• 한국환경생물학회:학술대회논문집
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• 한국환경생물학회 2003년도 학술대회
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• pp.7-8
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• 2003

• 한국주조공학회지
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• 제39권1호
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• pp.7-13
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• 2019

Few studies of large blooms over 700 mm thick among those used for the forging of raw materials have been reported. The cooling rate difference between the surface and the center of a large bloom is large, and the degradation of the mechanical properties is likely in cases involving excessively coarse precipitates resulted from the slow cooling rate of a large bloom after casting. Therefore, a schematic investigation of the growth behaviors of precipitates while varying their locations in blooms is necessary. The dissolution behaviors of precipitates were investigated by simulating a reheating process during which the bloom is heated to a high temperature. The segregation behavior of the as-cast large bloom was also investigated. Reheating specimens were obtained after an isothermal heat treatment at $1150^{\circ}C$ with various holding times to simulate the reheating process, with the samples undergoing a subsequent water quenching step. The precipitates were extracted using an electrolytic extractor and a particle size analysis was conducted with the aid of SEM, EDS, and TEM. In the present work, Al oxide, MnS and Nb carbide were mainly observed.

• ALGAE
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• 제19권1호
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• pp.23-30
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• 2004

The purpose of this study is to assess the effects that hydraulic-gun-aerators have on cyanobactedial bloom in Sayeon Dam Reservoir in Ulsan City, Korea. A total of nine hydraulic-gun-aerators are in operation at the reservoir withe 100 m spacing between each aerator to control severe cyanobacterial bloom in the dam reservoir. The field studies were performed an total four times at two sampling stations in the reservoir from July to August in 2001. The standing crops of phytoplankton did not changed significantly by the operation. The cell concentration of the cyanobacteria at the surface layer were reduced about 10%, which is a poor result for the dispersing cyandobacteria deeper into the water. The average surface temperature during the study was reduced by 2.0$^{\circ}C$ by the hydraulic-gun-aerators. The effect of the operation on the vertical distribution of DO concentration was clear. However, the hydraulic-gun-aerators were not expected to have an effect in the lowest layer of the hypolimnion. In the study, it was proposed that installation distance between each hydraulic-gun-aerator would be proper when they are apart about 120 m based on DO depth profiles.

• 대한환경공학회지
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• 제36권5호
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• pp.378-385
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• 2014

한강유역 조류경보제의 클로로필-a 농도는 남조류의 우점을 예측할 수 없어 본 연구에서는 남조류 개체수에 영향을 미치는 환경인자를 분석하여 남조류 우점 예측인자를 제시하였다. 2012년 1월~2013년 9월까지 하천의 계절변화에 따른 조류의 우점종을 분석한 결과, 저수온기인 1~4월에는 규조류, 5~6월에는 녹조류, 7~8월에는 남조류가 우점하는 것으로 나타났다. 또한, 남조류 개체수 증감에 영향을 미치는 영양염류(TN, TP), 기온, 강수량, 댐 방류량과의 상관성을 분석한 결과, 기온보다는 낮은 댐 방류량으로 댐 내의 체류시간이 길어져 남조류 개체수가 급속히 증가한 것으로 나타났다. 마지막으로 남조류 개체수와 TN:TP 농도 비를 분석한 결과 TN:TP 농도 비가 29 이하로 낮아질 때 남조류가 우점하는 것으로 분석되어 한강유역 조류경보제에 남조류 우점 예측인자인 TN:TP 농도 비를 도입할 필요가 있다.

• 환경영향평가
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• 제29권1호
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• pp.37-44
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• 2020

본 연구에서는 Chlorophyll-a (Chl-a)값을 빈도분석인 히스토그램(histogram)을 통해 녹조관리가 필요한 지점을 분류 하고자 하였다. 누적도수분포곡선(ogive curve)에 따라 지점별 녹조발생정도를 분석하였고, 히스토그램의 형태에 따라 관리지점을 3단계로 분류하였다. 4대강 중 한강에서 저농도의 Chl-a가 가장 많이 나타났고, 금강과 영산강 지점에서 높은 농도의 Chl-a가 빈번하게 나타났다. 히스토그램의 패턴에 따라 녹조의 관리 정도를 분류 할 수 있었는데, 한강의 경우 집중관리가 필요한 지점이 나타나지 않았고, 금강과 영산강은 대부분의 지점에서 녹조관리가 필요한 것으로 나타났다. 마지막으로 낙동강은 중류 및 하류 지점부터 녹조관리가 필요한 지점으로 분류되었다. 본 연구결과를 통해 빈도분석이 녹조발생의 우심지역 판단의 보조지표 활용 가능성 여부를 확인하였다.

• 한국어병학회지
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• 제34권2호
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• pp.255-259
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• 2021

This is the first report describing acute mass mortality occurred in juvenile olive flounder (Paralichthys olivaceus) caused by gas bubble disease (GBD). A total of 610 fish (average weight = 35 g), which were more than half of the fish acclimated at 17℃ in an aquarium, were killed within two days of acclimation. The dead and moribund fish showed excessively opened opercula and mouths, and occasionally, severe exophthalmia. Through microscopic observation, numerous gas emboli were found in the gills of the dead and live fish, while the fish were not infected with any microbial pathogens. The dissolved oxygen (DO) saturation level of the rearing water and seawater nearby the facility reached 145% and 286%, respectively, whereas other water quality parameters (such as salinity, pH, and chemical oxygen demand) were normal. The extreme saturation rate of seawater in the shore nearby seemed to be due to an enormous algal bloom that occurred there. Through molecular identification based on 18S rDNA sequences, the most dominant algal species was most closely related to Ulva californica (99.87% sequence identity) followed by U. prolifera, U. linza, and U. curvata (99.81%). Therefore, it can be concluded that supersaturated seawater due to mass algal bloom caused gas bubble disease in the olive flounder, leading to mass mortality. After technical adjustment, such as increased aeration, lowered water circulation rate, and inlet water filtration using micro-pore carbon filters, the DO level became normal, no further mortality occurred and the status of the fish was stabilized.

• 한국환경생물학회:학술대회논문집
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• 한국환경생물학회 2001년도 학술대회
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• pp.75-75
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• 2001

• 환경위생공학
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• 제15권1호
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• pp.1-6
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• 2000

A milky gray scum was observed at some water area of the lake Daecheong in the summer of 1997 and 1998. To identify a causing organism of scum and affecting factors, we observed the scum material by a phase contrast microscope and surveyed the phsico-chemical water quality during the outbreak of scum. The scum was found out to be clogging cysts of amoeboid protozoan, Asterocaelum sp.(Protozoea Sarcodina Aconchulinida), grazer of filamentous cyanobacteria, Anabaena genus. The protozoan scum appeared during Anabaena bloom period, which continued for a while. This protozoan was presumed acting as a regulator of Anabaena bloom in the lake Daecheong during the summer season. Moreover this is the first report on Asterocaelum sp. a grazing filamentous cyanobacteria occurred in Korean freshwater.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.469-472
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• 2006

The primary objective of this study was to gain insight into the characteristics of algal blooms in relation to the marine environment of the Korean Southern Coast, using more than 22 years worth of data since the first known occurrence of algal blooms. Algal blooms tend to occur when the precipitation or water temperature for a ten-day period prior to the annual bloom exceeds the long-term mean value. There are three notable causative species in six different inner bays, namely Prorocentrum sp., Skeletonema costatum, and Heterosigma akashiwo, and in addition, these three species appeared in different conditions of water temperature and salinity at each region.

• Journal of Microbiology and Biotechnology
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• 제16권2호
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• pp.212-218
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• 2006

Three out of fourteen Microcystis-dominant cyanobacterial blooms in Central India were found to be toxic to mice ($LD_{50}$ ranging from 35-450 mg bloom dry mass/kg body weight). The liver architecture of the treated mice showed characteristic symptoms of hepatotoxicity relative to the untreated controls, with increased enzyme activities of serum lactate dehydrogenase (LDH), serum glutamate oxaloacetate transaminase (SGOT), alkaline phosphatase (ALP), and serum glutamate pyruvate transaminase (SGPT). RP-HPLC revealed the presence of microcystin-LR, microcystin-RR, and desmethyl microcystin-RR in the given region to maximum amounts of 390, 1,030, and $860{\mu}g/g$ bloom dry weight, respectively, corresponding to a maximum of 2.8 mg/l microcystin-LR in the lake water. Further confirmation of the microcystin variants was conducted using a MALDI-TOF MS analysis.