Edge Transport and Self-Assembly of Passive Objects in a Chiral Active Fluid

Topological edge flow and dissipationless odd viscosity are two remarkable features of chiral active fluids composed of active spinners.These features can significantly influence the dynamics of suspended passive particles and the interactions between the particles.By computer simulations,we investigate the transport phenomenon of anisotropic passive objects and the self-assembly behavior of passive spherical particles in the active spinner fluid.It is found that in confined systems,nonspherical passive objects can stably cling to boundary walls and are unidirectionally and robustly transported by edge flow of spinners.Furthermore,in an unconfined system,passive spherical particles are able to form stable clusters that spontaneously and unidirectionally rotate as a whole.In these phenomena,strong particle-wall and interparticle effective attractions play a vital role,which originate from spinner-mediated depletion-like interactions and can be largely enhanced by odd viscosity of spinner fluids.Our results thus provide new insight into the robust transport of cargoes and the nonequilibrium self-assembly of passive intruders.

Verification of Energetic-Particle-Induced Geodesic Acoustic Mode in Gyrokinetic Particle Simulations

The energetic-particle-induced geodesic acoustic mode(EGAM)is studied using gyrokinetic particle simulations in tokamak plasmas.In our simulations,exponentially growing EGAMs are excited by energetic particles with a slowing-down distribution.The frequencies of EGAMs are always below the frequencies of GAMs,which is due to the non-perturbative contribution of energetic particles(EPs).The mode structures of EGAMs are similar to the corresponding mode structures of GAMs.Our gyrokinetic simulations show that a high EP density can enhance the EGAM growth rate,due to high EP free energy,and that EPs’temperature and the pitch angle of the distribution modify the EGAM frequency/growth rate by means of the resonance condition.Kinetic effects of the thermal electrons barely change the EGAM frequency,and have a weak damping effect on the EGAM.Benchmarks between the gyrokinetic particle simulations and a local EGAM dispersion relation exhibit good agreement in terms of EGAM frequency and growth rate.

Temperature Gradient, Toroidal and Ion FLR Effects on Drift-Tearing Modes

The influences of the temperature gradient and toroidal effects on drift-tearing modes have been studied using the Gyrokinetic Toroidal code.After the thermal force term is introduced into the parallel electron force balance equation,the equilibrium temperature gradient can cause a significant increase in the growth rate of the drift-tearing mode and a broadening of the mode structure.The simulation results show that the toroidal effects increase the growth rate of the drift-tearing mode,and the contours of the perturbation field“squeeze”toward the stronger field side in the poloidal section.Finally,the hybrid model for fluid electrons and kinetic ions has been studied briefly,and the dispersion relation of the drift-tearing mode under the influence of ion finite Larmor radius effects is obtained.Compared with the dispersion relation under the fluid model,a stabilizing effect of the ion finite Larmor radius is observed.

Quasi-Two-Dimensional Diffusion in Adherent Cells Revealed by Three-Dimensional Single Quantum Dot Tracking

Intracellular diffusion is critical for molecule translocation in cytoplasm and mediates many important cellular processes.Meanwhile,the diffusion dynamics is affected by the heterogeneous cytoplasm.Previous studies on intracellular diffusion are mainly based on two-dimensional(2 D)measurements under the assumption that the three-dimensional(3 D)diffusion is isotropic.However,the real behaviors of 3 D diffusion of molecules in cytoplasm are still unclear.Here,we have built a 3 D single-particle tracking(SPT)microscopy and studied the 3 D diffusion of quantum dots(QDs)in adherent A549 cells.Notably,we found that the intracellular diffusion of QDs is quasi-2 D,with the axial motion being severely confined.Further investigations demonstrated that disrupting the cytoskeleton component or endoplasmic reticulum(ER)does not alter the quasi-2 D diffusion pattern,although ER reduces the diffusion rates and slightly relieves the constraint in the axial diffusion.The preferred quasi-2 D diffusion is quite robust and attributed to the complex cytoarchitectures in the flat adherent cells.With the aid of 3 D SPT method,the quasi-2 D diffusion in cells was revealed,shedding new light on the physical nature of cytoplasm.