Formulations of children＇s rights rest on assumptions about the nature of childhood yet conceptions of childhood are not stable across time and space. Such conceptions can be understood as placing different emphases ...Formulations of children＇s rights rest on assumptions about the nature of childhood yet conceptions of childhood are not stable across time and space. Such conceptions can be understood as placing different emphases among three different factors： the child as subservient to parents and ancestors （Child 1）, as a young person requiring special protection and having characteristics distinct from adults （Child 2） and as a novice （Child 3）. Different social arrangements place relatively different emphases on these three factors in their overall conceptions of childhood. Adopting the distinction between Will and Interest rights （Archard 2002）, the paper considers how an emphasis on Child 1, 2 or 3 presupposes and demands a distinctive consideration of children＇s rights. The argument concludes with a reflection on how children＇s rights might be construed if the nature of adulthood is problematised alongside that of childhood. In this case, capabilities （as means to enable functionings） may prove a more fruitful concept than rights （as actual or possible existential conditions）.展开更多
The paper discusses the influence of ions on the formation of clouds, precipitation and thunderstorm electricity. Thermal ionization method is based on two core concepts： electrical micro- and macro-instability of cl...The paper discusses the influence of ions on the formation of clouds, precipitation and thunderstorm electricity. Thermal ionization method is based on two core concepts： electrical micro- and macro-instability of clouds. Cloud droplets increase in sizes in the ascending air under the influence of electric micro-instability. Macro-instability is responsible for the formation of space charges in convective clouds. Artificial rainfall and discharge of space charges of clouds may be caused by means of the electrical modification techniques. The key role in these processes belongs to thermionic production of artificial light and heavy ions, which are formed as the result of applying a pyrotechnic composition of potassium-magnesium compounds. Negative ions are hydrated and adsorbed by cloud droplets leading to their growth and further rainfall. An artificial ionized channel allows to change cloud conductivity, which prevents clouds from accumulating thunderstorm electricity. Electrical methods of cloud modification can be used for the artificial induction of precipitation, prevention of natural hazards, thunderstorms, tornadoes and heavy rains.展开更多
A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale v...A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale vortex structures represented by tangential vortices are obtained and compared with flow visualization. Also presented are three-dimensional spatial evolutions of coherent structure, which are of quasi two-dimensional Kelvin-Helmholtz instability and vortex rings as well as breaking up of the vortex rings with fully three-dimensional characteristics. Predicted results of mean velocity and turbulent intensity agree well with experiments. They are also compared with the results predicted by LES using standard Smagorinsky model and show good self-similarity. Turbulence spectrum of the predicted velocity shows the -5/3 decay for higher wave number, as expected for turbulent round jet flows. In addition, fl-test and y-test are carded out for the instantaneous velocity, showing that the present LES method can successfully predict the hierarchical structure of round jet.展开更多
A numerical study of the effect of discrete micro tip injection on unsteady tip clearance flow pattern in an isolated axial compressor rotor is presented, intending to better understand the flow mechanism behind stall...A numerical study of the effect of discrete micro tip injection on unsteady tip clearance flow pattern in an isolated axial compressor rotor is presented, intending to better understand the flow mechanism behind stall control measures that act on tip clearance flow. Under the influence of injection the unsteadiness of self-induced tip clearance flow could be weakened. Also the radial migration of tip clearance vortex is confined to a smaller radial extent near the rotor tip and the trajectory of tip clearance flow is pushed more downstream. So the injection is beneficial to improve compressor stability and increase static pressure rise near rotor tip region. The results of injection with different injected mass flow rates show that for the special type of injector adopted in the paper the effect of injection on tip clearance flow may be different according to the relative strength between these two streams of flow. For a fixed injected mass flow rate, reducing the injector area to increase injection velocity can improve the effect of injection on tip clearance flow and thus the compressor stability. A comparison of calculations between single blade passage and multiple blade passages validates the utility of single passage computations to investigate the tip clearance flow for the case without injection and its interaction with injected flow for the case with tip injection.展开更多
We investigate the nonlinear instability of a smooth steady density profile solution to the threedimensional nonhomogeneous incompressible Navier-Stokes equations in the presence of a uniform gravitational field,inclu...We investigate the nonlinear instability of a smooth steady density profile solution to the threedimensional nonhomogeneous incompressible Navier-Stokes equations in the presence of a uniform gravitational field,including a Rayleigh-Taylor steady-state solution with heavier density with increasing height(referred to the Rayleigh-Taylor instability).We first analyze the equations obtained from linearization around the steady density profile solution.Then we construct solutions to the linearized problem that grow in time in the Sobolev space H k,thus leading to a global instability result for the linearized problem.With the help of the constructed unstable solutions and an existence theorem of classical solutions to the original nonlinear equations,we can then demonstrate the instability of the nonlinear problem in some sense.Our analysis shows that the third component of the velocity already induces the instability,which is different from the previous known results.展开更多
Cannibalism is an intriguing life history trait, that has been considered primarily in the predator, in predator-prey population models. Recent experimental evidence shows that prey cannibalism can have a significant ...Cannibalism is an intriguing life history trait, that has been considered primarily in the predator, in predator-prey population models. Recent experimental evidence shows that prey cannibalism can have a significant impact on predator-prey population dyna- mics in natural communities. Motivated by these experimental results, we investigate a ratio-dependent Holling-Tanner model, where cannibalism occurs simultaneously in both the predator and prey species. We show that depending on parameters, whilst prey or predator cannibalism acting alone leads to instability, their joint effect can actually stabilize the unstable interior equilibrium. Furthermore, in the spatially explicit model, we find that depending on parameters, prey and predator cannibalism acting jointly can cause spatial patterns to form, while not so acting individually. We discuss ecologicalconsequences of these findings in light of food chain dynamics, invasive species control and climate change.展开更多
In this paper, the author at first develops a method to study convergence of the cascadealgorithm in a Banach space without stable assumption on the initial (see Theorem 2.1), andthen applies the previous result on th...In this paper, the author at first develops a method to study convergence of the cascadealgorithm in a Banach space without stable assumption on the initial (see Theorem 2.1), andthen applies the previous result on the convergence to characterizing compactly supportedrefinable distributions in fractional Sobolev spaces and Holder continuous spaces (see Theorems3.1, 3.3, and 3.4). Finally the author applies the above characterization to choosing appropriateinitial to guarantee the convergence of the cascade algorithm (see Theorem 4.2).展开更多
This paper deals with the stability analysis to a three-species food chain model with crossdiffusion, the results of which show that there is no Turing instability but crossdiffusion makes the model instability possib...This paper deals with the stability analysis to a three-species food chain model with crossdiffusion, the results of which show that there is no Turing instability but crossdiffusion makes the model instability possible. We then show that the spatial patterns are spotted patterns by using numerical simulations. In order to understand why the spatial patterns happen, the existence of the nonhomogeneous steady states is investigated. Finally, using the Leray-Schauder theory, we demonstrate that cross-diffusion creates nonhomogeneous stationary patterns.展开更多
文摘Formulations of children＇s rights rest on assumptions about the nature of childhood yet conceptions of childhood are not stable across time and space. Such conceptions can be understood as placing different emphases among three different factors： the child as subservient to parents and ancestors （Child 1）, as a young person requiring special protection and having characteristics distinct from adults （Child 2） and as a novice （Child 3）. Different social arrangements place relatively different emphases on these three factors in their overall conceptions of childhood. Adopting the distinction between Will and Interest rights （Archard 2002）, the paper considers how an emphasis on Child 1, 2 or 3 presupposes and demands a distinctive consideration of children＇s rights. The argument concludes with a reflection on how children＇s rights might be construed if the nature of adulthood is problematised alongside that of childhood. In this case, capabilities （as means to enable functionings） may prove a more fruitful concept than rights （as actual or possible existential conditions）.
文摘The paper discusses the influence of ions on the formation of clouds, precipitation and thunderstorm electricity. Thermal ionization method is based on two core concepts： electrical micro- and macro-instability of clouds. Cloud droplets increase in sizes in the ascending air under the influence of electric micro-instability. Macro-instability is responsible for the formation of space charges in convective clouds. Artificial rainfall and discharge of space charges of clouds may be caused by means of the electrical modification techniques. The key role in these processes belongs to thermionic production of artificial light and heavy ions, which are formed as the result of applying a pyrotechnic composition of potassium-magnesium compounds. Negative ions are hydrated and adsorbed by cloud droplets leading to their growth and further rainfall. An artificial ionized channel allows to change cloud conductivity, which prevents clouds from accumulating thunderstorm electricity. Electrical methods of cloud modification can be used for the artificial induction of precipitation, prevention of natural hazards, thunderstorms, tornadoes and heavy rains.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50176027 and 50706021)a grant from the Research Committee of The Hong Kong Polytechnic University (Grant No.G-U294)
文摘A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale vortex structures represented by tangential vortices are obtained and compared with flow visualization. Also presented are three-dimensional spatial evolutions of coherent structure, which are of quasi two-dimensional Kelvin-Helmholtz instability and vortex rings as well as breaking up of the vortex rings with fully three-dimensional characteristics. Predicted results of mean velocity and turbulent intensity agree well with experiments. They are also compared with the results predicted by LES using standard Smagorinsky model and show good self-similarity. Turbulence spectrum of the predicted velocity shows the -5/3 decay for higher wave number, as expected for turbulent round jet flows. In addition, fl-test and y-test are carded out for the instantaneous velocity, showing that the present LES method can successfully predict the hierarchical structure of round jet.
基金This work was supported by National Natural Science Foundation of China with project No.50406027.This support is gratefully acknowledged.
文摘A numerical study of the effect of discrete micro tip injection on unsteady tip clearance flow pattern in an isolated axial compressor rotor is presented, intending to better understand the flow mechanism behind stall control measures that act on tip clearance flow. Under the influence of injection the unsteadiness of self-induced tip clearance flow could be weakened. Also the radial migration of tip clearance vortex is confined to a smaller radial extent near the rotor tip and the trajectory of tip clearance flow is pushed more downstream. So the injection is beneficial to improve compressor stability and increase static pressure rise near rotor tip region. The results of injection with different injected mass flow rates show that for the special type of injector adopted in the paper the effect of injection on tip clearance flow may be different according to the relative strength between these two streams of flow. For a fixed injected mass flow rate, reducing the injector area to increase injection velocity can improve the effect of injection on tip clearance flow and thus the compressor stability. A comparison of calculations between single blade passage and multiple blade passages validates the utility of single passage computations to investigate the tip clearance flow for the case without injection and its interaction with injected flow for the case with tip injection.
基金supported by National Natural Science Foundation of China (Grant Nos. 11101044,11271051,11229101 and 91130020)National Basic Research Program of China (Grant No.2011CB309705)
文摘We investigate the nonlinear instability of a smooth steady density profile solution to the threedimensional nonhomogeneous incompressible Navier-Stokes equations in the presence of a uniform gravitational field,including a Rayleigh-Taylor steady-state solution with heavier density with increasing height(referred to the Rayleigh-Taylor instability).We first analyze the equations obtained from linearization around the steady density profile solution.Then we construct solutions to the linearized problem that grow in time in the Sobolev space H k,thus leading to a global instability result for the linearized problem.With the help of the constructed unstable solutions and an existence theorem of classical solutions to the original nonlinear equations,we can then demonstrate the instability of the nonlinear problem in some sense.Our analysis shows that the third component of the velocity already induces the instability,which is different from the previous known results.
文摘Cannibalism is an intriguing life history trait, that has been considered primarily in the predator, in predator-prey population models. Recent experimental evidence shows that prey cannibalism can have a significant impact on predator-prey population dyna- mics in natural communities. Motivated by these experimental results, we investigate a ratio-dependent Holling-Tanner model, where cannibalism occurs simultaneously in both the predator and prey species. We show that depending on parameters, whilst prey or predator cannibalism acting alone leads to instability, their joint effect can actually stabilize the unstable interior equilibrium. Furthermore, in the spatially explicit model, we find that depending on parameters, prey and predator cannibalism acting jointly can cause spatial patterns to form, while not so acting individually. We discuss ecologicalconsequences of these findings in light of food chain dynamics, invasive species control and climate change.
文摘In this paper, the author at first develops a method to study convergence of the cascadealgorithm in a Banach space without stable assumption on the initial (see Theorem 2.1), andthen applies the previous result on the convergence to characterizing compactly supportedrefinable distributions in fractional Sobolev spaces and Holder continuous spaces (see Theorems3.1, 3.3, and 3.4). Finally the author applies the above characterization to choosing appropriateinitial to guarantee the convergence of the cascade algorithm (see Theorem 4.2).
文摘This paper deals with the stability analysis to a three-species food chain model with crossdiffusion, the results of which show that there is no Turing instability but crossdiffusion makes the model instability possible. We then show that the spatial patterns are spotted patterns by using numerical simulations. In order to understand why the spatial patterns happen, the existence of the nonhomogeneous steady states is investigated. Finally, using the Leray-Schauder theory, we demonstrate that cross-diffusion creates nonhomogeneous stationary patterns.
