Microtopography may affect the distribution of forests through its effect on rain redistribution and soil water distribution on the semi-arid Loess Plateau,China.In this study,we investigated the characteristics of mi...Microtopography may affect the distribution of forests through its effect on rain redistribution and soil water distribution on the semi-arid Loess Plateau,China.In this study,we investigated the characteristics of microtopography on two shady slopes（slope A,5 hm2,uniform slope;slope B,5 hm2,microtopography slope） and surveyed the height,the diameter at breast height and the location（x,y coordinates） of all selected individual trees（Robinia pseudoacacia Linn.,Pyrus betulifolia Bunge,Populus hopeiensis Hu ＆ Chow,Armeniaca sibirica Lam.,Populus simonii Carr.and Ulmus pumila Linn.） on slope A and slope B in the watersheds of Wuqi county,Shaanxi province.Subsequently,the effects of microtopography on the spatial pattern of forest stands were analyzed using Ripley＇s K（r） function.The results showed that：（1） The maximal aggregation radiuses of the tree species on the uniform slope（slope A） were larger than 40 m,whereas those of the tree species on the microtopography slope（slope B） were smaller than 30 m.（2） On slope B,the spatial association of R.pseudoacacia with P.betulifolia,A.sibirica,P.simonii and U.pumila varied from being strongly negative to positive at microtopography scales.The spatial association of Populus hopeiensis Hu ＆ Chow with U.pumila also varied from being strongly negative to positive at microtopography scales.However,there was no spatial association between P.betulifolia and P.hopeiensis,P.betulifolia and A.sibirica,P.betulifolia and P.simonii,P.betulifolia and U.pumila,P.hopeiensis and A.sibirica,P.hopeiensis and P.simonii,A.sibirica and P.simonii,A.sibirica and U.pumila,and P.simonii and U.pumila.On slope A,the spatial association between tree species were strongly negative.The results suggest that microtopography may shape tree distribution patterns on the semi-arid Loess Plateau.展开更多
For practical applications of X-ray ghost imaging(XGI),the imaging time is a major challenge.In this paper,we propose a fast XGI scheme based on a continuous translation mask with etched aggregate patterns.High contra...For practical applications of X-ray ghost imaging(XGI),the imaging time is a major challenge.In this paper,we propose a fast XGI scheme based on a continuous translation mask with etched aggregate patterns.High contrastto-noise ratio images are obtained with an exposure time of only 4 s and 24 s for a 3.4 mm×3.8 mm and 5.9 mm×6.1 mm field-of-view,respectively.The spatial resolution can reach∼150μm.The influences of the sampling frequency,the mask scanning speed,and the detector integration time on image quality are examined,from which we demonstrate that the imaging time can be further reduced by increasing the mask translation speed.By applying a compressed sensing reconstruction algorithm,the exposure time is greatly reduced while maintaining image quality.Our method indicates a path for the development of future XGI applications.展开更多
基金financially supported by China National Scientific and Technical Innovation Research Project for 12~(th) Five Year Plan (2011BAD38B0601)the National Natural Science Foundation of China (41472313)the Natural Science Foundation of Shandong Province (ZR2011DM012,ZR2014DL002)
文摘Microtopography may affect the distribution of forests through its effect on rain redistribution and soil water distribution on the semi-arid Loess Plateau,China.In this study,we investigated the characteristics of microtopography on two shady slopes（slope A,5 hm2,uniform slope;slope B,5 hm2,microtopography slope） and surveyed the height,the diameter at breast height and the location（x,y coordinates） of all selected individual trees（Robinia pseudoacacia Linn.,Pyrus betulifolia Bunge,Populus hopeiensis Hu ＆ Chow,Armeniaca sibirica Lam.,Populus simonii Carr.and Ulmus pumila Linn.） on slope A and slope B in the watersheds of Wuqi county,Shaanxi province.Subsequently,the effects of microtopography on the spatial pattern of forest stands were analyzed using Ripley＇s K（r） function.The results showed that：（1） The maximal aggregation radiuses of the tree species on the uniform slope（slope A） were larger than 40 m,whereas those of the tree species on the microtopography slope（slope B） were smaller than 30 m.（2） On slope B,the spatial association of R.pseudoacacia with P.betulifolia,A.sibirica,P.simonii and U.pumila varied from being strongly negative to positive at microtopography scales.The spatial association of Populus hopeiensis Hu ＆ Chow with U.pumila also varied from being strongly negative to positive at microtopography scales.However,there was no spatial association between P.betulifolia and P.hopeiensis,P.betulifolia and A.sibirica,P.betulifolia and P.simonii,P.betulifolia and U.pumila,P.hopeiensis and A.sibirica,P.hopeiensis and P.simonii,A.sibirica and P.simonii,A.sibirica and U.pumila,and P.simonii and U.pumila.On slope A,the spatial association between tree species were strongly negative.The results suggest that microtopography may shape tree distribution patterns on the semi-arid Loess Plateau.
基金National Natural Science Foundation of China(61975229,12335016,11991073,W2412039,61805006)National Key R&D Program of China(2018YFB0504302)Strategic Priority Research Program of the CAS(XDA25030400,XDA25010100).
文摘For practical applications of X-ray ghost imaging(XGI),the imaging time is a major challenge.In this paper,we propose a fast XGI scheme based on a continuous translation mask with etched aggregate patterns.High contrastto-noise ratio images are obtained with an exposure time of only 4 s and 24 s for a 3.4 mm×3.8 mm and 5.9 mm×6.1 mm field-of-view,respectively.The spatial resolution can reach∼150μm.The influences of the sampling frequency,the mask scanning speed,and the detector integration time on image quality are examined,from which we demonstrate that the imaging time can be further reduced by increasing the mask translation speed.By applying a compressed sensing reconstruction algorithm,the exposure time is greatly reduced while maintaining image quality.Our method indicates a path for the development of future XGI applications.
