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ABSTRACT: A current debate in ecology centers on the extent to which ecosystem function depends on biodiversity. Here, we provide evidence from a long-term field manipulation of plant diversity that soil microbial communities, and the key ecosystem processes that they mediate, are significantly altered by plant species richness. After seven years of plant growth, we determined the composition and function of soil microbial communities beneath experimental plant diversity treatments containing 1–16 species. Microbial community bio-mass, respiration, and fungal abundance significantly increased with greater plant diversity, as did N mineralization rates. However, changes in microbial community biomass, activity, and composition largely resulted from the higher levels of plant production associated with greater diversity, rather than from plant diversity per se. Nonetheless, greater plant pro-duction could not explain more rapid N mineralization, indicating that plant diversity affected this microbial process, which controls rates of ecosystem N cycling. Greater N availability probably contributed to the positive relationship between plant diversity and productivity in the N-limited soils of our experiment, suggesting that plant–microbe in-teractions in soil are an integral component of plant diversity's influence on ecosystem function.
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ABSTRACT: The building sector accounts for nearly 41% of U.S. primary energy use. Various tools have been developed for estimating the embodied energy during the design and construction phase of a building. However, there is a lack of a comprehensive mechanism which can measure and control the energy flow occurring during the operation phase of a building. Loss of efficiency of building systems and deterioration of various building components can collectively reduce the performance of a building, which eventually results in more energy flow into a building in the form of more maintenance and replacement requirements, as well as, increased operational energy demand. This research analyses a building's deterioration mechanism and presents a system dynamics simulation based “Life Cycle Energy Framework” that couples material performance and energy simulation to arrive at an optimal maintenance and replacement cycle for major materials over the entire operation period of a building. The case study results indicate that the proposed framework can help various building stakeholders in understanding and limiting the energy usage of the building from the design phase until the end of life phase.
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ABSTRACT: Unexpected disruptive events in manufacturing systems always interrupt normal production conditions and cause production loss. A resilient system should be designed with the capability to suffer minimum production loss during disruptions, and settle itself to the steady state quickly after each disruption. In this paper, we define production loss (PL), throughput settling time (TST), and total underproduction time (TUT) as three metrics to measure system resilience, and use these measures to assist the design of multi-stage reconfigurable manufacturing systems. Numerical case studies are conducted to investigate how the system resilience is affected by different design factors, including system configuration, level of redundancy or flexibility, and buffer capacities.
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