The tropical cyanobacterium Cylindrospermopsis raciborskii is of particular concern for its invasive characteristics and production of the toxin cylindrospermopsin (CYN). The present study represents the first attempt to determine the distribution of C. raciborskii and CYN in tropical China. The presence of C. raciborskii and CYN, as well as the composition of phytoplankton, was determined from a total of 86 samples from 25 urban reservoirs for drinking water supply in Dongguan City of South China. The presence of C. raciborskii was observed in 21 of the 25 reservoirs and confirmed that this species has been widely distributed in the investigated reservoirs. C. raciborskii accounted for between 0.1 and 90.3 % of the total phytoplankton biomass and contributed to the majority of the phytoplankton in some reservoirs such as Tangkengbian and Xiagongyan. Its biomass was negatively correlated with NO3 (-)-N concentration and Secchi depth. Dissolved CYN was detected in more than one-half of the reservoirs with concentrations up to 8.25 μg L(-1), and it positively correlated with C. raciborskii biomass. Dissolved microcystins (MCs) were detected in 12 of the 25 reservoirs with a maximum concentration 1.99 μg L(-1). Our data strongly suggest that C. raciborskii and CYN could be important health hazards in urban reservoirs of South China and that more data are needed for further assessment.

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High-speed electrical machines at multi-MW power level are being designed to drive high-speed compressor trains in oil and gas industry applications and for directly driving generators with gas turbines for shipboard and mobile power generation applications. The paper describes a converter topology to address such high power high frequency drive requirements. The proposed topology uses a three-phase bridge with series-connected single-phase bridges in each phase to obtain a four-level configuration. Optimized low pulse-count synchronous switching is used to limit the switching frequency of the individual devices; yet obtain the required power quality under all operating condition of the machine without use of external harmonic filters. Method of switching optimization and predicted performance of the drive are presented. Experimental results from a lab-scale prototype are provided to validate the concept.

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