URBAN AND PERI URBAN HORTICULTURE AND THE CAPABILITY APPROACH THE CASE OF THE SOUTH-WEST PROVINCE OF CAMEROON

N° ISBN - 978-2-7380-1284-5International audienceThis paper uses the capability approach to analyse the impact of urban and peri urban horticulture on development in Africa. Is horticulture, considered as an innovation, able to improve the capabilities of people? This paper states that it is not the practice of horticulture which increases the capabilities of farmers but the level of capabilities that increases the chances of adopting horticulture. In order to answer the above question we have attempted to understand the context in which the agricultural sector and the farmers evolve in Africa, characterized by the urban transition towards a majority of urban population and the rise of nonfarm incomes. It appeared important to understand the underlying prerequisites for horticultural practices, that is, expensive agrochemical inputs and credit requirements

Les transformations de la végétation du bassin parisien par la modélisation des données polliniques holocènes

International audienceLa synthèse palynologique du Bassin parisien repose sur un corpus de 91 séquences de fonds de vallées qui résume l’histoire de la végétation holocène régionale. Parmi elles, 22 ont été utilisées pour reconstruire quantitativement le couvert végétal, en utilisant un nouveau modèle de reconstitution des paysages, REVEALS. Il corrige la relation non linéaire entre pollen et végétation et permet ainsi de convertir les assemblages polliniques en surfaces de couverture relatives aux différents taxons végétaux. Les dynamiques de ces plantes, ou groupes de plantes, reconstituent alors l’évolution de la structure des paysages du Bassin parisien durant l’Holocène

Magnetoconvection transient dynamics by numerical simulation

We investigate the transient and stationary buoyant motion of the Rayleigh-Bénard instability when the fluid layer is subjected to a vertical, steady magnetic field. For Rayleigh number, Ra, in the range 10^3-10^6, and Hartmann number, Ha, between 0 and 100, we performed three-dimensional direct numerical simulations. To predict the growth rate and the wavelength of the initial regime observed with the numerical simulations, we developed the linear stability analysis beyond marginal stability for this problem. We analyzed the pattern of the flow from linear to nonlinear regime. We observe the evolution of steady state patterns depending on Ra/Ha2 and Ha. In addition, in the nonlinear regime, the averaged kinetic energy is found to depend on Ra and to be independent of Ha in the studied range

Destabilization of a liquid metal by nonuniform Joule heating

We study the effect of an impressing AC magnetic field at the bottom of a liquid metal layer of thickness h. In this situation the fluid is set in motion by the buoyancy forces caused by internal heat sources. The heat sources, caused by the Joule effect induced by the AC field, present an exponentially decaying profile, with characteristic length δ. As the magnetic field is horizontal, the Lorentz force has no influence on the dynamics of the system since it contributes only to the magnetic pressure. We propose an analysis of both the transient and fully developed regimes using linear stability analysis (LSA) and direct numerical simulations (DNSs). The transient period is governed by the temporal evolution of the temperature field as well as the development of the convective instability, which can be concomitant and therefore requires adopting a transient LSA algorithm to track these two effects. The DNSs have been performed for various distributions of the heat sources and various total heat input. This corresponds to independently varying δ/h in the range 0.04≤δ/h≤0.45 and a Rayleigh number 1.1×104≤Ra≤1.2×105. We observe the relaxation of the temperature up to the steady conductive profile before the transition to the nonlinear regime when Ra is small, whereas for larger Ra, nonlinear effects appear during the relaxation of the temperature profile. The unsteadiness of the temperature field significantly alters the development of the instability because of a much smaller growth rate. Surprisingly, we observe that δ/h has only a limited influence on averaged quantities as well as on the patterns for both the linear and nonlinear regimes. This comes with the fact that the profiles present an apparent reflectional symmetry, despite the asymmetry of the governing equations

Magnetic field effects on liquid metal free convection

International audienceWe provide a numerical analysis of three-dimensional free convection of a liquid in a Rayleigh-Bénard configuration,subject to a steady and uniform magnetic field, using the finite volume code Jadim. The influence of the Hartmann andRayleigh numbers are studied. We compare our results to several experimental works. As suggested by previousexperiments, the magnetic field tends to lower the heat transfer at the walls. This is caused by a significant alteration ofthe flow structures, due to the Lorentz force. For slightly overcritical Rayleigh numbers, two-dimensional rolls appearbut the flow structure rapidly becomes three-dimensional as we increase the Rayleigh number. The magnetic field tendsto destroy those structures and the transition to a 3D flow is delayed to higher values of the Rayleigh number, when theHartmann number is increased. We show that the averaged heat transfer at the walls decreases, although it remains ofthe same order of magnitude. However the local structure of heat transfer is altered

Instabilité de Rayleigh-Bénard sous champ magnétique : structures et transfert de chaleur

Nous étudions l’influence d’un champ magnétique constant et vertical sur les structures de l’instabilité de Rayleigh-Bénard, ainsi que son effet sur les transferts de chaleur en paroi. Proche de la stabilité marginale, l’écoulement développe des structures fines qui s’élargissent lorsqu’on s’éloigne de cette stabilité marginale. Localement, le transfert de chaleur est modifié, les zones de fort transfertcorrespondant aux zones où la vitesse dirigée selon la normale sortante de la paroi est importante. Le transfert global est légèrement diminué par rapport au cas non magnétique

Ecuador Paraiso Escondido virus, a new flavivirus isolated from New World sand flies in Ecuador, is the first representative of a novel clade in the genus flavivirus

A new flavivirus, Ecuador Paraiso Escondido virus (EPEV), named after the village where it was discovered, was isolated from sand flies (Psathyromyia abonnenci, formerly Lutzomyia abonnenci) that are unique to the New World. This represents the first sand fly-borne flavivirus identified in the New World. EPEV exhibited a typical flavivirus genome organization. Nevertheless, the maximum pairwise amino acid sequence identity with currently recognized flaviviruses was 52.8%. Phylogenetic analysis of the complete coding sequence showed that EPEV represents a distinct clade which diverged from a lineage that was ancestral to the nonvectored flaviviruses Entebbe bat virus, Yokose virus, and Sokoluk virus and also the Aedes-associated mosquito-borne flaviviruses, which include yellow fever virus, Sepik virus, Saboya virus, and others. EPEV replicated in C6/36 mosquito cells, yielding high infectious titers, but failed to reproduce either in vertebrate cell lines (Vero, BHK, SW13, and XTC cells) or in suckling mouse brains. This surprising result, which appears to eliminate an association with vertebrate hosts in the life cycle of EPEV, is discussed in the context of the evolutionary origins of EPEV in the New World.The flaviviruses are rarely (if ever) vectored by sand fly species, at least in the Old World. We have identified the first representative of a sand fly-associated flavivirus, Ecuador Paraiso Escondido virus (EPEV), in the New World. EPEV constitutes a novel clade according to current knowledge of the flaviviruses. Phylogenetic analysis of the virus genome showed that EPEV roots the Aedes-associated mosquito-borne flaviviruses, including yellow fever virus. In light of this new discovery, the New World origin of EPEV is discussed together with that of the other flaviviruses