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771.
772.
The mechanisms for dust emission involve the saltation of sand-sized particles and the transfer of momentum from the atmosphere
to the surface. Roughness elements on aeolian surfaces influence the transfer of momentum through the partition of total momentum
flux into a pressure drag on roughness elements and a skin drag on substrate surface. The objective of this study is to better
understand the mechanisms for momentum transfer over rough surfaces and drag partition, so that better dust-emission parameterization
schemes can be developed. A large-eddy simulation model is implemented for the purpose. We perform computational simulations
of turbulent flows over individual and arrays of roughness elements. Further, we examine how roughness elements affect drag
partition and dust emission. The results lead to a possible new concept of dust emission over rough surfaces. 相似文献
773.
Shao Shuai Hu Bifeng Tao Yunhan You Qihao Huang Mingxiang Zhou Lianqing Chen Qiuxiao Shi Zhou 《Environmental geochemistry and health》2022,44(2):579-602
Environmental Geochemistry and Health - The source identification and apportionment of heavy metals (HMs) is a vital issue for restoring contaminated soil. In this study, qualitative approaches [a... 相似文献
774.
Stellite alloys, which have been widely used in the aerospace, automotive and chemical industries, are hard-to-cut cobalt-based materials. This study investigates the machinability of stellite 12 alloys with uncoated carbide cutting tool grades YG610 (K01-K10) and YT726 (K05-K10/M20) and SANDVIK coated carbide tool SNMG150612-SM1105 under dry cutting conditions. Both wear mechanisms and failure modes of the uncoated and coated tools were investigated with turning experiments. The results show that the coated tool SM1105 remarkably outperforms the uncoated tools; and the cutting tool YG610 generally outperforms YT726 under all cutting conditions. Built-up edge was found with YG610 in some cutting conditions and with SM1105 at cutting speed of 16 m/min. Tool surface burning marks were observed on YT726 at relatively higher cutting speeds. Wear develops slowly with coated tools SM1105 until VB reaches 0.2 mm at most conditions (except at v = 43 m/min, f = 0.25 mm/r). Excessive tool flank typically resulted in tool breakage at the cutting edge for uncoated tools. Abrasive and adhesive wear of cutting tools were observed at low cutting speeds while diffusion and chemical wear occurred at higher cutting speeds. 相似文献
775.
高校开设环境教育公共必修课探究 总被引:2,自引:0,他引:2
在高校中开设环境教育公共必修课,培养大学生的环境意识,提高环境素质,是实现可持续发展的一个重要措施。本文阐述了环境教育的内涵,论述了国内外高校环境教育的发展概况,分析了高校开设环境教育公共必修课的必要性。以济南市为例,对高校学生和教师分别进行了问卷调查,从学生的环境意识和环境行为、学校开设环境教育公共必修课的现状、师生对环境教育公共必修课的态度等方面进行了调查。结合调查结果。总结出中国高校环境教育公共必修课建设存在的主要问题,如高校对环境教育的重视不足、环境教育课程体系不合理、教学形式单一、师资力量薄弱等,并借鉴国外环境教育的经验,提出完善高校环境教育公共必修课的建议和措施。 相似文献
776.
以某化工生产企业废水为例,介绍了水解酸化-厌氧-SBR工艺处理高浓度苯甲酸类生产废水的工程实例,该工程设计规模为70m^3/d,综合进水CODcr高达15000mg/L。实践表明,该工艺处理苯甲酸类废水是一种经济有效的处理方法。利用水解酸化对废水进行预处理,不仅有效地去除了77%的CODcr,还大幅提高了废水的可生化性,使BOD5/COD值由原水的0.33升高到O.54,提高了废水的可生化性,减轻了后续生化处理的负荷,并使最终出水CODcr小于500mg/L,出水可达《污水综合排放标准》(GB8978~1996)三级排放标准。 相似文献
777.
用食藻虫引导沉水植物生态修复工程技术对上海市临港新城果园镇里塘河道富营养化水体进行了工程治理和生态修复,辅以种植沉水植物,采取开放式生态修复和治理。每月水质跟踪检测结果表明:该工程治理方法具有显著生态修复效果,水质得到明显改善;CODMn、TN、TP在最低平均值时分别比生态修复前下降了60.67%、85.36%、88.74%;氨氮、亚硝态氮和叶绿素a在生态修复中的最低平均值分别为0.088 mg/L、0.024 mg/L和5.31 mg/m3;试验期间,修复区水体TN、TP、NO2-N、NH4-N和CODMn显著低于对照区,水体透明度(SD)平均为150~180 cm,水质达到国家Ⅱ~Ⅲ类地表水水质标准。 相似文献
778.
Ju Zhang Yue Wang Zongyuan Shao Jing Li Shuting Zan Shoubiao Zhou Ruyi Yang 《环境科学学报(英文版)》2019,31(3):238-249
Microbes play important roles in the transport and transformation of selenium (Se) in the environment, thereby influencing plant resistance to Se and Se accumulation in plant. The objectives are to characterize the bacteria with high Se tolerance and reduction capacity and explore the significance of microbial origins on their Se tolerance, reduction rate and efficiency. Two bacterial strains were isolated from a naturally occurred Se-rich soil at tea orchard in southern Anhui Province, China. The reduction kinetics of selenite was investigated and the reducing product was characterized using scanning electron microscopy and transmission electron microscopy-energy dispersive spectroscopy. The bacteria were identified as Lysinibacillus xylanilyticus and Lysinibacillus macrolides, respectively, using morphological, physiological and molecular methods. The results showed that the minimal inhibitory concentrations (MICs) of selenite for L. xylanilyticus and L. macrolides were 120 and 220 mmol/L, respectively, while MICs of selenate for L. xylanilyticus and L. macrolides were 800 and 700 mmol/L, respectively. Both strains aerobically reduced selenite with an initial concentration of 1.0 mmol/L to elemental Se nanoparticles (SeNPs) completely within 36 hr. Biogenic SeNPs were observed both inside and outside the cells suggesting either an intra- or extracellular reduction process. Our study implied that the microbes from Se-rich environments were more tolerant to Se and generally quicker and more efficient than those from Se-free habitats in the reduction of Se oxyanions. The bacterial strains with high Se reduction capacity and the biological synthesized SeNPs would have potential applications in agriculture, food, environment and medicine. 相似文献
779.
HCl and SO_2 emission is one of the major concerns related to municipal solid waste incinerator(MSWI). In this study, a material flow analysis model was developed to estimate the HCl and SO_2 concentrations in the MSWI flue gases(FGs), and their concentrations in the full-scale MSWI were monitored. The calculated concentrations of HCl and SO_2 in the FG were 770–1300 mg/Nm~3 and 150–640 mg/Nm~3, respectively, in close agreement with the monitored values. More than 99% of Cl and 92% of S from the FG were captured into solid residues by the air pollution control(APC) systems. Moreover, since only 48.4%–67.5% of Cl and 21.3%–53.4% of S were transferred to the FG from the municipal solid waste(MSW), it was more reliable to estimate the source strengths and release amounts of HCl and SO_2 in the FG based on the amounts of Cl and S in the APC residues(AR) and exhaust gas rather than in the MSW. This simple method is easily applicable and the estimated results could provide scientific basis for the appropriate design and operation of the APC systems as well as corrosion control of heat recovery systems. 相似文献
780.
Methacrolein(MACR) and methyl vinyl ketone(MVK) are two major intermediate products from the photochemical oxidation of isoprene, the most important biogenic volatile organic compound. In addition, MACR and MVK have primary emissions. Investigating the sources and evolution of MACR and MVK could provide helpful information for the oxidative capacity of the atmosphere. In this study, hourly measurements of isoprene, MACR, and MVK were conducted at a receptor site in the Pearl River Delta region(PRD), i.e., the Heshan site(HS), from 22 October to 20 November, 2014. The average mixing ratios of isoprene,MACR and MVK were 151 ± 17, 91 ± 6 and 79 ± 6 pptv, respectively. The daily variations and the ratios of MVK/MACR during daytime and nighttime suggested that other sources besides isoprene photooxidation influenced the MACR and MVK abundances at the HS.Positive matrix factorization was utilized to resolve the sources of MACR and MVK. Five sources were identified and quantified, including biogenic emissions, biomass burning,secondary formation, diesel, and gasoline vehicular emissions. Among them, secondary formation made the greatest contribution to observed MACR and MVK with average contributions of ~ 45% and ~ 70%, respectively. Through the yields of secondary products from the oxidation of MACR and MVK by the OH radical and the concentrations of MACR and MVK, it was found that methylglyoxal and formaldehyde were the main oxidation products of MACR and MVK at the HS site. Overall, this study evaluated the roles of primary emissions on ambient levels of MACR and MVK and advanced the understanding of photochemical oxidation of MACR and MVK in the PRD. 相似文献