Aya Hagishima

Field measurements for estimating the convective heat transfer coefficient at building surfaces

To establish a comprehensive and qualitative prediction basis for the convective heat transfer coefficient (CHTC) for various urban canopy surfaces mainly consisting of building envelopes, a series of outdoor experiments were performed. Multi-point measurements of surface heat balance lead to a distribution of the CHTC on an actual building envelope. Several turbulent statistical values acquired at two different sites enabled the development of an experimental equation depicted by non-dimensional numbers that express a relationship between CHTC and wind velocity containing a turbulent factor. An important thing is the fact that the two measuring sites, one a rooftop slab and the other the vertical wall of a test dwelling, have different scales and different surface directions facing the wind.

An analysis of network reciprocity in Prisoner's Dilemma games using Full Factorial Designs of Experiment

Despite hundreds of studies on the Prisoners Dilemma (PD) game, understanding about network reciprocity remains a unsolved puzzle. Thus, we performed a series of Full Factorial Design of Experiments (FFDOE) to evaluate what dominates emerging cooperation in the PD game on various networks. The results qualitatively reveal the influence of each factor and show that some combinations of factors have complicated interactions. Remarkably, the choice of strategy update rule or update dynamics is much more important than the type of network imposed or, at least, the factorial effect of the average degree of the network reported by Nowak (Science 314, 5805, 1560-1563, 2006) and Ohtsuki et al. (Nature 441, 502-505, 2006). Furthermore, the decision of which PD game type to investigate (whether all PD games, PD-Chicken boundary games or Donor & Recipient games) is important for discussing network reciprocity.

Validation of methodology for utility demand prediction considering actual variations in inhabitant behaviour schedules

A data set of myriad and time-varying inhabitant behaviour schedules with a 15-min time resolution, generated by the authors in a previous study, is validated through a comparison analysis. The key idea of generating a set of raw schedule data from the restricted statistical information is called the ‘generate and kill’ concept, which is commonly used in the fields of artificial intelligence and multi-agent simulation. In the present study, we show three comparisons. The first and second compare the estimated demand with a time series of measured utility demand. These comparisons indicate that the generated data and the algorithm, as described by the authors, have the required robustness. Another comparison between the estimate and the annually averaged daily water demand of a residential area, consisting of 9327 residences, also shows an acceptable consistency.

What controls network reciprocity in the Prisoner's Dilemma game?

The evolutionary Prisoners Dilemma game in structured networks has been studied extensively to understand network reciprocity. However, in some cases results of these studies cannot be compared because not only the network structures but also the network parameters, rules for updating strategies, and update dynamics differ among them. In this study, we investigated the effect of experimental conditions by conducting a series of systematic factorial experiments. We found that those experimental assumptions are significantly important in network reciprocity, although we confirmed that network reciprocity can be basically explained by the average degree of the network (Nowak, 2006; Ohtsuki et al., 2006).

ANALYSIS OF THE INFLUENCE OF LANE CHANGING ON TRAFFIC-FLOW DYNAMICS BASED ON THE CELLULAR AUTOMATON MODEL

Many cellular automaton models (CA models) have been applied to analyze traffic flow. When analyzing multilane traffic flow, it is important how we define lane-changing rules. However, conventional models have used simple lane-changing rules that are dependent only on the distance from neighboring vehicles. We propose a new lane-changing rule considering velocity differences with neighboring vehicles; in addition, we embed the rules into a variant of the Nagel–Schreckenberg (NaSch) model, called the S-NFS model, by considering an open boundary condition. Using numerical simulations, we clarify the basic characteristics resulting from different assumptions with respect to lane changing.

Dangerous drivers foster social dilemma structures hidden behind a traffic flow with lane changes

Motivated by the fact that there are quite a few ill-mannered drivers who disregard traffic rules concerning lane-changing and maximum speed, we investigated an interesting question: whether or not social dilemma structures can be formed from a frequent dangerous lane-changing attitude in a typical traffic flow without any explicit bottlenecks. In our model system, two classes of driver-agents coexist: C agents (cooperative strategy) always keep to traffic regulations with respect to lane-changing and speed, while D agents (defective strategy) disregard them to move ahead. In relatively high-density flows, such as the metastable and high-density phases, we found structures that correspond to either n-person Prisoners Dilemma (n-PD) games or to quasi-PD games. In these situations, existing ill-mannered drivers create heavy traffic jams that reduce social efficiency.

Direct reciprocity in spatial populations enhances R-reciprocity as well as ST-reciprocity.

As is well-known, spatial reciprocity plays an important role in facilitating the emergence of cooperative traits, and the effect of direct reciprocity is also obvious for explaining the cooperation dynamics. However, how the combination of these two scenarios influences cooperation is still unclear. In the present work, we study the evolution of cooperation in 2×2 games via considering both spatial structured populations and direct reciprocity driven by the strategy with 1-memory length. Our results show that cooperation can be significantly facilitated on the whole parameter plane. For prisoners dilemma game, cooperation dominates the system even at strong dilemma, where maximal social payoff is still realized. In this sense, R-reciprocity forms and it is robust to the extremely strong dilemma. Interestingly, when turning to chicken game, we find that ST-reciprocity is also guaranteed, through which social average payoff and cooperation is greatly enhanced. This reciprocity mechanism is supported by mean-field analysis and different interaction topologies. Thus, our study indicates that direct reciprocity in structured populations can be regarded as a more powerful factor for the sustainability of cooperation.

Does copy-resistance enhance cooperation in spatial prisoner's dilemma?

We propose a novel idea for the so-called pairwise-Fermi process by considering copy-resistance when an agent copies a neighbors strategy, which implies that the focal agent with relatively affluent payoff vis-a-vis social average might be negative to copy her neighbors strategy even if her payoff is less than the neighbors payoff. Simulation results reveal that this idea with a revised strategy adaptation process significantly enhances cooperation for prisoners dilemma games played on time-constant networks.

Geometric Dependence of the Scalar Transfer Efficiency over Rough Surfaces

We performed a series of wind-tunnel experiments under neutral conditions in order to create a comprehensive database of scalar transfer coefficients for street surfaces using regular block arrays representing an urban environment. The objective is to clarify the geometric dependence of scalar transfer phenomena on rough surfaces. In addition, the datasets we have obtained are necessary to improve the modelling of scalar transfer used for computational simulations of urban environments; further, we can validate the results obtained by numerical simulations. We estimated the scalar transfer coefficients using the salinity method. The various configurations of the block arrays were designed to be similar to those used in a previous experiment to determine the total drag force acting on arrays. Our results are summarized as follows: first, the results for cubical arrays showed that the transfer coefficients for staggered and square layouts varied with the roughness packing density. The results for the staggered layout showed the possibility that the mixing effect of air can be enhanced for the mid-range values of the packing density. Secondly, the transfer coefficients for arrays with blocks of non-uniform heights were smaller than those for arrays with blocks of uniform height under conditions of low packing density; however, as the packing density increased, the opposite tendency was observed. Thirdly, the randomness of rotation angles of the blocks in the array led to increasing values of the transfer coefficients under sparse packing density conditions when compared with those for cubical arrays.

Determination of aerodynamic parameters of urban surfaces: methods and results revisited

Estimates of aerodynamic parameters, in particular roughness length z0 and displacement height d, are important for the analysis of the roughness of an urban surface, which affects processes that occur within the urban boundary layer such as pollutant dispersion and urban ventilation. Findings regarding the aerodynamic effects of various configurations of urban arrays were compiled from various studies. Several experimental, numerical and semi-empirical studies to estimate z0 and d were reviewed and compared with each other. The results can be summarized as follows: (1) the influence of the frontal area index (λf) on z0 is significant and their relationship has been confirmed by both experimental and numerical data; (2) compared to one-parameter and two-parameter fitting methods, the three-parameter fitting method is the least accurate; (3) the physical meaning of d remains vague because its definition as the height where surface drag acts may not be accurate for sharp-edged roughness blocks and (4) the peak values of z0 for uniform and heterogeneous block heights indicate presence of skimming or wake-interference flow effects, which may influence surface roughness. Finally, the semi-empirical models were found to be limited to cases derived from available experimental data, which normally involve uniform arrays of cubes.