• 수산해양기술연구
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• 제56권4호
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• pp.407-418
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• 2020

Mass mortality of mariculture fish due to high summer temperatures is a major issue in the mariculture industry in many coastal waters of Korea, yet measures to mitigate the impact are generally limited. We injected a micro-bubble of liquefied oxygen into the bottom of rockfish cages (about 6-8 m deep) in order to maximize the dispersal of micro-bubbled seawater and reduce fish mortality. The injection of low-temperature oxygen in micro-bubbles lowered the water temperature at the injection area by as much as 1℃ and increased dissolved oxygen concentration by 0.5 ppm. In early August, following a week with persistent high water temperature (above 28.5℃), there was an increase in fish mortality despite the micro-bubble system, which resulted in approximately 7% death of the total introduced fish population. However, this mortality appeared to be much lower than mortality reported in a neighboring mariculture facility (approximately 50% mortality). We also estimated the volume that can be recirculated with pumped seawater using a micro-bubble system. We suggest that this approach of injecting liquefied oxygen through a micro-bubble system may reduce fish mortality during high temperature periods.

• 한국콘텐츠학회논문지
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• 제19권11호
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• pp.445-450
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• 2019

본 연구는 자기공명영상 동적검사 시 자동주입기의 사용에 따라 조영제 역류로 인한 생리식염수의 오염 현상을 실험적으로 증명함으로써, 오염된 실린지 재사용 문제의 심각성을 인식시키고자 하였다. 연구방법은 조영제 주입 전 생리식염수와 주입 후 생리식염수를 각각 채취한 다음, T1 강조영상을 획득하여 신호강도를 측정하여 비교하였다. 생리식염수의 주입 후 신호강도가 주입 전에 비해 523.43% 통계적으로 높게 나타났다(p<0.05). 이는 조영제 주입에 따른 압력에 의해 조영제가 관을 통해 역류하여 압력이 낮은 반대쪽 생리식염수를 오염시킨 것으로 분석되었다. 결론적으로 조영제 주입 시 사용하는 실린지는 조영제 역류로 인해 교차오염이 발생하므로 정량적 분석을 위한 검사 시 동일한 환자의 검사라도 검사순서를 변경하거나 실린지를 교체하여 오류를 방지해야 한다.

• 한국치위생학회지
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• 제15권1호
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• pp.11-17
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• 2015

Objectives: The purpose of the study is to investigate the relationship between noise awareness, hearing ability, and dental hygiene performance in dental hygienists. Methods: The subjects were 234 dental hygienists in Seoul, Gyeonggi-do, and Incheon. The questionnaire consisted of 3 questions of general characteristics of the subjects, 1 question of noise awareness, 3 questions of hearing ability, 5 questions of dental hygiene performance, 1 question of noise reduction necessity, and 2 questions of noise control. Noise awareness, dental hygiene performance, and noise reduction necessity were measured by Likert 5 scale. Cronbach's alpha was 0.825 in dental hygiene performance reliability. Results: There was a significant difference in noise recognition by age(p<0.01) and working career(p<0.05). Those who pumped up the higher TV volume accounted for 31.6% and 3.0% had hearing impairment in the regular health checkup. 3.4% of the respondents complained of hearing loss, ear fluid, and equilibrium problem diagnosed by the doctors. The relationship between the type of workplace environment and task performance showed a significant difference. Those who work in the dental hospitals had high score of 3.43, while those who work in dental clinics had 3.20(p<0.05). The increased level of noise recognition affected the task performance and it is necessary to reduce the noise level. More try must be focused on the noise exposure prevention. Conclusions: In order to reduce the problems due to noise and improve their quality of life, it is necessary to change the noise recognition in the work place.

• 한국환경농학회지
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• 제23권4호
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• pp.234-239
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• 2004

[ $NO_3$ ]-N and T-N removal rates of cattail wetland cells were compared with those of reed wetland cells. The examined cells were a part of a pond-wetland system composed of two ponds in series and six wetland cells in parallel. Each wetland cell was 25m in length and 6m in width. Cattails (Typha angustifolia) were transplanted into three cells and reeds Phragmites australis) into another three ones in June 2000. Water of Sinyang stream flowing into Kohung Estuarine lake located in the southern part of the Korean Peninsula was pumped into the primary pond, its effluent was discharged into the secondary pond Effluent from the secondary pond was funneled into each cell. Two cattail and reed cells were chosen for this research. Water quantity and quality of influnt and effluent were analyzed front May 2001 through October 2001. The volume of influent and effluent of the cells averaged about $20.0\;m^3/day$ and $19.3\;m^3/day$, respectively. Hydraulic retention time was approximately 1.5 days. Influent $NO_3$-N concentration for the four cells averaged 2.39 mg/L. Effluent $NO_3$-N concentration far the cattail and reed cells averaged 1.74 and 1.78 mg/L, respectively. Average $NO_3$-N retention rate for the cattail and reed cells by mass was 30 and 29%, respectively. Influent T-N concentration far the four cells averaged 4.13 mg/L. Effluent T-N concentration for the cattail and reed cells averaged 2.55 and 2.61 mgL respectively. Average T-N retention rate for the cattail and reed cells by mass was 39 and 38%, respectively. $NO_3$-N and T-N concentrations in effluent from the cattail cells were significantly low (p=0.04), compared with those from the reed cells. Cattail wetland cells were more efficient for $NO_3$-N and T-N abatement than reed ones.

• 유기물자원화
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• 제23권2호
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• pp.28-35
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• 2015

본 연구에서는 학교 식당에서 배출되는 음식물류 폐기물을 준 회분식 액순환 건식 혐기성 소화를 이용해서 메탄가스를 생산하였다. 두 시스템이 운전되었는데, 각 시스템은 생물반응조와 액 저장조로 구성되었다. 각 생물반응조 바닥은 스크린이 설치되어 있어 2.5L의 분리된 액체는 액 저장조로 30분 동안 이송되고 이송이 끝나자마자 이송된 액은 반응조 상부로 투입된다. 이 같은 순환은 고농도의 VFAs를 가지는 액체를 반응조 상부로 공급하는 역할을 한다. 실험 초기에는 음식물류 폐기물/식종 미생물의 부피 비는 2:8이고 이는 9g VS/L의 유기물 부하로 나타낼 수 있다. 음식물류 폐기물 투입은 2주에 한번이었고, 평균 수분, 휘발물질, 회성분은 각각 65.91%, 32.73%과 1.36%로 파악되었다. 두 개의 고형물 부하가 연구되었는데, 각각 3.51g VS/d (System A)와 3.86g VS/d(System B)이다. 음식물류 폐기물 당 메탄 발생량은 각각 $6.30m^3CH_4/kgVS{\cdot}d$(System A)와 $4.94m^3CH_4/kgVS{\cdot}d$(System B)이다.