Based on soft-switched continuous conduction mode boost converter, a zero-voltage zero-current switching DC/DC converter is proposed by introducing a flyback-unit and a voltage-double-unit. The proposed converter can achieve high voltage gain without operating at extreme high duty cycle. Moreover, by replacing the output diode of conventional boost converter with an active switch, zero-voltage-switched turn-on of switches and zero-current-switched turn-off of diodes can be achieved, which reduce switching loss and alleviate reverse-recovery problem of diodes. Furthermore, the energy in leakage inductor can be transferred into the output of the converter to improve the efficiency. The operating characteristics and the voltage gain of the proposed converter are analysed. Experimental results of a 100 W prototype are provided to verify the theoretical analysis results.
Large-scale water conservancy projects bear much economic and social significance. However, there is a lack of systematic research on how such projects affect radioactivity levels in regional water bodies. For the first time, the present paper uses data for nearly 10 y at different impoundment levels during construction of the dam to analyze changes in water radioactivity concentration levels in China’s Three Gorges region, in order to provide a valuable reference for evaluating the impact of large-scale water conservancy projects on radioactivity concentration levels. Results show that gross α, gross β, U, Th, 226Ra, 40K, 90Sr and 137Cs levels in the water bodies of the Three Gorges region fall within normal limits and annual effective dose for the adults, children and infants are below the WHO recommended reference level of 0.1 mSv per y. The period where the sample was collected and spatial distribution are the main reasons why some radionuclides are not normally distributed. Different water levels during different periods result in large variations in the levels of certain radionuclides, indicating that water levels can have a strong influence on radionuclide levels in reservoir regions. Hence, when evaluating the impact of large-scale water conservancy projects on radioactivity levels, analysis should be carried out on samples collected during different periods in order to make accurate assessments.
Sino-Singapore Tianjin Eco-City is a cooperation project between Singapore and China that seeks not only to be sustainable, but also practical, scalable and replicable. A number of challenges exist at the site chosen for this unique project, in particular, scarce and polluted water resources. An urban landscape design that is water sensitive and maximises utilisation of stormwater as a resource and improves surface water quality is currently being prepared. Rationale and general design approach including unique challenges are discussed. Preliminary sizing and siting is presented. It is concluded that relevant overseas experience can be successfully applied in the Chinese context and that a Water Sensitive Urban Design and in particular, stormwater BMPs, are a key component of a sustainable Sino-Singapore Tianjin Eco-City.
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