• Elastomers and Composites
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• v.51 no.1
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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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• v.33 no.3
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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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• v.11 no.2
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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.

• Journal of Environmental Health Sciences
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• v.10 no.2
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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.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.3
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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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• v.16 no.2
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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.

• Educational Technology International
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• v.11 no.2
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• pp.105-121
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• 2010

Collaborative learning encourages the use of high-level cognitive strategies, critical thinking, and interpersonal relationships. Despite these advantages, most instructors reveal the difficulties of using project-based collaborative learning; a common problem is the failure of the group to work effectively together. Thus, this study attempted to provide practical advice on group composition with self-regulation. In a college course, 31 groups with 129 students were asked to discuss and prepare the final presentation material and present it together as a collaborative work. All students' self-regulation skills were measured at the beginning of the semester, and the collective self-regulation was computed as an average of the individual scores of each group. The results of regression analysis indicate that the group's collective self-regulation shows a highly significant positive effect on group performance and satisfaction, as self-regulation predicts individual academic performance. The results also show that there is a significant positive relationship between students' self-regulation and participation in group work.

• Korean Management Science Review
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• v.16 no.1
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• pp.137-156
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• 1999

Flexibility is a competitive weapon in the changing environment. In order to pursue the flexibility, Korean manufacturing companies must define the flexibility dimension clearly, build the appropriate manufacturing infrastructures and measure the right flexibility performance indicators. This paper found out as follows. First, Korean manufacturing companies' flexibility strategy groups were formed three types. They are flexibility superior group, middle flexibility group and flexibility inferior group. Second, when different types of flexibility strategy group measured their performances, the degree of importance of flexibility performance indicators were different among groups. Third, when different types of flexibility strategy group were pursued, the different manufacturing methods such as product/process design technology, analysis technology, production system management technology and non technological factors were used. Lastly, when different types of flexibility strategy group were pursued, the actual flexibility performances were different among groups.

• Macromolecular Research
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• v.11 no.3
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• pp.157-162
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• 2003

6FDA-based polyimides were prepared from the thermal imidization reaction of 6FDA with diamines of BAPAF, DAP, and DABA having a polar group of hydroxyL or carboxyl. Properties of the dense polyimide membranes were characterized and their gas permeation properties for H$_2$, $CO_2$, $O_2$, $N_2$, and CH$_4$ were investigated. Permeabilities, diffusion coefficients and diffusivity selectivities of polar group-containing polyimide membranes including 6FDA-BAPAF, 6FDA-DAP, and 6FDA-DABA polymer for the gases did not change largely. The separation properties of 6FDA-TrMPD polyimide membrane used as a reference polymer were compared with those of the polyimide membranes mentioned above. It was found that the polyimides of 6FDA-BAPAF, 6FDA-DAP, and 6FDA-DABA, which were soluble in alcohol or/and 2-methoxyethanol, could be applicable to the preparation of a dense composite membrane by dip-coating method.

• Animal Bioscience
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• v.35 no.9
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• pp.1454-1460
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• 2022

Objective: Early environmental enrichment in life can improve cognition in animals. The effect of prenatal auditory stimulation on learning ability and fear level in chick embryos remained unexplored. Therefore, this study investigated the effect of prenatal auditory stimulation on the learning ability and fear level of chicks. Methods: A total of 450 fertilized eggs were randomly divided into 5 groups, including control group (C), low-sound intensity music group (LM), low-sound intensity noise group (LN), high-sound intensity noise group (HN) and high-sound intensity music group (HM). From the 10th day of embryonic development until hatching, group LM and group LN received 65 to 75 dB of music and noise stimulation. Group HN and group HM received 85 to 95 dB of noise and music stimulation, and group C received no additional sound. At the end of incubation, the one-trial passive avoidance learning (PAL) task and tonic immobility (TI) tests were carried out, and the serum corticosterone (CORT) and serotonin (5-HT) concentrations were determined. Results: The results showed that compared with the group C, 65 to 75 dB of music and noise stimulation did not affect the PAL avoidance rate (p>0.05), duration of TI (p>0.05) and the concentration of CORT (p>0.05) and 5-HT (p>0.05) in chicks. However, 85 to 95 dB of music and noise stimulation could reduce duration of TI (p<0.05) and the concentration of CORT (p<0.05), but no significant effect was observed on the concentration of 5-HT (p>0.05) and PAL avoidance rate (p>0.05). Conclusion: Therefore, the prenatal auditory stimulation of 85 to 95 dB can effectively reduce the fear level of chicks while it does not affect the learning ability.