Present study raises a serious issue of wetland loss and transformation due to damming and water di-version.At present study,it is noticed that overall rainfall trend(-0.006)of the study period(1978-2015)remains uncha...Present study raises a serious issue of wetland loss and transformation due to damming and water di-version.At present study,it is noticed that overall rainfall trend(-0.006)of the study period(1978-2015)remains unchanged but riparian wetland area is attenuated after damming both pre monsoon(March to May)and post monsoon season(October to December).Total wetland area in pre-and post-monsoon seasons is respectively reduced from 42.2 km^(2) to 27.87 km^(2),and from 277.85 km^(2) to 220.90 km^(2) in post dam period.Transformation of frequently inundated wetland area into sparsely inundated wetland is mainly triggered by flow modification due to installation of Komardanga dam and Barrage over Punarbhaba and its major tributary Tangon river.Sparsely inundated seasonal wetland area is rapidly reclaimed for agricultural practice.This extreme issue will invite instability in socio-ecological setup of the neighbouring region.展开更多
The transition location of a boundary layer depends on the amplitude and characteristic of initial disturbances.The larger the amplitude and the amplification rate of the initial disturbances are,the more upstream the...The transition location of a boundary layer depends on the amplitude and characteristic of initial disturbances.The larger the amplitude and the amplification rate of the initial disturbances are,the more upstream the transition location is.However,the environment surrounding the flying vehicle is variable,so the amplitude and characteristic of the disturbances triggered in the boundary layer through receptivity are also variable.In this paper,how the transition location varies in response to the variation of the initial disturbance amplitudes is studied by using direct numerical simulation.The results show that if the initial disturbance amplitudes become smaller,the transition location moves downstream correspondingly,but there is a time delay compared to the time of arrival of the disturbances with reduced amplitudes.Moreover,the speed of moving downstream is appreciably lower than the propagation speed of the disturbances.On the other hand,if the amplitudes of the initial disturbances recover their original value,the transition would immediately take place whenever the disturbances reach the former transition location,but the laminar flow between the new and old transition locations would not become turbulent immediately.Theoretical explanations are provided based on the transition mechanism found by our group.展开更多
文摘Present study raises a serious issue of wetland loss and transformation due to damming and water di-version.At present study,it is noticed that overall rainfall trend(-0.006)of the study period(1978-2015)remains unchanged but riparian wetland area is attenuated after damming both pre monsoon(March to May)and post monsoon season(October to December).Total wetland area in pre-and post-monsoon seasons is respectively reduced from 42.2 km^(2) to 27.87 km^(2),and from 277.85 km^(2) to 220.90 km^(2) in post dam period.Transformation of frequently inundated wetland area into sparsely inundated wetland is mainly triggered by flow modification due to installation of Komardanga dam and Barrage over Punarbhaba and its major tributary Tangon river.Sparsely inundated seasonal wetland area is rapidly reclaimed for agricultural practice.This extreme issue will invite instability in socio-ecological setup of the neighbouring region.
基金was supported by the National Natural Science Foundation of China(Grant Nos.10632050 and 90716007)the National Basic Research Program of China(Grant No.2009CB724103)the Specialized Research Fund for the Doctoral Program of Higher Education
文摘The transition location of a boundary layer depends on the amplitude and characteristic of initial disturbances.The larger the amplitude and the amplification rate of the initial disturbances are,the more upstream the transition location is.However,the environment surrounding the flying vehicle is variable,so the amplitude and characteristic of the disturbances triggered in the boundary layer through receptivity are also variable.In this paper,how the transition location varies in response to the variation of the initial disturbance amplitudes is studied by using direct numerical simulation.The results show that if the initial disturbance amplitudes become smaller,the transition location moves downstream correspondingly,but there is a time delay compared to the time of arrival of the disturbances with reduced amplitudes.Moreover,the speed of moving downstream is appreciably lower than the propagation speed of the disturbances.On the other hand,if the amplitudes of the initial disturbances recover their original value,the transition would immediately take place whenever the disturbances reach the former transition location,but the laminar flow between the new and old transition locations would not become turbulent immediately.Theoretical explanations are provided based on the transition mechanism found by our group.
