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Feed-forward Frequency Compensator for APWM HB Flyback Converter
J.-H. Jung,S. Ahmed,J.-W. Baek 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
A feed-forward frequency compensator for the asymmetrical pulse-width modulated (APWM) half-bridge (HB) flyback converter is proposed to increase power conversion efficiency. Under variable input voltage, the APWM HB flyback converter cannot be satisfied with the soft commutation of the output rectifier because the variation of the PWM duty cycle induces an improper turn-off duration. It means that the resonance of the primary current can be out of the ZCS condition with respect to the input voltage variation. The proposed feed-forward frequency compensator can properly change the operating frequency of the converter to preserve the soft commutation of the output rectifier with respect to the input voltage variation. Experimental results using a 240 W prototype converter were obtained to verify that the proposed compensation algorithm can improve the power conversion efficiency under the input voltage and load variations.
Microbiological Quality of Alternative Water Sources in the Urban Environment
( J. P. S. Sidhu ),( W. Ahmed ),( L. Hodgers ),( K. Smith ),( S. Toze ) 한국물환경학회 2017 한국물환경학회·대한상하수도학회 공동 춘계학술발표회 Vol.2017 No.-
In Australia, decreasing rainfall, frequent drought and population growth in urban environments, along with an overall desire to achieve greater water sustainability, has increased the demand for alternative water sources such as stormwater, roof-harvested rainwater, and treated wastewater effluent. The potential public health risks associated with alternative water sources predominantly originate from the presence of enteric viruses, pathogenic bacteria, and protozoan parasites. Empirical data on the presence of pathogens is a prerequisite to accurately determine human health risks and the extent of treatment required prior to use for potable and nonpotable purposes. We have carried out a number of targeted studies on the microbiological quality of the roof-harvested rainwater, stormwater, and treated wastewater effluent in the Southeast Queensland (Australia). The main of aim these studies was to collect quantitative data on the presence of pathogens and make an assessment of the potential health risk associated with water reuse. A dedicated survey of the roof-harvested rainwater tanks in Brisbane has shown the presence of Campylobacter spp. (21%), Salmonella spp., (4%), and Giardia lamblia (13%). In addition, opportunistic pathogens Legionella spp. (99%) and Mycobacterium intracellulare (78%) were also detected\. The numbers of bacteria ranged up to 3.1 x 10<sup>6</sup> PCR detectable units (pdu) L<sup>-1</sup> for Legionella spp., 9.6 X 10<sup>5</sup> pdu L<sup>-1</sup> for P. aeruginosa, 6.8 X 10<sup>5</sup> pdu L<sup>-1</sup> for M. intracellulare, 6.6 x 10<sup>5</sup> pdu L<sup>-1</sup> for Acanthamoeba spp., 1.1 x 10<sup>5</sup> pdu L<sup>-1</sup> for M. avium, and 9.8 X 10<sup>3</sup> pdu L<sup>-1</sup> for L. pneumophila. The presence of potential opportunistic pathogens in tank water may present health risks if un-treated water is for potable and non-potable use in the house. Stormwater runoff from two urban catchments with different drainage area, impervious area, and land use, a potential source of pollution and population density was collected and analyzed for the presence of pathogens and fecal indicator bacteria. The mean FIB numbers in water samples collected after the storm event ranged from 10 <sup>3</sup> to 10<sup>4</sup> L<sup>-1</sup> for E. coli and 10 <sup>4</sup> to 10<sup>5</sup> L<sup>-1</sup> for Enterococcus spp. Salmonella enterica numbers varied between 10 to 2400 MPN L<sup>-1</sup>. Human adenovirus (HAdV) numbers in the stormwater varied between 10 to 10<sup>3</sup> pdu L<sup>-1</sup>, human polyomavirus (HPyV) numbers varied between 1 to 10<sup>3</sup> pdu L<sup>-1</sup>. Torque teno virus (HTtV) numbers varied between 10 to 7.45 x 10<sup>3</sup> pdu L<sup>-1</sup>. Somatic coliphages (Microviridae) was also widely prevalent with numbers varying between 10 to 10<sup>3</sup> pdu L<sup>-1</sup>. The results of this study suggest that enteric virus and bacterial pathogens frequently occur in the stormwater runoff in significant numbers which could lead to increased human health risks. A quantitative survey HAdV, HPyV, HTtV and somatic coliphage (Microviridae) numbers in influent and effluent samples was carried out from three wastewater treatment plants (WWTP) employing an activated sludge process to produce secondary treated effluent in Brisbane. HPyV, HAdV, HTtV and Microviridae were consistently detected in the primary influent in high numbers (10<sup>5</sup> to 10<sup>6</sup> pdu L<sup>-1</sup>) and secondary treated effluent (10<sup>2</sup> to 10<sup>3</sup> pdu L<sup>-1</sup>) across all three treatment plants. Under appropriate conditions, WWTPs with activated sludge process could be an effective treatment barrier with > 3 log10 removal of enteric. The results confirm the occurrence of enteric viruses in significant numbers in secondary treated effluent, tertiary treatment may be required prior to effluent reuse or discharged into the environmental to prevent exposure of people to health hazards.
Exploring Different Perceptions of Coach-Athlete Relationship
Bo Li,Stephen W. Dittmore,Jae-Ahm Park 한국코칭능력개발원 2015 International Journal of Coaching Science Vol.9 No.2
The study aimed to investigate how Chinese Olympians’ coach-athlete relationships differ from a convenience sample of Western Olympians within the context of the interpersonal constructs of Closeness, Co-orientation, and Complementary (three Cs). A total of 12 Olympians, including six Chinese Olympians and six Western Olympians, were invited to participate to this study. All participants had won medals at either World Championships or Olympic Games in their sports. A semi-structured interview was conducted with five open-ended questions about their coach-athlete relationships. Content analysis revealed Chinese Olympians have higher satisfaction than selected Western Olympians in terms of the commitment of coach and dedication of time of their coaches. Western athletes described the relationship as a partnership, but Chinese Olympians described the relationship as paternal. In addition, Chinese athletes were dominated in dyadic relationships since their personal lives were controlled by their coaches, while Western athletes were given more freedom and democracy by their coaches. With respect to gender, female athletes tended to train with male coaches but male athletes were more concerned with a coach’s knowledge rather than their gender. The study also indicated that athletes were more sensitive when they were in different gender coach-athlete relationships than in same gender relationships.
Water Vapor Adsorption and Hydrogen Peroxide Decomposition on Date Pit Carbonization Products
A.M. Youssef,Th. El-Nabarawy,S.A. Sayed Ahmed,W.E. Rashwan 한국탄소학회 2005 Carbon Letters Vol.6 No.4
Carbonization products C1, C2, C3, C4 and C5 were prepared by the carbonization of date pit in limited air, at 500, 600, 700, 800 and 1000℃, respectively. C1-V-600, C3-V-600, C1-V-1000 and C3-V-1000 were prepared by thermal treatment of C1 and C3 under vacuum at 600 and 1000℃. The textural properties were determined from nitrogen adsorption at 77 K and from carbon dioxide adsorption at 298 K. The surface pH, the FTIR spectra and the acid and base neutralization capacities of some carbons were investigated. The amounts of surface oxygen were determined by out-gassing the carbon-oxygen groups on the surface as CO2 and CO. The adsorption of water vapor at 308 K on C1, C2, C3 and C4 was measured and the decomposition of H2O2 at 308 K was also investigated on C1, C2, C3, C4 and C5. The surface area and the total pore volume decreased with the rise of the carbonization temperature from 500 to 1000℃. The adsorption of water vapor is independent on the textural properties, while it is related to the amount of acidic carbon-oxygen groups on the surface. The catalytic activity of H2O2 decomposition does not depend on the textural properties, but directly related to the amount of basic carbon-oxygen complexes out-gassed as CO, at high temperatures.