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巷道围岩塑性状态判定分析方法 总被引:8,自引:0,他引:8
本文依照莫尔-库仑屈服条件和非关联流动准则, 从地应力场及地下巷道开挖工程特点出发, 提出对围岩塑性屈服状态进行判定的方法。对无支护巷道和水泥锚杆支护巷道围岩进行有限元分析表明, 巷道开挖以后及时支设锚杆, 对出现塑性屈服的围岩起到了等效提高其刚度和强度的作用, 从而增加了围岩稳定性。与现场实测结果对比说明, 非关联流动准则比关联流动准则更符合实际。 相似文献
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根据大量资料分析和实地考察,对我国塑料大棚小气候开发利用进行了综述,并对蔬菜大棚气象服务进行探讨,为塑料大棚应用于农业产业化,取得更好经济效益,提供参考。 相似文献
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C. Ghag D.Yu. AkimovH.M. Araújo E.J. BarnesV.A. Belov A.A. BurenkovV. Chepel A. CurrieL. DeViveiros B. EdwardsV. Francis A. HollingsworthM. Horn G.E. KalmusA.S. Kobyakin A.G. KovalenkoV.N. Lebedenko A. Lindote M.I. LopesR. Lüscher K. LyonsP. Majewski A.St J. MurphyF. Neves S.M. PalingJ. Pinto da Cunha R. PreeceJ.J. Quenby L. ReichhartP.R. Scovell C. SilvaV.N. Solovov N.J.T. SmithP.F. Smith V.N. StekhanovT.J. Sumner C. ThorneR.J. Walker 《Astroparticle Physics》2011,35(2):76-86
The ZEPLIN-III experiment is operating in its second phase at the Boulby Underground Laboratory in search of dark matter WIMPs. The major upgrades to the instrument over its first science run include lower background photomultiplier tubes and installation of a plastic scintillator veto system. Performance results from the veto detector using calibration and science data in its first six months of operation in coincidence with ZEPLIN-III are presented. With fully automated operation and calibration, the veto system has maintained high stability and achieves near unity live time relative to ZEPLIN-III. Calibrations with a neutron source demonstrate a rejection of 60% of neutron-induced nuclear recoils in ZEPLIN-III that might otherwise be misidentified as WIMPs. This tagging efficiency reduces the expected untagged nuclear recoil background from neutrons during science data taking to a very low rate of ?0.2 events per year in the WIMP acceptance region. Additionally, the veto detector provides rejection of 28% of γ-ray induced background events, allowing the sampling of the dominant source of background in ZEPLIN-III - multiple scatter γ-rays with rare topologies. Since WIMPs will not be tagged by the veto detector, and tags due to γ-rays and neutrons are separable, this population of multiple scatter events may be characterised without biasing the analysis of candidate WIMP signals in the data. 相似文献
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Plastic pellets found stranded on beaches are hydrophobic organic materials and thus, they are a favourable medium for persistent organic pollutants to absorb to. In the present study, plastic pellets are used to determine the diffuse pollution of selected Greek beaches. Samples of pellets were taken from these beaches and were analyzed for PCBs, DDTs, HCHs, and PAHs. The observed differences among pellets from various sampling sites are related to the pollution occurring at each site. Plastic pellets collected in Saronikos Gulf beaches demonstrate much higher pollutant loading than the ones collected in a remote island or close to an agricultural area. Based on data collected in this study and the International Pellet Watch program, pollution in Saronikos Gulf, Greece, is comparable to other heavily industrialized places of the world. The present study demonstrates the potential of pellet watch to be utilized as a detailed-scale monitoring tool within a single country. 相似文献
69.
Denuncio P Bastida R Dassis M Giardino G Gerpe M Rodríguez D 《Marine pollution bulletin》2011,62(8):1836-1841
Plastic debris (PD) ingestion was examined in 106 Franciscana dolphins (Pontoporia blainvillei) incidentally captured in artisanal fisheries of the northern coast of Argentina. Twenty-eight percent of the dolphins presented PD in their stomach, but no ulcerations or obstructions were recorded in the digestive tracts. PD ingestion was more frequent in estuarine (34.6%) than in marine (19.2%) environments, but the type of debris was similar. Packaging debris (cellophane, bags, and bands) was found in 64.3% of the dolphins, with a lesser proportion (35.7%) ingesting fishery gear fragments (monofilament lines, ropes, and nets) or of unknown sources (25.0%). PD ingestion correlated with ontogenetic changes in feeding regimes, reaching maximum values in recently weaned dolphins. Because a simultaneous increase in gillnet entanglement and the bioaccumulation of heavy metals take place at this stage, the first months after trophic independence should be considered as a key phase for the conservation of Franciscana dolphin stocks in northern Argentina. 相似文献
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Magellanic penguins (Spheniscus magellanicus) are non-breeding winter visitors to the Brazilian coast. In 2008 and 2010, plastic items and other marine debris were found in the stomachs and intestines of 15% of 175 dead penguins collected in the Lagos Region of the state of Rio de Janeiro. One bird had its stomach perforated by a plastic straw, which may have caused its death. There are few records of penguins ingesting plastic litter, but previous studies have found similar levels of debris ingestion among Magellanic penguins stranded on the Brazilian coast (35.8% of 397 birds). The high incidence of marine debris in this species in Brazil may result at least in part from the predominance of juveniles reaching these waters, as juvenile penguins may have a broader diet than adults. It is unclear to what extent plastic ingestion affects the mortality rate in this species and whether the incidence in stranded birds reflects that in the entire population. The present study addresses the increasing impact of plastic debris on marine life. 相似文献