Évaluation des coûts de la dégradation des sols agricoles par l’érosion hydrique: Cas du Bassin versant "Tleta"

This paper proposes an appraisal of costs produced by water erosion within arable lands strongly exposed to erosion in the catchment area of Tleta, located in the Rif, in the north of Morocco. Adopted methodology is inventive as allows to distinguish the costs according to three severity levels of erosion while taking into account the compensatory contributions, often invisible, of adaptation measures implemented by farmers. The differences between the gross margins obtained in three zones, classified according to the intensity of erosion, are compared two to two. The ensuing losses of benefit for each degree of severity of water erosion are deduced from the discrepancies observed in relation to the slightly degraded zone. The opportunity costs of outstanding lab or resulting from the community mutual aid, identified as a current practice in the basin studied to mitigate the damage of erosion, are also estimated in each zone. The estimates obtained are extrapolated to the whole cereal area of the basin to determine the total cost engendered by water erosion. Key-words: Economic appraisal, degradation costs, water erosion, benefits loss, soil conservation, erosion cost, Rif, Morocco  Le présent article propose une évaluation des coûts produits par l’érosion hydrique au sein des terres agricoles fortement exposées à l’érosion dans le bassin versant Tleta situé dans le Rif, au nord du Maroc. La méthodologie adoptée est originale et permet de distinguer les coûts en fonction de trois niveaux de sévérité de l'érosion tout en prenant en compte les apports compensatoires, souvent invisibles, des mesures d'adaptation mises en œuvre par les agriculteurs. Les écarts entre les marges brutes obtenues dans trois zones, classées selon l'intensité de l'érosion, sont comparés deux à deux. Les pertes de bénéfices conséquentes à chaque degré de sévérité de l'érosion hydrique sont déduites des écarts observés par rapport à la zone faiblement dégradée. Les coûts d'opportunité du travail non rémunéré issu de l'entraide villageoise, identifiée comme pratique courante au niveau du bassin étudié pour pallier les dégâts de l'érosion, sont également estimés dans chacune des zones. Les estimations obtenues sont extrapolées à l'ensemble de la sole céréalière du bassin versant pour estimer le coût total produit par l'érosion hydrique. Mots clés : Évaluation économique, coûts de la dégradation, érosion hydrique, perte de bénéfices, conservation des sols, coûts de l'érosion, Rif, Maro

Islamisme, messianisme et utopie au Maghreb / Islamism, Messianism and utopia in Maghreb

Chekroun Mohamed. Islamisme, messianisme et utopie au Maghreb / Islamism, Messianism and utopia in Maghreb. In: Archives de sciences sociales des religions, n°75, 1991. pp. 127-150

Age-structured and delay differential-difference model of hematopoietic stem cell dynamics

International audienceIn this paper, we investigate a mathematical model of hematopoi-etic stem cell dynamics. We take two cell populations into account, quiescent and proliferating one, and we note the difference between dividing cells that enter directly to the quiescent phase and dividing cells that return to the proliferating phase to divide again. The resulting mathematical model is a system of two age-structured partial differential equations. By integrating this system over age and using the characteristics method, we reduce it to a delay differential-difference system, and we investigate the existence and stability of the steady states. We give sufficient conditions for boundedness and unbound-edness properties for the solutions of this system. By constructing a Lyapunov function, the trivial steady state, describing cell's dying out, is proven to be globally asymptotically stable when it is the only equilibrium. The stability analysis of the unique positive steady state, the most biologically meaningful one, and the existence of a Hopf bifurcation allow the determination of a stability area, which is related to a delay-dependent characteristic equation. Numerical simulations illustrate our results on the asymptotic behavior of the steady states and show very rich dynamics of this model. This study may be helpful in understanding the uncontrolled proliferation of blood cells in some hematological disorders

Équations différentielles et aux différences à retard pour des modèles dedynamique des cellules souches hématopoïétiques

International audienceAll functionally blood cells are generated in the bone marrow through hematopoiesis from a small population of cells called hematopoietic stem cells (HSCs). HSCs have the capacity to self-renew and also the capacity to differentiate into any types of blood cells. We consider a system of two age-structured partial differential equations, describing the evolution of HSC population. By integrating this system over the age and using the characteristics method, we reduce it to a system composed with a differential equation and a delay difference equation. We investigate the asymptotic stability of steady states and the existence of a Hopf bifurcation. We conclude our work by numerical simulations. Résumé ´ Equations différentielles et aux différences a retard pour des mod eles de dynamique des cel-lules souches hématopo¨étiques. Toutes les cellules sanguines sont produites dans la moelle osseuse lors de l' hématopo¨ esè a partir d'une petite population de cellules appelées cellules souches hématopo¨étiques (CSHs). Les CSHs ont la capacité de s'auto-renouveler et egalement de se différencier en tous types de cellules sanguines. Le syt eme mathématique que nous considérons pour modéliser ces populations de CSHs est un syst eme de deux equations aux dérivées partielles structurées en age. Par intégration suivant les caractéristiques , le mod ele est réduit a un syst eme composé d'uné equation différentielle et d'uné equation aux différences a retard. Nous etudions le comportement asymptotique des etats d'´ equilibre et l'existence d'une bifurcation de Hopf. Nous concluons notre travail par des simulations numériques .Toutes les cellules sanguines sont produites dans la moelle osseuse lors de l’hématopoïèse à partir d’une petite population de cellules appelées cellules souches hématopoïétiques (CSHs). Les CSHs ont la capacité de s’auto-renouveler et également de se différencier en tous types de cellules sanguines. Le sytème mathématique que nous considérons pour modéliser ces populations de CSHs est un système de deux équations aux dérivées partielles structurées en âge. Par intégration suivant les caractéristiques, le modèle est réduit à un système composé d’une équation différentielle et d’une équation aux différences à retard. Nous étudions le comportement asymptotique des états d’équilibre et l’existence d’une bifurcation de Hopf. Nous concluons notre travail par des simulations numériques

Global asymptotic stability for an age-structured model of hematopoietic stem cell dynamics

International audienceWe investigate a system of two nonlinear age-structured partial differential equations describing the dynamics of proliferating and quiescent hematopoietic stem cell populations. The method of characteristics reduces the age-structured model to a system of coupled delay differential and renewal difference equations with continuous time and distributed delay. By constructing a Lyapunov-Krasovskii functional, we give a necessary and sufficient condition for the global asymptotic stability of the trivial steady state, which describes the population dying out. We also give sufficient conditions for the existence of unbounded solutions, which describes the uncontrolled proliferation of hematopoietic stem cell population. This study may be helpful in understanding the behavior of hematopoietic cells in some hematological disorders

Mathematical analysis and global dynamics for a time-delayed Chronic Myeloid Leukemia model with treatment

In this paper, we investigate a time-delayed model describing the dynamics of the hematopoietic stem cell population with treatment. First, we give some property results of the solutions. Second, we analyze the asymptotic behavior of the model, and study the local asymptotic stability of each equilibrium: trivial and positive ones. Next, a necessary and sufficient condition is given for the trivial steady state to be globally asymptotically stable. Moreover, the uniform persistence is obtained in the case of instability. Finally, we prove that this system can exhibits a periodic solutions around the positive equilibrium through a Hopf bifurcation

FEM Prediction of Temperature and Residual Stresses Distribution During Friction Stir Welding of 2017A Aluminum Alloy

International audienceThe structures integrities containing welds are evaluated using numerical methods to characterize the residual stresses field induced during welding. These methods are mainly based on coupled thermal and mechanical analysis using the finite element method. The present paper deals with the case study of a straight welding of two plates in 2017A aircraft aluminum alloy

Numerical Simulation of Temperature Distribution and Material Flow During Friction Stir Welding 2017A Aluminum Alloys

This study describes the use of fluid dynamic code, FLUENT to model the flow of metal in the AA2017A case around the welding tool pin (FSW). A standard threaded tool profile is used for the analysis of phenomena during welding such as heat generation and flow of the material are included. The main objective is to gain a better understanding of the flow of material around a tool. The model showed a large number of phenomena similar to those of the real process. The model has also generated a sufficient amount of heat, which leads to a good estimate of the junction temperature. These results were obtained using a viscosity which is near the solidus softening