• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.6-9
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• 2008

The efficiency and life time of the proton exchange membrane (PEM) fuel cell system is critically changed with its humidity which should be maintained properly during dynamic operation. Membrane humidifier is required to regulate proper humidity level for the design point of the PEMFC system. In this study, we presented the performance of the cylindrical membrane humidifier which is operated as water-to-gas. Dry air pressure, liquid water flow temperature, and air flow rate were chosen as the operating parameters. Humidity level is expressed with dew point.

• 한국수소및신에너지학회논문집
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• 제32권6호
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• pp.497-505
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• 2021

Water management is essential to improve the performance of proton exchange membrane fuel cells. This study targets to understand the characteristics of water concentration in proton exchange membrane fuel cells at a dynamic load variable environment. The fuel cell model was developed to simulate nonlinear water transport in membrane by the MATLAB/Simulink^® (MathWorks, Natick, MA, USA) platform, and it calculates water content in membrane, ionic conductivity, and predicts fuel cell performance through one-dimensional analysis.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.21-24
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• 2008

Proton Exchange Membrane Fuel Cell (PEMFC) is an attractive candidate for residential power generator due to fast start-up and stop, high efficiency, low emission, and high power density. In this study, we employ short module stack to understand the performance of the unit cell of the stack in terms of operating temperatures. To simulate the practical fuel cell stack of residential power generator, the structure and active area of the short module stack is kept the same as that of the practical fuel cell. The results shows that the electric potential of short module stack is different from the number of cells times the potential of unit cell because of cell-to-cell variation.

• 전기화학회지
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• 제11권1호
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• pp.11-15
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• 2008

The composite membrane for direct methanol fuel cell (DMFC) was developed using $H_3O^+-{\beta}"-Al_2O_3$ powder and perfluorosulfonylfluroride copolymer (Nafion) resin. The perfluorosulfonylfluroride copolymer (Nafion) resin was mixed with $H_3O^+-{\beta}"-Al_2O_3$ powder and it was made to sheet form by hot pressing. The electrodes were prepared with 60 wt% PtRu/C and 60wt% Pt/C catalysts for anode and cathode, respectively. The morphology and the chemical composition of the composite membrane have been investigated by using SEM and EDXA, respectively. The composite membrane and $H_3O^+-{\beta}"-Al_2O_3$ were analyzed by using FT-IR and XRD. The methanol permeability of the composite membranes was also measured by gas chromatography (GC). The performance of the MEA containing the composite membrane (2wt% $H_3O^+-{\beta}"-Al_2O_3$) was higher than that of normal pure Nafion membrane at high operating temperature (e.g. $110^{\circ}C$), due to the homogenous distribution of $H_3O^+-{\beta}"-Al_2O_3$, which decreased the methanol permeability through the membrane and enhanced the water contents in the composite membrane.

• Journal of Plant Biology
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• 제36권4호
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• pp.383-389
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• 1993

Intact leaf과 detached epidermis에 있는 공변세포의 전기 생리학적 특성에 대한 빛과 이산화탄소의 효과를 조사하였다. 빛을 intact leaf의 abaxial side에 처리하면 공변세포막이 과분극 (hyperpolarization)되었다. 닭의장풀의 intact leaf에 있는 공변세포들은 빛에 의해 최대 13 mV 그리고 이산화탄소에 의해 42 mV까지 membrane potential difference(MPD)가 negative하게 변했다. 자주달개비에서도 비슷한 결과를 얻었다. 그러나, 빛과 이산화탄소를 detached epidermis에 있는 공변세포에 처리할 경우에는 공변세포의 MPD가 변하지 않았다. 위의 결과로부터, 엽육세포가 공변세포의 MPD 변화에 영향을 주는 것으로 사료되어, 엽육세포들을 광합성 억제제들을 침윤시켜 엽육세포 광합성의 어느 기작이 공변세포 MPD 변화에 영향을 주는지 조사하였다. CCCP로 침윤한 잎의 공변세포막은 적색광에 의해 약간 탈분극(depolarization)되었고, 이산화탄소에 의해 과분극되었다. 반면에, DCCD와 DCMU로 침윤한 경우에는 대조구 잎과 마찬자기로 적색광과 이산화탄소에 의해 과분극되었다. Azide로 침윤한 잎에 적색광을 처리하면 공변세포의MPD는 변하지 않았고, 이산화탄소를 처리하면 다른 처리구들에 비해 훨씬 감소한 막의 과분극을 보였다. 이는 azide가 잎에 손상을 유도하며 세포내 대사활성을 감소시킨 결과 이산화탄소에 의한 MPD 변화가 작았고, 적색광은 아무 효과도 보이지 않은 것으로 사료된다. 따라서, 엽육세포가 적색광을 감지하며 빛에 의해 유도된 공변세포막 과분극은 순환적 광인산화 반응에 의해 생성된 에너지에 의존하나 이산화타소에 의해 유도된 공변세포막 과분극은 광합성가 무관하다고 볼 수 있다. 또한 이산화탄소를 intact leaf에 처리하면 공변세포 액포가 알칼리화되는 것을 관찰하였는데, 이는 막의 과분극이 양성자 이온의 방출에 의해 일어난다는 것을 의미한다.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제30권4호
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• pp.271-281
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• 2004

Adenoid cystic carcinoma is malignant tumor in salivary gland, and its behavior is very invasive. Of all malignant tumor adenoid cystic carcinoma is occured in frequency of 4.4% in major salivary gland, and 1.29% in minor salivary gland. Histopathologically, adenoid cystic carcinoma is characterized by a cribriform appearance, and tubular form and solid nest type tumor can be seen. The tumor cell structure composed of modified myoepithelial cell, and basaloid cell. Extracellular matrix of this tumor cell contains variable ground substance with basement membrane component. Basement membrane matrix composed of collagen fibers, glycoproteins, proteoglycans, and its function is well known that it participate in differentiation, proliferation, and growth of tumor cell. Basement membrane molecule is essential for invasion of peripheral nerve, blood vessel, skeletal muscle in tumor cell of adenoid cystic carcinoma. In many studies, the tumor cell of adenoid cystic carcinoma containing modified myoepithelial cell participate in synthesis of proteoglycan. In this study, tissue sample of adenoid cystic carcinoma of human salivary gland were obtained from 15 surgical specimen, and all specimen were routinely fixed in 10% formalin and embedded. Serial $4-{\mu}m$ thick sections were cut from paraffin blocks. the histopathologic evaluation was done with light microscopy. And, the immunohistochemical staining, characteristics of glycosaminoglycan were observed. For biochemical analysis of glycosaminoglycan, isolation of crude glycosaminoglycan from tumor tissue and Western bolt analysis were carried out. With transmission electomicroscopy, tumor cell were observed. Biologic behavior of adenoid cystic carcinoma was observed with distribution and expression of basement membrane of glycosaminoglycan in tumor cells, The results obtained were as follows: 1. In immunohistochemical study, chondroitin sulfate is postively stained in tumor cell and interstitial space, dermatan sulfate is weakly stained in ductal cell. But keratan sulfate is negatively stained. 2. In immunohistochemical study, heparan sulfate is strong positive stained in tumor cell and basement membrane, especially in invasion area to peripheral nerve tissue. 3. In transmission electromicroscpic view, the tumor cells are composed modifed myoepithelial cells, and contains many microvilli and rough endoplasmic reticulum. 4. In Western blot analysis, the expression of glycosaminoglycan is expressed mostly in heparan sulfate. From the results obtained in this study, tumor cell of adenoid cystic carcinoma is composed modified myoepithelial cell, and glycosaminoglycan of basement membrane molecule of heparan sulfate and chondroitin sulfate mostly participate in the development and invasiveness of adenoid cystic carcinoma by immunohistochemical study and western blot analysis.

• The Journal of Advanced Prosthodontics
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• 제7권6호
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• pp.484-495
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• 2015

PURPOSE. This study was to evaluate the effects of bacterial cellulose (BC) membranes as a barrier membrane on guided bone regeneration (GBR) in comparison with those of the resorbable collagen membranes. MATERIALS AND METHODS. BC membranes were fabricated using biomimetic technology. Surface properties were analyzed, Mechanical properties were measured, in vitro cell proliferation test were performed with NIH3T3 cells and in vivo study were performed with rat calvarial defect and histomorphometric analysis was done. The Mann-Whitney U test and the Wilcoxon signed rank test was used (${\alpha}<.05$). RESULTS. BC membrane showed significantly higher mechanical properties such as wet tensile strength than collagen membrane and represented a three-dimensional multilayered structure cross-linked by nano-fibers with 60 % porosity. In vitro study, cell adhesion and proliferation were observed on BC membrane. However, morphology of the cells was found to be less differentiated, and the cell proliferation rate was lower than those of the cells on collagen membrane. In vivo study, the grafted BC membrane did not induce inflammatory response, and maintained adequate space for bone regeneration. An amount of new bone formation in defect region loaded with BC membrane was significantly similar to that of collagen membrane application. CONCLUSION. BC membrane has potential to be used as a barrier membrane, and efficacy of the membrane on GBR is comparable to that of collagen membrane.

• 한국수소및신에너지학회논문집
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• 제20권4호
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• pp.283-290
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• 2009

This study focuses on the performance characteristics of polymer electrolyte membrane fuel cell (PEMFC) using the AC impedance technique. The experiment was carried out to investigate the optimal operating conditions of PEMFC such as cell temperature, flow rate, humidified temperature and back-pressure. The fuel cell performance was analyzed by DC electronic-loader with constant voltage mode and expressed by voltage-current density. Additionally, AC impedance was measured to analysis of ohmic and activation loss and expressed by Nyquist plot. The results showed that the cell performance increased with increase of cell temperature, air flow rate, humidified temperature and backpressure. Also, the activation loss decreased as the increase of cell temperature, air flow rate, humidified temperature and backpressure.

• Advances in Energy Research
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• 제8권4호
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• pp.253-264
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• 2022

This paper deals with the effects of design (active area, current density, membrane conductivity) and operating parameters (temperature, relative humidity) on the performance of hydrogen-fuelled proton exchange membrane (PEM) fuel cell. The design parameter of a PEM fuel cell with the active area of the single cell considered in this study is 25 cm² (5 × 5). The operating voltage and current density of the fuel cell were 0.7 V and 0.5 A/cm² respectively. The variations of activation voltage, ohmic voltage, and concentration voltage with respect to current density are analyzed in detail. The membrane conductivity with variable relative humidity is also analyzed. The results show that the maximum activation overpotential of the fuel cell was 0.4358 V at 0.21 A/cm² due to slow reaction kinetics. The calculated ohmic and concentrated overpotential in the fuel cell was 0.01395 V at 0.76 A/cm² and 0.027 V at 1.46 A/cm² respectively.

• 한국미생물·생명공학회지
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• 제5권3호
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• pp.133-140
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• 1977

Nocardia sp의 세포내 징세포구조 및 tellurite 환원초소의 존재부위와 T. T. C. 환원부위를 전자현미경으로 관찰한 것을 요약하면 다음과 같다. 광포내 미세구조에 있어서 unit membrane을 가진 농양구조가 복잡한 형태를 하고 계포질에 내포되어있고 어떤 것은 막구조가 둥글게 감겨있는 형태도 있다. 금속, tellurate염외 석출이 세포질중에 나타나므로 tellurite 및 tellurate 환원효소는 세축질중에 존재한다는 것을 알 수 있다. 그리고T.T.C.의 환원은 세포막 및 세포내막양구조 부분에서 일어난다. 따라서 tellurate환원과 T.T.C.환원은 서로 상이한 부위에서 일어남을 알 수 있다. 구체내에 형성된 T.T.C. tellurate은 도정제인 osmic acid에 의하여 제기화되며, 더우기 탈수제로 사용하고 있는 ethanol에 녹고 아울러 포매각에도 녹기 때문에 약 95％의 formazane이 균체외로 용출되어 나오므로 검정시의 세포내에는 거의 formazane이 존재하지 않기 때문에 전자현미경상의 전자투과성인 부분은 원래 formazane이 형성되었던 부분인 것이다.