With abundant wind resources and high pressure imposed on en-vironmental protection, wind power development has a promising future. Butdue to intermittent nature, wind power can bring into full play only if being con-...With abundant wind resources and high pressure imposed on en-vironmental protection, wind power development has a promising future. Butdue to intermittent nature, wind power can bring into full play only if being con-nected into power grid to ensure its supply reliability and continuity, aswell as operational economy. However, technical and market barriers haveprevented wind power from integrating into power grid. To foster wind powerdevelopment, these barriers should be removed by both government incentivepolicies and sophisticated technologies.展开更多
We have studied the nucleation process of a two-dimensional kinetic Ising model subject to a bias oscillating external field, focusing on how the nucleation time depends on the oscillation frequency. It is found that ...We have studied the nucleation process of a two-dimensional kinetic Ising model subject to a bias oscillating external field, focusing on how the nucleation time depends on the oscillation frequency. It is found that the nucleation time shows a clear-cut minimum with the variation of oscillation frequency, wherein the average size of the critical nuclei is the smallest, indicating that an oscillating external field with an optimal frequency can be much more favorable to the nucleation process than a constant field. We have also investigated the effect of the initial phase of the external field, which helps to illustrate the occurrence of such an interesting finding.展开更多
We report the oscillating propagation of kink in a nondissipative Frenkel-Kontorova （FK） chain driven by external DC force, which is different from the usual propagation of localized modes with equal speed. When the...We report the oscillating propagation of kink in a nondissipative Frenkel-Kontorova （FK） chain driven by external DC force, which is different from the usual propagation of localized modes with equal speed. When the kink moves in the opposite direction of the external DC force, the kink will be accelerated and the potential of the FK chain in the external force field is transformed to be the kinetic energy of the kink. If the kink reaches the boundary of the FK chain, the kink will be bounced back and moves in the opposite direction, then the kink will be decelerated gradually and the kinetic energy of the kink ＆ transformed to be the potential of the FK chain in the external force field. If the speed of the kink reaches zero, the kink will move in the opposite direction again driven by the external DC force, and a new oscillating cycle begins. Simulation result demonstrates exactly the transformation between the kinetic energy of the kink and the potential of the FK chain in the external force field. The interesting energy exchange is induced by the special topology of kinks, and other localized modes, such as breathers and envelope solitons, have no the interesting phenomenon.展开更多
Spain became a net receiver country of a high number of foreigners entering the labour market in the first decade of the 21 st century. The ensuing economic crisis, beginning in 2007, led to the destruction of a large...Spain became a net receiver country of a high number of foreigners entering the labour market in the first decade of the 21 st century. The ensuing economic crisis, beginning in 2007, led to the destruction of a large number of companies and jobs. The objective of this paper is to analyze the relationship between educational level, employment and economic activity, in the Spanish and foreign working population in the Spanish labour market and the impact that the economic crisis is having on employment and self-employment. The hypotheses considered have been as followed--HI： The economic crisis mainly affects the less educated working population, both Spanish and foreign; H2： Self-employment is characterized by being an initiative of a working population with low educational levels for both population groups （Spanish and foreign）; H3： Employment is related to the productive economic structure. Micro-data from the Labour Force Survey 2009 （EPA in Spanish） has been used, compiled by Spains National Statistics Office （INE in Spanish）, and it has been applied Multiple Correspondence Analysis （MCA） to detect possible associations among the study variables （nationality, level of education, salaried employment, self-employment and economic activity）. The results show significant differences between both groups： Spanish and foreign working population. The study also shows how the crisis affects employment, and the important role played by the educational level of the working population, especially foreigners employed in certain economic activities.展开更多
This paper proposes a novel dynamic control approach for a cable-driven robot with high redundant actuation and cable tension limitations to perform tracking task while interacting with environment. In order for a cab...This paper proposes a novel dynamic control approach for a cable-driven robot with high redundant actuation and cable tension limitations to perform tracking task while interacting with environment. In order for a cable-driven exoskeleton robot to execute the task smoothly and safely, it is necessary to consider the tracking motion performance as well as passivity when interacting with the environment under the conditions of the actuation cables＇ redundancy and the pulling limitation. With the additional consideration of the maximum limitation of the cable tension, cable-driven robot actually can only apply a certain range of feasible wrench on the external environment, which makes the task executed by robot be restricted. In order to make designed wrench be feasible and keep the desired trajectory tracking ability, we present a new control method by extending PVFC （passive velocity field control） method considering tracking stability and passivity. The approach augmented a higher dimensional virtual flywheel dynamics in a specific orthogonal complement space of the cable＇s actuation space. After the final adjustment of the designed wrench with respect to the cable＇s constraint, this method is capable of driving the cable robot to complete the trajectory tracking task and realize the passivity.展开更多
The concept of using an externally applied magnetic field to add the drag force of a hypersonic reentry vehicle during the blackout was proposed by Bush in 1958.The increased drag force is caused by electromagnetic fo...The concept of using an externally applied magnetic field to add the drag force of a hypersonic reentry vehicle during the blackout was proposed by Bush in 1958.The increased drag force is caused by electromagnetic force that is introduced by interaction between the applied magnetic field and the weakly ionized airflow around the reentry vehicle.We investigated the influences of magnetic field intensities on the drag forces of a reentry vehicle by three dimensional(3-D)magnetohydrodynamics(MHD)simulation.The results showed that the drag fore exerted on the vehicle reached 25 kN when the magnetic field was 0.4 T.The drag force increased with the enhanced intial magnetic field.The bow shock was also pushed far away from the vehicle when the magnetic field was strengthened.展开更多
Based on a two-qubit isotropic Heisenberg XXX model with a constant external magnetic field,we construct a four-level entangled quantum heat engine(QHE).The expressions for several thermodynamic quantities such as the...Based on a two-qubit isotropic Heisenberg XXX model with a constant external magnetic field,we construct a four-level entangled quantum heat engine(QHE).The expressions for several thermodynamic quantities such as the heat transferred,the work and efficiency are derived.Moreover,the influence of the entanglement on the thermodynamic quantities is investigated analytically and numerically.Several interesting features of the variation of the heat transferred,the work and the efficiency with the concurrences of the thermal entanglement of different thermal equilibrium states are obtained.展开更多
A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are...A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are discussed in detail It is shown that, relative to the mass of particulate, the charge and magnetic field have a more considerable effect on the diffusion process, particularly on the resulting structure of the system. The dependence of diffusion coecient on the temperature is shown to be linearly changed over a wide range of temperature.展开更多
文摘With abundant wind resources and high pressure imposed on en-vironmental protection, wind power development has a promising future. Butdue to intermittent nature, wind power can bring into full play only if being con-nected into power grid to ensure its supply reliability and continuity, aswell as operational economy. However, technical and market barriers haveprevented wind power from integrating into power grid. To foster wind powerdevelopment, these barriers should be removed by both government incentivepolicies and sophisticated technologies.
基金V. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China （No.21125313, No.20933006,and No.91027012）
文摘We have studied the nucleation process of a two-dimensional kinetic Ising model subject to a bias oscillating external field, focusing on how the nucleation time depends on the oscillation frequency. It is found that the nucleation time shows a clear-cut minimum with the variation of oscillation frequency, wherein the average size of the critical nuclei is the smallest, indicating that an oscillating external field with an optimal frequency can be much more favorable to the nucleation process than a constant field. We have also investigated the effect of the initial phase of the external field, which helps to illustrate the occurrence of such an interesting finding.
基金supported by Scientific Research Fund of Hunan Provincial Education Department under Grant No. 07B075Interactive Project Fund of Xiangtan University under Grant No. 061ND09Dr. Shangyou Zeng's Initial Scientific Research Fund of Xiangtan University
文摘We report the oscillating propagation of kink in a nondissipative Frenkel-Kontorova （FK） chain driven by external DC force, which is different from the usual propagation of localized modes with equal speed. When the kink moves in the opposite direction of the external DC force, the kink will be accelerated and the potential of the FK chain in the external force field is transformed to be the kinetic energy of the kink. If the kink reaches the boundary of the FK chain, the kink will be bounced back and moves in the opposite direction, then the kink will be decelerated gradually and the kinetic energy of the kink ＆ transformed to be the potential of the FK chain in the external force field. If the speed of the kink reaches zero, the kink will move in the opposite direction again driven by the external DC force, and a new oscillating cycle begins. Simulation result demonstrates exactly the transformation between the kinetic energy of the kink and the potential of the FK chain in the external force field. The interesting energy exchange is induced by the special topology of kinks, and other localized modes, such as breathers and envelope solitons, have no the interesting phenomenon.
文摘Spain became a net receiver country of a high number of foreigners entering the labour market in the first decade of the 21 st century. The ensuing economic crisis, beginning in 2007, led to the destruction of a large number of companies and jobs. The objective of this paper is to analyze the relationship between educational level, employment and economic activity, in the Spanish and foreign working population in the Spanish labour market and the impact that the economic crisis is having on employment and self-employment. The hypotheses considered have been as followed--HI： The economic crisis mainly affects the less educated working population, both Spanish and foreign; H2： Self-employment is characterized by being an initiative of a working population with low educational levels for both population groups （Spanish and foreign）; H3： Employment is related to the productive economic structure. Micro-data from the Labour Force Survey 2009 （EPA in Spanish） has been used, compiled by Spains National Statistics Office （INE in Spanish）, and it has been applied Multiple Correspondence Analysis （MCA） to detect possible associations among the study variables （nationality, level of education, salaried employment, self-employment and economic activity）. The results show significant differences between both groups： Spanish and foreign working population. The study also shows how the crisis affects employment, and the important role played by the educational level of the working population, especially foreigners employed in certain economic activities.
基金This research has been partially supported by National Natural Science Foundation of China under Grant No. 61472117.
文摘This paper proposes a novel dynamic control approach for a cable-driven robot with high redundant actuation and cable tension limitations to perform tracking task while interacting with environment. In order for a cable-driven exoskeleton robot to execute the task smoothly and safely, it is necessary to consider the tracking motion performance as well as passivity when interacting with the environment under the conditions of the actuation cables＇ redundancy and the pulling limitation. With the additional consideration of the maximum limitation of the cable tension, cable-driven robot actually can only apply a certain range of feasible wrench on the external environment, which makes the task executed by robot be restricted. In order to make designed wrench be feasible and keep the desired trajectory tracking ability, we present a new control method by extending PVFC （passive velocity field control） method considering tracking stability and passivity. The approach augmented a higher dimensional virtual flywheel dynamics in a specific orthogonal complement space of the cable＇s actuation space. After the final adjustment of the designed wrench with respect to the cable＇s constraint, this method is capable of driving the cable robot to complete the trajectory tracking task and realize the passivity.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41204105,41104093,41174122)the Chinese Academy of Sciences (Grant No. KZZD-EW-01-3)
文摘The concept of using an externally applied magnetic field to add the drag force of a hypersonic reentry vehicle during the blackout was proposed by Bush in 1958.The increased drag force is caused by electromagnetic force that is introduced by interaction between the applied magnetic field and the weakly ionized airflow around the reentry vehicle.We investigated the influences of magnetic field intensities on the drag forces of a reentry vehicle by three dimensional(3-D)magnetohydrodynamics(MHD)simulation.The results showed that the drag fore exerted on the vehicle reached 25 kN when the magnetic field was 0.4 T.The drag force increased with the enhanced intial magnetic field.The bow shock was also pushed far away from the vehicle when the magnetic field was strengthened.
基金supported by the National Natural Science Foundation of China (Grant No. 11065008)
文摘Based on a two-qubit isotropic Heisenberg XXX model with a constant external magnetic field,we construct a four-level entangled quantum heat engine(QHE).The expressions for several thermodynamic quantities such as the heat transferred,the work and efficiency are derived.Moreover,the influence of the entanglement on the thermodynamic quantities is investigated analytically and numerically.Several interesting features of the variation of the heat transferred,the work and the efficiency with the concurrences of the thermal entanglement of different thermal equilibrium states are obtained.
基金Supported by National Magnetic Confinement Fusion Science Program under Grant No.2013GB111005the Foundation of Civil Aviation University of China under Grant No.08QD07X
文摘A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are discussed in detail It is shown that, relative to the mass of particulate, the charge and magnetic field have a more considerable effect on the diffusion process, particularly on the resulting structure of the system. The dependence of diffusion coecient on the temperature is shown to be linearly changed over a wide range of temperature.
