Soil erosion and nutrient loss due to erosion are world-wide problems. Similar to soil loss by erosion, soil nitrogen (N) loss by erosion in small catchments is affected by vegetation coverage. The practice of compreh...Soil erosion and nutrient loss due to erosion are world-wide problems. Similar to soil loss by erosion, soil nitrogen (N) loss by erosion in small catchments is affected by vegetation coverage. The practice of comprehensive management for catchments mainly by adjusting cropland, grassland and woodland areas was widely adopted to reduce soil and water loss in catchments of the Chinese Loess Plateau. Three experiments under natural and artificial rainfall conditions on N loss by erosion for a model catchment and for an actual catchment in Zhifanggou of Ansai County in China was performed to determine the relationships between comprehensive management and N loss by runoff in small catchments. The results for vegetation coverage of 60%, 40%, 20% and 0 show that runoff loss of ammonium, nitrate, and total N were 87.08, 44.31, 25.16, 13.71 kg/km(2); 85.50, 74.06, 63.95, 56.23 kg/km(2); and 0.18, 1.18, 1.98, 7.51 t/ km(2), respectively. Due to reduction in the size of cropped area on steeply sloping land, soil N loss by erosion in the catchments was decreased by 15.8% as compared with that in 1992, i.e., from 8 758.5 kg in 1992 to 7 562.2 kg in 1998. Whereas, catchments act as a filter for ammonium and nitrate in rain, the catchment filtering effects on nitrate is remarkably higher than that on ammonium. The enrichment of < 20 mum aggregate in sediment results in the enrichment of organic matter and total N in flood sediment. Greater vegetation coverage can effectively decrease soil erosion and total N loss. However, soil mineral N loss increased as vegetation coverage increased.展开更多
A thorough analysis on its natural environment as well as social economic status of the hilly-gullied loess region is presented. A small watershed, the dominant landscape unit of the region, has been singled out for f...A thorough analysis on its natural environment as well as social economic status of the hilly-gullied loess region is presented. A small watershed, the dominant landscape unit of the region, has been singled out for further and specific study on landscape pattern and function, its social and economic distinctions. The authors proposed several principles based on its eco-economic background study, which includes water balance and efficient use principle, co-development of grass and agro-forestry principle, location optimization principle. Integrated with detailed analysis of a small watershed, an eco-productive paradigm for the loess land's development based on a small watershed scale was worked out. It consists of circle pattern with villages at core for high efficient agriculture production, hierarchical pattern along the slope for eco-economic development, point-axis pattern for commodity production and circulation in small watersheds and core-margin pattern for exchanges among watersheds.展开更多
To manufacture plate by the combination of equal channel angular processing （ECAP） and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing （P-ECAP）, was studied....To manufacture plate by the combination of equal channel angular processing （ECAP） and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing （P-ECAP）, was studied. Extrusion of AL6005A plate used for the bullet train plate was investigated by finite element method. The relevant porthole dies involving ECAP technique in channels were designed. Dimensional changes in the scrap part of the extrudate obtained after extrusion from the P-ECAP die, with different channel angles, were predicted. Effects of the channel angle and extrusion speed on the maximum temperature of the workpiece and other field variables were evaluated. At the channel angle of 160° of P-ECAP dies, the extrudate exhibited the optimal performance and the least amount of extrudate scrap was obtained. The optimal extrusion speed was 3-5 mm/s. Moreover, with the increase in ram speed from 1 to 9 mm/s, the peak extrusion load increased by about 49% and the maximum temperature was increased by about 70 ℃. The effective strain exhibited ascending trend in the comer of the ECAP deformation zone. In the solder seam and the side of die bearing of extrudate, the maximum principal stresses were tensile stress.展开更多
文摘Soil erosion and nutrient loss due to erosion are world-wide problems. Similar to soil loss by erosion, soil nitrogen (N) loss by erosion in small catchments is affected by vegetation coverage. The practice of comprehensive management for catchments mainly by adjusting cropland, grassland and woodland areas was widely adopted to reduce soil and water loss in catchments of the Chinese Loess Plateau. Three experiments under natural and artificial rainfall conditions on N loss by erosion for a model catchment and for an actual catchment in Zhifanggou of Ansai County in China was performed to determine the relationships between comprehensive management and N loss by runoff in small catchments. The results for vegetation coverage of 60%, 40%, 20% and 0 show that runoff loss of ammonium, nitrate, and total N were 87.08, 44.31, 25.16, 13.71 kg/km(2); 85.50, 74.06, 63.95, 56.23 kg/km(2); and 0.18, 1.18, 1.98, 7.51 t/ km(2), respectively. Due to reduction in the size of cropped area on steeply sloping land, soil N loss by erosion in the catchments was decreased by 15.8% as compared with that in 1992, i.e., from 8 758.5 kg in 1992 to 7 562.2 kg in 1998. Whereas, catchments act as a filter for ammonium and nitrate in rain, the catchment filtering effects on nitrate is remarkably higher than that on ammonium. The enrichment of < 20 mum aggregate in sediment results in the enrichment of organic matter and total N in flood sediment. Greater vegetation coverage can effectively decrease soil erosion and total N loss. However, soil mineral N loss increased as vegetation coverage increased.
文摘A thorough analysis on its natural environment as well as social economic status of the hilly-gullied loess region is presented. A small watershed, the dominant landscape unit of the region, has been singled out for further and specific study on landscape pattern and function, its social and economic distinctions. The authors proposed several principles based on its eco-economic background study, which includes water balance and efficient use principle, co-development of grass and agro-forestry principle, location optimization principle. Integrated with detailed analysis of a small watershed, an eco-productive paradigm for the loess land's development based on a small watershed scale was worked out. It consists of circle pattern with villages at core for high efficient agriculture production, hierarchical pattern along the slope for eco-economic development, point-axis pattern for commodity production and circulation in small watersheds and core-margin pattern for exchanges among watersheds.
基金Project(B08040)supported by the Program of Introducing Talents of Discipline to Universities(111 Project),ChinaProject(2009ZX04005-031-11)supported by the National Science and Technology Special Program,China
文摘To manufacture plate by the combination of equal channel angular processing （ECAP） and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing （P-ECAP）, was studied. Extrusion of AL6005A plate used for the bullet train plate was investigated by finite element method. The relevant porthole dies involving ECAP technique in channels were designed. Dimensional changes in the scrap part of the extrudate obtained after extrusion from the P-ECAP die, with different channel angles, were predicted. Effects of the channel angle and extrusion speed on the maximum temperature of the workpiece and other field variables were evaluated. At the channel angle of 160° of P-ECAP dies, the extrudate exhibited the optimal performance and the least amount of extrudate scrap was obtained. The optimal extrusion speed was 3-5 mm/s. Moreover, with the increase in ram speed from 1 to 9 mm/s, the peak extrusion load increased by about 49% and the maximum temperature was increased by about 70 ℃. The effective strain exhibited ascending trend in the comer of the ECAP deformation zone. In the solder seam and the side of die bearing of extrudate, the maximum principal stresses were tensile stress.
