se·s en biologie ou bio-informatique qui s’intéresseraient à la data visualisation. Le second chapitre, décrit mon premier outil de visualisation de pangénome, publié dans le journal Bioinformatics sous le titre « Panache : a Web Browser-Based Viewer for Linearized Pangenomes ». J’y détaille la représentation visuelle utilisée dans Panache, jusqu’à la création d’une application web développée en JavaScript permettant l’exploration dynamique de données pangénomiques. Le troisième et dernier chapitre détaille le travail de conception d’un outil composite de visualisation de pangénomes, appelé SaVanache, permettant la navigation entre plusieurs niveaux d’échelle pangénomique. Quatre vues ont été identifiées : une vue de la diversité globale ; une vue des variations structurales ; une vue dédiée à la variation en présence / absence ; et une dernière vue dédiée au variations nucléotidiques. Je propose une nouvelle approche pour l’annotation et la représentation visuelle de variations structurelles au sein d’un graphe de pangénome, axée autour de la définition d’un chemin pivot servant de système de coordonnées principal.

Motivation Pangenomics evolved since its first applications on bacteria, extending from the study of genes for a given population to the study of all of its sequences available. While multiple methods are being developed to construct pangenomes in eukaryotic species there is still a gap for efficient and user-friendly visualization tools. Emerging graph representations come with their own challenges, and linearity remains a suitable option for user-friendliness. Results We introduce Panache, a tool for the visualization and exploration of linear representations of gene-based and sequence-based pangenomes. It uses a layout similar to genome browsers to display presence absence variations and additional tracks along a linear axis with a pangenomics perspective. Availability and implementation Panache is available at github.com/SouthGreenPlatform/panache under the MIT License.

In this paper, Computational Fluid Dynamics (CFD) approach was used to study patterns of Liquefied Natural Gas (LNG) vapor dispersion under different atmospheric stabilities. First of all, the Burro 8 field test was used to validate prediction results generated by Fluidyn- PANACHE, a CFD modeling software. The test data confirmed that PANACHE is able to describe the dense gas behavior of LNG vapor dispersion. The CFD predictions regarding lower flammable limit (LFL) distances and downwind maximum concentration were in approximate agreement with the test data. After this, the dispersion of LNG vapor, which results from its accidental release from the top of large-scale storage tank under different atmospheric stabilities, were simulated. The results showed that the influence of atmospheric stability on the vertical and lateral distributions of vapor cloud, the downwind near-ground gas concentrations and the LFL distance is significant. The vertical spread of cloud under unstable condition is slightly larger than that under neutral and stable conditions. The dilution of the LNG cloud is suppressed under stable condition due to weaker turbulent mixing. Also, stable atmospheric condition can increase the near-ground gas concentrations, the lateral distribution of the cloud and the LFL distance. The longitudinal distribution of the cloud near the ground under neutral condition is larger than that under unstable and stable condition.

Swing is extreme coordination. It’s a maintaining balance, equilibrium. It’s about executing very difficult rhythms with a panache and a feeling in the context of very strict time. So, everything a...

La lecture nationale qui reste attach��e �� la pi��ce depuis sa cr��ation requiert d�����tre expliqu��e, pr��cis��e et nuanc��e par une recontextualisation aussi bien litt��raire et historique que politique et culturelle. L���examen de la notion d���esprit fran��ais, de l���arri��re-fond militariste et patriotique du th����tre de la fin du si��cle, ��tay�� largement par la presse et les critiques de l�����poque, dessine un panorama qui se veut le plus juste possible.

International audience; Aircraft contrails may contribute to the global radiative forcing. In this context, the investigation of contrail formation in the near field of an aircraft may be helpful in developing strategies to reduce undesirable impacts. In this study, three-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations of contrails produced by commercial aircraft during cruise flights were performed. A realistic geometry (herein a Boeing 737) was taken into account, including the engine core and bypass flows, which allows several parametrical studies and avoids using parameterizations to describe the plume's dilution. The objective was to simulate the early development of contrails in a fresh plume whose dilution was obtained with a spatial simulation of jet/vortex interaction. A coupling was carried out with a chemical and a microphysical model implemented in the numerical simulation code CEDRE to simulate particle growth using an Eulerian approach. The implemented microphysics model can simulate water condensation onto soot particles, taking into account their activation by adsorption of sulfur species. Our simulations show that sulfur dioxide is converted into sulfur trioxide and sulfuric acid at a rate of conversion close to 3 %, which is in good agreement with other studies. Ice-crystal growth was faster when the fuel sulfur content (FSC) increased, allowing a visible contrail to appear earlier. These promising results confirm in situ observations and highlight the model's ability to simulate typical plume chemistry and complex microphysics/chemistry interactions coupled with detailed jet/vortex dynamics.; Contrails peuvent contribuer au rayonnement de la Terre le forçage dû à l'aviation. Dans ce contexte, l'enquête de la formation de contrail dans le champ proche d'un aéronef peut être utile pour mieux comprendre leurs impacts potentiels associés. Dans cette étude, trois dimensions Reynolds-Averaged Navier-Stokes (RANS) simulations de contrails produites par les avions commerciaux en vol de croisière ont été effectuées. Une géométrie réaliste (ici un Boeing 737) est pris en compte, y compris noyau de moteur et les débits de dérivation qui permet plusieurs études paramétriques possibles et évite d'utiliser paramétrisation pour la description de la dilution du panache. L'objectif est de simuler le développement précoce de contrails dans un panache frais dont la dilution est obtenue par une simulation spatiale de l'interaction jet / vortex. Un couplage est réalisé avec un modèle microphysique mis en œuvre dans le code CEDRE CFD pour simuler la croissance des particules en utilisant une approche Eulerian. Le modèle microphysique mis en œuvre est capable de simuler la condensation de l'eau sur les particules de suie, en tenant compte de leur activation par adsorption des espèces soufrées. Les présentes simulations montrent que le dioxyde de soufre est converti en trioxyde de soufre et d'acide sulfurique avec un taux de conversion proche de 3%, ce qui est en bon accord avec d'autres études. La croissance des cristaux de glace se trouve être plus rapide lorsque la teneur en soufre du carburant (FSC) est augmenté, conduisant à une traînée visible pour apparaître plus tôt. Ces résultats prometteurs confirment les observations in situ et mettent en évidence la capacité du modèle à prendre en compte panache typique chimie, microphysique complexes / interactions chimiques associées à la dynamique détaillées jet / vortex.

The present work focuses on two common fluid flow problems namely, Turbulent Rayleigh-Bénard Convection and Path instability of rising bubbles immersed in a liquid. Concerning Rotating Turbulent Rayleigh-Bénard Convection, the flow field and temperature field were measured respectively by Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF) in a vertical plan of symmetry of our cylindrical cell of aspect ratio 1. The weakening of the Large Scale Circulation with decreasing Rossby number - leading to its complete disappearance - was confirmed as well as the formation of vortex columns in the rotation dominated regime. By doing velocity cross correlations, it has been possible to prove experimentally that the vorticity of the columns change direction in the cell’s center. The velocity fluctuations in the cell are highly anisotropic and follow a scaling of Ro0.2 in the rotation affected regime. The temperature of the vortex columns as well as of individual plumes has been estimated by LIF measurements. Concerning the Path instability of rising bubbles, small bubbles rise in straight path, whereas beyond a critical size, bubbles rise in zigzag or helical path. Some new experimental points on the marginal stability curve have been obtained by working in silicon oils of 5 and 10 cst and in water. The agreement with the most recent numerical simulations is only partial. The rise velocity, frequency and amplitude of oscillation have also been measured and suggest a supercritical Hopf bifurcation.; Les présents travaux portent sur deux problèmes classiques de mécanique des fluides: la convection turbulente de Rayleigh-Bénard en rotation et l’instabilité de la trajectoire de bulles en ascension dans un liquide. Pour ce qui concerne la convection turbulente de Rayleigh-Bénard en rotation, les champs de vitesse et de température ont été mesurés respectivement par PIV (Particle Image Velocimetry) et par LIF (Laser Induced Fluorescence) dans le plan de symétrie vertical de notre cellule cylindrique de rapport d’aspect 1. Les résultats de PIV confirment l’affaiblissement de la circulation à grande échelle en fonction des nombres Rossby décroissants – jusqu’à sa disparition totale – ainsi que la formation de colonnes de vortex en régime dominé par la rotation. Par des corrélations croisées sur le champ de vitesse, il a été possible de montrer expérimentalement que la vorticité dans les colonnes changeait de signe au centre de la cellule. Les fluctuations de vitesses dans la cellule sont fortement anisotropiques et suivent une loi d’échelle en Ro0.2 en régime affecté par la rotation. La température des colonnes de vortex tout comme celle des panaches a été estimée par des mesures LIF. Pour ce qui concerne l’instabilité de la trajectoire de bulles en ascension, les bulles petites montent verticalement, alors qu’au-dessus d’une certaine taille, elles montent en zigzag ou en suivant une trajectoire hélicoïdale. De nouveaux points expérimentaux sur la courbe de stabilité marginale ont été obtenus en travaillant dans des huiles de silicone de 5 et 10 cst et dans l’eau. L’accord avec les résultats des simulations numériques les plus récentes n’est que partiel. La vitesse ascensionnelle, la fréquence et l’amplitude des oscillations ont été mesurées et suggèrent une bifurcation de Hopf supercritique

Un panache forcé d'un mélange hélium - air se développant dans une cavité avec deux évents est modélisé numériquement par simulations numériques directes. La configuration géométrique est choisie de façon à ce qu'une distribution bi-couche du mélange hélium - air se forme dans la cavité, ce qui est une hypothèse couramment posée dans les modèles industriels théoriques. Nous réalisons une série de calcul pour différentes sections horizontales afin d'identifier une géométrie minimale pour laquelle le panache d'hélium et la couche de mélange homogène se situant en partie haute de la cavité ne sont pas influencés par les parois latérales. Les résultats sont analysés en terme de structure d'écoulements et de distribution d'hélium dans la cavité, mais aussi de débits massiques d'air neuf et d'hélium traversant les évents, ceux-ci n'étant pas imposés comme condition limi

Turbulent convective flows over rough boundaries are ubiquitous in geophysical and engineering applications. Understanding the mechanisms of these interactions is substantial for improving the heat transfer efficiency. In this work we study the effects of wall roughness on the Rayleigh Bénard turbulence. Three dimensional direct numerical simulations (DNS) are performed using a parallel CFD code under the support of national high performance computers. The roughness elements are embedded over hotted surface using an immersed boundary method. The numerical configuration allow the identification of three successive regimes from a thermally resistant to highly enhanced heat transfer. Through a geometrical decomposition of the rough plate into plot and surrounding fluid, we examine their different behaviors, mainly the contribution to the heat transfer. We analyze the effects of roughness on thermal and viscous boundary layers structures and on the flow physics near the wall. Besides that, the comparison with experimental data at the roughness scale highlight the non homogeneity of thermal fluctuations around the obstacles. We also focused on the effects of roughness on the flow dynamics and on the properties of thermal plumes.; Les flux convectifs turbulents sur les surfaces rugueuses sont omniprésents dans les applications géophysiques mais aussi en ingénierie. Comprendre les mécanismes de ces interactions est crucial pour améliorer l'efficacité du transfert de chaleur. Dans ce travail, nous étudions les effets des rugosités sur la turbulence dans la cavité de Rayleigh Bénard. Des simulations numériques directes (DNS) tridimensionnelles sont effectuées en utilisant un code CFD parallèle employant das ressources informatiques intensives des supercalculateurs nationaux de haute performance. Les rugosités sont introduites sur une surface chaude en utilisant une méthode de frontières immergées. La configuration numérique permet l'identification de trois régimes successifs allant du thermiquement résistant jusqu'au régime du transfert de chaleur fortement intensifié. À travers une décomposition géométrique de la plaque rugueuse en partie solide et d'autre fluide, nous examinons leurs différents comportements, principalement leur contribution au transfert de chaleur. Nous analysons les effets de la rugosité sur les structures des couches limites thermiques et visqueuses et sur la physique de l'écoulement en proche parois. De plus, la comparaison avec les données expérimentales à l'échelle de rugosité met en évidence la non-homogénéité des fluctuations thermiques autour des obstacles. Nous nous sommes également intéressés aux effets des rugosités sur la dynamique de l'écoulement et les propriétés des panaches thermiques.

Turbulent convective flows over rough boundaries are ubiquitous in geophysical and engineering applications. Understanding the mechanisms of these interactions is substantial for improving the heat transfer efficiency. In this work we study the effects of wall roughness on the Rayleigh Bénard turbulence. Three dimensional direct numerical simulations (DNS) are performed using a parallel CFD code under the support of national high performance computers. The roughness elements are embedded over hotted surface using an immersed boundary method. The numerical configuration allow the identification of three successive regimes from a thermally resistant to highly enhanced heat transfer. Through a geometrical decomposition of the rough plate into plot and surrounding fluid, we examine their different behaviors, mainly the contribution to the heat transfer. We analyze the effects of roughness on thermal and viscous boundary layers structures and on the flow physics near the wall. Besides that, the comparison with experimental data at the roughness scale highlight the non homogeneity of thermal fluctuations around the obstacles. We also focused on the effects of roughness on the flow dynamics and on the properties of thermal plumes., Les flux convectifs turbulents sur les surfaces rugueuses sont omniprésents dans les applications géophysiques mais aussi en ingénierie. Comprendre les mécanismes de ces interactions est crucial pour améliorer l'efficacité du transfert de chaleur. Dans ce travail, nous étudions les effets des rugosités sur la turbulence dans la cavité de Rayleigh Bénard. Des simulations numériques directes (DNS) tridimensionnelles sont effectuées en utilisant un code CFD parallèle employant das ressources informatiques intensives des supercalculateurs nationaux de haute performance. Les rugosités sont introduites sur une surface chaude en utilisant une méthode de frontières immergées. La configuration numérique permet l'identification de trois régimes successifs allant du thermiquement résistant jusqu'au régime du transfert de chaleur fortement intensifié. À travers une décomposition géométrique de la plaque rugueuse en partie solide et d'autre fluide, nous examinons leurs différents comportements, principalement leur contribution au transfert de chaleur. Nous analysons les effets de la rugosité sur les structures des couches limites thermiques et visqueuses et sur la physique de l'écoulement en proche parois. De plus, la comparaison avec les données expérimentales à l'échelle de rugosité met en évidence la non-homogénéité des fluctuations thermiques autour des obstacles. Nous nous sommes également intéressés aux effets des rugosités sur la dynamique de l'écoulement et les propriétés des panaches thermiques.

International audience; Aircraft contrails may contribute to the global radiative forcing. In this context, the investigation of contrail formation in the near field of an aircraft may be helpful in developing strategies to reduce undesirable impacts. Contrail formation is also a complex topic, since several physical processes are involved, covering a large range of space and time scales, from the engine exit to the atmospheric global scale. In the near field of the aircraft, contrail formation is mainly dominated by microphysics and mixing processes between the propelling jets and the external flow (the so called jet-vortex interaction). In this study, three-dimensional Reynolds-Averaged Navier–Stokes (RANS) simulations of contrails produced by the Common Research Model wing/body/engine configuration during cruise flights is performed. In the present work, a dedicated internal nozzle geometry has been designed to replace the through flow nacelle of the original CRM configuration. Thus, the engine core and bypass flows are actually computed in the simulations, which allows several parametrical studies and avoids using parameterizations to describe the plume's dilution. The objective is to simulate the early development of contrails in a fresh plume whose dilution is obtained with a spatial simulation of jet/vortex interaction. A coupling is carried out with a chemical and a microphysical model implemented in the unstructured Navier-Stokes CFD code CEDRE to simulate particle growth using an Eulerian approach. The implemented microphysics model can simulate water condensation onto soot particles, taking into account their activation by adsorption of sulfur species. In this context, an adaptation grid mesh procedure has been used in order to generate an optimized unstructured mesh in the fluid zone of interest (i.e. vortex wake and jet exhaust).

Non-thermal plasmas generated in air at atmospheric pressure have numerous potential applications due to their non-equilibrium chemistry and ease of use. Their main advantages lie in the cost-efficient production of reactive and charged species compared to that of equilibrium chemistry. The aim of this thesis is to combine nanosecond repetitively pulsed discharges (NRP) with a microscale geometry. Using this combination, we seek to reduce the excessive heat release of NRP sparks, while nonetheless reaching high densities of reactive species and electrons. This work is comprised of three main parts. Our first goal is to study the breakdown phase, in which energy is deposited and charged species are produced. We employ both electrical characterization and optical emission spectroscopy in order to show that the NRP microplasma fully ionizes and dissociates the gas. The second part consists of the study of the recombination phase, in which the produced species recombine or survive. Results show that three-body recombination can explain the electron lifetime in this phase. Finally, we study the transport of plasma chemical species from the microplasma to a DC-biased conductive plate representing a substrate. By applying a voltage to this third electrode, we drive an electro-thermal plume via an ionic wind from the microplasma to the plate. This flow is investigated mainly by particle image velocimetry as well as Schlieren imaging. This work shows the capability of NRP microplasmas to produce high densities of reactive and charged species and transport them to a surface using an electrohydrodynamic plume.; Les plasmas froids d’air à pression atmosphérique sont très utiles pour un grand nombre d’applications grâce à leur chimie hors-équilibre et leur souplesse d’utilisation. Leur intérêt réside dans la production de certaines espèces réactives ou chargées avec un coût énergétique plus avantageux que la chimie à l’équilibre. L’objectif de cette thèse est de combiner les décharges nanosecondes répétitives pulsées (NRP) avec une géométrie micrométrique. Par cette combinaison, nous souhaitons palier au chauffage excessif des étincelles qui génèrent pourtant des fortes densités d’espèces. Notre étude se concentre en trois points principaux. Dans un premier temps la phase de claquage est étudiée ; c’est pendant cette étape que l’énergie est déposée et que les espèces sont produites. La combinaison des diagnostics électriques et de spectroscopie d’émission optique montrent que l’air est presque complètement dissocié et ionisé. Ensuite, nous nous intéressons à la phase de recombinaison qui conditionne la durée de vie de ces espèces. Les résultats mettent en évidence une réaction à trois corps comme mécanisme de recombinaison principal. Et enfin, le dernier point concerne le transport des espèces vers un substrat conducteur. En lui appliquant une tension, celui-ci nous permet de générer un écoulement de vent ionique provenant de la décharge. L’écoulement est étudié par vélocimétrie d’images de particules et imagerie Schlieren. Ce travail a permis de démontrer la capacité des NRP micro-plasmas dans la production contrôlée d’espèces réactives et chargées, mais aussi dans leur transport vers une surface par panache électro-aérodynamique.

Non-thermal plasmas generated in air at atmospheric pressure have numerous potential applications due to their non-equilibrium chemistry and ease of use. Their main advantages lie in the cost-efficient production of reactive and charged species compared to that of equilibrium chemistry. The aim of this thesis is to combine nanosecond repetitively pulsed discharges (NRP) with a microscale geometry. Using this combination, we seek to reduce the excessive heat release of NRP sparks, while nonetheless reaching high densities of reactive species and electrons. This work is comprised of three main parts. Our first goal is to study the breakdown phase, in which energy is deposited and charged species are produced. We employ both electrical characterization and optical emission spectroscopy in order to show that the NRP microplasma fully ionizes and dissociates the gas. The second part consists of the study of the recombination phase, in which the produced species recombine or survive. Results show that three-body recombination can explain the electron lifetime in this phase. Finally, we study the transport of plasma chemical species from the microplasma to a DC-biased conductive plate representing a substrate. By applying a voltage to this third electrode, we drive an electro-thermal plume via an ionic wind from the microplasma to the plate. This flow is investigated mainly by particle image velocimetry as well as Schlieren imaging. This work shows the capability of NRP microplasmas to produce high densities of reactive and charged species and transport them to a surface using an electrohydrodynamic plume.; Les plasmas froids d’air à pression atmosphérique sont très utiles pour un grand nombre d’applications grâce à leur chimie hors-équilibre et leur souplesse d’utilisation. Leur intérêt réside dans la production de certaines espèces réactives ou chargées avec un coût énergétique plus avantageux que la chimie à l’équilibre. L’objectif de cette thèse est de combiner les décharges nanosecondes répétitives pulsées (NRP) avec une géométrie micrométrique. Par cette combinaison, nous souhaitons palier au chauffage excessif des étincelles qui génèrent pourtant des fortes densités d’espèces. Notre étude se concentre en trois points principaux. Dans un premier temps la phase de claquage est étudiée ; c’est pendant cette étape que l’énergie est déposée et que les espèces sont produites. La combinaison des diagnostics électriques et de spectroscopie d’émission optique montrent que l’air est presque complètement dissocié et ionisé. Ensuite, nous nous intéressons à la phase de recombinaison qui conditionne la durée de vie de ces espèces. Les résultats mettent en évidence une réaction à trois corps comme mécanisme de recombinaison principal. Et enfin, le dernier point concerne le transport des espèces vers un substrat conducteur. En lui appliquant une tension, celui-ci nous permet de générer un écoulement de vent ionique provenant de la décharge. L’écoulement est étudié par vélocimétrie d’images de particules et imagerie Schlieren. Ce travail a permis de démontrer la capacité des NRP micro-plasmas dans la production contrôlée d’espèces réactives et chargées, mais aussi dans leur transport vers une surface par panache électro-aérodynamique.

Turbulent odor plumes play an important role in many chemically mediated behaviors, yet the fine scale spatial structure of plumes has not been measured in detail. With the use of a newly introduced microelectrochemical recording technique, we have measured, in some detail, the fine structure of an aquatic odor plume in the laboratory. We sampled a turbulent odor plume at 10 Hz with a spatial sampling area of 0.02 mm2, approximately that of a chemoreceptor sensillum of the lobster, Homarus americanus. A 3-min record was sampled at 63 different sites in 3 dimensions (x, y, z). As expected from time averaging models, the mean values of pulse parameters such as height and onset slope were greatest near the source. However, what cannot be described by time averaging models is the instantaneous distribution of pulses: periodically high peaks with steep concentration slopes (well above the local average and far above predictions from averaging models) can be found far away from the source. However, the probability of above-average pulse heights decreases with distance from the source in x, y, and z directions. The most intense odor fluctuations occurred along the x axis (the cross-sectional center of the plume). Odor profiles were analyzed with three different models of sensory filters; logarithmic, probability, and temporal filters. This analysis indicates that features contained within the plume structure could be used as directional cues for orienting animals. It remains to be demonstrated that animals use such sensory filters to extract biologically relevant spatial information from odor plumes.

La décharge non contrôlée d’ordures ménagères de Sidi Yahya se trouve à environ 7 km au sud-est de la ville d’Oujda (Maroc nord-oriental). Le tonnage total de déchets qui y sont déversés est de 1,2 à 1,5 million de tonnes pendant la période de l’exploitation (1990-2005). La surface totale qui a été entièrement utilisée est de 41 hectares. Les eaux souterraines, situées à 30 m environ sous le sol, circulent dans des terrains post-miocènes sur un substratum imperméable formé par les marnes du Miocène. Le sol est de type calcimagnésique peu profond, avec une couche plus ou moins importante de limons et d’argiles. Les eaux provenant des déchets eux-mêmes ou issues de la dégradation de la matière organique en conditions aérobies, ainsi que les eaux météoriques, en percolant à travers les déchets, s’enrichissent en divers polluants appelés lixiviats ou percolats. Afin de connaître la destination de ces percolats dans le sous-sol, une étude géophysique par imagerie électrique a été menée dans la partie dégagée de la décharge. Quatre profils de reconnaissance ont été réalisés selon le dispositif dipôle-dipôle. Les résultats de la prospection géoélectrique ont montré que les très faibles résistivités électriques (, The Sidi Yahya landfill is a uncontrolled landfill of household refuse. It is located in the commune of Sidi Yahya, approximately 7 km southeast of Oujda (Eastern Morocco). The total tonnage of waste produced was about 1.2 to 1.5 million metric tons for the period of the landfill exploitation (1990-2005). The total surface which was entirely used covers 41 hectares. The groundwater (water table at about 30 m depth) circulates in post-Miocene material underlain by an impermeable substratum formed by Miocene marls. The soil is calci-magnesic, with a more or less important layer of silt and clay. Water coming from the domestic waste itself or resulting from degradation of organic matter under aerobic conditions, as well as meteoric water that percolates through the waste, combine to form a leachate enriched in various pollutants. The main objective of this study was the detection of eventual groundwater pollution and estimation of the extent of the resulting underground pollution plume. A geophysical study using Electrical Resistivity Imagery was carried out. The location of profiles obtained with a dipole-dipole array (three profiles 23 m long and one profile 475 m long) was constrained by the available space in the landfill facility. The resistivity sections show the resistivity distribution to a depth of 30 m for short profiles and 50 m for the long profile. The results show very conductive layers with very low resistivity values (

Breakup between Greenland and Canada resulted in oceanic spreading in the Labrador Sea and Baffin Bay. These ocean basins are connected through the Davis Strait, a bathymetric high comprising primarily continental lithosphere, and the focus of the West Greenland Tertiary volcanic province. It has been suggested that a mantle plume facilitated this breakup and generated the associated magmatism. Plume-driven breakup predicts that the earliest, most extensive rifting, magmatism and initial seafloor spreading starts in the same locality, where the postulated plume impinged. Observations from the Labrador Sea–Baffin Bay area do not accord with these predictions. Thus, the plume hypothesis is not confirmed at this locality unless major ad hoc variants are accepted. A model that fits the observations better involves a thick continental lithospheric keel of orogenic origin beneath the Davis Strait that blocked the northward-propagating Labrador Sea rift resulting in locally enhanced magmatism. The Davis Strait lithosphere was thicker and more resilient to rifting because the adjacent Paleoproterozoic Nagssugtoqidian and Torngat orogenic belts contain structures unfavourably orientated with respect to the extensional stress field at the time.RÉSUMÉLa cassure entre le Groenland et le Canada a entraîné une expansion océanique de la mer du Labrador et de la baie de Baffin. Ces bassins océaniques sont reliés par le détroit de Davis, un haut bathymétrique constitué principalement de lithosphère continentale et de la province volcanique tertiaire de l'ouest du Groenland. Il a été suggéré qu'un panache du manteau a facilité cette cassure et généré le magmatisme associé. L’hypothèse d’une cassure produite par panache du manteau prédit que la première distension océanique, la plus importante, le magmatisme et l'expansion océanique initial se produisent là où le panache mantélique touche la croûte continentale. Or les observations dans la région de la mer du Labrador–baie de Baffin ne correspondent pas à ces prédictions. Et donc l'hypothèse du panache ne fonctionne pas dans cette région à moins que des facteurs ad hoc déterminants ne soient présents. Un modèle qui correspond mieux aux observations présuppose la présence d’une épaisse quille lithosphérique continentale d'origine orogénique sous le détroit de Davis qui aurait bloqué l’expansion océanique de la mer du Labrador vers le nord, ce qui aurait provoqué une augmentation du magmatisme localement. La lithosphère du détroit de Davis était plus épaisse et plus résistante à l’expansion océanique parce que les bandes orogéniques paléoprotérozoïques du Nagssugtoqidian et de Torngat renferment des structures défavorablement orientées par rapport au champ de contraintes d’extensions de l'époque.

Stable isotope data have been increasingly used to assess in situ biodegradation of organic contaminants in groundwater. The data are usually evaluated using the Rayleigh equation to evaluate whether isotope data follow a Rayleigh trend, to calculate the extent of contaminant biodegradation, or to estimate first-order rate constants. However, the Rayleigh equation was developed for homogeneous systems while in the subsurface, contaminants can migrate at different velocities due to physical heterogeneity. This paper presents a method to quantify the systematic effect that is introduced by applying the Rayleigh equation to field isotope data. For this purpose, the travel time distribution between source and sampling point is characterized by an analytical solution to the advection-dispersion equation. The systematic effect was evaluated as a function of the magnitude of physical heterogeneity, geometry of the contaminant plume, and degree of biodegradation. Results revealed that the systematic effect always leads to an underestimation of the actual values of isotope enrichment factors, the extent of biodegradation, or first-order rate constants, especially in the dispersion-dominant region representing a higher degree of physical heterogeneity. A substantial systematic effect occurs especially for the quantification of first order rate constants (up to 50% underestimation of actual rate) while it is relatively small for quantification of the extent of biodegradation (

For over 40 years, the National Institute of Neurological Disorders and Stroke/National Institutes of Health-funded Anticonvulsant Screening Program has provided a preclinical screening service for participants world-wide that helped identify/characterize new antiseizure compounds, a number of which advanced to the market for the treatment of epilepsy. The newly-renamed Epilepsy Therapy Screening Program (ETSP) has a refocused mission to identify novel agents which will help address the considerable remaining unmet medical needs in epilepsy. These include identifying antiseizure agents for treatment-resistant epilepsy, as well as anti-epileptogenic agents that will prevent the development of epilepsy or disease-modifying agents that will ameliorate or even cure established epilepsy and its comorbidities. This manuscript provides an overview of the ETSP's efforts aimed at identifying the next generation of therapeutic agents to further reduce the suffering from and burden of epilepsy.

Alors que la pratique de la liste semble évidente, sa présence dans un contexte littéraire peut surprendre. La réécriture par Éric Chevillard du conte des frères Grimm Le Vaillant Petit Tailleur est néanmoins remarquable par l’abondance de listes. Grâce à une définition précise et à l’étude de certains traits spécifiques, il est possible de relever et d’analyser dans cette œuvre un corpus complet, révélateur de nombreux effets. Porté par une dynamique d’hétérogénéité, Le Vaillant Petit Tailleur est ambigu : il repose souvent sur le comique et la vanité. Au travers d’une rivalité entre héros et narrateur, on y trouve aussi la fanfaronnade, l’orgueil, le goût du texte, on y trouve en somme le panache de la liste.

The particles collected in a sediment trap in the Gaoping Submarine Canyon provided a high resolution PAH profile that traces typhoon (Kalmaegi) induced particle movement. Results provide further evidence that submarine canyons are an effective conduit for transporting terrestrial contaminants such as PAHs, particularly as typhoon-related hyperpycnal plumes at river mouths and ensuing turbidity currents in the submarine canyon. Observations here show that two typhoon-triggered turbidity currents passed the sediment trap. The beginnings of the two turbidity currents showed strong pyrogenic signatures suggesting coal and biomass burning sources. These turbidity currents carried enormous amounts of particulate PAHs (510 kg in 12.5 h), which accounted for 4.2% of the annual PAH flux from the Gaoping River. The PAH signature allowed the typhoon effect to be broken into five stages: (I) period before the typhoon effect (marine sources), (II) typhoon induced currents (resuspended sediments), (III) down-canyon flow (pyrogenic particles from northwestern shelf), (IV) river plume impact with two turbidity currents (arrival of terrestrial particles), and (V) end of typhoon discharge of anthropogenic PAHs to the canyon head.

[1] Coal-fired power plants are one of the principal sources of mercury to the atmosphere. The form this mercury takes is the predominant factor determining its fate after emission. Recent ground-level field and modeling studies suggest that oxidized mercury in stack emissions is converted into elemental mercury in the plume. We present here aircraft-based plume mercury measurements taken by Environment Canada in 2000 at the Nanticoke Generating Station as part of the Health Canada Toxic Substances Research Initiative Metals in the Environment Research Network. Although the average mercury speciation observed in the Nanticoke plume (82% Hg0, 13% Hg(II)(g), 5% Hg(P), by mass) appears to be distinct from the average mercury speciation in the Nanticoke stacks (53% Hg0, 43% Hg(II)(g), 4% Hg(P)), we find that the in-plume elemental mercury concentrations as a whole can be explained by plume dilution after emission. The discrepancy between in-stack and in-plume Hg(II) concentrations is statistically significant, yet is not associated with a transformation of Hg(II) to Hg0. Sampling biases associated with the differing techniques used to measure Hg(II) in-stack and in-plume may reconcile the concentration discrepancy without invoking novel chemical reactions or physical processes. Although the mercury speciation of the Nanticoke plume influences local mercury deposition, the majority of the mercury emitted is transported out of the surrounding area.

Trans. ASME, Journal of Fluids Engineering, Vol.111, No. 1, pp. 69- 77, Mar.1989. Mean-flow and turbulence measurements have been obtained in two-dimensional vertical turbulent plumes in a nominally still ambient. The plumes were generated by injecting hot water vertically upwards from the bottom of a reservior containing cold water. A two-component Laser Doppler Anemometer (LDA) and a "coldfilm" resistance thermometer were used to obtain instantaneous velocity and temperature measurements in the plume. The present mean-flow measurements have confirmed many of the earlier measurements on plane plumes, but have also indicated some important differences. The use of the two-component LDA made it possible to obtain data on turbulent intensities, turbulent fluxes and other details of the structure of turbulence in plane plumes. The turbulence measurements have shown that the eddy viscosity and turbulence are significantly higher in the plume compared to an isothermal jet. Detailed measurements of energy balance suggest that buoyant production contributes substantially to this increase. U.S. National Science Foundation under Grant Nos. ENG77-22756 and CME 80-06797 U.S. National Science Foundation under Grant Nos. ENG77-22756 and CME 80-06797

Volcanic lightning, perhaps the most spectacular consequence of the electrification of volcanic plumes, has been implicated in the origin of life on Earth, and may also exist in other planetary atmospheres. Recent years have seen volcanic lightning detection used as part of a portfolio of developing techniques to monitor volcanic eruptions. Remote sensing measurement techniques have been used to monitor volcanic lightning, but surface observations of the atmospheric electric Potential Gradient (PG) and the charge carried on volcanic ash also show that many volcanic plumes, whilst not sufficiently electrified to produce lightning, have detectable electrification exceeding that of their surrounding environment. Electrification has only been observed associated with ash-rich explosive plumes, but there is little evidence that the composition of the ash is critical to its occurrence. Different conceptual theories for charge generation and separation in volcanic plumes have been developed to explain the disparate observations obtained, but the ash fragmentation mechanism appears to be a key parameter. It is unclear which mechanisms or combinations of electrification mechanisms dominate in different circumstances. Electrostatic forces play an important role in modulating the dry fall-out of ash from a volcanic plume. Beyond the local electrification of plumes, the higher stratospheric particle concentrations following a large explosive eruption may affect the global atmospheric electrical circuit. It is possible that this might present another, if minor, way by which large volcanic eruptions affect global climate. The direct hazard of volcanic lightning to communities is generally low compared to other aspects of volcanic activity. © Springer Science+Business Media B.V. 2006.

[1] Direct-sampling and remote-sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d < 10 μm) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d ∼ 1.15 μm. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emission flux of fine silicate particles was estimated as ∼1011 s-1, equivalent to ∼55 kg d-1. Sun photometry, aerosol spectrometry, and thermal precipitation were used to determine the overall particle size distribution of the plume (0.01 < d(μm) < 10). Sun photometry and aerosol spectrometry measurements indicate the presence of a large number of particles (assumed to be aqueous) with d ∼ 1 μm. Aerosol spectrometry measurements further show an increase in particle size as the nighttime approached. The emission flux of particles from Masaya was estimated as ∼1017 s-1, equivalent to ∼5.5 Mg d-1 where d < 4 μm. Copyright 2009 by the American Geophysical Union.

Samples of grass were collected at Masaya Volcano (Nicaragua; Rhynchelytrum repens and Andropogon angustatus) and the Piton de La Fournaise (around the April 2007 eruptive vent, La Réunion; Vetiveria zizanioides to investigate the controls on major and trace element concentrations in plants around active volcanic vents. Samples were analysed using inductively coupled plasma mass spectrometry for a wide range of elements, and atomic absorption spectroscopy for Hg. At Masaya, As, Cu, Mo, Tl and K concentrations in both grass species showed a simple pattern of variability consistent with exposure to the volcanic plume. Similar variability was found in A. angustatus for Al, Co, Cs, Hg and Mg. At the Piton de La Fournaise, the patterns of variability in V. zizanioides were more complex and related to variable exposures to emissions from both the active vent and lava flow. These results suggest that exposure to volcanic emissions is, for many elements, the main control on compositional variability in vegetation growing on active volcanoes. Thus, vegetation may be an important environmental reservoir for elements emitted by volcanoes and should be considered as part of the global biogeochemical cycles.

A small explosive eruption at Masaya volcano on 23 April 2001, in which a number of people were injured, was preceded by a distinct change in plume gas compositions. Open-path Fourier transform infrared spectroscopy (FTS) measurements show that the SO2/HCl molar ratio increased from 1.8 to 4.6 between April 2000 and April/May 2001. The SO2 flux decreased from 11 to 4 kg s-1 over this period. We interpret these changes to be the result of scrubbing of water-soluble magmatic gases by a rejuvenated hydrothermal system. A sequence of M 5 earthquakes with epicentres about 7 km from the volcano occurred in July 2000. These may have altered the fracture permeability close to the magmatic conduit, and caused increased magmatic-hydrothermal interaction, leading eventually to the phreatic explosion in 2001. Continuous FTS measurements at suitable volcanoes could provide useful information in support of eruption prediction and forecasting. © 2003 Elsevier Science B.V..

In the framework of the impact of aviation on climate change studies, the involvement of contrails is identified as one of the most uncertain components. In this context, this study aims to better describe the physico-chemical properties of the plume in the near-field of an aircraft, for they could be critical to contrails properties.To this end, RANS spatial simulations have been performed using the code CEDRE of ONERA, taking into account the microphysical processes, chemical reactions, and the air flow around and in the wake of a realistic civil transport aircraft. Microphysical models have been implemented in order to describe the soot activation processes and the condensation and evaporation of water upon their surface.A validation phase of the code has been carried out for each of the processes taken into account, showing good agreements with data from the literature. Sensitivity studies have also been performed in order to assess the impact of atmospheric parameters and exhaust characteristics on formed contrails properties. The increase of the fuel sulphur content leads to increased soot activation that results in a shorter contrail onset and increased contrail opacity. If the amount of emitted water is sufficient, the increase of the number of ejected soot particles causes an increase of ice concentration that results in an important increase of contrail opacity and surface area., Dans le cadre des études portant sur l’impact de l’aviation sur le changement climatique, les traînées de condensation font partie des phénomènes présentant le plus d’incertitudes quant à leur rôle. Dans ce contexte, l’étude vise à mieux décrire les caractéristiques physico-chimiques du panache dans le champ proche d’un avion, celles-ci pouvant conditionner les propriétés des traînées de condensation formées.Pour cela, des simulations spatiales tridimensionnelles de type RANS ont été réalisées à l’aide du code CEDRE de l’ONERA, prenant en compte les processus microphysiques, les réactions chimiques, et l’écoulement aérodynamique autour et dans le sillage d'une configuration réaliste d'un avion de transport civil. Les modèles microphysiques intégrés permettent de décrire les processus d’activation des particules de suie et les processus de condensation et d’évaporation d’eau à leur surface.Une phase de validation du code a été menée pour chacun des processus pris en compte, montrant un bon accord avec les données de la littérature. Des études de sensibilité ont également été conduites afin d’évaluer l’impact des paramètres atmosphériques et des caractéristiques des effluents sur les propriétés des cristaux de glace formés. L’augmentation de la teneur en soufre du carburant entraîne un accroissement de l’activité des suies et aboutit à une distance d’apparition plus courte et une opacité plus élevée des traînées de condensation. Lorsque la quantité d’eau émise est suffisante, l’augmentation du nombre de suies éjectées entraîne un accroissement de la concentration de glace, résultant en un fort accroissement de l’opacité et de la superficie de la traînée de condensation.

Turbulent asymmetric thermal plume evolves in a uniform upward flowing fluid in the region of mixed convection, where the far field velocity has a magnitude comparable to the velocities generated by the plume, are examined. In the process, a first order solution of the governing equation about the far stream velocity is obtained. The analytical results are compared with experimental data available in the literature as well as to simulations obtained using computational fluid dynamics. It is shown that in both cases the agreement is good.

The dispersion is mainly governed by wind field and depends on the planetary boundary layer (PBL) dynamics. Accurate representation of the meteorological weather fields would improve the dispersion assessments. In urban areas representation of wind around the obstacles is not possible for the pollution dispersion studies using Gaussian based modeling studies. It is widely accepted that computational fluid dynamics (CFD) tools would provide reasonably good solution to produce the wind fields around the complex structures and other land scale elements. By keeping in view of the requirement for the micro-scale dispersion, a commercial CFD model PANACHE with PANEPR developed by Fluidyn is implemented to study the micro-scale dispersion of air pollution over an urban setup at Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam a coastal station in the east coast of India under stable atmospheric conditions. Meso-scale module of the PANACHE model is integrated with the data generated at the site by IGCAR under RRE (Round Robin Exercise) program to develop the flow fields. Using this flow fields, CFD model is integrated to study the micro-scale dispersion. Various pollution dispersion scenarios are developed using hypothetical emission inventory during stably stratified conditions to understand the micro-scale dispersion over different locations of coastal urban set up in the IGCAR region of Kalpakkam.

Aerosol number concentrations were continuously measured at sites at Tsukuba and Mt. Haruna on the Kanto region of Japan by using optical particle counters (OPCs) from February to June 2007. Three specific dust events captured at the sites were analyzed by using lidar, backward trajectories, and model simulation in detail. The temporal variations in aerosol concentrations in the two Asian-dust events (K1 event: 31 March–3 April; K2 event: 25–28 May) were similar. Dust particles (≥2.0 μm in diameter) were transported in association with a synoptic-scale cold front, and they arrived at the Tsukuba site about 8 h after they were observed at the Mt. Haruna site, in association with the dissipation of a local front formed ahead of the cold front. However, the inflow patterns of dust particles differed between the K1 and K2 events. The K1 event flowed onto the Kanto Plain, detouring around the mountainous region, whereas the K2 event directly flowed across the mountains. The difference in inflow pattern was probably due to the blocking effects of the mountains and the formation of a stable layer near the surface. Preceding the dust plume arrival, an increase in the number concentration of small-aerosol particles (0.3–1.0 μm in diameter), which are considered to be spherical by lidar, was observed, but only at the Tsukuba site. This increase was possibly due to anthropogenic pollution transported over long distances from the continent and from domestic sources in the Kanto region. The third event was a local dust event, because it was observed only at the Tsukuba site (on 13 and 14 March) under dry conditions ( 10 m s −1 ).

Near-source observations of aerosol size distributions ( 1 [mu]m) ash particles. The number ratio of fine and coarse particles fluctuated strongly within short intervals of time, indicative of changes in the fragmentation energy. The near-source ash fallout was poorly sorted (interquartile range 16-80 [mu]m); ash grains sized

Thermal mixing in rivers is a common geophysical phenomenon that controls myriad processes, from aquatic ecological functions to stream and groundwater biogeochemistry. We present high-resolution remotely-sensed temperature distributions of thermal plumes discharging into rivers collected from Yellowstone National Park. Airborne (4 m pixel size) and ground-based (centimetre or better spatial resolution) images corroborate the presence of these mixing zones. They illustrate that thermal discharges in rivers may not be well-mixed with the bulk flow even after traversing distances corresponding to several stream widths. This allows for large thermal gradients (>30°C) to persist between the thermal discharge and the bulk flow. The plumes may have pronounced internal temperature gradients that vary in space and time. The images illustrate the potential of portable high-resolution sensors not only for acquiring observations needed for fundamental understanding of non-isothermal mixing processes but also for providing temperature distributions necessary for understanding many thermally-mediated processes.

Interest in the coastal dynamics of river plumes has mainly focused on large rivers, but plumes from the more numerous smaller rivers have important local consequences and may, in aggregate, be significant contributors to coastal circulation. We studied the dynamics of the plume from the Saco River in Saco Bay, Gulf of Maine, over a 3-year period. The transport and salinity in the region are governed by river discharge, tides, winds, and interaction with the Western Maine Coastal Current. The dynamics of the flow field vary with location within the plume and discharge. The far-field dynamics of the Saco River plume are dominated by inertial processes (hence qualifying it as a small-scale river plume), during times of low discharge, with low salinity water present both up and downstream of the river mouth, but are dominated by rotational processes during times of high discharge (thus qualifying it as a large-scale river plume), with buoyant water primarily advected downshelf. Near-field dynamics are governed by weak, subcritical flow during low discharge but strongly inertial, supercritical flow during high discharge. Offshore movement of the plume is not governed by Ekman dynamics but is instead a result of discharge, wind-induced vertical mixing, and the geography of the coastline and adjacent islands.