Kinetic theory of situated agents applied to pedestrian flow in a corridor

A situated agent-based model for simulation of pedestrian flow in a corridor is presented. In this model, pedestrians choose their paths freely and make decisions based on local criteria for solving collision conflicts. The crowd consists of multiple walking agents equipped with a function of perception as well as a competitive rule-based strategy that enables pedestrians to reach free access areas. Pedestrians in our model are autonomous entities capable of perceiving and making decisions. They apply socially accepted conventions, such as avoidance rules, as well as individual preferences such as the use of specific exit points, or the execution of eventual comfort turns resulting in spontaneous changes of walking speed. Periodic boundary conditions were considered in order to determine the density-average walking speed, and the density-average activity with respect to specific parameters: comfort angle turn and frequency of angle turn of walking agents. The main contribution of this work is an agent-based model where each pedestrian is represented as an autonomous agent. At the same time the pedestrian crowd dynamics is framed by the kinetic theory of biological systems.     

Nonlinear time series analysis of normal and pathological human walking

Characterizing locomotor dynamics is essential for understanding the neuromuscular control of locomotion. In particular, quantifying dynamic stability during walking is important for assessing people who have a greater risk of falling. However, traditional biomechanical methods of defining stability have not quantified the resistance of the neuromuscular system to perturbations, suggesting that more precise definitions are required. For the present study, average maximum finite-time Lyapunov exponents were estimated to quantify the local dynamic stability of human walking kinematics. Local scaling exponents, defined as the local slopes of the correlation sum curves, were also calculated to quantify the local scaling structure of each embedded time series. Comparisons were made between overground and motorized treadmill walking in young healthy subjects and between diabetic neuropathic (NP) patients and healthy controls (CO) during overground walking. A modification of the method of surrogate data was developed to examine the stochastic nature of the fluctuations overlying the nominally periodic patterns in these data sets. Results demonstrated that having subjects walk on a motorized treadmill artificially stabilized their natural locomotor kinematics by small but statistically significant amounts. Furthermore, a paradox previously present in the biomechanical literature that resulted from mistakenly equating variability with dynamic stability was resolved. By slowing their self-selected walking speeds, NP patients adopted more locally stable gait patterns, even though they simultaneously exhibited greater kinematic variability than CO subjects. Additionally, the loss of peripheral sensation in NP patients was associated with statistically significant differences in the local scaling structure of their walking kinematics at those length scales where it was anticipated that sensory feedback would play the greatest role. Lastly, stride-to-stride fluctuations in the walking patterns of all three subject groups were clearly distinguishable from linearly autocorrelated Gaussian noise. As a collateral benefit of the methodological approach taken in this study, some of the first steps at characterizing the underlying structure of human locomotor dynamics have been taken. Implications for understanding the neuromuscular control of locomotion are discussed. (c) 2000 American Institute of Physics.     

A glycine receptor is involved in the organization of swimming movements in an invertebrate chordate

Background  

Rhythmic motor patterns for locomotion in vertebrates are generated in spinal cord neural networks known as spinal Central Pattern Generators (CPGs). A key element in pattern generation is the role of glycinergic synaptic transmission by interneurons that cross the cord midline and inhibit contralaterally-located excitatory neurons. The glycinergic inhibitory drive permits alternating and precisely timed motor output during locomotion such as walking or swimming. To understand better the evolution of this system we examined the physiology of the neural network controlling swimming in an invertebrate chordate relative of vertebrates, the ascidian larva Ciona intestinalis.     

Determining an influencing area affecting walking speed on footpath: A case study of a footpath in CBD Bangkok,Thailand

Intuitively, the crowd density in front of a pedestrian will affect his walking speed along a footpath. Nevertheless, the size of the influencing area affecting walking speed has rarely been scrutinized in the past. This study attempts to determine the distance in front of pedestrians that principally affects their walking speed under normal conditions, using a case study of a footpath in Bangkok. We recorded pedestrian activities along a test section of 20 m, with an effective walking width of 2.45 m in the morning and at noon. The morning dataset was extracted for analyzing various influencing distances, ranging from 1 to 20 m in front of the pedestrian. The bi-directional walking speed–pedestrian density models were developed, for each tested distance, using linear regression analysis. It was found that an influencing length in the range of 5–8 m yields the highest correlation coefficients. In the case of high density conditions, the walking speed of the equally-split flow (50:50) was found to be higher than other proportional flow analyzed. The finding has useful implications on the improvement of the walking simulations in mesoscopic models.     

Pedestrian choice behavior analysis and simulation of vertical walking facilities in transfer station

Considering the interlayer height, luggage, the difference between queuing pedestrians, and walking speed, the pedestrian choice model of vertical walking facilities is established based on a support vector machine. This model is verified with the pedestrian flow data of Changchun light-rail transfer station and Beijing Xizhimen transfer station. Adding the pedestrian choice model of vertical walking facilities into the pedestrian simulation model which is based on cellular automata, the pedestrian choice behavior is simulated. In the simulation, the effects of the dynamic influence factors are analyzed. To reduce the conflicts between pedestrians in opposite directions, the layout of vertical walking facilities is improved. The simulations indicate that the improved layout of vertical walking facilities can improve the efficiency of pedestrians passing.     

Coupling between switching regulation and torque generation in bacterial flagellar motor

The bacterial flagellar motor plays a crucial role in both bacterial locomotion and chemotaxis. Recent experiments reveal that the switching dynamics of the motor depend on the rotation speed of the motor, and thus the motor torque, nonmonotonically. Here we present a unified mathematical model which treats motor torque generation based on experimental torque-speed curves and the torque-dependent switching based on the conformational spread model. The model successfully reproduces the observed switching rate as a function of the rotation speed, and provides a generic physical explanation independent of most details. A stator affects the switching dynamics through two mechanisms: accelerating the conformational flipping rate of individual rotor-switching units, which contributes most when the stator works at a high torque and thus a low speed; and influencing a larger number of rotor-switching units within unit time, whose contribution is the greatest when the motor rotates at a high speed. Consequently, the switching rate shows a maximum at intermediate speed, where the above two mechanisms find an optimal output. The load-switching relation may serve as a mechanism for sensing the physical environment, similar to the chemotaxis mechanism for sensing the chemical environment. It may also coordinate the switch dynamics of motors within the same cell.     

A composite micromotor driven by self-thermophoresis and Brownian rectification

Brownian motors and self-phoretic microswimmers are two typical micromotors, for which thermal fluctuations play different roles. Brownian motors utilize thermal noise to acquire unidirectional motion, while thermal fluctuations randomize the self-propulsion of self-phoretic microswimmers. Here we perform mesoscale simulations to study a composite micromotor composed of a self-thermophoretic Janus particle under a time-modulated external ratchet potential. The composite motor exhibits a unidirectional transport, whose direction can be reversed by tuning the modulation frequency of the external potential. The maximum transport capability is close to the superposition of the drift speed of the pure Brownian motor and the self-propelling speed of the pure self-thermophoretic particle. Moreover, the hydrodynamic effect influences the orientation of the Janus particle in the ratched potential, hence also the performance of the composite motor. Our work thus provides an enlightening attempt to actively exploit inevitable thermal fluctuations in the implementation of the self-phoretic microswimmers.     

驱动马达定向运动的随机动力学模型

本文在非对称周期势中考虑驱动马达的机械化学耦合,基于布朗马达的工作原理,利用MATLAB数值模拟驱动马达在一定实验条件下的运动特征.我们首先模拟了单个驱动马达的位移和速度随时间变化的图像,然后分别计算了多个驱动马达运动的平均速度,最后计算了不同负载力条件下马达运动速度的系综平均值.模拟结果表明驱动马达在定向运动中存在等待态和行走态,行走步长约为8.2nm,且马达运动具有一定的随机性.通过与实验比较,发现模型计算结果与实验吻合.     

Hydrodynamic scaling law in undulatory braking locomotion

Flow over a fish-like airfoil is numerically investigated to elaborate the hydrodynamics of the undulatory braking locomotion for an elongated eel-like body or long-based fin. For undulation with low frequency, we find that boundary layer separation occurs in a parameter region with wakes in which two vortex pairs are formed per undulatory period. The physical mechanism of separation is governed by the slip(the ratio of swimming-to-body-wave speed), and the critical value of the slip in an inertial flow regime is approximately 4/3 rather than 1, which is independent of steepness(or amplitude). The relationship between pressure drag and relative velocity(between phase speed and free stream velocity) changes from linear to quadratic, corresponding to two different flow structures; this happens due to boundary layer separation, and the piecewise scaling relationship between pressure drag and relative velocity is explicitly clarified. Considering the viscosity effects, the separation criterion and the scaling relationship in the case of an undulatory brake are both synthetically modified using the Reynolds number, with all the required parameters clearly expressed. The results of this study provide physical insight into understanding the flow structures and hydrodynamics of the undulatory braking locomotion, which has instructional significance to brake design.     

A Numerical Study of Jet Propulsion of an Oblate Jellyfish Using a Momentum Exchange-Based Immersed Boundary-Lattice Boltzmann Method

In present paper, the locomotion of an oblate jellyfish is numerically investigated by using a momentum exchange-based immersed boundary-Lattice Boltzmann method based on a dynamic model describing the oblate jellyfish. The present investigation is agreed fairly well with the previous experimental works. The Reynolds number and the mass density of the jellyfish are found to have significant effects on the locomotion of the oblate jellyfish. Increasing Reynolds number, the motion frequency of the jellyfish becomes slow due to the reduced work done for the pulsations, and decreases and increases before and after the mass density ratio of the jellyfish to the carried fluid is 0.1. The total work increases rapidly at small mass density ratios and slowly increases to a constant value at large mass density ratio. Moreover, as mass density ratio increases, the maximum forward velocity significantly reduces in the contraction stage, while the minimum forward velocity increases in the relaxation stage.     

Asymptotic normality in a two-dimensional random walk model for cell motility

We prove the asymptotic normality of a two-dimensional random walk describing the locomotion of cells on planar surfaces and calculate the asymptotic covariance matrix. The trajectories of the walk are random broken lines covered with constant speed, where the time intervals between turns as well as the turn angles are random and stochastically independent.     

相对论性电子在行波磁场中的自发辐射

相对论性电子在周期性磁场中的运动将产生自发辐射,这是产生自由电子激光的基础。本采用行波磁场作为周期性磁场,通过讨论可以看出,当电子通过这种磁场时将产生自发辐射,说明该磁场能作为自由电子激光器的摆动器。     

The exact probability distribution of a two-dimensional random walk

A calculation is made of the exact probability distribution of the two-dimensional displacement of a particle at timet that starts at the origin, moves in straight-line paths at constant speed, and changes its direction after exponentially distributed time intervals, where the lengths of the straight-line paths and the turn angles are independent, the angles being uniformly distributed. This random walk is the simplest model for the locomotion of microorganisms on surfaces. Its weak convergence to a Wiener process is also shown.     

Footstep sounds synthesis: Design,implementation, and evaluation of foot–floor interactions,surface materials,shoe types,and walkers’ features

This paper presents a novel footstep sound synthesizer based on physical and physically inspired models coupled with additive synthesis and signals multiplication. Several types of foot–floor interactions are simulated (e.g., different types of steps in walking and running or the sliding of the foot on the floor). Moreover, different types of shoes and ground materials (solid, aggregate, liquid, and hybrids) are synthesized, along with the modeling of some anthropomorphic features of the walkers (i.e., body size and foot-length). The design choices underlying the proposed synthesis methods were made according to four main points: (i) auditory perceptual relevance, i.e., ecological validity; (ii) cartoonification approach; (iii) parametric temporal control; (iv) real-time utilization. Moreover, four types of control for the involved synthesis algorithms are discussed. Firstly, a control strategy is proposed in order to generate sequences of footstep sounds. Secondly, the design choices underlying the tuning of the synthesis parameters are illustrated. Thirdly, a control strategy is presented to provide footstep sounds designers and foley artists with a tool to create perceptually compelling sounds in an intuitive manner. Fourthly, control techniques are discussed for the interactive case in presence of different types of locomotion interfaces along with their differences with the non-interactive control when locomotion is passively simulated. Finally, four perceptual experiments successfully assessed the validity of the proposed techniques.     

基于元胞自动机和复杂网络理论的双向行人流建模

通过设计行人行走倾向性调查实验,分析了行人的行走倾向性特征. 引入前进系数、右倾系数、超越系数以及影响修正系数等对元胞自动机(CA) 基本模型中的转移概率进行修正,建立了考虑行人行走倾向性特征的CA行人仿真模型. 针对该模型中的行人群体,依据k-近邻作用原理,构建行人复杂网络. 通过计算机仿真,揭示了行人流密度、速度和流量的关系以及仿真过程中出现的自组织现象.进一步分析仿真输出的行人流基本参数和行人复杂网络主要特征参数,发现对同一行人流,其平均速度和网络平均路径长度均随着行人流状态的改变而变化.最后, 通过平均路径长度和平均速度的数据拟合,得出两者之间存在着线性负相关关系的结论, 即具有较小网络平均路径长度的行人流具有较高的平均速度.     

基于异构计算的简单行走模型的吸引区域研究

被动行走机器人由于结构简单、能量利用率高而倍受青睐, 但其很容易跌倒, 因此准确把握最终步态与吸引区域成了关键. 由于面对非光滑系统, 大规模数值计算很难避免, 为此本文先提出基于CPU+GPU异构平台的Poincaré映射算法. 该算法可发挥最新平台计算潜力, 比传统CPU上算法快上百倍. 得益于此, 本文针对双足被动行走的最基本模型, 大规模地选取样点进行计算, 不仅清晰地得出吸引区域的形状轮廓和细节特征, 揭示了其内在分形结构, 还得到系统吸引集和吸引区域随倾角k的变化关系, 发现了新的稳定三周期步态和倍周期分岔混沌现象, 并研究了吸引区域.     

Heavy flags undergo spontaneous oscillations in flowing water

By immersing a compliant yet self-supporting sheet into flowing water, we study a heavy, streamlined, and elastic body interacting with a fluid. We find that above a critical flow velocity a sheet aligned with the flow begins to flap with a Strouhal frequency consistent with animal locomotion. This transition is subcritical. Our results agree qualitatively with a simple fluid dynamical model that predicts linear instability at a critical flow speed. Both experiment and theory emphasize the importance of body inertia in overcoming the stabilizing effects of finite rigidity and fluid drag.     

On the Complete Integrability of the Discrete Nahm Equations

The discrete Nahm equations, a system of matrix valued difference equations, arose in the work of Braam and Austin on half-integral mass hyperbolic monopoles. We show that the discrete Nahm equations are completely integrable in a natural sense: to any solution we can associate a spectral curve and a holomorphic line-bundle over the spectral curve, such that the discrete-time DN evolution corresponds to walking in the Jacobian of the spectral curve in a straight line through the line-bundle with steps of a fixed size. Some of the implications for hyperbolic monopoles are also discussed.     

Fluorescence enhancement of Ln doped nanoparticles

Fluorescence emission of Ln³⁺ doped nanoparticles is influenced by many factors. Enhancement of fluorescence emission of Ln³⁺ doped nanoparticles can be achieved either through an external approach or an internal adjustment. The external approaches mainly include application of core/shell configuration and metal or semiconductor nanoparticles. Varying the crystal phase of the nanoparticle or introducing a codopant sensitizer are the internal approaches frequently used to obtain fluorescence enhancement, which are through inner adjustments to change the local structure, local symmetry and interaction with active ions. In the current work, efforts to obtain luminescence enhancement in Ln³⁺ doped nanoparticles through external or internal approaches are reviewed. The important roles of local symmetry and asymmetric interactions with optically active ions are extensively discussed.     

Motion and mixing for multiple ferromagnetic microswimmers

This paper concerns the interaction of several ferromagnetic microswimmers, their motion and the resulting fluid mixing. Each swimmer consists of two ferromagnetic beads joined by an elastic link, and is driven by an external, time-dependent magnetic field. The external field provides a torque on a swimmer and, together with the varying attraction between the magnetic beads, generates a time-irreversible motion leading to persistent swimming in a low Reynolds number environment. The aim of the present paper is to consider the interactions between several swimmers. A regime is considered in which identical swimmers move in the same overall direction, and their motion is synchronised because of driving by the external field. It is found that two swimmers tend to encircle one another while three undergo more complicated motion that may involve the braiding of swimmer trajectories. By means of approximations it is established that the interaction between pairs of swimmers gives circulatory motion which falls off with an inverse square law and is linked to their overall speed of motion through the fluid. As groups of two or more swimmers move through the fluid they process fluid, leaving behind a trail of fluid that has undergone mixing: this is investigated by following streak lines numerically.