• Korean Journal of Metals and Materials
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• v.46 no.9
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• pp.593-603
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• 2008

In this study, effects of alloying elements on the sticking occurring during hot rolling of five kinds of ferritic STS430J1L stainless steels were investigated by analyzing high-temperature hardness and oxidation behavior of the rolled steels. Hot-rolling simulation tests were conducted by a high-temperature wear tester which could simulate actual hot rolling. The simulation test results revealed that the sticking process proceeded with three stages, i.e., nucleation, growth, and saturation. Since the hardness continuously decreased as the test temperature increased, whereas the formation of Fe-Cr oxides in the rolled steel surface region increased, the sticking of five stainless steels was evaluated by considering both the high-temperature hardness and oxidation effects. The addition of Zr, Cu, or Si had a beneficial effect on the sticking resistance, while the Ni addition did not show any difference in the sticking. Particularly in the case of the Si addition, Si oxides formed first in the initial stage of high-temperature oxidation, worked as initiation sites for Fe-Cr oxides, accelerated the formation of Fe-Cr oxides, and thus raised the sticking resistance by about 10 times in comparison with the steel without Si content.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.3
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• pp.285-293
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• 2016

The high velocity oxygen fuel(HVOF) thermal spray is a kind of surface modification techniques to produce the sprayed coating layer. This process is to form the coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. The efficiency of thermal spraying is dropped, however, because the semi-molten powder in a spray process become a factor that degrades the mechanical property by the formed pore within the coating layer. Therefore, it is necessary to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesive force. In this study, to improve the wear resistance, corrosion resistance and heat resistance, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps used in ironworks are manufactured with STS $420J_2$ and are coated by the powders of WC-Co-Cr and WC-Cr-Ni including the WC of high hardness using a HVOF thermal sprayer developed in this laboratory. These are called by the surface-modified plungers. The surface roughness, hardness, and surface and cross-sectional microstructure of these two surface-modified and conventional ceramic plungers are measured and compared before operation with after operation for 100 days. It is found that the values of centerline average surface roughness and maximum height for conventional ceramic plunger are 9.5 to 10.8 and 5.2 to 5.7 times higher than those of surface-modified ones coated by WC-Co-Cr and WC-Cr-Ni because the fine tops and bottoms on surface roughness curve of conventional ceramic plunger are approximately 100 times higher than those of surface-modified ones. In addition, the pores and scratches in the surface microstructure are considerably formed in the order of conventional ceramic, WC-Cr-Ni and WC-Co-Cr surface-modified plungers. The greater the WC content of high hardness powder is less the change in the plunger surface.

• Journal of The Korean Association For Science Education
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• v.35 no.4
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• pp.565-572
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• 2015

The purpose of this paper is to offer an analysis on the research trends of web-based inquiry learning effectiveness in science education, and to present suggestions for future studies. This study compiled data on 43 articles in Korea and international journals. The content analysis of articles published were from academic journals related to science education and educational technology from 2000 to 2014. The results are as follows: Among domestic articles, the participants ranged from school children to high school students. On the contrary, among foreign articles, the participants are centralized on secondary school students; most used experimental studies; most of the studies resulted with web-based inquiry learning in science education showing effectiveness on science learning performance or science inquiry ability; all web-based inquiry learning were designed using different models of teaching and learning, with the result in the case of domestic research, the utilized models refer to the STS learning model, Internet utilization problem-center inquiry learning model, Procedural model, while in the case of overseas research, the utilized models are SCY, IBLE, and TESI model. Implications of the findings are then discussed, which implies considerations for further research related to web-based inquiry learning.

• Journal of Science Education
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• v.37 no.2
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• pp.294-309
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• 2013

This study addressed the awareness of social issues related to science of future elementary school teachers. Fukushima Nuclear Power Plant Accident was used by concrete issue connected with SSI for this study. Twelve second-year students attending a university of education participated in the study, who were taking a class of science teacher preparation at that time that consists of the content of the elementary science education courses. The study revealed that all the pre-service elementary teachers recognized Fukushima Nuclear Power Plant Accident and received such information through various medias. In particular, they were receiving more information about the Nuclear Power Plant Accident through the internet than any other media by using the internet a lot, and also gained additional information through the internet. However, despite the fact that they recognized Nuclear Power Plant Accident, they neither had much information about it nor had been interested in SSI such as the Nuclear Power Plant Accident. Moreover, they had been basically uneducated about SSI. Despite of having no interest in SSI such as Nuclear Power Plant Accident, the study revealed that the pre-service elementary teachers recognized that scientific problems such as Nuclear Power Plant Accident may affect a society closely. In addition, they together sympathized with the point that SSI education should be applied on the current education courses by identifying the problem in application. As the study revealed above, the application of SSI education to the formal education courses as well as more lively research on that subject is very important and urgent for boosting interest in science subjects and enlightening the nature of science that is one of the objectives of science education.

• Journal of The Korean Association For Science Education
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• v.23 no.5
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• pp.443-457
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• 2003

The research aimed to compare science curriculum between Korea and Israel and find out characteristics of science curriculum in Israel at middle school level. The middle school 'science' of the 7th revised national curriculum in Korea and middle school 'science and technology' in Israel were compared. Among characteristics of the Israel curriculum of 'science and technology,' distinct ones are as follows: First, 'science and technology' was most highly emphasized with the largest number of time allotment among all subjects at middle school level in Israel. Second, the contents of 'science and technology' were classified into seven areas of 'energy and interaction', 'materials', 'organism', 'earth and the universe', 'technological systems and products' . 'information and communication',and 'ecosystems' rather than four areas of energy, materials, life and earth in Korea. Third, 'organism' was allocated with the highest number of hours among seven areas. Fourth, objectives of each content of 'science and technology' were divided into three categories: scientific aspect, technological aspect, and social value and objectives of each category were related to one another. This characteristic seems to stress STS, multidisciplinary, and interdisciplinary approaches in 'science and technology' in Israel. Such characteristics of the 'science and technology' education in Israel are likely to make significant contributions to establish human resources of highly developing science and technology including IT, BT, NT, ST in the future society. Reflecting upon the characteristics of 'science and technology' education in Israel, Korea might seek for ways to improve its national power based on science and technology through strengthening science and emphasizing science and technology contents among school curriculum.