In this paper, we apply system dynamics to model a queuing system wherein the manager of a service facility adjusts capacity based on his perception of the queue size; while potential and current customers react to the managers decisions. Current customers update their perception based on their own experience and decide whether to remain patronizing the facility, whereas potential customers estimate their expected waiting time through word of mouth and decide whether to join the facility or not. We simulate the model and analyze the evolution of the backlog of work and the available service capacity. Based on this analysis we propose two alternative decision rules to maximize the managers cumulative profits. Then, we illustrate how we have developed an experiment to collect information about the way human subjects taking on the role of a manager in a lab environment face a situation in which they must adjust the capacity of a service facility.
This work evaluates the impact of existing policies in the Brazilian National Plan for Logistics and Transport (PNLT) on CO2 emissions due to the transport of domestic cargo. We build a formal system dynamics model capturing the causal relationships influencing the modal shift from road to cabotage transport of cargo in Brazil. Scenarios are charted to understand the impact of PNLT policies on CO2 emissions(?) and the implications for the transport infrastructure. Our analysis shows that pressure to reduce CO2 emissions plays a critical role accelerating the modal shift from road to cabotage.
The purpose of this paper is to briefly discuss the presence of the archetype Success-to-the-Successful in the energy system and to analyse policy options in the presence of this archetype in the energy system. More precisely, the paper aims at finding conditions under which the path dependent allocation of investments directed to the conventional energy-technology sector can be alleviated, in order to encourage investments in alternative energies and technologies. The discussion draws on a stylized and highly aggregated model of the energy system, which is based on system dynamics. Sensitivity analyses are used as the major diagnostic tool to identify options to break away from the current dominant path of energy production and use, and the investments made in it. The value of this paper lies in the clear articulation of a complex and fuzzy topic, with the help of modelling and simulation. Implications for research comprise a further elaboration of the simulation studies within the energy field.
Obesity results from many influences including genetic and environmental. But eating and physical activity are the two fundamental factors which influence obesity development. This work investigates how food consumption choices and the extent of physical activity have an influence on weight, BMI and the prevalence of obesity in a population of children aged 2-15 years. Around forty years ago, the weight profile of the child (or adult) population was not particularly abnormal. But with increases in energy-dense food consumption and reductions in physical activity, weight, BMI and the prevalence of obesity has increased dramatically, especially since the 1990s. Results from our model can explain these trends. If no interventions are taken to counteract them then these markers will continue to increase in the future with consequent health effects as the children become adults. In an effort to uncover the most effective interventions, this study highlights the role that a system dynamics model can play to help manage the problem in childhood, particularly through considering behavioural changes. In anticipated developments of this research it is suggested that the Theory of Planned Behaviour could be used as a framework to identify the motivational factors that influence children in their eating and physical activity habits.
During a long time, studies on project management were focused on duality between temporary organization (the project) and permanent organization to explain the lack of learning form the project. If the literature review emphasizes learning process and knowledge production during life cycle of project, they both disappear once the project finishes because of a lack of knowledge management capitalization. However we think that the real causes of the success or failure of the projects find their roots elsewhere that in knowledges capitalization. From our point of view, the performance of the project could be explained starting from the concept of the organizational capacity of the project team. The organizational capacity is a collective skill. It authorizes to combine and go into action relevant resources, as teams project attitude (motivation) and teams project aptitude (innovation), organizational competences focused on good relationship at work, coordination, tasks integration, etc . In this way we have developed a dynamic model of projects performance based on organizational capacity. From this model and one of the main question results from this model is: Could organizational capacity improve the project path and behind the success or failure of the project?
The paper investigates the potential of urban transit buses to provide an early market for hydrogen proton exchange membrane fuel cells (PEM FCs) in road transport. System Dynamics has already been used to explore the transition towards the large scale use of hydrogen fuel cells in road transport as a whole. Given the importance of establishing early and niche markets first, on the route to mainstream markets, this paper focuses on one early market in road transport which is considered to be particularly important: urban transit buses. A System Dynamics model has been developed in order to address this particular market in detail. The model is currently still being refined; however results generated so far suggest that the market uptake of PEM FC buses will not be rapid and will require significant public support.
In this brief communication, we argue for more systematic and self-conscious attention, within the field of system dynamics, to the process of knowledge sharing for the purposes of model construction. After explaining our rationale, we provide a number of examples showing how various groups of people---often those with central roles in the problems being modeled---are marginalized, their voices mute or silent. We recognize the valuable work of a number of SD modelers, emphasizing their work in western, often corporate, worlds. However, there are special problems that emerge when important members of the would-be client population are comparatively powerless, under-educated or even illiterate, as is the case in many international natural resource contexts---contexts likely to become more important as attempts to cope with climate change increase. We then provide some practical suggestions for addressing such communication problems. We believe that SD can be of great value in the analysis of natural resource conflicts, climate change mitigation and adaptation, the development of improved management systems, and in policy formulation and evaluation. The anthropological perspective may provide insights that will allow for better integration of the views of marginalized peoples into SD models.
An earlier Conference paper used a small model to illustrate oscillations in local responses to health disparities. It was noted that further work would address medium term trends and thresholds shaping public action to eliminate health disparities. This paper begins to address those issues using Heckathorns model of The Dynamics and Dilemmas of Collective Action. Among many other things the model illustrates the implications of hypotheses related to the relative fitness of voluntary action, norms of reciprocity and selective incentives or sanctions. The hypotheses can be used to explore implications of the governance variable in the causal loop diagram adopted by the WHO Commission on Social Determinants of Health. The conclusion is that the model (a) provides a framework for analysing elite responses evident in decisions made and avoided by governance groups with duties to promote public health, and (b) has the theoretical depth necessary to be recognised as a canonical situation model as defined by David Lane.