Le financement de l'agriculture au Nord Cameroun : rapport de mission (Garoua du 1 - 9 mai 1999)

La mission d'appui à l'équipe CIRAD basée à Garoua avait pour objectifs : - 1. la mise en place d'un stage de DEA sur la problématique du financement de l'agriculture dans le Nord du Cameroun. Ce stage devrait permettre de former une économiste camerounaise sur la question, d'élargir le champ d'investigation du PRASAC et de l'IRAD aux disciplines de la socio-économie, et de renforcer les liens de collaboration entre le CIRAD, les organismes de recherche nationaux et l'Université de Ngaoundéré, - 2. la révision du projet d'ATP sur la traction animale, - 3. le démarrage d'une animation scientifique au sein du PRASAC sur le thème du financement de l'agriculture. (Résumé d'auteur

Analytic inversion of a Radon transform on double circular arcs with applications in Compton Scattering Tomography

In this work we introduce a new Radon transform which arises from a new modality of Compton Scattering Tomography (CST). This new system is made of a single detector rotating around a fixed source. Unlike some previous CST, no collimator is used at the detector. Such a system allows us to collect scattered photons coming from two opposite sides of the source-detector segment, hence the manifold of the associated Radon transform is a family of double circular arcs. As first main theoretical result, an analytic inversion formula is established for this new Radon transform. This is achieved through the formulation of the transform in terms of circular harmonic expansion satisfying the consistency conditions in Cormack's sense. Moreover, a fast and efficient numerical implementation via an alternative formulation based on Hilbert transform is carried out. Simulation results illustrate the theoretical feasibility of the new system. From a practical point of view, an uncollimated detector system considerably increases the amount of collected data, which is particularly significant in a scatter imaging system.Comment: 14 pages, 5 figure

Strategic outsourcing and precision agriculture: towards a silent reorganization of agricultural production in France ?

In France as in other European countries, farm outsourcing has been developing for the past twenty years. Today, this phenomenon concerns both small and large farms. What is surprising is the growing number of farmers who outsource precision farming operations that involve sophisticated technologies and specialized expertise. This stylized fact is rather counter-intuitive to the known result of transaction cost theory, according to which in the presence of specific assets, ownership prevails over outsourcing. The objective of our study is to analyze the determinants of these new agricultural outsourcing practices associated with precision agriculture. We start with the transaction costs and property rights frameworks, then discuss recent theoretical contributions of relational contracts to explain the possibility of outsourcing in the presence of high asset specificity. Empirical evidences are provided for France using a mixed research methodology. Based on original data from surveys of 1200 farmers and of 20 of medium and large custom operators, our methodology combines an estimation of discrete choice models of outsourcing for different levels of asset specificity and case studies of major farm outsourcing organizational schemes. Our results show that in the presence of high specific assets, outsourcing can be preferred to ownership for strategic reasons. This phenomenon is counter-intuitive from the point of view of transaction cost theory, but is possible when one considers possible ex-ante incentive mechanisms (expectation of specialization gains, inclusion of a bonus based on the value of the output in the formal contract, participation of a third party), and informal incentive mechanisms built through repeated interactions

Renal dysfunction independently predicts muscle mass loss in patients following liver transplantation

Liver transplantation (LT) is the only curative treatment for cirrhosis. However, the presence of complications can impact outcomes following LT. Sarcopenia, or muscle mass loss, is highly prevalent in patients with cirrhosis and is associated with longer hospitalization stays and a higher infection rate post-surgery. We aimed to identify patients at higher risk of early sarcopenia post-LT. METHODS: This retrospective study included 79 cirrhotic patients who underwent LT. Muscle mass was evaluated using the third lumbar spine vertebra skeletal muscle mass index (SMI) and sarcopenia was defined using established cut-off values. Computerized tomography (CT) scans performed within six-month peri-operative period (three months pre- and post-LT) were included in the study. Complications and comorbidities were collected and correlated to SMI post-LT and predictive models for SMI post-LT were constructed. RESULTS: The overall prevalence of sarcopenia was 46% and 62% before and after LT, respectively. Newly developed sarcopenia was found in 42% of patients. Post-LT sarcopenia was associated with longer hospital stays (54±37 vs 29±10 days, p = 0.002), higher number of infection (3±1 vs 1±2, p = 0.027), and greater number of complications (5±2 vs 3±2, p <0.001) compared to absence of sarcopenia. Multivariate analyses showed that the SMI post-LT was independently associated with pre-LT renal function markers, the glomerular filtration rate (GFR) and creatinine (Model 1, GFR: β = 0.33; 95% CI = 0.04–0.17; p = 0.003; Model 2, Creatinine: β = –0.29; 95% CI = –0.10 to –0.02; p = 0.009). CONCLUSIONS: The present study highlights the potential role of renal dysfunction in the development and persistence of sarcopenia after LT

Receptor binding and degradation of urokinase-type plasminogen activator by human mesangial cells

Receptor binding and degradation of urokinase-type plasminogen activator by human mesangial cells. The binding of [125I] labeled urokinase-type plasminogen activator (u-PA) was studied on human mesangial cells (MC) in culture. The binding of active [125I]u-PA at 37°C reached a plateau after 30 minutes of incubation and remained stable for at least four hours. When the supernatant was analyzed with trichloracetic acid (TCA), TCA soluble radioactive material could be detected after a lag phase of 30 minutes, and then increased linearly for four hours. Analysis by electrophoresis on SDS PAGE and autoradiography of the cell associated radioactivity and of the intracellular content showed that active u-PA and u-PA complexed to plasminogen activator inhibitor type-1 (PAI-1) were bound to the cell surface, but only u-PA/PAI-1 complexes were internalized and degraded. Therefore, the Kd and the number of binding sites were determined by competitive inhibition curves at 4°C using diisopropyl-fluorophosphate (DFP) u-PA. Scatchard plots showed a Kd = 400 ± 30 pM, and Bmax = 240,000 ± 25,000 sites/cell. Excess of the amino terminal fragment of u-PA (ATF) completely blocked the specific binding of [125I]u-PA, confirming that the binding of u-PA was independent of the presence of the active site and/or of the formation of complexes with PAI-1. 3H thymidine incorporation by mesangial cells after stimulation with 100nM active u-PA showed that u-PA had a moderate but significant mitogenic effect, in contrast to inactive u-PA and ATF. However, this mitogenic effect was not accompanied by a proliferative effect. Pretreatment of mesangial cell with a phosphoinositol-specific phospholipase C decreased the binding of [125I]u-PA by 60%, indicating that the majority of the u-PA receptor is anchored in the membrane by a phosphatidylinositol group. These results, together with a positive labeling of MC with monoclonal antibodies to the receptor of U937 cells, and the positive RNA hybridization with the cDNA probe for the human receptor cloned from U937 cells, indicate that the u-PA receptor on mesangial cells is identical to the one of U937 cells. In conclusion, human mesangial cells in culture express a specific receptor for u-PA, which could play a major role in the regulation of u-PA activity by degrading u-PA complexed to PAI-1

Daytime Sleep Enhances Consolidation of the Spatial but Not Motoric Representation of Motor Sequence Memory

Motor sequence learning is known to rely on more than a single process. As the skill develops with practice, two different representations of the sequence are formed: a goal representation built under spatial allocentric coordinates and a movement representation mediated through egocentric motor coordinates. This study aimed to explore the influence of daytime sleep (nap) on consolidation of these two representations. Through the manipulation of an explicit finger sequence learning task and a transfer protocol, we show that both allocentric (spatial) and egocentric (motor) representations of the sequence can be isolated after initial training. Our results also demonstrate that nap favors the emergence of offline gains in performance for the allocentric, but not the egocentric representation, even after accounting for fatigue effects. Furthermore, sleep-dependent gains in performance observed for the allocentric representation are correlated with spindle density during non-rapid eye movement (NREM) sleep of the post-training nap. In contrast, performance on the egocentric representation is only maintained, but not improved, regardless of the sleep/wake condition. These results suggest that motor sequence memory acquisition and consolidation involve distinct mechanisms that rely on sleep (and specifically, spindle) or simple passage of time, depending respectively on whether the sequence is performed under allocentric or egocentric coordinates

Pratiques agricoles pour la réduction des produits phytosanitaires. le rôle de l’apprentissage collectif

En partant d’une expérience multi-partenariale originale de MAET-DCE portée par une coopérative, ce travail se propose d’analyser le rôle de l’apprentissage collectif sur la réduction des risques liés à l’adoption de pratiques agricoles alternatives. Le processus de transmission de l’information technique ainsi que les formes de coordination associées ont été analysés en mobilisant des approches principalement de l’économie institutionnelle traitant de l’incertitude et des modalités actuelles du conseil en agriculture. L’analyse montre que l’action de la coopérative est au centre de la création conjointe de plusieurs catégories de biens, reposant sur différents types de transaction informationnelle.Based on an original multi-partnership experience of agri-environmental measure (MAET-DCE) carried by a cooperative, this study aims to analyse the role of collective learning on the reduction of risks associated with the adoption of alternative agricultural practices. The process of transmission of technical information and the associated forms of coordination have been analysed using a conceptual framework inspired by works done in institutional economics on uncertainty and extension service in agriculture. The analysis shows that the cooperative is at the center of the joint production of different categories of goods, based on different types of informational transactions

Rational design of an estrogen receptor mutant with altered DNA-binding specificity

Although artificial C2-H2 zinc fingers can be designed to recognize specific DNA sequences, it remains unclear to which extent nuclear receptor C4 zinc fingers can be tailored to bind novel DNA elements. Steroid receptors bind as dimers to palindromic response elements differing in the two central base pairs of repeated motifs. Predictions based on one amino acid—one base-pair relationships may not apply to estrogen receptors (ERs), which recognize the two central base pairs of estrogen response elements (EREs) via two charged amino acids, each contacting two bases on opposite DNA strands. Mutagenesis of these residues, E203 and K210 in ERα, indicated that both contribute to ERE binding. Removal of the electric charge and steric constraints associated with K210 was required for full loss of parental DNA-binding specificity and recognition of novel sequences by E203 mutants. Although some of the new binding profiles did not match predictions, the double mutation E203R-K210A generated as predicted a mutant ER that was transcriptionally active on palindromes of PuGCTCA motifs, but not on consensus EREs. This study demonstrates the feasibility of designing C4 zinc finger mutants with novel DNA-binding specificity, but also uncovers limitations of this approach