A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caus...A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caused by convection in the low troposphere is the main producer of positive vorticity, while vertical vorticity transferred by the tilting term from the horizontal vorticity compensates the upward output of cyclonic vorticity. Scale analyses of the vorticity equation suggest that the advection of planetary vorticity can be neglected owing to the low latitude, which is di?erent from the larger scale systems in high latitude areas. In addition, the distribution of relative vorticity tendency on pressure level is not uniform. A vortex will move along the vector from the negative to the positive vorticity tendency region. The mechanism of the phenomenon—that nearly all of the convectively ascending region is located southward/southeastward of the vortex center—is also discussed. Convergence with regard to latent heat release would be in favor of the spin-up of meso-vortex, however, the horizontal vorticity caused by wind shear is tilted by vertical motion due to convection. Consequently, the negative and positive vorticity tendencies are located symmetrically about the convective center, which suggests that the vortex southward movement is dynamically driven by convection.展开更多
This brief review summarizes recent theoretical and experimental results which predict and establish the existence of quantum droplets(QDs),i.e.,robust two-and three-dimensional(2D and 3D)self-trapped states in Bose-E...This brief review summarizes recent theoretical and experimental results which predict and establish the existence of quantum droplets(QDs),i.e.,robust two-and three-dimensional(2D and 3D)self-trapped states in Bose-Einstein condensates(BECs),which are stabilized by effective self-repulsion induced by quantum fluctuations around the mean-field(MF)states[alias the Lee-Huang-Yang(LHY)effect].The basic models are presented,taking special care of the dimension crossover,2D→3D.Recently reported experimental results,which exhibit stable 3D and quasi-2D QDs in binary BECs,with the inter-component attraction slightly exceeding the MF self-repulsion in each component,and in single-component condensates of atoms carrying permanent magnetic moments,are presented in some detail.The summary of theoretical results is focused,chiefly,on 3D and quasi-2D QDs with embedded vorticity,as the possibility to stabilize such states is a remarkable prediction.Stable vortex states are presented both for QDs in free space,and for singular but physically relevant 2D modes pulled to the center by the inverse-square potential,with the quantum collapse suppressed by the LHY effect.展开更多
The characteristics of a flow in spinning devices are one of the fundamental problems innew-type spinning.In this paper the vortex flow in interior of the shell-case was studied by usingexperimental methods,which incl...The characteristics of a flow in spinning devices are one of the fundamental problems innew-type spinning.In this paper the vortex flow in interior of the shell-case was studied by usingexperimental methods,which include flow visualization and laser doppler techniques.The flow sur-vey by measurement has been compared with that photographed by flow visualization method,andshows a fairly good conformity.The results of experiments are similar to those by numericalevaluation.展开更多
文摘A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caused by convection in the low troposphere is the main producer of positive vorticity, while vertical vorticity transferred by the tilting term from the horizontal vorticity compensates the upward output of cyclonic vorticity. Scale analyses of the vorticity equation suggest that the advection of planetary vorticity can be neglected owing to the low latitude, which is di?erent from the larger scale systems in high latitude areas. In addition, the distribution of relative vorticity tendency on pressure level is not uniform. A vortex will move along the vector from the negative to the positive vorticity tendency region. The mechanism of the phenomenon—that nearly all of the convectively ascending region is located southward/southeastward of the vortex center—is also discussed. Convergence with regard to latent heat release would be in favor of the spin-up of meso-vortex, however, the horizontal vorticity caused by wind shear is tilted by vertical motion due to convection. Consequently, the negative and positive vorticity tendencies are located symmetrically about the convective center, which suggests that the vortex southward movement is dynamically driven by convection.
基金Y.L.acknowledges the supports of the National Natural Science Foundation of China(Grant Nos.11874112 and 11905032)the Key Research Projects of General Colleges in Guangdong Province through grant No.2019KZDXM001+1 种基金the Foundation for Distinguished Young Talents in Higher Education of Guangdong through grant No.2018KQNCX279The work of BAM on this topic was supported,in part,by grant No.1286/17 from the Israel Science Foundation.
文摘This brief review summarizes recent theoretical and experimental results which predict and establish the existence of quantum droplets(QDs),i.e.,robust two-and three-dimensional(2D and 3D)self-trapped states in Bose-Einstein condensates(BECs),which are stabilized by effective self-repulsion induced by quantum fluctuations around the mean-field(MF)states[alias the Lee-Huang-Yang(LHY)effect].The basic models are presented,taking special care of the dimension crossover,2D→3D.Recently reported experimental results,which exhibit stable 3D and quasi-2D QDs in binary BECs,with the inter-component attraction slightly exceeding the MF self-repulsion in each component,and in single-component condensates of atoms carrying permanent magnetic moments,are presented in some detail.The summary of theoretical results is focused,chiefly,on 3D and quasi-2D QDs with embedded vorticity,as the possibility to stabilize such states is a remarkable prediction.Stable vortex states are presented both for QDs in free space,and for singular but physically relevant 2D modes pulled to the center by the inverse-square potential,with the quantum collapse suppressed by the LHY effect.
文摘The characteristics of a flow in spinning devices are one of the fundamental problems innew-type spinning.In this paper the vortex flow in interior of the shell-case was studied by usingexperimental methods,which include flow visualization and laser doppler techniques.The flow sur-vey by measurement has been compared with that photographed by flow visualization method,andshows a fairly good conformity.The results of experiments are similar to those by numericalevaluation.
