Search

ABSTRACT The effectiveness of using siliceous-aluminous fly ash and cement in solidifying Dunkirk marine sediments was investigated by means of laboratory tests to evaluate the compatibility of solidified material as [...]

Nitrogen and sulfur dual-doped mesoporous carbons were prepared through a facile template-mediated pyrolyzing method using poly(ethyleneimine) (PEI) as sources of nitrogen (N) and carbon (C), ferrous sulfate (FeSO4 7H2O) as both precursor of sulfur (S) and activation reagent along with nanoscaled silica as sacrificial supports. The as-prepared doped mesoporous carbons show perfect supercapacitive performances, which have been demonstrated by cyclic voltammetry and constant-current charge/discharge cycling techniques. The specific capacitance (SC) of the as-prepared electrode can reach 279 F/g at a current density of 1 A/g. Even at a high rate capability of 100 A/g, the electrode still shows the SC value as high as 240 F/g, retaining 86% of that at 1 A/g. Regarding the effect of electrolyte concentrations (1-6M KOH), 3 M KOH gives the best performance. The above results indicate that the doped mesoporous carbon electrodes developed in this work are promising for use in energy storage devices.

The increasing cost associated with high-quality materials has lead to the need for sediments to be treated and then used in road construction in the context of durable development. Therefore, the modification and stabilisation of Dunkirk marine sediments by using lime is necessary to study for their potential use in road construction. Based on the physical characteristics of untreated sediments, a series of laboratory tests to investigate the geotechnical properties of untreated sediments and lime-treated sediments, such as unconfined compressive strength tests, standard oedometer tests, direct shear tests and triaxial tests, were performed. Lime was added in percentages of 3% and 6%, by weight of dry sediments. The test results show a significant improvement in unconfined compressive strength and shear strength due to the addition of lime. From the strain–stress relationship of compressive strength tests, it can be found that the failure mode of solidified sediments develops gradually from plastic failure to brittle failure, while the failure strength increases and the failure strain decreases with lime content. Compared with untreated sediments, the shear strength parameters of solidified sediments determined by direct shear tests, such as internal friction angle and cohesion, are increased owing to the pozzolanic reaction between lime and clay minerals. Using the oedometer apparatus, it is observed that after lime treatment, the preconsolidation pressure, the coefficient of consolidation and the compression index are increased, while the swelling index is decreased. The characteristics of the deviator stress–axial strain relation and the pore water pressure distribution under different confining stresses are compared with untreated and treated sediments, and the effect of lime content on cohesion and internal friction angle determined by triaxial tests is discussed.

Poor housing conditions are known to be associated with infectious diseases such as high Coronavirus disease 2019 (COVID-19) incidences. Transmission causes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in poor housing conditions can be complex. An understanding of the exact mechanism of transmission can help to pinpoint contributing environmental issues. Here, we investigated a Hong Kong COVID-19 outbreak in early 2021 in four traditional Tong Lau houses with subdivided units. There are more than 80 subdivided units of less than 20 m2floor area each on average. With a total of 34 confirmed COVID-19 cases, the outbreak had an attack rate of 25.4%, being one of the highest attack rates observed in Hong Kong, and ranked among the highest attack rates in reported outbreaks internationally. Tracer gas leakage and decay measurements were performed in the drainage system and in the subdivided units to determine the transport of infectious aerosols by the owner-modified sophisticated wastewater drainage pipe networks and the poor ventilation conditions in some subdivided units. The results show that the outbreak was probably due to multiple transmission routes, i.e. by the drainage pipe spread of stack aerosols, which is enhanced by poor ventilation in the subdivided units.

A hybrid fiber amplifier (HFA) comprising an erbium-doped fiber amplifier (EDFA) and a discrete compensating Raman amplifier (DCRA) can compensate both the span loss and the chromatic dispersion. The gain saturation and nonlinear effect induced in the HFA are discussed. The experimental results show that although the EDFA-DCRA has lower noise figure than the DCRA-EDFA configuration, it induces gain saturation and the nonlinear effect. When designing an HFA, the setup of the DCRA-EDFA configuration is proved a better choice. © 2004 Society of Photo-Optical Instrumentation Engineers.