The study focuses on the evaluation of global solar radiation on a horizontal level. The estimate of the solar layer was made on the basis of mathematical model obtained from the relations of Angstrom–Prescott, Allen and Sabbagh. The different proposed models have been implemented by using MATLAB and Excel. The models were evaluated using MPE, NSE, RMSE and MBE. The outcome of this shows that the Angstrom–Prescott model is the most suitable for the calculation of global solar radiation in the sites of Mongo with values of 5.887 kWh/m². For the site of Bokoro, the Allen model is the most adapted for the calculation of global solar radiation which is 5.872 kWh/m². On the other hand, the Sabbagh model is appropriate for the sites of Abeche, N’Djamena, Ati and Moussoro with respective values of 6.354, 5.742, 5.523 and 6.126 kWh/m². The obtained results show that the Sahelian zone of Chad has a good solar potential and consequently suitable for the exploitation of solar energy systems.

We utilize the multiple linear regression method to analyse meteorological data for eight cities in Burkina Faso. A correlation between the monthly mean daily global solar radiation on a horizontal surface and five meteorological and geographical parameters, which are the mean daily extraterrestrial solar radiation intensity, the average daily ratio of sunshine duration, the mean daily relative humidity, the mean daily maximum air temperature, and the sine of the solar declination angle, was examined. A second correlation is established for the entire country, using, this time, the monthly mean global solar radiation on a horizontal surface and the following climatic variables: the average daily ratio of sunshine duration, the latitude, and the longitude. The results show that the coefficients of correlation vary between 0.96 and 0.99 depending on the station while the relative errors spread between −3.16% (Pô) and 3.65% (Dédougou). The maximum value of the RMSD which is 312.36 kJ/m² is obtained at Dori, which receives the strongest radiation. For the entire cities, the values of the MBD are found to be in the acceptable margin.

Cet article analyse les déterminants du choix des méthodes de lutte contre les pestes, dans les plantations de café et de cacao des communautés paysannes du sud-Cameroun. Les méthodes sont chimiques, traditionnelles, et mixtes. Pour capter l'influence des variables socio-économiques sur la probabilité d'utilisation des différentes méthodes, un modèle logit multinomial a été utilisé. Les résultats obtenus révèlent les variables qui influencent significativement le choix des différents moyens utilisés par les planteurs. Il se dégage que les déterminants socio-économiques de l'adoption des méthodes de protection des cultures, sont différents de l'une à l'autre. Afin d'atténuer les conséquences néfastes dues à l'utilisation abusive des produits synthétiques, cette observation doit être prise en compte pour la mise en place des politiques de vulgarisation des systèmes de protection intégrée.

Modelling effective thermal properties is crucial for optimizing the thermal performance of materials such as new green insulating fibrous media. In this study, a numerical model is proposed to calculate the effective thermal conductivity of these materials. The fibers are considered to be non-overlapping and randomly oriented in space. The numerical model is based on the finite element method. Particular attention is paid to the accuracy of the results and the influence of the choice of the representative elementary volume (REV) for calculation (cubic or rectangular parallelepiped slice). The calculated effective thermal conductivity of fibrous media under different boundary conditions is also investigated. A set of usual mixed boundary conditions is considered, alongside the uniform temperature gradient conditions. The REV rectangular slice and uniform temperature gradient boundary conditions provide a more accurate estimate of the effective thermal conductivity and are therefore recommended for use in place of the usual cubic representative elementary volume and the usual mixed boundary conditions. This robust model represents a principal novelty of the work. The results are compared with experimental and analytical data previously obtained in the literature for juncus maritimus fibrous media, for different fiber volume fractions, with small relative deviations of 7%. Analytical laws are generally based on simplified assumptions such as infinitely long fibers, and may neglect heat transfer between different phases. Both short and long fiber cases are considered in numerical calculations.