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871.
在建筑火灾和一些紧急突发事件中,特殊人群不能使用正常人的紧急疏散通道,也不能达到正常人的疏散速度,而这个问题在目前的消防设计和消防规范中基本上没有得到解决.在分析特殊人群疏散行为规律的基础上,选取医院住院楼的标准层进行了疏散模拟,得出了一些重要结果,对疏散设计具有指导作用.最后提出了特殊人群的疏散设计方法,主要包括AORS系统和特殊报警系统的设计. 相似文献
872.
鱼类性别分化是在性别决定机制的控制下,鱼类未分化的性腺向卵巢或精巢发育,并出现第2性征的过程,受自身内分泌系统的精确调控。环境内分泌干扰物能通过干扰内源激素的合成、释放、转运、代谢、结合和作用等过程影响鱼类的内分泌机能,从而对鱼类的性别分化产生影响。介绍了鱼类性别分化的模式和过程以及内分泌系统对鱼类性别分化的调控作用,综述了环境内分泌干扰物对鱼类性别比例、配子发生、性腺发育和第2性征的影响,从性类固醇激素的合成以及性别分化相关基因的表达两个方面探讨了环境内分泌干扰物影响鱼类性别分化的作用机制,并展望了该领域未来的研究方向。 相似文献
873.
Panyue ZHANG Tian WAN Guangming ZHANG 《Frontiers of Environmental Science & Engineering》2012,6(5):753-760
Gravitational thickening is the prevailing method to reduce sludge volume but the process is slow and usually requires addition of polyelectrolyte(s). This paper investigated the potential benefits of sonication on enhancing the sludge gravitational thickening with very low energy dose, so called “weak ultrasound”. Results showed that weak sonication significantly changed the sludge settlability and the main mechanism was release of the loosely bounded extracellular polymeric substances. The changes in sludge behaviors by sonication were strongly influenced by power density and sonication duration. Lower sound frequency was slightly better than higher frequency. Weak sonication (<680 kJ·kg-1 DS) improved the sludge gravitational thickening while high ultrasonic energy deteriorated the process. Considering both the sludge thickening efficiency and energy consumption, the optimum conditions were 0.15 W·mL-1, 7 s, and 25 kHz. Under such conditions, the energy dose was only 155 kJ·kg-1 DS, much lower than literature reports, and the sludge settling time was shortened from 24 h to 12?h. Weak sonication could substitute expensive polyelectrolyte coagulant for sludge thickening. Combination of weak sonication and polyelectrolyte could further reduce the settling time to 6 h. The final water content of the thickened sludge was not changed after sonication or polyelectrolyte addition. 相似文献
874.
Mingsong WU Junli HUANG Yuling ZHANG Shijie YOU Shaofeng LI Zhilin RAN Yu TIAN 《Frontiers of Environmental Science & Engineering》2012,6(1):75-81
Microcystins, which represents one kind of cancerogenic organic compounds, is abundant in eutrophication water. The effects of reaction factors on chlorine dioxide (ClO2) for removal of low-concentration Microcystin-LR, Microcystin-RR, and Microcystin-YR in water as well as the reaction mechanisms was investigated by using enzyme-linked immunosorbent assay (ELISA) kit and gas chromatography–mass spectrometry (GC-MS). The results showed that MC-LR, MC-RR, and MC-YR could be efficiently decomposed by ClO2. The degradation efficiency was shown positively correlated to the concentration of ClO2 and reaction time; while the effect of reaction temperature and pH is slight. The kinetic constants and activation energies of the reaction of MC-LR, MC-RR, and MC-YR with ClO2 are determined as 459.89, 583.15, 488.43 L·(mol·min)-1 and 64.78, 53.01, 59.15 kJ·mol-1, respectively. As indicated by high performance liquid chromatography mass spectrometer (HPLC-MS) analysis, degradation should be accomplished via destruction of Adda group by oxidation, with the formation of dihydroxy substituendums as end products. This study has provided a fundamental demonstration of ClO2 serving as oxidizing disinfectant to eliminate microcystins from raw water source. 相似文献
875.
2013~2014年北京市NO2时空分布研究 总被引:2,自引:0,他引:2
根据2013~2014年北京市NO2监测数据,对比分析了全年及重污染日NO2时空分布特征.结果表明:2013年NO2平均浓度为56μg/m3,2014年北京市NO2年均浓度为56.7μg/m3.年均及重污染日NO2月均浓度均呈波浪型分布,日变化呈双峰型分布;空间分布上北部及西部山区NO2浓度明显低于中心城区及南部地区. NO2浓度与PM2.5、CO、NO呈正相关关系,与O3、OX无明显相关性;全年NO2光解速率峰值平均在0.105/min左右,重污染日光解速率峰值平均在0.026/min左右;全年及重污染期间,氮氧化速率分别为0.142±0.061、0.190±0.036;高浓度NO2既有利于O3生成,又对重污染的形成起到了促进作用;重污染日特定条件下北京市NO2的两种转化机制以转化为NO3-过程为主导.经计算2000~2014年北京市机动车的保有量与NO2浓度的相关系数R为-0.84,机动车NOx排放量对北京市NO2浓度的变化有显著的影响. 相似文献
876.
针对2012年在福建沿海致鲍鱼大量死亡、造成了巨大经济损失的米氏凯伦藻赤潮,为验证鲍鱼短时间内大量死亡的原因是否来源于米氏凯伦藻自身的毒性效应,本文初步研究了不同环境条件下,分离自赤潮现场的一株米氏凯伦藻(Karenia mikimotoi)对皱纹盘鲍(Haliotis discus hannai)的急性毒性效应。实验过程中,监测了曝气与非曝气条件下,环境因素中氨氮(TAN)、pH、DO的变化。研究发现,曝气条件下,实验体系中DO的变动范围为7.3~7.8 mg/L,pH的变动范围为7.5~8.2,TAN浓度的变动范围为0.0035~0.084 mg/L(能维持贝类正常生存),此时米氏凯伦藻趋近于赤潮现场藻细胞数量时(3107/L),鲍鱼48 h死亡率为33.3%,96 h内死亡率达100%,说明此时鲍鱼的急剧死亡是由米氏凯伦藻本身的毒性效应引起的。在非曝气条件下, DO由7.1 mg/L降低至1.8 mg/L,实验体系中pH的变动范围为7.2~8.1,TAN的变动范围为0.007~0.051 mg/L,此时米氏凯伦藻藻细胞数量为3107/L时,鲍鱼16 h内死亡率达100%,说明低氧的环境条件可以导致赤潮对鲍鱼的毒性效应加剧。由此可以推测,赤潮发生时皱纹盘鲍短时间内的大量死亡与米氏凯伦藻本身的毒性效应有关,而低氧等环境条件可以导致毒性效应加剧。 相似文献
877.
Tian WAN Guangming ZHANG Fengwei DU Junguo HE Pan WU 《Frontiers of Environmental Science & Engineering》2014,8(6):967-972
An innovative advanced wastewater treatment process combining biologic aerated filter (BAF) and sulfur/ ceramisite-based autotrophic denitrification (SCAD) for reliable removal of nitrogen was proposed in this paper. In SCAD reactor, ceramisite was used as filter and Ca (HCO3)2 was used for supplying alkalinity and carbon source. The BAF-SCAD was used to treat the secondary treatment effluent. The performance of this process was investigated, and the impact of temperature on nitrogen removal was studied. Results showed that the combined system was effective in nitrogen removal even at low temperatures (8℃). Removal of total nitrogen (TN), NH4+ -N, NO3-N reached above 90% at room temperature. Nitrification was affected by the temperature and nitrification at low temperature (8℃) was a limiting factor for TN removal. However, denitrification was not impacted by the temperature and the removal of NO3 -N maintained 98% during the experimental period. The reason of effective denitrification at low temperature might be the use of easily dissolved Ca(HCO3)2 and high-flux ceramisite, which solved the problem of low mass transfer efficiency at low temperatures. Besides, vast surface area of sulfur with diameter of 2-6 mm enhanced the rate of microbial utilization. The removal of nitrate companied with the production of SO42-, and the average concentration of SO27 was about 240mg.L^-1. These findings would be beneficial for the application of this process to nitrogen removal especially in the winter and cold regions. 相似文献
878.
879.
880.
国外旅游生态效率研究综述 总被引:9,自引:3,他引:6
旅游生态效率由生态效率概念衍生而来,是一个描述旅游单位经济产出环境影响大小的变量。提升旅游生态效率可以获得双向效应,也就是在创造新的市场就业机会的同时,降低成本和减少环境影响。国外旅游生态效率相关研究成果集中于以下几个方面:生态效率的概念、特征与理论模型;旅游生态效率理论的演化与应用;旅游生态效率提升的规划及措施;旅游者对生态效率战略的感知与态度;旅游生态效率规划实施的动力与阻力等。国外旅游生态效率研究具有研究范围和视角比较宽泛、研究方法手段丰富多样、研究案例较为典型、研究结论实践应用价值较大等特征。深化旅游生态效率的理论研究和案例分析,不仅为旅游可持续发展研究开拓了一个新方向,也为低碳旅游、旅游碳交易、旅游碳税等政策的制定提供了科学依据,具有重要的理论创新和实践应用价值。 相似文献