A time-optimal aircraft-following model based on Pontryagin's minimum principle

A time-optimal aircraft-following model is introduced to address air traffic flow interference by velocity reduction. The objective function is set up as minimizing the recovery time during which the separation minima are not infringed and the separation of the air traffic flow returns to the initial separation at the terminal time. Pontryagin＇s minimum principle is used to solve the optimum aircraft-following velocity control law. An analytical minimum safe following separation is also provided under the time-optimal control law. The simulation results show that the precision first-order tracking accuracy is achieved without losing the separation.

Rapid adaptive substitution of L226Q in HA protein increases the pathogenicity of H9N2 viruses in mice

Background:Since the first human infection with H9N2 virus was reported in 1998,the number of cases of H9N2 infection has exceeded one hundred by 2021.However,there is no systematic description of the biological characteristics of H9N2 viruses isolated from humans.Methods:Therefore,this study analyzed the pathogenicity in mice of all available H9N2 viruses isolated from human cases in China from 2013 to 2021.Results:Although most of the H9N2 viruses analyzed showed low or no pathogenicity in mice,the leucine to glutamine substitution at residue 226(L226Q)in the hemagglutinin(HA)protein rapidly emerged during the adaptation of H9N2 viruses,and was responsible for severe infections and even fatalities.HA amino acid 226Q conferred a remarkable competitive advantage on H9N2 viruses in mice relative to viruses containing 226L,increasing their virulence,infectivity,and replication.Conclusion:Thus,our study demonstrates that the adaptive substitution HA L226Q rapidly acquired by H9N2 viruses during the course of infection in mice contributed to their high pathogenicity.

Integrating the optical tweezers and spanner onto an individual single-layer metasurface

Optical tweezers(OTs)and optical spanners(OSs)are powerful tools of optical manipulation,which are responsible for particle trapping and rotation,respectively.Conventionally,the OT and OS are built using bulky three-dimensional devices,such as microscope objectives and spatial light modulators.Recently,metasurfaces are proposed for setting up them on a microscale platform,which greatly miniaturizes the systems.However,the realization of both OT and OS with one identical metasurface is posing a challenge.Here,we offer a metasurface-based solution to integrate the OT and OS.Using the prevailing approach based on geometric and dynamic phases,we show that it is possible to construct an output field,which promises a high-numerical-aperture focal spot,accompanied with a coaxial vortex.Optical trapping and rotation are numerically demonstrated by estimating the mechanical effects on a particle probe.Moreover,we demonstrate an on-demand control of the OT-to-OS distance and the topological charge possessed by the OS.By revealing the OT–OS metasurfaces,our results may empower advanced applications in on-chip particle manipulation.

The complex Maxwell stress tensor theorem:The imaginary stress tensor and the reactive strength of orbital momentum.A novel scenery underlying electromagnetic optical forces

We uncover the existence of a universal phenomenon concerning the electromagnetic optical force exerted by light or other electromagnetic waves on a distribution of charges and currents in general,and of particles in particular.This conveys the appearence of underlying reactive quantities that hinder radiation pressure and currently observed timeaveraged forces.This constitutes a novel paradigm of the mechanical effciency of light on matter,and completes the landscape of the optical,and generally electromagnetic,force in photonics and classical electrodynamics;widening our understanding in the design of both llumination and particles in optical manipulation without the need of increasing the illuminating power,and thus lowering dissipation and heating.We show that this may be accomplished through the minimization of what we establish as the reactive strength of orbital(or canonical)momentum,which plays against the optical force a role analogous to that of the reactive power versus the radiation effciency of an antenna.This long time overlooked quantity,important for current progress of optical manipulation,and that stems from the complex Maxwell theorem of conservation of complex momentum that we put forward,as well as its alternating flow associated to the imaginary part of the complex Maxwell stress tensor,conform the imaginary Lorentz force that we introduce in this work,and that like the reactive strength of orbital momentum,is antagonistic to the well-known time-averaged force;thus making this reactive Lorentz force indirectly observable near wavelengths at which the time-averaged force is lowered.The Minkowski and Abraham momenta are also addressed.

Artificial potential field-empowered dynamic holographic optical tweezers for particle-array assembly and transformation

Owing to the ability to parallel manipulate micro-objects,dynamic holographic optical tweezers(HOTs)are widely used for assembly and patterning of particles or cells.However,for simultaneous control of large-scale targets,potential collisions could lead to defects in the formed patterns.Herein we introduce the artificial potential field(APF)to develop dynamic HOTs that enable collision-avoidance micro-manipulation.By eliminating collision risks among particles,this method can maximize the degree of parallelism in multi-particle transport,and it permits the implementation of the Hungarian algorithm for matching the particles with their target sites in a minimal pathway.In proof-of-concept experiments,we employ APF-empowered dynamic HOTs to achieve direct assembly of a defect-free 8×8 array of microbeads,which starts from random initial positions.We further demonstrate successive flexible transformations of a 7×7 microbead array,by regulating its tilt angle and inter-particle spacing distances with a minimalist path.We anticipate that the proposed method will become a versatile tool to open up new possibilities for parallel optical micromanipulation tasks in a variety of fields.