The types, contents and morphologies of crystalline Fe oxides and their relations to phosphate adsorptionon the clay fractions in soils with variable charge in southern China were investigated by means of XRD, TEM,EMA...The types, contents and morphologies of crystalline Fe oxides and their relations to phosphate adsorptionon the clay fractions in soils with variable charge in southern China were investigated by means of XRD, TEM,EMA and chemical analysis methods.Results indicated that the types and contents of crystalline Fe oxidesvaried with the soils examined. The dominant crystalline Fe oxide was hematite in the latosols and goethitesin the red soils.In yellow-brown soils, the only crystalline Fe oxide was goethite.The difference between Aldand Alo came mainly from the Al substituting for Fe in the pe oxides. The crystal morphology of goethiteappeared mainly as subrounded flat or iso-dimensional rather than acicular particles. Hematites occurredin plates of various thickness. Their MCDa/MCDc ratios in the latosols and red soils were generally above1.5 and below 1.5, respectively. The MCD values of goethites and hematites were 15-25nm and 20-35nm,and their specific surface areas were 80-120m￣2/g and 35-75m￣2/g, respectively.The goethite crystals weregenerally smaller. Variations of the total amounts of crystalline Fe oxi es in clay fractions were not related tophosphate adsorption. The types, contents and morphologies of crystalline Fe oxides in the soils remarkablyaffected phosphate adsorption characteristics of the soils. The phosphate adsorption of goethite was muchgreater than that of hematite. The higher the MCD /MCDc rotio of hematite, the lower the phosphateadsorption.展开更多
Combined with the existing stochastic lightning parameterization scheme, a classic tripole charge structure in thunderstorms is assumed in the paper, and then 2-dimensional fine-resolution lighting discharge simulatio...Combined with the existing stochastic lightning parameterization scheme, a classic tripole charge structure in thunderstorms is assumed in the paper, and then 2-dimensional fine-resolution lighting discharge simulations are performed to quantitatively investigate the effect of lower positive charge(LPC) on different types of lightning. The results show:(1) The LPC plays a key role in generating negative cloud-to-ground(CG) flashes and inverted intra-cloud(IC) lightning, and with the increase of charge density or distribution range of LPC region, lightning type changes from positive polarity IC lightning to negative CG flashes and then to inverted IC lightning.(2) Relative to distribution range of charge regions, the magnitude of charge density of the LPC region plays a dominant role in lightning type. Only when the maximal charge density value of LPC region is within a certain range, can negative CG flashes occur, and the occurrence probability is relatively fixed.(3) In this range, the charge density and distribution range of LPC region jointly determine the occurrence of negative CG flashes, which has a linear boundary with the trigger condition of IC lightning.(4) The common effect of charge density and distribution range of the LPC region is to change the distribution of positive potential well of bottom part of thunderstorms, and inverted IC lightning occurs when the initial reference potential is close to 0 MV, and negative CG flashes occur when the initial reference potential is far less than 0 MV.展开更多
文摘The types, contents and morphologies of crystalline Fe oxides and their relations to phosphate adsorptionon the clay fractions in soils with variable charge in southern China were investigated by means of XRD, TEM,EMA and chemical analysis methods.Results indicated that the types and contents of crystalline Fe oxidesvaried with the soils examined. The dominant crystalline Fe oxide was hematite in the latosols and goethitesin the red soils.In yellow-brown soils, the only crystalline Fe oxide was goethite.The difference between Aldand Alo came mainly from the Al substituting for Fe in the pe oxides. The crystal morphology of goethiteappeared mainly as subrounded flat or iso-dimensional rather than acicular particles. Hematites occurredin plates of various thickness. Their MCDa/MCDc ratios in the latosols and red soils were generally above1.5 and below 1.5, respectively. The MCD values of goethites and hematites were 15-25nm and 20-35nm,and their specific surface areas were 80-120m￣2/g and 35-75m￣2/g, respectively.The goethite crystals weregenerally smaller. Variations of the total amounts of crystalline Fe oxi es in clay fractions were not related tophosphate adsorption. The types, contents and morphologies of crystalline Fe oxides in the soils remarkablyaffected phosphate adsorption characteristics of the soils. The phosphate adsorption of goethite was muchgreater than that of hematite. The higher the MCD /MCDc rotio of hematite, the lower the phosphateadsorption.
基金supported by the National Basic Research Program of China(Grant No.2014CB441403)the National Natural Science Foundation of China(Grant No.41175003)Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘Combined with the existing stochastic lightning parameterization scheme, a classic tripole charge structure in thunderstorms is assumed in the paper, and then 2-dimensional fine-resolution lighting discharge simulations are performed to quantitatively investigate the effect of lower positive charge(LPC) on different types of lightning. The results show:(1) The LPC plays a key role in generating negative cloud-to-ground(CG) flashes and inverted intra-cloud(IC) lightning, and with the increase of charge density or distribution range of LPC region, lightning type changes from positive polarity IC lightning to negative CG flashes and then to inverted IC lightning.(2) Relative to distribution range of charge regions, the magnitude of charge density of the LPC region plays a dominant role in lightning type. Only when the maximal charge density value of LPC region is within a certain range, can negative CG flashes occur, and the occurrence probability is relatively fixed.(3) In this range, the charge density and distribution range of LPC region jointly determine the occurrence of negative CG flashes, which has a linear boundary with the trigger condition of IC lightning.(4) The common effect of charge density and distribution range of the LPC region is to change the distribution of positive potential well of bottom part of thunderstorms, and inverted IC lightning occurs when the initial reference potential is close to 0 MV, and negative CG flashes occur when the initial reference potential is far less than 0 MV.
