1,742 research outputs found

    Equilibrium responses of global net primary production and carbon storage to doubled atmospheric carbon dioxide: sensitivity to changes in vegetation nitrogen concentration

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    We ran the terrestrial ecosystem model (TEM) for the globe at 0.5° resolution for atmospheric CO2 concentrations of 340 and 680 parts per million by volume (ppmv) to evaluate global and regional responses of net primary production (NPP) and carbon storage to elevated CO2 for their sensitivity to changes in vegetation nitrogen concentration. At 340 ppmv, TEM estimated global NPP of 49.0 1015 g (Pg) C yr−1 and global total carbon storage of 1701.8 Pg C; the estimate of total carbon storage does not include the carbon content of inert soil organic matter. For the reference simulation in which doubled atmospheric CO2 was accompanied with no change in vegetation nitrogen concentration, global NPP increased 4.1 Pg C yr−1 (8.3%), and global total carbon storage increased 114.2 Pg C. To examine sensitivity in the global responses of NPP and carbon storage to decreases in the nitrogen concentration of vegetation, we compared doubled CO2 responses of the reference TEM to simulations in which the vegetation nitrogen concentration was reduced without influencing decomposition dynamics (“lower N” simulations) and to simulations in which reductions in vegetation nitrogen concentration influence decomposition dynamics (“lower N+D” simulations). We conducted three lower N simulations and three lower N+D simulations in which we reduced the nitrogen concentration of vegetation by 7.5, 15.0, and 22.5%. In the lower N simulations, the response of global NPP to doubled atmospheric CO2 increased approximately 2 Pg C yr−1 for each incremental 7.5% reduction in vegetation nitrogen concentration, and vegetation carbon increased approximately an additional 40 Pg C, and soil carbon increased an additional 30 Pg C, for a total carbon storage increase of approximately 70 Pg C. In the lower N+D simulations, the responses of NPP and vegetation carbon storage were relatively insensitive to differences in the reduction of nitrogen concentration, but soil carbon storage showed a large change. The insensitivity of NPP in the N+D simulations occurred because potential enhancements in NPP associated with reduced vegetation nitrogen concentration were approximately offset by lower nitrogen availability associated with the decomposition dynamics of reduced litter nitrogen concentration. For each 7.5% reduction in vegetation nitrogen concentration, soil carbon increased approximately an additional 60 Pg C, while vegetation carbon storage increased by only approximately 5 Pg C. As the reduction in vegetation nitrogen concentration gets greater in the lower N+D simulations, more of the additional carbon storage tends to become concentrated in the north temperate-boreal region in comparison to the tropics. Other studies with TEM show that elevated CO2 more than offsets the effects of climate change to cause increased carbon storage. The results of this study indicate that carbon storage would be enhanced by the influence of changes in plant nitrogen concentration on carbon assimilation and decomposition rates. Thus changes in vegetation nitrogen concentration may have important implications for the ability of the terrestrial biosphere to mitigate increases in the atmospheric concentration of CO2 and climate changes associated with the increases

    THE ARMY COMBAT CLOTH FACE COVER

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    This project defines specific procurement and contracting strategies that were available for the expeditious requisition of the Army Combat Cloth Face Cover (CCFC) program based on Department of Defense (DOD) acquisition policies and the Federal Acquisition Regulation. Selected primary documentation of DOD and U.S. Army regulation, detailed acquisition documentation, DOD and Army directives, data from other federal organizations, and published research data were used to identify the acquisition process, responsibilities, and authorities of the Army. The analysis defines multiple acquisition approaches within the Adaptive Acquisition Framework (AAF), including Major Capability Acquisition, Middle Tier of Acquisition, and Urgent Capability acquisition approaches. Furthermore, the analysis determined that the most expeditious approach for the CCFC effort was using the Urgent Capability Acquisition pathway under the emergency authorization. The AAF urgent acquisition approach that the Army agencies utilized should be applied to other similar rapid requirements or future unplanned rapid acquisitions to help generate a more streamlined acquisition approach that will not only focus on quality from a safety perspective, but also meet an aggressive schedule.Lieutenant Colonel, United States ArmyCaptain, United States ArmyApproved for public release. Distribution is unlimited

    Interactions between carbon and nitrogen dynamics in estimating net primary productivity for potential vegetation in North America

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    We use the terrestrial ecosystem model (TEM), a process-based model, to investigate how interactions between carbon (C) and nitrogen (N) dynamics affect predictions of net primary productivity (NPP) for potential vegetation in North America. Data on pool sizes and fluxes of C and N from intensively studied field sites are used to calibrate the model for each of 17 non-wetland vegetation types. We use information on climate, soils, and vegetation to make estimates for each of 11,299 non-wetland, 0.5° latitude × 0.5° longitude, grid cells in North America. The potential annual NPP and net N mineralization (NETNMIN) of North America are estimated to be 7.032 × 1015 g C yr−1 and 104.6 × 1012 g N yr−1, respectively. Both NPP and NETNMIN increase along gradients of increasing temperature and moisture in northern and temperate regions of the continent, respectively. Nitrogen limitation of productivity is weak in tropical forests, increasingly stronger in temperate and boreal forests, and very strong in tundra ecosystems. The degree to which productivity is limited by the availability of N also varies within ecosystems. Thus spatial resolution in estimating exchanges of C between the atmosphere and the terrestrial biosphere is improved by modeling the linkage between C and N dynamics. We also perform a factorial experiment with TEM on temperate mixed forest in North America to evaluate the importance of considering interactions between C and N dynamics in the response of NPP to an elevated temperature of 2°C. With the C cycle uncoupled from the N cycle, NPP decreases primarily because of higher plant respiration. However, with the C and N cycles coupled, NPP increases because productivity that is due to increased N availability more than offsets the higher costs of plant respiration. Thus, to investigate how global change will affect biosphere-atmosphere interactions, process-based models need to consider linkages between the C and N cycles

    Potential Direct and Indirect Effects of Global Cellulosic Biofuel Production on Greenhouse Gas Fluxes from Future Land-use Chage

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    http://globalchange.mit.edu/research/publications/2240The production of cellulosic biofuels may have a large influence on future land emissions of greenhouse gases. These effects will vary across space and time depending on land-use policies, trade, and variations in environmental conditions. We link an economic model with a terrestrial biogeochemistry model to explore how projections of cellulosic biofuels production may influence future land emissions of carbon and nitrous oxide. Tropical regions, particularly Africa and Latin America, are projected to become major producers of biofuels. Most biofuels production is projected to occur on lands that would otherwise be used to produce crops, livestock and timber. Biofuels production leads to displacement and a redistribution of global food and timber production along with a reduction in the trade of food products. Overall, biofuels production and the displacement of other managed lands increase emissions of greenhouse gases primarily as a result of carbon emissions from deforestation and nitrous oxide emissions from fertilizer applications to maximize biofuel crop production in tropical regions. With optimal application of nitrogen fertilizers, cellulosic biofuels production may enhance carbon sequestration in soils of some regions. As a result, the relative importance of carbon emissions versus nitrous oxide emissions varies among regions. Reductions in carbon sequestration by natural ecosystems caused by the expansion of biofuels have minor effects on the global greenhouse gas budget and are more than compensated by concurrent biofuel-induced reductions in nitrous oxide emissions from natural ecosystems. Land policies that avoid deforestation and fertilizer applications, particularly in tropical regions, will have the largest impact on minimizing land emissions of greenhouse gas from cellulosic biofuels production.This research was supported in part by the David and Lucile Packard Foundation to the MBL, Department of Energy, Office of Science (BER) grants DE-FG02-94ER61937, DE-FG02- 93ER61677, DE-FG02-08ER64648, EPA grant XA-83240101, NSF grant BCS-0410344, and the industrial and foundation sponsors of the MIT Joint Program on the Science and Policy of Global Change

    Collective behaviour without collective order in wild swarms of midges

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    Collective behaviour is a widespread phenomenon in biology, cutting through a huge span of scales, from cell colonies up to bird flocks and fish schools. The most prominent trait of collective behaviour is the emergence of global order: individuals synchronize their states, giving the stunning impression that the group behaves as one. In many biological systems, though, it is unclear whether global order is present. A paradigmatic case is that of insect swarms, whose erratic movements seem to suggest that group formation is a mere epiphenomenon of the independent interaction of each individual with an external landmark. In these cases, whether or not the group behaves truly collectively is debated. Here, we experimentally study swarms of midges in the field and measure how much the change of direction of one midge affects that of other individuals. We discover that, despite the lack of collective order, swarms display very strong correlations, totally incompatible with models of noninteracting particles. We find that correlation increases sharply with the swarm's density, indicating that the interaction between midges is based on a metric perception mechanism. By means of numerical simulations we demonstrate that such growing correlation is typical of a system close to an ordering transition. Our findings suggest that correlation, rather than order, is the true hallmark of collective behaviour in biological systems.Comment: The original version has been split into two parts. This first part focuses on order vs. correlation. The second part, about finite-size scaling, will be included in a separate paper. 15 pages, 6 figures, 1 table, 5 video

    Land-Use Change, Soil Process and Trace Gas Fluxes in the Brazilian Amazon Basin

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    We measured changes in key soil processes and the fluxes of CO2, CH4 and N2O associated with the conversion of tropical rainforest to pasture in Rondonia, a state in the southwest Amazon that has experienced rapid deforestation, primarily for cattle ranching, since the late 1970s. These measurements provide a comprehensive quantitative picture of the nature of surface soil element stocks, C and nutrient dynamics, and trace gas fluxes between soils and the atmosphere during the entire sequence of land-use change from the initial cutting and burning of native forest, through planting and establishment of pasture grass and ending with very old continuously-pastured land. All of our work is done in cooperation with Brazilian scientists at the Centro de Energia Nuclear na Agricultura (CENA) through an extant official bi-lateral agreement between the Marine Biological Laboratory and the University of Sao Paulo, CENA's parent institution

    Finite-size scaling as a way to probe near-criticality in natural swarms

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    Collective behaviour in biological systems is often accompanied by strong correlations. The question has therefore arisen of whether correlation is amplified by the vicinity to some critical point in the parameters space. Biological systems, though, are typically quite far from the thermodynamic limit, so that the value of the control parameter at which correlation and susceptibility peak depend on size. Hence, a system would need to readjust its control parameter according to its size in order to be maximally correlated. This readjustment, though, has never been observed experimentally. By gathering three-dimensional data on swarms of midges in the field we find that swarms tune their control parameter and size so as to maintain a scaling behaviour of the correlation function. As a consequence, correlation length and susceptibility scale with the system's size and swarms exhibit a near-maximal degree of correlation at all sizes.Comment: Selected for Viewpoint in Physics; PRL Editor's Suggestio

    The use of classification and regression tree to predict 15-year survival in community-dwelling older people

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    Previous research has identified various risk factors for mortality in older people. The aim of this paper was to use Classification and Regression Tree to predict 15-year survival in community-dwelling older people. Data were obtained from a United Kingdom representative sample of 1042 community-dwelling people aged 65 and over. Outcome was time from 1985 interview to death or censorship on February 29, 2000. Classification and Regression Tree is a non-parametric technique widely used in medical domain classification. We applied CART to the set of risk-factors identified in a previous research. The selected CART model is based on age, dose of drug prescribed and handgrip measures. It predicts survival with a sensitivity rate of 76.3% and a specificity rate of 66.3%. The selection of variables are consistent with previous research. Finally, we observed the range of risk factors and their combination associated with increased and decreased mortality

    Regional Consortium of Community-Engaged Researchers: Brainstorming for Gerontology Research Opportunities

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    Moderators: A. James Lee, PhD, Karen Devereaux Melillo, PhD, A-GNP-C, FAANP, FGSA, Co-Directors, UMass Lowell Center for Gerontology Research and Partnership; Deborah D’Avolio, Ph.D., BC-ACNP, ANP, Associate Professor, School of Nursing, Center for Gerontology Research and Partnership, Member Session Presenters A.James Lee, PhD Karen Devereaux Melillo Deborah D’Avolio Center for Gerontology Research and Partnership Members Session Description The Regional Consortium of Community-Engaged Gerontology Researchers was founded to expand opportunities for collaborative research, publication, and research funding. It was launched by the UMass Lowell Center for Gerontology Research and Partnerships in collaboration with the UMass CCTS Community Engagement and Research Section in 2013. Since then, the Regional Consortium has met annually at the UMCCTS Community Engagement and Research Symposium, and key recommendations and partnerships have resulted in sharing of resources and potential collaborations. The purpose of this interactive breakout session is to expand the gerontology researcher network and brainstorm research ideas around community-engaged research opportunities. Utilizing a group facilitator, attendees will engage in dialogue about action steps, potential research collaborations, and funding opportunities

    Tents, Beds and Clothing: The Evocative Objects of Contemporary Art Textile

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    The vast collection of textiles, fabrics and fibres from Vesuvian sites, kept at the MANN (National Archaeological Museum of Naples), represents one of the most interesting and, until now, less explored bequests of a not marginal aspect of ancient culture, among whose ‘folds’ it is possible to trace important elements of an history that crosses the sphere of production, distribution, habits and society of Pompeii and, more generally, of Roman culture. The contribution intends to present the first results of a work of research and documentation on this precious textile material and the task of reinterpreting, that the research group is carrying out in order to illustrate a process of dissemination and cultural promotion of the complex knowledge that is kept in it
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