Network flow of mobile agents enhances the evolution of cooperation

We study the effect of contingent movement on the persistence of cooperation on complex networks with empty nodes. Each agent plays Prisoner's Dilemma game with its neighbors and then it either updates the strategy depending on the payoff difference with neighbors or it moves to another empty node if not satisfied with its own payoff. If no neighboring node is empty, each agent stays at the same site. By extensive evolutionary simulations, we show that the medium density of agents enhances cooperation where the network flow of mobile agents is also medium. Moreover, if the movements of agents are more frequent than the strategy updating, cooperation is further promoted. In scale-free networks, the optimal density for cooperation is lower than other networks because agents get stuck at hubs. Our study suggests that keeping a smooth network flow is significant for the persistence of cooperation in ever-changing societies.Comment: 7 pages, 5 figure

Many-particle simulation of the evacuation process from a room without visibility

We study the evacuation process from a smoky room by means of experiments and simulations. People in a dark or smoky room are mimicked by ``blind'' students wearing eye masks. The evacuation of the disoriented students from the room is observed by video cameras, and the escape time of each student is measured. We find that the disoriented students exhibit a distinctly different behavior compared with a situation in which people can see and orient themselves. Our experimental results are reproduced by an extended lattice gas model taking into account the empirically observed behavior. Our particular focus is on the mean value and distribution of escape times. For a large number of people in the room, the escape time distribution is wide because of jamming. Surprisingly, adding more exits does not improve the situation in the expected way, since most people use the exit that is discovered first, which may be viewed as ``herding effect'' based on accoustic interactions. Moreover, the average escape time becomes minimal for a certain finite number of people in the dark or smoky room. These non-linear effects have practical implications for emergency evacuation and the planning of safer buildings.Comment: For related work see http://www.helbing.or

Traffic Behavior in CA Model of Vehicular Traffic through a Series of Signals

We study the traffic states and fundamental diagram of vehicular traffic controlled by a series of traffic lights using a deterministic cellular automaton (CA) model. The CA model is not described by a set of rules but is given by a difference equation. The vehicular traffic varies highly with both signal’s characteristics and vehicular density. The dependence of fundamental diagram on the signal’s characteristics is derived. At a low value of cycle time, the fundamental diagram displays the typical trapezoid, while it shows a triangle at a high value of cycle time. The dynamic transitions among distinct traffic states depend greatly on the signal’s characteristics. The dependence of the transition points on the cycle time split and offset time is found

Stability Analysis and Stabilization Strategies for Linear Supply Chains

Due to delays in the adaptation of production or delivery rates, supply chains can be dynamically unstable with respect to perturbations in the consumption rate, which is known as "bull-whip effect". Here, we study several conceivable production strategies to stabilize supply chains, which is expressed by different specifications of the management function controlling the production speed in dependence of the stock levels. In particular, we will investigate, whether the reaction to stock levels of other producers or suppliers has a stabilizing effect. We will also demonstrate that the anticipation of future stock levels can stabilize the supply system, given the forecast horizon is long enough. To show this, we derive linear stability conditions and carry out simulations for different control strategies. The results indicate that the linear stability analysis is a helpful tool for the judgement of the stabilization effect, although unexpected deviations can occur in the non-linear regime. There are also signs of phase transitions and chaotic behavior, but this remains to be investigated more thoroughly in the future.Comment: For related work see http://www.helbing.or

Development of an Ultra High Resolution Scanning Electron Microscope by Means of a Field Emission Source and In-Lens System

An ultra high resolution scanning electron microscope, which is composed of a cold cathode field emission gun and an in-lens system for specimens, has been developed. Probe size is estimated 0.8nm at 30kV by calculation and confirmed experimentally using high atomic number samples such as fine Pt particles sputter-coated on carbon. Three stage ion pumps for the column and a turbo molecular pump for the specimen chamber have been used for a totally dry vacuum system. Applications for fine metal oxide particles and biological samples observed directly without any metal coating, and applications chosen especially to show lower voltage performance, are shown