• Journal of Ocean Engineering and Technology
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• v.27 no.3
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• pp.79-84
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• 2013

The seawater pipes in the engine rooms of ships are surrounded by severely corrosive environments caused by fast flowing seawater containing chloride ions, high conductivity, etc. Therefore, it has been reported that seawater leakage often occurs at a seawater pipe because of local corrosion. In addition, the leakage area is usually welded using shielded metal arc welding with various electrodes. In this study, when seawater pipes were welded with four types of electrodes(E4311, E4301, E4313, and E4316), the difference between the corrosion resistance values in their welding zones was investigated using an electrochemical method. Although the corrosion potential of a weld metal zone welded with the E4316 electrode showed the lowest value compared to the other electrodes, its corrosion resistance exhibited the best value compared to the other electrodes. In addition, a heat affected zone welded with the E4316 electrode also appeared to have the best corrosion resistance among the electrodes. Furthermore, the corrosion resistance of the weld metal zone and heat affected zone exhibited relatively better properties than that of the base metal zone in all of the cases welded with the four types of electrodes. Furthermore, the hardness values of all the weld metal zones were higher than the base metal zone.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.375-375
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• 2012

Graphene is a sp2-hybridized carbon sheet with an atomic-level thickness and a wide range of graphene applications has been intensely investigated due to its unique electrical, optical, and mechanical properties. In particular, hybrid graphene structures combined with various nanomaterials have been studied in energy- and sensor-based applications due to the high conductivity, large surface area and enhanced reactivity of the nanostructures. Conventional metal-catalytic growth method, however, makes useful applications difficult since a transfer process, used to separate graphene from the metal substrate, should be required. Recently several papers have been published on direct graphene growth on the two dimensional planar substrates, but it is necessary to explore a direct growth of hierarchical nanostructures for the future graphene applications. In this study, uniform graphene layers were successfully synthesized on highly dense dielectric nanowires (NWs) without any external catalysts. We also demonstrated that the graphene morphology on NWs can be controlled by the growth parameters, such as temperature or partial pressure in chemical vapor deposition (CVD) system. This direct growth method can be readily applied to the fabrication of nanoscale graphene electrode with designed structures because a wide range of nanostructured template is available. In addition, we believe that the direct growth growth approach and morphological control of graphene are promising for the advanced graphene applications such as super capacitors or bio-sensors.

• Korean Journal of Soil Science and Fertilizer
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• v.46 no.5
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• pp.386-390
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• 2013

Recently, special attention has been given to acid rain and its problem to environment such as acid precipitation and air pollution in East Asia. In the present study, rainwater samples were collected from Apr to Nov in 2012. The samples were chemically characterized for the assessment of emission sources. Suwon and Yeoju regions, typical agricultural areas in South Korea, were chosen for study sites. Ion composition and cation-affected neutralization were determined to evaluate the contribution of cations to the acidity of rainwater. Ion and electrical conductivity between the measured and the estimated showed high correlation. The cations observed in Suwon and Yeoju were $Na^+$ > $NH_4{^+}$ > $K^+$ > $Ca^{2+}$ > $Mg^{2+}$ > $H^+$ and $Na^+$ > $K^+$ > $NH_4{^+}$ > $Ca^{2+}$ > $Mg^{2+}=H^+$, respectively. The anions of all sites were $SO{_4}^{2-}$ > $NO_3{^-}$ > $Cl^-$. While the amounts of sulfate, one of the major dissolved components of rainwater, were 77.6 and 75.6 ueq $L^{-1}$ in Suwon and Yeoju, the ones of NSS-$SO{_4}^{2-}$ (Non-Sea Salt sulfate) were 83 and 82% in Suwon and Yeoju, respectively. The comparison of observed pH values ($pH_{obs}$) with the theoretical pH values ($pH_{the}$) showed that the neutralization of rain water considerably went along during the study periods. The highest amounts of rainfall throughout the year in Suwon and Yeoju were 572.3 and 484.6 mm in July, and its corresponding nitrogen loadings in Suwon and Yeoju were 5.28 and 3.50 kg $ha^{-1}$, respectively. The major ion contents for crop growth with $SO{_4}^{2-}$, $Ca^{2+}$, $K^+$ and $Mg^{2+}$ were 51.7, 5.2, 11.8 and 1.8 kg $ha^{-1}$ in Suwon and 34.2, 4.0, 4.2 and 1.1 kg $ha^{-1}$ in Yeoju.

• Journal of Soil and Groundwater Environment
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• v.22 no.5
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• pp.71-81
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• 2017

The hydrogeochemical characteristics of groundwater in the small waterworks are examined with 81 groundwater samples in Ulju region, Ulsan. The pH ranged in 6.3-8.2 and did not exceed the drinking water standards. Electrical conductivity ranged from $50{\mu}S/cm$ to $1,719{\mu}S/cm$. It indicated that the electrical conductivities in groundwaters at the study area are relatively low, compared with other groundwaters in Ulsan area. The calcium concentrations in groundwaters ranged from 3.55 to 113.01 mg/L, and sodium concentrations ranged from 2.02 to 65.50 mg/L. Nitrate concentrations ranged from 0 to 100.56 mg/L and potassium concentrations ranged from N.D (not detected) to 2.50 mg/L. Major cations and anions were mainly derived from the water-rock interaction involving feldspar, gypsum and calcite. The groundwaters were mainly the $Ca-(Na)-HCO_3$ type, classified as the early stage of groundwater evolutions. The correlation between electrical conductivities and Ca concentrations in groundwaters was relatively high ($R^2=0.74$). In the correlations between ions, the correlation coefficient between $SO_4$ and Ca was 0.65 and between Mg and $HCO_3$ was 0.65.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.171.2-171.2
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• 2016

The 2-dimensiona electron gas (2DEG) layers have opened tremendous interests in the heterooxide interfaces formed between two insulating materials, especially between LaAlO3 and $SrTiO_3$. The 2DEG layers exhibit extremely high mobility and carrier concentrations along with metallic transport phenomena unlike the constituent oxide materials, i.e., $LaAlO_3$ and $SrTiO_3$. The current work inserted artificially the interfacial layer, $Sr_xCa_{1-x}TiO_3$ between $LaAlO_3$ and $SrTiO_3$, with the aim to controlling the 2-dimensional transports. The insertion of the additional materials affect significantly their corresponding electrical transports. Such features have been probed using DC and AC-based characterizations. In particular, impedance spectroscopy was employed as an AC-based characterization tool. Frequency-dependent impedance spectroscopy have been widely applied to a number of electroceramic materials, such as varistors, MLCCs, solid electrolytes, etc. Impedance spectroscopy provides powerful information on the materials system: i) the simultaneous measurement of conductivity and dielectric constants, ii) systematic identification of electrical origins among bulk-, grain boundary-, and electrode-based responses, and iii) the numerical estimation on the uniformity of the electrical origins. Impedance spectroscopy was applied to the $LaAlO_3/Sr_xCa_{1-x}TiO_3/SrTiO_3$ system, in order to understand the 2-dimensional transports in terms of the interfacial design concepts. The 2-dimensional conduction behavior system is analyzed with special emphasis on the underlying mechanisms. Such approach is discussed towards rational optimization of the 2-dimensional nanoelectronic devices.

• Composites Research
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• v.30 no.5
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• pp.288-296
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• 2017

The focus of this study is to experimentally investigate the heat dissipation characteristics of poly (methyl methacrylate) (PMMA) composite films with phase change materials (PCM) to resolve heat build-up problems encountered in various electronic devices. In this study, two different types of phase change materials were used to fabricate the composite films by compression molding method and PCM paste sealing method then compared. It was observed in this study that the heat dissipation capability of PCM/PMMA composite films was remarkably enhanced by applying graphite sheet or graphene film into the composite due to their high thermal conductivity. These PCM/ PMMA composite films were attached on the hot spot inside smart phone and tested its surface temperature change according to time. The heat dissipation capability of PCM/PMMA composite film incorporated smart phone was increased 154% and hybrid PCM/PMMA composite film incorporated smart phone was increased 286% over the reference, respectively.

• Asian-Australasian Journal of Animal Sciences
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• v.30 no.9
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• pp.1340-1349
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• 2017

Objective: This study aimed to evaluate the microbiological and cellular milk profile for the diagnosis of subclinical mastitis in female buffaloes and to assess risk factors for predisposition of the disease. Methods: Analyses were carried out by standard plate count (SPC), identification of species and antibiotic resistance, somatic cell count (SCC), electrical electrical conductivity of milk (ECM), and lactoferrin content in milk. Teat cups were swabbed to evaluate risk factors, observing hyperkeratosis, milking vacuum pressure and cleanliness of the site. Hence, 30 female buffaloes were randomly selected (15 from a group in early lactation and 15 in late lactation). Results: The most common bacteria in the microbiological examination were Staphylococcus spp., Streptococcus spp. and Corynebacterium sp. In the antibiotic sensitivity test, 10 (58.82%) of the 17 antibiotics tested were sensitive to all isolates, and resistant bacteria were Streptococcus uberis, Streptococcus dysgalactiae, Streptococcus haemolyticus, and Escherichia coli. It was observed that positive samples in the microbiological examination showed total bacterial count between $9.10{\times}10^3$ to $6.94{\times}10^6$ colony forming units/mL, SCC between 42,000 to 4,320,000 cells/mL and ECM ranging from 1.85 to 7.40 mS/cm. It was also found that the teat cups had high microbial counts indicating poor hygiene, and even faults in the cleanliness of the animals' waiting room were observed. It is concluded that values of SCC above 537,000 cells/mL and ECM above 3.0 mS/mL are indications of mammary gland infection for this herd; however, the association of these values with a microbiological analysis is necessary to more accurately evaluate the health status of mammary glands with subclinical mastitis. Conclusion: Through phenotypic characterization of bacteria involved in the samples, the genera Staphylococcus spp., Streptococcus spp., and Corynebacterimum bovis were the most prevalent in this study. Faults in environment and equipment hygienization are factors that are directly associated with mastitis.

• Journal of the Korean Applied Science and Technology
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• v.34 no.2
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• pp.260-270
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• 2017

Zirconia has white color and physical, chemical stability, also using in high temperature materials and various industrial structural ceramics such as heat insulating materials and refractories due to their low thermal conductivity, excellent strength, toughness, and corrosion resistance. If hydrophobically modified zirconia is introduced into a hydrophobic acrylate coating solution, the hardness, chemical, electrical, and optical properties will be improved due to the better dispersibility of inorganic particle in organic coating media. Thus, we introduced $-CH_3$ group through silylation reaction using either trimethylchlorosilane(TMCS) or hexamethyldisilazane(HMDZ) on zirconia surface. The $Si-CH_3$ peaks derived from TMCS and HMDZ on hydrophobically modified zirconia surface was confirmed by FT-IR ATR spectroscopy, and introduction of silicon was confirmed by FE-SEM/EDS and ICP-AES. In addition, the sedimentation rate result in acrylate monomer of the modified zirconia showed the improved dispersibility. Comparison of the sizes of a pristine and the modified zirconia particles, which were clearly measured not by the normal microscope but by particle size analysis, provided a pulverizing was occurred by physical force during the silylation process. From the BET analysis data, the specific surface area of zirconia was approximately $18m^2/g$ and did not significantly change during modification process.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.6
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• pp.662-669
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• 2015

There has been an increased interest in the mitigation of wax deposition because wax, which usually accumulates in subsea oil-production systems, interrupts stable oil production and significantly increases the cost. To guarantee a required oil flow by mitigating wax deposition, we need to obtain a reliable estimation of the wax deposition. In this research, we perform simulations to understand the major mechanisms that lead to wax deposition, namely molecular diffusion, shear stripping reduction, and aging. While the model variables (shear reduction multiplier, wax porosity, wax thermal conductivity, and molecular diffusion multiplier) can be measured experimentally, they have high uncertainty. We perform an analysis of these variables and the amount of water and gas in the multiphase flow to determine these effects on the behavior of wax deposition. Based on the results obtained during this study for a higher wax porosity and molecular diffusion multiplier, we were able to confirm the presence of thicker wax deposits. As the shear reduction multiplier decreased, the thickness of the wax deposits increased. As the amount of water increased, there was also an increase in the amount of wax deposits until 40% water cut and decreased. As the amount of gas increased, the amount of wax deposits increased because of the loss of the light hydrocarbon component in the liquid phase. The results of this study can be utilized to estimate the wax deposition behavior by comparing the experiment (or field) and simulation data.

• Korean Journal of Soil Science and Fertilizer
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• v.31 no.2
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• pp.204-210
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• 1998

The experiment was conducted to obtain the basic data required to characterize and improve rhizosphere environment of salt-accumulated greenhouse(SAG) soils by comparing the soil properties and the microbial flora of such soils to those of unprotected arable upland(UAU) soils. Soils were sampled from greenhouses and unprotected upland fields around the country. Microbial propulation, biomass C content and soil chemical properties were of interest. Population density of fluorescent Pseudomonas was high in UAU soils, while those of pathogenic Fusarium sp. and fluorescent Pseudomonas were low in SAG soils. With increasing soil organic matter(OM) content, the population densities of Bacillus sp., fluorescent Pseudomonas sp., Enterobacteriaceae, and microbial biomass C content increased. As soil electrical conductivity(EC) increased higher than $5.1dS\;m^{-1}$, the ratios of bacteria to fungi(B/F) and actinomycetes to fungi(A/F) and the population density of fluorescent Pseudomonas decreased remarkably. The soil pH was positively related to the population density of aerobic bacteria, while it was negatively related to that of fungi. The soil OM content was significantly correlated to the population densities of actinomycetes($r=0.226^*$). Bacillus sp.($r=0.334^{**}$), Enterobacteriaceae($r=0.276^*$), and the microbial biomass C content($R=0.439^{**}$). The population density of actinomycetes was also significantly correlated with soil exchangeable Ca($r=0.334^{**}$) and Mg($r=0.352^{**}$).