Designing a reasonable M/G/1 retrial queue system that enhances service efficiency and reduces energy consumption is a challenging issue in Information and Communication Technology systems. This paper presents an M/G/1 retrial queue system incorporating random working vacation (RWV) and improved service efficiency during vacation (ISEV) policies, and examines its optimal queuing strategies. The RWV policy suggests that the server takes random working vacations during reserved idle periods, effectively reducing energy consumption. In contrast, the ISEV policy strives to augment service efficiency during regular working periods by updating, inspecting or maintaining the server on vacations. The system is transformed into a Cauchy problem to investigate its well-posedness and stability, employing operator semigroup theory. Based on the system’s stability, steady-state performance measures, such as service efficiency, energy consumption and expected costs, are quantified using the steady-state solution. The paper subsequently demonstrates the existence of optimal queuing strategies that achieve maximum efficiency and minimum expected costs. Finally, two numerical experiments are provided to illustrate the effectiveness of the system.

We investigate the reengineeering of interbank networks with a specific focus on capital increase. We consider a scenario where all other components of the network’s infrastructure remain stable (a practical assumption for short-term situations). Our objective is to assess the impact of raising capital on the network’s robustness and to address the following key aspects. First, given a predefined target for network robustness, our aim is to achieve this goal optimally, minimizing the required capital increase. Second, in cases where a total capital increase has been determined, the central challenge lies in distributing this increase among the banks in a manner that maximizes the stability of the network. To tackle these challenges, we begin by developing a comprehensive theoretical framework. Subsequently, we formulate an optimization model for the network’s redesign. Finally, we apply this framework to practical examples, highlighting its applicability in real-world scenarios.

To pursue business innovation with PSS, many different PSS concepts are designed and evaluated. Various business models of a PSS design concept are devised and evaluated as well. Evaluation of the economic sustainability of PSS business models is critical. This paper presents a systematic method to evaluate the economic sustainability of PSS business models using a system dynamics modelling template. System dynamics modelling task is challenging for practitioners due to the variety of variables comprising business model strategies and their complex interrelationships. To enable the modelling task, a system dynamics modelling template composed of six modules of customer acquisition, channel acquisition, profit creation, resource acquisition, PSS provision, and partnership pattern has been devised. The PSS business model evaluation method has been illustrated using a smart study experience management service system design case to demonstrate the proposed system dynamics modelling template can reflect the case-specific business model which consists of the particular business model strategies.

This paper examines ex-ante impacts of two policy interventions that improve productivity of local-breed cows through artificial insemination (AI) and producers’ access to distant markets through a dairy market hub. The majority of cattle in Kilosa district in Tanzania are local low productivity breeds kept by smallholders and agro-pastoralists. Milk production is seasonal, which constrains producers’ access to distant urban markets, constrains producers’ incomes and restricts profitability in dairy processing. We developed and evaluated an integrated system dynamics (SD) simulation model that captures many relevant feedbacks between the biological dynamics of dairy cattle production, the economics of milk market access, and the impacts of rainfall as an environmental factor. Our analysis indicated that in the short (1 year) and medium (5-year) term, policy interventions have a negative effect on producers’ income due to high AI costs. However, in the long term (5+ years), producers’ income from dairy cattle activities markedly increases (by, on average, 7% per year). The results show the potential for upgrading the smallholder dairy value chain in Kilosa, but achievement of this result may require financial support to producers in the initial stages (first 5 years) of the interventions, particularly to offset AI costs, as well as additional consideration of post-farm value chain costs. Furthermore, institutional aspects of dairy market hub have substantial effects on trade-offs amongst performance measures (e.g. higher profit vs. milk consumption at producer's household) with gain in cumulative profit coming at the expense of a proportional and substantial reduction in home milk consumption.

Like many other oceanic islands around the globe, environmental conditions, social circumstances and forces of globalization combine to challenge the sustainability of the Galapagos Archipelago of Ecuador. This paper describes a food-supply system in Galapagos that is mainly controlled by population growth, weak local agriculture, imports from mainland Ecuador and the influence of a growing tourism industry. We use system dynamics (SD) as a modeling technique in this paper to identify the main driving forces operating on the Galapagos food system to create a series of future scenarios and to examine the subsequent implications across the supply system structures. We model the supply side of the food system using secondary data collected from governmental and non-governmental sources. We find that the consumption profile of the local inhabitants of the Galapagos is on average higher than consumption in the Ecuadorian mainland. This fact, plus rapid growth of the local population fueled by the tourism industry, has created a decrease in per capita local food production and an increase on food import dependence that now, challenges the sustainability of the archipelago. Imports are the largest source of food in the archipelago. Approximately 75% of the agricultural food supply was transported from the mainland in 2017. Our model projects that this fraction will increase to 95% by 2037 with no changes in food policy. Moreover, any plan to increase tourism arrivals must be accompanied by a plan to address the subsistence needs of the new population that the tourism industry attracts. Policies to promote local agricultural growth should be central to the development strategy implemented in the Galapagos.

In a globalized and hegemonically organized international economy, the economic fundamentals and policy choices of the hegemon often have spillover effects for peripheral economies. This is a well-recognized dynamic of the contemporary political economy, but it was true during the first age of globalization as well. Motivated by literature examining the impact of the U.S. macroeconomic conditions on other economies throughout the international system, this article advances a systemic theory of financial crisis and applies it to the long nineteenth century, when British hegemony reigned. My main motivation is the earliest example of a systemic theory of financial crisis, Charles Kindleberger's Hegemonic Stability Theory. However, while Charles Kindleberger focused on the stability brought about by a hegemonically structured international economy, I emphasize the dynamics of volatility present in this type of system. I argue that a hierarchical distribution of economic activity in the international system means that the financial cycle of the most central country influences the financial conditions in peripheral countries that lead to financial crisis. Evidence from financial crises which occurred in the long nineteenth century supports this theory.

System dynamics models are typically used to simulate the behaviour of the problem system under discussion environment, to help understand and solve complex problems. Group model building is a social process for including client groups in the system dynamics modelling process. Recent evidence suggests group model building is useful in supporting durable group decisions by supporting the mental models of participants to become more aligned. There have been several mechanisms proposed to explain these effects. This paper creates a combined model that links the five best-supported mechanisms. The combined model suggests five core conditions of group model building that contributes to its success: completing a structured task, producing a tangible artefact, representing system complexity, the portrayal of causal links, and easy modification or transformation of the artefact by participants. Practitioners are encouraged to use group decision approaches that integrate these conditions.

Background: With rapid aging, Singapore faces an increasing proportion of the population with age-related dementia. We used system dynamics methodology to estimate the number and proportion of people with mild, moderate, and severe dementia in future years and to examine the impact of changing family composition on their likely living arrangements.

Methods: A system dynamics model was constructed to estimate resident population, drawing birth and mortality rates from census data. We simulate future mild, moderate, and severe dementia prevalence matched with estimates of total dementia prevalence for the Asian region that includes Singapore. Then, integrating a submodel in which family size trends were projected based on fertility rates with tendencies for dependent elderly adults with dementia to live with family members, we estimate likely living arrangements of the future population of individuals with dementia.

Results: Though lower than other previous estimates, our simulation results indicate an increase in the number and proportion of people in Singapore with severe dementia. This and the concurrent decrease in family size point to an increasing number of individuals with dementia unlikely to live at home.

Conclusions: The momenta of demographic and illness trends portend a higher number of individuals with dementia less likely to be cared for at home by family members. Traditions of care for frail elderly found in the diverse cultures of Singapore will be increasingly difficult to sustain, and care options that accommodate these demographic shifts are urgently needed.

Even with the rapid changes in the level of complexity and the uncertainty of the environment in which Belgian sea fisheries operate, fisheries management in Belgium is still mainly based on restrictive policy instruments founded in the biological approach of fisheries management science. Since they will continue to play an important role, this paper evaluated changes in three restrictive policy instruments and their effect on future fleet performance and dynamics, i.e. maximum fishing days, total quota-restrictions and licences. These effects are tested through scenarios in a microeconomic simulation model, including sensitivity analysis. This study opts for a dynamic simulation model based on a microeconomic approach of fleet dynamics using system dynamics as a modelling technique (operational base: Vensim®DSS). The results indicated that changes in maximum fishing days and total quota resulted in higher fluctuations in fleet performance and dynamics compared to changes in licences. Furthermore, changes in maximum fishing days and total quota had a direct impact on fleet performance, though not always as expected, whereas licences only affected fleet performance indirectly since they only limit the entry of new vessels to the fleet and they can block the growth of successful sub fleets. The outcomes of this study are translated into practical recommendations for improving fisheries management. Firstly, policy makers need to be more aware of misperceptions of feedback. Secondly, the results proved that altering only one type of restrictive policy instrument at a time often fails to meet desired outcomes. Therefore, policy makers need to find a balance in combining policy instruments. Finally, this paper opens the discussion on the future value of restrictive policy instruments in the rapidly changing, complex and uncertain fisheries environment. It suggests rethinking their use from “preserving a status quo and social peace” toward a driving factor in “stimulating fleet dynamics”.