• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.306-310
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• 2007

Characteristics of GDL (Gas Diffusion Layer) mainly determine the gas diffusion and water removal in a cell, thereby changing the performance and affecting durability of PEFC. To optimize the water management and understand the two phase flow in a GDL, it is important to study the behaviors of GDL micro structure under the real operating condition. In the clamped condition of cell, the GDL beneath the rib is more compressed than beneath the channel. Many researches on physical, electrochemical, mechanical behaviors of gas diffusion layer has been conducted. However, changes in surface properties under clamped condition have rarely studied. In present study, the morphology of broken connections of carbon fibers and detachment of PTFE coatings on the fibers were shown from the microscopic observations. In addition, changes in wetting properties of GDL by compression were investigated by using XPS and liquid uptake methods. The hydrophobic characteristics of GDL surface beneath the rib of the flow field plate are changed due to the deformation of micro structure.

• Transactions of the Korean hydrogen and new energy society
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• v.17 no.3
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• pp.347-352
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• 2006

분자전해질연료전지 내의 다공성 기체확산층은 반응가스의 확산과 전자이동통로의 역할을 수행할 뿐만 아니라 전기화학반응에 의해 공기극에서 생성된 수분(기상 혹은 액상)을 반응면으로부터 분리판 채널 방향으로 이동시켜 배출시키는 중요한 역할을 한다. 따라서 물관리를 통한 성능향상을 위해서는 기체 확산층의 구조 및 재료특성에 대한 심도 릴은 연구가 필요하다. 실제 단위전지 체결시 기체확산층은 분리판의 리브(rib)에 의해 눌리게 되며, 그 부분의 기공 크기 분포의 변화를 야기한다. 또한 리브 전단부분에서 탄소 섬유가 손상을 입으며, 탄소 섬유를 감싸고 있는 PTFE coating이 벗겨지게 되어 표면화학적 특성이 달라진다. 본 연구에서는 단위전지 체결 시 분리판에 의해 눌리는 기체확산층의 기공 크기 분포 변화를 측정하였으며, 기공의 소수성에서 친수성으로의 변화를 알아보았다. Mercury 기공 측정기와 PMI 기공 측정기는 큰 기공 분포의 변화에, 질소의 흡/탈착을 이용한 BET 방식은 작은 크기의 기공 분포 변화 관찰에 사용되었다. 체결압에 의한 탄소섬유의 구조적 변화와 아울러 표면의 습윤 정도의 변화를 XPS와 물/알콜 Uptake를 이용해 알아보았다. 이 연구를 바탕으로 물관리를 통한 연료전지 성능 향상을 위한 최적 GDL 선정에 기반이 되는 자료를 도출하였다.

• Analytical Science and Technology
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• v.13 no.5
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• pp.573-583
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• 2000

Activated carbon fibers (ACFs) were prepared from various precursors of plantic, synthetic, and mixed fabrics of viscous rayon and cotton. Their adsorption performances of phenol and methylene blue in aqueous phase were evaluated through their adsorption isotherms, adsorption rates and breakthrough curves. The two adsorbates showed type I adsorption isotherm on ACFs. Adsorption rates to ACFs were 100 fold faster than to GAC. The effective diffusion coefficients of the adsorbates in ACFs were twenty fold greater than in GAC. The ACFs removed completely ten organic pollutants from a prepared water specimens through the 2nd column of a natural filtration method where 50 L of the water samples were treated.

• Journal of the Korean Institute of Landscape Architecture
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• v.40 no.5
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• pp.33-42
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• 2012

This study aims to establish the performance standard for natural type landscape stone GFRC. The required performance such as material performance, structural safety performance, durability performance, and landscape performance were selected through an examination of domestic and overseas performance related references and examples, and through the questionnaires obtained from 40 experts, and the verified items and performance standards were proposed. Among the required performances, the material performance(glass fiber content, air-dried gravity), structural safety performance(flexural strength, compressive strength), durability performance(crack, corrosion resistance), and landscape performance(texture, efflorescence) were selected through the questionnaires obtained from the experts. In the case of material performance and structural safety performance with the corresponding standards that existed, final performance evaluation standard was proposed by conducting a test and comparing it with the existing standard sample, and in the case of durability performance and landscape performance on which standard does not existed, they were verified by measuring directly through field examination of formative landscape items such as artificial waterfall etc. In this study, performance standard for the material on natural type landscaping rocks GFRC and items which can be evaluated after construction such as material performance, structural safety performance, durability performance, landscape performance, and so forth were proposed, however, follow up study for pro-environmental and ecological performance standard which were recently gaining force would be required through a continuous monitoring for the construction samples afterwards.

• Elastomers and Composites
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• v.37 no.4
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• pp.224-233
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• 2002

This study has investigated the flame retardant properties of EPDM rubber with the addition of various flame retardants. Carbon black, stearic acid, zinc oxide cross-linking agent were mixed with EPDM rubber to produce the base rubber E0 without the addition of flame retardants. Phosphorus flame retardant Tricrecyl phosphate(TCP) was added to E0 in 0.5, 1, 1.5, 2 phr to make E1~E4 samples and red phosphorus was added in 3, 6, 9, 12 phr to make E5~E8 samples. A flame retardant of the bromine family Decabromodiphenyloxide(DBDPO), and a chlorinated paraffin retardant of the chlorine family was added to E0 in 3, 6, 9, 12 phr to make E9~E12 and E13~E16 samples, repectively. Basic physical properties such as tensile strength, tear strength and hardness were measured for all the rubber samples with various flame retardant additions. There was no substantial differences. On the other hand, Oxygen index and UL94 were measured to study flame retardant properties. From oxygen index measurements E0 sample showed a value of 23.5%, indicating the improvement of flame retardant properties. Also from UL94 measurements, it was found that addition of red phosphorus resulted in maximum flame retardant effect. It was found that increasing the amount of addition resulted in decreasing combustion rate and improving flame retardant effect regardless of the kind of flame retardant.

• Restorative Dentistry and Endodontics
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• v.37 no.2
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• pp.123-126
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• 2012

It is often presumed that apical periodontitis follows total pulp necrosis, and consequently root canal treatment is commonly performed. Periapical lesion development is usually caused by bacteria and its byproduct which irritate pulp, develop pulpitis, and result in necrosis through an irreversible process. Afterwards, apical periodontitis occurs. This phenomenon is observed as an apical radiolucency in radiographic view. However, this unusual case presents a spontaneous healing of periapical lesion, which has developed without pulp necrosis in a vital tooth, through conservative treatment.

• Food Science and Preservation
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• v.31 no.3
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• pp.423-432
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• 2024

In this study, a vacuum tumbler with 4 impellers (DVT) was designed and applied for thawing frozen pork (vacuum -60 kPa, jacket 35℃, 1 rpm). Quality characteristics of the thawed pork were compared with those of industrially thawed meat by natural air at room temperature (NAT) and imported vacuum tumbler (IVT). The thawing time for frozen pork (303.36 kg) using DVT (165 min) was much shorter than that of NAT (4,200 min). DVT-thawed pork had lower drip loss (0.85%) than NAT (2.08%). DVT-thawed pork showed a pH of 5.92, a total bacterial count of 1.96±0.02 log CFU/g and no coliforms. Deteriorations in fat (TBARS 0.31±0.01 MDA mg/kg) and protein (VBN 5.67±1.98 mg%) in DVT-thawed pork were significantly lower than those of NAT (p<0.05). DVT-thawed pork had a high water-holding capacity (WHC, 97.5%). The hardness (34.59±0.46 N) and chewiness (188.21±0.17) of cooked DVT-thawed pork were about 5-6 times lower than those of NTA. Microstructure (SEM) showed myofibrillar damage in NAT-thawed pork, whereas dense myofibrillar structure was observed in DVT-thawed pork. DVT was better or similar to IVT in all evaluation parameters. The designed DVT is expected to be used as an efficient thawing method in terms of processing time and yield and to produce thawed meat with high WHC, soft texture, and low spoilage by minimizing tissue damage.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.165-172
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• 2012

In this study, the physical, mechanical, structural, and environmental performances based on field measured data were evaluated to check the suitability of concrete for ecological preservation and cultivation of a hydrophilic environment. More specifically, the study is focused on developing an environmentally friendly functional concrete with river ecology restoration and natural river early formation capabilities. The mechanical performance evaluation results showed that the increase in mix rate of the PVA (Poly Vinyl Alcohol) reinforcement fibers and silica fume caused an increase in the strength. The optimal mix rate was found to be 0.05 volume % PVA fiber and approximately 10% silica fume. The frost resistance evaluation showed that superior performance was gained when 0.05 volume % PVA fiber and 15% silica fume was mixed simultaneously. In the structural performance evaluation, the bending strength was improved by 47.7% compared to plain concrete when mixed with 0.05 volume % PVA fiber. The flexural toughness also saw significant improvement. The environmental monitoring of field performance showed that grasses germinated most rapidly, but the growth of red poppies, a plant that germinates in the spring, was most active with passing of time. Coverage measurements in all of the monitoring locations found favorable coverage of over 95% after 12 weeks. The study results showed that the environmentally friendly functional concrete had outstanding environmental performance.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.225-230
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• 2005

At present, there are several problems related with sand mat which is used as a way to accelerate consolidation settlement, to act like an underground drainage layer and to increase trafficability simultaneously. First of all, the unbalance of the demand and supply of sand is one of the biggest problems, which causes not only price rise but also delay of the term of the total construction work. Secondly, the damage of ecosystem and scenery is triggered by thoughtless sand dredging or mining. So, the need that sand mat should be replaced with a new environmentally friendly material has been increased. Fiber mat may be one of the proper materials that suits the need. Therefore, we intended to compare the drainage properties of sand mat with those of fiber mat by experimental model tests. On the basis of the test results, fiber mat took shorter period of consolidation than sand mat and the amount of settlement in the farmer showed a little bit bigger than in the latter. As a conclusion, the substitutability of sand mat with fiber mat could be placed highly in view of drainage efficiency. Furthermore, when fiber mat is used, it has an advantage that spoiled soil of the construction site or nearby site can be used for the purpose of increasing trafficability in addition to a role of drainage layer.

• Journal of Naturopathy
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• v.11 no.2
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• pp.100-108
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• 2022

Background: It has been reported that various substances exist in wild Conyza canadensis, but I think that the overall compositional analysis is still insufficient. Purposes: This study was to set extraction conditions and search for various nutritional components in the wild C. canadensis. Methods: Various extracts were extracted and analyzed using different analytical instruments to suggest and study the conditions for component analysis. Results: As for the general nutritional components of C. canadensis leaf extract, carbohydrates were 46.4%, crude protein 26.5%, moisture 16.3%, raw meal 9.5%, and natural fat 1.2%. The dietary fiber content was 30.76%. Free fructose, glucose, sucrose, and maltose were separated, and the amount of fructose was as high as 4,144.2 mg/100 g. In addition, we found 64.87 mg/g of K, 4.09 mg/g of P, 1.77 mg/g of Mg, and 0.16 mg/g of disodium in the extracts. A total of 20 fatty acids have appeared. In addition, unsaturated fatty acids (octadecenoic acid, octadecadienoic acid, and linolenic acid) were detected. Linolenic acid was high at 54.1%. The saturated fatty acid content was 0.39 g/100 g, and the trans fatty acid content was 0.01 g/100 g. No cholesterol was found in the plant. Riboflavin was at 0.4 mg/100 g, with six essential amino acids and 24 amino acids. Conclusions: As a result of the primary research on the plant, various nutritional and functional ingredients exist in the extract, and natural healing uses are available.