Diffusion of Nanoparticles in Semidilute Polymer Solutions： A Multiparticle Collision Dynamics Study

The diffusion of nanoparticles immersed in semidilute polymer solutions is investigated by a hybrid mesoscopic multiparticle collision dynamics method. Effects of polymer concentration and hydrodynamic interactions among polymer monomers are focused. Extensive simulations show that the dependence of diffusion coefficient D on the polymer concentration c agrees with Phillies equation D-exp （-αc^δ） with a scaling exponent δ≈0.97 which coincides with the experimental one in literature. For increasing nanoparticle size, the scaling prefactor α increases monotonically while the scaling exponent always keeps fixed. Moreover, we also study the diffusion of nanoparticle without hydrodynamic interactions and find that mobility of the nanoparticle slows down, and the scaling exponent is obviously different from the one in experiments, implying that hydrodynamic interactions play a crucial role in the diffusion of a nanoparticle in semidilute polymer solutions.

A new collision avoidance model for pedestrian dynamics

The pedestrians can only avoid collisions passively under the action of forces during simulations using the social force model, which may lead to unnatural behaviors. This paper proposes an optimization-based model for the avoidance of collisions, where the social repulsive force is removed in favor of a search for the quickest path to destination in the pedestrian＇s vision field. In this way, the behaviors of pedestrians are governed by changing their desired walking direction and desired speed. By combining the critical factors of pedestrian movement, such as positions of the exit and obstacles and velocities of the neighbors, the choice of desired velocity has been rendered to a discrete optimization problem. Therefore,it is the self-driven force that leads pedestrians to a free path rather than the repulsive force, which means the pedestrians can actively avoid collisions. The new model is verified by comparing with the fundamental diagram and actual data. The simulation results of individual avoidance trajectories and crowd avoidance behaviors demonstrate the reasonability of the proposed model.

Review of quantum collision dynamics in Debye plasmas

Hot,dense plasmas exhibit screened Coulomb interactions,resulting from the collective effects of correlated many-particle interactions.In the lowest particle correlation order(pair-wise correlations),the interaction between charged plasma particles reduces to the DebyeeHu¨ckel(Yukawa-type)potential,characterized by the Debye screening length.Due to the importance of Coulomb interaction screening in dense laboratory and astrophysical plasmas,hundreds of theoretical investigations have been carried out in the past few decades on the plasma screening effects on the electronic structure of atoms and their collision processes employing the DebyeeHu¨ckel screening model.The present article aims at providing a comprehensive review of the recent studies in atomic physics in Debye plasmas.Specifically,the work on atomic electronic structure,photon excitation and ionization,electron/positron impact excitation and ionization,and excitation,ionization and charge transfer of ion-atom/ion collisions will be reviewed.

Atomic structure and collision dynamics with highly charged ions

The research progresses on the investigations of atomic structure and collision dynamics with highly charged ions based on the heavy ion storage rings and electron ion beam traps in recent 20 years are reviewed.The structure part covers test of quantum electrodynamics and electron correlation in strong Coulomb field studied through dielectronic recombi-nation spectroscopy and VUV/x-ray spectroscopy.The collision dynamics part includes charge exchange dynamics in ion-atom collisions mainly in Bohr velocity region,ion-induced fragmentation mechanisms of molecules,hydrogen-bound and van de Waals bound clusters,interference,and phase information observed in ion-atom/molecule collisions.With this achievements,two aspects of theoretical studies related to low energy and relativistic energy collisions are presented.The applications of data relevant to key atomic processes like dielectronic recombination and charge exchanges involving highly charged ions are discussed.At the end of this review,some future prospects of research related to highly charged ions are proposed.

Molecular Dynamics Simulation of C_(60)-C_(60) Collision

The formation process of C^o-complex in C_(60)-C_(60) collision has been clearly demonstrated by a molecular dynamics simulation.The complex^with a peanut-shell-like structuref is in a quite stable dynamical state.The results are consistent with recent observations.

Collision Dynamics of Dissipative Matter-Wave Solitons in a Perturbed Optical Lattice

We investigate the stability and collision dynamics of dissipative matter-wave solitons formed in a quasi-one- dimensional Bose-Einstein condensate with linear gain and three-body recombination loss perturbed by a weak optical lattice. It is shown that the linear gain can modify the stability of the single dissipative soliton moving in the optical lattice. The collision dynamics of two individual dissipative matter-wave solitons explicitly depend on the linear gain parameter, and they display different dynamical behaviors in both the in-phase and out-of-phase interaction regimes.

Quantum entanglement dynamics based on composite quantum collision model

By means of composite quantum collision models,we study the entanglement dynamics of a bipartite system,i.e.,two qubits S1 and S2 interacting directly with an intermediate auxiliary qubit SA,while SA is in turn coupled to a thermal reservoir.We are concerned with how the intracollisions of the reservoir qubits influence the entanglement dynamics.We show that even if the system is initially in the separated state,their entanglement can be generated due to the interaction between the qubits.In the long-time limit,the steady-state entanglement can be generated depending on the initial state of S1 and S2 and the environment temperature.We also study the dynamics of tripartite entanglement of the three qubits S1,S2,and SA when they are initially prepared in the GHZ state and separated state,respectively.For the GHZ initial state,the tripartite entanglement can be maintained for a long time when the collision strength between the environment qubits is sufficiently large.

Simulation of microswimmer hydrodynamics with multiparticle collision dynamics

In this review we discuss the recent progress in the simulation of soft active matter systems and in particular the hydrodynamics of microswimmers using the method of multiparticle collision dynamics,which solves the hydrodynamic flows around active objects on a coarse-grained level.We first present a brief overview of the basic simulation method and the coupling between microswimmers and fluid.We then review the current achievements in simulating flexible and rigid microswimmers using multiparticle collision dynamics,and briefly conclude and discuss possible future directions.

The Excitation Energy and the Entrance Channel Dynamics in Heavy Ion Collision at Intermediate Energy

The relationship between the energy storage and the entrance channel dyna-mics(i.e.incident energy,impact parameter,and collision system)is studied by usingthe BUU model.The effects of the mass asymmetry of the entrance channel on theexcitation properties of the compound systems are specially discussed.

Multi-USV Formation Collision Avoidance via Deep Reinforcement Learning and COLREGs

Dear Editor,This letter focuses on the collision avoidance for a multi-unmanned surface vehicle(multi-USV)system.A novel multi-USV collision avoidance(MUCA)algorithm is proposed.Firstly,in order to get a more reasonable collision avoidance policy,reward functions are constructed according to international regulations for preventing collisions at sea(COLREGS)and USV dynamics.

MD Simulation of Diffusion Behaviors in Collision Welding Processes of Al-Cu, Al-Al, Cu-Cu

To investigate the effects of material combinations and velocity conditions on atomic diffusion behavior near collision interfaces,this study simulates the atomic diffusion behavior near collision interfaces in Cu-Al,Al-Al and Cu-Cu combinations fabricated through collision welding using molecular dynamic(MD)simulation.The atomic diffusion behaviors are compared between similar metal combinations(Al-Al,Cu-Cu)and dissimilar metal combinations(Al-Cu).By combining the simulation results and classical diffusion theory,the diffusion coefficients for similar and dissimilar metal material combinations under different velocity conditions are obtained.The effects of material combinations and collision velocity on diffusion behaviors are also discussed.The diffusion behaviors of dissimilar material combinations strongly depend on the transverse velocity,whereas those of the similar material combinations are more dependent on the longitudinal velocity.These findings can provide guidance for optimizing welding parameters.

Charging Properties and Particle Dynamics of Chang’e-5 Lunar Sample in an External Electric Field

Facing the challenges of in-situ utilization of lunar regolith resources,applying an external electric field to manipulate lunar particles has become a promising method for space particle control,which mainly depends on the particle charging properties in the applied electric field.Using the surficial lunar regolith samples brought back from the Moon by the Chang’e-5 mission(CE5 LS),this work successively studied their charging properties,particle dynamics,and their collision damages to aerospace materials under the action of an external electric field in high-vacuum conditions.The results indicated that the charging pro-cess and electrostatic projection of lunar regolith particles under high-vacuum conditions were different from those under atmosphere conditions.The particle diameter range of CE5 LS used in the experiment is 27.7-139.0 lm.For electric field strength of 3-12 kV·cm^(-1),the charge obtained by CE5 LS is 4.8×10^(-15)-4.7×10^(-13) C and the charge-to-mass ratio is 1.2×10^(-5)-6.8×10^(-4) C·kg^(-1).The CE5 LS is easier to be negatively charged in an external electric field.Furthermore,significant damages were observed on the target impact surfaces,indicating severe influences of lunar regolith particles on aerospace materials.Our work contributes to a more comprehensive understanding of physical mechanisms controlling the lunar regolith shielding and utilization,and will inspire broad efforts to develop the lunar in-situ engi-neering solutions.

Dynamic Plastic Analysis of Ship-Platform Collision

This paper studies intensively the problems of ship-platform collision. The ship and platform are treated as one structural system connected with spring elements and then motion equation of the collision system is established. A nonlinear force-displacement relationship is derived for the simulation of local dent in a hit member and the yield surface of a dented tubular section is developed to consider the reduction of load carrying capacity of hit members. Large deformations, plasticity and strain-hardening of the beam-column element are taken into account by combining the elastic large displacement analysis theory with the plastic node method. The effect of the hydrodynamic forces acting on the platform, the rubber fender the property of the local dent and the buckling behavior of beam-column on collision are analyzed. The numerical simulation of the nonlinear dynamic response is carried out by Wilson theta method with updated Newton-Raphson iteration. And the numerical example of the dynamic response of a offshore platform in ship-platform collision is also present.

Dynamic Path Following Control of a Ground Ackerman Steering Robot to Avoid a Collision

A novel method is proposed to dynamically control the path following of a ground Ackerman steering robot to avoid a collision.The method consists of collision prediction module,collision avoidance module and global path following module.The elliptic repulsive potential field method（ER-PFM）and the enhanced vector polar histogram method（VPH＋）based on the Ackerman steering model are proposed to predict the collision in a dynamic environment.The collision avoidance is realized by the proposed cost function and speed control law.The global path following process is achieved by pure pursuit.Experiments show that the robot can fulfill the dynamic path following task safely and efficiently using the proposed method.

Stochastic dynamic simulation of railway vehicles collision using data-driven modelling approach

Using stochastic dynamic simulation for railway vehicle collision still faces many challenges,such as high modelling complexity and time-consuming.To address the challenges,we introduce a novel data-driven stochastic process modelling(DSPM)approach into dynamic simulation of the railway vehicle collision.This DSPM approach consists of two steps:(i)process description,four kinds of kernels are used to describe the uncertainty inherent in collision processes;(ii)solving,stochastic variational inferences and mini-batch algorithms can then be used to accelerate computations of stochastic processes.By applying DSPM,Gaussian process regression(GPR)and finite element(FE)methods to two collision scenarios(i.e.lead car colliding with a rigid wall,and the lead car colliding with another lead car),we are able to achieve a comprehensive analysis.The comparison between the DSPM approach and the FE method revealed that the DSPM approach is capable of calculating the corresponding confidence interval,simultaneously improving the overall computational efficiency.Comparing the DSPM approach with the GPR method indicates that the DSPM approach has the ability to accurately describe the dynamic response under unknown conditions.Overall,this research demonstrates the feasibility and usability of the proposed DSPM approach for stochastic dynamics simulation of the railway vehicle collision.

Dynamic Response Analysis of Beams with Oblique Collision

Adopting a dynamic contact numerical method, some problems such as the central collision, transverse collision and oblique collision between two beams are researched. Numerical expressions for these cases are deduced. Using a self-developed finite element program some examples are computed, and compared with the analytical solution of the central collision, this numerical algorithm is proved to be reliable. For the other numerical results that have no analytical solution to be used to compare with, they are also reasonable through the theoretical analysis. For the transverse and oblique collision, the ideal results can be obtained by using a smaller time step.

Synchronous Dynamic Adjusting: An Anti-Collision Algorithm for an RF-UCard System

An RF-UCard system is a contactless smartcard system with multiple chip operating systems and multiple applications. A multi-card collision occurs when more than one card within the reader’s read field and thus lowers the efficiency of the system. This paper presents a novel and enhanced algorithm to solve the multi-card collision problems in an RF-UCard system. The algorithm was originally inspired from framed ALOHA-based anti-collision algorithms applied in RFID systems. To maximize the system efficiency, a synchronous dynamic adjusting (SDA) scheme that adjusts both the frame size in the reader and the response probability in cards is developed and evaluated. Based on some mathematical results derived from the Poisson process and the occupancy problem, the algorithm takes the estimated card quantity and the new arriving cards in the current read cycle into consideration to adjust the frame size for the next read cycle. Also it changes the card response probability according to the request commands sent from the reader. Simulation results show that SDA outperforms other ALOHA-based anti-collision algorithms applied in RFID systems.

Novel quantum phenomena induced by strong magnetic fields in heavy-ion collisions

The relativistic heavy-ion collisions create both hot quark–gluon matter and strong magnetic fields, and provide an arena to study the interplay between quantum chromodynamics and quantum electrodynamics. In recent years, it has been shown that such an interplay can generate a number of interesting quantum phenomena in hadronic and quark–gluon matter. In this short review, we first discuss some properties of the magnetic fields in heavy-ion collisions and then give an overview of the magnetic fieldinduced novel quantum effects. In particular, we focus on the magnetic effect on the heavy flavor mesons, the heavyquark transports, and the phenomena closely related to chiral anomaly.

A Crashworthy Device Against Ship-OWT Collision and Its Protection Effects on the Tower of Offshore Wind Farms

At present, more and more offshore wind farms have been built anti ntnnerous projects are on the drawing tables. Therefore, the study on the safety of collision between ships and offshore wind turbines （OWT） is of great practical signifieance. The present study takes the advantage of the famous LS-DYNA explicit code to simulate the dynamic proeess of the collision between a typical 3MW offshore wind turbine model with monopile fi）undation and a simplified 2000t-class ship model. In the simulation, the added mass effect of the ship, contact nonlinearity of collision, material nonlinearity of steel and aluminum foam and adaptive mesh tectmique for large structure deformation have been taken into considera- tion. Proposed is a crashworthy device for OWF of new conceptual steel sphere shell-cireular ring aluminum foam pad, and the good pe.rfurmanee of the device under the conditions of ship-OWT front impact and side impact has been verified from the views of theoretical analysis and numerical results. The new crashworthy device can effectively smooth the contact force and reduce the top structure dynamic response, using its own structure plastic deformation to absorb most of the ship collision enerty. As a result, the main structure of the OWF and the inside key electric control equipments can be saved by scarifying the structural plastic deformation of new sphere crashworthy device. What is more, the sphere configuratiun design of the crashworthy device can effectively guide the ship to run away from the main OWT structure and reduce the damage of the ship and OWT to some degree during side impact.

Local Path Planning and Tracking Control of Vehicle Collision Avoidance System

Automotive collision avoidance technology can effectively avoid the accidents caused by dangerous traffic conditions or driver's manipulation errors.Moreover,it can promote the development of autonomous driving for intelligent vehicle in intelligent transportation.We present a collision avoidance system,which is composed of an evasive trajectory planner and a path following controller.Considering the stability of the vehicle in the conflict-free process,the evasive trajectory planner is designed by polynomial parametric method and optimized by genetic algorithm.The path following controller is proposed to make the car drive along the designed path by controlling the vehicle's lateral movement.Simulation results show that the vehicle with the proposed controller has good stability in the collision process,and it can ensure the vehicle driving in accordance with the planned trajectory at different speeds.The research results can provide a certain basis for the research and development of automotive collision avoidance technology.