Conséquences pour le secteur agricole français de diverses options en matière de réforme de la Politique Agricole Commune

Etudes et recherches ; 12Trois volets composent cette étude. Le premier consiste en la mesure de la variabilité des charges variables, des marges et des revenus bruts par culture dans la population agricole de différentes régions françaises ou de différents pays de la CEE. Cette variabilité doit être mesurée non sur la seule espérance mathématique (la "moyenne") mais aussi sur la variance. L'idée sous-jacente est que la prise en compte de cette variabilité devrait permettre de mieux cerner les effets d'une réforme de la PAC donnant un rôle important à des seuils déterminés à partir de critères moyens (les rendements des cultures par exemple). Les modèles à coefficients aléatoires mis en œuvre donnent des résultats peu satisfaisants. Le second volet porte sur l'incidence effective des mesures réformant la PAC sur le secteur de production végétale. Le modèle AROPAJ qui repose sur un système d'offre multiproducteur (38 groupes de producteurs) et multiproduit (les principales cultures de vente, les fourrages et prairies, l'auto-consommation de céréales pour l'alimentation animale) est utilisé à cet effet. Nous restons ici dans le cas où les groupes sont différenciés selon leurs caractéristiques moyennes, chaque groupe étant supposé homogène. Différents scénarios sont simulés et analysés dans une optique de court terme. Ce sont d'une part une extrapolation des mesures actuelles (baisse des prix, aide au retrait des terres), et d'autre part une mise en oeuvre des mesures "Mac Sharry". Cette partie est complétée par un volet "environnement" (impact d'une taxation des engrais). Sont en particulier présentés les effets de ces mesures sur les offres et surfaces de différents produits, la marge brute agricole et le budget hors restitution du FEOGA. Le dernier volet s'attache particulièrement à représenter des échanges intracommunautaires d'une part, entre membres de la CEE et pays tiers d'autre part en réaction aux mesures affectant les prix et les niveaux de production. Ces effets sont mesurés à l'aide de modèles économétriques d'exportation prenant en compte un effet de report entre marché communautaire et marché avec les pays tiers, ceci pour chacun des principaux pays exportateurs de la CEE, et pour chacune des trois céréales principales : le blé tendre, le maïs et l'orge. Sur les deux derniers volets de l'étude, il apparaît que les mesures Mac Sharry se traduisent pas un transfert monétaire important au sein des groupes de producteurs (des producteurs de grande culture vers les éleveurs), et des consommateurs vers le contribuable. Le surplus collectif augmenterait faiblement (si l'on considère un coût public nul pour la dépense budgétaire) au prix d'un accroissement sensible du budget du FEOGA hors restitution. L'effet sur les restitutions qui permettrait ce gain collectif serait toutefois limité

Relationship between dynamical heterogeneities and stretched exponential relaxation

We identify the dynamical heterogeneities as an essential prerequisite for stretched exponential relaxation in dynamically frustrated systems. This heterogeneity takes the form of ordered domains of finite but diverging lifetime for particles in atomic or molecular systems, or spin states in magnetic materials. At the onset of the dynamical heterogeneity, the distribution of time intervals spent in such domains or traps becomes stretched exponential at long time. We rigorously show that once this is the case, the autocorrelation function of the renewal process formed by these time intervals is also stretched exponential at long time.Comment: 8 pages, 4 figures, submitted to PR

Testing interactive effects of global environmental changes on soil nitrogen cycling

Responses of soil nitrogen (N) cycling to simultaneous and potentially interacting global environmental changes are uncertain. Here, we investigated the combined effects of elevated CO2, warming, increased precipitation and enhanced N supply on soil N cycling in an annual grassland ecosystem as part of the Jasper Ridge Global Change Experiment (CA, USA). This field experiment included four treatments-CO2, temperature, precipitation, nitrogen-with two levels per treatment (ambient and elevated), and all their factorial combinations replicated six times. We collected soil samples after 7 and 8 years of treatments, and measured gross rates of N mineralization, N immobilization and nitrification, along with potential rates of ammonia oxidation, nitrite oxidation and denitrification. We also determined the main drivers of these microbial activities (soil ammonium and nitrate concentrations, soil moisture, soil temperature, soil pH, and soil CO2 efflux, as an indicator of soil heterotrophic activity). We found that gross N mineralization responded to the interactive effects of the CO2, precipitation and N treatments: N addition increased gross N mineralization when CO2 and precipitation were either both at ambient or both at elevated levels. However, we found limited evidence for interactions among elevated CO2, warming, increased precipitation, and enhanced N supply on the other N cycling processes examined: statistically significant interactions, when found, tended not to persist across multiple dates. Soil N cycling responded mainly to single-factor effects: long-term N addition increased gross N immobilization, potential ammonia oxidation and potential denitrification, while increased precipitation depressed potential nitrite oxidation and increased potential ammonia oxidation and potential denitrification. In contrast, elevated CO2 and modest warming did not significantly affect any of these microbial N transformations. These findings suggest that global change effects on soil N cycling are primarily additive, and therefore generally predictable from single factor studies

Fatty Acid Methyl Esters as Biosolvents of Epoxy Resins: A Physicochemical Study

The C8 to C18 fatty acid methyl esters (FAME) have been compared as solvents for two epoxy resin pre-polymers, bisphenol A diglycidyl ether (DGEBA) and triglycidyl paminophenol ether (TGPA). It was found that the solubilization limits vary according to the ester and that methyl caprylate is the best solvent of both resins. To explain these solubility performances, physical and chemical properties of FAME were studied, such as the Hansen parameters, viscosity, binary diffusion coefficient and vaporization enthalpy. Determination of the physicochemical parameters of FAME was carried out by laboratory experimentations and by calculation from bibliographic data. The Hansen parameters of FAME and epoxy resins pre-polymers were theoretically and experimentally determined. The FAME chain length showed a long dependence on the binary diffusion parameters and kinematic viscosity, which are mass and momentum transport properties. Moreover, the vaporization enthalpy of these compounds was directly correlated with the solubilization limits

Using Topological Statistics to Detect Determinism in Time Series

Statistical differentiability of the measure along the reconstructed trajectory is a good candidate to quantify determinism in time series. The procedure is based upon a formula that explicitly shows the sensitivity of the measure to stochasticity. Numerical results for partially surrogated time series and series derived from several stochastic models, illustrate the usefulness of the method proposed here. The method is shown to work also for high--dimensional systems and experimental time seriesComment: 23 RevTeX pages, 14 eps figures. To appear in Physical Review

Sweating sickness : relative curative effect of hyperimmune serum and a precipitated immunoglobulin suspension and immunoblot identifiation of proposed immunodominant tick salivary gland proteins

Although of low morbidity, sweating sickness is readily induced in calves by infestation with positive Hyalomma truncatum adult ticks. This epitheliotrophic disease has no specific cure except by the administration of hyperimmune serum obtained from animals which have recovered and are subsequently immune to the disease. Treatment with hyperimmune serum, however, has associated problems of donor availability, possible serum contamination and i.v. administration of a relatively large volume. This paper compares the treatment and cure of sweating sickness using unrefined hyperimmune serum and that of an experimental suspension. The latter proved relatively inefficient probably due to a low concentration of effective immunoglobulins. Immunoblot analyses of the sera of affected animals, using tick salivary glands as antigen during the course of the trial revealed 4 tick salivary gland proteins with molecular masses of between 27-33 kDa. These are proposed as being associated with sweating sickness immunodominance.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Transport in rough self-affine fractures

Transport properties of three-dimensional self-affine rough fractures are studied by means of an effective-medium analysis and numerical simulations using the Lattice-Boltzmann method. The numerical results show that the effective-medium approximation predicts the right scaling behavior of the permeability and of the velocity fluctuations, in terms of the aperture of the fracture, the roughness exponent and the characteristic length of the fracture surfaces, in the limit of small separation between surfaces. The permeability of the fractures is also investigated as a function of the normal and lateral relative displacements between surfaces, and is shown that it can be bounded by the permeability of two-dimensional fractures. The development of channel-like structures in the velocity field is also numerically investigated for different relative displacements between surfaces. Finally, the dispersion of tracer particles in the velocity field of the fractures is investigated by analytic and numerical methods. The asymptotic dominant role of the geometric dispersion, due to velocity fluctuations and their spatial correlations, is shown in the limit of very small separation between fracture surfaces.Comment: submitted to PR

Global, regional and national burdens of non-melanoma skin cancer attributable to occupational exposure to solar ultraviolet radiation for 183 countries, 2000-2019: A systematic analysis from the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury.

A World Health Organization (WHO) and International Labour Organization (ILO) systematic review reported sufficient evidence for higher risk of non-melanoma skin cancer (NMSC) amongst people occupationally exposed to solar ultraviolet radiation (UVR). This article presents WHO/ILO Joint Estimates of global, regional, national and subnational occupational exposures to UVR for 195 countries/areas and the global, regional and national attributable burdens of NMSC for 183 countries, by sex and age group, for the years 2000, 2010 and 2019. We calculated population-attributable fractions (PAFs) from estimates of the population occupationally exposed to UVR and the risk ratio for NMSC from the WHO/ILO systematic review. Occupational exposure to UVR was modelled via proxy of occupation with outdoor work, using 166 million observations from 763 cross-sectional surveys for 96 countries/areas. Attributable NMSC burden was estimated by applying the PAFs to WHO's estimates of the total NMSC burden. Measures of inequality were calculated. Globally in 2019, 1.6 billion workers (95 % uncertainty range [UR] 1.6-1.6) were occupationally exposed to UVR, or 28.4 % (UR 27.9-28.8) of the working-age population. The PAFs were 29.0 % (UR 24.7-35.0) for NMSC deaths and 30.4 % (UR 29.0-31.7) for disability-adjusted life years (DALYs). Attributable NMSC burdens were 18,960 deaths (UR 18,180-19,740) and 0.5 million DALYs (UR 0.4-0.5). Men and older age groups carried larger burden. Over 2000-2019, attributable deaths and DALYs almost doubled. WHO and the ILO estimate that occupational exposure to UVR is common and causes substantial, inequitable and growing attributable burden of NMSC. Governments must protect outdoor workers from hazardous exposure to UVR and attributable NMSC burden and inequalities