• Structural Engineering and Mechanics
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• v.84 no.2
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• pp.155-165
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• 2022

The use of electricity and communication between electronic devices is increasing daily, which makes the stability of electrical power supply vital. Since the 1990s, large earthquakes have occurred frequently causing considerable direct damage to electrical power facilities as well as secondary damage, such as difficulty in restoring functions due to the interruption of electric power supply. Therefore, it is very important to establish measures to protect electrical power facilities, such as transformers and switchboards, from earthquakes. In this study, a 154 kV transformer whose service life had expired was installed on the base fabricated by simulating the field conditions and conducting the shaking table tests. The dynamic characteristics and seismic behavior of the 154 kV transformer were analyzed through the resonance frequency search test and seismic simulation test that considers the front, rear, left, and right directions. Since the purpose of this study is to analyze the acceleration amplification in the bushing due to the acceleration amplification, the experimental results were analyzed focusing on the acceleration response and the converted acceleration amplification ratio rather than the failure due to the displacement response of the transformer. The seismic force amplification at the transformer bushing was evaluated by simulating the characteristics of electrical power facilities in South Korea, and compared with the IEC TS 61463 acceleration amplification factor. Finally, the amplification factor at zero period acceleration (ZPA) modified for each return period was summarized. The results of this study can be used as data to define the amplification factor at ZPA of the transformer bushing, simulating the characteristics of electrical power facilities in Korea.

• Journal of the Korean Electrochemical Society
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• v.19 no.3
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• pp.69-79
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• 2016

Lithium ion battery with high energy density is expanding its application area to electric automobile and electricity storage field beyond existing portable electric devices. Such expansion of an application field is demanding higher characteristic and stable long life characteristic of an anode material, the natural graphite that became commercialized in lithium ion battery. This thesis produced cathode by using natural graphite anode material, analyzed creation of the cathode SEI film created due to initial reaction by using electrolyte additives, VC (vinylene carbonate), VEC (vinyl ethylene carbonate), and FEC (fluoroethylene carbonate), and considered correlation with the accompanying electrochemical transformation. This study compared and analyzed the SEI film variation of natural graphite cathode according to the electrolyte additive with SEI that is formed at the time of initial filling and cathode of $60^{\circ}C$ life characteristic. At the time of initial filling, the profile showed changes due to the SEI formation, and SEI was formed in No-Additive in approximately 0.9 V through EVS, but for VC, VEC, and FEC, the formation reaction was created above 1 V. In $60^{\circ}C$ lifespan characteristic evaluation, the initial efficiency was highest in No-Additive and showed high contents percentage, but when cycle was progressed, the capacity maintenance rate decreased more than VC and FEC as the capacity and efficiency at the time of filling decreased, and VEC showed lowest performance in efficiency and capacity maintenance rate. Changes of SEI could not be verified through SEM, but it was identified that as the cycle of SEI ingredients was progressed through FT-IR, ingredients of Alkyl carbonate ($RCO_2Li$) affiliation of the $2850-2900cm^{-1}$ was maintained more solidly and the resistance increased as cycle was progressed through EIS, and specially, it was identified that the resistance due to No-Additive and SEI of VEC became very significant. Continuous loss of additives was verified through GC-MS, and the loss of additives from partial decomposition and remodeling of SEI formed the non-uniform surface of SEI and is judged to be the increase of resistance.

• Journal of The Korean Association For Science Education
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• v.37 no.2
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• pp.253-262
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• 2017

This study aims at investigating the perceptions of science teachers about the role of visual representations in the teaching of electromagnetism, and finding out how science teachers use visual representations in their teaching of electromagnetism and the difficulties they experience in dealing with those representations. A total of 121 science teachers responded to the online survey. The results showed that most of the teachers agreed to the significance of using visual representations in the classroom but regarded their role as means of simply delivering science knowledge rather than constructing or generating knowledge. For the three visual representations widely used in teaching of electromagnetism in secondary schools (electrostatic induction on electroscope, magnetic field around current carrying wire, structure and principle of electric motor), the teachers preferred teacher-centered use of visual representations rather than student-centered and teacher's construction of representations were the most frequent among four types of use; interpretation, construction, application, and evaluation. The difficulties of teaching with these three visual representations were categorized into several factors; teachers, students, the characteristics of the representations, and lack of resources and classroom environment. Teachers' limited perceptions about the role of visual representations were associated with the ways of using visual representations in their teaching. Implications for the effective use of visual representations for science learning and teaching were discussed.

• Geophysics and Geophysical Exploration
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• v.7 no.2
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• pp.136-147
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• 2004

In this study, the characteristics of magnetotelluric (MT) responses due to a three-dimensional (3-D) body are analyzed with 3-D numerical modeling. The first model for the analysis consists of a single isolated conductive body embedded in a resistive homogeneous half-space. The second model has an additional conductive overburden while the other conditions remain the same as the first one. The analysis of apparent resistivities shows well that the 3-D effects are dominant over some frequency range for the first model. Two mechanisms, current channeling and induction, for secondary electric fields due to the conductive body are analyzed at various frequencies: at high frequencies induction is more dominant than channeling, while at low frequencies channeling is more dominant than induction. Tippers have a strong relation to the position of anomalous body and the real and imaginary parts of induction vector also indicate the position of anomalous body. off-line conductive anomaly sometimes causes severe problem in 2-D interpretation. In such case, induction vector analysis can give information on the existence and location of the anomalous body. Each parameter of the second model shows similar responses as those of the first model. The only difference is that the magnitude of all parameters is decreased and that the domain showing the 3-D effects becomes narrower. As shown in this study, the analysis of 3-D effects provides a useful and effective means to understand the 3-D subsurface structure and to interpret MT survey data.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.369-377
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• 2013

This paper deals with the state of charge(SOC) and life cycle evaluation algorithm for lead-acid battery, which is essential factor of the electric vehicle(EV) and the stabilization of renewable energy in the smart grid. In order to perform the effective operation of the lead-acid battery, SOC and life cycle evaluation algorithm is required. Specific gravity with the change of electrolyte temperature inside battery case should be obtained to evaluate the SOC of lead-acid battery, however it is difficult to measure the electrolyte temperature of sealed type lead-acid battery. To overcome this problem, this paper proposes the equation of thermal transmission to compensate internal temperature of the lead-acid battery. Also, it is difficult to exactly evaluate the life cycle of battery, depending on the operation conditions of lead-acid battery such as charging and discharging state, self discharging rate and environmental issue. In order to solve the problem, this paper presents the concept for gravity accumulation of charge and discharge cycle, which is the value converted at $20^{\circ}C$. By using the proposed algorithm, this paper propose the test device based on the Labview software. The simulation results show that it is a practical tool for the maintenance of lead-acid battery in the field of industry.

• Geophysics and Geophysical Exploration
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• v.15 no.2
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• pp.66-74
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• 2012

This paper presents development of a three-dimensional marine controlled-source electromagnetic (mCSEM) modeling algorithm and its application to a salt and reservoir model to examine detectability of mCSEM for a reservoir under complex subsurface structures. The algorithm is based on the finite difference method, and employs the secondary field formulation for an accurate and fast calculation of modeling responses. The algorithm is verified for a two-layer model by comparing solutions not only with analytic solutions but also with those from other 3D modeling algorithm. We calculate and analyze electric and magnetic fields and their normalized responses for a salt and reservoir model due to three sources located at boundaries between a salt, a reservoir, and background. Numbers and positions of resistive anomalies are informed by normalized responses for three sources, and types of resistive anomalies can be informed when there is a priori information about a salt by seismic exploration.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.9
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• pp.611-615
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• 2001

Y$_2$O$_3$ thin films have been proposed as a buffering insulator of metal/ferroelectric/insulator/semiconductor field effect transistor(MFISFET)-type ferroelectric random access memory (FRAM). In this study, $Y_2$O$_3$ thin films were etched with inductively coupled plasma(ICP). The etch rates of $Y_2$O$_3$ and YMnO$_3$, and the selectivity of $Y_2$O$_3$ to YMnO$_3$ were investigated by varying Cl$_2$/(Cl$_2$＋Ar) gas mixing ratio. The maximum etch rate of $Y_2$O$_3$, and the selectivity of $Y_2$O$_3$ to YMnO$_3$ were 302$\AA$/min, and 2.4 at Cl$_2$/(Cl$_2$＋Ar) gas mixing ratio of 0.2 respectively. Optical emission spectroscopy(OES) was used to understand the effects of gas combination on the etch rate of $Y_2$O$_3$ thin film. The surface reaction of the etched $Y_2$O$_3$ thin films was investigated by x-ray photoelectron spectroscopy (XPS). XPS analysis confirmed that there was chemical reaction between Y and Cl. This result was confirmed by secondary ion mass spectroscopy(SIMS) analysis.

• The Journal of the Korea Contents Association
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• v.21 no.2
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• pp.85-99
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• 2021

Graphene, called the "dream material" is drawing attention as a groundbreaking new material that will lead the era of the 4th Industrial Revolution. Graphene has high strength, excellent electrical and thermal conductivity, excellent optical permeability, and excellent gas barrier properties. In this paper, as the South Korean government recently announced Green New Deal and Digital New Deal policy, we analyze graphene technology, which is also attracting attention for its application to Corona 19 biosensor, to understand its national R&D trend and knowledge structure, and to explore the possibility of its application. Firstly, 4,054 cases of national R&D project information for the last 10 years are collected from the National Science & Technology Information Service(NTIS) to analyze the trend of graphene-related R&D. Besides, projects classified as green technology are analyzed concerning the government's Green New Deal policy. Secondly, text mining analysis is conducted by collecting 500 recent graphene-related articles from e-newspapers. According to the analysis, the field with the largest number of projects was found to be high-efficiency secondary battery technology, and the proportion of total research funds was also the highest. It is expected that South Korea will lead the development of graphene technology in the future to become a world leader in diverse industries including electric vehicles, cellular phone batteries, next-generation semiconductors, 5G, and biosensors.