Removal of Pb by EDTA-washing in the presence of hydrophobic organic contaminants or anionic surfactant

Heavy metals and organic contaminants often coexist in contaminated soils, of which the remediation requires a combined or sequential use of surfactant and chelant in chemical-enhanced soil washing. This study investigated the Pb removal by EDTA-washing in the presence of the coexisting hydrophobic organic contaminants (marine diesel fuel, MDF) or anionic surfactant (sodium dodecyl sulfate, SDS). The results of batch experiments indicated a negative impact of MDF on Pb removal, whereas a positive or negative influence of SDS depending on the molar ratio of [EDTA]:[Pb]. The surface of MDF-contaminated soil was partially covered by free-phase MDF limiting the interaction between EDTA and sorbed Pb, especially at [EDTA]:[Pb]=1:1. Despite the ability of SDS itself for extracting Pb to some extent, probably through electrostatic interaction and dissolution of soil organic matter (SOM), the addition of SDS into EDTA solution only slightly enhanced Pb removal at [EDTA]:[Pb]=1:1 but inhibited at [EDTA]:[Pb]=2:1. This may be attributed to the SOM dissolution and the potential formation of ternary surface complexes, respectively. Along the same line of reasoning, it was not surprising that the optimal sequence for Pb removal was EDTA- followed by SDS-washing rather than the reverse sequence or simultaneous EDTA- and SDS-washing.     

CFD analysis of ventilation effectiveness in a public transport interchange

A study was conducted into the ventilation effectiveness of a ventilation system within a public transport interchange (PTI) in Hong Kong. A computational fluid dynamics (CFD), steady state computational model of the PTI was used to investigate and predict the typical pollutant emission pattern for buses. In Hong Kong, the displacement ventilation (DV) scheme is often employed for the PTI. The numerical simulation investigates the effectiveness of the DV system in removing pollutants from the occupied zone. An alternative model is proposed where the supply is located at the ceiling and the exhausts are located at the lower part of the columns. It was found that both systems could adequately ventilate the PTI; however, the ceiling based air supply system is able to provide improved thermal comfort and indoor air quality (IAQ).     

Selective oxidation of cyclohexane in supercritical carbon dioxide

A feasibility study into the novel concept of using molecular oxygen to carry out one-step catalytic oxidation of cyclohexane to adipic acid in supercritical carbon dioxide over two types of catalysts, namely and Ag polyoxometallate, the silver decamolybdodivanadophosphate was carried out. Poor activity and selectivity towards adipic acid were initially noted over the aqueous micellar catalyst for the cyclohexane oxidation in supercritical carbon dioxide while under comparable conditions, the same catalyst gave a high activity for alkylaromatics oxidation to corresponding acids. It was later found that the adipic acid, being the extremely polar oxidised products, was virtually insoluble in the supercritical phase, which was rapidly degraded to carbon oxides after its prolonged contact with catalyst and O₂. Thus, the one-step cyclohexane oxidation to adipic acid with good selectivity can only be achieved by modifying the solvent with acetic acid or methanol, which enabled isolation of the acid from further oxidation. On the other hand, , in methanol modified supercritical carbon dioxide gave an impressive selectivity for cyclohexane conversion to other oxygenates.     

Using social network analysis to combat counterfeiting

Counterfeiting undoubtedly produces great harm to companies and the society. This article presents a study on the application of social network analysis (SNA) to combating this problem. The supply chain can be viewed as a network of parties involved in delivering value to consumers. Normally, SNA is used to analyse relationships between people. In this study, it is utilised to analyse supply chains for the identification of parties that are likely to be involved in counterfeiting activities. After identifying the suspects in a supply chain, the company can deter and detect counterfeiting by tightening surveillance on these parties. The feasibility of using SNA as an anti-counterfeiting tool is investigated in a case study, the findings of which indicate that SNA can effectively help companies to prevent sources of counterfeit products from infiltrating into the supply chain. Problematic parties can be identified by characterising the following features: high degree of centrality, high closeness of centrality and high betweenness of centrality.     

A new Ka-band microstrip Y-junction circulator with a ferrite sphere

A novel microstrip circulator with a magnetized ferrite sphere is proposed for millimetre wave communications. A three-dimensional finite difference time-domain (FDTD) approach for the analysis of this ferrite sphere-based microstrip circulator is presented. The electromagnetic fields inside the ferrite junction are calculated by using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. Frequency-dependent insertion loss, isolation and reflection loss of circulator are calculated over a wide band of frequencies with a single FDTD run. Experimental results at the Ka-band are presented and compared with theoretical simulation. Good agreement is found between them.     

Modeling the heat diffusion process in the abiotic layers of green roofs

Green roofs have been increasingly installed to alleviate some common environmental problems. The thermal benefit of living vegetation on rooftop has been extensively studied. The individual and joint contribution of the non-living green roof layers, namely soil, rockwool (water storage) and plastic drainage layers, to thermal performance of green roof has seldom been assessed. This study evaluates the insulating and cooling effects of these abiotic materials. A one-dimensional theoretical model was developed to assess the heat diffusion process in the layers. The model was validated with empirical results from three experimental plots. A calibration procedure was successfully applied to determine key model parameters. The model can capture the most critical features of temperature variations and thermal performance of common abiotic green roof materials. The appreciable water-retention capacity of rockwool plays the dual role of supplying water to the soil to enhance evaporative cooling, and increasing the specific heat capacity of the green roof. The plastic drainage sheet with ample air spaces serves as an excellent thermal insulator. The model remains robust despite seasonal and weather variabilities. Our research findings contradict with some researches in the temperate region that the thermal dissipation in green roofs with dense vegetation is lower than thermally insulated bare roofs. The theoretical model could be used to simulate the micro-environmental conditions and predict the thermal performance of different materials to improve green roof design.     

Biophysical properties and thermal performance of an intensive green roof

Green roofs have been increasingly enlisted to alleviate urban environmental problems associated with urban heat island effect and stormwater quantity and quality. Most studies focus on extensive green roofs, with inadequate assessment of the complex intensive type, subtropical region, and thermal insulation effect. This study examines the physical properties, biological processes, and thermal insulation performance of an intensive green roof through four seasons. An experimental woodland installed on a Hong Kong building rooftop was equipped with environmental sensors to monitor microclimatic and soil parameters. The excellent thermal performance of the intensive green roof is verified. Even though our site has a 100 cm thick soil to support tree growth, we found that a thin soil layer of 10 cm is sufficient to reduce heat penetration into building. Seasonal weather variations notably control transpiration and associated cooling effect. The tree canopy reduces solar radiation reaching the soil surface, but the trapped air increases air temperature near the soil surface. The substrate operates an effective heat sink to dampen temperature fluctuations. In winter, the subtropical green roof triggers notable heat loss from the substrate into the ambient air, and draws heat upwards from warmer indoor air to increase energy consumption to warm indoor air. This finding deviates from temperate latitude studies. The results offer hints to optimize the design and thermal performance of intensive green roofs.     

Infrared colloidal lead chalcogenide nanocrystals: synthesis, properties, and photovoltaic applications

Simple solution phase, catalyst-free synthetic approaches that offer monodispersed, well passivated, and non-aggregated colloidal semiconductor nanocrystals have presented many research opportunities not only for fundamental science but also for technological applications. The ability to tune the electrical and optical properties of semiconductor nanocrystals by manipulating the size and shape of the crystals during the colloidal synthesis provides potential benefits to a variety of applications including photovoltaic devices, light-emitting diodes, field effect transistors, biological imaging/labeling, and more. Recent advances in the synthesis and characterization of colloidal lead chalcogenide nanocrystals and the achievements in colloidal PbS or PbSe nanocrystals solar cells have demonstrated the promising application of infrared-emitting colloidal lead chalcogenide nanocrystals in photovoltaic devices. Here, we review recent progress in the synthesis and optical properties of colloidal lead chalcogenide nanocrystals. We focus in particular upon the size- and shape-controlled synthesis of PbS, PbSe, and PbTe nanocrystals by using different precursors and various stabilizing surfactants for the growth of the colloidal nanocrystals. We also summarize recent advancements in the field of colloidal nanocrystals solar cells based on colloidal PbS and PbSe nanocrystals.     

A Graphics Processing Unit Accelerated Genetic Algorithm for Affine Invariant Matching of Broken Contours

Past research works have demonstrated matching of fragmented contours can be effectively accomplished with the integration of genetic algorithms and migrant principle. Despite the success, the computation involved in the evaluation of the fitness function is substantial. To overcome this problem, a new formulation on the fitness evaluation targeted for graphics processing unit (GPU) has been developed and presented in this paper. Experimental results reveal that the proposed solution is capable of reducing the matching time while maintaining high success rates.