• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.896-903
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• 2002

The susceptibility of SCC for the weldment and PWHT specimens of HT-60 steel was evaluated using a slow strain rate method under applied potential by means of the potentiostat in synthetic seawater. In case of the parent, anodic polarization voltage was inappropriate in elongating the time to failure(TTF). -0.8V corresponding to cathodic protection range is most effective in improving the SCC resistance against corrosive environment. In case of the weldment, the values of reduction of area(ROA) and TTF at -0.68V corresponding to cathodic polarization value were 45.2% and 715,809sec which were the largest and longest life among other applied potentials. Those were vise versa at -1.1V. In case of the PWHT specimens, TTF and ROA at -0.68V was longest and largest like the weldment. Besides, PWHT is effective in prolonging the time to failure of the welded off-shore structure due to softening of effect. Regardless of the weldment and PWHT specimen, as corrosion rate gets higher, TTF becomes shorter and deformation behaviour for the weldment and PWHT specimen at -1.1V was shown to be irregular. Finally, it was found that specimens showed brittle fracture at -1.1V, but more ductile fracture accompanying the micro-cracks at applied potential of -0.68V.

• Solar Energy
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• v.17 no.4
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• pp.13-22
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• 1997

Drag reduction produced by the dilute solution of polymer under turbulent flow in a rotating disk apparatus(RDA) was investigated in this study for the purpose of potential application to the Ocean Thermal Energy Conversion(OTEC) system. Four different molecular weights of poly(ethylene oxide)(PEO) were used as drag reducing additives, and synthetic seawater was adopted as a solvent. Experiments were undertaken to observe the dependence of drag reduction on various factors such as polymer molecular weight, polymer concentration and the rotating speed of the disk. The concentration dependence on the drag reduction of this polymer system was shown to obey an empirical drag reduction equation of the Virk's universal correlation.

• Journal of Marine Bioscience and Biotechnology
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• v.2 no.3
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• pp.174-186
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• 2007

Amphora coffeaeformis and Achnanthes longipes are commonly found as dominant benthic microalgae in Jeju coastal water throughout the year. In order to investigate pharmaceutical uses of these diatoms, each single species was isolated with micropipette under phase contrast microscope and subcultured with synthetic seawater media which was enriched with F/2 media, trace metal solution and $Na_2SiO_3$). Growth characteristics of these species were also determined with different combination of salinity, nutrients concentration and temperature. Thereafter, mass culture of each species was done based on the maximum growth condition. Biomass was collected after two weeks of mass culture and freeze dried for antioxidant study. The antioxidant properties of different fractions (n-hexane, chloroform and ethylacetate) obtained by solvent fractionation of 80% methanolic extract of two microalgae were investigated for free radical, reactive oxygen species scavenging (Super oxide, Hydrogen peroxide, Hydroxyl radical and Nitric oxide), metal chelating and lipid peroxidation inhibition activities. All fractions of A. longipes showed higher $DPPH^{\cdot}$ (free radical) scavenging activities (n-hexane: 89.0%, Chloroform: 76.0%, Ethylacetate: 66.0%, Methanol: 90.6% and aqueous residue: 63.0%). N-hexane fraction of A. longipes showed significantly higher activity (49.0%) on nitric-oxide. Ethylacetate fraction of A. longipes and aqueous residue of A. coffeaeformis exhibited 64.0% and 75.6% metal chelating activity which was higher than commercial antioxidants (${\alpha}$-tocopherol: 18.0% and BHT: 16.0%). The n-hexane fraction of A. coffeaeformis had 67.5% activity on $DPPH^{\cdot}$. Chloroform and n-hexane fractions of A. coffeaeformis exhibited 46.2% and 47.6% $H_2O_2$ scavenging effects which were closely similar to commercial antioxidants (${\alpha}$-tocopherol: 49.2% and BHT: 58.6%). Chloroform and ethylacetate fractions of A. longipes and fraction of n-hexane and chloroform of A. coffeaeformis showed better lipid peroxidation activities than ${\alpha}$-tocopherol. These data suggest that both organic and aqueous fractions have good antioxidative compounds with different antioxidant properties.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.62-68
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• 2001

In order to characterize the microscopic fracture behaviour of the weldment din stress corrosion cracking(SCC) phenomena, SCC and acoustic emission(AE) tests were carried out simultaneously and the correlation between mechanical paramenters obtained from SCC and AE tests was investigated. In the case of base metal, much more AE events were produced at -0.5V than at -0.8V because of the dissolution mechanism before the maximum load. Regardless of the applied voltages to the specimens, however, AE events decreased after the maximum load. In the case of weldment, lots of AE events with larger amplitude $range(40{\sim}100dB)$ were produced because of the singularities of weld HAZ in comparision to the base metal and post-weld heat-treated(PWHT) specimens. Numerous and larger cracks for the weldment were observed on the fractured surfaces by SEM examination. From these results, it was concluded that SCC for the weldment appeared most severely in synthetic seawater. Weld HAZ was softened by PWHT which also contributed to the reduced susceptibility to corrosive environment in comparison to the weldment.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.212-219
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• 2003

This study is to evaluate the characteristics of SCC at the welded region of high strength steel using acoustic emission(AE) method. Specimens were loaded by a slow strain rate method in synthetic seawater and the damage process was monitored simultaneously by AE method. Corrosive environment was controlled using the potentiostat, in which -0.8V and -1.1V were applied to the specimens. In the case of one-pass weldment subjected to -0.8V, much more AE counts were detected compared with the PWHT specimen. It was verified through the cumulative counts that coalescence of micro cracks and cracks for the one pass weldment with -0.8V were mostly detected. In case of the one pass weldment subjected to -1.1V, time to failure became shorter and AE counts were produced considerably as compared with that of the two pass weldment. It was shown that AE counts and range of AE amplitude have close relations with the number and size as well as width of the cracks which were formed during the SCC.

• Journal of Life Science
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• v.33 no.8
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• pp.680-691
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• 2023

Peak oil, climate change, and microplastics caused by the production and usage of petroleum-based plastics have threatened the sustainability of our daily life, and this has emerged as a recent global issue. To solve this global issue, the production and usage of biodegradable eco-friendly bioplastics such as polyhydroxyalkanoates (PHAs) has been suggested as an alternative. Therefore, in this review, the present status of global PHA manufacturers, the advantages of the production of PHAs using marine-origin microorganisms (with their productivity potential) and further required research and development strategies for cost-competitive production of PHAs using marine-based microorganisms were investigated. In this review, PHAs produced from marine microorganisms were found to have similar physical properties to petroleum-based plastics but with several advantages that can reduce the costs of PHA production. Those advantages include, seawater used in the medium preparation step, and osmotic-based cell lysis technology used in the separation and purification steps. However, the PHA productivities from marine microorganisms showed somewhat lower efficiencies than those from the commercial strains isolated from terrestrial environments. In order to solve the problem, further research strategies using synthetic microbiology-based technology, the development of long-term continuous culture technology, and solutions to improve PHA efficiency are required to meet future market demands for alternative bioplastics.

• Korean Journal of Remote Sensing
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• v.39 no.5_1
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• pp.695-713
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• 2023

In coastal waters, phytoplankton,suspended particulate matter, and dissolved organic matter intricately and nonlinearly alter the reflectivity of seawater. Neural network technology, which has been rapidly advancing recently, offers the advantage of effectively representing complex nonlinear relationships. In previous studies, a three-stage neural network was constructed to extract the inherent optical properties of each component. However, this study proposes an algorithm that directly employs a deep neural network. The dataset used in this study consists of synthetic data provided by the International Ocean Color Coordination Group, with the input data comprising above-surface remote-sensing reflectance at nine different wavelengths. We derived inherent optical properties using this dataset based on a deep neural network. To evaluate performance, we compared it with a quasi-analytical algorithm and analyzed the impact of log transformation on the performance of the deep neural network algorithm in relation to data distribution. As a result, we found that the deep neural network algorithm accurately estimated the inherent optical properties except for the absorption coefficient of suspended particulate matter (R² greater than or equal to 0.9) and successfully separated the sum of the absorption coefficient of suspended particulate matter and dissolved organic matter into the absorption coefficient of suspended particulate matter and dissolved organic matter, respectively. We also observed that the algorithm, when directly applied without log transformation of the data, showed little difference in performance. To effectively apply the findings of this study to ocean color data processing, further research is needed to perform learning using field data and additional datasets from various marine regions, compare and analyze empirical and semi-analytical methods, and appropriately assess the strengths and weaknesses of each algorithm.