Matching Items (4)
Description
Free/Libre Open Source Software (FLOSS) is the product of volunteers collaborating to build software in an open, public manner. The large number of FLOSS projects, combined with the data that is inherently archived with this online process, make studying this phenomenon attractive. Some FLOSS projects are very functional, well-known, and successful, such as Linux, the Apache Web Server, and Firefox. However, for every successful FLOSS project there are 100's of projects that are unsuccessful. These projects fail to attract sufficient interest from developers and users and become inactive or abandoned before useful functionality is achieved. The goal of this research is to better understand the open source development process and gain insight into why some FLOSS projects succeed while others fail. This dissertation presents an agent-based model of the FLOSS development process. The model is built around the concept that projects must manage to attract contributions from a limited pool of participants in order to progress. In the model developer and user agents select from a landscape of competing FLOSS projects based on perceived utility. Via the selections that are made and subsequent contributions, some projects are propelled to success while others remain stagnant and inactive. Findings from a diverse set of empirical studies of FLOSS projects are used to formulate the model, which is then calibrated on empirical data from multiple sources of public FLOSS data. The model is able to reproduce key characteristics observed in the FLOSS domain and is capable of making accurate predictions. The model is used to gain a better understanding of the FLOSS development process, including what it means for FLOSS projects to be successful and what conditions increase the probability of project success. It is shown that FLOSS is a producer-driven process, and project factors that are important for developers selecting projects are identified. In addition, it is shown that projects are sensitive to when core developers make contributions, and the exhibited bandwagon effects mean that some projects will be successful regardless of competing projects. Recommendations for improving software engineering in general based on the positive characteristics of FLOSS are also presented.
ContributorsRadtke, Nicholas Patrick (Author) / Collofello, James S. (Thesis advisor) / Janssen, Marco A (Thesis advisor) / Sarjoughian, Hessam S. (Committee member) / Sundaram, Hari (Committee member) / Arizona State University (Publisher)
Created2011
Description
Landscape restoration is a global priority as evidenced by the United Nations’ 2020 goal to restore 150 million hectares of land worldwide. Restoration is particularly needed in estuaries and their watersheds as society depends on these environments for numerous benefits. Estuary restoration is often undermined by social-ecological scale mismatch, the incongruence between governing units and the bio-physical resources they seek to govern. Despite growing recognition of this fact, few empirical studies focus on scale mismatches in environmental restoration work. Using a sub-basin of Puget Sound, Washington, U.S.A., I analyze scale mismatches in estuary restoration. I take a network science approach because governance networks can bridge scale mismatches. I combine quantitative social network analysis (SNA), geographic information systems (GIS), and qualitative interview analysis.
Spatial network analysis reveals several areas with weak scale mismatch bridging networks. These weak social networks are then compared to ecological restoration needs to identify coupled social-ecological restoration concerns. Subsequent study investigates jurisdictional and sectoral network integration because governance siloes contribute to scale mismatch. While the network is fairly well integrated, several sectors do not interact or interact very little. An analysis of collaboration reasons disentangles the idea of generic collaboration. Among three relationship types considered, mandated relationships contribute almost 5.5 times less to perceived collaboration productivity than shared interest relationships, highlighting the benefits of true collaborations in watershed governance. Lastly, the effects of scale mismatch on individual restoration projects and landscape level restoration planning are assessed through qualitative interview analysis. Results illustrate why human-environment processes should be included in landscape restoration planning. Social factors are not considered as constraints to restoration but rather part of the very landscape fabric to be restored. Scale mismatch is conceptualized as a complex social-ecological landscape pattern that affects the flow of financial, human, and natural capital across the landscape. This represents a new way of thinking about scale mismatch and landscape restoration in complex multi-level governance systems. In addition, the maps, network diagnostics, and narratives in this dissertation can help practitioners in Puget Sound and provide proofs of concepts that can be replicated elsewhere for restoration and broader conservation sciences.
Spatial network analysis reveals several areas with weak scale mismatch bridging networks. These weak social networks are then compared to ecological restoration needs to identify coupled social-ecological restoration concerns. Subsequent study investigates jurisdictional and sectoral network integration because governance siloes contribute to scale mismatch. While the network is fairly well integrated, several sectors do not interact or interact very little. An analysis of collaboration reasons disentangles the idea of generic collaboration. Among three relationship types considered, mandated relationships contribute almost 5.5 times less to perceived collaboration productivity than shared interest relationships, highlighting the benefits of true collaborations in watershed governance. Lastly, the effects of scale mismatch on individual restoration projects and landscape level restoration planning are assessed through qualitative interview analysis. Results illustrate why human-environment processes should be included in landscape restoration planning. Social factors are not considered as constraints to restoration but rather part of the very landscape fabric to be restored. Scale mismatch is conceptualized as a complex social-ecological landscape pattern that affects the flow of financial, human, and natural capital across the landscape. This represents a new way of thinking about scale mismatch and landscape restoration in complex multi-level governance systems. In addition, the maps, network diagnostics, and narratives in this dissertation can help practitioners in Puget Sound and provide proofs of concepts that can be replicated elsewhere for restoration and broader conservation sciences.
ContributorsSayles, Jesse Saemann (Author) / Turner II, B L (Thesis advisor) / Childers, Daniel L. (Committee member) / Janssen, Marco A (Committee member) / Arizona State University (Publisher)
Created2015
Description
Foraging strategies in social animals are often shaped by change in an organism's natural surrounding. Foraging behavior can hence be highly plastic, time, and condition dependent. The motivation of my research is to explore the effects of dispersal behavior in predators or parasites on population dynamics in heterogeneous environments by developing varied models in different contexts through closely working with ecologists. My models include Ordinary Differential Equation (ODE)-type meta population models and Delay Differential Equation (DDE) models with validation through data. I applied dynamical theory and bifurcation theory with carefully designed numerical simulations to have a better understanding on the profitability and cost of an adaptive dispersal in organisms. My work on the prey-predator models provide important insights on how different dispersal strategies may have different impacts on the spatial patterns and also shows that the change of dispersal strategy in organisms may have stabilizing or destabilizing effects leading to extinction or coexistence of species. I also develop models for honeybee population dynamics and its interaction with the parasitic Varroa mite. At first, I investigate the effect of dispersal on honeybee colonies under infestation by the Varroa mites. I then provide another single patch model by considering a stage structure time delay system from brood to adult honeybee. Through a close collaboration with a biologist, a honeybee and mite population data was first used to validate my model and I estimated certain unknown parameters by utilizing least square Monte Carlo method. My analytical, bifurcations, sensitivity analysis, and numerical studies first reveal the dynamical outcomes of migration. In addition, the results point us in the direction of the most sensitive life history parameters affecting the population size of a colony. These results provide novel insights on the effects of foraging and Varroa mites on colony survival.
ContributorsMessan, Komi Segno (Author) / Kang, Yun (Thesis advisor) / Castillo-Chavez, Carlos (Thesis advisor) / Degrandi-Hoffman, Gloria D (Committee member) / Janssen, Marco A (Committee member) / Arizona State University (Publisher)
Created2017
Description
This work is an assemblage of three applied projects that address the institutional and spatial constraints to managing threatened and endangered (T & E) terrestrial species. The first project looks at the role of the Endangered Species Act (ESA) in protecting wildlife and whether banning non–conservation activities on multi-use federal lands is socially optimal. A bioeconomic model is used to identify scenarios where ESA–imposed regulations emerge as optimal strategies and to facilitate discussion on feasible long–term strategies in light of the ongoing public land–use debate. Results suggest that banning harmful activities is a preferred strategy when valued species are in decline or exposed to poor habitat quality. However such a strategy cannot be sustained in perpetuity, a switch to land–use practices characteristic of habitat conservation plans is recommended. The spatial portion of this study is motivated by the need for a more systematic quantification and assessment of landscape structure ahead of species reintroduction; this portion is further broken up into two parts. The first explores how connectivity between habitat patches promotes coexistence among multiple interacting species. An agent–based model of a two–patch metapopulation is developed with local predator–prey dynamics and density–dependent dispersal. The simulation experiment suggests that connectivity levels at both extremes, representing very little risk and high risk of species mortality, do not augment the likelihood of coexistence while intermediate levels do. Furthermore, the probability of coexistence increases and spans a wide range of connectivity levels when individual dispersal is less probabilistic and more dependent on population feedback. Second, a novel approach to quantifying network structure is developed using the statistical method of moments. This measurement framework is then used to index habitat networks and assess their capacity to drive three main ecological processes: dispersal, survival, and coexistence. Results indicate that the moments approach outperforms single summary metrics and accounts for a majority of the variation in process outcomes. The hierarchical measurement scheme is helpful for indicating when additional structural information is needed to determine ecological function. However, the qualitative trend between network indicator and function is, at times, unintuitive and unstable in certain areas of the metric space.
ContributorsSalau, Kehinde Rilwan, 1985- (Author) / Janssen, Marco A (Thesis advisor) / Fenichel, Eli P (Thesis advisor) / Anderies, John M (Committee member) / Abbott, Joshua K (Committee member) / Arizona State University (Publisher)
Created2013