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47 results on '"Ecole polytechnique de Thiès"'

1. Within-host dynamics of lysogen and non-lysogen bacteria with spontaneous prophage induction phenomenon

Author

Ndongmo Teytsa, Hyacinthe, Seydi, Ousmane, Tsanou, Berge, Djidjou-Demasse, Ramsès, Maladies infectieuses et vecteurs : écologie, génétique, évolution et contrôle (MIVEGEC), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Université de Montpellier (UM), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Faculté des Sciences - Université de Dschang [Cameroun], Université de Dschang, and ANR-21-CE45-0004,QUASAR,Résistance quantitative aux antimicrobiens: stratégies de contrôle et adaptation évolutive de la virulence parasitaire et de la résistance(2021)

Subjects
Within-host competition, Nonlinear dynamical systems, SPI, Age structured model, Phage therapy, Hopf bifurcation, [MATH]Mathematics [math]
Abstract

Bacteriophages or phages (viruses of bacteria) play numerous roles in shaping the diversity of bacterial communities within the human gut. Either a phage-infected bacterial cell immediately starts a lysis mechanisms (virulent/lytic infection), or it enters a stable state within the host as a prophage (lysogeny), until a trigger event, called Spontaneous Prophage Induction (SPI), allows the lysis phenomenon. We develop an approach to address the role of SPI within phage-bacteria interactions and the influence of lysogeny on the success of phage therapy. This is based on a model structure in terms of time since infection. Our analysis suggests that SPI allows lysogen bacteria to have a competitive advantage over their non-lysogenic counterparts. Moreover, the model exhibits the bistability phenomenon such that, depending on the initial conditions, the dynamic can either converge towards a purely temperate state (only lysogens and temperate phages persist) or a purely lytic state (only nonlysogens and virulent phages persist). We also highlight the existence of SPI's critical values leading to the coexistence of all states through periodic oscillations. Finally, the model suggests that efficient bacteria control through phage therapy can be achieved by minimizing lysogens' offspring.

Published
2023

2. Linking within-and between-host scales for understanding the evolutionary dynamics of quantitative antimicrobial resistance

Author

Djidjou-Demasse, Ramsès, Mann-Manyombe, Martin, Mendy, Abdoulaye, Seydi, Ousmane, Maladies infectieuses et vecteurs : écologie, génétique, évolution et contrôle (MIVEGEC), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Université de Montpellier (UM), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, ANR-21-CE45-0004,QUASAR,Résistance quantitative aux antimicrobiens: stratégies de contrôle et adaptation évolutive de la virulence parasitaire et de la résistance(2021), and Djidjou-Demasse, Ramsès

Subjects
[SDV.SPEE] Life Sciences [q-bio]/Santé publique et épidémiologie, Antimicrobial resistance Evolutionary dynamics Nested models Non-linear dynamical system, Nested models, [MATH.MATH-DS]Mathematics [math]/Dynamical Systems [math.DS], [MATH.MATH-DS] Mathematics [math]/Dynamical Systems [math.DS], Evolutionary dynamics, [SDV.SPEE]Life Sciences [q-bio]/Santé publique et épidémiologie, Antimicrobial resistance, Non-linear dynamical system
Abstract

Understanding both the epidemiological and evolutionary dynamics of antimicrobial resistance is a major public health concern. In this paper, we propose a nested model, explicitly linking the withinand between-host scales, in which the level of resistance of the host population is viewed as a continuous quantitative trait. The within-host dynamics is based on integro-differential equations structured by the resistance level, while the between-host scale is additionally structured by the time since infection. This model simultaneously captures the dynamics of the bacteria population, the evolutionary transient dynamics which lead to the emergence of resistance, and the epidemic dynamics of the host population. Moreover, we precisely analyze the model proposed by particularly performing the uniform persistence and asymptotic results. Finally, we discuss the impact of the treatment rate of the host population in controlling both the epidemic outbreak and the average level of resistance, either if the within-host scale therapy is a success or failure. We also explore how transitions between infected populations (treated and untreated) can impact the average level of resistance, particularly in a scenario where the treatment is successful at the within-host scale.

Published
2022

3. Growth bound and threshold dynamic for nonautonomous nondensely defined evolution problems

Author

Ramses DJIDJOU-DEMASSE, Ousmane Seydi, Maladies infectieuses et vecteurs : écologie, génétique, évolution et contrôle (MIVEGEC), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Université de Montpellier (UM), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, and Djidjou-Demasse, Ramsès

Subjects
Threshold dynamics, evolutionary systems, Reproduction number, Growth bound, [MATH.MATH-DS]Mathematics [math]/Dynamical Systems [math.DS], [MATH.MATH-DS] Mathematics [math]/Dynamical Systems [math.DS], [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Reproduction number Growth bound Threshold dynamics evolutionary systems Mathematics Subject Classification 34K20 37B55 47D62 47N60 92D25, [MATH.MATH-AP] Mathematics [math]/Analysis of PDEs [math.AP], Mathematics Subject Classification 34K20, 37B55, 47D62, 47N60, 92D25
Abstract

Note: Please see pdf for full abstract with equations. We propose a general framework for simultaneously calculating the threshold value for population growth and determining the sign of the growth bound of the evolution family generated by the problem below dv(t)/dt = Av(t) + F(t)v(t) − V(t)v(t), where A : D(A) ⊂ X → X is a Hille-Yosida linear operator (possibly unbounded, non-densely defined) on a Banach space (X, ∥ · ∥), and the maps t ∈ R 7→ V(t) ∈ L(X0,X), t ∈ R 7→ F(t) ∈ L(X0,X) are p-periodic in time and continuous in the operator norm topology. We give applications of our approach for two general examples of an age-structured model, and a delay differential system. Other examples concern the dynamics of a nonlocal problem arising in population genetics and the dynamics of a structured human-vector malaria model. Mathematics Subject Classification 34K20; 37B55; 47D62; 47N60; 92D25

Published
2022

4. Flow invariance for non densely defined Cauchy problems

Author

Moustapha Dieye, Ramsès Djidjou-Demasse, Ousmane Seydi, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Maladies infectieuses et vecteurs : écologie, génétique, évolution et contrôle (MIVEGEC), and Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Université de Montpellier (UM)

Subjects
Viability, Hille-Yosida operator, Comparison theorem, [MATH]Mathematics [math]
Abstract

In this work, we find necessary and sufficient conditions in order that a family of sets {C(t), t ∈ J} be invariant for a Cauchy problem. We prove the existence and uniqueness of the solution using viability for timedependent closed convex sets to the case of non densely defined Cauchy problem. Moreover, we propose several characterizations of conditions that lead to the viability theorem. Finally, a comparison principle for semilinear problems, when the nonlinear part is only defined in a closed convex set, is established.

Published
2022

5. Mangrove zonation mapping in West Africa, at 10-m resolution, optimized for inter-annual monitoring

Author

Lombard, Florent, Soumaré, Safietou, Andrieu, Julien, Josselin, Didier, Études des Structures, des Processus d’Adaptation et des Changements de l’Espace (ESPACE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Institut Français de Pondichéry (IFP), Ministère de l'Europe et des Affaires étrangères (MEAE)-Centre National de la Recherche Scientifique (CNRS), and This work was supported under grant IDEX UCA JEDI and by the CNRS UMR 7300 ESPACE

Subjects
OBIA, Ecology, Times series, [SDE.MCG]Environmental Sciences/Global Changes, Applied Mathematics, Ecological Modeling, [SHS.GEO]Humanities and Social Sciences/Geography, Computer Science Applications, Computational Theory and Mathematics, Modeling and Simulation, Machine learning, Sentinel-1, Sentinel-2, Mangrove, Ecology, Evolution, Behavior and Systematics
Abstract

International audience; The surface area of mangrove ecosystems in Senegal have fluctuated substantially over several decades. Satellite data at 10 to 30-m resolution, which has been available since the 1980s, has allowed the mapping and quantification of these dynamics. However, the plant formations have reorganized internally; this has not been well-documented, possibly because there is no established method for detecting zonation of the Senegalese mangrove. This paper proposes a two-step method for mapping the zonation of the Saloum Delta mangrove. First, mangrove surfaces were detected using machine learning methods from an object-based time series. Finally, a typology was developed through object-based clustering using time-series metrics derived from the harmonic regression modeling of the vegetation fraction. A comparison with field data allowed us to determine the number of classes and discriminating variables. The results showed that the selected method resulted in an overall accuracy of 97.55% (Kappa = 95.42) for the land cover at 4 classes (Water, Mangrove, Salt flats, Other land covers), with an F1-Score of 98.91% for the mangroves. Second, our results suggest that the annual trend of the vegetation fraction at the object scale is effective in differentiating mangrove zonation into three classes based on canopy density and stand height (HM: High mangrove; LDM: Low and dense mangrove; LOM: Low and open mangrove). Finally, the temporal stability of the classes and uncertainty around the magnitudes of the plant fraction values per class were assessed by Bayesian inference. An overall accuracy of 85.5% can be expected to identify the zonation typology on an inter-annual scale. This mapping technique can be used to characterize the rate of change in zonation in response to environmental changes and to guide management strategies.

Published
2023

6. Principal spectrum point and application to nonlocal dispersal operators

Author

Djidjou-Demasse, Ramsès, Kandé, Mocatar, Seydi, Ousmane, Maladies infectieuses et vecteurs : écologie, génétique, évolution et contrôle (MIVEGEC), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Université de Montpellier (UM), Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD), Ecole polytechnique de Thiès, and Ecole Polytechnique de Thiès

Subjects
Nonlocal diffusion operators, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Principal eigenvalue, Resolvent positive operator, Asynchronous exponential growth
Abstract

We propose a general framework for a sufficient condition of the existence of the principal eigenpair to the eigenvalue problem L[u]+H[u] = λu, (λ, u) ∈ R×X, where L : X → X is a positive bounded linear operator and H : D(H) ⊂ X → X a closed, possibly unbounded linear operator in the Banach space (X, ∥ • ∥). Criteria for (i) the existence of a principal eigenpair, (ii) Asynchronous Exponential Growth (AEG) and, (iii) continuity result of the spectral bound are given, without necessarily specifying forms of operators for the above problem. The criteria are then applied to generalize some results in the existing literature in context of nonlocal dispersal operators. Our results are applied to a model of a chemostat and a model of a spatial evolution of a man-environment disease.

Published
2022
Full Text
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7. Cartographie par télédétection des variations spatio-temporelles de la couverture végétale spontanée face à la variabilité pluviométrique au Sahel : approche multiscalaire

Author

Oumar Marega, Julien Andrieu, Ababacar Fall, José-Luis San Emeterio, Centre d'Etudes pour le Développement des Territoires et l'Environnement (CEDETE), Université d'Orléans (UO), Université Paris Diderot - Paris 7 (UPD7), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Études des Structures, des Processus d’Adaptation et des Changements de l’Espace (ESPACE), Université Côte d'Azur (UCA)-Avignon Université (AU)-Université Nice Sophia Antipolis (... - 2019) (UNS), and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)

Subjects
Risque d'inondation, 010504 meteorology & atmospheric sciences, Basses eaux, télédétection, Climate, 0211 other engineering and technologies, 02 engineering and technology, 01 natural sciences, remote sensing, land cover, Flooding, Sahel, Evolution des températures, Modèle de mélange, Crues, Températures moyennes mondiales, pluviométrie, Hydrologie, Missing model, Etiage, Inondation, Extreme rainfall, General Medicine, [SHS.GEO]Humanities and Social Sciences/Geography, Geography, Geochemical tracers, [SDE]Environmental Sciences, occupation du sol, Low water, NDVI, Pluies extrêmes, rainfall, lcsh:G1-922, Flood, Meteorology, Global mean temperatures, vegetation, Irrégularité pluviométrique, Traceurs géochimiques, Flood risk, Crue, végétation, Adaptation of agriculture, lcsh:Physical geography, Météorologie, 021101 geological & geomatics engineering, 0105 earth and related environmental sciences, Hydrochimie, Forest cover, changes mapping, Hydrochemistry, Climat, Temperature evolution, Adaptation de l'agriculture, Forestry, 15. Life on land, [SDE.ES]Environmental Sciences/Environmental and Society, Floods, Rainfall irregularity, Land use, cartographie des changements, Couvert forestier, lcsh:GB3-5030, lcsh:Geography (General)
Abstract

International audience; The Sahel is a fragile region, characterized in recent decades by profound changes in land use, which are the result of complex interactions between societies and their environment. These phenomena, which modulate and transform the landscape, take place on several spatial and temporal scales. However, few studies have highlighted this multidimensional reality, most generally focusing only on the local or regional level, and on a single site. In this study, we mobilized two scales (local and regional) on three different sites. On the one hand, we performed a diachronic mapping of land cover by the analysis of multispectral Landsat images and, on the other hand, we studied its articulation with NDVI and rainfall time series.The results bring out an original synthesis of the land cover trends observed in the Sahelian agro-pastoral zone. They help understanding the complexity of the multi-scale phenomena that characterize the evolution of Sahelian areas. If the analysis of the time series confirms, as has been observed by several authors, an overall regreening trend on a regional basis as a result of the improvement in rainfall conditions from the 1990s, the diachronic analyzes proposed in this study found significant contrasts at finer scales. Considering the total area mapped (Landsat images covering each region), the areas of vegetation cover progression between 1999 and 2010 represent 18 % of the Gourma area and 27 % for Fakara. In terms of net change between 1999 and 2010, in Fakara which has the highest rate of progression (+13 %), the Dantiandou municipality shows, in contrast, a negative rate (-35 %) which is not the case in the two other studied municipalities: +7 % for Téssékré (in Ferlo) and +12 % for Hombori (in Gourma).; La bande sahélienne est une région fragile, caractérisée ces dernières décennies par des changements profonds de l'occupation du sol, résultats de processus biophysiques et de complexes interactions entre les sociétés et leur environnement. Ces processus, qui modulent et transforment le paysage, s'expriment à plusieurs échelles spatiales et temporelles. Pourtant peu de travaux mettent en valeur cette réalité multidimensionnelle et rares sont les approches comparatives multiscalaires. Dans cette étude, deux échelles (locale et régionale) ont été conjointement mobilisées, sur trois sites. La cartographie diachronique de la couverture du sol par l'analyse d'images multispectrales Landsat et son articulation avec l'analyse des séries temporelles (pluviométrie et NDVI) ont été couplées.Les résultats mettent en lumière une synthèse originale des tendances observées concernant les changements d'occupation du sol par la végétation en zone agropastorale sahélienne. Ils permettent de mieux cerner la complexité du caractère multiscalaire de l'évolution des espaces sahéliens. À la suite de nombreux auteurs, l'analyse des séries temporelles confirme globalement une tendance au reverdissement à l'échelle régionale comme résultat de l'amélioration des conditions pluviométriques à partir des années 1990. Cependant les analyses diachroniques proposées dans cette étude ont révélé d'importants contrastes puisque par rapport à la surface totale cartographiée (emprise des images Landsat couvrant chaque région) les surfaces de progression de la couverture végétales entre 1999 et 2010 correspondent à 18 % de la zone du Gourma et 27 % pour le Fakara. En termes d'évolution nette entre 1999 et 2010, dans le Fakara, qui présente le plus fort taux de progression (+13 %), la commune de Dantiandou montre, à l'inverse, un taux négatif (-35 %), ce qui n'est pas le cas des deux autres communes étudiées : +7 % pour Téssékré (dans le Ferlo) et +12 % pour Hombori (dans le Gourma).

Published
2022

8. Global Dynamics of a Spore Producing Pathogens Epidemic System with Nonlocal Diffusion Process

Author

Djidjou-Demasse, Ramsès, Lemdjo, Cassandra, Seydi, Ousmane, Maladies infectieuses et vecteurs : écologie, génétique, évolution et contrôle (MIVEGEC), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Université de Montpellier (UM), Département de Mathématiques Université de Yaoundé 1 = Department of Mathematics [Yaoundé, Cameroon], Université de Yaoundé I, Ecole polytechnique de Thiès, and Ecole Polytechnique de Thiès

Subjects
spore producing pathogens, [MATH.MATH-DS]Mathematics [math]/Dynamical Systems [math.DS], population dynamics, Quantitative Biology::Populations and Evolution, nonlocal diffusion
Abstract

International audience; In this paper, we analyze a nonlocal spatial epidemic model presenting the diffusion process of a spore producing plant pathogens responsible of one of the most destructive cocoa pods disease. The global existence, compactness and dissipativity of the semiflow generated by the system are established. By defining a threshold number (the basic reproduction number), we first express conditions for the existence of non-trivial stationary states. Next, we show that the qualitative dynamics of the model range from the extinction (i.e. the global stability of the disease-free stationary state), to the persistence (i.e. the global stability of the endemic stationary state) of the epidemics. Finally, we go through some simulations of our general analysis.

Published
2022

9. Remote sensing mapping of vegetation land cover change with regard to rainfall variability in the Sahel: a multiscale approach

Author

MAREGA, OUMAR, Emeterio, José-Luis San, FALL, Ababacar, Andrieu, Julien, Centre d'Etudes pour le Développement des Territoires et l'Environnement (CEDETE), Université d'Orléans (UO), Université Paris Diderot - Paris 7 (UPD7), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Études des Structures, des Processus d’Adaptation et des Changements de l’Espace (ESPACE), Université Côte d'Azur (UCA)-Avignon Université (AU)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA), Institut Français de Pondichéry (IFP), and Ministère de l'Europe et des Affaires étrangères (MEAE)-Centre National de la Recherche Scientifique (CNRS)

Subjects
changes mapping, NDVI, télédétection, rainfall, [SHS.GEO]Humanities and Social Sciences/Geography, [SDE.ES]Environmental Sciences/Environmental and Society, remote sensing, land cover, vegetation, Sahel, [SDE]Environmental Sciences, cartographie des changements, pluviométrie, végétation, occupation du sol
Abstract

International audience; The Sahel is a fragile region, characterized in recent decades by profound changes in land use, which are the result of complex interactions between societies and their environment. These phenomena, which modulate and transform the landscape, take place on several spatial and temporal scales. However, few studies have highlighted this multidimensional reality, most generally focusing only on the local or regional level, and on a single site. In this study, we mobilized two scales (local and regional) on three different sites. On the one hand, we performed a diachronic mapping of land cover by the analysis of multispectral Landsat images and, on the other hand, we studied its articulation with NDVI and rainfall time series.The results bring out an original synthesis of the land cover trends observed in the Sahelian agro-pastoral zone. They help understanding the complexity of the multi-scale phenomena that characterize the evolution of Sahelian areas. If the analysis of the time series confirms, as has been observed by several authors, an overall regreening trend on a regional basis as a result of the improvement in rainfall conditions from the 1990s, the diachronic analyzes proposed in this study found significant contrasts at finer scales. Considering the total area mapped (Landsat images covering each region), the areas of vegetation cover progression between 1999 and 2010 represent 18 % of the Gourma area and 27 % for Fakara. In terms of net change between 1999 and 2010, in Fakara which has the highest rate of progression (+13 %), the Dantiandou municipality shows, in contrast, a negative rate (-35 %) which is not the case in the two other studied municipalities: +7 % for Téssékré (in Ferlo) and +12 % for Hombori (in Gourma).; La bande sahélienne est une région fragile, caractérisée ces dernières décennies par des changements profonds de l'occupation du sol, résultats de processus biophysiques et de complexes interactions entre les sociétés et leur environnement. Ces processus, qui modulent et transforment le paysage, s'expriment à plusieurs échelles spatiales et temporelles. Pourtant peu de travaux mettent en valeur cette réalité multidimensionnelle et rares sont les approches comparatives multiscalaires. Dans cette étude, deux échelles (locale et régionale) ont été conjointement mobilisées, sur trois sites. La cartographie diachronique de la couverture du sol par l'analyse d'images multispectrales Landsat et son articulation avec l'analyse des séries temporelles (pluviométrie et NDVI) ont été couplées.Les résultats mettent en lumière une synthèse originale des tendances observées concernant les changements d'occupation du sol par la végétation en zone agropastorale sahélienne. Ils permettent de mieux cerner la complexité du caractère multiscalaire de l'évolution des espaces sahéliens. À la suite de nombreux auteurs, l'analyse des séries temporelles confirme globalement une tendance au reverdissement à l'échelle régionale comme résultat de l'amélioration des conditions pluviométriques à partir des années 1990. Cependant les analyses diachroniques proposées dans cette étude ont révélé d'importants contrastes puisque par rapport à la surface totale cartographiée (emprise des images Landsat couvrant chaque région) les surfaces de progression de la couverture végétales entre 1999 et 2010 correspondent à 18 % de la zone du Gourma et 27 % pour le Fakara. En termes d'évolution nette entre 1999 et 2010, dans le Fakara, qui présente le plus fort taux de progression (+13 %), la commune de Dantiandou montre, à l'inverse, un taux négatif (-35 %), ce qui n'est pas le cas des deux autres communes étudiées : +7 % pour Téssékré (dans le Ferlo) et +12 % pour Hombori (dans le Gourma).

Published
2021

10. Are the Fouta Djallon Highlands Still the Water Tower of West Africa?

Author

Julien Andrieu, Yves Boulvert, Jean-Louis Couture, Bachir Tanimoun, Luc Ferry, Gwenaelle Dejacquelot, Aliou Barry, Luc Descroix, Fatoumata Binta Sombily Diallo, Ange Bouramanding Diedhiou, Jean-Pierre Vandervaere, Ababacar Fall, Lamine Konaté, Mahamadou Diakité, Bernadette Nka Nnomo, Amirou Diallo, Safietou Soumaré, Eugenia Gallese, Honoré Dacosta, Yaya Sakho, Kadiatou Diallo, Sylvie Paméla Manga, Ansoumana Bodian, Jean Albergel, Gil Mahé, Kourahoye Diallo, Jean-Claude Bader, Didier Orange, Bakary Faty, Jean-Claude Olivry, Nadine Braquet, Andrew Ogilvie, Laurent Lambert, Ilia Amadou, Saly Sambou, Patrimoines locaux, Environnement et Globalisation (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU), Patrimoines et Territoires de l'eau (LMI PATEO), Patrimoines Locaux et Gouvernance (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Direction de la Gestion et la Planification des Ressources en Eau (DGPRE), Université Assane SECK de Ziguinchor (UASZ), Université de Lorraine (UL), Université Félix Houphouët-Boigny (UFHB), School of Public Administration and Development Economics, Doha Institute for Graduate Studies, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Études des Structures, des Processus d’Adaptation et des Changements de l’Espace (ESPACE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA), Université Côte d'Azur (UCA), Gestion de l'Eau, Acteurs, Usages (UMR G-EAU), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Centre de recherche pluridisciplinaire en Lettres, Langues, Sciences Humaines et des Sociétés (Pléiade), Université Paris 13 (UP13), Hydrosciences Montpellier (HSM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Université Gamal Abdel Nasser de Conakry, Institut Universitaire des Hautes Etudes de Guinée (IUHEG), Laboratoire d'étude des Interactions Sol - Agrosystème - Hydrosystème (UMR LISAH), Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, NBA Niger Basin Authority, Direction Nationale de l'Hydraulique [Guinée], Girardel - Laboratoire Leïdi (Leïdi), Université Gaston Berger de Saint-Louis Sénégal (UGB), Institut de Recherche pour le Développement (IRD), Independent Consultant, Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD), Grdr Migrations, Citoyenneté, Développement, Organisation Pour la Mise en Valeur du Bassin du Fleuve Sénégal (OMVS), Institut de Recherches Géologiques et Minières (IRGM), Organisation pour la Mise en Valeur du Bassin du Fleuve Gambie (OMVG), Ecologie fonctionnelle et biogéochimie des sols et des agro-écosystèmes (UMR Eco&Sols), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Service National des Sols (SENASOLS), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), European Union, via AICS (Agenzia Italiana de Cooperazione per il Sviluppo) ENV/2017/383-744/AP n, Sorbonne Université (SU)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Université Côte d'Azur (UCA)-Avignon Université (AU)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), and Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )

Subjects
Fula society, lcsh:Hydraulic engineering, depletion (or recession) coefficient, 010504 meteorology & atmospheric sciences, Geography, Planning and Development, 0207 environmental engineering, 02 engineering and technology, Aquatic Science, 01 natural sciences, Biochemistry, Natural (archaeology), West africa, Vegetation cover, lcsh:Water supply for domestic and industrial purposes, lcsh:TC1-978, basement, sandstone, runoff coefficient, 020701 environmental engineering, soil water holding capacity, 0105 earth and related environmental sciences, Water Science and Technology, lcsh:TD201-500, geography, Plateau, geography.geographical_feature_category, Fouta Djallon, 15. Life on land, 6. Clean water, Basement (geology), 13. Climate action, Threatened species, [SDE]Environmental Sciences, Physical geography, Surface runoff, Tower, water tower
Abstract

A large share of surface water resources in Sahelian countries originates from Guinea&rsquo, s Fouta Djallon highlands, earning the area the name of &ldquo, the water tower of West Africa&rdquo, This paper aims to investigate the recent dynamics of the Fouta Djallon&rsquo, s hydrological functioning. The evolution of the runoff and depletion coefficients are analyzed as well as their correlations with the rainfall and vegetation cover. The latter is described at three different space scales and with different methods. Twenty-five years after the end of the 1968&ndash, 1993 major drought, annual discharges continue to slowly increase, nearly reaching a long-term average, as natural reservoirs which emptied to sustain streamflows during the drought have been replenishing since the 1990s, explaining the slow increase in discharges. However, another important trend has been detected since the beginning of the drought, i.e., the increase in the depletion coefficient of most of the Fouta Djallon upper basins, as a consequence of the reduction in the soil water-holding capacity. After confirming the pertinence and significance of this increase and subsequent decrease in the depletion coefficient, this paper identifies the factors possibly linked with the basins&rsquo, storage capacity trends. The densely populated areas of the summit plateau are also shown to be the ones where vegetation cover is not threatened and where ecological intensification of rural activities is ancient.

Published
2020

11. Dynamique spatio-temporelle de la mangrove de Kafountine dans l'estuaire de la Basse-Casamance des années 1972 à nos jours : Approche par télédétection

Author

Safietou Soumaré, ABABACAR FALL, Julien Andrieu, Oumar Marega, Barnabé Dieme, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Études des Structures, des Processus d’Adaptation et des Changements de l’Espace (ESPACE), Université Côte d'Azur (UCA)-Avignon Université (AU)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU), Centre d'Etudes pour le Développement des Territoires et l'Environnement (CEDETE), Université d'Orléans (UO), Université Nice Sophia Antipolis (1965 - 2019) (UNS), and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA)

Subjects
[SHS.ENVIR]Humanities and Social Sciences/Environmental studies, [SHS.GEO]Humanities and Social Sciences/Geography, [SDE.ES]Environmental Sciences/Environmental and Society, ComputingMilieux_MISCELLANEOUS, [SHS]Humanities and Social Sciences
Abstract

International audience

Published
2020

12. Enriching geolocalized dataset with POIs descriptions at large scale

Author

Stéphane Gançarski, Hubert Naacke, Ibrahima Gueye, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Bases de Données (BD), LIP6, Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), and Naacke, Hubert

Subjects
Information retrieval, [INFO.INFO-DB]Computer Science [cs]/Databases [cs.DB], Point of interest, Computer science, Computation, [INFO.INFO-DS]Computer Science [cs]/Data Structures and Algorithms [cs.DS], [INFO.INFO-DS] Computer Science [cs]/Data Structures and Algorithms [cs.DS], 02 engineering and technology, Set (abstract data type), 020204 information systems, Computer cluster, Spark (mathematics), 0202 electrical engineering, electronic engineering, information engineering, [INFO.INFO-DC] Computer Science [cs]/Distributed, Parallel, and Cluster Computing [cs.DC], [INFO.INFO-DB] Computer Science [cs]/Databases [cs.DB], 020201 artificial intelligence & image processing, [INFO.INFO-DC]Computer Science [cs]/Distributed, Parallel, and Cluster Computing [cs.DC], Scale (map), ComputingMilieux_MISCELLANEOUS
Abstract

We present an efficient method to enrich a geolocalized dataset with contextual description about Points of Interest (POI). We implemented our solution using two large scale datasets: YFCC [14] and Geonames [2]. A practical problem we have encountered is the size of the manipulated data. Actually, the YFCC geolocalized dataset accounts for 45 million entries that we propose to cross with 12 millions of Geonames POIs. We show that using the Apache Spark cluster computing platform and the GeoSpark [18] spatial join library as-is lead to inefficient computation because of the important bias in the data. We propose a method to distribute the data non uniformly according to the data bias, which greatly improves the spatial join performance. Moreover, we propose a method to select among a set of close POIs, those which are the most relevant with the YFCC entries. The resulting enriched dataset will be made publicly available and should contribute to better validate future works on large scale POI recommendation.

Published
2020

13. Inverse estuaries in West Africa : evidence of the rainfall recovery ?

Author

Ange-Bouramanding Diedhiou, Victor Mendy, Julien Andrieu, Awa Diop, Djiby Sow, Yancouba Sané, Mamadou Thior, Jean-Pierre Vandervaere, Arame Dièye, Bamol Ali Sow, Jean-Pierre Montoroi, Safietou Soumaré, Yasmin Bouaita, Marie-Jeanne Senghor, Luc Descroix, Saloum Coly, Alexandre Badiane, Sylvie-Paméla Manga, Bakary Faty, Joseph Mingou, Eric Machu, Boubacar Demba Ba, ORSTOM, Université Assane SECK de Ziguinchor (UASZ), Laboratoire d'Algèbre, de Cryptologie, de Géométrie Algébrique et Applications (LACGAA), Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD), Patrimoines Locaux et Gouvernance (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Patrimoines locaux, Environnement et Globalisation (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU), Patrimoines et Territoires de l'eau (LMI PATEO), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Université de Lorraine - UFR Sciences humaines et sociales - Metz (UL UFR SHS), Université de Lorraine (UL), LMI ECLAIRS, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Université Côte d'Azur (UCA), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Direction de la Gestion et la Planification des Ressources en Eau (DGPRE), Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Études des Structures, des Processus d’Adaptation et des Changements de l’Espace (ESPACE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Sorbonne Université (SU)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), and UFR Sciences humaines et sociales - Metz [Université de Lorraine] (UL UFR SHS)

Subjects
Wet season, lcsh:Hydraulic engineering, 010504 meteorology & atmospheric sciences, [SDE.MCG]Environmental Sciences/Global Changes, Geography, Planning and Development, drought, 010501 environmental sciences, Aquatic Science, water salinity, 01 natural sciences, Biochemistry, West africa, lcsh:Water supply for domestic and industrial purposes, lcsh:TC1-978, Dry season, West Africa, 14. Life underwater, mangrove 1 Problematics, 0105 earth and related environmental sciences, Water Science and Technology, Hydrology, lcsh:TD201-500, geography, mangrove, geography.geographical_feature_category, Estuary, 15. Life on land, 6. Clean water, State of the Art, Salinity, Fresh water, 13. Climate action, inverse estuaries, Period (geology), Environmental science, Mangrove
Abstract

In West Africa, as in many other estuaries, enormous volumes of marine water are entering the continent. Fresh water discharge is very low, and it is commonly strongly linked to rainfall level. Some of these estuaries are inverse estuaries. During the Great Sahelian Drought (1968&ndash, 1993), their hyperhaline feature was exacerbated. This paper aims to describe the evolution of the two main West African inverse estuaries, those of the Saloum River and the Casamance River, since the end of the drought. Water salinity measurements were carried out over three to five years according to the sites in order to document this evolution and to compare data with the historical ones collected during the long dry period at the end of 20th century. The results show that in both estuaries, the mean water salinity values have markedly decreased since the end of the drought. However, the Saloum estuary remains a totally inverse estuary, while for the Casamance River, the estuarine turbidity maximum (ETM) is the location of the salinity maximum, and it moves according to the seasons from a location 1&ndash, 10 km downwards from the upstream estuary entry, during the dry season, to a location 40&ndash, 70 km downwards from this point, during the rainy season. These observations fit with the functioning of the mangrove, the West African mangrove being among the few in the world that are markedly increasing since the beginning of the 1990s and the end of the dry period, as mangrove growth is favored by the relative salinity reduction. Finally, one of the inverse estuary behavior factors is the low fresh water incoming from the continent. The small area of the Casamance and Saloum basins (20,150 and 26,500 km&sup2, respectively) is to be compared with the basins of their two main neighbor basins, the Gambia River and the Senegal River, which provide significant fresh water discharge to their estuary.

Published
2020

14. Spectral Intrinsic Decomposition Method for Adaptive Signal Representation

Author

Abdoulaye Thioune, Oumar Niang, Eric Delechelle, Jacques Lemoine, Laboratoire Images, Signaux et Systèmes Intelligents (LISSI), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Laboratoire d'Analyse Numérique et Informatique [Sénégal] (LANI), Université Gaston Berger de Saint-Louis Sénégal (UGB), Ecole polytechnique de Thiès, and Ecole Polytechnique de Thiès

Subjects
[SPI.OTHER]Engineering Sciences [physics]/Other, Mathematical optimization, Partial differential equation, Article Subject, Signal reconstruction, Computer science, Noise reduction, ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, MathematicsofComputing_NUMERICALANALYSIS, 020206 networking & telecommunications, 02 engineering and technology, Matrix decomposition, Signal Processing, 0202 electrical engineering, electronic engineering, information engineering, 020201 artificial intelligence & image processing, Decomposition method (constraint satisfaction), Algorithm, Eigenvalues and eigenvectors, Interpolation
Abstract

International audience; In this paper we propose a new method called Spectral Intrinsic Decomposition (SID) for the representation of non-linear signals. This approach is based on the spectral decomposition of Partial Differential Equations (PDE)- based operators which interpolate the characteristic points of a signal. The SID's components which are the eigenvectors of these PDE interpolation operators underlie the new signal decomposition-reconstruction method. The usefulness and the efficiency of this method is illustrated, in signal reconstruction or denoising aim, on some examples using artifical and pathological signals.

Published
2012

15. Inferring the seasonal evolution of phytoplankton groups in the Senegalo-Mauritanian upwelling region from satellite ocean-color spectral measurements

Author

Salam Sawadogo, Daouda Diouf, Carlos Mejia, Yves Dandonneau, Julien Brajard, G. Gasc, Awa Niang, Michel Crépon, Ousmane Farikou, Sylvie Thiria, Institut universitaire des sciences et techniques d'Abéché, École Supérieure Polytechnique de Dakar (ESP), Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Processus de la variabilité climatique tropicale et impacts (PARVATI), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Coupling environmental data and simulation models for software integration (Clime), Inria Paris-Rocquencourt, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), Institut Pierre-Simon-Laplace (IPSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National d'Études Spatiales [Toulouse] (CNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)

Subjects
0106 biological sciences, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, biology, 010604 marine biology & hydrobiology, Oceanography, Stellar classification, biology.organism_classification, 01 natural sciences, Reflectivity, Geophysics, Diatom, SeaWiFS, Space and Planetary Science, Geochemistry and Petrology, Ocean color, Climatology, Phytoplankton, Earth and Planetary Sciences (miscellaneous), Upwelling, Environmental science, Satellite, 14. Life underwater, 0105 earth and related environmental sciences
Abstract

International audience; We have investigated the phytoplankton dynamics of the Senegalo-Mauritanian upwelling region, which is a very productive region, by processing a 13 year set of SeaWiFS satellite ocean-color measurements using a PHYSAT-like method. We clustered the spectra of the ocean-color normalized reflectance (reflectance normalized by a reflectance dependent on chlorophyll-a concentration only) into 10 significant spectral classes using a Self-Organized Map (SOM) associated with a hierarchical ascendant classification (HAC). By analyzing a 13 year climatology of these classes, we have been able to outline a coherent scenario describing the Senegalo-Mauritanian upwelling region in terms of spatiotemporal variability of phytoplankton groups: during the onset of the upwelling (December–February), we mainly observed nanoeukaryote-type phytoplankton in the coastal area; in April–May, the period corresponding to the maximum chlorophyll-a concentration, the nanoeukaryote types were replaced by diatom types. This scenario is in agreement with microscope phytoplankton cell observations done during several past cruises.

Published
2015

16. Effect of the interfacial transition zone and the nature of the matrix-aggregate interface on the overall elastic and inelastic behaviour of concrete under compression: a 3D numerical study

Author

Siham Kamali-Bernard, Dame Keinde, Ibrahima Khalil Cissé, Fabrice Bernard, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)

Subjects
Environmental Engineering, Materials science, Aggregate (composite), Interface (Java), Compression (physics), Matrix (mathematics), [SPI.GCIV]Engineering Sciences [physics]/Civil Engineering, Local analysis, Transition zone, Composite material, Mortar, Elastic modulus, ComputingMilieux_MISCELLANEOUS, Civil and Structural Engineering
Abstract

A 3D numerical model is developed to study the elastic and inelastic behaviour of concrete with consideration of the interfacial transition zone and the nature of the matrix – aggregate interface. Concrete is represented as a bi-phasic or tri-phasic material, consisting of spherical aggregates embedded in a matrix (mortar) surrounded or not by a transition zone. The matrix–aggregates interface is modelled taking into account a perfect contact and a sliding one. Numerical elastic modelling results are in a good agreement with those obtained by Hashin and Monteiro analytical model. Numerical results of the overall behaviour modelling show a slight influence of the transition zone on the mechanical behaviour of concrete. In contrast, a significant influence of the nature of the matrix – aggregate contact is demonstrated and explained based on local analysis of stress distribution in the material.

Published
2014

17. Effect of Aggregate Type on the Concrete Matrix/Aggregates Interface and its Influence on the Overall Mechanical Behavior. A Numerical Study

Author

Fabrice Bernard, Dame Keinde, Siham Kamali-Bernard, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)

Subjects
Materials science, Aggregate (composite), business.industry, Interface (Java), Mechanical Engineering, 0211 other engineering and technologies, 02 engineering and technology, Structural engineering, Type (model theory), 021001 nanoscience & nanotechnology, Finite element method, Matrix (mathematics), [SPI.GCIV]Engineering Sciences [physics]/Civil Engineering, Mechanics of Materials, 021105 building & construction, Compressive test, General Materials Science, Composite material, 0210 nano-technology, business, ComputingMilieux_MISCELLANEOUS
Abstract

This paper investigates the effect of siliceous, limestone and plastic aggregates on the compressive behavior of concrete. Firstly, the matrix/aggregates interface is characterized using a scanning electronic microscope. Compressive test is then simulated on a 3D numerical concrete using finite element method. The influence of the matrix/aggregates interface quality is quantified. The results give a new insight and help on the understanding of the contribution of the nature of the aggregate on the overall mechanical behavior of concretes.

Published
2014

18. Senegalese Ferlo : geographical approach of the vulnerability of sahelian anthroposystems

Author

FALL, Ababacar, FALL, Ababacar, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Centre de recherche pluridisciplinaire en Lettres, Langues, Sciences Humaines et des Sociétés (Pléiade), Université Paris 13 (UP13), Université Paris 13 - Sorbonne Paris Cité, and Frédéric ALEXANDRE

Subjects
VULNERABILITY, FERLO, ECOSYSTEME, [SDE.MCG]Environmental Sciences/Global Changes, [SHS.GEO] Humanities and Social Sciences/Geography, SAHEL, PASTORALISME, [SHS.GEO]Humanities and Social Sciences/Geography, ANTHROPOSYSTEME, DEGRADATION, RESILIENCE, VULNERABILITE, [SDE.ES]Environmental Sciences/Environmental and Society, PASTORALISM, ANTHROPOSYSTEM, [SDE.MCG] Environmental Sciences/Global Changes, [SHS.ENVIR] Humanities and Social Sciences/Environmental studies, [SHS.ENVIR]Humanities and Social Sciences/Environmental studies, ECOSYSTEM, [SDE.ES] Environmental Sciences/Environmental and Society
Abstract

The pastoral anthroposystem of Senegalese Ferlo evolves in an environment historically neglected by agricultural policies because of its characteristics particular biophysics, unfavorable to the agriculture and to the shape of development other than the extensive breeding. This primacy of the itinerant breeding is nowadays more and more disputed by the development of the farming in a context marked by the improvement of the conditions of the rainfall in West-African Sahel, soil depletion in the Groundnut Basin and the multiplication of agricultural development at the valley of the Senegal River. By combining the analysis of remote sensing imagery for mapping land cover changes by the vegetation cover, the study of flora and vegetation landscape and the exploitation of the investigations in villages and camps, this thesis attempts to define the geography of the vulnerability of rural populations and ecosystems which they use. So, pastoralists evolve with daily adaptation strategies in these circles inside Senegal marked by deep ecological instability and by the transformations at work in the Senegalese rural society. These socio-environmental changes contribute to the dynamics of plant landscapes and raise the question of ecosystem degradation., L’anthroposystème pastoral du Ferlo sénégalais évolue dans un milieu historiquement négligé par les politiques agricoles en raison de ses caractéristiques biophysiques particulières, peu favorables à l’agriculture et à une forme de mise en valeur autre que l’élevage extensif, incluant une transhumance. Celui-ci permet d’exploiter des ressources très variables dans l’espace et dans le temps. Cette primauté de l’élevage itinérant est de nos jours de plus en plus contestée par le développement de l’agriculture dans un contexte marqué par l’amélioration des conditions de la pluviosité dans tout le Sahel ouest-africain, de l’épuisement des terres du Bassin aracohidier et de la multiplication des aménagements agricoles au niveau de la vallée du fleuve Sénégal. En combinant l’analyse d’images de télédétection pour la cartographie d’évolution de l’occupation du sol par le couvert végétal, l’étude de la flore et du paysage végétal et l’exploitation d’enquêtes dans les villages et les campements du Ferlo, ce mémoire de thèse tente de cerner la géographie de la vulnérabilité des populations rurales et des écosystèmes qu’elles utilisent. Ainsi les éleveurs et les pasteurs évoluent-ils avec des stratégies d’adaptation quotidienne dans ces milieux du Sénégal intérieur marqués par l’instabilité écologique profonde et par les transformations à l’oeuvre dans la société rurale sénégalaise. Ces changements socio-environnementaux considérables contribuent ainsi à la dynamique des paysages végétaux et par-delà pose la question de la dégradation des écosystèmes.

Published
2014

19. Le Mali contemporain

Author

Rémi Generoso, Jean-Etienne Bidou, Bourema F. Ballo, Ibrahima Khalil Cisse, Pierre Morand, Vincent Geronimi, A. Kodio, Claire Mainguy, Isabelle Droy, Famory Sinaba, Brunet-Jailly, J. (ed.), Charmes, Jacques (ed.), Konaté, D. (ed.), Bureau d'Économie Théorique et Appliquée (BETA), Institut National de la Recherche Agronomique (INRA)-Université de Strasbourg (UNISTRA)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Observatoire du Développement Humain Durable (ODHD), Aménagement, Développement, Environnement, Santé et Sociétés (ADES), Centre National de la Recherche Scientifique (CNRS)-Université Bordeaux Segalen - Bordeaux 2-Université Bordeaux Montaigne, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Unité mixte internationale Résiliences (UMI RESILIENCES), Centre ivoirien de recherches économiques et sociales (CIRES)-Université de Cocody, Les Afriques dans le monde (LAM), Institut de Recherche pour le Développement (IRD)-Université Bordeaux Montaigne-Institut d'Études Politiques [IEP] - Bordeaux-Sciences Po Bordeaux - Institut d'études politiques de Bordeaux (IEP Bordeaux)-Centre National de la Recherche Scientifique (CNRS), Centre d'études sur la mondialisation, les conflits, les territoires et les vulnérabilités (Cemotev), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), EconomiX, Université Paris Nanterre (UPN)-Centre National de la Recherche Scientifique (CNRS), Université des sciences sociales et de gestion de Bamako, Institut d'Economie Rurale, Université de Lorraine (UL)-Université de Strasbourg (UNISTRA)-Institut National de la Recherche Agronomique (INRA)-Centre National de la Recherche Scientifique (CNRS), Université Bordeaux Segalen - Bordeaux 2-Université Bordeaux Montaigne-Centre National de la Recherche Scientifique (CNRS), and Sciences Po Bordeaux - Institut d'études politiques de Bordeaux (IEP Bordeaux)-Institut de Recherche pour le Développement (IRD)-Institut d'Études Politiques [IEP] - Bordeaux-Université Bordeaux Montaigne-Centre National de la Recherche Scientifique (CNRS)

Subjects
Sociology, [SHS.ENVIR]Humanities and Social Sciences/Environmental studies, société malienne, [SHS.ANTHRO-SE]Humanities and Social Sciences/Social Anthropology and ethnology, Niger (delta intérieur), Mali, SOC026000, [SHS]Humanities and Social Sciences, décentralisation, JHB
Abstract

International audience; La guerre au nord du pays et les bouleversements politiques récents au Mali ont suscité une interrogation lancinante : « Comment en est-on arrivé là ? » De façon générale, les recherches en sciences sociales permettent-elles d’éclairer les trajectoires des sociétés et des nations, et, lorsque l’on s’arrête plus particulièrement sur l’histoire récente du Mali, que peuvent apporter des résultats de recherche pour la compréhension de la terrible séquence d’événements militaires et politiques survenus de 2012 à début 2013 ?

Published
2014

20. Exploration of the T-Interval-Connected Dynamic Graphs: the Case of the Ring

Author

David Ilcinkas, Ahmed Mouhamadou Wade, Laboratoire Bordelais de Recherche en Informatique (LaBRI), Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB), Algorithmics for computationally intensive applications over wide scale distributed platforms (CEPAGE), Université Sciences et Technologies - Bordeaux 1-Inria Bordeaux - Sud-Ouest, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Centre National de la Recherche Scientifique (CNRS), Combinatoire et Algorithmique, Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB), See paper for details., ANR-11-BS02-0014,DISPLEXITY,Calculabilité et complexité en distribué(2011), Ilcinkas, David, BLANC - Calculabilité et complexité en distribué - - DISPLEXITY2011 - ANR-11-BS02-0014 - BLANC - VALID, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, ANR-13-JS02-0002,MACARON,Bouger et Calculer: Agents, Robots et Réseaux(2013), Université de Bordeaux (UB)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux 1 (UB)-Inria Bordeaux - Sud-Ouest, and Université de Bordeaux (UB)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[INFO.INFO-DS]Computer Science [cs]/Data Structures and Algorithms [cs.DS], [INFO.INFO-DS] Computer Science [cs]/Data Structures and Algorithms [cs.DS], 0102 computer and information sciences, 02 engineering and technology, Exploration problem, [INFO.INFO-DM]Computer Science [cs]/Discrete Mathematics [cs.DM], 01 natural sciences, Stability (probability), Theoretical Computer Science, Combinatorics, 0202 electrical engineering, electronic engineering, information engineering, Connection (algebraic framework), Time complexity, Mathematics, Dynamic graphs, Discrete mathematics, Mobile agent, Ring (mathematics), Unit of time, 020206 networking & telecommunications, T-interval-connectivity, [INFO.INFO-DM] Computer Science [cs]/Discrete Mathematics [cs.DM], Computational Theory and Mathematics, 010201 computation theory & mathematics, Theory of computation, Interval (graph theory), 020201 artificial intelligence & image processing, Exploration, [INFO.INFO-DC]Computer Science [cs]/Distributed, Parallel, and Cluster Computing [cs.DC], Focus (optics)
Abstract

In this paper, we study the T-interval-connected dynamic graphs from the point of view of the time necessary and sufficient for their exploration by a mobile entity (agent). A dynamic graph (more precisely, an evolving graph) is T-interval-connected (T ≥ 1) if, for every window of T consecutive time steps, there exists a connected spanning subgraph that is stable (always present) during this period. This property of connection stability over time was introduced by Kuhn, Lynch and Oshman (Kuhn et al. 14) (STOC 2010). We focus on the case when the underlying graph is a ring of size n, and we show that the worst-case time complexity for the exploration problem is 2n − T − Θ(1) time units if the agent knows the dynamics of the graph, and $n+ \frac {n}{\max \{1, T-1\} } (\delta -1) \pm {\Theta }(\delta )$ time units otherwise, where δ is the maximum time between two successive appearances of an edge.

Published
2013

21. About a Partial Differential Equation-Based Interpolator for Signal Envelope Computing: Existence Results and Applications

Author

Eric Delechelle, Abdoulaye Thioune, Mary Teuw Niane, Oumar Niang, Jacques Lemoine, Laboratoire Images, Signaux et Systèmes Intelligents (LISSI), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Laboratoire d'Analyse Numérique et Informatique [Sénégal] (LANI), Université Gaston Berger de Saint-Louis Sénégal (UGB), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Laboratoire d'étude et de recherche en instrumentation, signaux et systèmes (LERISS), and EA412-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)

Subjects
[SPI.OTHER]Engineering Sciences [physics]/Other, Mathematical optimization, Denoising, Partial differential equation, Article Subject, Computer science, Signal and Image Restoration, Noise reduction, MathematicsofComputing_NUMERICALANALYSIS, Partial Differential Equations, 020206 networking & telecommunications, 02 engineering and technology, Signal Representation, Upper and Lower Envelope, Space (mathematics), Signal, Hilbert–Huang transform, Image (mathematics), Signal Processing, 0202 electrical engineering, electronic engineering, information engineering, Applied mathematics, Partial derivative, 020201 artificial intelligence & image processing, Empirical Mode Decomposition, Uniqueness
Abstract

International audience; This paper models and solves the mathematical problem of interpolating characteristic points of signals by a Partial Differential Equation (PDE) based approach. The existence and uniqueness results are established in an appropriate space whose regularity is similar to cubic spline one. We show how this space is suitable for the Empirical Mode Decomposition (EMD) sifting process. Numerical schemes and computing applications are also presented for signal envelopes calculation. The test results show the usefullness of the new PDE-interpolator in some pathological cases like for input class functions that are not so regular as in the cubic splines case. Some image filtering tests strengthen the demonstration of PDE interpolator performance.

Published
2013
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22. Etude de l'amélioration de latérites du Sénégal par ajout de sable

Author

Ndiaye, Massamba, Magnan, Jean Pierre, CISSE, Ibrahima Khalil, Cisse, Lamine, Sols, Roches et Ouvrages Géotechniques (IFSTTAR/GERS/SRO), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Communauté Université Paris-Est, Département Géotechnique, Environnement, Risques naturels et Sciences de la terre (IFSTTAR/GERS), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université de Lyon-PRES Université Nantes Angers Le Mans (UNAM)-PRES Université Paris-Est-PRES Université de Grenoble, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Agence des Travaux et de Gestion des Routes, Communauté Université Paris-Est-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR), and Cadic, Ifsttar

Subjects
SENEGAL, [SPI.GCIV]Engineering Sciences [physics]/Civil Engineering, CONSTRUCTION ROUTIERE, DUNE, [SPI.GCIV] Engineering Sciences [physics]/Civil Engineering, SABLE, [SPI.MECA]Engineering Sciences [physics]/Mechanics [physics.med-ph], [SPI.MECA] Engineering Sciences [physics]/Mechanics [physics.med-ph], LATERITE, STABILISATION DES SOLS, TRAITEMENT DES SOLS
Abstract

Le mélange des latérites avec des matériaux granulaires comme du sable ou des matériaux concassés permet d'améliorer leurs propriétés pour les rendre compatibles avec une utilisation routière. L'article rend compte des essais effectués sur deux latérites du Sénégal, traitées par ajout de sable de dune et dont les caractéristiques sont comparées aux spécifications du CEBTP de 1972 pour les routes à faible trafic en zone tropicale. La lithostabilisation avait pour objectif de diminuer l'indice de plasticité, tout en conservant la valeur de l'indice CBR et en vérifiant que la courbe granulométrique reste dans le fuseau spécifié pour une utilisation en couche de fondation ou couche de base de route à faible trafic. L'étude montre que l'indice CBR réagit différemment d'une latérite à l'autre et commente l'évolution possible des spécifications pour tenir compte de l'expérience des dernières décennnies.

Published
2013

23. Multivariate analysis of the Senegalo-Mauritanien area by merging satellite remote sensing ocean color and SST observations

Author

Awa Niang, Michel Crépon, Julien Brajard, O. Farikou, C. Mejia, S. Sawadogo, Sylvie Thiria, Institut universitaire des sciences et techniques d'Abéché, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, École Supérieure Polytechnique de Dakar (ESP), Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut Pierre-Simon-Laplace (IPSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, 010505 oceanography, General Arts and Humanities, Statistical index, Intertropical Convergence Zone, 01 natural sciences, Multi sensor, Sea surface temperature, Geography, Oceanography, 13. Climate action, Ocean color, Satellite remote sensing, Climatology, Upwelling, Satellite, 14. Life underwater, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

The Senegalo-Mauritanian upwelling is a very productive upwelling occurring along the West coast of Africa. The seasonal and inter-annual variability of the upwelling region between 9° and 22°N and 14° and 25°W was studied by merging monthly ocean color data and sea surface temperature provided by satellite sensors during twelve years from 1998 up to 2010. We combined these two parameters to obtain a unique index describing the spatio-temporal variability of the upwelling. We used a classification methodology consisting in a neural network topological map and a hierarchical ascendant classification. Six classes can explain most of the variability of this region, one of them (class 6) being dedicated to the coastal upwelling water, another being the signature of the Gulf of Guinea dome water (class 2), a third one to case 2 water (class 5). The classes can be considered as multi-factorial statistical indices allowing us to characterize the different water types of this region and to investigate their variability. It is shown that the upwelling extent is maximum in February-March, minimum in August-September. Its variability is linked to that of the wind and to the ITCZ position. The Gulf of Guinea waters moves northward in June and relaxes to their southward position in December. During the twelve years of observation, we were not able to evidence climatic trends of the SST and Chl-a concentration. The methodology we have developed can be used in a large variety of problems implying multi sensor measurements.

Published
2013

24. Partial Differential Equation-Based Approach for Empirical Mode Decomposition: Application on Image Analysis

Author

Oumar Niang, Jacques Lemoine, Abdoulaye Thioune, Eric Delechelle, Mouhamed Cheikh El Gueirea, Laboratoire Images, Signaux et Systèmes Intelligents (LISSI), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Laboratoire d'Analyse Numérique et Informatique [Sénégal] (LANI), Université Gaston Berger de Saint-Louis Sénégal (UGB), Laboratoire d'étude et de recherche en instrumentation, signaux et systèmes (LERISS), EA412-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), SIRIUS, Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Laboratoire Images, Signaux et Systèmes Intelligents ( LISSI ), Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ) -Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ), CIR, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Soualah, Oussama, Amirat, Yacine, and CIR, LISSI

Subjects
[SPI.OTHER]Engineering Sciences [physics]/Other, Mathematical optimization, restoration, [INFO.INFO-TS] Computer Science [cs]/Signal and Image Processing, Noise reduction, [ INFO.INFO-NI ] Computer Science [cs]/Networking and Internet Architecture [cs.NI], inpainting, Inpainting, [SCCO.COMP]Cognitive science/Computer science, 02 engineering and technology, [INFO] Computer Science [cs], PDE, Hilbert–Huang transform, Image (mathematics), [INFO.INFO-NI]Computer Science [cs]/Networking and Internet Architecture [cs.NI], [INFO.INFO-TS]Computer Science [cs]/Signal and Image Processing, [SCCO.COMP] Cognitive science/Computer science, 0202 electrical engineering, electronic engineering, information engineering, Decomposition (computer science), EMD, [INFO]Computer Science [cs], image, Empirical mode decomposition, ComputingMilieux_MISCELLANEOUS, [SPI.SIGNAL] Engineering Sciences [physics]/Signal and Image processing, Mathematics, Partial differential equation, [INFO.INFO-NI] Computer Science [cs]/Networking and Internet Architecture [cs.NI], [SPI.OTHER] Engineering Sciences [physics]/Other, SIGNAL (programming language), mean envelope, 020206 networking & telecommunications, Computer Graphics and Computer-Aided Design, partial differential equation, 020201 artificial intelligence & image processing, Algorithm, signal, [SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing, Software, Interpolation
Abstract

International audience; The major problem with Empirical Mode Decomposition (EMD) algorithm is its lack of a theoretical framework. So, it is difficult to characterize and evaluate this approach. In this paper, we propose in the two dimensional case, the use of an alternative implementation to the algorithmic definition of the so-called sifting process used in the original Huangs Empirical Mode Decomposition method. This approach, especially based on Partial Differential Equations (PDE) was presented by O. Niang and al. in previous works, in 2005 and 2007 and lays on a nonlinear diffusion-based filtering process to solve the meanenvelope estimation problem. In 1D case, the efficiency of the PDE-based method, compared to the original EMD algorithmic version, is also illustrated in recent paper [1]. Recently, several bidimensional extensions for EMD method were proposed. Despite some efforts, 2D versions for EMD appear poorly performing and are very time consuming. So in this work, an extension to 2D space of the PDE-based approach is extensively described. This approach has been applied in case of both signal and image decomposition. Obtained results confirm the usefulness of the new PDE-based sifting process for decomposition of various kinds of data. Some results have been provided in the case of image decomposition. The effectiveness of the approach encourages its usage in a number of signal and image applications such as denoising, detrending, or texture analysis.

Published
2012

25. A New Signal Denoising Method using Iterative Thresholding of the Spectral Intrinsic Decomposition

Author

Niang, Oumar, Thioune, Abdoulaye, Guerra, Mouhamed Ould, Deléchelle, Eric, Lemoine, Jacques, Amirat, Yacine, Laboratoire Images, Signaux et Systèmes Intelligents (LISSI), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Laboratoire d'Analyse Numérique et Informatique [Sénégal] (LANI), Université Gaston Berger de Saint-Louis Sénégal (UGB), Ecole polytechnique de Thiès, and Ecole Polytechnique de Thiès

Subjects
[SPI.OTHER]Engineering Sciences [physics]/Other, Physics::Instrumentation and Detectors, [SPI.OTHER] Engineering Sciences [physics]/Other
Abstract

International audience; This paper presents a new signal denoising method based on the classical three step procedure analysis-threshold- synthesis and the Spectral Intrinsic Decomposition (SID). This method consists of an iterative thresholding of the SID components. If the wavelets denoising approach depends on the choice of the wavelet form, the SID-denoising proposed in this paper is self adaptive. The SID-based removal method reduces noise and can retain useful discontinuities of the signal as e ectively as the wavelet techniques based on soft thresholding.

Published
2012

26. A spectral approach for sifting process in empirical mode decomposition

Author

Oumar Niang, Eric Delechelle, Jacques Lemoine, Laboratoire Images, Signaux et Systèmes Intelligents (LISSI), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Laboratoire d'Analyse Numérique et Informatique [Sénégal] (LANI), Université Gaston Berger de Saint-Louis Sénégal (UGB), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Amirat, Yacine, Laboratoire d'étude et de recherche en instrumentation, signaux et systèmes (LERISS), EA412-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), SIRIUS, Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Laboratoire Images, Signaux et Systèmes Intelligents ( LISSI ), Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ), Laboratoire d'étude et de recherche en instrumentation, signaux et systèmes ( LERISS ), EA412-Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ), and Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ) -Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 )

Subjects
[SPI.OTHER]Engineering Sciences [physics]/Other, Mathematical optimization, [ INFO.INFO-TS ] Computer Science [cs]/Signal and Image Processing, Iterative method, 02 engineering and technology, [ SPI.SIGNAL ] Engineering Sciences [physics]/Signal and Image processing, PDE, Regularization (mathematics), Hilbert–Huang transform, Tikhonov regularization, mean-envelope, transient, [INFO.INFO-TS]Computer Science [cs]/Signal and Image Processing, Convergence (routing), 0202 electrical engineering, electronic engineering, information engineering, EMD, Electrical and Electronic Engineering, Mathematics, Diffusion equations, Partial differential equation, [SPI.OTHER] Engineering Sciences [physics]/Other, inverse problems, eigenvalues, empirical mode decomposition (EMD), 020206 networking & telecommunications, Inverse problem, Signal Processing, 020201 artificial intelligence & image processing, Decomposition method (constraint satisfaction), Algorithm, [SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing, mode mixing
Abstract

International audience; In this paper, we propose an alternative to the algorithmic definition of the sifting process used in the original Huang's empirical mode decomposition (EMD) method. Although it has been proven to be particularly effective in many applications, EMD method has several drawbacks. The major problem with EMD is the lack of theoretical Framework which leads to difficulties for the characterization and evaluation this approach. On top of the mathematical model, there are other concerns with mode mixing and transient phenomena, such as intermittency or pure tones separation. This paper follows a previous published nonlinear diffusion-based filtering to solve the mean-envelope estimation in sifting process. The major improvements made in this present work are a non-iterative resolution scheme for the previously proposed partial differential equation (PDE), a new definition of the stopping function used in the PDE framework, and finally an automatic regularization process based on inverse problem theory to deal with mode mixing or transient detection problem. Obtained results confirm good properties of the new version of the PDE-based sifting process and its usefulness for decomposition of various kinds of data. The efficiency of the method is illustrated on some examples using informative and pathological signals for which standard EMD algorithm fails.

Published
2010

27. Empirical Mode Decomposition: Contribution to Mathematical Modeling and Application in Signal and Image Processing

Author

Niang, Oumar, Amirat, Yacine, Laboratoire Images, Signaux et Systèmes Intelligents (LISSI), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Laboratoire d'Analyse Numérique et Informatique [Sénégal] (LANI), Université Gaston Berger de Saint-Louis Sénégal (UGB), Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Université Paris XII Val de Marne, and Jacques Lemoine

Subjects
shrinkage par EMD, [INFO.INFO-TS] Computer Science [cs]/Signal and Image Processing, Image Processing, shrinkage par ondelettes, Analyse Temps-Fréquence, Wavelets, Analyse Multi-résolution, Enveloppe moyenne, [INFO.INFO-TS]Computer Science [cs]/Signal and Image Processing, Méthodes Spectrales, Inpainting, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Spectral Methods, Équations aux Dérivées Partielles, Ondelettes, Banc de Filtres, [MATH.MATH-AP] Mathematics [math]/Analysis of PDEs [math.AP], Mean Envelope, [SPI.SIGNAL] Engineering Sciences [physics]/Signal and Image processing, Caracteristics points, Mathematical Modeling, Tikhonov regularization, Algorithme de Poursuite, Filters Banks, Partial Differential Equations, Analyse d'Images, Interpolation, Time-frequency Analysis, Décomposition Modale Empirique, Empirical Mode Decomposition, Multi-resolution Analysis, Points Caractéristiques, wavelets shrinkage, Régularisation de Tikhonov, [SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing, Modélisation mathématique, EMD shrinkage
Abstract

The EMD technique is a new tool for representing non linear and non-stationary signal as a sum of components called Intrinsic Mode Functions (IMF). The EMD decomposition can be compared with a wavelet one. However the main limit of the use of this method is lack of theoretical basis. There wasn't existence or convergence results before this work. In this work we replace within EMD algorithm, the mean envelope detection of a signal by asymptotic solutions of Partial Differential Equations (PDE) systems . Thus by a variational method, we prove the convergence of the algorithm and establish the IMF existence result. The orthogonality property of EMD algorithm is also studied on appropriate space. Two novel applications in signal and image processing are presented : intermittency and mode mixing extractions by Thikonov regularization, and restoration by EMD shrinkage. Finally the model can be a starting point of a study of the unicity of EMD decomposition., La Décomposition Modale Empirique (EMD), est une méthode de décomposition multi-résolution de signaux en fonctions Modes Intrinsèques (IMF) et cela, de manière auto-adaptative. En la couplant avec la transformée de Hilbert, elle devient une méthode d'analyse Temps-Fréquence , la transformée de Hilbert-Huang, permettant d'étudier bon nombre de classes de signaux. Malgré ces nombreuses applications, l'une des plus importantes limites de l'EMD est son manque de formalisme mathématique. A la place d'une interpolation par splines cubiques utilisée dans l'EMD classique, nous avons estimé l'enveloppe moyenne par une solution d'un système d'EDP. Par une méthode variationnelle, nous avons établi un cadre théorique pour prouver les résultats de convergence, d'existence de modes et la propriété de presque orthogonalité de l'EMD. La comparaison avec des bancs de filtres itératifs et les ondelettes, montre l'aspect multi-résolution de l'EMD. Deux nouvelles applications en traitement du signal et de l'image sont présentées : l'extraction des intermittences et mode mixing et la restauration par shrinkage par EMD. Enfin le modèle peut servir de base pour l'étude de l'unicité de la décomposition.

Published
2007

28. Exploration of Dynamic Cactuses with Sub-logarithmic Overhead

Author

David Ilcinkas, Ahmed Mouhamadou Wade, Laboratoire Bordelais de Recherche en Informatique (LaBRI), Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB), Laboratoire Traitement de l’Information et Systèmes Intelligents (LTISI), Ecole Polytechnique de Thiès, A. M. Wade is partially supported by the African Center of Excellence in Mathematics, Computer Scienceand ICT (CEA-MITIC)., ANR-16-CE40-0023,DESCARTES,Abstraction modulaire pour le calcul distribué(2016), and ANR-16-CE25-0009,ESTATE,Auto-stabilisation et amélioration de la sûreté dans les environnements distribués évoluant dans le temps(2016)

Subjects
Mobile agent, Ring (mathematics), Logarithm, Cactus graph, 0102 computer and information sciences, 02 engineering and technology, Binary logarithm, 01 natural sciences, Upper and lower bounds, Theoretical Computer Science, Vertex (geometry), Combinatorics, Connectivity over time, Computational Theory and Mathematics, 010201 computation theory & mathematics, Simple (abstract algebra), TheoryofComputation_ANALYSISOFALGORITHMSANDPROBLEMCOMPLEXITY, 0202 electrical engineering, electronic engineering, information engineering, 020201 artificial intelligence & image processing, Exploration, [INFO.INFO-DC]Computer Science [cs]/Distributed, Parallel, and Cluster Computing [cs.DC], Connectivity, Dynamic graphs, MathematicsofComputing_DISCRETEMATHEMATICS, Mathematics
Abstract

We study the problem of exploration by a mobile entity (agent) of a class of dynamic networks, namely constantly connected dynamic graphs. This problem has already been studied in the case where the agent knows the dynamics of the graph and the underlying graph is a ring of n vertices (Ilcinkas and Wade 2018). In this paper, we consider the same problem and we suppose that the underlying graph is a cactus graph (a connected graph in which any two simple cycles have at most one vertex in common). We propose an algorithm that allows the agent to explore these dynamic graphs in at most $O(n\frac {\log n}{\log \log n})$ time units. We show that the lower bound of the algorithm is ${\varOmega }(n\frac {\log n}{(\log \log n)^{2}})$ time units (for infinitely many n).

Published
2020

29. Exploration of carrier-based time-varying networks: The power of waiting

Author

David Ilcinkas, Ahmed Mouhamadou Wade, Laboratoire Bordelais de Recherche en Informatique (LaBRI), Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB), Laboratoire Traitement de l’Information et Systèmes Intelligents (LTISI), Ecole Polytechnique de Thiès, Ahmed Wade partially supported by the African Center of Excellence in Mathematics, Computer Science and ICT (CEA-MITIC)., ANR-16-CE40-0023,DESCARTES,Abstraction modulaire pour le calcul distribué(2016), and ANR-10-IDEX-0003,IDEX BORDEAUX,Initiative d'excellence de l'Université de Bordeaux(2010)

Subjects
Discrete mathematics, Mobile agent, Class (set theory), General Computer Science, Computer science, C-graph, Multiplicative function, Context (language use), 0102 computer and information sciences, 02 engineering and technology, 01 natural sciences, Graph, Theoretical Computer Science, Power (physics), Set (abstract data type), 010201 computation theory & mathematics, 0202 electrical engineering, electronic engineering, information engineering, 020201 artificial intelligence & image processing, Exploration, [INFO.INFO-DC]Computer Science [cs]/Distributed, Parallel, and Cluster Computing [cs.DC], Time complexity, Dynamic graphs
Abstract

We study the problem of exploration by a mobile entity (agent) of a class of highly dynamic networks, namely the carrier graphs (the C-graphs, modeling public transportation systems, among others). These are defined by a set of carriers following infinitely their prescribed route along the stations of the network. Flocchini, Mans, and Santoro [9] studied this problem in the case when the agent must always travel on the carriers and thus cannot wait on a station. They described the necessary and sufficient conditions for the problem to be solvable and proved that the optimal worst-case number of time units (and thus of moves) to explore a n-node C-graph of k carriers and maximal period p is in Θ ( k p 2 ) in the general case. In this paper, we study the impact of the ability to wait at the stations. We exhibit the necessary and sufficient conditions for the problem to be solvable in this context, and we prove that waiting at the stations allows the agent to reduce the optimal worst-case number of moves by a multiplicative factor of at least Θ ( p ) , while the worst-case time complexity is reduced to Θ ( n p ) . (In any connected carrier graph, we have n ≤ k p .) We also show some complementary optimal results in specific cases (same period for all carriers, highly connected C-graphs). Finally this new ability allows the agent to completely map the C-graph, in addition to just exploring it.

Published
2020

30. A Malaria Control Model using Mobility Data: An Early Explanation of Kedougou Case in Senegal

Author

Stéphane Gançarski, Lynda Bouzid Khiri, Idrissa Sarr, Ibrahima Gueye, Hubert Naacke, Bases de Données (BD), LIP6, Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Traitement de l’Information et Systèmes Intelligents (LTISI), Ecole Polytechnique de Thiès, and Cheikh Anta Diop University of Dakar

Subjects
FOS: Computer and information sciences, Estimation, Computer science, Process (engineering), Populations and Evolution (q-bio.PE), 1. No poverty, Systems and Control (eess.SY), medicine.disease, Electrical Engineering and Systems Science - Systems and Control, Outcome (game theory), Data science, 3. Good health, Computer Science - Computers and Society, FOS: Biological sciences, Computers and Society (cs.CY), Realm, FOS: Electrical engineering, electronic engineering, information engineering, medicine, Single person, [INFO]Computer Science [cs], Quantitative Biology - Populations and Evolution, Malaria control, Malaria, Block (data storage)
Abstract

International audience; Studies in malaria control cover many areas such as medicine, sociology, biology, mathematics, physics, computer science and so forth. Researches in the realm of mathematics are conducted to predict the occurrence of the disease and to support the eradication process. Basically, the modeling methodology is predominantly deterministic and based on differential equations which take into account important clinical and biological features. Yet, if the individual characteristics matter when modeling the disease, the overall estimation of the epidemic evolution relies on a non-specified percentage of the global population : it is not based on the state of health of each individual. The goal of this paper is to propose a model that relies on a daily evolution of the individual’s state, which depends on their mobility and the characteristics of the area they visit. Thus, the mobility data of a single person moving from one area to another, gathered thanks to mobile networks, is the essential building block to predict the disease outcome. We implement our solution and demonstrate its effectiveness through empirical experiments. The results show how promising the model is in providing possible insights into the failure of the disease control in the Kedougou region.

Published
2020

31. Intégration d'ontologies médicales : améloriation par association des maladies humaines à leurs plus pertinents signes caratéristiques

Author

Sow, Adama, Guissé, Abdoulaye, Niang, Oumar, Ranwez, Sylvie, Sylvie Ranwez, Ecole Inter-États des Sciences et Médecine Vétérinaires de Dakar (EISMV), Laboratoire Traitement de l’Information et Systèmes Intelligents (LTISI), Ecole Polytechnique de Thiès, Laboratoire d'Informatique de Paris-Nord (LIPN), Université Sorbonne Paris Cité (USPC)-Institut Galilée-Université Paris 13 (UP13)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Images, Signaux et Systèmes Intelligents (LISSI), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), and AFIA

Subjects
web de données, diagnostic médical, [INFO]Computer Science [cs], ontologies médicales, [INFO] Computer Science [cs], intégration d'ontologies, systèmes e-santé
Abstract

National audience; Guérir un patient malade nécessite un diagnostic médical avant de proposer un traitement ap-proprié. Avec l'explosion des connaissances médicales, nous nous intéressons à leur exploitation pour aider le médecin à collecter des informations et prendre des décisions lors du processus de diagnostic médical. Le présent article propose une ontologie à partir d'une intégration de plusieurs ontologies et terminologies médicales existantes et ouvertes. Nous constituons une nouvelle ontologie fédératrice couvrant toutes les maladies humaines en incluant des liens avec leurs signes caractéristiques pertinents. Pour prendre en compte cette association, l'ontologie produite est alimentée continuellement par apprentissage des signes à partir d'une base de cas réels de diagnostics cliniques confirmés et validés.

Published
2018

32. Experimental study of the freezing point of Al2O3/Water

Author

Maré, Thierry, Ousmane, Sow, Salma, Halelfadl, Lebourlout, Sylvain, Cong Tam, Nguyen, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, université de Moncton, université Moncton, département génie mécanique faculté ingénierie-département génie mécanique faculté ingénierie, Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], [PHYS.MECA.THER]Physics [physics]/Mechanics [physics]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2012

33. Experimental Study of the Freezing Point gamma-Al2O3/Water Nanofluid

Author

Salma Halelfadl, Sylvain Lebourlout, Ousmane Sow, Cong Tam Nguyen, Thierry Maré, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)

Subjects
Materials science, 020209 energy, Mechanical Engineering, Thermodynamics, 02 engineering and technology, [SPI.MECA]Engineering Sciences [physics]/Mechanics [physics.med-ph], 021001 nanoscience & nanotechnology, Freezing point, Colloid, [SPI.GCIV]Engineering Sciences [physics]/Civil Engineering, Nanofluid, Thermal, 0202 electrical engineering, electronic engineering, information engineering, 0210 nano-technology, Supercooling
Abstract

Nanofluids are colloidal suspensions made of nanometer-sized particles dispersed in a conventional fluid. Their unusual thermal properties explain intensive investigations for several thermal and industrial applications. In this work, an experimental investigation was performed to measure the freezing point and to study the supercooling point made of alumina γ-Al2O3 nanoparticles with 30 nm diameter size and deionized water. Particles' volume fraction used in this work is ranging from 1% to 4%. The T-historic method based on the measurement of the point of inflexion was performed to measure the thermal properties such as the freezing point and the latent heat of solidification of the nanofluids for different concentrations. The results show that the supercooling degree decreases for the high particles volume concentrations and that the agglomeration does not influence the temperature of the freezing point. However, it makes the freezing process longer.

Published
2012

34. Comparison of the thermal performances of two nanofluids at low temperature in a plate heat exchanger

Author

Frederic Bazantay, Thierry Maré, Salma Halelfadl, Steven Duret, Ousmane Sow, Patrice Estellé, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Pôle Cristal, Centre Technique Froid et Climatisation, Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), IUT de Saint Malo (IUT de Saint Malo), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), and Université de Rennes (UR)

Subjects
Materials science, Convective heat transfer, 020209 energy, General Chemical Engineering, Aerospace Engineering, Thermodynamics, 02 engineering and technology, Nanofluid, Physics::Fluid Dynamics, [SPI]Engineering Sciences [physics], Experimental, 0202 electrical engineering, electronic engineering, information engineering, Pressure drop, Fluid Flow and Transfer Processes, Exchanger of heat plates, Viscosity, Mechanical Engineering, Plate heat exchanger, Transfers of convective heat, 021001 nanoscience & nanotechnology, Thermal conduction, Nuclear Energy and Engineering, Heat transfer, Heat spreader, [PHYS.MECA.THER]Physics [physics]/Mechanics [physics]/Thermics [physics.class-ph], [SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], Nanoparticles, Plate fin heat exchanger, 0210 nano-technology
Abstract

International audience; The objective of this study is to compare experimentally the thermal performances of two types of commercial nanofluids. The first is composed of oxides of alumina (Al2O3) dispersed in water and the second one is aqueous suspensions of nanotubes of carbons (CNTs). The viscosity of the nanofluids is measured as a function of the temperature between 2 and 10°C. An experimental device, containing three thermal buckles controlled in temperature and greatly instrumented permits to study the thermal convective transfers. The evolution of the convective coefficient permits to study the convective thermal transfers. The evolution of the convective coefficient is presented according to the Reynolds number, at low temperature from 0 to 10°C and for the two aforementioned nanofluids. An assessment of the pressure drops in the circuit as well as of the powers of the circulator and outputs is dealt with.

Published
2011

35. Amélioration de l'efficacité énergétique d'un refroidisseur à partir de la granulométrie du bilan des débits d'air

Author

Samaké, Ousmane, Sow, Ousmane, Maré, Thierry, Diop, A., Sene, A., Diallo, O., Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], [PHYS.MECA.THER]Physics [physics]/Mechanics [physics]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2011

36. Modeling and simulation in dynamic mode of a triple effect desalination system coupled to a plane solar collector

Author

Jamel Orfi, Thierry Maré, Mamadou Adj, Ousmane Sow, Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)

Subjects
Engineering, 020209 energy, Ocean Engineering, 02 engineering and technology, 7. Clean energy, Desalination, Modeling and simulation, 020401 chemical engineering, Heat exchanger, 0202 electrical engineering, electronic engineering, information engineering, 0204 chemical engineering, Process engineering, ComputingMilieux_MISCELLANEOUS, Water Science and Technology, Computer simulation, business.industry, Environmental engineering, Solar energy, Pollution, 6. Clean water, Volumetric flow rate, Brine, [SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], [PHYS.MECA.THER]Physics [physics]/Mechanics [physics]/Thermics [physics.class-ph], business, Solar desalination
Abstract

In traditional solar desalination stills, operating by phase change, a profitability problem exists, because the quantity of produced fresh water is rather small (3 to 4 liters per day per square meter of collecting surface). This article gives an account, via numerical simulation, of the time evolution of the various parameters and variables characterizing a triple effect system functioning on solar energy. It also gives an idea of the evolution of produced fresh water, brine discharge, and feed flowrate, and thus highlights the improvement of the daily water production per square meter. This simulation also shows the influence of the presence of salt on the thermodynamic characteristics of salt water solutions. Finally, a system of regulation of feed flowrates makes it possible to control salinity and thus to avoid the filling of salt into components of the installation like heat exchangers. The modelling of the system presented in this study, is based on the conservation equations of mass and energy fo...

Published
2010

37. Estimation du retrait d'un sédiment fluvial - Influence d'un traitement à la chaux

Author

Fall, Magatte, Rangeard, Damien, Molez, Laurent, Jauberthie, Raoul, Garay, Dulce Izaskun, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Laboratoire de Matériaux, Mécanique et Hydraulque, Ecole Polytechnique de Thiès, MT Rhéo, Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Rennes 1 (UR1), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes)

Subjects
[SPI.GCIV]Engineering Sciences [physics]/Civil Engineering
Abstract

National audience; Ce travail s'intéresse à la caractérisation du retrait d'un sédiment fluvial. Plusieurs méthodes de mesure du retrait sont utilisées et comparées. Une méthode basée sur la mesure du retrait linéique horizontal par analyse d'image est proposée. Cette méthode est ensuite appliquée à la détermination du retrait linéique total et de la limite de retrait d'un sédiment fluvial. On met notamment en évidence l'influence de la matière organique, de la teneur en kaolin du matériau sur le retrait de celui-ci. Enfin, l'influence d'un ajout de chaux est étudiée. On montre notamment que celui-ci permet de réduire le retrait linéique total du matériau. ABSTRACT. This study deals with shrinkage measurement on dredged materials. Three methods of shrinkage measurement are tested. A method, based on the measurement of the horizontal linear shrinkage by image analysis is proposed. This method is applied on shrinkage characteristics determination of the sediment. The influence of a lime treatment and of the kaolin content is reported.

Published
2010

38. Etude expérimentale du point de congélation d’un nanofluide : eau AL2O3

Author

Maré, Thierry, Ousmane, Sow, Frederic, Bazantay, Lebourlout, Sylvain, Cong Tam, Nguyen, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Pôle Cristal, Centre Technique Froid et Climatisation, université de Moncton, université Moncton, département génie mécanique faculté ingénierie-département génie mécanique faculté ingénierie, Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2010

39. Etude expérimentale des performances thermiques d’un nanofluide : eau γAl2O3, cas d’un échangeur à plaques à basse température

Author

Maré, Thierry, Sow, Ousmane, Frederic, Bazantay, Lebourlout, Sylvain, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Pôle Cristal, Centre Technique Froid et Climatisation, Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2010

40. Contrôle des risques de colmatages par régulation sur les installations de dessalement à multiples effets

Author

M.T, Seck, Ousmane, Sow, Sawadogo, S., Maré, Thierry, Ndoye, B, Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2010

41. 'pour un développement durable': actes colloque CIFEM2010

Author

Maré, Thierry, Ousmane, Sow, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Thierry Maré Ousmane Sow, Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2010

42. Estimation de la production d’eau d’un distillateur Flash par utilisation de l’énergie d’une dalle exposée au rayonnement solaire

Author

Fall, S.M, Sow, Ousmane, Maré, Thierry, Sene, M, Adj, M., Ndoye, B, Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2010

43. Experimental and numerical study of mixed convection with reverse flow in coaxial double-duct heat exchanger

Author

Maré, Thierry, Galanis, Nicolas, ionut, voicu, Miriel, Jacques, Ousmane, Sow, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Université de Sherbrooke (UdeS), Laboratoire Matériaux Mécanique et Energétique (lmme), and Ecole Polytechnique de Thiès

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2008

44. Optimization of the number of effect in the desalination plants for multiple effects

Author

Ousmane, Sow, Maré, Thierry, Miriel, Jacques, mohamed, adj, c, tahya, Laboratoire Matériaux Mécanique et Energétique (lmme), Ecole Polytechnique de Thiès, Laboratoire de Génie Civil et Génie Mécanique (LGCGM), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)

Subjects
[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2008

45. Mathematical model of Ehrlichia chaffeensis transmission dynamics in dogs.

Author

Agusto FB, Djidjou-Demasse R, and Seydi O

Subjects
Animals, Dogs, Models, Biological, Ehrlichia chaffeensis, Ehrlichiosis epidemiology, Ehrlichiosis veterinary, Ticks, Tick-Borne Diseases
Abstract

Ehrlichia chaffeensis is a tick-borne disease transmitted by ticks to dogs. Few studies have mathematical modelled such tick-borne disease in dogs, and none have developed models that incorporate different ticks' developmental stages (discrete variable) as well as the duration of infection (continuous variable). In this study, we develop and analyze a model that considers these two structural variables using integrated semigroups theory. We address the well-posedness of the model and investigate the existence of steady states. The model exhibits a disease-free equilibrium and an endemic equilibrium. We calculate the reproduction number ( T 0 ). We establish a necessary and sufficient condition for the bifurcation of an endemic equilibrium. Specifically, we demonstrate that a bifurcation, either backward or forward, can occur at T 0 = 1 , leading to the existence, or not, of an endemic equilibrium even when T 0 < 1 . Finally, numerical simulations are employed to illustrate these theoretical findings.

Published
2023
Full Text
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46. A model of the 2014 ebola epidemic in west Africa with contact tracing.

Author

Webb G, Browne C, Huo X, Seydi O, Seydi M, and Magal P

Abstract

A differential equations model is developed for the 2014 Ebola epidemics in Sierra Leone and Liberia. The model describes the dynamic interactions of the susceptible and infected populations of these countries. The model incorporates the principle features of contact tracing, namely, the number of contacts per identified infectious case, the likelihood that a traced contact is infectious, and the efficiency of the contact tracing process. The model is first fitted to current cumulative reported case data in each country. The data fitted simulations are then projected forward in time, with varying parameter regimes corresponding to contact tracing efficiencies. These projections quantify the importance of the identification, isolation, and contact tracing processes for containment of the epidemics.

Published
2015
Full Text
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47. Partial differential equation-based approach for empirical mode decomposition: application on image analysis.

Author

Niang O, Thioune A, El Gueirea MC, Deléchelle E, and Lemoine J

Abstract

The major problem with the empirical mode decomposition (EMD) algorithm is its lack of a theoretical framework. So, it is difficult to characterize and evaluate this approach. In this paper, we propose, in the 2-D case, the use of an alternative implementation to the algorithmic definition of the so-called "sifting process" used in the original Huang's EMD method. This approach, especially based on partial differential equations (PDEs), was presented by Niang in previous works, in 2005 and 2007, and relies on a nonlinear diffusion-based filtering process to solve the mean envelope estimation problem. In the 1-D case, the efficiency of the PDE-based method, compared to the original EMD algorithmic version, was also illustrated in a recent paper. Recently, several 2-D extensions of the EMD method have been proposed. Despite some effort, 2-D versions for EMD appear poorly performing and are very time consuming. So in this paper, an extension to the 2-D space of the PDE-based approach is extensively described. This approach has been applied in cases of both signal and image decomposition. The obtained results confirm the usefulness of the new PDE-based sifting process for the decomposition of various kinds of data. Some results have been provided in the case of image decomposition. The effectiveness of the approach encourages its use in a number of signal and image applications such as denoising, detrending, or texture analysis.

Published
2012
Full Text
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