Search

As the connection between river and ocean, the estuaries are greatly affected by human activities and has sensitive and fragile ecological environment. In this study, the degree of contamination and potential ecological risk level of 8 heavy metals in the surface sediments of Oujiang Estuary were investigated. The results showed that Oujiang Estuary was moderately contaminated with heavy metals, and Cd was moderate even considerable contamination and potential ecological risks. The molecular diversity and community composition of total and active benthic foraminifera were revealed using hight-hroughput sequencing based on small subunit rDNA and rRNA amplification. A total of 19 genera for total benthic foraminifera were identified, while only 11 genera for active benthic foraminifera were found. The total benthic foraminifera community had higher species diversity and richness than those of active communities. Alveolinella, Nummulites, Parasorites, Globorotalia and Calcarina exhibited a significantly negative correlation with Cd, indicating that these species might be sensitive to Cd pollution. [ABSTRACT FROM AUTHOR]

Benthic foraminifera are good indicators for monitoring marine environmental pollution and recovery of marine ecosystem. In this study, high-throughput sequencing based on small subunit rDNA and rRNA amplifications was used to assess total and active benthic foraminifera diversity and community composition in intertidal sediments near China Resources Wenzhou Power Plant. The results showed that the closer to the power plant, the lower the diversity and richness of both total and active foraminifera are. The total assemblages had higher values of species diversity and richness than active communities. a total of 33 and 25 foraminifera genera were identified using DNA-based and RNA-based HTS, respectively. The dominant genera included Vellaria, Stainforthia and Miliammina in total foraminiferal communities, and became Ammonia, Miliammina and Notorotalia in active foraminiferal communities at the station slightly away from the power plant; while only one dominant genus, Haplomyxa, was detected close to the power plant. [ABSTRACT FROM AUTHOR]

Riverine systems are primary habitats for aquatic species. Great efforts have been made to understand interaction between aquatic organism and various environmental factors in specific reaches of a river, yet little was known about how to identify habitats in river networks. In this paper, a comprehensive approach was proposed for identification of aquatic habitats in hierarchical river systems in terms of integrated geocodes synthesized through over-layer of multiple factors such as geologic periods, climatic conditions, water sources, geomorphic characteristics and river patterns. Using this approach in the Yellow River Basin over an area of 758,600 km2, six groups of aquatic habitats were classified by clustering of 85 geocodes, and 313 sub-habitats were further identified by considering both surface composition (e.g., lithological features and soil texture) and topographic property (e.g., elevation and slope) in the loess geomorphic regions. Consequently, the contribution of the headwater streams to diversity of aquatic habitats among rivers and mid-sized rivers to the diversity within a river has been revealed by coupling of the geocode-based habitats and the river networks. The present study is of significance to efficient capture of habitat diversity and better understanding of biodiversity in rivers of different stream orders. [ABSTRACT FROM AUTHOR]

Natural frequencies and modal shapes of machine tools have position-dependent characteristics owing to their dynamic behaviors changing with the positions of moving parts. It is time-consuming and difficult to evaluate the dynamic behaviors of machine tools and their machining accuracy at different positions. In this paper, a Kriging approximation model coupled with finite element method is proposed to substitute the dynamic equations for obtaining the position-dependent natural frequencies of a machine tool, as well as relative positions between the tool and the workpiece during the machining process. Based on the proposed method, dynamic performance optimization design of the machine tool is conducted under the condition of minimum relative positions. Three case studies are illustrated to demonstrate the implementation of the proposed method. [ABSTRACT FROM AUTHOR]

The structural, elastic, dynamical and thermodynamic properties of CdXP2 (X = Si, Ge) with chalcopyrite semiconductors have been calculated by using the projector augmented wave method within the generalized gradient approximation. The obtained lattice constants and elastic constants of CdXP2 (X = Si, Ge) are compared with the available experimental and other theoretical results, and the agreements between them are quite well. Also, the elastic anisotropy of CdXP2 (X = Si, Ge) have been evaluated. In addition, the phonon dispersion curves and the corresponding phonon density of states of CdXP2 (X = Si, Ge) have been determined by virtue of a linear response approach to density functional perturbation theory method successfully. Finally, the Helmholtz free energy F, internal energy E, entropy S and the constant volume specific heat CV have also been predicted based on quasi-harmonic approximation. [ABSTRACT FROM AUTHOR]

The ground state parameters such as lattice constants, bulk modulus and elastic constants are calculated for chalcopyrite structure AgAlS2 by using density functional theory (DFT). The obtained lattice constants and elastic constants are agree well with available theoretical or experimental results. The bulk modulus B, shear modulus G, Young's modulus E and wave velocity of AgAlS2 are also obtained for the first time. In addition, the equation of state of AgAlS2 in the pressure range of 0-10 GPa and up to a temperature of 1000 K has also been obtained. [ABSTRACT FROM AUTHOR]