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가정용 가습기의 사용자 습관에 따른 실내공기 중 바이오에어로졸의 발생특성
김익현,김기연,김대근,Kim, Ik-Hyeon,Kim, Ki Youn,Kim, Daekeun 한국환경보건학회 2012 한국환경보건학회지 Vol.38 No.6
Objectives: This study was performed in order to evaluate the generation characteristics of airborne bacteria and fungi while operating a household humidifier, in consideration of user habits. Methods: Microbial samples were collected in a closed chamber with a total volume of 2.76 $m^3$, in which a humidifier was operated according to experimental strategies. A cultivation method based on the viable counts of mesophilic heterotrophic bacteria and fungi was performed. Experimental strategies were divided into three classes: the type of water in the water reservoir (tap water, cooled boiled water); the frequency of filling the reservoir (refill every day, no refill); and the sterilization method (sterilization function mode, humidifier disinfectants). Results: Significant increases in the concentration of airborne bacteria were observed while the humidifier was in operation. The concentration had increased to 2,407 $CFU/m^3$ by 120 hours when tap water filled the reservoir without any application of sterilization, while for cooled boiled water, it was merely 393 $CFU/m^3$ at a similar time point. Usages of disinfectant in the water tank were more effective in decreasing bioaerosol generation compared to sterilization function mode operation. Generation characteristics of airborne fungi were similar to those of bacteria, but the levels were not significant in all experiments. Calculated exposure factor can be used as an indicator to compare biorisk exposure. Conclusion: This study identified the potential for bioaerosol generation in indoor environments while operating a household humidifier. User practices were critical in the generation of bioaerosol, or more specifically, airborne bacteria. Proper usage of a humidifier ensures that any biorisks resulting from generated bioaerosol can be prevented.
실험실 규모 하수슬러지 퇴비화공정에서 기계적 교반이 배출가스 내 부유세균과 내독소의 발생특성에 미치는 영향
김익현(Ik Hyeon Kim),김기연(Ki Youn Kim),배재근(Chae Gun Phae),김대균(Dae Kyun Kim) 大韓環境工學會 2012 대한환경공학회지 Vol.34 No.3
본 연구는 퇴비화 공정에서 발생되는 배출가스 내 생물학적 인자의 발생 특성을 파악하기 위하여 퇴비단 온도변화에 따른 부유세균과 내독소의 발생농도를 관찰하였다. 실험은 도시하수슬러지를 대상으로 실험실 규모의 기계적 교반이 가능한 퇴비화 장치(반응기 부피 0.06 m3)에서 실시되었다. 부유세균은 미교반 퇴비화 공정에서 퇴비단 온도변화와 유사한 발생경향을 보였지만 통계적 유의성이 다소 낮았고(p > 0.05), 최고 발생농도는 1.03 × 105 CFU/m3이었다. 내독소는 기계교반 퇴비화 공정에서 퇴비단의 온도변화와 유사한 발생경향을 보였으며(통계적 유의성: p < 0.05), 최고 발생농도는 1,415 EU/m3이었다. 퇴비화 공정의 기계적 교반이 퇴비단 미생물의 활성과 이에 따른 배출가스 중 내독소 발생 증가에 영향을 미친 것으로 보인다. 내독소의 발생농도와 부유세균의 발생농도는 유사한 발생 경향을 보였으며, 특히 미교반 퇴비화공정에서 높은 통계적 상관성이 나타났다(통계적 유의성: p < 0.01). This study was performed to investigate the concentration variation of airborne bacteria and endotoxin by the temperature in the compost pile in order to identify the generation characteristics of biological factors in the exhaust gases generated from labscale sludge compositing reactors (0.06 m3 of total reactor volume). Airborne bacteria showed the highest concentration of generation (1.03 × 105 CFU/m3) in the composting reactor without mechanical agitation, and similar change tendency to temperature variation of composting, but somewhat lower statistical significance (p > 0.05). In the compost reactor with mechanical agitation, endotoxin showed similar generation characteristic to temperature variation of composting (statistical significance; p < 0.05) and the highest generation concentration to 1,415 EU/m3. Mechanical agitation of the composting process affected activity of microorganism and positive generation of endotoxin in exhaust gases. Endotoxin and airborne bacteria showed similar tendency of generation, especially the highest statistical correlation was observed in the compost reactor without mechanical agitation (statistical significance; p < 0.01).
인지 기능 수행 시 BOLD 신호 크기에 기반 한 영역별 대뇌 편측화
정순철(Soon Cheol Chung),손진훈(Jin Hun Shon),김익현(Ik Hyeon Kim),이수열(Soo Yeol Lee) Korean Society for Precision Engineering 2005 한국정밀공학회지 Vol.22 No.1
This study compared cerebral lateralization index based on the area of neural activation with that based on the intensity of neural activation. For this purpose, 8 right-handed male college students (the mean age - 23.5 years) and 10 right-handed male college students (the mean age - 25.1 years) participated respectively in researches on visuospatial and verbal task brain function. Functional brain images were taken from 3T MRI using the single-shot EPI method. The result of measuring cerebral lateralization index based on the area of neural activation suggested that the right hemisphere is dominant in visuospatial tasks and the left one is in verbal tasks. However, the dominance is not sufficient to locate the exact part of the brain for these tasks. When cerebral lateralization index was computed based on the intensity of neural activation, it was derived that the area of cerebral lateralization closely related to visuospatial tasks is the superior parietal lobe, and the area of cerebral lateralization closely related to verbal tasks is the inferior and middle frontal lobes. Thus, cerebral lateralization index by area based on the intensity of neural activation as proposed by this study can determine the dominance of the cerebrum by area, so is helpful for accurate and quantitative determination of cerebral lateralization.
고농도의 산소 공급이 공간지각 과제 수행 시 젊은 성인 남자의 대뇌 편측화에 미치는 영향
정순철(Soon Cheal Chung),손진훈(Jin Hun Shon),김익현(Ik Hyeon Kim) Korean Society for Precision Engineering 2004 한국정밀공학회지 Vol.21 No.8
The present study attempted to investigate the effects of supply of highly concentrated (30%) oxygen on human ability of visuospatial cognition and cerebrum lateralization, compared to air of normal oxygen concentration (21 %). The experiment consisted of two runs, one for visuospatial cognition test with normal air (21 % of oxygen) and for visuospatial cognition test with more oxygen in the air (30% of oxygen). Each run was composed of four blocks and each block included eight control tasks and five visuospatial tasks. Functional brain images were taken from 3T MRI using the single-shot EPI method. The result of task performance showed the accuracy increased at 30%s concentration of oxygen rather than 21 %s. There were more activations observed at the left and right hemisphere, but there was decrease cerebrum lateralization with 30% oxygen administration. Thus, it is concluded that the positive effect on the visuospatial cognitive performance level by the highly concentrated oxygen administration was due to increase of cerebrum activation and decrease of cerebrum lateralization.