• 한국전산유체공학회지
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• 제16권2호
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• pp.66-74
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• 2011

The SCR catalyst in coal-fired power plant is eroded by the collision of fly ash on the catalyst surface. However the erosion of SCR catalyst by the collision of fly ash has not been fully studied, especially in terms of fluid dynamics. Hence, in the present study, we focus on the gas and solid flows inside the SCR catalyst duct and their consequent effect on the erosion characteristics. For this purpose, computational fluid dynamics is applied to investigate the two-phase flows and to evaluate the erosion rate for different flow and particle injection conditions. Also, the erosion rate and pressure drop of commonly used square shape are compared with equilateral triangle and hexagon shapes. The pressure drop of SCR catalyst is increased when SCR catalyst surface area per unit volume increases. The erosion rate of SCR catalyst is enhanced when the particle velocity, mass flow rate of particle, particle diameter and cell density of SCR catalyst are increased. From the results, the pressure drop and erosion rate at the catalyst surface can be minimized by reducing cell density of SCR catalyst to decrease particle velocity and number of particle impacts.

• 한국재료학회지
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• 제22권6호
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• pp.285-291
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• 2012

Hydroxyapatite (HA) is well known as a biocompatible and bioactive material. HA has been practically applied as bone graft materials in a range of medical and dental fields. In this study, two types of dense hydroxyapatite ceramics were prepared from natural bones and synthetic materials. The biocompatibility of HA ceramics for supporting osteoblast cell growth and cytotoxicity using an in vitro MG-63 cell line model were respectively evaluated. Artificial hydroxyapatite shows relative density of 93% with 1-2 ${\mu}m$ after sintering, but a hydroxyapatite compact derived from bovine bone has low sintered density of 85% with a small content of MgO. Irrespective of the starting raw materials, both types of sintered hydroxyapatite displayed similar biocompatibility in the tests. FE-SEM observations showed that most MG-63 cells had a stellar shape and formed an intercellular matrix containing fibers on sintered HA. The cells were well attached and grown over the HA surface, indicating that there was no toxicity.

• Bulletin of the Korean Chemical Society
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• 제33권2호
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• pp.670-674
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• 2012

The photovoltaic performance of solid-state dye-sensitized solar cells employing hole transport material (HTM), 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), has been investigated in terms of HTM overlayer thickness. Two important parameters, soak time and spin-coating rate, are varied to control the HTM thickness. Decrease in the period of loading the spiro-MeOTAD solution on $TiO_2$ layer (soak time) leads to decrease in the HTM overlayer thickness, whereas decrease in spin-coating rate increases the HTM overlayer thickness. Photocurrent density and fill factor increase with decreasing the overlayer thickness, whereas open-circuit voltage remains almost unchanged. The improved photocurrent density is mainly ascribed to the enhanced charge transport rate, associated with the improved charge collection efficiency. Among the studied HTM overlayer thicknesses, ca. 230 nm-thick HTM overlayer demonstrates best efficiency of 4.5% at AM 1.5G one sun light intensity.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.50.1-50.1
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• 2010

결정질 실리콘 태양전지의 원가에서 Wafer는 60~70%의 매우 높은 비중을 차지하고 있다. 많은 연구들이 원가 절감을 위하여 Wafer의 두께를 감소시키는 것에 집중하고 있다. 그러나 Wafer 두께의 감소는 태양전지의 효율 감소와 공정 진행 중에 파손율이 상승하는 등의 문제가 발생한다. 이에 본 논문에서는 결정질 태양전지 구조 중에서 24.7% 이상의 최고 변환 효율을 갖는 PERL(Passivated Emitter, Rear Locally diffuse) 구조를 대상으로 wafer 두께 감소에 따른 변환 효율 감소의 원인과 해결 방안을 제시하고자 한다. Simulation으로 확인한 결과 370 um 두께의 wafer에서 24.2 %의 효율은 50 um 두께의 wafer에서는 20.8 %로 감소함을 확인할 수 있었다. 얇아진 wafer에서 감소한 효율을 개선하기 위하여 후면 recombination velocity, 후면 fixed charge density, 후면 산화막 두께 등을 다양화하여, 각각의 경우에 대한 cell의 효율 변화를 살펴보았다. 그 결과 후면 recombination velocity, 후면 fixed charge density, 후면 산화막 두께를 최적화 하여, 각각 2.8 %p, 1.5 %p, 2.8 %p의 효율 개선 효과를 얻었다. 위 세 가지 효과를 동시에 적용하면 50 um wafer에서 370 um wafer 효율의 결과와 근접한 24.2 %의 효율을 얻을 수 있었다. 향후에는 위의 결과를 바탕으로 실제 실험을 통하여 확인할 계획이다.

• 공업화학
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• 제10권5호
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• pp.731-736
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• 1999

식물성 천연 유지인 콩기름을 peracetic acid로 에폭시화 시킨 후에 황산 촉매 하에서 메탄올과 반응시켜서 OH-value가 186(mg KOH/g)인 폴리올을 합성하였다. 합성한 폴리올에 계면활성제로는 silicon계 B-8409를, 발포제로는 증류수를, 촉매로는 dimethylcyclohexylamine을, 이소시아네이트로는 polymeric MDI를 사용하여 폴리우레탄 포옴을 합성하였다. 형성된 포옴의 밀도, 압축강도, 압축탄성률, cell의 구조 등을 조사하였다. MDI의 당량비를 변화시켜 가며 포옴을 형성시켜 보았으며, MDI index를 105로 고정하고, 발포제, 계면활성제, 촉매의 양을 각각 변화시켜 가며 포옴을 형성시켜 보았다. MDI index가 증가할수록 밀도와 압축 물성이 증가하였다.

• 한국자동차공학회논문집
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• 제14권4호
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• pp.68-76
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• 2006

The minimization of maximum DPF wall temperature and the fast Light-off during regeneration are the targets for the high durability of the DPF system and the high efficiency of regeneration. In order to predict transient thermal response of DPF, one-channel numerical modeling has been adopted. The effect of the ratio of length to diameter(L/D), cell density, the amount of soot loading on temporal thermal response and regeneration characteristics has been numerically investigated under two different running conditions: city driving mode and high speed mode. The results indicate that the maximum wall temperature of DPF increase with increasing 'L/D' in 'High speed mode'. For 'City driving mode', the maximum wall temperature decreases with increasing 'L/D' in the range of $'L/D{\geq}0.6'$. The maximum temperature decreases with increasing cell density because heat conduction and heat capacity are increased. It is also found that the effect of amount of soot loading on light-off time is negligible.

• 대한기계학회논문집B
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• 제24권9호
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• pp.1264-1276
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• 2000

Light-off catalyst has been used for minimization of cold-start emissions. Improved cold-start performance of light-off catalyst needs the optimal design in terms of flow distribution, geometric surface area, precious metal loading, cell density and space velocity. In this study, these influential factors are numerically investigated using integrated numerical technique by considering not only 3-D fluid flow but also heat and mass transfer with chemical reactions. The present results indicate that uneven catalyst loading of depositing high active catalyst at upstream of monolith is beneficial during warm-up period but its effect is severely deteriorated when the space velocity is above 100,000 $hr^{-1}$ To maximize light-off performance, this study suggests that 1) a light-off catalyst be designed double substrate type; 2) the substrate with high GSA and high PM loading at face be placed at the front monolith; and 3) the cell density of the rear monolith be lower to reduce the pressure drop.

• 한국환경과학회지
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• 제21권1호
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• pp.105-111
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• 2012

The effects of substrate size on the growth of microphytobenthos Achnanthes sp., Amphora sp., Navicula sp. and Nitzschia sp. were examined using glass beads in order for phytoremediation in the benthic layer of coastal waters. The glass beads used in this study were 0.09~0.15 mm (G.B 1), 0.25~0.50 mm (G.B 2), 0.75~1.00 mm (G.B 3) and 1.25~1.65 mm (G.B 4). No addition of glass bead used as control. The specific growth rate and maximum cell density of four microphytobenthos species were increasing with decreasing size of glass beads. Moreover, the control experiment without added attachment substrates showed the lowest specific growth rate and maximum cell density. Therefore, the suitable attachment substrates for mass culture of microphytobenthos seems to be important in order for phytoremediation using microphytobenthos.

• 환경생물
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• 제28권2호
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• pp.79-85
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• 2010

To examine the effect of Codium fragile on blood cholesterol and lipid metabolism, hyperlipidemia was induced in experimental animal rats through the administration of a hypercholesterolemic diet. Codium fragile powder was then administered to the rats for 5 weeks, after which, blood biochemical changes such as blood cholesterol, Aspartate Aminotransferase (AST: serum SGOT) and Alanine Aminotransferase (ALT: serum SGPT) enzyme activity, etc. were determined. And histological changes in liver cells were examined using an electron microscope. Codium fragile treatment resulted in a significant reduction of the levels of total cholesterol, blood triglyceride and low-density cholesterol (LDL. Chol) compared to the control rats. In contrast the expression levels of high-density cholesterol (HDL. chol.) were increased. The AST value of the Codium fragile administration group was significantly reduced and the blood ALT value of the Codium fragile group showed a significant decrease in comparison to the negative control group. In summary, this study demonstrated the beneficial possibilities of Codium fragile in improving the abnormality of lipid metabolism caused by liver cell damage and hyperlipidemia.

• 신재생에너지
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• 제3권1호
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• pp.60-67
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• 2007

Catalyst coated membrane [CCM] type and catalyst coated substrate [CCS] type of membrane electrode assembly [MEA] were manufactured and evaluated their performance. Degradation test were conducted to find the difference of long term stability in two types of MEA and the factor for performance degradation problem occurred. Performance degradation test of single cell in two different types of MEA were carried out when current density was $200mA/cm^{2}$. The degradation test had proceeded for 230 hours and performance degradation was checked by I-V curve and impedance measurement at regular intervals. Also, MEA before/after operation and changes of catalyst layer were characterized by SEM, TEM, and XRD. Maximum power density of CCM type was higher than that of CCS type. Meanwhile, an increase of particle size of catalyst and an increase of impedance resistance after long term operation were observed. In the case of using CCM type MEA, the performance was deteriorated 38% of initial performance. In the case of using CCS type MEA, the performance was deteriorated 43% of initial performance. In consideration of difference of initial performance, performance of CCM type is higher than that of CCS type but both types had similar problems during degradation test.