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771.
772.
论述了输油泵站控制系统及微波通信系统遭受雷击的危害及原因,有针对性地采取了各种防雷的有效措施,完善微波通讯和站控及网络防雷保护系统,为确保输油安全生产提供了有利保证. 相似文献
773.
对几种浮选剂在荆门石化污水处理场的处理效果进行了对比,结果表明岳阳云溪XY-Ⅱ和江苏武进PAFC比现有PAC浮选剂的处理效果佳,且运行成本低. 相似文献
774.
Vullo R 《Die Naturwissenschaften》2011,98(6):545-549
Sharks are known to have been ammonoid predators, as indicated by analysis of bite marks or coprolite contents. However, body
fossil associations attesting to this predator–prey relationship have never been described so far. Here, I report a unique
finding from the Late Jurassic of western France: a complete specimen of the Kimmeridgian ammonite Orthaspidoceras bearing one tooth of the hybodont shark Planohybodus. Some possible tooth puncture marks are also observed. This is the first direct evidence of such a trophic link between these
two major Mesozoic groups, allowing an accurate identification of both organisms. Although Planohybodus displays a tearing-type dentition generally assumed to have been especially adapted for large unshelled prey, our discovery
clearly shows that this shark was also able to attack robust ammonites such as aspidoceratids. The direct evidence presented
here provides new insights into the Mesozoic marine ecosystem food webs. 相似文献
775.
Chunyan Liu Kai Wang Shixie Meng Xunhua Zheng Zaixing Zhou Shenghui Han Deli Chen Zhiping Yang 《Agriculture, ecosystems & environment》2011,140(1-2):226-233
One-year winter wheat–summer maize rotation is the most popular double cropping system in north-central China, and this highly productive system is an important source of nitrous oxide (N2O) and nitric oxide (NO) emissions due to the high fertilizer N and irrigation water inputs. To sustain the high crop production and mitigate the detrimental impacts of N2O and NO emissions, improved management practices are extensively applied. The aim of this study is therefore to evaluate the effects of an improved management practice of irrigation, fertilization and crop straw on grain yield and N2O and NO emissions for a wheat–maize rotation field in northern China. Using automated and manual chamber measuring systems, we monitored N2O and NO fluxes for the conventional (CT, 2007–2008), improved (IT, 2007–2008), straw-amended (WS, 2008–2009), straw-not-amended (NS, 2008–2009), and no N-fertilizer treatments (WS–NN, 2008–2009), respectively, for one rotation-year. The grain yields were determined for CT and IT for three rotation-years (2005–2008) and for WS, NS and WS–NN for one rotation-year (2008–2009). The improved management of irrigation and fertilization reduced the annual N fertilization rate and irrigation amount by 17% and 30%, respectively; increased the maize yield by 7–14%; and significantly decreased the N2O and NO emissions by 7% (p < 0.05) and 29% (p < 0.01), respectively. The incorporation of wheat straw increased the cumulative N2O and NO emissions in the following maize season by 58% (p < 0.01) and 13%, respectively, whereas the effects of maize straw application were not remarkable. The N2O and NO emission factors of applied N were 2.32 ± 2.32% and 0.42 ± 1.69% for wheat straw and 0.67 ± 0.23% and 0.54 ± 0.15% for chemical N-fertilizers, respectively. Compared to conventional management practices using high application rates of irrigation water and chemical N-fertilizer as well as the field burning of crop straw, the improved management strategy presented here has obvious environmentally positive effects on grain yield and mitigation of N2O and NO emissions. 相似文献
776.
Some emerging technologies are expected to be pivotal for solving many of the environmental challenges faced today, especially those related to energy. However, many of these technologies may incur significant environmental impacts over their life cycle, while having environmental benefits during their use. This paper presents results of a Life Cycle Assessment (LCA) of a proposed type of nanophotovoltaic, quantum dot photovoltaic (QDPV) module. The LCA is confined to the stages of raw materials acquisition, manufacturing, and use. The impacts of QDPV are compared with other types of PV modules and energy sources - both renewable and nonrenewable. To provide a comprehensive comparative assessment, QDPV modules were compared with mature as well as emerging PV types for which data are available. Comparative assessment with other types of energy sources includes coal, oil, lignite, natural gas, diesel, nuclear, wind, and hydropower.QDPV modules may have the potential to overcome two current barriers of solar technology: low efficiencies and high manufacturing costs. If higher efficiencies are realized, QDPV modules could pave the way to large scale implementation of solar energy, helping nations move toward greater energy independence. On the other hand, candidate materials as quantum dots for solar cell applications are mostly compound semiconductors such as cadmium selenide, cadmium telluride, and lead sulfide which may be toxic and for which renewable options are limited. Toxic effects of these materials may be exacerbated by their nanoscale features.The LCA was carried out using the software SimaPro, and the Ecoinvent Life Cycle Inventory (LCI) database supplemented with available literature and patent information. Our results indicate that while QDPV modules have shorter Energy PayBack Time (EPBT), lower Global Warming Potential (GWP), SOx and NOx emissions than other types of PV modules, they have higher heavy metal emissions, underscoring the need for investigation of emerging technologies, especially nano-based ones, from a life cycle perspective. QDPV modules are better in all impact categories assessed than carbon-based energy sources but they have longer EPBT than wind and hydropower and higher GWP. 相似文献
777.
Risk assessment on disinfection by-products of drinking water of different water sources and disinfection processes 总被引:3,自引:0,他引:3
The occurrences of trihalomethanes (THMs) and haloacetics (HAAs) in the water supply in Beijing and Canada were investigated. The concentrations of THMs and HAAs in Beijing and Canada were below the maximum contaminant levels specified by the USEPA and WHO standards. The multi-pathway risk assessment (assessed through oral ingestion, dermal absorption and inhalation exposure to drinking water) was used to assess the cancer risk and the hazard index of THMs and HAAs from fifteen waterworks in Beijing, China and three treatment plants using different disinfection processes in Canada. Residents in Beijing and residents who were served by three treatment plants using different disinfection processes in Canada had a higher risk of cancer through oral ingestion than through the other two pathways. The cancer risk resulted from disinfection by-products (DBPs) was 8.50E-05(for males), 9.25E-05(for females) in Beijing, China, while it was 1.18E-04, 1.44E-04 in Canada. The risk was higher when water treatment plants used surface water source than when they used ground water source and mixture water source in Beijing. The risk showed different changes in three treatment plants using different disinfection processes in Canada. The lifetime cancer risk for THMs followed the order: Plant 2>Plant 1>Plant 3. And, the lifetime cancer risk for HAAs was: Plant 1>Plant 2>Plant 3. 相似文献
778.
779.
780.
为了促进西北干旱区中小城市的快速、稳定的发展,解决该地区中小城市的水资源短缺问题,以水价作为出发点,充分利用水价格的经济杠杆作用,制定出该地区中小城市的水价。以西北干旱区中具有代表性的城市石河子为例,通过实地调研,得到石河子居民、居民生活用水情况、现行水价、居民家庭节水情况、居民的心理承受水价以及平时生活的节水意识等情况,通过分析,得出居民的心理承受偏低,现行水价仍有一定的上调空间,调价范围为1.58~2.31元/m3,最高可调至4.11元/m3。结合石河子的水价,为西北干旱区的中小城镇的水价改革、提高水资源的利用率等提出一些切实可行的建议。 相似文献