Qing-Yi Hao

Origin of the Scaling Law in Human Mobility: Hierarchy of Traffic Systems

Uncovering the mechanism leading to the scaling law in human trajectories is of fundamental importance in understanding many spatiotemporal phenomena. We propose a hierarchical geographical model to mimic the real traffic system, upon which a random walker will generate a power-law-like travel displacement distribution with tunable exponent, and display a scaling behavior in the probability density of having traveled a certain distance at a certain time. The simulation results, analytical results, and empirical observations reported in D. Brockmann et al. [Nature (London) 439, 462 (2006)] agree very well with each other.

Phase transition in random walks coupled with evolutionary game

We investigate a non-equilibrium process of random walk coupled with evolutionary game on one-dimensional periodic lattices. A first-order phase transition is observed, i.e., the cooperator ratio suddenly decreases at a critical density ρcr. The defector ratio remains constant when the density ρ>ρcr, but it decays exponentially when ρ<ρcr. The behavior is compared with that studied by Barato and Hinrichsen (Phys. Rev. Lett., 100 (2008) 165701). The evolution of cooperator ratio and the system flux have also been studied via Monte Carlo simulation and mean-field analysis.

Theoretical analysis and simulation for a facilitated asymmetric exclusion process

Driven diffusive systems are important models in nonequilibrium state statistical mechanics. This paper studies an asymmetric exclusion process model with nearest rear neighbor interactions associated with energy. The exact flux expression of the model is obtained by a cluster mean-field method. Based on the flux expression, the properties of the fundamental diagram have been investigated in detail. To probe the energys influence on the coarsening process of the system, Monte Carlo simulations are carried out to acquire the monotonic phase boundary in energy-density space. Above the phase boundary, the system is inhomogeneous and the normalized residence distribution p(s) is nonmonotonically decreasing. Under the phase boundary, the system is homogeneous and p(s) is monotonically decreasing. Further study comparatively shows that the system has turned into a microscopic inhomogeneous state from a homogeneous state before the system current arrives at maximum, if nearest rear neighbor interactions are strong. Our findings offer insights to deeply understand the dynamic features of nonequilibrium state systems.

Unidirectional Pedestrian Flow in a Lattice Gas Model Coupled with Game Theory

This paper studies unidirectional pedestrian flow in a channel by using a lattice gas model with parallel update rule. Game theory is introduced to deal with the conflict that several pedestrians intend to move to the same site. A pedestrian is either a co operator (C) or defector (D) when he or she wants to move into the same lattice as other pedestrians. Moreover, he or she could change the strategy (C or D) in the next conflict. The fundamental diagram of pedestrian flow in the channel has been investigated in details, and differences from the model with random sequential update rule have been observed. The co operators fraction is shown to exhibit an interesting non-monotonic dependence on pedestrian density. It is interesting to find that change of co operators fraction alters exponentially before the system comes to steady state. How the parameters p and q in the payoff matrix of game influence mean flow and co operators fraction is also investigated.

Exponential decay of spatial correlation in driven diffusive system: A universal feature of macroscopic homogeneous state

Driven diffusive systems have been a paradigm for modelling many physical, chemical, and biological transport processes. In the systems, spatial correlation plays an important role in the emergence of a variety of nonequilibrium phenomena and exhibits rich features such as pronounced oscillations. However, the lack of analytical results of spatial correlation precludes us from fully understanding the effect of spatial correlation on the dynamics of the system. Here we offer precise analytical predictions of the spatial correlation in a typical driven diffusive system, namely facilitated asymmetric exclusion process. We find theoretically that the correlation between two sites decays exponentially as their distance increases, which is in good agreement with numerical simulations. Furthermore, we find the exponential decay is a universal property of macroscopic homogeneous state in a broad class of 1D driven diffusive systems. Our findings deepen the understanding of many nonequilibrium phenomena resulting from spatial correlation in driven diffusive systems.

Flow Improvement By Providing Partial Traffic Information For Road Users

In this paper, we investigate two two-route traffic models, i.e. asymmetric and symmetric two-route traffic models, with mean velocity information feedback strategy. The simulation results show that, for asymmetric two-route model, average flux can be significantly improved if only partial road information is provided for road users. However, for symmetric two-route model, average flux of the two routes adopting information feedback cannot outweigh the flux of two routes chosen completely at random. We explain the results by studying the vehicle number on two routes. We hope the study may provide a good suggestion to the design of Advanced Traveler Information Systems.

Impact of holding umbrella on uni- and bi-directional pedestrian flow: experiments and modeling

ABSTRACT In this paper, the impact of holding an umbrella on the uni- and bi-directional flow has been investigated via experiment and modeling. In experiments, pedestrians walk clockwise/anti-clockwise in a ring-shaped corridor under the normal situation and holding umbrella situation. In the unidirectional flow, the flow rate under the holding umbrella situation decreases from 0.1 to 0.25 ped/s/m when compared to the normal situation. In the holding umbrella situation, the bidirectional flow rate even reduces to 0.2 ped/s/m in contrast to the unidirectional flow. In the bidirectional flow, pedestrians segregate into two opposite moving streams very quickly under the normal situation and have right-walking preference. Under the holding umbrella situation, spontaneous lane formation also occurs. However, pedestrians can easily separate into three or four lanes. Moreover, the merge of lanes is observed, and clockwise/anti-clockwise pedestrians are not always in the inner/outer lane. The simulation results by an improved social force model considering the umbrella size are in agreement with the experimental ones.