Tuna ranching is a value-added economic activity along the coast of Baja California in Mexico involving the live capture and transport of migrating juvenile bluefin tuna to pens located near shore, where they are fed for a period of months then harvested and shipped fresh for the high-end sushi market, which is centered in Japan but expanding elsewhere. Ranching is nested within the entire global tuna fishing and processing business. Little is known outside the industry about the functioning of Mexican tuna ranching, which differs in important ways compared to its Australian and Mediterranean counterparts, and does not involve the harvest of reproducing age animals. Our analysis and exploratory modeling exercise identify several factors and issues that merit closer examination. A feedback perspective can shed light on whether Mexican ranching activities have the potential to become sustainable.
This paper describes a recent activity where scholars from two disciplines met to consider possible systemic causes of repeating failure during a three-decade long IT modernization project in the US government. From the system dynamics perspective, the problem appears to be related to a dynamic and repeating management failure with an embedded project management model. We decided to use a simple project model to develop this perspective. Our initial attempt shows some of the anticipated dynamics of project escalation. More important, though, was the discussion of the problem itself that was launched by the use of a formal model. We believe that this approach has provided insight into how to approach a more focused and grounded analysis of the problem domain.
We argue that it is possible to explain much of the history of the worlds shipping markets since 1950 as the interaction of two balancing feedback loops: a capacity adjustment loop which creates a 20-year wave, and a capacity utilization adjustment loop which generates a 4-year cycle. We show how this insight has been used rather successfully since the early 1980s for practical forecasting of turning points in the shipping market 1 - 4 years ahead of time. The basic mechanisms in the shipping system create a strong deterministic backbone which is visible through the exogenous noise, and hence predictable with useful precision. Our experience leads to a number of questions concerning system dynamics best practice, for future research.
The paper argues that current world developments are starting to resemble the "pollution crisis" scenario in The Limits to Growth book from 1972. Ongoing global warming increasingly demonstrate the reality of two major structural assumptions in the Limits to Growth models: namely 1) long reaction delays from pollution levels to corrective action, and 2) self-reinforcing feedback from the pollution level to pollution absorption time, and back to the pollution level. If left unchecked, these mechanisms could generate a climate crisis in the 21st century. The paper seeks to highlight the strength in high level system dynamics conceptualization.
System Dynamics provides a suitable framework for modeling diseases that can bring together biological, epidemiological, clinical, and public health issues in a manageable way. In this paper, we discuss models for the development and transmission of parasite-borne diseases which involve a primary host (e.g. a human), a vector(e.g. a mosquito), and a parasite . The models discussed here are being applied to different diseases; this paper will refer primarily to results for filaria. We first examine models for the biology of the disease in a vector and in a host, and for disease transmission between two humans through a vector. We then discuss a model for disease transmission in a population of vectors interacting with a population of hosts. We examine the effect of different control strategies, including preventive measures as well as treatment, and also possible effects of changes in the environment. We point out some of the complexities inherent in the biological processes, and the variability resulting from change in the values of the parameters in the system.
Please see the "Paper" file for the speech given at the conference announcing the award winners. The 2007 winner of the Dana Meadows Student Award for the best student paper presented at the annual conference is: David Wheat, System Dynamics Group, University of Bergen (Norway). His paper is entitled " The Feedback Method of Teaching Macroeconomics: Is it Effective?" 2007 Honorable Mentions (all equally ranked): H. Willem Geert Phaff, Delft University of Technology "Visualising the Effects of Non-linearity by Creating Dynamic Causal Diagrams" and Firat Incioglu, Bogaziçi University, Instanbul "A Dynamic Simulation Model for Long-Term Hypertension Progression."
Several case studies have documented myopic allocation of organizational resources among capabilities that payoff in short vs. long-term. We capture a general class of organizational resource allocation problems in a simple model that exhibits the typical worse-before-better dynamics commonly believed to be responsible for persistence of myopic policies. Next we examine the endogeneity of resources and the impact of competitive pressures on the efficiency of allocation policies. Endogenous resources and competition are both shown to significantly shift the optimal allocation towards myopic policies. Short-term policies become beneficial as they strengthen the positive loop between performance, resources, and capabilities. In fact strategic selection of allocation policy in a competitive market can force the firms to allocate all the resources to the short-term capability. These results provide an alternative explanation for the persistence of myopic organizational decision-rules that does not rest on psychological and learning arguments.
The objective of this paper is to examine the concepts of holism and reductionism as they relate to System Dynamics (SD) and to a lesser extent Systems Thinking (ST) then to relate the findings of that examination to some of the disillusionment with SD and the resultant lack of commercial take up. This paper looks at the concepts of Reductionism and Holism as applied throughout the literature in a broad range of academic areas from medicine and philosophy to physics and looks at different definitions of holism, and reductionism. Practical applications of Reductionist and Holistic principles are examined. From this analysis the fundamental nature of SD as a Holistic/Reductionist methodology is deduced and differentiated from the more generally holistic nature of ST. From this basis the conclusion that SD is a reductionist methodology in practice, though not necessarily described as such by practitioners, is postulated. The paper recommends that there be further work carried out in the field of theoretical and practical holism and greater awareness of these issues within the practitioner community. Within the conclusions there is a pointer for some further fundamental areas of work.
In a 2006 paper in the Journal of Economic Issues, Professor Gregory Hayden argued that system dynamics is an inadequate tool for explaining the institutional systems principles of hierarchy, feedback and openness. The purpose of this paper is to show that Professor Haydens claims are, for the most part, misguided and, in some instances, patently incorrect. Moreover, we will reinforce the view that combining system dynamics with institutional economics can be a very powerful approach to heterodox economic analysis
The emergence of vulnerability black markets enhances the opportunities for malicious actors to launch exploits toward computer networks, to commit cyber-crime and to perform other unlawful activities. Asymmetric information, inadequate software testing, lack of incentive to improve quality of the software are presumed to be the most important grounds of the software vulnerability problems. This work is a preliminary model to build a structure that may explain the factors influencing the emergence of vulnerability black market and to simulate undesired consequences from desired effect to eliminate software vulnerabilities. The purpose of the research is to provide better understanding for information security community about the dynamic features of the software vulnerability and the vulnerability black market problems.