It is shown that an impulsive force acting on a particle perpendicular to its velocity vector cannot change its direction of motion without increasing its kinetic energy. If the particle’s kinetic energy is to remain...It is shown that an impulsive force acting on a particle perpendicular to its velocity vector cannot change its direction of motion without increasing its kinetic energy. If the particle’s kinetic energy is to remain unchanged, the impulsive force must have a component in the direction opposite to the direction of motion. This situation is also realized in the case of a continuous force acting perpendicular to the velocity vector of the particle, when the particle's motion is viewed as a sequence of infinitesimal steps.展开更多
The FY-2C meteorological satellite had been working well for 8 years as of October 19, 2012. Though the satellite was originally designed to work for 3 years, it still operates steadily. As the nation's first oper...The FY-2C meteorological satellite had been working well for 8 years as of October 19, 2012. Though the satellite was originally designed to work for 3 years, it still operates steadily. As the nation's first operational first-generation geo- stationary meteorological satellite, FY-2C works together with the following satellites FY-2D, FY-2E and FY-2F, in a operational mode of two operational plus two backup ones. FY-2C, FY-2D and FY-2E were the second batch satellites of FY-2 series展开更多
In China, economic growing speed converts from high speed to moderate and high speed; economic structure enters from moderate and low end to moderate and high end; development power converts from investment drive to i...In China, economic growing speed converts from high speed to moderate and high speed; economic structure enters from moderate and low end to moderate and high end; development power converts from investment drive to innovation drive, and investment of resource and environ- ment factors presents declining trend. Spatial pattern of economy development is changing greatly, which needs eco-civilization construction and en- vironmental protection field continuously adjusting focus, environmental rules and laws correspondingly regulating, eco-civilization construction and environmental protection field also entering into new normal state. It requires scientifically understanding, actively adapting to and responding to new normal state of eco-civilization construction and environmental protection,and fighting a tough fight. Firstly, we should handle with the relationship between environment and economy, and strive to explore the way of environmental protection. Secondly, we should insist protection priority and prevention oriented,and promote transformation of environmental management strategy. Finally, we should accelerate to promote eco-civilization system reform and environmental protection management system reform, and further promote environmental protection work in Xi＇an on new level from eight aspects.展开更多
The bolt anchoring force is closely related to the shear properties of the anchor interface. The shear stress distribution of full-length grouted bolts is analyzed based on the stress-strain relationship among the bol...The bolt anchoring force is closely related to the shear properties of the anchor interface. The shear stress distribution of full-length grouted bolts is analyzed based on the stress-strain relationship among the bolt, grout, rock mass and bond interface,considering the shear properties of the grout and contact interface bonding behavior. In this case, the interfacial shear stress of the grout and rock mass and the bolt axial force are obtained under pull-out and normal working conditions. The results show that the peak shear stress of the interface with the shear deformation of the bond interface is significantly lower than that without it when the pull-out force is applied. When designing bolt parameters of grade IV and V rock mass, the relative deformation between the rock mass and anchor should be considered, with a “unimodal” to “bimodal” shear stress distribution.In the case of a low elastic modulus of rock masses,both the shear stress concentration and distribution range are obvious, and the neutral point is near the bolt head. As the elastic modulus increases, the shear stress concentration and distribution range are reduced, and the neutral point moves towards the distal end. As a result, the optimum length of fulllength grouted bolts can be determined by in-situ pull-out tests and decreases with the increased elastic modulus of the rock mass.展开更多
文摘It is shown that an impulsive force acting on a particle perpendicular to its velocity vector cannot change its direction of motion without increasing its kinetic energy. If the particle’s kinetic energy is to remain unchanged, the impulsive force must have a component in the direction opposite to the direction of motion. This situation is also realized in the case of a continuous force acting perpendicular to the velocity vector of the particle, when the particle's motion is viewed as a sequence of infinitesimal steps.
文摘The FY-2C meteorological satellite had been working well for 8 years as of October 19, 2012. Though the satellite was originally designed to work for 3 years, it still operates steadily. As the nation's first operational first-generation geo- stationary meteorological satellite, FY-2C works together with the following satellites FY-2D, FY-2E and FY-2F, in a operational mode of two operational plus two backup ones. FY-2C, FY-2D and FY-2E were the second batch satellites of FY-2 series
文摘In China, economic growing speed converts from high speed to moderate and high speed; economic structure enters from moderate and low end to moderate and high end; development power converts from investment drive to innovation drive, and investment of resource and environ- ment factors presents declining trend. Spatial pattern of economy development is changing greatly, which needs eco-civilization construction and en- vironmental protection field continuously adjusting focus, environmental rules and laws correspondingly regulating, eco-civilization construction and environmental protection field also entering into new normal state. It requires scientifically understanding, actively adapting to and responding to new normal state of eco-civilization construction and environmental protection,and fighting a tough fight. Firstly, we should handle with the relationship between environment and economy, and strive to explore the way of environmental protection. Secondly, we should insist protection priority and prevention oriented,and promote transformation of environmental management strategy. Finally, we should accelerate to promote eco-civilization system reform and environmental protection management system reform, and further promote environmental protection work in Xi＇an on new level from eight aspects.
基金funded by the Natural Science Foundation of China(Grants Nos.52179113,42207199,41831278)。
文摘The bolt anchoring force is closely related to the shear properties of the anchor interface. The shear stress distribution of full-length grouted bolts is analyzed based on the stress-strain relationship among the bolt, grout, rock mass and bond interface,considering the shear properties of the grout and contact interface bonding behavior. In this case, the interfacial shear stress of the grout and rock mass and the bolt axial force are obtained under pull-out and normal working conditions. The results show that the peak shear stress of the interface with the shear deformation of the bond interface is significantly lower than that without it when the pull-out force is applied. When designing bolt parameters of grade IV and V rock mass, the relative deformation between the rock mass and anchor should be considered, with a “unimodal” to “bimodal” shear stress distribution.In the case of a low elastic modulus of rock masses,both the shear stress concentration and distribution range are obvious, and the neutral point is near the bolt head. As the elastic modulus increases, the shear stress concentration and distribution range are reduced, and the neutral point moves towards the distal end. As a result, the optimum length of fulllength grouted bolts can be determined by in-situ pull-out tests and decreases with the increased elastic modulus of the rock mass.
