• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.9-16
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• 2013

Recent years have witnessed a strong need for eco-friendly and energy-efficient systems owing to global environmental problems. A heat exchanger is a well-known mechanical rig that has long been used in many energy systems. The use of a heat exchanger in an airplane engine has been attempted. In this case, the heat exchanger should be redesigned to be compact, lightweight, and highly reliable, and the issue of mechanical integrity gains importance. Therefore, in this study, we proposed a method for evaluating the mechanical integrity of a tube-type heat exchanger. A U-shaped single tube was used as an example, and its behavior and stress distribution were studied using fluid-structure interaction (FSI) analysis.

• Korean Journal of Mineralogy and Petrology
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• v.34 no.2
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• pp.121-131
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• 2021

Magnesium (Mg) present in carbonate minerals as impurities has been used as a geochemical proxy to infer the environmental conditions where the minerals precipitated. The reliability of Mg geochemical proxies requires fundamental understanding of Mg incorporation into minerals based on accurate speciation of Mg ²⁺ in the crystal structure, which is determined mainly by application of X-ray absorption spectroscopy (XAS). However, high uncertainties are involved in interpreting the XAS spectra of minerals containing trace amount of Mg ²⁺. Because density function theory (DFT) can predict an XAS spectrum for a crystal structure, DFT calculations can reduce the uncertainties in the interpretation of the XAS spectrum. In this study, we calculated ab initio Mg K-edge absorption spectra of Mg silicates and (hydr)oxides based on DFT and analyzed the correlation between the calculated spectra and Mg structural parameters. Our ab initio Mg K-edge absorption spectra well reproduced the key features of the experimental spectra. The absorption-edge positions of the calculated spectra showed the weak positive correlation with the average Mg-O bond distance or Mg effective coordination number. The current study shows that DFT-based core-level spectroscopy method is a powerful tool in providing standard Mg K-edge spectra of diverse Mg minerals and determining the Mg chemical species within carbonate minerals.

• Korean Chemical Engineering Research
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• v.57 no.2
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• pp.205-209
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• 2019

The exquisite structure and attractive biological properties of biominerals have great potential and increased interest for use in a wide range of medical and industrial applications. Calcium carbonate biomineralization, mainly controlled by shell matrix proteins, has been used as a representative model to understand the biomineralization mechanism. In this study, in vitro calcium carbonate crystallization was carried out under room temperature and atmospheric pressure using recombinant shell matrix protein GRP_BA and artificial shell matrix protein GG1234. Both proteins inhibited the growth of typical rhombohedral calcite crystals in the calcium carbonate crystallization using $CaCl_2$ solution and $(NH_4)_2CO_3$ vapor, and spherulitic calcite crystals with rosette-like structures were synthesized in both the presence of GRP_BA and GG1234. These results might be caused by the properties of block-like domain structure and intrinsically disordered proteins. We expect that this study can contribute to enhance understanding of the calcium carbonate biomineralization controlled by shell matrix proteins.

• The Journal of the Korea Contents Association
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• v.19 no.2
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• pp.269-276
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• 2019

This research was conducted by targeting pregnant women in the trial operation of dental hygiene care program with the focus on non-surgical periodontal treatments at the Maternal and Child Health center in the public health center. This study was conducted to provide basic data to dental hygienists who operate oral health promotion programs by targeting pregnant women of the local community through the evaluation on structure, the assessment process and results from the pilot program at the public health center. The targets are nine pregnant women who have been involved in the Dental hygiene care program three times. An evaluation on the structure, process and results according to the Indicators of each program were conducted. The results of dental hygiene care program found that the retention rate decreased. The retention of the probing pocket depth larger than 4mm was 40.4% to 14.0%(p<0.05). The retention rate of the gingival bleeding teeth was 4.6% to 2.7% (p=0.180). PHP Index improved. 1.7 points in the 1st to 1.4 points in the 3rd in the case of the second pregnant woman and 2.4 points in the 1st to 1.3 points (p<0.05) in the 3rd in the case of the third pregnant woman. The applicable and expandable possibility of the dental hygiene care program with the focus on non-surgical periodontal treatments at the Community Health Center is significant in the result of this study. In the future, long-term operation and ongoing monitoring of this program is needed.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.29 no.3
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• pp.124-133
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• 2011

The purpose of this study is to interpret the landscape characteristics of Changdeokgung's rear garden with the idea of Yijing(意境) the way to have a sense of an imaginative object. A term of Jing(境) in Yi-jing means a boundary of man's consciousness. On the boundary of consciousness for an imaginative object, there is a situation of man's emotion to be called Qingjing(情境) to meet an object, and beyond Qingjing, there is Yijing, a consciousness of the idea and the truth. The Structure of the Yijing is an analytical framework in this study. It is clarified that the idea of Yijing and landscape characteristics of changdeokgung's rear garden to analyze works of kings and related historical documents. In result, there were three kings named Injo, Sukjeong and Jeongjo who played big roles to develop the rear garden. First, Injo had built physical structure of the rear garden, the second Sukjong enjoyed Qingjing with composing the poems of Sangrimshipkyoung(上林十景), Jeongjo clearly had made a boundary of idea of Yijing broaden. It is an effective way to interpret imaginative characteristics of our traditional landscape through the concept of Yijing the useful way to understand and systemize a subject of idealistic consciousness.

• Journal of the Korean Geosynthetics Society
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• v.20 no.1
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• pp.1-8
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• 2021

In urban areas, structures are installed deep underground in the lower part of the structure to utilize space. Therefore, a retaining wall is used to prevent earth pressure from the ground when constructing a structure. Due to the development of construction technology, retaining wall applied to excavation work are used to prevent danger such as falling rocks and landslides in temporary facilities when construction or retaining walls are installed. In general, the application of a retaining wall to a temporary facility during the embankment construction is the case of expanding an existing roads or railways. Therefore, it is necessary to study the retaining wall applied to the embankment construction such as the double-track site of the high-speed railway. In this study, two types of common one row H-pile retaining wall and two types of IER retaining wall were analyzed, and the stability of the retaining wall applied to the construction of double-track of the high-speed railway was analyzed. The earth retaining wall is a construction method that combines forced pile applied to the stabilization of the slope with the wall of the earth retaining wall. As a result of the analysis, the IER retaining wall had maximum lateral displacement of 19.0% compared to the type with H-plie installed only in the front while dynamic load was applied. In addition, the slower the speed of high-speed railway, the more displacement occurred, and the results show that more caution is needed when designing the ground in low-speed sections.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.313-319
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• 2022

AlGaN/GaN based HfO₂ MOSHEMT (metal oxide semiconductor high electron transistor) with different gate recess depth was simulate to demonstrate a successful normally-off operation of the transistor. Three types of the HEMT structures including a conventional HEMT, a gate-recessed HEMT with 3 nm thick AlGaN layer, and MIS-HEMT without AlGaN layer in the gate region. The conventional HEMT showed a normally-on characteristics with a drain current of 0.35 A at V_G = 0 V and V_DS = 15 V. The recessed HEMT with 3 nm AlGaN layer exhibited a decreased drain current of 0.15 A under the same bias condition due to the decrease of electron concentration in 2DEG (2-dimensional electron gas) channel. For the last HEMT structure, distinctive normally- off behavior of the transistor was observed, and the turn-on voltage was shifted to 0 V.

• Journal of the Korea Institute of Building Construction
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• v.22 no.1
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• pp.69-80
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• 2022

The proportion of buildings over 30 years old in Korea has increased, from 29.0% in 2005 to 37.8% in 2019. These old buildings were built during a time in which there was a lack of building-related safety standards in areas such as fire safety performance. Worse, during their years of use, many such old buildings have had illegal changes and extensions made, making them more vulnerable in terms of safety. Fire safety investigations are being conducted to prevent large-scale disasters in multi-use buildings, but no investigation has been conducted at the regional district level, where small-scale old buildings are concentrated. Therefore, to identify fire risk factors in the old building district where old buildings are concentrated, the composition characteristics of the buildings were first analyzed. To examine the spatial characteristics of old building districts in order to derive fire risk factors, the results of this analysis based on the structure, use, roof type, and year of approval for use are as follows. It was found through our analysis that as of the date of approval for the use of the building, the main structure of the building has the greatest impact.

• Korea Trade Review
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• v.43 no.6
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• pp.51-70
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• 2018

This study is to define the relationship between capital structure and the market share in the global shipping market, estimating the debt-equity ratio. To analyze the impact of the debt-equity ratio on market share, this study collected data from the 100 largest shipping companies from 2010 to 2017. Results identified that global shipping lines moderate their debt-equity rates to 62%, and all of them strategically utilize debt in order to increase market share in global shipping market. In comparison between the group focused on cargo volume and another group focused on freight rates, it is found that the group focused on cargo volume increase their handling cargo volume through increasing the debt rates. Another group used debt rate for reducing the freight rate and enhancing market power. Furthermore, after classifying the samples into high-growth and low-growth companies, this study compared the group focused on cargo volume and another group focused on freight rates. As a result, the low-growth group showed more significant impacts of the debt rate on market share than the high-growth group. The results of this study provide useful insight for future strategic decision making of shipping lines in the global shipping market.

• Korea Trade Review
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• v.48 no.2
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• pp.129-151
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• 2023

This study explores whether market share matters for ERPT and also for the effects of FTA on ERPT among exporting countries in the four major fishery import markets - frozen pollock, frozen mackerel, frozen tuna, and frozen spawn in South Korea. In addition, I investigate whether market share matters for price competition among exporting countries. For this, I estimate the export price equation based on the maximum likelihood method by utilizing data on export price in terms of Korean currency, and the cross rate between South Korea and the exporting countries from 2010:M1 to 2019:M12 for the four major fishery import markets. According to the findings, the market share of exporting countries in the import markets matters for the positive effects of FTA on ERPT; however, it is hard to find the relation between the market share of exporting counties and ERPT. In addition, I find little evidence on the effects of market share on price competition structures among exporting countries. I believe that this study helps domestic fishery producers to understand that ERPT, the effect of FTA on ERPT, and price competition structures among exporting countries would be affected by the market share of each exporting country in the major fishery import markets in South Korea. Also, this study would help domestic fishery producers to think about how to deal with the effects of the change in the exchange rate on fishery markets for each FTA partner according to its market share after FTA is effective.