In recent years, it has shown that a generalized thresholding algorithm is useful for inverse problems with sparsity constraints. The generalized thresholding minimizes the non-convex p-norm based function with p <...In recent years, it has shown that a generalized thresholding algorithm is useful for inverse problems with sparsity constraints. The generalized thresholding minimizes the non-convex p-norm based function with p < 1, and it penalizes small coefficients over a wider range meanwhile applies less bias to the larger coefficients.In this work, on the basis of two-level Bregman method with dictionary updating(TBMDU), we use the modified thresholding to minimize the non-convex function and propose the generalized TBMDU(GTBMDU) algorithm.The experimental results on magnetic resonance(MR) image simulations and real MR data, under a variety of sampling trajectories and acceleration factors, consistently demonstrate that the proposed algorithm can efficiently reconstruct the MR images and present advantages over the previous soft thresholding approaches.展开更多
Droughts may be caused by both natural and anthropogenic factors and delimitation of them is crucial for identification of exposed areas.This study concentrated on the application of the threshold level method combine...Droughts may be caused by both natural and anthropogenic factors and delimitation of them is crucial for identification of exposed areas.This study concentrated on the application of the threshold level method combined with GIS modelling applied to hydrogeological drought characterization.The first step was to define groundwater drought periods and analysis of drought intensity and duration based on long-term monitoring data from points evenly spaced within the study area.Then the distribution of hydrogeological drought intensity was identified combining a geostatistical kriging method with the type of geographical region.Utilizing GIS modelling with integration of several parameters the final map was created showing vulnerability and exposure of the area to hydrogeological drought.Studies indicate that the area most exposed to drought is located in the north eastern part of Lower Silesia being influenced by water abstraction and mining activity as well as drought.展开更多
基金the National Natural Science Foundation of China(Nos.6136200161365013 and 51165033)+3 种基金the Natural Science Foundation of Jiangxi Province(Nos.20132BAB211030 and 20122BAB211015)the Technology Foundation of Department of Education in Jiangxi Province(Nos.GJJ 13061 and GJJ14196)the National Postdoctoral Research Funds(No.2014M551867)the Jiangxi Advanced Projects for Postdoctoral Research Funds(No.2014KY02)
文摘In recent years, it has shown that a generalized thresholding algorithm is useful for inverse problems with sparsity constraints. The generalized thresholding minimizes the non-convex p-norm based function with p < 1, and it penalizes small coefficients over a wider range meanwhile applies less bias to the larger coefficients.In this work, on the basis of two-level Bregman method with dictionary updating(TBMDU), we use the modified thresholding to minimize the non-convex function and propose the generalized TBMDU(GTBMDU) algorithm.The experimental results on magnetic resonance(MR) image simulations and real MR data, under a variety of sampling trajectories and acceleration factors, consistently demonstrate that the proposed algorithm can efficiently reconstruct the MR images and present advantages over the previous soft thresholding approaches.
文摘Droughts may be caused by both natural and anthropogenic factors and delimitation of them is crucial for identification of exposed areas.This study concentrated on the application of the threshold level method combined with GIS modelling applied to hydrogeological drought characterization.The first step was to define groundwater drought periods and analysis of drought intensity and duration based on long-term monitoring data from points evenly spaced within the study area.Then the distribution of hydrogeological drought intensity was identified combining a geostatistical kriging method with the type of geographical region.Utilizing GIS modelling with integration of several parameters the final map was created showing vulnerability and exposure of the area to hydrogeological drought.Studies indicate that the area most exposed to drought is located in the north eastern part of Lower Silesia being influenced by water abstraction and mining activity as well as drought.
