121 research outputs found

    Exploring the performance limits of the ALICE Time Projection Chamber and Transition Radiation Detector for measuring identified hadron production at the LHC

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    The Time Projection Chamber (TPC) and Transition Radiation Detector (TRD) are the main tracking and particle identification devices in the ALICE experiment at the CERN LHC. This thesis studies aspects of their performance beyond the original designs. This includes extending the TPC momentum measurement for cosmic rays to sub-TeV scale, investigating a robust identification method for electrons and hadrons by the TRD, and developing new approaches to characterize the TPC and TRD signals. These studies lead to an intriguing observation of the transition radiation from sub-TeV cosmic muons, and a universal method -- the TPC coherent fit -- to extract yields of different particle species with momentum from 0.5 to above 20 GeV/c. With the TPC coherent fit, transverse momentum spectra (0.6 < pt < 20 GeV/c) of pions, kaons and protons at mid-rapidity (|y|<~0.8) in pp collisions at sqrt(s) = 2.76 and 7 TeV and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV at the LHC are measured. In this unified approach both the anomalous enhancement of the proton-to-pion ratio at moderate pt (2-8 GeV/c) (the so-called baryon anomaly) and the nuclear modification of particle yields up to high pt (> 10 GeV/c) in Pb-Pb collisions are observed. The particle production is also studied in jets from pp collisions at 7 TeV and the results are well described by Perugia-0 tune of PYTHIA6

    Spatiotemporal variation of marsh vegetation productivity and climatic effects in Inner Mongolia, China

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    Net primary productivity (NPP) is a vital ecological index that reflects the ecological function and carbon sequestration of marsh ecosystem. Inner Mongolia has a large area of marshes, which play a crucial role in the East Asian carbon cycle. Under the influence of climate change, the NPP of Inner Mongolian marsh has changed significantly in the past few decades, but the spatiotemporal variation in marsh vegetation NPP and how climate change affects marsh NPP remain unclear. This study explores, for the first time, the spatiotemporal variation of marsh NPP and its response to climatic change in Inner Mongolia based on the MODIS-NPP and climate datasets. We find that the long-term average annual NPP of marsh is 339.85 g⋅C/m2 and the marsh NPP shows a significantly increasing trend (4.44 g⋅C/m2/a; p &lt; 0.01) over Inner Mongolia during 2000–2020. Spatially, the most prominent increase trend of NPP is mainly distributed in the northeast of the region (Greater Khingan Mountains). The partial correlation results show that increasing autumn and summer precipitation can increase the NPP of marsh vegetation over Inner Mongolia. Regarding the temperature effects, we observe a strong asymmetric effect of maximum (Tmax) and minimum (Tmin) temperature on annual NPP. A high spring Tmax can markedly increase marsh NPP in Inner Mongolia, whereas a high Tmin can significantly reduce it. In contrast to spring temperature effects on NPP, a high summer Tmax can decrease NPP, whereas a high Tmin can increase it. Our results suggest different effects of seasonal climate conditions on marsh vegetation productivity and highlight the influences of day-time and night-time temperatures. This should be considered in simulating and predicting marsh carbon sequestration in global arid and semi-arid regions

    Long-range angular correlations on the near and away side in p&#8211;Pb collisions at

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    Effect of fires on soil organic carbon pool and mineralization in a Northeastern China wetland

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    Fire occurs frequently over wetland, but little is known of its impact on soil carbon variations and carbon mineralization, process that are potentially important in global carbon cycle. To investigate this issue, we have designed and implemented a two-year field campaign to quality the effects of fire seasonality and frequency on soil carbon abundance and carbon mineralization in a wetland of the Sanjiang Plain in Northeastern China. A total of 4 burning experiments were conducted over 12 wetland plots from autumn 2007 to spring 2009. Our results show that after burning soil organic carbon (OC) increased in the burned soils during the first two growing seasons. Fire effects on dissolved organic carbon (DOC) and microbial biomass carbon (MBC), however, were more subtle. During the first post-burning growing season, the levels of DOC and MBC were higher than in the unburned soil. The increase however was temporary, and there was no significant difference between the burned and unburned soils in the second growing season. Carbon mineralization rate increased after burning, and CO2 emission rates were higher from burned soils than from unburned soils. Our findings suggest that burning increased CO2 emission to the atmosphere not only during the combustion process, but also through biogeochemical processes in an extended post-burning period
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