By using the equations describing typhoons in the atmosphere, the steady three-dimensional stream fieldand the corresponding pressure and temperature fields are obtained. The three-dimensional velocity fields construc...By using the equations describing typhoons in the atmosphere, the steady three-dimensional stream fieldand the corresponding pressure and temperature fields are obtained. The three-dimensional velocity fields construct anonlinear autonomuos system in the physical space. It is shown that the center of typhoon is a local minimum pressurewith positive vertical vorticity and horizontal convergence in lower levels and a local maximum pressure with negativevertical vorticity and horizontal divergence in the upper levels. Because there exits two saddle-focus points in the autnomous system, there exist the spiral patterns, in which the winds blow spirally in and out of the center in the lowerand upper levels in the Northern Hemisphere and cause the ascending motion near the center and dascending motionnear the edge, respectively . All these are in fair conformity with the observations. It implies that the rotation of earthand the viscosity of air play an important role in the spiral structure of typhoons.展开更多
Spiral patterns widely exist in both macroscopic and microscopic systems such as hearts,bacteria,and active matters but have never been reported at molecular length scale.The emergence of spiral patterns has considera...Spiral patterns widely exist in both macroscopic and microscopic systems such as hearts,bacteria,and active matters but have never been reported at molecular length scale.The emergence of spiral patterns has considerable impacts on the trajectories of the objects and thus usually relates to various physical,chemical,biological and physiological processes.In this paper,we show that,down to the length scale of only several Angstroms,asymmetric molecules exhibit spiral patterns in their trajectories within finite time based on the under-damped Langevin equation and demonstrated by molecular dynamics simulation.The key to this observation lies in the asymmetric molecular architecture that leads to a translation-rotation coupling.This finding enriches the knowledge of spiral patterns to the molecular length scale,provides a new insight into the understanding of various processes at the molecular level,and may evoke new ideas on the understanding of the vortices in turbulence.展开更多
Flasher origami pattern has been widely utilized to improve the stowage efficiency of deployable structures.Nevertheless,flasher origami cannot be folded fully flat,and they still have great potential for optimization...Flasher origami pattern has been widely utilized to improve the stowage efficiency of deployable structures.Nevertheless,flasher origami cannot be folded fully flat,and they still have great potential for optimization in terms of storage volume and folding creases.In this paper,a flat foldable equiangular spiral folding pattern inspired by the sunflower disk is introduced.Then,a parametric design method for this equiangular spiral crease diagram is introduced in detail.Subsequently,a kinematic model of the equiangular spiral folding pattern is established based on the kinematic equivalence between rigid origami and spherical linkages.A simulation of the developed model demonstrates that the equiangular spiral folding pattern can be folded flat.Using the folded ratio as an evaluation index,the calculated results and experiments show that the equiangular spiral crease pattern can yield fewer creases and improve stowage efficiency in comparison to flasher origami pattern.Equiangular spiral folding pattern can save a considerable amount of space and provide a new approach to spatially deployable structures.展开更多
文摘By using the equations describing typhoons in the atmosphere, the steady three-dimensional stream fieldand the corresponding pressure and temperature fields are obtained. The three-dimensional velocity fields construct anonlinear autonomuos system in the physical space. It is shown that the center of typhoon is a local minimum pressurewith positive vertical vorticity and horizontal convergence in lower levels and a local maximum pressure with negativevertical vorticity and horizontal divergence in the upper levels. Because there exits two saddle-focus points in the autnomous system, there exist the spiral patterns, in which the winds blow spirally in and out of the center in the lowerand upper levels in the Northern Hemisphere and cause the ascending motion near the center and dascending motionnear the edge, respectively . All these are in fair conformity with the observations. It implies that the rotation of earthand the viscosity of air play an important role in the spiral structure of typhoons.
基金supported by the National Natural Science Foun-dation of China(Grant Nos.12475032 and 12005062)the Supercomputing Center of the Chinese Academy of Sciences,Shanghai Snowlake Technology Co.,Ltd.,and the Shanghai Super-Computer Center of China。
文摘Spiral patterns widely exist in both macroscopic and microscopic systems such as hearts,bacteria,and active matters but have never been reported at molecular length scale.The emergence of spiral patterns has considerable impacts on the trajectories of the objects and thus usually relates to various physical,chemical,biological and physiological processes.In this paper,we show that,down to the length scale of only several Angstroms,asymmetric molecules exhibit spiral patterns in their trajectories within finite time based on the under-damped Langevin equation and demonstrated by molecular dynamics simulation.The key to this observation lies in the asymmetric molecular architecture that leads to a translation-rotation coupling.This finding enriches the knowledge of spiral patterns to the molecular length scale,provides a new insight into the understanding of various processes at the molecular level,and may evoke new ideas on the understanding of the vortices in turbulence.
基金supported in part by National Key R&D Program of China(Grant No.2018YFB1304600)CAS Interdisciplinary Innovation Team(Grant No.JCTD-2018-11)the Natural Science Foundation of China(Grant No.51775541).
文摘Flasher origami pattern has been widely utilized to improve the stowage efficiency of deployable structures.Nevertheless,flasher origami cannot be folded fully flat,and they still have great potential for optimization in terms of storage volume and folding creases.In this paper,a flat foldable equiangular spiral folding pattern inspired by the sunflower disk is introduced.Then,a parametric design method for this equiangular spiral crease diagram is introduced in detail.Subsequently,a kinematic model of the equiangular spiral folding pattern is established based on the kinematic equivalence between rigid origami and spherical linkages.A simulation of the developed model demonstrates that the equiangular spiral folding pattern can be folded flat.Using the folded ratio as an evaluation index,the calculated results and experiments show that the equiangular spiral crease pattern can yield fewer creases and improve stowage efficiency in comparison to flasher origami pattern.Equiangular spiral folding pattern can save a considerable amount of space and provide a new approach to spatially deployable structures.
