• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.4
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• pp.148-159
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• 2021

This study estimates the region of freshwater influence (ROFI) by Han River discharge in the Yeomha channel, Gyeonggi Bay. A 3-D numerical model, which is validated for reproducibility of variation in current velocity and salinity, is applied in Gyeonggi Bay. Distance of freshwater influence (DOFI) is defined as the distance from the entrance of Yeomha channel to the point where surface salinity is 28 psu. Model scenarios were constructed by dividing the Han River discharge into 10 categories (200~10,000 m³/s). The relation equation between freshwater discharge and DOFI was calculated based on performing a non-linear regression analysis. ROFI in Yeomha channel expands from the southern sea area of Ganghwa-do to the northern sea area of Yeongheung-do as the intensity of Han River discharge increases. The discharge and DOFI are a proportional relationship, and the increase rate of DOFI gradually decreases as discharge increases. Based on the relation equation calculated in this study, DOFI in the Yeomha channel can be estimated through the monthly mean Han River discharge. Accordingly, it will be possible to respond and predict problems related to damage to water quality and ecology due to rapid freshwater runoff.

• Journal of Marine Life Science
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• v.7 no.2
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• pp.86-93
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• 2022

The ecotoxicity test method using Undaria pinnatifida spore is challenging to use throughout the year. Since U. pinnatifida female gametophytes can be cultured in the laboratory, they can be used for ecotoxicity testing at any time. Changes in female gametophyte survival rate and relative growth rate in U. pinnatifida exposed to various environmental conditions were analyzed. The female gametophyte of U. pinnatifida was exposed to salinity (5~40 psu), temperature (5~30℃), pH (4~10), and light intensity (0~120 μmol photon m^-2 s^-1). Based on the highest average value, the survival rate of female gametophyte was highest at a temperature of 20℃, salinity 27.5 psu, pH 8, and light intensity 30 μmol photon m^-2 s^-1. And the relative growth rate was highest at a temperature of 15℃, salinity 35 psu, pH 9, and light intensity of 60 μmol photon m^-2 s^-1. As a result of this study, the method using the optimal conditions for the survival rate and relative growth rate is expected to be a practical test method that can complement the current method.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.126-137
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• 2011

This study simulate three-dimensional ocean circulation patterns using the EFDC model in the Kwangyang Bay and Jinju Bay, considering tide, water temperature and salinity. The numerical model results were verified using observed data. The model results well reproduced the observed data. As a result, ocean circulation patterns in the study area show convergence and divergence in the middle area of Noryang waterway and Daebang waterway, the residual flow patterns show typical two-layer circulation. According to the change of the density stratification in the Kwangyang Bay and Jinju Bay, the effect of fresh water is dominant in study area. In the case of Jinju Bay, although it is strongly influenced by the Namgang fresh water, also it is affected by Seomjin River when there is no discharge by Namgang Dam. On the other hand, the stratification of the Kwangyang Bay is relatively enhanced by the discharge of Namgang Dam.

• Journal of the Korea Organic Resources Recycling Association
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• v.15 no.2
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• pp.118-127
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• 2007

This study investigated the effect of varying TS concentration levels using supernatant of food waste. The experiment was performed at varying TS concentration levels ranging from 5% to 10% by a $35^{\circ}C$-mesophilic digestion reactor, dual digestion system with acid and methane fermenters combined. As a result, removal efficiency and stabilization were observed at TS concentration of 7~8%, But the removal efficiency notably decreased at 8% or higher TS level. At a stabilized phase of the reactor, more than $0.3m^3/kg{\cdot}vs$ gas was produced, with phenomena such as salt accumulation and increase of pH level being unnoticed. These results indicate that the increase of anaerobic digestion of food waste supernatant TS content has an effect on reaction and that it is necessary to control and operate concentration within 8%, given that the effect is stronger at 8% or higher.

• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.2
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• pp.3-14
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• 2001

In order to predict nutrient circulation in Hakata bay, we have developed an ecosystem model named the Sediment-Water Ecological Model (SWEM). The model, consisting of two sub-models with hydrodynamic and biological models, simulates the circulation process of nutrient between water column and sediment, such as nutrient regeneration from sediments as well as ecological structures on the growth of phytoplankton and zooplankton. This model was applied to prevent eutrophication in Hakata bay, located in western Japan. The calculated results of the tidal currents by the hydrodynamic model showed good agreement with the observed currents. Moreover, SWEM simulated reasonably well the seasonal variations of water quality, and reproduced spatial heterogeneity of water quality in the bay, observed in the field. According to the simulation of phosphorus circulation at the head of the bay, it was predicted that the regeneration process of phosphorus across the sediment-water interface had a strong influence on the water quality of the bay.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.5
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• pp.1259-1268
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• 2015

The sonic layer depth (SLD) variability is important for understanding the acoustic properties of the upper ocean that influence acoustic communications, acoustic tomography, and naval operations related to searching and detecting marine underwater vessels. Generally, the SLD is the acoustical equivalent of the mixed layer depth (MLD), although they are defined differently. In this study the SLD was compared with the MLD over the annual cycle in the East Sea using an available set of temperature-salinity observation profiles. For the comparison, various definitions and methods of the MLD had applied. As a result, the SLD in the East Sea is slight similar to the curvature method applied MLD, but the other MLD have severe differences with the SLD. Futhermore, a parabolic equation transmission model is used to evaluate the cutoff frequency trapped in surface duct. It follow that there is an optimum frequency for propagation at which the loss of sound is minimum.

• Journal of the Korea Organic Resources Recycling Association
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• v.12 no.4
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• pp.130-138
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• 2004

Food wastes with different regional origins were mixed with bulking agent such as paper mill sludge or night soil, and aged for 21 days or 28 days. And aged food wastes were fed to the earthworm(tiger worm, Eisenia fetida) for 60 days. There were no significant physico-chemical differences among the food wastes with different regional origins. EC values and NaCl concentrations in food wastes were too high for earthworms to survive. Food wastes mixed with paper mill sludge were vermicomposted more efficiently than food wastes mixed with night soil, but the over-all vermicomposting rates on the food wastes were much lower than that on paper mill sludge because EC values and NaCl concentrations were still high for earthworm to compost the feeds. Earthworm population did not increase its biomass on the food wastes mixed with paper mill sludge or night soil, whereas earthworm population fed with paper mill sludge increased its biomass by 20% for 60 days. It could be concluded that a solution for reducing NaCl concentrations in food waste should be developed to vermicompost food waste.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.46 no.5
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• pp.565-570
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• 2013

Physiological studies on the salinity tolerance with respect to survival rate and body composition changes of the abalone Haliotis discus hannai were conducted by rapidly changing the salinity in an indoor rearing system. The survival rate of the control (35 psu), 30 and 25 psu groups at $15^{\circ}C$ was 100%. The survival rate of the 20 psu group was $35{\pm}5.0%$. Survival rate of the 15 psu group was 0%. At $15^{\circ}C$ and 35, 30, 25, 20, 15 psu, the moisture contents of abalone muscle were $82.1{\pm}0.7$, $82.5{\pm}0.7$, $84.9{\pm}0.5$, $86.9{\pm}0.3$ and $86.6{\pm}0.4%$, respectively. Crude lipid contents were $0.47{\pm}0.03$, $0.47{\pm}0.03$, $0.47{\pm}0.09$, $0.77{\pm}0.09$ and $0.63{\pm}0.03%$, respectively and crude ash contents were $1.30{\pm}0.12$, $1.33{\pm}0.15$, $1.13{\pm}0.23$, $1.87{\pm}0.15$ and $1.40{\pm}0.31%$, respectively. At salinity below 20 psu, these values increased compared with the control. The general components of abalone muscles significantly increased below 20 psu, while amino acid composition showed no significant difference with salinity and water temperature.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.2 no.2
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• pp.87-91
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• 1997

Ecological stability of the Lake Shihwa, artificially made by the construction of the Shihwa Dike, was evaluated by the species composition and variation in biomass of zooplankton. Species composition and seasonal variation in biomass in the seaside stations were similar to those observed in nearby bays and coastal zone. However, those in the lake sites showed very different patterns. The brackish water copepod, Sinocaianus tenellus, held the first rank in every season (with more than 66% in spring, 98% in summer and fall, and 80% in winter). The species composition was very simple and the biomass (in terms of total individuals $m^{-3}$) varied markedly with season up to the order of $10^4$ magnitude. These results imply that the lake ecosystem made by the construction of Sihwa dike is in very unstable stage probably due to the input of industrial wastes as well as unpredictable variation in salt content caused by irregular control of the watergate of the dike and resultant irregular flow direction of the water through the gate.

• Membrane Journal
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• v.21 no.3
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• pp.236-246
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• 2011

In this study, we used prepared a cylindrical module consisting 100 hollow fibers of commercialized (hydrophobic) polyethylene membrane of $0.4{\mu}m$ pore size and systematically studied performance of direct contact membrane distillation (DCMD) and sweep gas membrane distillation (SGMD) in terms of variation of permeate flux and salt rejection with respect to temperature drop across the membrane, salt concentrations in feed, and flow rates of cooling water and sweep gas. SGMD was regarded as DCMD with a sweep gas layer between permeate-side membrane surface and cooling water. Sweep gas flow decreases the permeate flux from that of DCMD by providing an additional gas-layer resistance. We compared DCMD and SGMD performance by using mass balance with a fitting parameter (${\omega}$), indicating fraction of permeate flow rate.