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401.
402.
介绍了新型火灾自动保护型漏电断路器的工作原理、功能和试验情况.该漏电断路器既能解决人身电击保护的问题,又有自动防止电气火灾的功能,推广应用前景广阔. 相似文献
403.
Water Security in Uzbekistan: Implication of Return Waters on the Amu Darya Water Quality 总被引:1,自引:0,他引:1
Crosa G Stefani F Bianchi C Fumagalli A 《Environmental science and pollution research international》2006,13(1):37-42
- DOI: http://dx.doi.org/10.1065/espr2006.01.007
Goal, Scope and Background Amu Darya river, one of the main water resources of Uzbekistan, shows a relevant longitudinal enrichment of soluble contents
which strongly limits the human uses of its waters. Because of the low natural run-off processes, salts and pollutants are
mainly driven to the river by the return waters used for washing and irrigating the surrounding lands. The influence of return
waters on stream quality is dramatically relevant in the lower reaches of the river where almost all the flowing waters have
been previously used for the agriculture practises. To provide analytical evidence on the potential effects of return waters
on the quality of the Amu Darya river, the paper reports and comments data on salinity and metals contents of the waters flowing
in the artificial channel network of Bukhara and in the Amu Darya river, from Bukhara up to the dam forming the Tuyamuyn Hydro
Complex (THC).
Methods A total of 15 sampling sites were selected for the analytical survey: Two sites were located on the Amu Darya river downstream
from the inflow of the return waters from Bukhara, two in the river entering in the THC, and three downstream from the dam
forming the reservoir complex. The waters entering and leaving the Bukhara agricultural area were sampled in two main collectors,
while the waters flowing in the channel system were sampled in six distinct collectors. The following parameters were considered
in the survey: pH, Oxygen, Hardness, Salinity, Conductivity, P-PO4 3–, P tot, N tot, N-NO3 2–, N-NO2 –, COD, Ca2+, Mg2+, Fe,
Mn, Zn, Cr, Cu, Ni, Cd, Pb.
Results and Discussion Salt concentrations below 1000 mg/l were measured in the Amu Darya waters upstream to Bukhara. In the drainage system, salinity
exceeds the palatability limit and reaches the maximum peak of 3200 mg/l in the outflow collector. Due to dilution effects,
salinity returns to lower values (400–700 mg/l) along the Amu Darya river downstream from Bukhara; calcium and magnesium resulted
the major constituents of the overall salinity. No serious metal contaminations were detected in the waters entering and leaving
the examined channel system. Differently, the Amu Darya waters upstream to the THC showed a relevant metal contamination,
with Cr, Ni, Fe concentrations exceeding the limits for human consumption. In the downstream sites, located in the Tuyamuyn
Hydro Complex and in the Amu Darya river flowing out from this reservoir, excluding Fe, all the examined metals showed lover
concentrations and values below the normative limits.
Conclusion The direct human consumption of the lower Amu Darya waters is strongly limited by salinity and by metal contamination. Although
the salinity of the return waters from the Bukhara drainage system results in above normal limits, no corresponding increases
were measured in the Amu Darya river downstream from the return water inflow at the time of the survey. As for the metal contamination
of the Amu Darya river, the survey revealed the presence of relevant sources of metal contamination downstream from Bukhara
external to the agricultural drainage system. This contamination resulted in reduced sedimentation processes taking place
in the limnetic zones of the Amu Darya river upstream to the dam forming the Tuyamuyn Hydro Complex.
Recommendation and Outlook To fully understand the longitudinal increase of Amu Darya salinity, an evaluation of the cumulative effects of the loads
from the main agricultural areas is required, also by using mass-balance models. As for the metals, an investigation should
be addressed to identify the anthropogenic sources of contaminations present in the lower Amu Darya region and the metal loads
should be diverted. 相似文献
404.
Info-Gap Decision Theory for Assessing the Management of Catchments for Timber Production and Urban Water Supply 总被引:3,自引:0,他引:3
While previous studies have examined how forest management is influenced by the risk of fire, they rely on probabilistic estimates
of the occurrence and impacts of fire. However, nonprobabilistic approaches are required for assessing the importance of fire
risk when data are poor but risks are appreciable. We explore impacts of fire risk on forest management using as a case study
a water catchment in the Australian Capital Territory (ACT) (southeastern Australia). In this forested area, urban water supply
and timber yields from exotic plantations are potential joint but also competing land uses. Our analyses were stimulated by
extensive wildfires in early 2003 that burned much of the existing exotic pine plantation estate in the water catchment and
the resulting need to explore the relative economic benefits of revegetating the catchment with exotic plantations or native
vegetation. The current mean fire interval in the ACT is approximately 40 years, making the establishment of a pine plantation
economically marginal at a 4% discount rate. However, the relative impact on water yield of revegetation with native species
and pines is very uncertain, as is the risk of fire under climate change. We use info-gap decision theory to account for these
nonprobabilistic sources of uncertainty, demonstrating that the decision that is most robust to uncertainty is highly sensitive
to the cost of native revegetation. If costs of native revegetation are sufficiently small, this option is more robust to
uncertainty than revegetation with a commercial pine plantation. 相似文献
405.
为解决故障电弧断路器动作响应滞后、效率低等问题,基于电气火灾多发原因与防控实验装置、功率因素可调式负载柜,搭建故障电弧模拟实验台,研究故障电弧断路器响应时间影响因素,利用功率分析仪统计断路器响应时间。研究结果表明:纯电阻电路中,断路器响应时间随碳电极直径增大而缩短;在负载功率P=800,2 000 W条件下,碳电极直径D≥2 mm时,断路器瞬时保护率达100%;负载功率P=3 200 W时,断路器瞬时保护率小于50%;碳电极直径D为1,2 mm时,断路器最佳负载功率保护区间分别为[1 200,1 600] W,[800,2 400] W,碳电极直径为2 mm的保护区间范围较宽,安全可靠性更高;感性电路中,断路器响应时间随功率因数减小而延迟,功率因数对断路器动作响应时间的影响随负载功率增加而降低。研究结果可为故障电弧断路器响应时间的设定提供参考。 相似文献
406.
Shuyu Chen Run Li Yaqi Shen Lu Zhan Zhenming Xu 《Frontiers of Environmental Science & Engineering》2022,16(11):146