Though the size of System Dynamics models should be compact focusing on the main feedback loops determining system behavior one kind of model can become quite large: multi-national, multi-sectoral spatially differentiated models. The paper briefly presents such a model called ASTRA (=Assessment of Transport Strategies), which is developed in several versions over the past eight years. The purpo...

This paper describes one of the latest in a series of system dynamics models developed during the FEAST (Feedback, Evolution And Software Technology) investigation into software evolution processes. The intention of early models was to simulate real-world processes in order to increase understanding of such processes. The work resulted in a number of lessons learnt, in particular, with regard t...

This paper deals with the theory of codimension one bifurcations applied to a dynamical system derivedfrom applying Pontryagin 's maximum principIe to an optimal control problem for economic fisheries management. Changes in the number and/or the stability of stationary states as well as the appearance of closed orbits, are analyzed. Some necessCl.'Y and/or sufficient conditions are established ...

Reform of drug procurement is being extensively implemented and expanded in China, especially in today's big data environment. However, the pattern of supply mode innovation lags behind procurement improvement. Problems in financial strain and supply break frequently occur, which affect the stability of drug supply. Drug Pooling System is proposed and applied in a few pilot cities to resolve th...

System dynamics models provide a detailed mathematical description of the complex interactions between numerous variables. Software packages, such as iThink and Vensim, allow policy makers to easily adapt, implement and explore these models. By testing various scenarios through an analysis of the model with different parameter values it is possible to investigate and visualise the long-term eff...

in this decade, due to the current competitive environment,reputation of industrial brands is markedly dependent upon theperformance of their supply chain. therefore, it is necessary to examinethe factors affecting their supply chain so as to increase the competitivenessof their chain. productivity is among the most important factorsin the advancement of industry and its evaluation requires the...

We propose a method for incorporating multiple linguistic variables into a system dynamics framework. A simple example is used to illustrate the procedures necessary to define linguistic variables using triangular membership functions within the VENSIM Simulation Environment. We illustrate the operations of linguistic variables through a sales and service model where two linguistic variables i....