Quantitative evaluation of ecological toxicity effect of real heavy metal combined pollution in site soil

Quantitative evaluation of ecological effect of combined pollution of heavy metals in real site soil is considered as a great issue in ecological risk assessment of contaminated sites. In this work, a quantitative ecological assessment approach for combined contaminated soil in field by heavy metals was developed based on “top-down” and “bottom-up” knowledge, which was made up of three steps, namely, “screening of effective biomarkers-identification of dominant pollutants-evaluation of joint effect of different exposure types/contaminants”. Finally, taking an abandoned electronic planting site in Jiangsu Province as a case, the developed approach was verified using soil microcosm of earthworm. Results of the experiment by taking the biomarkers including malondialdehyde (MDA), metallothionein (MT), catalase (CAT), superoxide dismutase (SOD), reduced glutathione (GSH)as effect endpoints, suggested that the bioaccumulation of main heavy metal contaminants including Cd, Cu, Zn, Ni, Pb and Cr by earthworms ranged in an order: Cd>Cu>Zn>Ni>Pb>Cr. Principal component analysis (PCA)revealed that GSH, CAT and MDA were screened as effective biomarkers, and heavy metals Cd and Zn were dominant contaminants. It was found that there was a significant multivariate linear relationship between the change of GSH and concentrations of total Cd and DTPA-Zn in soil. And the change of MDA could be predicted by DTPA-Cd in soil. The change of CAT activity was predictive by the total Zn in soil and the bioaccumulated Zn in earthworm. Evaluation of half effect dose (EC50) based on the site-specific soil properties and heavy metal contamination characteristics revealed that the sensitivity of the 3 screened effective biomarkers ranged in an order: GSH>CAT>MDA. Interactions will occur in between different heavy metals and exposure types (e.g., between soil total Cd and DTPA-Zn corresponding to GSH change), and (or) in between different exposure types of the same heavy metal (e.g., between soil total Zn and bioaccumulated Zn corresponding to the change of CAT activity)

Bi-velocity discrete particle swarm optimization and its application to multicast routing problem in communication networks

This paper proposes a novel bi-velocity discrete particle swarm optimization (BVDPSO) approach and extends its application to the NP-complete multicast routing problem (MRP). The main contribution is the extension of PSO from continuous domain to the binary or discrete domain. Firstly, a novel bi-velocity strategy is developed to represent possibilities of each dimension being 1 and 0. This strategy is suitable to describe the binary characteristic of the MRP where 1 stands for a node being selected to construct the multicast tree while 0 stands for being otherwise. Secondly, BVDPSO updates the velocity and position according to the learning mechanism of the original PSO in continuous domain. This maintains the fast convergence speed and global search ability of the original PSO. Experiments are comprehensively conducted on all of the 58 instances with small, medium, and large scales in the OR-library (Operation Research Library). The results confirm that BVDPSO can obtain optimal or near-optimal solutions rapidly as it only needs to generate a few multicast trees. BVDPSO outperforms not only several state-of-the-art and recent heuristic algorithms for the MRP problems, but also algorithms based on GA, ACO, and PSO

Analysis and Design of Leaky-Wave Antenna with Low SLL Based on Half-Mode SIW Structure

This paper presents a novel leaky-wave antenna based on the Half-Mode Substrate Integrated Waveguide (HMSIW) structure with low side lobe level. The effect of the structural parameters of the LWAs on the radiation performances is studied. Using beam-forming technique, the leakage loss factor α along the radiation aperture is designed in a tapered way by controlling the aperture depth along the structure. This controls the radiated power along the antenna aperture and finally achieves the radiation pattern with low SLL. Furthermore, the antenna structure is optimized to get an even lower SLL

Differential evolution with two-level parameter adaptation

The performance of differential evolution (DE) largely depends on its mutation strategy and control parameters. In this paper, we propose an adaptive DE (ADE) algorithm with a new mutation strategy DE/lbest/1 and a two-level adaptive parameter control scheme. The DE/lbest/1 strategy is a variant of the greedy DE/best/1 strategy. However, the population is mutated under the guide of multiple locally best individuals in DE/lbest/1 instead of one globally best individual in DE/best/1. This strategy is beneficial to the balance between fast convergence and population diversity. The two-level adaptive parameter control scheme is implemented mainly in two steps. In the first step, the population-level parameters F p and CR p for the whole population are adaptively controlled according to the optimization states, namely, the exploration state and the exploitation state in each generation. These optimization states are estimated by measuring the population distribution. Then, the individual-level parameters F i and CR i for each individual are generated by adjusting the population-level parameters. The adjustment is based on considering the individual's fitness value and its distance from the globally best individual. This way, the parameters can be adapted to not only the overall state of the population but also the characteristics of different individuals. The performance of the proposed ADE is evaluated on a suite of benchmark functions. Experimental results show that ADE generally outperforms four state-of-the-art DE variants on different kinds of optimization problems. The effects of ADE components, parameter properties of ADE, search behavior of ADE, and parameter sensitivity of ADE are also studied. Finally, we investigate the capability of ADE for solving three real-world optimization problems

Application of stress index in evaluating toxicological response of soil microbial community to contaminants in soils

Toxic effects of chemical contaminants on soil microbial community structure and function have been widely studied. However, it is difficult to assess risks regarding soil microbial toxicity. In the ratio to reference approach, the stress index (SI) is used to indicate the relative change of biological response of organisms compared to a reference. In this study, the SI approach was used to assess the soil microbial stress levels of multiple heavy metal contaminated urban soil in three sites. Soil microbial community functional parameters suggested that two heavy metal contaminated sites (G and D) had apparently higher stress indexes relative to the reference site, N. Use of those similar microbial community functional parameters revealed that parameters such as N and C mineralization and alkaline phosphatase activity were sensitive to the addition of the herbicide Siduron. Soil G, which had the highest microbial stress index, showed more severe impairment when amended with Siduron, while soil N and soil D showed dose-dependent responses to Siduron. Overall, the results of this study indicated that, when compared with direct use of real data describing microbial parameters, use of SI in ecological risk assessment is more indicative and helpful.</p

Factors Influencing Earthworm Fauna in Parks in Megacity Beijing, China: An Application of a Synthetic and Simple Index (ESI)

Complicated factors in urban areas have been reported to impact the density, biomass, and diversity of earthworm fauna. Urban parks provide essential habitats for earthworm fauna. However, how earthworm fauna are impacted by park traits, such as construction age, distance to city center, visitor volumes, sizes of greenspaces/parks, and attractiveness, etc., still remains unknown. These traits are well characterized by the impacts of urbanization intensity and administration quality of parks in megacities. Therefore, 16 parks with gradients of construction ages and geographical locations in Beijing city were selected for investigation. Furthermore, an earthworm synthetic and simple index (ESI) for characterizing earthworm community has been developed to compensate for the lack of robustness by using single ecological indexes. The results showed that earthworm population density (38.6 ind/m2) and biomass (34.0 g/m2) in parks were comparable to those in other land use types in Beijing. Ecological groupings were dominated by disturbance-tolerant endogeic and deep soil-inhabiting anecic groups, and most of them were adults. The earthworm population was influenced by urbanization intensity, while the earthworm community composition, species biodiversity, and ESI were affected by administration quality of parks. The soil moisture and microbial biomass carbon were the key factors in shaping earthworm assemblages. ESI could be employed as an effective indicator in depicting character of earthworm fauna. This study highlighted the impacts of park traits on earthworms in urban parks. The variation in park traits that influence earthworm fauna was probably attributed to soil properties

A New Kind of Circular Polarization Leaky-Wave Antenna Based on Substrate Integrated Waveguide

A new kind of circular polarization leaky-wave antenna with N-shaped slots cut in the upper side of substrate integrated waveguide (SIW) is investigated and presented. The radiation pattern and polarization axial ratio of the leaky-wave antenna are studied. The results show that the width of N-shaped slots has significant effect on the circular polarization property of the antenna. By properly choosing structural parameters, the SIW based leaky-wave antenna can realize circular polarization with excellent axial ratio in 8 GHz satellite band

Reduction of the In-Band RCS of Microstrip Patch Antenna by Using Offset Feeding Technique

This paper presents a method for implementing a low in-band scattering design for microstrip patch antennas based on the analysis of structural mode scattering and radiation characteristics. The antenna structure is first designed to have the lowest structural mode scattering in a desired frequency band. The operating frequency band of the antenna is then changed to coincide with that of the lowest structural mode scattering by adjusting the feed position on the antenna (offset feeding) to achieve an antenna with low in-band radar cross section (RCS). In order to reduce the level of cross polarization of the antenna caused by offset feeding, symmetry feeding structures for both single patch antennas and two-patch arrays are proposed. Examples that show the efficiency of the method are given, and the results illustrate that the in-band RCS of the proposed antennas can be reduced by as much as 17 dBsm for plane waves impinging from the normal direction compared to patch antennas fed by conventional methods