• Corrosion Science and Technology
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• v.17 no.6
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• pp.287-291
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• 2018

In this study, corrosion behavior of a SA178-A alloy used in the boiler tube of a district heating system was investigated in different environments where it was exposed to pure water, district heating (DH) water, and filtered district heating (FDH) water. After the corrosion test, the surface morphology was examined for observation of the number of pitting sites and pitting area fraction, using a scanning electron microscope. The DH water and FDH water conditions resulted in a lower corrosion potential and pitting potential, and revealed a significantly higher corrosion rate than the pure water condition. The pitting sites in the DH water (pH 9.6) were approximately eighteen times larger than those in the pure water (pH 9.6). Compared to the DH water, the corrosion potential became more noble in the FDH water condition, where iron ions were reduced through filtration. However, the corrosion rate increased in the FDH water due to an increased concentration of chloride ions, which deteriorated the stability of passive film.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.44.4-45
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• 2018

(4179) Toutatis (Toutatis hereafter) is one of the Near-Earth Asteroids which has been studied most rigorously not only via ground-based photometric, spectroscopic, polarimetric, and radar observations, but also via the in-situ observation by the Chinese Chang'e-2 spacecraft. However, one of the most fundamental physical properties, the geometric albedo, is less determined. In order to derive the reliable geometric albedo and further study the physical condition on the surface, we made photometric observations of Toutatis near the opposition (i.e., the opposite direction from the Sun). We thus observed it for four days on 2018 April 7-13 using three 1.6-m telescopes, which consist of the Korean Microlensing Telescope Network (KMTNet). Since the asteroid has a long rotational period (5.38 and 7.40 days from Chang'e-2, Zhao et al., 2015), the continuous observations with KMTNet matches the purpose of our photometric study of the asteroid. The observed data cover the phase angle (Sun-asteroid-observer's angle) of 0.65-2.79 degree. As a result, we found that the observed data exhibited the magnitude changes with an amplitude of ~0.8 mag. We calculated the time-variable geometrical cross-section using the radar shape model (Hudson & Ostro 1995), and corrected the effect from the observed data to derive the geometric albedo. In this presentation, we will present our photometric results. In addition, we will discuss about the regolith particles size together with the polarimetric properties based on the laboratory measurements of albedo-polarization maximum.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.4
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• pp.412-417
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• 2022

Capacitive-type humidity sensors with a high sensitivity and fast response/recovery times have attracted a great attention in non-contact respiration biological signal monitoring applications. However, complicated fabrication processes involving high-temperature heat treatment for the hygroscopic film is essential in the conventional ceramic-based humidity sensors. In this study, a non-toxic ceramic/metal halide (BaTiO₃(BT)/NaCl) humidity sensor was prepared at room temperature using a solvent-free aerosol deposition process (AD) without any additional process. Currently prepared BT/NaCl humidity sensor shows an excellent sensitivity (245 pF/RH%) and superior response/recovery times (3s/4s) due to the NaCl ionization effect resulting in an immense interfacial polarization. Furthermore, the non-contact respiration signal variation using the BT/NaCl sensor was determined to be over 700% by maintaining the distance of 20 cm between the individual and the sensor. Through the AD-fabricated sensor in this study, we expect to develop a non-contact biological signal monitoring system that can be applied to various fields such as respiratory disease detection and management, infant respiratory signal observation, and touchless skin moisture sensing button.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.373-383
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• 2021

The effect of Cr addition to high Mn steel on flow-accelerated corrosion (FAC) behavior in a neutral aqueous environment was evaluated. For comparison, two types of conventional ferritic steels (API X70 steel and 9% Ni steel) were used. A range of experiments (electrochemical polarization and impedance tests, weight loss measurement, and metallographic observation of corrosion scale) were conducted. This study showed that high Mn steel with 3% Cr exhibited the highest resistance to FAC presumably due to the formation of a bi-layer scale structure composed of an inner Cr enriched Fe oxide and an outer Mn substituted partially with Fe oxide on the surface. Although the high Mn steels had the lowest corrosion resistance at the initial corrosion stage due to rapid dissolution kinetics of Mn elements on their surface, the kinetics of inner scale (i.e. Cr enriched Fe oxide) formation on Cr-bearing high Mn steel was faster in dynamic flowing condition compared to stagnant condition. On the other hand, the corrosion scales formed on API X70 and 9% Ni steels did not provide sufficient anti-corrosion function during the prolonged exposure to dynamic flowing conditions.

• Journal of the Mineralogical Society of Korea
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• v.27 no.2
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• pp.63-72
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• 2014

This study is conducted to investigate mineralogical characteristics and estimate firing temperature and condition of earthenwares in the 5-6th Century which are found at ancient tombs in Gyo-dong, Gyo-ri, Changnyeong-eup, Changnyeong-gun, Gyeongsangnam-do, TKorea by applying petrological methods. For this study, mineralogical analysis, microtexture observation and chemical analysis were conducted. According to observations using a polarization microscope, the potshreds are mainly composed of quartz and feldspar and consist of some felsic volcanics, tempers, opaques and mullite, hematite and spinel were found under XRD and FTIR analysis. The flow pastes are observed in many potshreds, and it indicate that this textures made by the mixing process or the pottery made from the mixture of 2 sorts of clays at least. They dose not show the features of the potshreds firing under temperature of $1,200-1,300^{\circ}C$ rather than the earthenware firing under relatively low temperature of $1,000^{\circ}C$ approximately because of the existence of a number of pores and the crystals of the specific minerals. The growths mostly of mullite on the surface and into the cracks of the potshreds indicate that the firing condition was not uniform to make even temperature and oxidation. Most of the pottery shreds have felsic volcanic fragments and some of them have cristobalite which is formed at the temperature of more than 1,470^{\circ}C$. But considering the estimated firing temperature, these are not formed during firing but included in the original clay.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.890-899
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• 2014

Austenitic stainless steel is widely used in various industries due to its excellent corrosion resistance. However, Cr carbides precipitation along the grain boundaries after heat treatment or welding may develop Cr depleted zone, which acts as a preferential site for intergranular corrosion attack. To resolve this, carbon stabilizing element such as Ti or Nb are added to suppress formation of Cr carbides. However, there are few reports on corrosion characteristics under seawater environment of the stabilized stainless steel. This study investigated the effects of alloying contents on the electrochemical characteristics in seawater of stainless steel containing stabilizing element(Ti and Nb). To achieve this, the changes on the microstructure due to alloying were observed with microscope, and the electrochemical characteristics were determined by measurement of natural potential and potentiodynamic polarization experiments. The microscopic observation revealed that all specimens had inclusions other than the austenite matrix phase due to the addition of alloying elements. Such inclusions are considered to have different electrochemical characteristics from those of the matrix, and thus a clear distinction was found according to the type of stabilizers and the contents. The results of this study suggest that it is important to consider the effects of alloying contents on the electrochemical characteristics in seawater with the addition of Ti or Nb into austenitic stainless steel.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.3
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• pp.270-280
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• 2016

This paper investigates the evolution of EM admittance of piezoelectric transducers mounted on a notched beam from wave propagation perspective. A finite element analysis is adopted to obtain numerical solutions for Lamb waves reverberating on the notched beam. The mode-converted Lamb wave signals due to a notch are extracted by using the polarization characteristics of piezoelectric transducers collocated on the beam. Then, a series of temporal spectrums are computed to demonstrate the evolution of EM admittance through fast Fourier transform of the mode-converted Lamb wave signals which are consecutively truncated in the time domain. When truncation time is relatively small, the corresponding temporal spectrum is governed by the characteristics of the input driving frequency. As truncation time becomes large, however, the modal characteristics of the notched beam play a crucial role in the temporal spectrum within the input driving frequency band. This implies that mode-converted Lamb waves reverberating on the beam contributes to the resonance of the beam. The root mean square values are computed for the temporal spectrums in the vicinity of each resonance frequency. The root mean square values increase monotonically with respect to truncation time for any resonance frequencies. Finally the implications of the numerical observation are discussed in the context of damage detection of a beam.

• Corrosion Science and Technology
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• v.13 no.1
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• pp.28-35
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• 2014

Recently, the fuel oil of diesel engines of marine ships has been increasingly changed to heavy oil of low quality as the oil price is getting higher and higher. Therefore, the spiral gear attached at the motor of the oil purifier which plays an important role to purify the heavy oil is also easy to expose at severe environmental condition due to the purification of the heavy oil in higher temperature. Thus, the material of the spiral gear requires a better mechanical strength, wear and corrosion resistance. In this study, the heat treatment(tempering) with various holding time at temperature of $500^{\circ}C$ was carried out to the alloy of Cu-7Al-2.5Si as centrifugal casting, and the properties of both hardness and corrosion resistance with and without heat treatment were investigated with observation of the microstructure and with electrochemical methods, such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram, and a.c. impedance. in natural seawater solution. The ${\alpha}$, ${\beta}^{\prime}$ and ${\gamma}_2$ phases were observed in the material in spite of no heat treatment due to quenching effect of a spin mold. However, their phases, that is, ${\beta}^{\prime}$ and ${\gamma}_2$ phases decreased gradually with increasing the holding time at a constant temperature of $500^{\circ}C$. The hardness more or less decreased with heat treatment, however its corrosion resistance was improved with the heat treatment. Furthermore, the longer holding time, the better corrosion resistance. In addition, when the holding time was 48hrs, its corrosion current density showed the lowest value. The pattern of corroded surface was nearly similar to that of the pitting corrosion, and this morphology was greatly observed in the case of no heat treatment. It is considered that ${\gamma}_2$ phase at the grain boundary was corroded preferentially as an anode. However, the pattern of general corrosion exhibited increasingly due to decreasing the ${\gamma}_2$ phase with heat treatment. Consequently, it is suggested that the corrosion resistance of Cu-7Al-2.5Si alloy can be improved with the heat treatment as a holding time for 48 hrs at $500^{\circ}C$.

• Korean Journal of Heritage: History & Science
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• v.45 no.3
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• pp.160-173
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• 2012

Roofing tile research conducted in Korea so far is mostly related to studies on roofing tile patterns excavation report on the roof tile klin site in the aspects of archeology architecture and history of art. There have been continuous studies on kiln ground and manufacture techniques of roofing tiles. However it is difficult to find roofing tiles research based on scientific experiments. The research on this paper performs physical and chemical experimental study to understand order, manufacturing techniques and other characteristics of Chosun Dynasty roofing tiles excavated in Dongdaemun stadium. As for physical experimental study water absorption, specific gravity, whole-rock Magnetic susceptibility rate and Differential Thermal Analysis are conducted. As for chemical experimental study, neutron activation analysis(NAA), microstructure observation, X-ray diffractometry(XRD) analysis are conducted. Result of neutron activation analysis and statistical analysis on piece of roof tile 22 samples clearly show that the roofing tile samples are from different time line and places. It also shows different composition when compare average value of rare earth resources per findspots. It means roofing tiles were manufactured from clay mineral from several places. Close inspection using XRD and polarization microscope reveals that main components of roofing tiles are quartz and felspar. Mica and Illite are found partially. XRD analysis shows mullite mineral composition which occurs when roofing tile is calcined around $1000^{\circ}C$. Differential thermal analysis shows gradual exothermic peak near $900^{\circ}C$. Based on these results, it is assumed that roofing tile is made at $900{\sim}1000^{\circ}C$. result of XRD analysis shows mullite were made near $1000^{\circ}C$. in Differential Thermal Analysis shows gradual exothermic peak near $900^{\circ}C$. this results shows that roof tiles were made near 900~1000 near $1000^{\circ}C$ mean value of whole-rock Magnetic susceptibility rate. When performed comparative analysis using whole-rock Magnetic susceptibility rate average value, findspots provided no certain classification to arrange. Nonetheless low whole-rock Magnetic susceptibility rate 0.2~0.78(${\times}103$ SI unit) is found when roofing tile patterns are Pasangmun, Taesangmun, Eosangmun, Kyukjamun, Heongsunmun. Overall absorptivity is 14~21%. It is similar to 14~18% of roofing tile from Chosun Dynasty. There is only 1.4~2.5g/cm3 of roof tile sample specific gravity. The analysis finds no difference in specific gravity by findspots.

• Journal of Popular Narrative
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• v.25 no.1
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• pp.55-85
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• 2019

In this article, we examine the real meaning behind the stories in which the N-po Generation (Millennial Generation) is depicted, through the observation of entertainment programs, TV series, and movies. This could be an opportunity to investigate the aspects of emotional customs of our era, which have been described by television media as portraying the complex and multifaceted reality in the most mundane and popular manner while influencing the public. Problems with youth unemployment, the polarization of life, and instability are not only global issues but situations that specifically occur in South Korea. It is thus vital to pay attention to the inner side of the N-po Generation who enjoy Sohwakhaeng (small but certain happiness) by eating alone as the placebo effect of this tough reality. This is an agenda that should be viewed as a problem in the fundamental design of South Korean society. The consciousness of the problem shown in the TV series has been drawing attention. The TV series Because depicts a love narrative that concentrates on emotions in a relationship that started between housemates due to poverty and housing problems, leading to marriage. Thus, the TV series persuasively dramatized 'confluent love' in the N-po Generation. In the movie , Miso can be regarded as a symbol that represents the emergence of a new generation of cultural sensitivity. There is a suggestion in the sequence of that identifies the pursuit of taste with the discovery of identity. The TV series is a growth narrative that deals heavily with youth unemployment, temporary workers, fragmented families, and dating violence. The housemates in find emotional stability through interaction with each other, and courageously approach their individual problems. In the process, images of women, who are empathetic towards others and are willing to jointly solve their problems, are calmly depicted to reveal a story of growth revolving around a ground emotional community. The current problem that South Korean society should contemplate is how to be fully human beyond mere survival, and how to further seek the conditions of human existence. In that sense, what we should pursue is a notion of 'publicness', which can put several generations together. Because of the reality that confliction between generations must be triggered, in order to make a passage of sympathizing, mass media's sensitivity training becomes more important. This may be the duty of mass media.