Quantum Nondemolition Measurement of the Collective Motional Energy of Two Trapped Ions

We propose a quantum nondemolition measurement of the collective motional energy of two trapped ions for the first time.It is based on the excitation of the two ions by two lasers with appropriate frequencies and amplitudes.The scheme also provides a new possibility of preparing vibrational Fock states and laser cooling.

Graph dynamical networks for forecasting collective behavior of active matter

After decades of theoretical studies,the rich phase states of active matter and cluster kinetic processes are still of research interest.How to efficiently calculate the dynamical processes under their complex conditions becomes an open problem.Recently,machine learning methods have been proposed to predict the degree of coherence of active matter systems.In this way,the phase transition process of the system is quantified and studied.In this paper,we use graph network as a powerful model to determine the evolution of active matter with variable individual velocities solely based on the initial position and state of the particles.The graph network accurately predicts the order parameters of the system in different scale models with different individual velocities,noise and density to effectively evaluate the effect of diverse condition.Compared with the classical physical deduction method,we demonstrate that graph network prediction is excellent,which could save significantly computing resources and time.In addition to active matter,our method can be applied widely to other large-scale physical systems.

Bacterial turbulence in gradient confinement

We investigate a novel form of non-uniform living turbulence at an extremely low Reynolds number using a bacterial suspension confined within a sessile droplet. This turbulence differs from homogeneous active turbulences in two or threedimensional geometries. The heterogeneity arises from a gradient of bacterial activity due to oxygen depletion along the droplet’s radial direction. Motile bacteria inject energy at individual scales, resulting in local anisotropic energy fluctuations that collectively give rise to isotropic turbulence. We find that the total kinetic energy and enstrophy decrease as distance from the drop contact line increases, due to the weakening of bacterial activity caused by oxygen depletion. While the balance between kinetic energy and enstrophy establishes a characteristic vortex scale depending on the contact angle of the sessile drop. The energy spectrum exhibits diverse scaling behaviors at large wavenumber, ranging from k-1/5to k-1,depending on the geometric confinement. Our findings demonstrate how spatial regulation of turbulence can be achieved by tuning the activity of driving units, offering insights into the dynamic behavior of living systems and the potential for controlling turbulence through gradient confinements.

Flowrate behavior and clustering of self-driven robots in a channel

In this paper,the collective motion of self-driven robots is studied experimentally and theoretically.In the channel,the flowrate of robots increases with the density linearly,even if the density of the robots tends to 1.0.There is no abrupt drop in the flowrate,similar to the collective motion of ants.We find that the robots will adjust their velocities by a serial of tiny collisions.The speed-adjustment will affect both robots involved in the collision,and will help to maintain a nearly uniform velocity for the robots.As a result,the flowrate drop will disappear.In the motion,the robots neither gather together nor scatter completely.Instead,they form some clusters to move together.These clusters are not stable during the moving process,but their sizes follow a power-law-alike distribution.We propose a theoretical model to simulate this collective motion process,which can reproduce these behaviors well.Analytic results about the flowrate behavior are also consistent with experiments.

Phonon Dispersion in Ca70Mg30 Metallic Glass

The phonon dispersion curves （PDC） of Ca70Mg30 metallic glass has been studied at room temperature in terms of phonon eigen frequencies of longitudinal and transverse modes employing three different approaches proposed by Hubbard and Beeby （J. Phys. C： Solid State Phys. 13 （1969） 556）, Takeno and Goda （Prog. Theor. Phys. 45 （1971） 331; 47 （1972） 790） and Bhatia and Singh （Phys. Rev. B 31 （1985） 4751）. The well recognized model potential of Gajjar et al. is employed successfully to explain electron-ion interaction in the metallic glass. The effective pair potential is used to generate the pair correlation function g（r）. The local field correction function （Int. J. Mod. Phys. B 17 （2003） 6001） is used for the first time to introduce the exchange and correlation effects on the aforesaid properties. The present findings of PDCs are found to be in agreement with the available theoretical as well as experimental data. The thermodynamic and elastic properties, i.e. longitudinal and transverse sound velocities, isothermal bulk modulus, modulus of rigidity, Poisson＇s ratio, Young＇s modulus and Debye temperature, are also investigated successfully.

MECHANISM IN PNEUMOTRANSPORT OF THE FIBROID SUBSTANCE

In this paper,the mechanism of pneumotransport of the fibroid material is discussed. It is thought that the motion of air relative to the material is the filtration of the air passing through the porous medium which is composed of the cluster of fibroid material. It is found that the deviations of the experimental data with the theoretical results are within experimental error.

High-Speed Geometric Quantum Computation with Trapped Thermal Ions via Vibrational Mode Decay

We utilize the general displacement operator proposed recently [C.Y. Chen, et al., Phys. Rev. A 74 （2006） 032328] to investigate a high-speed geometric quantum computation via vibrational mode decay of two trapped thermal ions. We find that, under some special conditions, the geometric phase gating is somewhat faster in the heating case than in the ideal case. We also investigate analytically the influence from the vibrational mode heating on the fidelity and the success probability of the implementation.

Distributed stereoscopic rotating formation control of networks of second-order agents

Distributed stereoscopic rotating formation control of networks of second-order agents is investigated. A distributed control protocol is proposed to enable all agents to form a stereoscopic formation and surround a common axis. Due to the existence of the rotating mode, the desired relative position between every two agents is time-varying, and a Lyapunov-based approach is employed to solve the rotating formation control problem. Finally, simulation results are provided to illustrate the effectiveness of the theoretical results.

Collective cell behaviors manipulated by synthetic DNA nanostructures

Cellular collective motion in confluent epithelial monolayers is involved in many processes such as embryo development,carcinoma invasion,and wound healing.The development of new chemical strategies to achieve largescale control of cells’collective motion is essential for biomedical applications.Here a series of DNA nanostructures with different dimensions were synthesized and their influences on cells’collective migration and packing behaviors in epithelial monolayers were investigated.We found that the framed DNA nanoassemblies effectively reduced the cells’speed by increasing the rigidity of cells,while the lipid-DNA micelles had a more pronounced effect on cells’projection area and shape factor.These DNA nanostructures all significantly enhanced the dependence of cells’speed on their shape factor.Our results indicate that cells’mobility in monolayers can be manipulated by chemical intercellular interactions without any genetic intervention.This may provide a new chemical strategy for tissue engineering and tumor therapy.

A survey of the pursuit-evasion problem in swarm intelligence

For complex functions to emerge in artificial systems,it is important to understand the intrinsic mechanisms of biological swarm behaviors in nature.In this paper,we present a comprehensive survey of pursuit–evasion,which is a critical problem in biological groups.First,we review the problem of pursuit–evasion from three different perspectives:game theory,control theory and artificial intelligence,and bio-inspired perspectives.Then we provide an overview of the research on pursuit–evasion problems in biological systems and artificial systems.We summarize predator pursuit behavior and prey evasion behavior as predator–prey behavior.Next,we analyze the application of pursuit–evasion in artificial systems from three perspectives,i.e.,strong pursuer group vs.weak evader group,weak pursuer group vs.strong evader group,and equal-ability group.Finally,relevant prospects for future pursuit–evasion challenges are discussed.This survey provides new insights into the design of multi-agent and multi-robot systems to complete complex hunting tasks in uncertain dynamic scenarios.

Lattice Boltzmann Simulations of Two Linear Microswimmers Using the Immersed Boundary Method

The performance of a single or the collection of microswimmers strongly depends on the hydrodynamic coupling among their constituents and themselves.We present a numerical study for a single and a pair of microswimmers based on lattice Boltzmann method(LBM)simulations.Our numerical algorithm consists of two separable parts.Lagrange polynomials provide a discretization of the microswimmers and the lattice Boltzmann method captures the dynamics of the surrounding fluid.The two components couple via an immersed boundary method.We present data for a single swimmer system and our data also show the onset of collective effects and,in particular,an overall velocity increment of clusters of swimmers.

Social networks improve leaderless group navigation by facilitating long-distance communication

Group navigation is of great importance for many animals, such as migrating flocks of birds or shoals of fish. One theory states that group membership can improve navigational accuracy compared to limited or less accurate individual naviga- tional ability in groups without leaders （＂Many-wrongs principle＂）. Here, we simulate leaderless group navigation that includes social connections as preferential interactions between individuals. Our results suggest that underlying social networks can reduce navigational errors of groups and increase group cohesion. We use network summary statistics, in particular network motifs, to study which characteristics of networks lead to these improvements. It is networks in which preferences between individuals are not clustered, but spread evenly across the group that are advantageous in group navigation by effectively enhancing long-distance information exchange within groups. We suggest that our work predicts a base-line for the type of social structure we might expect to find in group-living animals that navigate without leaders

Numerical study of dynamic zigzag patterns in migrating epithelial tissue

Collective cell migration plays a crucial role in embryonic development, metastasis, and wound healing. Nevertheless, to the best of our knowledge, how the coordination between the cell motility and deformations affects the collective motion of epithelial cells is not fully understood. In this work, we propose a modified self-propelled Voronoi model for epithelial cell migration incorporating the coupling between the self-propulsion of cells and the polarization of the cell elongation. At a high coupling strength,we observe the emergence of backward traveling band structures formed by highly aligned cells, which can be regulated by cell elongations or shape anisotropy. Increasing the cell shape anisotropy, we find that large bands split into multiple small microbands. The latter essentially forms a dynamic zigzag pattern, in which the angle between the polarization direction of the bands and the migration direction switches alternatively between π/4 and-π/4 because the cells are forced to move preferentially in the anterior direction. We also analyzed the disclinations in the cell monolayer, force distribution near the domain boundaries and the shape alignment of the epithelial monolayer during the formation of this dynamic pattern. The present findings may further our understanding of stripe pattern formations in living systems and inspire potential designs for cell sorting.

Quantum essence of particle superfluidity

Life systems show an ultralow energy consumption in their high-efficiency bio-activities,implying a high-flux transport of ions and molecules with an ultralow resistivity.A collective motion(CM)of these particles is necessary for this kind of behaviors,different from the traditional Newtonian diffusion.The CM is an ordered particle state,resulting from the balance between attraction and repulsion of the particles,in which the attraction is a necessary condition.The ultralow resistivity of electronic or atomic fluid at low temperature is already described phenomenologically by introducing the interparticle attraction.Here,we try to establish a phenomenological expression for the quantum state of ion or molecule CM at ambient temperature,by also considering the attraction of particles.These studies suggest that the Bose-Einstein condensate potentially exists widely.

Dynamic ordering transitions in charged solid

The phenomenon of group motion is common in nature,ranging from the schools of fish,birds and insects,to avalanches,landslides and sand drift.If we treat objects as collectively moving particles,such phenomena can be studied from a physical point of view,and the research on many-body systems has proved that marvelous effects can arise from the simplest individuals.The motion of numerous individuals presents different dynamic phases related to the ordering of the system.However,it is usually difficult to study the dynamic ordering and its transitions through experiments.Electron bubble states formed in a two-dimensional electron gas,as a type of electron solids,can be driven by an external electric field and provide a platform to study the dynamic collective behaviors.Here,we demonstrate that the noise spectrum is a powerful method to investigate the dynamics of bubble states.We observed not only the phenomena of dynamically ordered and disordered structures,but also unexpected alternations between them.Our results show that a dissipative system can convert between chaotic structures and ordered structures when tuning global parameters,which is concealed in conventional transport measurements of resistance or conductance.Moreover,charging the objects to study the electrical noise spectrum in collective motions can be an additional approach to revealing dynamic ordering transitions.