Numerical study on interaction between eddies and the Kuroshio Current east of Taiwan,China

We investigated the interaction between mesoscale eddies and the Kuroshio Current east of Taiwan,China,using a fine-resolution regional general circulation model.Mesoscale eddies are injected into a region east of Taiwan,China,according to the quasi-geostrophic theory of stratified fluids.Modeled eddies propagated westward at the velocity of the first baroclinic mode Rossby wave.When eddies collide with the Kuroshio Current east of Taiwan,China,the spatial structure and volume transport of the Kuroshio Current shows a significant variation.The upper 600 m of the anticyclonic eddy cannot cross the Kuroshio Current to reach the region west of the Kuroshio Current;rather,these waters flow northward along the eastern side of the Kuroshio Current.The upper water carried by the anticyclonic eddies cannot reach the shelf of the East China Sea(ECS).In contrast,the waters in the upper layer of the cyclonic eddy reach the western side of the Kuroshio Current and then flow northward.The dynamic mechanism analysis shows that the interaction between the Kuroshio Current and the cyclonic(anticyclonic)eddy decrease(increase)the horizontal potential vorticity(PV)gradient,or PV barrier,whereby the cyclonic(anticyclonic)eddy can(cannot)cross the Kuroshio Current.This study implies that the continental shelf could potentially be influenced by cyclonic eddies in the open ocean,which can transport heat and material from the upper open ocean across the Kuroshio Current to the shelf waters.

Mechanically reprogrammable Pancharatnam-Berry metasurface for microwaves

Metasurfaces have enabled the realization of several optical functionalities over an ultrathin platform,fostering the exciting field of flat optics.Traditional metasurfaces are achieved by arranging a layout of static meta-atoms to imprint a desired operation on the impinging wavefront,but their functionality cannot be altered.Reconfigurability and programmability of metasurfaces are the next important step to broaden their impact,adding customized on-demand functionality in which each meta-atom can be individually reprogrammed.We demonstrate a mechanical metasurface platform with controllable rotation at the meta-atom level,which can implement continuous Pancharatnam–Berry phase control of circularly polarized microwaves.As the proof-of-concept experiments,we demonstrate metalensing,focused vortex beam generation,and holographic imaging in the same metasurface template,exhibiting versatility and superior performance.Such dynamic control of electromagnetic waves using a single,low-cost metasurface paves an avenue towards practical applications,driving the field of reprogrammable intelligent metasurfaces for a variety of applications.

Moiré-driven electromagnetic responses and magic angles in a sandwiched hyperbolic metasurface

Recent moiréconfigurations provide a new platform for tunable and sensitive photonic responses,as their enhanced light–matter interactions originate from the relative displacement or rotation angle in a stacking bilayer or multilayer periodic array.However,previous findings are mostly focused on atomically thin condensed matter,with limitations on the fabrication of multilayer structures and the control of rotation angles.Structured microwave moiréconfigurations are still difficult to realize.Here,we design a novel moiréstructure,which presents unprecedented capability in the manipulation of light–matter interactions.Based on the effective medium theory and S-parameter retrieval process,the rotation matrix is introduced into the dispersion relation to analyze the underlying physical mechanism,where the permittivity tensor transforms from a diagonal matrix to a fully populated one,whereas the permeability tensor evolves from a unit matrix to a diagonal one and finally becomes fully filled,so that the electromagnetic responses change drastically as a result of stacking and rotation.Besides,the experiment and simulation results reveal hybridization of eigenmodes,drastic manipulation of surface states,and magic angle properties by controlling the mutual rotation angles between two isolated layers.Here,not only a more precisely controllable bilayer hyperbolic metasurface is introduced to moiréphysics,the findings also open up a new avenue to realize flat bands at arbitrary frequencies,which shows great potential in active engineering of surface waves and designing multifunctional plasmonic devices.

OSCILLATION CRITERIA FOR STRONGLY SUPERLINEAR AND STRONGLY SUBLINEAR HIGHER ORDER DYNAMIC EQUATIONS ON TIME SCALES

We establish some new criteria for the oscillation of even order nonlinear dynamic equation. We study the case of strongly super-linear and the case of strongly sub-linear subject to various conditions.