Browsing by Subject "Modularity"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Epidemic dynamics in heterogeneous populations(2012-08) Hladish, Thomas Joseph; Meyers, Lauren Ancel; Wilke, Claus O.; Bull, James J.; Keitt, Timothy H.; Sawyer, Sara L.Epidemiological models traditionally make the assumption that populations are homogeneous. By relaxing that assumption, models often become more complicated, but better representations of the real world. Here we describe new computational tools for studying heterogeneous populations, and we examine consequences of two particular types of heterogeneity: that people are not all equally likely to interact, and that people are not all equally likely to become infected if exposed to a pathogen. Contact network epidemiology provides a robust and flexible paradigm for thinking about heterogeneous populations. Despite extensive mathematical and algorithmic methods, however, we lack a programming framework for working with epidemiological contact networks and for the simulation of disease transmission through such networks. We present EpiFire, a C++ applications programming interface and graphical user interface, which includes a fast and efficient library for generating, analyzing and manipulating networks. EpiFire also provides a variety of traditional and network-based epidemic simulations. Heterogeneous population structure may cause multi-wave epidemics, but urban populations are generally assumed to be too well mixed to have such structure. Multi-wave epidemics are not predicted by simple models, and are particularly problematic for public health officials deploying limited resources. Using a unique empirical interaction network for 103,000 people in Montreal, Canada, we show that large, urban populations may feature sufficient community structure to drive multi-wave dynamics, and that highly connected individuals may play an important role in whether communities are synchronized. Finally, we show that heterogeneous immunity is an important determinant of influenza epidemic size. While many epidemic models assume a homogeneously susceptible population and describe dynamics for one season, the trans-seasonal dynamics of partially immunizing diseases likely play a critical role in determining both future epidemic size and pathogen evolution. We present a multi-season network model of a population exposed to a pathogen conferring partial cross-immunity that decays over time. We fit the model to 25 years of influenza-like illness epidemic data from France using a novel Bayesian technique. Using conservative priors, we estimate important epidemiological quantities that are consistent with empirical studies.Item Implications of complex connectivity patterns, disturbance, Allee effects, and fisheries in the dynamics of marine metapopulations(2014-05) Peña-Baca, Tania Sarith; Keitt, Timothy H.; Gonzalez-Guzman, Laura ImeldaNearshore populations have been depleted and some have not yet recovered. Therefore, theoretical studies focus on improving fisheries management and designing marine protected areas (MPAs). Depleted populations may be undergoing an Allee effect, i.e. a decrease in fitness at low densities. Here, I constructed a marine metapopulation model that included pre- and post-dispersal Allee effects using a network theory approach. Networks represent metapopulations as groups of nodes connected by dispersal paths. With this model I answered four questions: What is the role of Allee effects on habitat occupancy? Are MPAs effective in recovering exploited populations? What is the importance of larval dispersal patterns in preventing local extinctions due to exploitation and Allee effects? Can exploitation fragment nearshore metapopulations? When weak Allee effects are included, habitat occupancy drops as larval retention decreases because more larvae are lost to unsuitable habitat. With strong Allee effects habitat occupancy also drops at high larval retention because more larvae are needed to overcome the Allee effect. Post-dispersal Allee effects seem more detrimental for nearshore metapopulations. MPA effectiveness seems also lower in a post-dispersal Allee effect scenario. In overexploited systems, local populations that go extinct are also less likely to recover even after protecting the whole coastline. In exploited nearshore metapopulations with Allee effects, local occupancy or the recovery of local populations depends not only on larval inflow from neighbor populations, but also on larval inflow for these neighbors. Nearshore metapopulations with intense fishing mortality and Allee effects may also suffer a decrease in dispersal strength and fragmentation. Population fragmentation occurs when large populations are split into smaller groups. A tool for detecting partitioning in a network is modularity. The modularity analysis performed for red abalone in the Southern California Bight showed that exploitation increases partitioning through time before the entire metapopulation collapses. These findings call for research effort in estimating the strength of potential Allee effects to prevent stock collapse and assess MPA effectiveness, evaluating the predictability of local occupancy by centrality metrics to help identify important sites for conservation, and using modularity analysis to quantify the health of exploited metapopulations to prevent their collapse.Item A modular language for describing actions(2009-12) Ren, Wanwan; Lifschitz, Vladimir; Boyer, Robert; Gelfond, Michael; Novak, Gordon; Porter, BruceThis dissertation is about the design of a modular language for describing actions. The modular action description language, MAD, is based on the action language C+. In this new language, the possibility of "importing" a module allows us to describe actions by referring to descriptions of related actions introduced earlier, rather than by listing all effects and preconditions of every action explicitly. The use of modular action descriptions eliminates the need to reinvent theories of similar domains over and over again. Another advantage of this representation style is that it is similar to the way humans describe actions in terms of other actions. We first define the syntax of a fragment of MAD, called mini-MAD, and then extend it to the full version of MAD. The semantics of mini-MAD is defined by grounding action descriptions and translating them into C+. However, for the full version of MAD, it would be difficult to define grounding. Instead, we use a new approach to the semantics of variables in action descriptions, which is based on more complex logical machinery---first-order causal logic. Grounding is important as an implementation method, but we argue that it should be best avoided in the definition of the semantics of expressive action languages. We show that, in application to mini-MAD, the two semantics are equivalent. Furthermore, we prove that MAD action descriptions have some desirable, intuitively expected mathematical properties. We hope that MAD will make it possible to create a useful general-purpose library of standard action descriptions and will contribute in this way to solving the problem of generality in Artificial Intelligence.Item Modular microcontroller design(Texas Tech University, 1999-05) Abraham, Bobby K.Integrated Circuits (IC) have developed from its earliest forms of MSI, LSI level circuits to VLSI (Very Large- Scale Integration) and ULSI (Ultra Large- Scale Integration) circuits. Along with the rapid advancement in processing technology which made this possible, the complexity in design and design concerns increased. More time is consumed in designing a IC than producing it. As a result, the cost of design is a major concern. To minimize the effects of cost and time in producing an IC, the industry started adopting a "Design Reuse" concept. This is facilitated by modular design approach where the same design is reused for a new product. The whole digital system is realized in form of modules. Individual modules can also be expanded to higher bit configurations by cascading it with other modules of the same kind. IC industries use in-house designed modules for its products. These modules are not available due to proprietary and commercial reasons. This thesis presents a comprehensive insight into modular design approach and applies this approach towards implementing a microcontroller. A fully functional microprogrammable control unit is designed and simulated which could be later used as building block (module) for further designs.Item Questioning modern approaches to flexibility : 50 years of learning from the School Construction Systems Development (SCSD) project(2016-05) Lee, Joshua David; Moore, Steven A., 1945-; Cleary, Richard; Dangel, Ulrich; Holleran, Michael; Hunt, Bruce; Liedl, PetraThe culture of design has struggled with how to address modernity’s quickening rates and forms of change. Between the dialectical dispositions of Parmenidean permanence and Heraclitean impermanence, a wide array of hybrid approaches emerged during the 20th century under the polysemic banner of flexibility. This dissertation questions flexibility as a design approach towards sustainability by providing a longitudinal analysis of a particularly robust mid-century modern experiment called the School Construction Systems Development (SCSD) project. In 1961 an influential group of philanthropists, architects, government officials, industry representatives, and school superintendents met to address various challenges facing schools at the time. They decided that an open, prefabricated, and integrated system of building components was needed that could afford four modes of flexibility—spatial variety, immediate change, long-range changeability, and expansion. The SCSD project was launched with sufficient financial backing from the Ford Foundation when a consortium of California school districts agreed to use the system on their anticipated projects and signed a joint powers agreement that guaranteed enough business to entice industry to develop components in accordance with the first performance specification to be used in the American building industry. The building system that resulted from this collaborative effort was adapted to the unique needs of thirteen unique schools, which have all been altered significantly over time. This dissertation builds upon and questions the findings of earlier studies of the SCSD through an in-depth, mixed methods examination of four representative projects. Archival research, personal observations, re-photography, re-surveying, plan evaluations, interviews, and a manufacturers’ advertisement analysis are triangulated and synthesized using the tools of grounded theory and actor-network theory. The results document the transformation of the intentions and receptions of the SCSD by various relevant social groups over 50 years. These new findings provide a great deal of useful insight for architects, educators, product designers, historic preservationists, and others about the affordances of spatial flexibility as a strategy for sustainability, the difficulties associated with technological transfer, the impact of unstable market conditions, the importance of user input during the planning process, and the need for long-term social relations to sustain sociotechnical innovations.