We examined the competitive ability of larval toads (Bufo gargarizans ) and frogs (Rana kukunoris ) which co-occur in natural pools in the Jiuzhaigou Nature Reserve. We measured the activity level, growth rate, ma...We examined the competitive ability of larval toads (Bufo gargarizans ) and frogs (Rana kukunoris ) which co-occur in natural pools in the Jiuzhaigou Nature Reserve. We measured the activity level, growth rate, mass at metamorphosis and larval period in a laboratory experiment. Tadpoles of B. gargarizans were significantly more active when food was abundant than scarce, while there was no significant difference in the activity of R. kukunoris tadpoles at different food levels. At low food availability, mass at metamorphosis and growth rate of R. kukunoris were significantly increased in the presence of B. gargarizans, whereas the presence of R. kukunoris had no significant effect on the mass and growth rate of B. gargarizans. In all treatments, the larval period of B. gargarizans at low food availability was the shortest. These results suggest that B. gargarizans can adapt to different food levels by changing their activity rate. At high food level, B. gargarizans increased activity to gain more food. At low food level, B. gargarizans decreased activity and achieved early metamorphosis. However, when food resources were limited, R. kukunoris could gain more food than B.gargarizans .展开更多
Operating principle of water three-way valve with high flow for individual hydraulic prop in coal was presented in this paper, its strict and precise mathematical model was established, its flow field was simulated nu...Operating principle of water three-way valve with high flow for individual hydraulic prop in coal was presented in this paper, its strict and precise mathematical model was established, its flow field was simulated numerically by software Fluent, and its dynamic characteristics were analyzed during the work process such as raising leg, loading and overflow, the influence of the related parameters on high-flow water three-way valve was determined. The results as follows: during the raising leg stage and early raising leg stage, when the damping ratio increases, the overshoot of system decreases and the setting time reduces, and the dynamic response performance has a significant improvement. During the loading stage and the overflow stage, the pressure in plunger chamber of single hydraulic prop, the output flow and the displacement of the high-flow water three-way valve decrease with the decreasing of the external load. The spring stiffness of the safety valve directs the flow and the spool's displacement of the safety valve, and it can be used to control the high-flow three-way valve's sensitivity.展开更多
Allochthonous organic matter plays an important role in nutrient cycling and energy mobilization in freshwater ecosystems. However, the subsidies of this carbon source in floodplain ecosystems have not yet well unders...Allochthonous organic matter plays an important role in nutrient cycling and energy mobilization in freshwater ecosystems. However, the subsidies of this carbon source in floodplain ecosystems have not yet well understood. We used a Bayesian mixing model and stable isotopes (613C and 815N) of primary food resources and dominant molluscs species, to estimate the relative importance of allochthonous carbon sources for consumers in a representative sub-lake of Poyang Lake during a prolonged dry season. Our study inferred that terrestrial-derived carbon from Carex spp. could be the primary contributor to snails and mussels in Dahuchi Lake. The mean percentage of allochthonous food resources accounted for 35%- 50% of the C incorporated by these consumers. Seston was another important energy sources for benthic consumers. However, during the winter and low water-level period, benthic algae and submerged vegetation contributed less carbon to benthic consumers. Our data highlighted the importance of terrestrial organic carbon to benthic consumers in the wetlands of Poyang Lake during the prolonged dry period. Further, our results provided a perspective that linkages between terrestrial and aquatic ecosystems might be facilitated by wintering geese via their droppings.展开更多
湖泊是重要的淡水资源,准确了解湖泊水体动态变化有利于水资源可持续利用和社会经济发展。本研究基于Google Earth Engine(GEE)平台,以Joint Research Centre(JRC)全球地表水数据集和Landsat遥感影像为数据源,分析了1984—2018年大型湖...湖泊是重要的淡水资源,准确了解湖泊水体动态变化有利于水资源可持续利用和社会经济发展。本研究基于Google Earth Engine(GEE)平台,以Joint Research Centre(JRC)全球地表水数据集和Landsat遥感影像为数据源,分析了1984—2018年大型湖泊——太湖水体的动态变化,并利用改进的归一化差异水体指数(MNDWI)研究了太湖面积变化趋势。结果表明:1984—2018年,太湖湖泊面积呈增加趋势,共增加45.31 km^2,湖泊面积呈夏季低、春冬季高的特点,东太湖是太湖面积发生变化的主要区域。与1984年相比,2018年太湖88.9%的水体未发生任何变化,0.3%的水体永久性消失。湖泊面积变化受自然和人为因素的共同影响,农业灌溉、渔业养殖、围湖垦殖、水利工程设施和土地利用类型转移等导致湖泊面积减少;年降水量增加和环境保护政策的实施是湖泊面积增加的主要原因。本研究结果可为实施水资源可持续管理提供参考,亦验证了基于GEE平台开展水体长期变化监测的可行性。展开更多
文摘We examined the competitive ability of larval toads (Bufo gargarizans ) and frogs (Rana kukunoris ) which co-occur in natural pools in the Jiuzhaigou Nature Reserve. We measured the activity level, growth rate, mass at metamorphosis and larval period in a laboratory experiment. Tadpoles of B. gargarizans were significantly more active when food was abundant than scarce, while there was no significant difference in the activity of R. kukunoris tadpoles at different food levels. At low food availability, mass at metamorphosis and growth rate of R. kukunoris were significantly increased in the presence of B. gargarizans, whereas the presence of R. kukunoris had no significant effect on the mass and growth rate of B. gargarizans. In all treatments, the larval period of B. gargarizans at low food availability was the shortest. These results suggest that B. gargarizans can adapt to different food levels by changing their activity rate. At high food level, B. gargarizans increased activity to gain more food. At low food level, B. gargarizans decreased activity and achieved early metamorphosis. However, when food resources were limited, R. kukunoris could gain more food than B.gargarizans .
基金Supported by the National Natural Science Foundation of China (51075001) the Nature Science Research Project of Anhui Province (KJ2009A020)
文摘Operating principle of water three-way valve with high flow for individual hydraulic prop in coal was presented in this paper, its strict and precise mathematical model was established, its flow field was simulated numerically by software Fluent, and its dynamic characteristics were analyzed during the work process such as raising leg, loading and overflow, the influence of the related parameters on high-flow water three-way valve was determined. The results as follows: during the raising leg stage and early raising leg stage, when the damping ratio increases, the overshoot of system decreases and the setting time reduces, and the dynamic response performance has a significant improvement. During the loading stage and the overflow stage, the pressure in plunger chamber of single hydraulic prop, the output flow and the displacement of the high-flow water three-way valve decrease with the decreasing of the external load. The spring stiffness of the safety valve directs the flow and the spool's displacement of the safety valve, and it can be used to control the high-flow three-way valve's sensitivity.
基金Supported by the National Natural Science Foundation of China(Nos.41471088,41301077)
文摘Allochthonous organic matter plays an important role in nutrient cycling and energy mobilization in freshwater ecosystems. However, the subsidies of this carbon source in floodplain ecosystems have not yet well understood. We used a Bayesian mixing model and stable isotopes (613C and 815N) of primary food resources and dominant molluscs species, to estimate the relative importance of allochthonous carbon sources for consumers in a representative sub-lake of Poyang Lake during a prolonged dry season. Our study inferred that terrestrial-derived carbon from Carex spp. could be the primary contributor to snails and mussels in Dahuchi Lake. The mean percentage of allochthonous food resources accounted for 35%- 50% of the C incorporated by these consumers. Seston was another important energy sources for benthic consumers. However, during the winter and low water-level period, benthic algae and submerged vegetation contributed less carbon to benthic consumers. Our data highlighted the importance of terrestrial organic carbon to benthic consumers in the wetlands of Poyang Lake during the prolonged dry period. Further, our results provided a perspective that linkages between terrestrial and aquatic ecosystems might be facilitated by wintering geese via their droppings.