Changes in the serial resistance Of a- Si, a-/μc-Si and mono-crystalline PV modules during the year
The changes in the serial resistance Rs of amorphous (a- Si) and amorphous/microcrystalline (a-/μc-Si) tandem silicon-based solar cells is a criterion to analyze the process of light -induced degradation and thermal healing of defects described by the Staebler - Wronski effect. Measurements under laboratory conditions show that the serial resistance increases during the light-induced degradation. Our annual measurement of a- Si, a-/μc-Si and mono-crystalline (c-Si) solar cells under field test conditions will verify this and it will improve the possibility of predicting the behavior of thin-film silicon photovoltaic cells. For a year, the complete current-voltage curve was measured every minute, recorded and analyzed. This data has been transferred into the equivalent circuit diagram for solar cells.
Defect relaxation in amorphous silicon: Stretched exponentials, the Meyer-Neldel rule, and the Staebler-Wronski effect.
Annealing and production of metastable defects in disordered solids is explained quantitatively with a model in which defect relaxation is a local phenomenon. The stretched-exponential time dependence of defect relaxation and the Meyer-Neldel rule for the relaxation-time constant are natural consequences of this model. The results are obtained by using an exponential distribution of activation barriers for transitions between the two states of the local defect. The model, applied to data in hydrogenated amorphous silicon, a-Si:H, gives an exponential distribution of barriers with a characteristic temperature of 220 \ifmmode^\circ\else\textdegree\fi{}C, roughly equal to the accepted freeze-in temperature for defect distributions in a-Si:H. The model explains that long degradation times convert defects with higher barriers and this results in longer annealing times. The microscopic models of the metastable defects in a-Si:H, weak-bond breaking and carrier trapping by charged dangling bonds, are discussed in the framework of this defect-relaxation model.
Drivers of Live Cattle Price in the Livestock Trading System of Central Cameroon
Livestock production and trade are critical for the food security and welfare of rural households in sub-Saharan Africa. In Cameroon, animal trade consists mainly of live cattle commercialized through livestock markets. Identifying the factors contributing to cattle price formation is critical for designing effective policies for sustainable production and for increasing food availability. In this study, we evaluated the influence of a range of individual- and market-level factors on the price of cattle that were sold in all transactions (n = 118,017) recorded over a 12-month period from 31 livestock markets in the main cattle production area of the country. An information-theoretic approach using a generalized additive mixed-effect model was implemented to select the best explanatory model as well as evaluate the robustness of the identified drivers and the predictive ability of the model. The age and gender of the cattle traded were consistently found to be important drivers of the price (p < 0.01). Also, strong, but complex, relationships were found between cattle prices and both local human and bovine population densities. Finally, the model highlighted a positive association between the number of incoming trading connections of a livestock market and the price of the traded live cattle (p < 0.01). Although our analysis did not account for factors informing on specific phenotypic traits nor breed characteristics of cattle traded, nearly 50% of the observed variation in live cattle prices was explained by the final model. Ultimately, our model gives a large scale overview of drivers of cattle price formation in Cameroon and to our knowledge is the first study of this scale in Central Africa. Our findings represent an important milestone in designing efficient and sustainable animal health management programme in Cameroon and ensure livelihood sustainability for rural households.