This paper reports the dynamic changes of soil and water loss in the red soil region of Southern China since the 1950s. The red soil region covers eight provinces: Jiangxi, Zhejiang, Fujian, Anhui, Hubei, Hunan, Guang...This paper reports the dynamic changes of soil and water loss in the red soil region of Southern China since the 1950s. The red soil region covers eight provinces: Jiangxi, Zhejiang, Fujian, Anhui, Hubei, Hunan, Guangdong and Hainan. From the 1950s to 1986, the annual rate of soil erosion increased by 3.4%. From 1986 to 1996 and from 1996 to 2000, the annual rates of soil erosion decreased by 2.0% and 0.32%, respectively. Field surveys showed that from 2000 to 2005, the area of soil and water loss decreased annually by 1.2%. This decrease was a result of large-scale erosion control activities across China. Although the eroded soil has been restored, the restoration process is very slow and full restoration will take a long time. Our report suggests that controlling soil and water loss is a challenging task, and additional measures must be taken to effectively control the soil erosion in the red soil region.展开更多
Upset condition encountered by an aircraft in flight could pose great threat to flight safety, which is of chief importance in civil aviation. The causal factors have the nonlinear and multiple characteristics, and as...Upset condition encountered by an aircraft in flight could pose great threat to flight safety, which is of chief importance in civil aviation. The causal factors have the nonlinear and multiple characteristics, and as a result the conventional envelope protection system cannot successfully do with the condition. So dynamic envelope based on differential manifold theory, which can take more coupling factors into account, is proposed as a basis to design a novel envelope protection system. Then the relationship between the dynamic envelope and the control coefficient or pilot command is obtained, and the result shows that the dynamic envelope can be enlarged with the change of control coefficient. Furthermore, quantification of flight security is realized via defining relative distance between flight state and dynamic envelope, which can detect whether there is a risk for an aircraft in flight. Finally, an envelope protection system based on dynamic envelope enlargement is proposed on the basis. NASA＇s Generic Transport Model encountering hazard gust wind in climbing phase is taken as an example to verify the system＇s feasibility. The result shows that the system can give a better operation encountering upset condition and to a certain extent reduce the number of accidents or incidents.展开更多
In the present paper the variational solution of velocity profile for an incompressible laminar and fully developed flow in isosceles triangular ducts is derived by applying the Kantovorich method. The theoretical and...In the present paper the variational solution of velocity profile for an incompressible laminar and fully developed flow in isosceles triangular ducts is derived by applying the Kantovorich method. The theoretical and experimental results of pressure loss are also given. The velocity distribution model, additional pressure loss coefficient and calculating method of inlet length in the entrance region of isosceles triangular ducts are also derived, which are suitable for various kinds of vertex angles. The calculations and experiments are also performed for two models: the isosceles triangular channels with vertex angles 2a=45.1 and 2a= 60 . Comparisons are made between the theoretical analysis in this paper and those of the other authors. It can be seen that the present analytical result is of high. accuracy and wide practicability, and agrees well with the authors' experiment.展开更多
In this paper,areas and main factors of wind erosion in black earth region of Northeast China were systematically analyzed,as well as the development trend of wind erosion in black earth region of Northeast China.In a...In this paper,areas and main factors of wind erosion in black earth region of Northeast China were systematically analyzed,as well as the development trend of wind erosion in black earth region of Northeast China.In addition,development trend of wind erosion in black earth region of Northeast China was analyzed from the aspects of the geographic position,climatic change law in recent 40 years and effects of northeast sand land desertification on wind erosion in black earth region,which had provided references for the research and prevention of wind erosion in soil of black earth region of Northeast China.展开更多
基金funded by the "973" Program of China (2007CB407206)the ISSCAS Innovation Program (ISSASIP0602)the Knowledge Innovation Project of the Chinese Academy of Sciences (KZCX2-YW-438)
文摘This paper reports the dynamic changes of soil and water loss in the red soil region of Southern China since the 1950s. The red soil region covers eight provinces: Jiangxi, Zhejiang, Fujian, Anhui, Hubei, Hunan, Guangdong and Hainan. From the 1950s to 1986, the annual rate of soil erosion increased by 3.4%. From 1986 to 1996 and from 1996 to 2000, the annual rates of soil erosion decreased by 2.0% and 0.32%, respectively. Field surveys showed that from 2000 to 2005, the area of soil and water loss decreased annually by 1.2%. This decrease was a result of large-scale erosion control activities across China. Although the eroded soil has been restored, the restoration process is very slow and full restoration will take a long time. Our report suggests that controlling soil and water loss is a challenging task, and additional measures must be taken to effectively control the soil erosion in the red soil region.
基金supported by the National Key Basic Research Program of China (No.2015CB755805)
文摘Upset condition encountered by an aircraft in flight could pose great threat to flight safety, which is of chief importance in civil aviation. The causal factors have the nonlinear and multiple characteristics, and as a result the conventional envelope protection system cannot successfully do with the condition. So dynamic envelope based on differential manifold theory, which can take more coupling factors into account, is proposed as a basis to design a novel envelope protection system. Then the relationship between the dynamic envelope and the control coefficient or pilot command is obtained, and the result shows that the dynamic envelope can be enlarged with the change of control coefficient. Furthermore, quantification of flight security is realized via defining relative distance between flight state and dynamic envelope, which can detect whether there is a risk for an aircraft in flight. Finally, an envelope protection system based on dynamic envelope enlargement is proposed on the basis. NASA＇s Generic Transport Model encountering hazard gust wind in climbing phase is taken as an example to verify the system＇s feasibility. The result shows that the system can give a better operation encountering upset condition and to a certain extent reduce the number of accidents or incidents.
文摘In the present paper the variational solution of velocity profile for an incompressible laminar and fully developed flow in isosceles triangular ducts is derived by applying the Kantovorich method. The theoretical and experimental results of pressure loss are also given. The velocity distribution model, additional pressure loss coefficient and calculating method of inlet length in the entrance region of isosceles triangular ducts are also derived, which are suitable for various kinds of vertex angles. The calculations and experiments are also performed for two models: the isosceles triangular channels with vertex angles 2a=45.1 and 2a= 60 . Comparisons are made between the theoretical analysis in this paper and those of the other authors. It can be seen that the present analytical result is of high. accuracy and wide practicability, and agrees well with the authors' experiment.
基金Supported by National Natural Science Foundation of China(40901136)~~
文摘In this paper,areas and main factors of wind erosion in black earth region of Northeast China were systematically analyzed,as well as the development trend of wind erosion in black earth region of Northeast China.In addition,development trend of wind erosion in black earth region of Northeast China was analyzed from the aspects of the geographic position,climatic change law in recent 40 years and effects of northeast sand land desertification on wind erosion in black earth region,which had provided references for the research and prevention of wind erosion in soil of black earth region of Northeast China.
