• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.238-244
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• 2017

Plasma ion nitriding has been widely used in various industries to improve the mechanical properties of materials, especially stainless steels by increasing the surface hardness. It has the particular advantages of less distortion compared to that in the case of hardening of steel, gas nitriding, and carburizing; in addition, it allows treatment at low-temperatures, and results in a high surface hardness and improved corrosion resistance. Many researchers have demonstrated that the plasma ion nitriding process should be carried out at temperatures of below $450^{\circ}C$ to improve corrosion resistance via the formation of the expanded austenite phase(S-phase). Most experimentals studied to date have been carried out in chloride solutions like HCl or NaCl. However, the electrochemical characteristics for the chloride solutions and natural seawater differ. Hence, in this work, plasma ion nitriding of 304 stainless steels was performed at various temperatures, and the electrochemical characteristics corresponding to the different process temperatures were analyzed for the samples in natural seawater. Finally the optimum plasma ion nitriding temperature that resulted in the highest corrosion resistance was determined.

• Journal of Aquaculture
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• v.6 no.4
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• pp.273-284
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• 1993

Ion concentrations and osmolarities of the body fluid and oxygen consumption of the larvae of the freshwater crab, Eriocheir japonicus under the influence of various salinities and water temperatures were studied. The levels of $Na^+\;and\;Cl^-$ ions in the body fluid of the crab placed in the low salinities (freshwater and $30\%$ seawater) were higher at the low temperature $(16^{\circ}C)$ than high temperature $(30^{\circ}C)$. However, the crab in the high salinity $(90\%\; seawater)$, those ions in the body fluid were higher at the high temperature $(30^{\circ}C)$ than the low temperature $(10^{\circ}C)$ When the zoea larvae were young (first and second stages), the ion concentrations of the body fluid were more affected by salinities and temperatures of the media. The salinity levels of the media more influenced the levels of $K^+$ ions of the body fluid of the larvae than the temperature. The osmolarities of the body fluid of the larvae were almost isotonic when they were placed at $70\%$ seawater $(24.5\%o)$. Oxygen consumption of individual larva was lower in zoea 1 and 2 stages than the other stage larvae. The high oxygen consumption of the larvae was observed at $70\%$ seawater compared to the other salinity levels.

• Journal of Environmental Science International
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• v.8 no.5
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• pp.587-592
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• 1999

The purpose of this study was to identify the controlling factors to construct tidal flat ecosystems having similar characteristics as natural ones. We transplanted the soil in a constructed tidal flat to a natural one and vice versa. Parameters monitored after these transplantations were silt content, organic matter, bacterial population and oxidation-reduction potential. Moreover, the relationship among silt content, organic matter and bacterial population was investigated by laboratory column experiment. The silt content, organic matter, bacterial population and vertical profile of oxidation-reduction potential in the soil transplanted from the constructed tidal flat to the natural one changed to similar values to those in the natural one. On the contrary, all the parameters for the soil transplanted from the natural tidal flat to the constructed one changed to similar values as those in the constructed one. The silt contents in thses two transplanted solis were in proportion to the organic carbon contents and bacterial population. Similarly, the bacterial population in laboratory column experiment increased with the increase in silt and organic matter contents. It seemed to be important to select a place to enhance accumulative of silt and/or to maintain the silt content by hydrodynamic control of seawater in order to construct a tidal flat having similar characteristics as natural one.

• Journal of Aquaculture
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• v.8 no.2
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• pp.117-131
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• 1995

In order to improve the present running seawater system for seedling production of marine fishes, rearing experiments with the juveniles of black seabream (Acanthopagrus schlegeli) and oblong rockfish (Sebastes oblongus) were conducted. The recirculating seawater system (F) equipped with the rotating biological contactors and the running seawater system (R) were used. Environmental factors, growth, survival rate and rearing density of the fish were compared between two systems during the experimental period. In the rearing experiment of black seabream, water temperature in F was fluctuated with surrounding air temperature and was higher than that in R. Specific gravity of the rearing seawater in F was relatively stable in the range of 1.0252 to 1.0266, while that in R was greatly fluctuated. pH in F turned out to be 7.51, but pH in R was similar to that in the natural seawater. Dissolved nitrite and nitrate in F were higher than those in R. While no significant differences in the growth of black seabream juveniles were recognized between two systems, survival rates of fishes in F were higher than those of fishes in R. In the rearing experiment of oblong rockfish, water temperature in F was higher than that in R. Specific gravity in F was slightly higher than that in R which showed relatively less fluctuation in the range of 1.0253 to 1.0270. pH in F turned out to be 7.96, but pH in R was similar to that in the natural seawater. Dissolved nitrite and nitrate in F were higher than those in R, but ammonia was lower in F. The juveniles of oblong rockfish reared in F grew significantly faster in their total length and body weight than those in R (P<0.05). However, survival rates of fishes between two systems showed no significant differences.

• Korean Journal of Food Science and Technology
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• v.52 no.1
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• pp.89-93
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• 2020

Vibrio vulnificus, an opportunistic pathogen, causes septicaemia when raw shellfish and fish are eaten by patients with hepatic diseases or reduced immunity. In this study, we evaluated inhibitory effects of some natural products on V. vulnificus growth using 96-well microplate assay. We found that Phyllanthus emblica L., Rosa chinensis Jacq., Rosa rugose Thub., and Chukrasia tabularis A. Juss. significantly inhibited V. vulnificus growth in Luria-Bertani (LB) broth. Among these four extracts, the inhibition diameter of Chukrasia tabularis was 16.00 ± 0.58 mm in disc diffusion assay on V. vulnificus growth. In addition, these four natural products protected HeLa cells from V. vulnificus-induced cytotoxicity. A cocktail containing these four products showed an inhibitory effect on V. vulnificus growth in seawater and shellfish by reducing its growth by 75.7% and 97%, respectively. These results suggest that these four natural products are safe and effective natural antimicrobial candidates to prevent V. vulnificus infection.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.17 no.1
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• pp.1-8
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• 2012

The objective of the present study was carried out to clarify the effects of deep sea water on the growth and maturation of $Porphyra$ (Rhodophyta, Bangiales). Foliose thalli for indoor culture were collected from Yeongok ($P.$ $okamurae$) in Gangwon Prefecture, Tongyeong ($P.$ $suborbiculata$ f. $latifolia$) and Namhae ($P.$ $yezoensis$ f. $narawaensis$) in Gyongnam Prefecture respectively. Monospores were cultured at five temperatures (5, 10, 15, 20 and $25^{\circ}C$) with a photon irradiance of $80{\mu}m^{-2}s^{-1}$ under photoperiods of 14L:10D and 10L:14D in surface, deep and mixed seawater in respectively. The fast growth of foliose thalli were observed in $P.$ $suborbiculata$ f. $latifolia$ cultured at deep seawater under $15^{\circ}C$ and 10L:14D. In three species, the optimum growth occurred at 10 and $15^{\circ}C$ under deep and mixed seawater and short day-length. In general, monospores from the cultured thalli were liberated within three weeks after incubation under $10-25^{\circ}C$ and both photoperiods. From the result of this study, deep seawater is considered that the natural species of the genus $Porphyra$ can be useful for the development as the new cultivars.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.883-889
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• 2014

It is generated for cavitation erosion due to the local static boiling by pressure differentials in high speed rotating fluid environment. The cavitation is influenced by various elements such as pressure, velocity, temperature, pH of fluid and medium. In particular, the damage of material is accelerated due to the electrochemical corrosion by $C1^-$ and cavitation erosion due to cavities in seawater. In this paper, hence, it investigated for martensite stainless steel the damage behavior with applied current density and cavitation time in natural seawater solution. Less damage depth at the cavitation condition was observed than static condition as a result of galvanostatic experiment. Furthermore, it was shown that dramatic increase of weightloss, damage rate and damage depth after 3 hour of cavitation test.

• Asian Journal of Atmospheric Environment
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• v.5 no.3
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• pp.157-163
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• 2011

Atmospheric aerosol deposition caused by Asian dust (KOSA) events provide nutrients, trace metals, and organic compounds over the Pacific Ocean that enhance ocean productivity and carbon sequestration and, thus, influence the atmospheric carbon dioxide concentrations and climate. Using dust particles obtained from the snow layers on Mt. Tateyama and the surface sand of Loess Plateau in incubation experiments with natural seawater samples on a shipboard, we demonstrate that dust-particle additions enhanced the bacterial growth on the first day of incubation. Gram-positive bacterial group and alpha-proteobacteria were specifically detected form seawater samples including the mineral particles. Although the remarkable dynamics of trace elements and nutrients depend on dust-particle additions, it is possible that organic compounds present in the mineral particles or transported microbial cells could also contribute to an increase in the quantities of bacteria. The chlorophyll concentrations at fractions of every size indicated a similar pattern of change between the seawater samples with and without the dust-particle additions. In contrast, the chlorophyll measurement using submersible fluorometer revealed that the dynamics of phytoplankton composition were influenced by the dust-particles treatments. We conclude that the phytoplankton that uses the bacterial products would increase their biomass. We show that KOSA deposition can potentially alter the structures of bacterial communities and indirectly influence the patterns of marine primary production in the Pacific Ocean.

• Ocean and Polar Research
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• v.37 no.3
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• pp.201-209
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• 2015

To examine the effects of increased $CO_2$ concentration and seawater temperature on the photosynthesis and growth of forest forming Ecklonia cava (Laminariales, Phaeophyta), sporophytic discs and gametophytes were cultured under three $pCO_2$ concentrations (380, 750, 1000 ppm), four temperatures (5, 10, 15, $20^{\circ}C$ for sporophytes; 10, 15, 20, $25^{\circ}C$ for gametophytes), and two irradiance levels (40, $80{\mu}mol$ photons $m^{-2}s^{-1}$) for 5 days. Photosynthetic parameter values ($ETR_{max}$, $E_k$, and ${\alpha}$) were generally higher as sporophytic discs were grown under low temperature and increased $CO_2$ concentration at 750 ppm. However, photosynthesis of Ecklonia sporophytes was severely inhibited under a combination of high temperature ($20^{\circ}C$) and 1000 ppm $CO_2$ concentration at the two photon irradiance levels. The growth of gametophytes was maximal at the combination of 380 ppm (present seawater $CO_2$ concentration) and $25^{\circ}C$. Minimal growth of gametophytes occurred at enriched $pCO_2$ concentration levels (750, 1000 ppm) and high temperature of $25^{\circ}C$. The present results imply that climate change which is increasing seawater temperature and $pCO_2$ concentration might diminish Ecklonia cava kelp beds because of a reduction in recruitments caused by the growth inhibition of gametophytes at high $pCO_2$ concentration. In addition, the effects of increased temperature and $pCO_2$ concentration were different between generations - revealing an enhancement in the photosynthesis of sporophytes and a reduction in the growth of gametophytes.

• Journal of the Korean institute of surface engineering
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• v.51 no.2
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• pp.87-94
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• 2018

Various sealing techniques were applied to the anodized 5083 aluminum alloy for marine environment to reduce corrosion and cavitation erosion damage. Electrochemical experiments and cavitation erosion tests were conducted to evaluate the corrosion resistance and cavitation resistance of the anodic oxide film treated with sealing in natural seawater solution. Then, damaged surface morphology was analyzed by scanning electron microscope(SEM) and 3D microscope. As the results of the electrochemical experiments, it was observed that the surface damage of all the experimental conditions in the anodic polarization experiment was locally grown by the combination of crack and corrosion damage. In the Tafel analysis, the corrosion resistance of all sealing treatment conditions was improved compared to the anodizing. On the other hand, cavitation erosion tests showed that the anodizing and all the sealing treatment conditions generated local pit damage by cavitation erosion attack and grew to crater damage in the observation of damaged surface by SEM. Also, the weight loss and the surface damage depth measured with the experiment time presented that most of the sealing treatment conditions showed better cavitation erosion resistance than the anodizing, and they had an incubation period at the beginning of the experiment.