• Atmosphere
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• v.17 no.2
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• pp.185-193
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• 2007

This study investigates urbanization effect in warming trend of surface air temperature over Korea. The data used in this study consist of the daily minimum and maximum temperatures during the period of 32 years(1968-1999) from 16 stations of KMA. To calculate magnitude and trend of urbanization effect, stations were classified into urban and rural stations using population statistics. Urban stations were defined as those with population densities greater than 1000 persons per kilometer squared in 1995. The others were defined as rural stations. The urban stations were also subdivided into two groups according to their population totals. For estimates of urban effect magnitude, temperature change was calculated by comparing 16-year mean values between 1968-83 and 1984-99. Then, the difference between each urban station and every rural station was calculated. During the analysis period of 32 years, maximum temperature increase is $1.22^{\circ}C$. In the total temperature increase, urban effect is estimated by 28.7%. For minimum temperature, it becomes larger by about 10% than that in maximum temperature. Therefore, urban effect in an increasing trend of minimum temperature is 38.9% in the change of $1.13^{\circ}C$.

• Atmosphere
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• v.29 no.4
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• pp.463-480
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• 2019

This study classified heavy rain types from K-means clustering for the hourly relationship between rainfall intensity and cloud top height over the Korean peninsula, and then examined their statistical characteristics for the period of June~August 2013~2018. Total rainfall amount of warm-type events was 2.65 times larger than that of the cold-type, whereas the lightning frequency divided by total rainfall for the warm-type was only 46% of the cold-type. Typical cold-type cases exhibited high cloud top height around 16 km, large reflectivity in the upper layer, and frequent lightning flashes under convectively unstable condition. Phenomenally, the cold-type cases corresponded to cloud cluster or multi-cell thunderstorms. However, two warm-type cases related to Changma and typhoon were characterized by heavy rainfall due to long duration, relatively low cloud top height and upper-level reflectivity, and the absence of lightning under the convectively neutral and extremely humid conditions. This study further confirmed that the forecast skill of rainfall could be improved by applying correction factor with the overestimation for cold-type and underestimation for warm-type cases in the Local Data Assimilation and Prediction System (LDAPS) operational model (e.g., BIAS score was improved by 5%).

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.847-849
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• 1992

Fluorine-doped ($SnO_2$:F) thin films obtained by pyrosol deposition method have been exposed to R.F. excited pure hydrogen plasma under the following conditions; substrate temperature of 200$^{\circ}C$, $H_2$ pressure of 1 Torr, R.F. input power of 50 mW/$\textrm{cm}^{2}$, $H_2$ flow rate of 30cc/min and exposure time of 15-600 seconds. It is found that the sheet resistance of the films remains unchanged or rather slightly reduces for initial exposure time of 30-60 seconds, but increases sharply with further increasing the exposure time. The optical transmittance of $SnO_2$:F films slows a rapid fall with increasing exposure time except for a film obtained with a solution having $CH_3OH/H_2O$ mol ratio of 2.65, its degradations at the exposure time of 30-60 seconds are about 7-15%. In addition, the exposure of the films to hydrogen plasma atmosphere leads to remarkable changes in the microstructure and chemical composition, which should be attributed to the reduction of $SnO_2$ to SnO and to elemental Sn.

• Journal of Engineering Education Research
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• v.20 no.1
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• pp.53-62
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• 2017

This paper explored how university students viewed flipped learning from their own perspectives. Using qualitative research methods, 5 students from a Computer Graphics course at a mid-scale university in Seoul were interviewed for this purpose. Researchers collected data about their learning experiences, emotions, and reflections about flipped learning in general and its components such as online materials, in-class activities, and instructor guidance. Research findings indicated that students were not so much conscious about the unfamiliarity of the class, the increased work load, nor the online lectures. They rather prioritized 'what they could actually learn' from the course, and thus defined flipped learning as a method which enabled students to constantly check and fill in the gaps in their learning through team-based activities and prompt feedback from the professor. A combination of students' positive attitude and active participation in team-based activities, the overall atmosphere of the department which supported interactivity and collaboration, the professor's emphasis on learning-by-doing and student-centered learning appeared to form their notions of flipped learning. The use of technology did not appear to heavily impact students' conceptions of flipped learning. Researchers suggest that pedagogical beliefs of the professor, culture surrounding the learner, and the good match between the course content and instructional strategies are central for designing a successful flipped learning class.

• East Asian Journal of Business Economics (EAJBE)
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• v.9 no.2
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• pp.11-19
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• 2021

Purpose - The increase in organizational citizenship behavior is important in that it creates a cooperative atmosphere within the organization. Proving how OCB toward coworkers changes in negative leadership situations such as abusive supervision is a new research stream. Therefore, this study examines the main effects of the supervisor's abusive supervision on OCB of subordinates for coworkers, and then attempts to clarify that the perceived LMX differentiation of team members play a moderating role. Research design, data, and methodology - First, we examine the effects of the supervisor's abusive supervision on OCB of subordinates in the team toward colleagues. Second, the degree of perceived LMX differentiation is measured to verify the moderating effect of abusive supervision on OCB toward coworkers. Result - Hypothesis 1 is that abusive supervision has a negative effect on coworkers' OCB. Hypotheses 2-1, 2-2, and 2-3 test the moderating effect of perceived LMX differentiation, and the relationship between abusive supervision and coworkers' OCB will change according to the perceived degree of LMX differentiation. Conclusion - It is significant in that the scope of abusive supervision research has been expanded through the team level moderator of perceived LMX differentiation, away from the research on abusive supervision that was mainly discussed at the level of dyadic relationship (between the supervisor and the one subordinate).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.22-26
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• 2013

PTCR ceramics of $(Ba_{0.998}Sm_{0.002})TiO_3+0.001MnCO_3+xSiO_2$ (x=1, 2, 3, 4, 5, 6 mol%) were fabricated by solid state method. Disk samples of diameter 5 mm and thickness about 1mm were sintered at $1,290^{\circ}C$ for 2 h in reduced atmosphere of $5%H_2-95%N_2$ followed by re-oxidation at $600^{\circ}C$ for 30 min. in $20%O_2-80%N_2$.and their microstructures and electrical properties were investigated with SEM and Multimeter. The color of sintered samples was strongly dependent on $SiO_2$ content showing that the color of samples with $SiO_2$ of 1~2 mol% was gray but that of samples with $SiO_2$ of 4~6 mol% was changed from gray to blue, which seems to be related with the reduction of samples due to the oxygen vacancies created during the sintering in reduced atmosphere. $SiO_2$ content had a great influence on the microstructure and the electrical properties. With increasing $SiO_2$ content, the grain size of samples increased and the resistivity as well as the resistivity jump ($R_{285}/R_{min}$) decreased, which is considered to be attributed to the resistivity change at grain interior and grain boundary due to the fast mass transfer through $SiO_2$ liquide phase during the sintering. Samples with 2 mol% $SiO_2$ has the resistivity of $202{\Omega}cm$ and the resistivity jump of 3.28. It is expected that $SiO_2$ doped $BaTiO_3$ based PTC ceramics can be used for multilayered PTC thermistor due to the resistance to the sintering in reduced atmosphere.

• Journal of the Korean Institute of Gas
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• v.14 no.1
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• pp.15-20
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• 2010

The interest on the utilization of landfill gases and biogases for energy production has been increasing due to environment concerns and global warming caused by burning fossil fuels, renewable nature of these gases. Using those synthesis gases to generate energy with engine encourages more efficient collection reducing emissions into the atmosphere and generates revenues for the operators. However the lower calorific value of synthesis gases than that of LPG or CNG affects the combustion stability and power output. Thus it becomes necessary to address disadvantages involved by studying synthesis gases in technological perspective. This paper discussed synthesis gas as a fuel for 60kW dual-fuel engine to produce power in an effective way. The methane diluted with $N_2$ was used as a fuel and developed ECU and injector driver facilitated the investigations with diesel fuel.

• Applied Chemistry for Engineering
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• v.10 no.4
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• pp.531-536
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• 1999

Experiments on micro-leak of water were carried out with the water injecting simulator in liquid sodium atmosphere. The leak path was plugged by the sodium-water reaction products in the 2.25Cr-1Mo steel specimen. However, leak paths re-opened in most cases. The self-wastage patterns were not affected by the sodium temperature in the re-opened specimen. The diameter of the defected area, including the re-opened part, was about 5 min. It took 143, 40.7 and 34.7 minutes to re-open the leak path at 450, 475, and $510^{\circ}C$, respectively. It was concluded that the reopening time decreased with the increasing temperature.

• Journal of Sensor Science and Technology
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• v.23 no.2
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• pp.94-98
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• 2014

Aluminum nitride (AlN) thin films with a TiN buffer layer have been fabricated on SUS430 substrate by RF reactive magnetron sputtering at room temperature under 25~75% $N_2$ /Ar. The characterization of film properties were performed using surface profiler, X-ray diffraction, X-ray photoelectron spectroscopy(XPS), and pressure-voltage measurement system. The deposition rates of AlN films were decreased with increasing the $N_2$ concentration owing to lower mass of nitrogen ions than Ar. The as-deposited AlN films showed crystalline phase, and with increasing the $N_2$ concentration, the peak of AlN(100) plane and the crystallinity became weak. Any change in the preferential orientation of the as-deposited AlN films was not observed within our $N_2$ concentration range. But in the case of 50% $N_2$ /Ar condition, the peak of (002) plane, which is determinant in pressure sensing properties, appeared. XPS depth profiling of AlN/TiN/SUS430 revealed Al/N ratio was close to stoichiometric value (45:47) when deposited under 50% $N_2/Ar$ atmosphere at room temperature. The output signal voltage of AlN sensor showed a linear behavior between 26~85 mV, and the pressure-sensing sensitivity was calculated as 7 mV/MPa.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.12
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• pp.815-819
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• 2014

Aluminum nitride (AlN) thin film and TiN film as a buffer layer were deposited on INCONEL 600 substrate by reactive RF magnetron sputtering at room temperature(R.T.) under 25~75% $N_2/Ar$ atmosphere. The as-deposited AlN films at 25~50% $N_2/Ar$ showed a polycrystalline phase of hexagonal AlN, and an amorphous phase. The peak of AlN (002) plane, which was determinant on a performance of piezoelectric transducer, became strong with increasing the $N_2/Ar$ ratio. Any change in the preferential orientation of the as-deposited AlN films was not observed within our $N_2$ concentration range. The piezoelectric sensing properties of AlN module were performed using pressure-voltage measurement system. The output signal voltage of AlN module showed a linear behavior between 20~80 mV in 1~10 MPa range, and the pressure-sensing sensitivity was calculated as 3.6 mV/MPa.