1,075 research outputs found

    The changing faces of soil organic matter research

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    This work contributes to the projects N-Circle (BB/N013484/1), DEVIL NE/M021327/1) and U-GRASS (NE/M017125/1). MST and WJR were supported by U.S. Department of Energy funding under contract DE-AC02-05CH11231. We are grateful to Dr John M. Kimble for providing the idea for this paper through a remembered conversation in around 1996.Peer reviewedPostprin

    Single shot cathode transverse momentum imaging in high brightness photoinjectors

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    In state of the art photoinjector electron sources, thermal emittance from photoemission dominates the final injector emittance. Therefore, low thermal emittance cathode developments and diagnostics are very important. Conventional thermal emittance measurements for the high gradient gun are time-consuming and thus thermal emittance is not measured as frequently as quantum efficiency during the lifetime of photocathodes, although both are important properties for the photoinjector optimizations. In this paper, a single shot measurement of photoemission transverse momentum, i.e., thermal emittance per rms laser spot size, is proposed for photocathode rf guns. By tuning the gun solenoid focusing, the electrons' transverse momenta at the cathode are imaged to a downstream screen, which enables a single shot measurement of both the rms value and the detailed spectra of the photoelectrons' transverse momenta. Both simulations and proof of principle experiments are reported

    Soil carbon fluxes and stocks in a Great Lakes forest chronosequence

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    Author Posting. © The Authors, 2008. This is the author's version of the work. It is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Global Change Biology 15 (2009): 145-155, doi:10.1111/j.1365-2486.2008.01741.x.We measured soil respiration and soil carbon stocks, as well as micrometeorological variables in a chronosequence of deciduous forests in Wisconsin and Michigan. The chronosequence consisted of (1) four recently disturbed stands, including a clearcut and repeatedly burned stand (burn), a blowdown and partial salvage stand (blowdown), a clearcut with sparse residual overstory (residual), and a regenerated stand from a complete clearcut (regenerated); (2) four young aspen (Populus tremuloides) stands in average age of 10 years; (3) four intermediate aspen stands in average age of 26 years; (4) four mature northern hardwood stands in average age of 73 years; and (5) an old-growth stand approximately 350 years old. We fitted site-based models and used continuous measurements of soil temperature to estimate cumulative soil respiration for the growing season of 2005 (days 133 to 295). Cumulative soil respiration in the growing season was estimated to be 513, 680, 747, 747, 794, 802, 690, and 571 gC m-2 in the burn, blowdown, residual, regenerated, young, intermediate, mature, and old-growth stands, respectively. The measured apparent temperature sensitivity of soil respiration was the highest in the regenerated stand, and declined from the young stands to the old-growth. Both cumulative soil respiration and basal soil respiration at 10˚C increased during stand establishment, peaked at intermediate age, and then decreased with age. Total soil carbon at 0-60 cm initially decreased after harvest, and increased after stands established. The old-growth stand accumulated carbon in deep layers of soils, but not in the surface soils. Our study suggests a complexity of long-term soil carbon dynamics, both in vertical depth and temporal scale.This work was primarily funded by the Office of Science/BER, U.S. Department of Energy Terrestrial Carbon Processes program (DE-FG02-00ER63023 and DE-FG02-03ER63682), and NASA Terrestrial Ecology Program (NNG05GD51G)

    Mineral soil carbon fluxes in forests and implications for carbon balance assessments

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    Forest carbon cycles play an important role in efforts to understand and mitigate climate change. Large amounts of carbon (C) are stored in deep mineral forest soils, but are often not considered in accounting for global C fluxes because mineral soil C is commonly thought to be relatively stable. We explore C fluxes associated with forest management practices by examining existing data on forest C fluxes in the northeastern US. Our findings demonstrate that mineral soil C can play an important role in C emissions, especially when considering intensive forest management practices. Such practices are known to cause a high aboveground C flux to the atmosphere, but there is evidence that they can also promote comparably high and long-term belowground C fluxes. If these additional fluxes are widespread in forests, recommendations for increased reliance on forest biomass may need to be reevaluated. Furthermore, existing protocols for the monitoring of forest C often ignore mineral soil C due to lack of data. Forest C analyses will be incomplete until this problem is resolved. © 2013 Blackwell Publishing Ltd

    Potential future dynamics of carbon fluxes and pools in New England forests and their climatic sensitivities: A model-based study

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    Projections of terrestrial carbon (C) dynamics must account for interannual variation in ecosystem C exchange associated with climate change, increasing atmospheric CO2 concentration, and species dynamics. We used a dynamic ecosystem model to (i) project the potential dynamics of C in New England forests under nine climate change scenarios (CCSs) for the 21st century and (ii) examine the sensitivity of potential C dynamics to changes in climate and atmospheric CO2 concentration. Our results indicated that forest net primary productivity (NPP) and soil heterotrophic respiration (RH) averaged 428 and 279 gC/m2/yr and New England forests sequestered CO 2 by 149 gC/m2/yr in the baseline period (1971-2000). Under the nine future CCSs, NPP and RH were modeled to increase by an average rate of 0.85 and 0.56 gC/m2/yr2 during 1971-2099. The asymmetric increase in NPP and RH resulted in New England forests sequestering atmospheric CO2 at a net rate of 0.29 gC/m2/yr2 with increases in vegetation and soil C. Simulations also indicated that climate warming alone decreases NPP, resulting in a net efflux of C from forests. In contrast, increasing precipitation by itself stimulates CO 2 sequestration by forests. At the individual cell level, however, changes in temperature or precipitation can either positively or negatively affect consequent C dynamics. Elevation of CO2 levels was found to be the biggest driver for modeled future enhancement of C sequestration. Without the elevation of CO2 levels, climate warming has the potential to change New England forests from C sinks to sources in the late 21st century. ©2014. American Geophysical Union. All Rights Reserved

    Exposure of RC building structures to the marine environment of the Valencia coast

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    [EN] As the marine atmosphere is very harmful to reinforced concrete (RC) structures, buildings situated close to the sea are at a high risk of suffering damage. Such is the case for many of the buildings near the coast in Valencia (Spain). Most of these buildings were built between 1968 and 2007, and nowadays their RC structures are seriously damaged. This paper describes the condition of 1816 buildings that were inspected in 14 towns along the Valencia coast. From these inspections, there have been identified the main factors which are the most significant in the damage of these RC structures by the aggressive marine conditions. These factors include environmental characteristics, urban parameters, and the construction system of the buildings.Moreno, JD.; Pellicer, TM.; Adam, JM.; Bonilla Salvador, MM. (2018). Exposure of RC building structures to the marine environment of the Valencia coast. Journal of Building Engineering. 15:109-121. https://doi.org/10.1016/j.jobe.2017.11.016S1091211

    Competing Interactions in DNA Assembly on Graphene

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    We study the patterns that short strands of single-stranded DNA form on the top graphene surface of graphite. We find that the DNA assembles into two distinct patterns, small spherical particles and elongated networks. Known interaction models based on DNA-graphene binding, hydrophobic interactions, or models based on the purine/pyrimidine nature of the bases do not explain our observed crossover in pattern formation. We argue that the observed assembly behavior is caused by a crossover in the competition between base-base pi stacking and base-graphene pi stacking and we infer a critical crossover energy of eV. The experiments therefore provide a projective measurement of the base-base interaction strength
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