This study describes the spatial and temporal variation of a drought index and makes inferences regarding the environmental factors that influence this variability in the Hengduan Mountains. A drought index is typical...This study describes the spatial and temporal variation of a drought index and makes inferences regarding the environmental factors that influence this variability in the Hengduan Mountains. A drought index is typically used to determine the moisture conditions and the magnitude of water deficiency in a given area. Based on data from 26 meteorological stations over the period 1960-2012, the spatial and temporal variations of the drought index were analyzed using a thin plate smoothing splines method that considered elevation as a covariate. The drought index was estimated based on the potential evapotranspiration(E0) as defined by the Penman Monteith model modified by FAO(1998). The results of the reported analysis showed that the drought index in the Hengduan Mountains has been decreasing since 1960 at a rate of-0.008/a. This represented a progressive shift from the "sub-humid" class, which typified the wider area in the Hengduan Mountains, toward the "humid" class, which appeared in the Hengduan Mountains areas. The drought index was relatively high in the north and low in the south and the variation of the drought index varied with seasons. The drought index showed increasing trends in summer and autumn and it is greater in autumn than in summer, while it showed a decreasing trend in spring and winter. Drought index is inversely proportional to the soil relative humidity and Normalized Difference Vegetation Index(NDVI).展开更多
A novel technique of producing azimuthal index 1>1 doughnut beam of good quality by use of multi-liquid crystal cells is presented, it has the advantages of high conversion efficiency and flexibility.
In this paper a gradient index media plate is described. The media plate has some properties similar to the Schmidt aspherical corrective plate. In the catadioptiric system,Duncan T. Moors has studied a axial gradien...In this paper a gradient index media plate is described. The media plate has some properties similar to the Schmidt aspherical corrective plate. In the catadioptiric system,Duncan T. Moors has studied a axial gradient index corrective plate and gave a better result. His plate,in fact,is a zero power plate with two Spherical surfaces of different radius of curvature. However ,my plate is a parallel plate designed forth a shallow radial gradient index media. The spherical aberration of the gradient index corrector with parallel plane ed eliminate the spherical aberration of the spherical primary mirror in the catadioptiric system. In this paper the aberrational correction is analyzed. In the conventional optical systems,this gradient index plate is used to provide the precorrectional quantity of the spherical aberration of the optical lee systems. The refractive index in such a media in the lens systems is given in the same way.展开更多
基金support for this research of Chinese Postdoctoral Science Foundation (2016T90961, 2015M570864)Openended fund of State Key Laboratory of Cryosphere Sciences, Chinese Academy of Sciences (SKLCSOP-2014-11)+2 种基金Project of Northwest Normal University (China) Young Teachers Scientific Research Ability Promotion Plan (NWNU-LKQN13-10)Project of National Natural Science Foundation of China (41271133, 41273010, 41361106, 41261104)Project of Major National Research Projects of China (No. 2013CBA01808)
文摘This study describes the spatial and temporal variation of a drought index and makes inferences regarding the environmental factors that influence this variability in the Hengduan Mountains. A drought index is typically used to determine the moisture conditions and the magnitude of water deficiency in a given area. Based on data from 26 meteorological stations over the period 1960-2012, the spatial and temporal variations of the drought index were analyzed using a thin plate smoothing splines method that considered elevation as a covariate. The drought index was estimated based on the potential evapotranspiration(E0) as defined by the Penman Monteith model modified by FAO(1998). The results of the reported analysis showed that the drought index in the Hengduan Mountains has been decreasing since 1960 at a rate of-0.008/a. This represented a progressive shift from the "sub-humid" class, which typified the wider area in the Hengduan Mountains, toward the "humid" class, which appeared in the Hengduan Mountains areas. The drought index was relatively high in the north and low in the south and the variation of the drought index varied with seasons. The drought index showed increasing trends in summer and autumn and it is greater in autumn than in summer, while it showed a decreasing trend in spring and winter. Drought index is inversely proportional to the soil relative humidity and Normalized Difference Vegetation Index(NDVI).
文摘A novel technique of producing azimuthal index 1>1 doughnut beam of good quality by use of multi-liquid crystal cells is presented, it has the advantages of high conversion efficiency and flexibility.
文摘In this paper a gradient index media plate is described. The media plate has some properties similar to the Schmidt aspherical corrective plate. In the catadioptiric system,Duncan T. Moors has studied a axial gradient index corrective plate and gave a better result. His plate,in fact,is a zero power plate with two Spherical surfaces of different radius of curvature. However ,my plate is a parallel plate designed forth a shallow radial gradient index media. The spherical aberration of the gradient index corrector with parallel plane ed eliminate the spherical aberration of the spherical primary mirror in the catadioptiric system. In this paper the aberrational correction is analyzed. In the conventional optical systems,this gradient index plate is used to provide the precorrectional quantity of the spherical aberration of the optical lee systems. The refractive index in such a media in the lens systems is given in the same way.
