• Safety and Health at Work
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• 제13권1호
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• pp.73-77
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• 2022

Background: Whole-body vibration (WBV) exposure of coal mine dumper operators poses numerous health hazards. The case-control study was aimed at assessing the relative musculoskeletal health risk of dumper operators' exposure to WBV with reference to the nonexposed group. Methods: Measurements of WBV exposure were taken at the operator-seat interface using a human vibration analyzer for 110 dumper operators in three coal mines. This vibration measurement was supplemented by a questionnaire survey of 110 dumper operators exposed to WBV and an equal number of workers not exposed to WBV. The relative risk of musculoskeletal disorders (MSDs) has been assessed through the case-control study design. Results: ISO guidelines were used to compare the health risk. It was observed that the prevalence of pain in the lower back was 2.52 times more in the case group compared to the control group. The case group of Mine-2 was 2.0 times more prone to vibration hazards as compared to Mine-3. Conclusion: The case group is more vulnerable to MSDs than the control group. The on-site measurement as well as the response of the dumper operators during the questionnaire survey corroborates this finding.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1468-1475
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• 2023

Enhancement of wear resistance of components used in fast reactors is necessary for long service life of the components. Plasma nitriding is a promising surface modification technology to impart high hardness and improved wear resistance of various steel components. This study discusses the characterization of chrome nitrided SS316L casing ring used in secondary sodium pump of fast breeder reactor and its stability under long term sodium exposure. Microstructural and hardness analysis showed that stress relieved component could be chrome nitrided successfully to a thickness of about 100 ㎛. Assessment of in-sodium performance of the chrome nitrided casing ring subjected to long term exposure up to 5000h at 550℃, showed retention of chrome nitrided layer with a case depth almost similar to that before sodium exposure. A slight decrease in the hardness was observed due to prolonged high temperature sodium exposure. Tribological studies indicate very low coefficient of friction indicating the retention of good wear resistance of the coating even after long term sodium exposure.

• 한국식생활문화학회지
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• 제35권4호
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• pp.342-350
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• 2020

This study examined the methods used in household doenjang (Korean soybean paste) production. Nine hundred forty-three responses were obtained using a nationwide, questionnaire-based survey (2018-2019) with non-probabilistic snowballing sampling. Consistent with previous studies, the respondents were primarily over the age of 50 years (97.1%) and female (97.9%). In addition to soybeans, the most used ingredients were red pepper (85.8%) and charcoal (85.5%), which most respondents obtained through direct farming (50.4-59.9%). Seasonal production occurred later in the higher latitude regions (Gyeonggi-do, Gangwon-do, Chungcheong-do) (p < 0.01), which have lower average temperatures, and the fermentation period was shorter in the lower latitude regions (Jeolla-do, Gyeongsang-do, Jeju-do) (p < 0.01), which have higher average temperatures. There were no significant regional differences in the season when doenjang was made, with most production occurring during January and February (81.1%). Most respondents (71.3%) made doenjang using homemade meju (soybean block used as a starter) in a traditional way to allow the microorganisms to be naturally inoculated. These results could be used as a basis for future research on topics such as starter development, standardized production, and safety of household doenjang.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2000년도 추계 기술심포지움 논문집
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• pp.89-92
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• 2000

테입 캐스터를 이용하여 바인더/가소제, 글말함량 비율이 다른 LTCC 테입을 제작한 후 특성평가를 하고자 하였다. 슬러리 조성은 서로 다른 바인더/가소제 그리고 분말함량에 따라 각각 4개 조성으로 구성하였다. 모든 슬러리에서 발포나 핀홀이 없는 미려한 표면을 갖는 테입을 얻을 수 있었다. 가장 우수한 기계적 특성 특성은 B/P=3.0, 분말함량 70vo1%인 두께 52 $\mu\textrm{m}$인 테입에서 인장강도 4.6MPa, 신을 29.5%의 특성을 얻을 수 있었다.

• Elastomers and Composites
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• 제51권1호
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• pp.1-9
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• 2016

Characterization of the UV oxidation for raw natural rubber (NR) was investigated in controlled conditions through image and FT-IR analysis. The UV oxidation was performed on a thin film of natural rubber coated on a KBr window at 254 nm and room temperature to exclude the thermal oxidation. Before or after exposure to UV light, image of the NR thin film was observed at a right or tilted angle. FT-IR absorption spectra were measured in transmission mode with the UV irradiation time. The UV oxidation of NR was examined by the changes of absorption peaks at 3425, 1717, 1084, 1477, 1377, and $833cm^{-1}$ which were assigned to hydroxyl group (-OH), carbonyl group (-C=O), carbon-oxygen bond (-C-O), methylene group $(-CH_2-)$, methyl group $(-CH_3)$, and cis-methine group $(cis-CCH_3=CH-)$, respectively. During the initial exposure period, the results indicated that the appearance of carbonyl group was directly related to the reduction of cis-methine group containing carbon-carbon double bond (-C=C-). Most of aldehydes or ketones from carbon-carbon double bonds were formed very fast by chain scission. A lot of long wide cracks with one orientation at regular intervals which resulted in consecutive chain scission were observed by image analysis. During all exposure periods, on the other hand, it was considered that the continuous increment of hydroxyl and carbonyl group was closely related to the decrement of methylene and methyl group in the allylic position. Therefore, two possible mechanisms for the UV oxidation of NR were suggested.

• Journal of Microbiology and Biotechnology
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• 제33권3호
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• pp.356-362
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• 2023

The 2'-fucosyllactose (2'-FL) is the richest components in a human milk oligosaccharide. Several studies have reported that 2'-FL has beneficial effects in infants. However, there are few studies on its immune-enhancing effects. This research aimed to examine the immune-enhancing effect of 2'-FL on immunosuppression by cyclophosphamide (CCP) in ICR mice. Mice were orally administered distilled water or 0.5 mg/kg B.W. 2'-FL for 14 days. An immunocompromised mouse model was induced using CCP 80 mg/kg B.W. at 12-14 days. Using the CCP had effects on reducing their body weight, organ weight, spleen index, natural killer (NK) cell activity, and cytokines concentration and expression. This study also used concanavalin A-mediated T-cell proliferation to verify the immune-enhancing effects in the sample. Body weight, spleen index, organ weight, and cytokine levels were measured to estimate the immune-enhancing effects. The body weight at 14 days tended to increase, and the spleen weight and index significantly increased in the 2'-FL group compared to the CCP group. The NK cell activity increased in the 2'-FL group compared to the CCP group, but there was no significant difference. The concentration of interleukin (IL)-2 tended to recover in the 2'-FL group compared to the CCP group. The 2'-FL group showed a significant increase of IL-10 and IFN-gamma concentration compared to the CCP group. In addition, there was a trend of increased IL-10 mRNA expression compared to the CCP group. These results revealed that 2'-FL improved CCP-induced immunosuppression, suggesting that 2'-FL may have the potential to enhance the immune system.

• Educational Technology International
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• 제11권2호
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• pp.77-103
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• 2010

The purpose of this study was to develop an instructional model using new technologies aiming to secure students' learnability and to enhance the public school values in the rural districts. The present study attempts to suggest a practical e-learning instructional and learning model named Group Dynamics- based Debate Instructional Model', which utilizes unique technology environment conditions in most. To develop the model, concepts of group dynamics and debate-based instructional models were reviewed. And in-service teachers in two public schools in a certain rural district were interviewed in order to collect and analyze their needs for a teaching and learning model with which they utilizes unique technology conditions as environment in most. Based on literature review and the need analysis, a group dynamics-based debate instructional model has been suggested in terms of conceptual model. And then expert assessment composing of five in-service teachers from the model schools was implemented twice in order to acquire the suggested model validation, followed by the model validation by a group of experts. Then a revised group dynamics-based debate instructional model has been finally suggested. The group dynamics-based debate instructional model is expected to build up members' affective connection in the process, to generate group value, or collective intelligence, and to establish positive discussion culture. Furthermore, beyond of just utilizing the existing materials, learners are encouraged to develop and collect their own materials and data such as expert's interview, or public news for their argument or refutation. In doing so, learners enhance their learnability as well as accountability, prompting self-directed learning, and establishing appropriate discussion culture resulting in positive learning outcomes.

• 한국환경보건학회지
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• 제10권2호
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• pp.79-87
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• 1984

The purpose of the study is to determine the effects of Zn in lead poisoning rats by way of examining interaction mechanism of Pb and Zn. The fifty-five rats were Pb divided into four groups such as Zn group, group, Pb and Zn group, and control group. The rats of Zn group and of Zn and Pb group were subdivided into four groups by dose of Zn respectively 250mg/l, 500mg/l, 1, 000mg/l and 2, 000 mg/l. The rats having been fed the above mentioned chemicals, were weighed every five days for fifty-five days, and the subjects were slaughtered for measuring $\delta$-ALAD activities in blood and the accumulation amount of the chemicals in livers and kidneys. The results of the study are summarized as following 1. As for body weight gains, those of the control group rats were the highest, and those of Pb group the lowest. 2. $\delta$-ALAD activities of Pb group showed the tendency of decrease in comparison with those of control group. In Zn group, the subgroups of 250mg/l and 500mg/l showed higher activities than control group, whereas the subgroups of 1, 000mg/l and 2.000mg/l showed lower. 3. Hb value of Pb group was lower than that of control group. In Zn group, Hb value of the groups of 250mg/l and 500mg/l was a little higher than that of control group, while that of the groups of 1, 000mg/l and 2, 000mg/l was lower. 4. The amount of Pb and Zn accumulated in liver was much higher than in kidney. The amount of Pb accumulated in organs of Zn and Pb group decreased gradually in contrast to high concentration of Zn.

• 한국기계가공학회지
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• 제14권3호
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• pp.9-14
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• 2015

The Direct Metal Tooling (DMT) process is a kind of additive manufacturing processes, which is developed using various commercial steel powders, such as P20, P21, SUS420, and other non-ferrous metal powders. The DMT process is a versatile process that can be applied to various fields, such as the molding industry, the medical industry, and the defense industry. Among them, the application of the DMT process to the molding industry is one of its most attractive and practical applications, since the conformal cooling channel cores of injection molds can be fabricated at a slightly expensive cost by using the hybrid fabrication method of DMT technology compared with parts fabricated with machining technology. The main objectives of this study are to provide various characteristics of the parts made using the DMT process compared with the same parts machined from bulk materials and evaluate the performance of the injection mold equipped with a conformal cooling channel core fabricated using the hybrid method of the DMT process.

• Educational Technology International
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• 제16권2호
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• pp.167-181
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• 2015

The purpose of this study was to examine the effects of using learner-created DST to communicate academic information on the creativity and flow of university students. The sample consisted of 100 undergraduate students who were assigned to either the DST group or the expository instruction group. The DST group created digital stories, and the expository group were taught using an expository instructional method. An achievement test, the Creativity Personality Scale (CPS), and the Flow State Scale (FSS) were used to collect data. The results showed that the achievement scores of the DST group were higher than those of the expository group, and the scores on the patience sub-factor of the CPS of the DST group significantly differed from those of the expository instruction group. Finally, the scores on the seven sub-factors of the FSS of the DST group differed significantly from those of the expository instruction group. The findings of this study suggest that the DST can be applied as teaching and learning method in a university class.