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排序方式: 共有2697条查询结果,搜索用时 15 毫秒
131.
Zheng J Wu F Yamada M Liao H Liu C Wan G 《Environmental pollution (Barking, Essex : 1987)》2008,152(2):314-321
Studies on the distribution and isotope compositions of fallout Pu are important for source characterization of possible future non-fallout Pu contamination in aquatic environments, and useful for dating of recent sediments to understand the pollution history of environmental contaminants. We present the historical record of atmospheric Pu fallout reconstructed from a sediment core from Lake Hongfeng, China. The Pu activity profile was in agreement with the 137Cs profile. Inventories were 50.7 Bq m(-2) for 239+240Pu and 1586 Bq m(-2) for 137Cs. The average 240Pu/239Pu atom ratio was 0.185+/-0.009, indicating that Pu originated from global stratospheric fallout rather than from direct tropospheric or close-in fallout from the Chinese nuclear testing conducted in the 1970s. Our data suggested that Lake Hongfeng would be an ideal setting for monitoring atmospheric fallout and environmental changes in this region. 相似文献
132.
Hang Seok Choi Seock Joon Kim Kwan Tae Kim 《Journal of Material Cycles and Waste Management》2008,10(1):1-6
The mixing characteristics of a passive scalar in the turbulent flow of a selective catalytic reduction process were numerically
and experimentally investigated, focusing especially on an injection nozzle with multiple holes for the reducing agent. The
multihole injection nozzle studied has six holes that are perpendicular to the ambient flue gas flow and are located near
the tip of the nozzle. Large eddy simulation was applied to the turbulent flow and mixing fields to elucidate the mixing mechanism
of the proposed nozzle compared with the single-hole nozzle that is commonly used in the conventional selective catalytic
reduction process. From the results, there exist broader regions of higher turbulent intensities for the multihole nozzle
than for the conventional single-hole nozzle. These regions are well matched with the positions of high vorticity in the near
upstream region of the jet flow issuing from the multiple holes of the nozzle. Consequently, the high turbulent intensities
and vorticity magnitudes lead to intensified mixing between the flue gas and the reducing agent. Hence, the most suitable
molar ratio between NOx and the reducing agent for the catalytic reaction can be easily obtained within a shorter physical
mixing length as a result of the enhanced scalar mixing. Finally, the numerical results were applied to a trial design version
of a multihole nozzle, and this nozzle was experimentally tested to confirm its mixing performance. 相似文献
133.
The practice of contaminant transport and remediation has shown significant progress in recent years. However, despite the
significant progress made, remediation efforts are often delayed by extremely long breakthrough curve tails that render efforts
to bring the level of contaminants below the regulatory standards inefficient. One hypothesis is that these long tails are
due to the reservoir-like slow diffusive processes in soil micropore zones. This study compares the effects of micropores
at macroscopic and microscopic levels and establishes a link between these approaches for validation and calibration purposes.
The link between macroscopic and microscopic levels is established through comparisons and testing of the two models while
incorporating appropriate scale and boundary effects. Despite the differences in conceptual approaches and simulation time,
the two approaches rendered meaningful results. The link helps forecast the effects of micropore zone transport processes
in the subsurface efficiently and thus allows development of numerical tools that could contribute towards more efficient
remediation design. 相似文献
134.
通过研究分析污泥龄(SRT)对富磷污水除磷的LSP&PNR污泥减量新工艺运行效果的影响,结果发现,延长污泥龄有利于提高系统的厌氧释磷能力,但不影响其总的除磷率,同时磷的回收比例增大,当SRT=50 d时,磷回收率取得最大值70.4%;LSP&PNR系统污泥龄增加,还有利于污泥产率的降低.试验还发现,排富磷污水除磷的长污泥龄LSP&PNR系统的除磷效率与污泥产率之间不存在制约关系,即系统可以同时获得优异的污泥减量与生物除磷效果,当SRT=50 d时,每降解1 kg COD仅产生0.143 kg污泥,而除磷率达最高值92.8%;LSP&PNR系统中SRT、DO与SVI之间存在一定的相关性,在供氧充足(DO=0.8~1.5 mg/L)条件下,SRT增加,SVI越高,但对于SRT为50 d的LSP&PNR系统,稳定运行时没有污泥膨胀之虞. 相似文献
135.
136.
劳动力外出务工对承灾体恢复力的影响——以河北省邢台县旱灾调查为例 总被引:1,自引:0,他引:1
农村劳动力资源是构成农户承灾体恢复力的重要因素.一般认为农村劳动力外出务工,可以提高农户家庭的经济水平,进而提升农户的旱灾恢复力.通过对河北省邢台县的实地调查研究发现,劳动力外出务工与农户承灾体恢复力间存在着微妙的关系.研究表明,户主外出务工模式不仅在农业生产的灾后恢复上,而且在农户家庭经济的恢复上均有积极的意义.对于子女外出务工家庭而言,子女不愿意再从事农业生产,并且子女的务工收入对家庭的贡献十分有限,即子女外出务工对家庭旱灾恢复力影响较小. 相似文献
137.
138.
Effects of salinity on endogenous rhythm of the Manila clam, Ruditapes philippinarum (Bivalvia: Veneridae) 总被引:1,自引:0,他引:1
The Manila clam Ruditapes philippinarum, an intertidal bivalve, was exposed to different salinity regimes (from 31.0–31.7‰ down to 20‰, 15‰, 10‰, 5‰), and the endogenous
rhythm in its oxygen consumption was studied using an automatic intermittent-flow respirometer. When exposed to salinities
reduced from 31.5‰ to 20‰ and 15‰ under otherwise constant conditions, the clams recovered a clear endogenous circatidal rhythm
in their oxygen-consumption rate after having dampened periods of 12 h and 48 h, respectively. At salinities less than 10‰,
however, the oxygen-consumption rate was depressed greatly at the beginning of the experiment for about 36 h and then increased
to a level higher than normal, but the rhythm of oxygen consumption was not recovered. The results of this study indicate
that the Manila clam, a euryhaline organism, cannot maintain a normal metabolic activity at a salinity lower than 15‰. All
clams were dead after exposure at a salinity of 5‰ for 7 days.
Received: 28 February 2000 / Accepted: 26 August 2000 相似文献
139.
D. Kim T. Okamoto T. Oda K. Tachibana K.S. Lee A. Ishimatsu Y. Matsuyama T. Honjo T. Muramatsu 《Marine Biology》2001,139(4):625-632
Although the ichthyotoxic mechanism of Chattonella marina is still unknown, several lines of evidence suggest that the reactive oxygen species (ROS), such as superoxide anion (O2-), hydrogen peroxide (H2O2), and hydroxyl radical (·OH), produced by C. marina are involved in the mortality of fish exposed to this flagellate. Recently, we found that the cell-free supernatant prepared from C. marina, which is considered to contain the glycocalyx, showed NADPH-dependent O2- generation. In this study, we prepared antiserum against the crude glycocalyx of C. marina. Using indirect immunofluorescence, it was confirmed that the antiserum specifically reacted with C. marina cells. In addition to C. marina, the antiserum also reacted with other raphidophycean flagellates such as Heterosigma akashiwo, Olisthodiscus luteus, and Fibrocapsa japonica, whereas no reactivity was observed against six other flagellate species tested. These results suggest that raphidophycean flagellates have common epitopes recognized by the antiserum. Interestingly, immunohistochemical analysis of paraformaldehyde-fixed gill lamellae from yellowtail exposed to C. marina revealed that the antiserum stained the surface of gill lamellae, while no such staining pattern was observed in control gill lamellae. These results suggest that the glycocalyx may be discharged when C. marina cells are inhaled into the fishes' mouths and then come into contact with the gill surface. Based on the present results, together with our previous findings, we propose that continuous accumulation of the discharged glycocalyx on the gill surface occurs during C. marina exposure, which may be responsible for the ROS-mediated severe gill tissue damage leading to fish death. 相似文献