• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.4 no.2
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• pp.71-78
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• 2000

The chlorination of municipal drinking water supplies leads to the formation of so-called disinfection by-products(DBPs), many of which have been reported to cause harmful health effects based on animal studies. This study was conducted: 1) to observe seasonal changes in the major DBPs at four sampling sites on a drinking water distribution system located in Chunchon, Kangwon Do; and 2) to examine the effects of major water quality parameters on the formation of DBPs. During the field sampling, the water temperature, pH, and total and free chlorine residuals were all measured. The water samples were then analyzed for total organic carbon(TOC) and eight disinfection by-products in the laboratory. Chloroform, dichloroacetic acid, and trichloroacetic acid were the major constituents of the measured DBPs. The concentrations of the total DBPs were highest in fall, particularly in October, and lowest in summer. The concentrations of the total DBPs increased with increasing TOC concentrations. Multiple regression analyses showed that the concentrations of chloroform, bromodichloromethane, and chloral hydrate were linearly correlated with the pH. Other water parameters were not included in the regression equations. Accordingly, these results suggest that TOC and pH are both important factors in the formation of DBPs.

• Journal of Engineering Education Research
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• v.13 no.5
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• pp.25-28
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• 2010

The objective of this project is to cultivate interest among junior high school students toward Science & Technology. Six simple experiments will be introduced to the participants (junior high school students) of this project which is focusing on the basic principles of engineering including law of motion, free-fall, force, energy, friction and work. Our student team has been assigned to design six set of experiment according to the principles. The experiments are easy to understand and simple to assemble by the students of age 13 to 15. Experimental manuals were written by the members using simple words complete with figure so that all the participants can understand the procedure of each experiment. In order to make sure the manuals are practically working, the experiment sets were tested and the results were compared with actual theory. As a result, we believe that the experiments can be done by the students within less supervision. The students are able to set up the experiments by using some simple equipment around them. By doing this experiments, we can further our understanding and explain better the principles of energy, force and work.

• Journal of Korean Elementary Science Education
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• v.28 no.1
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• pp.24-34
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• 2009

The purpose of this study is to examine the effects of background knowledge on problem solving. To achieve this aim, I proposed the model which shows problem solving process centering around background knowledge, conducted the lessons concerning the concept 'weightlessness' on pre-service elementary teachers, and then classified the pre-service elementary teachers into several groups by the difference of the results presented in the process of solving the problems on weightlessness. And I examined qualitatively the effects of background knowledge on problem solving through the interview with 11 volunteers. On the cause of the failing the problem solving, the failure of acquiring or activating the background knowledge related to the learning concept was most frequently, secondly the use of the background knowledge unrelated to the learning concept, and thirdly the failure of understanding the teaming concept. To acquire or activate the background knowledge related to the teaming concept was more difficult than to understand the new teaming concept, and the cases that use the background knowledge unrelated to the learning concept failed to solve problem. The result of interview, all interviewee understood the learning concept correctly, but all of them who fail to acquire or activate the background knowledge related to the learning concept, or use the background knowledge unrelated to the learning concept, could not solve the problem.

• Journal of the Korean Society of Safety
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• v.32 no.6
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• pp.40-45
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• 2017

Chemical accidents generated during maintenance, repair, and normal operation, such as dispersion, fire, and explosions, can cause massive losses like a 2012 hydro fluorine leak in Gumi, South Korea. Since this accident, many researches have studied physical mitigation systems. However, due to many difficulties including potential costs and lack time, it is really hard for many companies to install mitigation systems without prior knowledge. Thus, the efficacy of mitigation system should be evaluated. This study assesses a dike design considering the fluid velocity at an open hole when a leakage accident occurs. It is assumed that leakage materials follow a free fall motion. Throughout case studies, a current KOSHA guide for a dike design was evaluated and new guidelines handling various conditions were proposed.

• Ocean and Polar Research
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• v.36 no.4
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• pp.515-524
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• 2014

The Korea Institute of Ocean Science and Technology has acquired detailed biological, chemicophysical, and geological data in the northeastern Pacific through a manganese nodule program since 1983. Plenty of manganese nodules were collected to estimate the amount of resources by free-fall grab and box corer. The collected manganese nodules have been archived systematically in the rock and mineral storage section of the Library of Marine Samples (LIMS) since 2012. The LIMS provides essencial information on the stored samples including sample name, nodule type, sampling location, depth, and equipment. Although a high quality database of the information system is under construction, the samples have tagged information for manganese nodules like chemical composition, morphology, weight, size, abundance, and photograph. In this study, we attempted to provide information on the well-organized and easily accessible archived manganese nodule samples for future studies and to introduce the usefulness of the LIMS.

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.35-41
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• 2018

Chemical accidents generated during maintenance, repair, and normal operation, such as dispersion, fire, and explosions, can cause massive losses like a 2012 hydro fluorine leak in Gumi, South Korea. Since this accident, many researches have studied physical mitigation systems. However, due to the lack of potential costs and time, it is really hard for many companies to install mitigation systems without prior knowledge. Thus, the efficacy of mitigation system should be evaluated. This study assesses a dike design considering the fluid velocity at an open hole when a leakage accident occurs. It is assumed that leakage materials follow a free fall motion. Throughout case studies, a current KOSHA guide for a dike design was evaluated and new guidelines handling various conditions were proposed.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1510-1512
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• 2004

Platform Screen Door System is a facility on platform to separate platform from track, having automatic sliding door structures interlocked to opening and closing of train door with integrated control unit. When a train comes to a stop at a designed position at a station, onboard ATC/ATO system transmits train berth signal to wayside signaling system. In case of automatic/driverless operation, opening and closing of the Platform Screen Door will be controlled by wayside signaling system. Unfortunately, we often see the case in news that passengers fall into track and their contact with train lead to critical accidents. However, passengers will be free from such accidents on the platform with the Platform Screen Door System. Especially during the rush hours, to ensure passenger's safety and smooth getting on & off, it is necessary to arrange. some station staffs on the platform without the Platform Screen Door System. On the other hand, the Platform Screen Door System will realize such operation by fewer staffs. Due to the above reasons, the Platform Screen Door System is becoming more popular in subway system recently.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.7
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• pp.369-378
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• 2018

Full-scale seismic retrofit of old and deteriorated masonry buildings requires a lot of cost and time. In such buildings, installing an emergency evacuation space can be considered as an alternative. In this study, requirements of the earthquake-proof table used as an emergency evacuation space for buildings hit by earthquake are investigated. Load conditions required for the table, including the impact effects due to building debris drop, are explained. To investigate the impact effects in more detail, weight drop test is performed for an prototype earthquake-proof table. In the test, the weight of the falling object and free fall height were considered as the main test parameters. The results showed that the duration of impact is very short (0.0226~0.0779sec), and thus the impact forces increase to 15.8~45.2 times the weight of the falling object. Based on these results, design considerations and performance verification criteria of the earthquake-proof table as an emergency evacuation space are given.

• Journal of The Korean Association For Science Education
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• v.16 no.2
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• pp.164-174
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• 1996

본연구는 자유낙하 운동에 대학 학생의 개념을 이 개념의 역사적 변천 과정과 비교하여 분석하였다. 네 연령층(ll세,13세, 15세, 17세)으로부터 총 737명이 설문조사에 참여하였으며,설문에서 주어전 문항들은 자유낙하 운동과 관련하여 과거의 과학자(예를 들어, 아리스토텔레스, 임페루스 이론가, 갈릴레오)들이 고민하였던 핵심 문제를 반영하는 것이었다. 설문에는 세 문항이 포함되었으며,각 문항은 자유낙하 운동에 관한 세 가지 측면(즉,운동의 원인,낙하높이와 낙하속력의 관계,낙하 체의 무게와 낙하속력의 관계)에 각각 관련된 것이었다. 낙하운동의 원인에 대혜서, 전체 학생의 4.3%, 25.5%. 62.7%가 아리스토텔레스,임페루스스,갈릴레오적 관점을 각각 지닌 것으로 나타났다. 낙하높이와 낙하속력의 관계에 대혜서는,20.0% 와 29.0%의 학생들이 각각 아리스토텔레스와 갈릴레오적 관점을 지닌 것으로 냐타났다. 그리고 낙하체와 무게와 낙하속력의 관계에 대혜서는,19.0%,34.8%,42.2%의 학생들이 아리스토텔레스,임페루스,갈리레오적 관점을 지닌 것으로 나타났다. 개별 문항에서 부분적으로 임페루스적 관점으로부터 갈릴레오적 관점으로의 변화가 나타났으나,전체적으로 연령이 증가함에 따라 학생의 개념이 현대적 관점으로 변화한다고 판단 하기는 어려웠다. 그리고 본 연구로부터 학생의 개념과 그 개념의 역사적 변천 과정에 사이에 상당한 유사성과 함께 차이점이 존제함을 알 수 있었다.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.36.1-36.1
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• 2016

This is a presentation of the paper published as Kimm et al. 2016, ApJ, 823, 52. We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with $Mhalo{\sim}4{\times}107Msun$ at z>10 using cosmological radiation-hydrodynamics simulations. We find that very compact (${\leq}1$ pc) and massive (${\sim}6{\times}105Msun$) clusters form rapidly when pristine gas collapses isothermally with the aid of efficient $Ly{\alpha}$ emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short (${\ll}1Myr$), a large fraction of the collapsed gas is turned into stars before stellar feedback processes blow out the gas and shut down star formation. Although the early stage of star formation is limited to a small region of the central star-forming disk, we find that the disk quickly fragments due to metal enrichment from supernovae. Sub-clusters formed in the fragmented clouds eventually merge with the main cluster at the center. The simulated clusters closely resemble the local GCs in mass and size but show a metallicity spread that is much wider than found in the local GCs. We discuss a role of pre-enrichment by Pop III and II stars as a potential solution to the latter issue. Although not without shortcomings, it is encouraging that a naive blind (not tuned) cosmological simulation presents a possible channel for the formation of at least some massive GCs.