Xiaoping Zheng

Zeolitic imidazolate framework-8 as a luminescent material for the sensing of metal ions and small molecules

We present a rare example of Zeolitic Imidazolate Framework-8 (ZIF-8), Zn(MeIM)2•(DMF)•(H2O)3, as luminescent probes with multi-function sensitivity to detect metal ions and small molecules. Our results show that the luminescence intensity of ZIF-8 is strongly sensitive to Cu2+ and Cd2+ ions and small molecules such as acetone. In particular, the luminescence intensity of desolvated ZIF-8 proportionally decreases to the concentration of Cu2+, while increases to the concentration of Cd2+ owing to the recognition of element-imidazole nitrogen sites. The luminescence intensity increases gradually with the increase of amounts of acetone in the standard desolvated ZIF-8-emulsions. These results reveal that the ZIFs might be a good luminescent sensor for metal ions and small molecules.

Effect of heterogeneous investments on the evolution of cooperation in spatial public goods game.

Understanding the emergence of cooperation in spatial public goods game remains a grand challenge across disciplines. In most previous studies, it is assumed that the investments of all the cooperators are identical, and often equal to 1. However, it is worth mentioning that players are diverse and heterogeneous when choosing actions in the rapidly developing modern society and researchers have shown more interest to the heterogeneity of players recently. For modeling the heterogeneous players without loss of generality, it is assumed in this work that the investment of a cooperator is a random variable with uniform distribution, the mean value of which is equal to 1. The results of extensive numerical simulations convincingly indicate that heterogeneous investments can promote cooperation. Specifically, a large value of the variance of the random variable can decrease the two critical values for the result of behavioral evolution effectively. Moreover, the larger the variance is, the better the promotion effect will be. In addition, this article has discussed the impact of heterogeneous investments when the coevolution of both strategy and investment is taken into account. Comparing the promotion effect of coevolution of strategy and investment with that of strategy imitation only, we can conclude that the coevolution of strategy and investment decreases the asymptotic fraction of cooperators by weakening the heterogeneity of investments, which further demonstrates that heterogeneous investments can promote cooperation in spatial public goods game.

Understanding Cooperative Behavior Based on the Coevolution of Game Strategy and Link Weight

In reality, the dependency relationship among individuals is heterogeneous and time-varying. Based on this fact, we present a new mechanism of coevolution of game strategy and link weight when analyzing the evolution of cooperation. In detail, we model the population on a regular network, on which the relationship between players is depicted by a weighted link, and prisoner’s dilemma has been applied to describe the interaction of players. Further, the impact of this mechanism on the cooperative behavior has been outlined. By conducting large-scale Monte Carlo simulations, we can easily draw a conclusion that this mechanism can promote cooperation efficiently. Compared with the traditional case, when the temptation of defection b is large, the fraction of cooperation is still able to keep in a high level. With a comprehensive examination of the distribution of stable link weight, it is evident that the coevolution mechanism would deviate the initial distribution. This mechanism induces the heterogeneity of players, which enhances the fraction of cooperation. Numerical simulations also indicate that an intermediate value of Δ/δ warrants an optimal resolution of prisoner’s dilemma. The mechanism of coevolution of game strategy and link weight has a practical significance and will provide new insight for the further research.

Back-calculation of the strength and location of hazardous materials releases using the pattern search method

Predicting quickly and accurately the strength and location of hazardous materials releases becomes a critical problem in emergency rescue. A technique that coupled the concentrations observed in the downwind direction of the source with a dispersion model was presented to back-calculate the strength and location of the release source by using the pattern search method. The technique was described as an optimization problem with an objective function constructed from a sum of squared errors between the observed concentrations and the calculated concentrations. The utility of the pattern search method was illustrated by testing the simulation data with practical data. The advantages of the method were demonstrated by a comparison with a gradient-based algorithm and an intelligent optimization algorithm. The computations indicate that this method can achieve optimal solutions in a relatively shorter time, hence more efficiently meeting the needs of emergency rescue.

Behavioral evolution in evacuation crowd based on heterogeneous rationality of small groups

It is widely accepted that crowds are composed primarily of small groups. Based on this fact, the evacuation crowd is divided into small groups based on the rationality, and then the impact of rationality and ratios of small groups on the behavioral evolution is explored. Among the crowds, the rational small group allocates their investment based on the quality of game groups. By means of Monte-Carlo simulation, it is found that rational allocation will promote the cooperation, which concisely introduces the Matthew effect. The higher the rational degree is, the more significant cooperation promotion effect will be, and the decreasing of corresponding phase transition points will also be more remarkable. Then, the effect of the ratio of small group 1 is discussed. The results show that the fraction of cooperation in the crowd is negatively correlated with the ratio of small group 1. Lastly, the phase diagram for fraction of cooperation corresponding to different rationality and ratios of small group 1 is depicted by scanning of parameter spaces extensively. The phase diagram vividly shows the roles of rationality and ratio of small group 1. In conclusion, this paper reveals the behavioral evolution in evacuation crowd in some extent by introducing the heterogeneous rationality of small groups. Simultaneously, the framework of this paper is instructional for the future study of the behavioral evolution in evacuation crowd with multi small groups.

Forecasting model for pedestrian distribution under emergency evacuation

Pedestrian distribution forecasting on the road network is developed to support the evacuation decision-making. The numbers of evacuees distributed on each road link are stochastic, uncertain and multi-dependent. Therefore, a Gaussian Bayesian networks (GBN) based forecasting model is presented, considering the pedestrian flow characteristics, optimization of evacuation route and evacuation decision-making. In the forecasting model, the route choice probabilities obtained by minimizing evacuation time are applied to correct the regression coefficients of GBN. Finally, an example is provided to illustrate the usefulness of this model. Research shows that this model not only reflects the complexity and dynamics of evacuation process but also performs an accurate forecasting on the time development of the pedestrian distributed in the evacuation space.

Effect of heterogeneous sub-populations on the evolution of cooperation

Understanding origin of cooperation denotes one of the most challenging conundrums across myriad disciplines. Different from previous assumption that all the individuals have identical dilemma, here we put forward a heterogeneous sub-population model on regular lattices and complex networks: players face different dilemmas and cooperation tendency inside and outside sub-population. In details, each agent will play different games with the opponents from his own sub-population or from a different sub-population. By means of numerous simulations, we find that sub-population is a useful way to resolve social dilemmas, which is universally effective for interaction topology. Interestingly, less sub-populations can guarantee the optimal environment of cooperation, the continuous increment of sub-population number in turn impedes the evolution of cooperation, which though seems better than the traditional scenario (namely, pure prisoners dilemma or snowdrift game on network). Moreover, the fraction of cooperation also depends on the related scale of such sub-populations. From the viewpoint of microscopic dynamics, we further explore the transition probability of different strategies and the organization of cooperator clusters. Because this framework of heterogeneous sub-populations is close to realistic life, we hope that it can provide new insight to resolve the social dilemmas.

Measuring the steady state of pedestrian flow in bottleneck experiments

Experiments with pedestrians could depend strongly on initial conditions. Comparisons of the results of such experiments require to distinguish carefully between transient state and steady state. Thus a modified version of the Cumulative Sum Control Chart algorithm is proposed to robustly detect steady states from density and speed time series of bottleneck experiments. The threshold of the detection parameter in the algorithm is calibrated using an autoregressive model. Comparing the detected steady states with manually selected ones, the modified algorithm gives robust and reproducible results. For the applications, three groups of bottleneck experiments are analysed and the steady states are detected. The results reconfirm that the specific flow is constant as bottleneck width changes. Moreover, we proposed a criterion to judge the difference between the flows in all states and in steady states, which is the ratio of pedestrian number to bottleneck width. The critical value of the ratio is found to be approximately 115 persons/m. This conclusion applies not only for the analysis of existing bottleneck experiments but also for the design of new bottleneck experiments and the validation of evacuation models. Furthermore, the range of steady state in time series of pedestrian characteristics could be effectively controlled by adjusting the value of the ratio.

Social Stratification and Cooperative Behavior in Spatial Prisoners' Dilemma Games

It has been a long-lasting pursuit to promote cooperation, and this study aims to promote cooperation via the combination of social stratification and the spatial prisoners’ dilemma game. It is previously assumed that agents share the identical payoff matrix, but the stratification or diversity exists and exerts influences in real societies. Thus, two additional classes, elites and scoundrels, derive from and coexist with the existing class, commons. Three classes have different payoff matrices. We construct a model where agents play the prisoners’ dilemma game with neighbors. It indicates that stratification and temptation jointly influence cooperation. Temptation permanently reduces cooperation; elites play a positive role in promoting cooperation while scoundrels undermine it. As the temptation getting larger and larger, elites play a more and more positive and critical role while scoundrels’ negative effect becomes weaker and weaker, and it is more obvious when temptation goes beyond its threshold.

Validation of FDS+Evac for pedestrian simulations in wide bottlenecks

In this study, the reliability of FDS+Evac (FDS 6.0.1, Evac 2.4.1) is investigated by a series of well-controlled laboratory experiments. The parameters controlling the free speed and the anisotropy of social force between pedestrians are calibrated based on the experimental values. With the adjusted values of the parameters, FDS+Evac is able to reproduce the experimental process with respect to the flow through the bottleneck. However, other pedestrian characteristics in the simulations do not match with those in the experiments. This study shows that the validation of FDS+Evac should not only consider single pedestrian characteristics. More careful calibration of parameters and comprehensive analysis are necessary before FDS+Evac is used for security-related applications in general.