Based on trajectory equations of gas bubble,an eddy-bubble interaction(EBI)model was developed. This model considered the effect of non-drag forces and took the eddy-bubble interaction time as the refreshing time scal...Based on trajectory equations of gas bubble,an eddy-bubble interaction(EBI)model was developed. This model considered the effect of non-drag forces and took the eddy-bubble interaction time as the refreshing time scale of turbulent fluctuations.The relationship between the crossing-eddy time and the eddy lifetime was discussed,and the predicted distributions of radial,axial velocities of bubbles and gas holdup were also given. Compared with eddy lifetime(EL)model,the EBI model gives somewhat smaller axial velocity in the upper circulation region and larger velocity in the lower circulation region,causing that fewer bubbles reach the lower circulation region and gas holdup becomes higher in the upper circulation region.The predicted gas holdup by the EBI model approaches closer to the experimental data in the discharge stream region.展开更多
By Monte Carlo simulations, the effect of the dispersion of particle size distribution on the spatial density distributions and correlations of a quasi one-dimensional polydisperse granular gas with fractal size distr...By Monte Carlo simulations, the effect of the dispersion of particle size distribution on the spatial density distributions and correlations of a quasi one-dimensional polydisperse granular gas with fractal size distribution is investigated in the same inelasticity. The dispersive degree of the particle size distribution can be measured by a fractal dimension dr, and the smooth particles are constrained to move along a circle of length L, colliding inelastically with each other and thermalized by a viscosity heat bath. When the typical relaxation time τ of the driving Brownian process is longer than the mean collision time To, the system can reach a nonequilibrium steady state. The average energy of the system decays exponentially with time towards a stable asymptotic value, and the energy relaxation time τB to the steady state becomes shorter with increasing values of df. In the steady state, the spatial density distribution becomes more clusterized as df increases, which can be quantitatively characterized by statistical entropy of the system. Furthermore, the spatial correlation functions of density and velocities are found to be a power-law form for small separation distance of particles, and both of the correlations become stronger with the increase of df. Also, tile density clusterization is explained from the correlations.展开更多
We study theoretically the effect of weak external magnetic fields on persistent spin helix states in semiconductor two-dimensional electron gases with both Rashba and linear-in-momentum Dresselhaus spin-orbit couplin...We study theoretically the effect of weak external magnetic fields on persistent spin helix states in semiconductor two-dimensional electron gases with both Rashba and linear-in-momentum Dresselhaus spin-orbit coupling.We show that in the presence of weak external magnetic fields, some basic properties of a persistent spin helix state,including the dispersion relation between the decay time and the magnitude of the wavevector, the maximum decay time and the value of the characteristic magnitude of the wavevector at which the maximum decay time occurs, will all depend sensitively on the directions of applied external magnetic fields.展开更多
基金Supported by the National Natural Science Foundation of China（20776121） the Scientific Fund of Hunan Provincial Education Department（07C765 07C744）
文摘Based on trajectory equations of gas bubble,an eddy-bubble interaction(EBI)model was developed. This model considered the effect of non-drag forces and took the eddy-bubble interaction time as the refreshing time scale of turbulent fluctuations.The relationship between the crossing-eddy time and the eddy lifetime was discussed,and the predicted distributions of radial,axial velocities of bubbles and gas holdup were also given. Compared with eddy lifetime(EL)model,the EBI model gives somewhat smaller axial velocity in the upper circulation region and larger velocity in the lower circulation region,causing that fewer bubbles reach the lower circulation region and gas holdup becomes higher in the upper circulation region.The predicted gas holdup by the EBI model approaches closer to the experimental data in the discharge stream region.
基金supported by National Natural Science Foundation of China under Grant Nos.10675048 and 1068006the Natural Science Foundation of Xianning College under Grant No.KZ0916
文摘By Monte Carlo simulations, the effect of the dispersion of particle size distribution on the spatial density distributions and correlations of a quasi one-dimensional polydisperse granular gas with fractal size distribution is investigated in the same inelasticity. The dispersive degree of the particle size distribution can be measured by a fractal dimension dr, and the smooth particles are constrained to move along a circle of length L, colliding inelastically with each other and thermalized by a viscosity heat bath. When the typical relaxation time τ of the driving Brownian process is longer than the mean collision time To, the system can reach a nonequilibrium steady state. The average energy of the system decays exponentially with time towards a stable asymptotic value, and the energy relaxation time τB to the steady state becomes shorter with increasing values of df. In the steady state, the spatial density distribution becomes more clusterized as df increases, which can be quantitatively characterized by statistical entropy of the system. Furthermore, the spatial correlation functions of density and velocities are found to be a power-law form for small separation distance of particles, and both of the correlations become stronger with the increase of df. Also, tile density clusterization is explained from the correlations.
基金Supported by the National Natural Science Foundation of China under Grant No.10874049
文摘We study theoretically the effect of weak external magnetic fields on persistent spin helix states in semiconductor two-dimensional electron gases with both Rashba and linear-in-momentum Dresselhaus spin-orbit coupling.We show that in the presence of weak external magnetic fields, some basic properties of a persistent spin helix state,including the dispersion relation between the decay time and the magnitude of the wavevector, the maximum decay time and the value of the characteristic magnitude of the wavevector at which the maximum decay time occurs, will all depend sensitively on the directions of applied external magnetic fields.
