Urbanisation et viabilité de l’activité maraîchère : cas d’une ville à statut particulier au Bénin (Parakou)

Les villes des pays en développement sont en pleines mutations caractérisées par une augmentation de la taille de la population et une urbanisation. Ces deux facteurs les soumettent à deux défis majeurs. Le premier concerne l’approvisionnement des populations en produits alimentaires frais et le deuxième est relatif au problème foncier auquel font face ceux qui produisent ces produits alimentaires. Ce papier se consacre à l’étude des contraintes foncières auxquelles sont confrontés les maraichers urbains. La ville de Parakou, la troisième ville à statut particulier du Bénin, a entrepris ces dernières années une politique d’urbanisation pour répondre à la nécessité de trouver de l’espace pour loger les habitants et installer les infrastructures adéquates à son développement. Cela se traduit par l’occupation des espaces utilisés pour la production maraîchère installant de ce fait les acteurs de cette activité dans une insécurité foncière. L’objectif de l’étude est d’analyser les impacts du développement de la ville de Parakou sur les activités des maraichers. La démarche méthodologique utilisée, essentiellement qualitative, est basée sur un recensement des sites de production maraîchère de la ville et sur des entretiens avec les acteurs concernés par cette activité. Les résultats obtenus ont montré que sur les sept sites maraichers recensés dont un est en cours de fermeture, aucun n’offre une garantie d’investissements durables pour les maraichers car ils ne détiennent aucun titre de propriété sécurisée. Il apparaît aussi que dans la ville de Parakou, rien n’est fait pour faciliter le développement de la production maraîchère qui assure la sécurité alimentaire de sa population.The cities of developing countries are in complete mutation. This mutation is characterized by an increase of their population and urbanization. These two factors submit them to two major challenges. The first concerns how the populations can get supplies of trucks and the second is relative to the land problem to which urban market gardeners face. This paper studies the land pressure the urban market gardeners are confronted with. Parakou, the third Benin City with particular status, undertook these last years, an urbanization policy in order to find accommodations for the residents and to install adequate infrastructures for its development. The urbanization led to the occupation of the lands used for the market gardening for other purposes, putting the market gardeners in land insecurity. The objective of the study is to analyze the impacts of the urbanization of Parakou City on the market gardening. We used a qualitative methodology based on an inventory of market gardening sites in the city and on interviews with the actors concerned by this activity. One out of the seven recorded sites is under closure. None of them gave a guarantee to the market gardeners for undertaking sustainable investment because they don't have any secured property title. It appears also that, nothing is made to facilitate the development of market production that assures people food security in Parakou

Performance analysis of Hurst exponent estimators using surrogate-data and fractional lognormal noise models: Application to breathing signals from preterm infants

International audienceThe use of the Hurst exponent (H) to quantify the fractal characteristics of biological signals and its potential to detect abnormalities has aroused, recently, the interest of many researchers. Numerous techniques to estimate H are described in the literature, yet the choice of the most performing one is not straightforward. In this paper, we proposed some tests using artificial signals from experimental data and stochastic models to evaluate the robustness of three estimation techniques. Different surrogate-data tests, including a novel method to parametrize the degree of correlation in experimental signals with H (Hurst-adjusted surrogates), were first carried out. Then, simulated signals with prescribed H were obtained from fractional Gaussian noise modified properly to follow the lognormal laws observed in empirical data. The tests were applied to examine detrended fluctuation analysis (DFA), discrete wavelet transform and least squares based on standard deviation (LSSD) methods in the particular case of inter-breath interval signals from preterm infants. Simulations showed that none of the estimators were robust for every breathing pattern (regular, erratic and periodic) and should not be applied blindly without performing the preliminary tests proposed here. The LSSD technique was the most precise in general, but DFA was more robust with highly spiked patterns

Role of Permissive Neuraminidase Mutations in Influenza A/Brisbane/59/2007-like (H1N1) Viruses

Neuraminidase (NA) mutations conferring resistance to NA inhibitors were believed to compromise influenza virus fitness. Unexpectedly, an oseltamivir-resistant A/Brisbane/59/2007 (Bris07)-like H1N1 H275Y NA variant emerged in 2007 and completely replaced the wild-type (WT) strain in 2008–2009. The NA of such variant contained additional NA changes (R222Q, V234M and D344N) that potentially counteracted the detrimental effect of the H275Y mutation on viral fitness. Here, we rescued a recombinant Bris07-like WT virus and 4 NA mutants/revertants (H275Y, H275Y/Q222R, H275Y/M234V and H275Y/N344D) and characterized them in vitro and in ferrets. A fluorometric-based NA assay was used to determine Vmax and Km values. Replicative capacities were evaluated by yield assays in ST6Gal1-MDCK cells. Recombinant NA proteins were expressed in 293T cells and surface NA activity was determined. Infectivity and contact transmission experiments were evaluated for the WT, H275Y and H275Y/Q222R recombinants in ferrets. The H275Y mutation did not significantly alter Km and Vmax values compared to WT. The H275Y/N344D mutant had a reduced affinity (Km of 50 vs 12 µM) whereas the H275Y/M234V mutant had a reduced activity (22 vs 28 U/sec). In contrast, the H275Y/Q222R mutant showed a significant decrease of both affinity (40 µM) and activity (7 U/sec). The WT, H275Y, H275Y/M234V and H275Y/N344D recombinants had comparable replicative capacities contrasting with H275Y/Q222R mutant whose viral titers were significantly reduced. All studied mutations reduced the cell surface NA activity compared to WT with the maximum reduction being obtained for the H275Y/Q222R mutant. Comparable infectivity and transmissibility were seen between the WT and the H275Y mutant in ferrets whereas the H275Y/Q222R mutant was associated with significantly lower lung viral titers. In conclusion, the Q222R reversion mutation compromised Bris07-like H1N1 virus in vitro and in vivo. Thus, the R222Q NA mutation present in the WT virus may have facilitated the emergence of NAI-resistant Bris07 variants

An edge-on translucent dust disk around the nearest AGB star L2 Puppis - VLT/NACO spectro-imaging from 1.04 to 4.05 microns and VLTI interferometry

As the nearest known AGB star (d=64pc) and one of the brightest (mK-2), L2 Pup is a particularly interesting benchmark object to monitor the final stages of stellar evolution. We report new lucky imaging observations of this star with the VLT/NACO adaptive optics system in twelve narrow band filters covering the 1.0-4.0 microns wavelength range. These diffraction limited images reveal an extended circumstellar dust lane in front of the star, that exhibits a high opacity in the J band and becomes translucent in the H and K bands. In the L band, extended thermal emission from the dust is detected. We reproduce these observations using Monte-Carlo radiative transfer modeling of a dust disk with the RADMC-3D code. We also present new interferometric observations with the VLTI/VINCI and MIDI instruments. We measure in the K band an upper limit to the limb-darkened angular diameter of theta_LD = 17.9 +/- 1.6 mas, converting to a maximum linear radius of R = 123 +/- 14 Rsun. Considering the geometry of the extended K band emission in the NACO images, this upper limit is probably close to the actual angular diameter of the star. The position of L2 Pup in the Herzsprung-Russell diagram indicates that this star has a mass around 2 Msun and is probably experiencing an early stage of the asymptotic giant branch. We do not detect any stellar companion of L2 Pup in our adaptive optics and interferometric observations, and we attribute its apparent astrometric wobble in the Hipparcos data to variable lighting effects on its circumstellar material. We however do not exclude the presence of a binary companion, as the large loop structure extending to more than 10 AU to the North-East of the disk in our L band images may be the result of interaction between the stellar wind of L2 Pup and a hidden secondary object. The geometric configuration that we propose, with a large dust disk seen almost edge-on, appears particularly favorable to test and develop our understanding of the formation of bipolar nebulae.Comment: 16 pages, 15 figure

GAS FLOWS WITH HEAT TRANSFER IN MICRO CHANNELS: CLARIFICATIONS ABOUT THE NUSSELT NUMBER

International audienceThis paper deals with the modelling of weakly rarefied and dilute gas flows in heated micro channels by the continuum approach, valid for Knudsen numbers smaller than about 0.1. The first order slip and thermal jump model usually used for the forced convection of gas flows in long micro channels between two infinite plates is discussed. Indeed, in the huge literature related to this subject, it appears that simplified models are often used without justifying them and recurrent errors propagate from one paper to the other. The erroneous models particularly concern the heat transfer analysis and the energy equation. The compatibility of the pressure work and viscous dissipation in the energy equation with the power of the viscous forces at the walls and the choice of an appropriate Nusselt number are particularly discussed. Our aim is to provide a consistent model for gaseous micro-flows and the linked heat transfer. Then, a dimensional and asymptotic analysis is performed in the context of long micro channels. An analytical solution for the temperature field and the Nusselt number is proposed in the case of a compressible gas flow in a long micro-channel maintained at a constant wall temperature. This solution is compared with the numerical solution of the full model taking into account the first order slip and thermal jump conditions at the walls, the power of the viscous forces in the wall heat flux, the thermal creep term, the pressure work and the viscous dissipation in the bulk. The vanishing values of the Nusselt number measured in the experiments by Demsis et al. (2009, 2010) are explained for the first time

Improved detection of molecular markers of atherosclerotic plaques using sub-millimeter PET imaging

Since atherosclerotic plaques are small and sparse, their non-invasive detection via PET imaging requires both highly specific radiotracers as well as imaging systems with high sensitivity and resolution. This study aimed to assess the targeting and biodistribution of a novel fluorine-18 anti-VCAM-1 Nanobody (Nb), and to investigate whether sub-millimetre resolution PET imaging could improve detectability of plaques in mice. The anti-VCAM-1 Nb functionalised with the novel restrained complexing agent (RESCA) chelator was labelled with [F-18]AlF with a high radiochemical yield (>75%) and radiochemical purity (>99%). Subsequently, [F-18]AlF(RESCA)-cAbVCAM1-5 was injected in ApoE(-/-) mice, or co-injected with excess of unlabelled Nb (control group). Mice were imaged sequentially using a cross-over design on two different commercially available PET/CT systems and finally sacrificed for ex vivo analysis. Both the PET /CT images and ex vivo data showed specific uptake of [F-18]AlF(RESCA)-cAbVCAM1-5 in atherosclerotic lesions. Non-specific bone uptake was also noticeable, most probably due to in vivo defluorination. Image analysis yielded higher target-to-heart and target-to-brain ratios with the beta-CUBE (MOLECUBES) PET scanner, demonstrating that preclinical detection of atherosclerotic lesions could be improved using the latest PET technology

Unsupervised Performance Analysis of 3D Face Alignment

We address the problem of analyzing the performance of 3D face alignment (3DFA) algorithms. Traditionally, performance analysis relies on carefully annotated datasets. Here, these annotations correspond to the 3D coordinates of a set of pre-defined facial landmarks. However, this annotation process, be it manual or automatic, is rarely error-free, which strongly biases the analysis. In contrast, we propose a fully unsupervised methodology based on robust statistics and a parametric confidence test. We revisit the problem of robust estimation of the rigid transformation between two point sets and we describe two algorithms, one based on a mixture between a Gaussian and a uniform distribution, and another one based on the generalized Student's t-distribution. We show that these methods are robust to up to 50% outliers, which makes them suitable for mapping a face, from an unknown pose to a frontal pose, in the presence of facial expressions and occlusions. Using these methods in conjunction with large datasets of face images, we build a statistical frontal facial model and an associated parametric confidence metric, eventually used for performance analysis. We empirically show that the proposed pipeline is neither method-biased nor data-biased, and that it can be used to assess both the performance of 3DFA algorithms and the accuracy of annotations of face datasets

La complexité attributionnelle aspects théoriques, instrument de mesure et études exploratoires /

Également disponible en version papierTitre de l'écran-titre (visionné le 10 fév. 2010)Bibliogr.: p. 68-6