• Composites Research
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• v.36 no.5
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• pp.303-309
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• 2023

In this paper, a Progressive Damage and Failure Analysis (PDFA) modeling method was developed using ABAQUS/EXPLICIT to predict in-plane damage and delamination for Open-Hole Compression (OHC) testing. The proposed PDFA model was constructed based on Hashin criteria and cohesive behavior. The strength and stiffness of OHC specimens with three types of stacking sequences [(45/-45/0₂)₃]_s , [(45/0/-45/90)₃]_s and [45/-45/0/45/-45/90/(45/-45)₂]_s were compared to comprehensively evaluate the validity of the Finite Element(FE) model of PDFA. The strength and stiffness of the OHC specimens were predicted relatively well, with less than a percentage error 10.0 %. For the numerical simulation case for each layup, the damage initiation/evolution of OHC specimens were evaluated for delamination and tension/compression matrix damage before and after failure.

• Journal of the Korean Chemical Society
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• v.68 no.3
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• pp.160-175
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• 2024

The purpose of this study is to examine the effects of a Chemistry I class based on an artificial intelligence (AI) classification model. To achieve this, the research investigated the development and application of a class utilizing an AI classification model in Chemistry I classes conducted at D High School in Gyeongbuk during the first semester of 2023. After selecting the curriculum content and AI tools, and determining the curriculum-AI integration education model as well as AI hardware and software, we developed detailed activities for the program and applied them in actual classes. Following the implementation of the classes, it was confirmed that students' self-efficacy improved in three aspects: chemistry concept formation, AI value perception, and AI-based maker competency. Specifically, the chemistry classes based on text and image classification models had a positive impact on students' self-efficacy for chemistry concept formation, enhanced students' perception of AI value and interest, and contributed to improving students' AI and physical computing abilities. These results demonstrate the positive impact of the Chemistry I class based on an AI classification model on students, providing evidence of its utility in educational settings.

• Journal of The Korean Association For Science Education
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• v.29 no.6
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• pp.626-638
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• 2009

The purpose of this study was to investigate the perception of the scientifically gifted high school students to the research and education (R&E) program. 270 scientifically gifted high school students participating in R&E program were sampled and surveyed according to the R&E' purpose, the process of topic selection, the advantage, and disadvantage of R&E. 4 students among them were interviewed in depth. Students perceived the purposes and advantages of R&E as fostering the scientist' qualifications, providing the research opportunities, and improving the inquiry ability and the disadvantages of R&E as the time consumption in research, the participation as a sideline, and the difficulty of contents. The R&E program was mainly composed of a pre-determined topic, fixed procedures, and expert's settlements in the problem-emerging situation and was not cognitive but technical apprenticeship. In addition, students considered the participation of R&E as a chance of experience about the high techniques and the valuable instruments instead of the improvement on the creative problem-solving ability. The role of mentors in the R&E program is so important that it affects largely on the productive participation and the perceptions of science and scientists.

• Journal of The Korean Association For Science Education
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• v.26 no.2
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• pp.212-221
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• 2006

The purposes of this study were to examine the characteristics of teacher help in small group Thinking Science(TS) activities and analyze the way students respond to teacher help. For this study, twenty-four 5th grade and twenty-four 7th grade students were selected, to undertake TS activities. Out of the 8 activities students participated in, the verbal interactions in activity 4 and 6, by students in four small groups, which incorporated relatively active argumentation was analyzed. Students' cognitive level was identified through a science reasoning task and the students were grouped heterogeneously according to their cognitive level. This study showed that teachers predominately used simple confirmation questions in preference to metacognitive question. Also, teacher help varied according to one's personal traits, work experience and degree of activity recognition. It was discovered that when the teacher provided student appropriate metacognitive questions and sufficient feedback, students actively engaged in argumentation. On the other hand, when the teacher asked simple confirmation questions and interfered in the activity, students did not participate in argumentation actively.

• Journal of the Korean Electrochemical Society
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• v.27 no.1
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• pp.32-39
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• 2024

The key components of a Phosphoric acid fuel cell (PAFC) are an electrode catalyst, an electrolyte matrix and a gas diffusion layer (GDL). In this study, we introduced a microporous layer on the GDL of PAFC to enhance liquid electrolyte management and overall electrochemical performance of PAFC. MPL is primarily used in polymer electrolyte membrane fuel cells to serve as an intermediate buffer layer, effectively managing water within the electrode and reducing contact resistance. In this study, electrodes were fabricated using GDLs with and without MPL to examine the influence of MPL on the performance of PAFC. Internal resistance and polarization curves of the unit cell were measured and compared to each other to assess the impact of MPL on PAFC electrode performance. As the results, the application of MPL improved power density from 170.2 to 192.1 mW/cm². MPL effectively managed electrolyte and water within the matrix and electrode, enhancing stability. Furthermore, the application of MPL reduced internal resistance in the electrode, resulting in sustained and stable performance even during long-term operation.

• Design & Manufacturing
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• v.17 no.4
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• pp.33-41
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• 2023

Excessive use of plastic bottles contributes to a significant environmental issue due to the high volume of plastic waste generated. To address this, efforts are needed to reduce the weight of plastic bottles. However, indiscriminate weight reduction may compromise the essential rigidity required for plastic bottles. Extensive research on rib shape for pressure vessels are exists, but there is a few research of rib shapes to enhance the stiffness of plastic bottles. The following results were obtained from the analyses conducted in this study. 1) Among the rib cross-sections of square, trapezoid, and triangle, the buckling critical load of PET bottles with square-shaped ribs is improved by about 14% compared to the buckling critical load of PET bottles without ribs. 2) The buckling critical load is improved by about 18% when a square-shaped rib with an aspect ratio of 0.2 is applied, compared to the buckling critical load of the bottle without the rib. 3) When longitudinal and transverse square ribs were applied to the axial direction of the PET bottle, the buckling critical load was improved by about 32% and 58% compared to the buckling critical load of the PET bottle without ribs, respectively, indicating that applying longitudinal ribs is effective in reinforcing the stiffness of PET bottles. 4) When 14 transverse ribs were applied, the maximum improvement was about 48% compared to the buckling critical load of the plastic bottle without ribs. 5) When 3 longitudinal ribs were applied on each side, the maximum improvement was about 76% compared to the buckling critical load of the bottle without ribs. Therefore, it was concluded that for effective stiffness reinforcement of a 500ml square bottle with a thickness of 0.5mm, 3 square-shaped ribs with an aspect ratio of 0.2 should be applied in the longitudinal direction relative to the axial direction of the bottle.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.1 s.53
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• pp.195-204
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• 2009

Application of steel plates is one of widely used methods for shear strengthening of reinforced concrete beams that are insufficient of shear capacity. While the existing method applying solid steel plates provides good shear rigidity, however, it is concerned by brittle bond failure patterns, inefficient material usage, and low constructability. The use of strap type steel plates has also shortcomings of low strenthening effect due to small interface bonding area and ununified behavior between plates and main body. Therefore, this study aims to introduce the shear strengthening method using slit type steel plate, which can solve out the problems aforementioned, and to verify its strengthening effects on shear capacity. A total of 13 specimens strengthened by slit type steel plates were fabricated with primary test parameters of plate width, slit spacing, and plate thickness. The test results from this study were also compared to those from the existing research on RC beams strengthened by strap type steel plates, and the strengthening effects on shear capacity of specimens having bonded slit type steel plates were quantitatively analyzed. The test results showed that the RC beams strengthened by slit type steel plates had greater shear capacities than those with strap type steel plates, which is considered to be the effects of improved composite behavior and larger interface bonding area in the RC beams strengthened by the slit type steel plates.

• Journal of Wetlands Research
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• v.26 no.3
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• pp.298-310
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• 2024

In this study, we analyzed the results of previous studies on different types of agricultural ecosystems to understand how environmental factors in soils, which serve as significant carbon reservoirs within agricultural ecosystems, a type of terrestrial ecosystem, affect soil carbon storage and soil respiration. As a result, most previous studies have been conducted on paddy field and facility cultivation area. And, the carbon storage in the soil and the soil's chemical properties, such as soil pH, electrical conductivity, soil organic matter content, and total nitrogen content, were higher in paddy field and orchard compared to field, facility cultivation area, and other cultivation area. The soil respiration in paddy field was also higher than in other types of agricultural ecosystems. Furthermore, soil carbon storage showed a significant correlation with soil organic matter (R²=0.7237, p=0.0000), total nitrogen (R²=0.8419, p=0.0000), and available phosphorus (R²=0.3123, p=0.0024), while soil respiration had a significant relationship with soil organic matter (R²=0.5644, p=0.0000). In this study, agricultural ecosystems were found to act as carbon sinks, with soil carbon storage measured at 49.1±8.9 tons C ha^-1 in orchard, 31.8±6.9 tons C ha^-1 in paddy field, and 25.3±28.0 tons C ha^-1 in facility cultivation area. Therefore, agricultural ecosystems need to manage soil carbon storage and carbon emissions through proper soil nutrient management.

• Journal of the Korea Organic Resources Recycling Association
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• v.17 no.2
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• pp.59-72
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• 2009

In order to utilize sewage sludge as a heat source of energy, it goes without saying that the fuel should be clean and pose no threat to the environment. As a consequent, it should not contain even minute quantities of heavy metals / impurities. The SOCA (Sludge-Oil-Coal- Agglomerates) fuel can meet all these requirements. SOCA being a solid fuel can be gasified for the production of clean energy. Wet catalytic gasification is the most appropriate process for SOCA containing nearly 60% water. It is important to note that the SOCA thus obtained inherits ca. 40~50% of sulfur from the coal used. It can poison the catalyst during catalytic gasification process. Consequently, it becomes important to choose a proper catalyst for the gasification. Calcium was found to be ideal choice as a catalyst for the gasification of SOCA. The optimal gasification was performed at $850^{\circ}C$ with water vapor. The role of fuel-N is of utmost importance in the gasification of SOCA. The gasification should be controlled to reduce the production of HCN to a minimum and enhance its conversion to $N_2$ and/or $NH_3$.

• Journal of Aerospace System Engineering
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• v.18 no.4
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• pp.81-88
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• 2024

The payload BioCabinet of CAS500-3 is designed for 3D stem cell differentiation, culture, and analysis utilizing bio 3D printing techniques in space. The 3D printing technique was initially developed for orbital use; however, it lacks separate validation for extreme launch vibration environments, necessitating a design that mitigates the launch load on the payload. This paper proposes a passive vibration isolator with a low-stiffness elastic support structure and high damping characteristics to reduce the launch loads affecting the BioCabinet. We explore the high-damping characteristics through the superelastic effects of SMA (Shape Memory Alloys) and a multi-layered structure incorporating viscoelastic tape. The effectiveness of the proposed vibration isolation system was confirmed via launch vibration tests on a qualification model.