• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.4
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• pp.457-463
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• 2024

(Bi_1/2Na_1/2)TiO₃(BNT) piezoelectric ceramics are one of the promising materials that can replace Pb(Zr, Ti)O₃(PZT) piezoelectric ceramics due to the high electromechanical strain properties. However, it is still difficult to use practical applications because the required electric field for inducing electromechanical strain is relatively higher than that of PZT ceramics. To overcome this problem, it has been intensively studied on doping impurity or modifying other ABO₃ for BNT-based piezoelectric ceramics. Therefore, this study investigated the effects of La₂O₃ doping on the phase transition behavior and electromechanical strain properties in BNT-SrTiO₃ (BNT-ST) lead-free piezoelectric ceramics. In the case of the temperature-dependent dielectric properties, it was confirmed that a phase transition from ferroelectrics to relaxors is induced with increasing La₂O₃ content. As a result, the electromechanical strain properties of BNT-ST ceramics were improved. The highest S_max/E_max value corresponding to 300 pm/V was obtained at 2 mol% La₂O₃-dopped BNT-ST ceramics. Accordingly, this study successfully demonstrated that La₂O₃ doping is effective on the inducing phase transition from ferroelectrics to relaxors and the improving electromechanical strain properties of BNT-ST lead-free piezoelectric ceramics.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.199-200
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• 2019

Although accidents in the domestic construction industry have been decreased gradually, deaths in the construction sites have been occupied 49.9 percent of the total industry and deaths from fall accident have been accounted for 59.7 percent of the construction industry. In order to prevent fall accident, Occupation Safety and Health Act(OSHA) was enacted for setting management standards and detailed regulations was designed by the Ministry of Employment and Labor. Although government has been pushed for companies and workers to comply the regulations, currently, many domestic construction sites have been violated. On the other hand, in safety-advanced countries such as the United States, Japan, and the EU, industrial accidents have been decreased due to continual application of adapted safety policies according to characteristic in each country. Therefore, it is necessary to analyze laws and polices of advanced countries and apply them to domestic construction sites in order to reduce fall accidents. Therefore, the objective of this study is to compare domestic laws related fall accident with advanced countries laws. In the future, the results of this study will be utilized as a reference to reinforce Occupation Safety and Health Act(OSHA).

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.207-208
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• 2019

Currently, as the public interest for environmental issues has grown rapidly, the needs for G-SEED have also increased. However, as investment according to eco-friendly elements is inevitable to receive G-SEED certification, it is necessary to find out whether or not the sales price of apartments have increased compared to investment costs. Therefore, the objective of this study is to analyze the sales price of apartments according to G-SEED by using T-test. To achieve the objective, First, variables affecting on the sales price of apartments are selected. Second, the data are collected by using GIS(Geographic Information System). Third, after testing the normality, a comparison analysis is conducted on the sales price between G-SEED certified and non-certified apartments by using T-test. As a result, it is concluded that G-SEED certified apartments are more expensive than non-certified apartments. In the future, these findings can be utilized to develop of apartments price calculation model based on the G-SEED.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.180-181
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• 2019

South Korea has long been without major earthquakes. But 317 public facilities have been damaged by Po-Hang earthquake. Among them, 103 educational facilities suffered 25.6 billion won worth of damage. This is the most damaging of public facilities. The earthquake damage was mainly centered on non-seismic retrofit educational facilities and masonry architectural wall systems installed on the outer walls of buildings. Therefore, the purpose of this study is to develop a filling material that can be applied to the non-seismic retrofit of masonry architectural wall systems installed on the outer walls of educational facilities. To achieve the objective, first, set the filling material requirements. Second, set the sequence model of experiments and prepare for the experiment. Third, after the experiment, analyze the results obtained through the experiment. Forth, the optimal filling material is selected by comparing the analyzed results with the requirements. As a results, E-S-X sample using epoxy resin were selected for the seismic retrofit of masonry architectural wall systems in educational facilities. In the future, this study can be used as a basic material for developing seismic reinforcement methods guidelines in domestic existing educational facilities.

• Journal of Engineering Education Research
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• v.22 no.4
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• pp.22-31
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• 2019

This study aims to elucidate the relationship between physics and mathematics to predict achievement for the college level of engineering courses. For the last 4 years, more than 3,000 engineering college freshmen of this study took the diagnostic tests on three subjects, which were physics, mathematics, and chemistry before enrollment. We studied how strongly these diagnostic scores can predict each general college course grades. The correlation between the physics diagnostic scores and the course grades in physics was .264, which was significantly lower than the correlation between the mathematics scores and the physics grades, .311. This stronger prediction of the mathematical diagnostic scores for the general course grades was not found when predicting the grades in chemistry. We therefore conclude that mathematical preparation can unexpectedly predict future achievement in physics better than physics preparation due to the academic interrelationships between mathematics and physics.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.3
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• pp.211-216
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• 2019

In order to utilize the marine environment in various fields such as renewable energy and offshore plant, it is necessary to utilize the far and deep ocean. However, there is still a limit to overcome and utilize the extreme deep-sea environment. Currently, the mooring system, which is the representative position control method of floating structure, has a structural and economic limit to expand the installation range to extreme deep-sea environment. Research has been conducted to utilize wave energy by developing floater using flapping foil as an alternative for station keeping in the deep sea by University of Ulsan. Based on the research, a model test was conducted for application to actual structures. In this study, we investigate how the floating body with passive flapping foils move in regular waves with different periods and study the condition of the model that can maintain its position within a certain range by overcoming the movement.

• Journal of Korean Society on Water Environment
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• v.27 no.2
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• pp.210-217
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• 2011

In results of accomplishing fundamental study to improve the flocculant-mixing of the Flash-Mixer in Onsan Water-Treatment Plant at the small cost, We obtained 8.9% of mixing-efficiency from the field data and 3.2% of the characteristic flow-ratio as the available maximum volume-ratio in this Water-Treatment Plant. The optimum elements with the deflector diameter of 400 mm and deflector angle of $145^{\circ}$ at the flow ratio of 3.2% could be obtained from the expanded study on the ground of the fundamental study. Finally, the efficiency could be improved about 510% from 8.9% to 45.4% and the average turbidity could be improved about 14%.

• Korean Journal of Metals and Materials
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• v.49 no.5
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• pp.419-424
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• 2011

Carbon nanotubes (CNTs) were directly synthesized on a copper (Cu) plate as a current collector by the catalytic thermal vapor deposition method for an electric double-layer capacitor (EDLC) electrode. The diameters of vertically aligned CNTs grown on the Cu plate were 20~30 nm. From cyclic voltammetry (CV) results, the CNTs/Cu electrode showed high specific capacitance with typical profiles of EDLCs. Rectangularshaped CV curves suggested that the CNTs/Cu electrode could be an excellent candidate for an EDLC electrode. The specific capacitances were in a range of 25~75 F/g with a scan rate of 10~100 mV/s and KOH electrolyte concentration 1~6 M, and were maintained up to 1000 charge/discharge cycles due to strong adhesion between the Cu substrate and the CNTs.

• Journal of Powder Materials
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• v.28 no.6
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• pp.509-517
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• 2021

Smart materials capable of changing their characteristics in response to stimuli such as light, heat, pH, and electric and magnetic fields are promising for application to flexible electronics, soft robotics, and biomedicine. Compared with conventional rigid materials, these materials are typically composed of soft materials that improve the biocompatibility and allow for large and dynamic deformations in response to external environmental stimuli. Among them, smart magnetic materials are attracting immense attention owing to their fast response, remote actuation, and wide penetration range under various conditions. In this review, we report the material design and fabrication of smart magnetic materials. Furthermore, we focus on recent advances in their typical applications, namely, soft magnetic actuators, sensors for self-assembly, object manipulation, shape transformation, multimodal robot actuation, and tactile sensing.

• Research in Community and Public Health Nursing
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• v.32 no.2
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• pp.186-194
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• 2021

Purpose: This study was conducted to find out the association between dual-use of the electronic cigarette (EC) and conventional cigarette (CC) and depression among undergraduate students. Methods: The participants of this study were 225 undergraduate students who were attending two universities located in Ulsan metropolitan city. Descriptive statistics and multiple regression were conducted to analyze the data. Results: Nicotine dependence and depression were significantly higher in the dual-use group than in the single-use group. Dual-use of the EC and CC was significantly associated with depression among undergraduate students. In addition, quality of sleep was significantly associated with depression among undergraduate students. Conclusion: In order to prevent depression among undergraduate students, it is necessary to improve the awareness of the danger of dual use of the EC and CC.