The DArk Matter Particle Explorer(DAMPE),also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at~10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar. 相似文献
Iron-rich groundwater flowing into wetlands is a worldwide environmental pollution phenomenon that is closely associated with the stability of wetland ecosystems. Combined with high phosphorus(P) loading from agricultural runoff, the prediction of the evolution of wetland vegetation affected by compound contamination is particularly urgent. We tested the effects of anaerobic iron-rich groundwater discharge in a freshwater marsh by simulating the effect of three levels of eutrophic water on native plants(Glyceria spiculosa(Fr. Schmidt.) Rosh.). The management of wetland vegetation with 1–20 mg/L Fe input is an efficient method to promote the growth of plants, which showed an optimum response under a 0.10 mg/L P surface water environment. Iron-rich groundwater strongly affects the changes in ecological niches of some wetland plant species and the dominant species. In addition, when the P concentration in a natural body of water is too high, the governance effect of eutrophication might not be as expected. Under iron-rich groundwater conditions, the δ~(13)C values of organs were more depleted, which can partially explain the differences in δ~(13)C in the soil profile. Conversely, the carbon isotope composition of soil organic carbon is indicative of past changes in vegetation. The results of our experiments confirm that iron-rich groundwater discharge has the potential to affect vegetation composition through toxicity modification in eutrophic environments. 相似文献
The factors affecting permeability change under repeated mining of coal seams are important study aspects that need to be explored. This study combined various stress variation characteristics of protective seam mining and simplified the stress path of repeated mining in protective seam mines. Based on the results from the bespoke gas flow and displacement testing apparatus, seepage tests for simulated repetitive mining were carried out. The results simulated the actual behavior very well. With any drastic increase in the mining influence, the axial deviation stress in the stress path increased, and the greater the difference in coal permeability during the unloading and stress recovery stage, the more substantial the increase in permeability. The change in coal permeability was significantly influenced by the severity of simulated repeated mining cycles. When the mining stress exceeded a critical value, the permeability of the coal sample increased with the increase in the number of loading and unloading cycles, but the reverse was true when the mining stress was lower than the critical value. The effective sensitivity of seepage to the applied stress decreased with an increase in the number of stress cycles. With a decrease in the deviation stress, that is, with lower severity of mining influence, the effective sensitivity of coal seepage to stress gradually decreased.
Natural Resources Research - The coal fire area in the Wuda coalfield is divided into four parts based on the degree of burning and on surface characteristics: sub-area B is characterized by... 相似文献