Vegetation cover degradation is still a very common problem in many parts of Morocco;moreover, it affects straight up the amount of the annual soil loss rate. The analytical approach used in this study, respectively, ...Vegetation cover degradation is still a very common problem in many parts of Morocco;moreover, it affects straight up the amount of the annual soil loss rate. The analytical approach used in this study, respectively, includes remote sensing techniques, application of USLE (Universal Soil Loss Equation) and overlay analysis in a raster Geographic Information System (GIS) environment, employing available information on the region covering the Kalaya catchment. Thus, this procedure allowed the calculation of the NDVI (Normalized Difference Vegetation Index), the execution of two types of classification (unsupervised and supervised) for 1999 and 2010 imagery and eventually the prediction of soil erosion risk in the watershed in question. The main outcome was the production of multidate vegetation cover maps, land use maps and soil loss risk maps. The overlay of two maps allowed us to highlight the changes occurred in this area, which evidence the high anthropogenic impact on the dynamics of land use and vegetation cover. The results suggest that the outputs of this study can be used for predicting rate of soil loss, which varied from 31.68 t·ha-1·yr-1 in 1999 to 34.74 t·ha-1·yr-1 in 2010.展开更多
In a survival analysis context, we suggest a new method to estimate the piecewise constant hazard rate model. The method provides an automatic procedure to find the number and location of cut points and to estimate th...In a survival analysis context, we suggest a new method to estimate the piecewise constant hazard rate model. The method provides an automatic procedure to find the number and location of cut points and to estimate the hazard on each cut interval. Estimation is performed through a penalized likelihood using an adaptive ridge procedure. A bootstrap procedure is proposed in order to derive valid statistical inference taking both into account the variability of the estimate and the variability in the choice of the cut points. The new method is applied both to simulated data and to the Mayo Clinic trial on primary biliary cirrhosis. The algorithm implementation is seen to work well and to be of practical relevance.展开更多
文摘Vegetation cover degradation is still a very common problem in many parts of Morocco;moreover, it affects straight up the amount of the annual soil loss rate. The analytical approach used in this study, respectively, includes remote sensing techniques, application of USLE (Universal Soil Loss Equation) and overlay analysis in a raster Geographic Information System (GIS) environment, employing available information on the region covering the Kalaya catchment. Thus, this procedure allowed the calculation of the NDVI (Normalized Difference Vegetation Index), the execution of two types of classification (unsupervised and supervised) for 1999 and 2010 imagery and eventually the prediction of soil erosion risk in the watershed in question. The main outcome was the production of multidate vegetation cover maps, land use maps and soil loss risk maps. The overlay of two maps allowed us to highlight the changes occurred in this area, which evidence the high anthropogenic impact on the dynamics of land use and vegetation cover. The results suggest that the outputs of this study can be used for predicting rate of soil loss, which varied from 31.68 t·ha-1·yr-1 in 1999 to 34.74 t·ha-1·yr-1 in 2010.
文摘In a survival analysis context, we suggest a new method to estimate the piecewise constant hazard rate model. The method provides an automatic procedure to find the number and location of cut points and to estimate the hazard on each cut interval. Estimation is performed through a penalized likelihood using an adaptive ridge procedure. A bootstrap procedure is proposed in order to derive valid statistical inference taking both into account the variability of the estimate and the variability in the choice of the cut points. The new method is applied both to simulated data and to the Mayo Clinic trial on primary biliary cirrhosis. The algorithm implementation is seen to work well and to be of practical relevance.
