4,293 research outputs found

    Chapter 5: Corporations

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    Forecasting hypoxia in the Chesapeake Bay and Gulf of Mexico: model accuracy, precision, and sensitivity to ecosystem change

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    Increasing use of ecological models for management and policy requires robust evaluation of model precision, accuracy, and sensitivity to ecosystem change. We conducted such an evaluation of hypoxia models for the northern Gulf of Mexico and Chesapeake Bay using hindcasts of historical data, comparing several approaches to model calibration. For both systems we find that model sensitivity and precision can be optimized and model accuracy maintained within reasonable bounds by calibrating the model to relatively short, recent 3 year datasets. Model accuracy was higher for Chesapeake Bay than for the Gulf of Mexico, potentially indicating the greater importance of unmodeled processes in the latter system. Retrospective analyses demonstrate both directional and variable changes in sensitivity of hypoxia to nutrient loads.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90830/1/1748-9326_6_1_015001.pd

    Exploring estuarine eutrophication sensitivity to nutrient loading

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109763/1/lno20135820569.pd

    Atlas of Anchorage Community Indicators

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    The Anchorage Community Indicators (ACI) project is designed to make information (extracted from data) accessible so that conversations about the health and well-being of Anchorage may become more completely informed. Policy makers, social commentators, service delivery systems, and scholars often stake out positions based on anecdotal evidence or hunches when, in many instances, solid, empirical evidence could be compiled to support or challenge these opinions.The Atlas of Anchorage Community Indicators makes empirical information about neighborhoods widely accessible to many different audiences. The initial selection of indicators for presentation in the Atlas was inspired by Peter Blau and his interest in measures of heterogeneity (diversity) and inequality and by the work of the Project on Human Development in Chicago Neighborhoods. In both cases the measures they developed were well-conceptualized and validated. The Atlas presents community indicators at the census block group level derived from data captured in the 2000 U.S. Census and the 2005 Anchorage Community Survey. All maps in the Atlas are overlaid by Community Council boundaries to facilitate comparisons across maps.Introduction / COMMUNITY COUNCIL BOUNDARY MAPS / Eagle River Community Councils / North Anchorage Community Councils / South Anchorage Community Councils / Girdwood Community Councils / CENSUS-DERIVES INDICATORS AT BLOCK GROUP LEVEL / 1. Concentrated Affluence / 2. Concentrated Disadvantage / 3. Housing Density / 4. Immigrant Concentration / 5. Index of Concentration at Extremes / 6. Industrial Heterogeneity / 7. Multiform Disadvantage / 8. Occupational Heterogeneity / 9. Population Density / 10. Racial Heterogeneity / 11. Ratio of Adults to Children / 12. Residential Stability / 13. Income Inequality // APPENDIX: ACI Technical Report: Initial Measures Derived from Censu

    The International Space Station Supports International Polar Year (IPY)

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    Every day, ISS astronauts photograph designated sites and dynamic events on the Earth's surface using digital cameras equipped with a variety of lenses. Depending on observation parameters, astronauts can collect high resolution (4-6 m pixel size) or synoptic views (lower resolution but covering very large areas) digital data in 3 (red-green-blue) color bands. ISS crews have daily opportunities to document a variety of high-latitude phenomena. Although lighting conditions, ground track and other viewing parameters change with orbital precessions and season, the 51.6o orbital inclination and 400 km altitude of the ISS provide the crew an unique vantage point for collecting image-based data of polar phenomena, including surface observations to roughly 65o latitude, and upper atmospheric observations that reach nearly to the poles. During the 2007-2009 timeframe of the IPY, polar observations will become a scientific focus for the CEO experiment; the experiment is designated ISS-IPY. We solicit requests from scientists for observations from the ISS that are coordinated with or complement ground-based polar studies. The CEO imagery website for ISS-IPY provides an on-line form that allows IPY investigators to interact with CEO scientists and define their imagery requests. This information is integrated into daily communications with the ISS astronauts about their Earth Observations targets. All data collected are cataloged and posted on the website for downloading and assimilation into IPY projects. Examples of imagery and detailed information about scientific observations from the ISS can also be downloaded from the ISS-IPY web site

    Stroke saturation on a MEMS deformable mirror for woofer-tweeter adaptive optics

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    High-contrast imaging of extrasolar planet candidates around a main-sequence star has recently been realized from the ground using current adaptive optics (AO) systems. Advancing such observations will be a task for the Gemini Planet Imager, an upcoming "extreme" AO instrument. High-order "tweeter" and low-order "woofer" deformable mirrors (DMs) will supply a >90%-Strehl correction, a specialized coronagraph will suppress the stellar flux, and any planets can then be imaged in the "dark hole" region. Residual wavefront error scatters light into the DM-controlled dark hole, making planets difficult to image above the noise. It is crucial in this regard that the high-density tweeter, a micro-electrical mechanical systems (MEMS) DM, have sufficient stroke to deform to the shapes required by atmospheric turbulence. Laboratory experiments were conducted to determine the rate and circumstance of saturation, i.e. stroke insufficiency. A 1024-actuator 1.5-um-stroke MEMS device was empirically tested with software Kolmogorov-turbulence screens of r_0=10-15cm. The MEMS when solitary suffered saturation ~4% of the time. Simulating a woofer DM with ~5-10 actuators across a 5-m primary mitigated MEMS saturation occurrence to a fraction of a percent. While no adjacent actuators were saturated at opposing positions, mid-to-high-spatial-frequency stroke did saturate more frequently than expected, implying that correlations through the influence functions are important. Analytical models underpredict the stroke requirements, so empirical studies are important.Comment: 16 pages, 10 figure
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