The ac recombination velocity of the excess minority carriers, in the back surface of a silicon solar cell with a vertical junction connected in series, is developed through Einstein's law giving the diffusion coefficient of minority carriers according to temperature, through mobility. The frequency spectrum of both, amplitude and phase, are produced for the diffusion coefficient and the recombination velocity in the rear face, in order to identify the parameters of equivalent electric models.

New expressions of back surface recombination of excess minority carriers in the base of silicon solar are expressed dependent on both, the thickness and the diffusion coefficient which is in relationship with the doping rate. The optimum thickness thus obtained from the base of the solar cell allows the saving of the amount of material needed in its manufacture without reducing its efficiency.

Artisanal and small-scale gold mining (ASGM) represents a significant economic activity for communities in developing countries. In southeastern Senegal, this activity has increased in recent years and has become the main source of income for the local population. However, it is also associated with negative environmental, social, and health impacts. Considering the recent development of ASGM in Senegal and the difficulties of the government in monitoring and regulating this activity, this article proposes a method for detecting and mapping ASGM sites in Senegal using Sentinel 2 data and the Google Earth Engine. Two artisanal mining sites in Senegal are selected to test this approach. Detection and mapping are achieved following a processing pipeline. Principal component analysis (PCA) is applied to determine the optimal period of the year for mapping. Separability and threshold (SEaTH) is used to determine the optimal bands or spectral indices to discriminate ASGM from other land use. Finally, automatic classification and mapping of the scenes are achieved with support vector machine (SVM) classifier. The results are then validated based on field observations. The PCA and examination of spectral signatures as a function of time indicate that the best period for discriminate ASGM sites against other types of land use is the end of dry season, when vegetation is minimal. The classification results are presented as a map with different categories of land use. This method could be applied to future Sentinel scenes to monitor the evolution of mining sites and may also be extrapolated to other relevant areas in the Sahel.

Excess minority carrier's diffusion equation in the base of monofaciale silicon solar cell under frequency modulation of polychromatic illumination is resolved. Using conditions at the base limits involving recombination velocities Sf and Sb, respectively at the junction (n+/p) and back surface (p+/p), the expression of the excess minority carriers' density  is determined. The density of photocurrent Jph (T, ) is represented according to the recombination velocity at the junction for different temperature values. The expression of the ac back surface recombination velocity Sb of minority carriers is then deduced depending on frequency of modulation, temperature, electronic parameters (D) and the thickness of the base. Bode and Nyquist diagrams are used to analyze, both diffusion coefficient and back surface recombination of excess minority carriers submitted to Umklap process.

Dans l’espace du Gandiol, les activités économiques traditionnelles étaient la pêche et l’agriculture avec lesquelles la population a une longue tradition. En 2003, les fortes pluies enregistrées dans le Haut bassin du fleuve Sénégal expliquent l’augmentation massive du débit du fleuve consécutivement à l’addition des ondes de crue. Pour empêcher des inondations dans la ville de Saint-Louis, une brèche a été ouverte. Cependant, cette brèche a eu des effets négatifs sur l’agriculture et beaucoup d’espèces de poissons. Elle a, aussi, entrainé des modifications écologiques se manifestant par l’apparition de certaines espèces aquatiques : Anadara Senilis, Carasostrea Gasar. Dès lors, l’étude de l’exploitation de l’espèce Anadara senilis dans le parc national de la langue de Barbarie (commune de Ndiebène Gandiol) fait l’objet de cette contribution. La méthodologie adoptée intègre les enquêtes de terrain sous forme de questionnaires et de guides d’entretien et le traitement des données quantitatives et qualitatives. Les résultats montrent que la collecte des coquillages est progressivement devenue la principale activité des femmes. Cette activité est pratiquée dans un but essentiellement lucratif et a eu des impacts considérables tant au niveau socioéconomique qu’environnemental. C’est pourquoi, l’encadrement des exploitants est souhaitable pour une gestion durable de cette ressource renouvelable.