Two-phase modeling of sediment clouds

A sediment cloud release in stagnant ambient fluid occurs in many engineering applications. Examples include land reclamation and disposal of dredged materials. The detailed modeling of the distinct characteristics of both the solid and fluid phases of the sediment cloud is hitherto unavailable in the literature despite their importance in practice. In this paper, the two-phase mixing characteristics of the sediment cloud are investigated both experimentally and theoretically. Experiments were carried out to measure the transient depth penetration and the lateral spread of the sediment cloud and its entrained fluid using the laser induced fluorescence technique, with a range of particle sizes frequently encountered in the field (modeled at laboratory scale). A two-phase model of the sediment cloud that provides detailed predictions of the mixing characteristics of the individual phases is also proposed. The entrained fluid characteristics are solved by an integral model accounting for the buoyancy loss (due to particle separation) in each time step. The flow field induced by the sediment cloud is approximated by a Hill’s spherical vortex centered at the centroid and with the size of the entrained fluid. The particle equation of motion under the effect of the induced flow governs each computational particle. A random walk model using the hydrodynamic diffusion coefficient is used to account for the random fluctuation of particles in the dispersive regime. Overall, the model predictions of the two-phase mixing characteristics are in good agreement with the experimental data for a wide range of release conditions.     

Quinone profiles of microbial communities in sediments of Haihe River�CBohai Bay as influenced by heavy metals and environmental factors

A total of 11 sediment samples were collected from the sites along Haihe River?CBohai Bay, with site 1 at the beginning of Haihe River and site 11 in Bohai Bay, about 150 km away from site 1. Quinone profiles were used for the analysis of microbial community as influenced by pollutants in water and sediments, such as heavy metals, and other environmental factors. Nineteen species of quinones were found at site 1 while only six species at sites 10 and 11. Both the diversity of quinone species (DQ) and the number of quinones were higher in the sediments from Haihe River and the near-sea area of Bohai Bay than in those from the deep-sea area. The ?? diversity values were significantly higher, while Jaccard indexes of similarity were much lower among non-contiguous pairs of sites as compared with the contiguous ones. Cluster analysis indicated that quinone profiles may be grouped into two main clusters (sites 1?C7 and sites 8?C11), and there were higher similarities within the groups than between groups. Quinone species composition varied at different sites. Ubiquinones such as UQ-8, UQ-9, and UQ-10 and menaquinones such as MK-6, MK-7, MK-8 were isolated from all the sites and accounted for the largest proportions. Pearson correlation analysis revealed that both the number of quinone species and DQ correlated positively with total organic carbon contents in water and sediments, but negatively correlated with salinity and electroconductivity and did not correlate significantly with heavy metal contents in water.     

Effectiveness of protected areas for vertebrates based on taxonomic and phylogenetic diversity

Establishing protected areas is the primary goal and tool for preventing irreversible biodiversity loss. However, the effectiveness of protected areas that target specific species has been questioned for some time because targeting key species for conservation may impair the integral regional pool of species diversity and phylogenetic and functional diversity are seldom considered. We assessed the efficacy of protected areas in China for the conservation of phylogenetic diversity based on the ranges and phylogenies of 2279 terrestrial vertebrates. Phylogenetic and taxonomic diversity were strongly and positively correlated, and only 12.1–43.8% of priority conservation areas are currently protected. However, the patterns and coverage of phylogenetic diversity were affected when weighted by species richness. These results indicated that in China, protected areas targeting high species richness protected phylogenetic diversity well overall but failed to do so in some regions with more unique or threatened communities (e.g., coastal areas of eastern China, where severely threatened avian communities were less protected). Our results suggest that the current distribution of protected areas could be improved, although most protected areas protect both taxonomic and phylogenetic diversity.     

A Comparison Study of Wheat Gluten Composites Filled with Dialdehyde Starch and Native Starch

Environmentally friendly green composites were prepared by blending Wheat gluten (WG) as matrix, dialdehyde starch (DAS) as filler and glycerol as plasticizer followed by compression molding of the mixture at 110 °C. The properties of the WG/DAS composite are compared with those of the WG/native wheat starch (NWS) composites. While tensile strength and strain at break decrease with increasing NWS content in the WG/NWS composites, a small content of DAS could improve tensile strength and strain at break simultaneously in the WG/DAS composites. The WG/DAS composites exhibit reduced moisture absorption in comparison with the WG/NEW composites. Formation of chemical bonding between DAS and WG is beneficial for the dispersion of DAS in the WG matrix and WG/DAS composites exhibit improved mechanical properties and reduced moisture absorption over the WG/NWS composites.     

Biogeochemistry of two types of permeable reactive barriers, organic carbon and iron-bearing organic carbon for mine drainage treatment: Column experiments

Permeable reactive barriers (PRBs) are an alternative technology to treat mine drainage containing sulfate and heavy metals. Two column experiments were conducted to assess the suitability of an organic carbon (OC) based reactive mixture and an Fe⁰-bearing organic carbon (FeOC) based reactive mixture, under controlled groundwater flow conditions. The organic carbon mixture contains about 30% (volume) organic carbon (composted leaf mulch) and 70% (volume) sand and gravel. The Fe⁰-bearing organic carbon mixture contains 10% (volume) zero-valent iron, 20% (volume) organic carbon, 10% (volume) limestone, and 60% (volume) sand and gravel. Simulated groundwater containing 380 ppm sulfate, 5 ppm As, and 0.5 ppm Sb was passed through the columns at flow rates of 64 (the OC column) and 62 (the FeOC column) ml d^− 1, which are equivalent to 0.79 (the OC column) and 0.78 (the FeOC column) pore volumes (PVs) per week or 0.046 m d^− 1 for both columns. The OC column showed an initial sulfate reduction rate of 0.4 µmol g (OC)^− 1 d^− 1 and exhausted its capacity to promote sulfate reduction after 30 PVs, or 9 months of flow. The FeOC column sustained a relatively constant sulfate reduction rate of 0.9 µmol g (OC)^− 1 d^− 1 for at least 65 PVs (17 months). In the FeOC column, the δ³⁴S values increase with the decreasing sulfate concentration. The δ³⁴S fractionation follows a Rayleigh fractionation model with an enrichment factor of 21.6‰. The performance decline of the OC column was caused by the depletion of substrate or electron donor. The cathodic production of H₂ by anaerobic corrosion of Fe probably sustained a higher level of SRB activity in the FeOC column. These results suggest that zero-valent iron can be used to provide an electron donor in sulfate reducing PRBs. A sharp increase in the δ¹³C value of the dissolved inorganic carbon and a decrease in the concentration of HCO₃⁻ indicate that hydrogenotrophic methanogenesis is occurring in the first 15 cm of the FeOC column.     

城市交通环境中NO_X浓度和噪声相关性的探讨

为了研究交通环境中NOX浓度和噪声的相关性 ,探索一种更为简洁的环境监测手段解决城市道路交通环境问题 ,在和兴路上沿道路横断面布点 ,对NOX浓度和噪声进行监测。实验表明 ,在交通环境中 ,对于同一点不同时刻的NOX浓度和噪声值有一定的相关性 ,而对同一时刻不同点则无明显的相关性。     

天然气集配气站综合防雷技术改造

随着天然气生产向自动化、网络化、智能化方向的迅猛发展,大部分天然气集配气站都建立和完善了自动计量、视频监控、生产数据传输、无线通讯等系统。但是随着电气仪表设备和数据线的增多,系统受雷击或因雷电影响受损的概率陡然增加,特别是近几年,天然气集配气站内计量、控制系统设备频繁出现雷击损坏现象。因此,对天然气集配气站实施综合防雷技术改造十分必要。     

火灾危险源与火灾隐患之辨析

通过归纳总结危险源定义和分类,引申出火灾危险源的定义和分类.就火灾隐患定义在不同领域的运用提出了广义和狭义火灾隐患之分,并就火灾危险源与火灾隐患之间的关系阐述了一些观点.     

天然气水合物的灾害效应

天然气水合物是21世纪理想的后继替代能源,同时也是一种危险能源。阐明了天然气水合物与全球气候变暖、海洋灾害、百慕大三角之谜之间的内在联系,指出在开发利用天然气水合物时必须有足够的防范意识和技术措施。