• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.431-431
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• 2016

Typical Cu(In,Ga)Se2 (CIGS)-based solar cells have a buffer layer between CIGS absorber layer and transparent ZnO front electrode, which plays an important role in improving the cell performance. Among various buffer materials, chemical bath deposition (CBD)-ZnS is being steadily studied to alternative to conventional CdS and the efficiency of CBD-ZnS/CIGS solar cell shows the comparable values with that of CdS/CIGS solar cell. The intriguing thing is that reversible changes occur after exposure to illumination due to the metastable defect states in completed ZnS/CIGS solar cell, which induces an improvement of solar cell performance. Thus, it implies that the understanding of metastable defects in CBD-ZnS/CIGS solar cell is important issue. In this study, we fabricate the ITO/i-ZnO/CBD-ZnS/CIGS/Mo/SLG solar cells by controlling the NH4OH mole concentration (from 2 M to 3.5 M) of CBD-ZnS buffer layer and observe their conversion efficiency with and without light soaking for 1 hr. From the results, NH4OH mole concentration and light exposure can significantly affect the CBD-ZnS/CIGS solar cell performance. In order to investigate that which layer can contain metastable defect states to influence on solar cell performance, impedance spectroscopy and capacitance profiling technique with exposure to illumination have been applied to CBD-ZnS/CIGS solar cell. These techniques give a very useful information on the density of states within the bandgap of CIGS, free carriers density, and light-induced metastable effects. Here, we present the rearranged charge distribution after exposure to illumination and suggest the origin of the metastable defect states in CBD-ZnS/CIGS solar cell.

• International Journal of Industrial Entomology and Biomaterials
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• v.9 no.2
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• pp.173-181
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• 2004

To delay the onset of apoptosis in the culture, transformed Tn 5B1-4 cells harboring anti-apoptotic genes, bcl-2 and baculovirus p35, have been established and analyzed for their anti-apoptotic ability in suspension culture using spinner flasks. In the suspension culture at agitation speeds of 100 rpm and 200 rpm, the cell growth of cell clone expressing Bcl-2 protein was much higher than other two clones and the maximum cell density of the clone was 6.0 ${\times}$ 10$^{6}$ cells/ml and 6.2 ${\times}$ 10$^{6}$ cells/ml at day three of the incubation. On the other hand, the cell growth of cell clone expressing baculovirus protein P35 was much higher than other two clones in suspension culture at agitation speed of 300 rpm and the maximum cell density of the clone was 6.1 ${\times}$ 10$^{6}$ cells/ml at day three of the incubation. Based on the pattern of genomic DNA laddering and the microscopic observation of apoptotic bodies, the more apoptotic bodies are induced in Tn 5B1-4 control cell clone at higher agitation speed. This result shows that the shear stress can be a main factor in inducing apoptosis in spinner flask culture. At low agitation speed, cell clone expressing Bcl-2 was more effective in delaying the onset of apoptosis than the cell clone expressing P35. On the other hand, at high agitation speed, cell clones expressing baculovirus P35 was more effective in delaying the onset of apoptosis than the cell clone expressing Bcl-2. Therefore, anti-apoptotic genes, bcl-2 and baculovirus p35, can playa distinct role depending on agitation speed in the suspension culture.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.415-418
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• 1999

The characteristics of VRLA (valve regulated Iead-acid) battery with the tubular positive plate and gel type electrolyte were examined as a function of active material filling density. The filling density of positive plate was 3.2 g/mL, 3.4 g/mL, and 3.6 g/mL, respectively. These VRLA batteries were cycled with 100% DOD (depth of discharge) at the $C_5/5$ rate, followed by IU-type recharge with $I_{max}=0.2C_{10}/10$ and a final voltage V=2.40 V/cell. The test was performed in a thermostatic room at $25{\pm}1^{\circ}C$. The result indicated that the initial capacity was independent of active material filling density, i.e., the highest initial capacity was 3.4 g/mL of filling density and the lowest was 3.6 g/mL. On aspect of the cycle-life performance of the VRLA battery, the filling density of 3.6 g/mL was similar to that of 3.4 g/mL in the positive plate, and both were higher than that of 3.2 g/mL. Water-loss and degradation of the VRLA battery were decreased according to an increase of the filling density in the positive plate. The optimum filling density of the active material was 3.4~3.6 g/mL.

• Carbon letters
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• v.4 no.3
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• pp.121-125
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• 2003

The Pt-Ru/Carbon as an anode catalyst supported on the commercial activated carbon (AC) having high surface area and micropore was characterized for application of Direct Methanol Fuel Cell (DMFC). The Pt-Ru/AC anode catalyst used in this experiment showed the performance of $600\;mA/cm^2$ current density at 0.3 V. The borohydride reduction process using $NaBH_4$, denoted as a process A, showed much higher current and power densities than process B prepared by changing the reduction and washing process of process A. The particle sizes are strongly affected by the reduction process than the specific surface area of raw active carbon and the sizes are almost constant when the specific surface area of carbon are over than the $1200\;m^2/g$. Smaller particle size of catalyst and more narrow intercrystalite distance increased the performance of DMFC.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.13-16
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• 2007

Fuel cell was used as a propulsion system for unmanned aerial vehicles (UAV) in the present study. Fuel cell propulsion system are an ideal alternative power source with high energy density for high-endurance UAV. Fuel cell power system provides UAV up to five times the energy densiη of existing batteries. Sodium borohydride, stored in liquid state, was selected as a hydrogen source. Hydrogen generation system consists of catalytic reactor, pump, fuel cartridge, and separator. Hybrid power management system (PMS) between fuel cell and lithium-polymer ba야ery was developed. Motor, pump, and fans， operated on battery power controlled by feedback signals of fuel cell system. Battery was recharged by surpuls powr of fuel cell.

• Advances in Energy Research
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• v.2 no.1
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• pp.21-31
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• 2014

The use of a microporous membrane along with Au/C catalyst for direct glycerol alkaline fuel cell was investigated. In comparison with Nafion 112, the microporous Celgard 3401 membrane provides a better cell performance due to the lower ionic resistance as confirmed by impedance spectra. The single cell using Au/C as anode catalyst prepared by using PVA protection techniques provided a higher maximum power density than the single cell with commercial PtRu/C at $18.65mW\;cm^{-2}$ The short-term current decay studies show a better stability of Au/C single cell. The higher activity of Au/C over PtRu/C was owing to the lower activation loss of Awe. The magnitude of current decay indicates a low problem of glycerol crossover from anode to cathode side. The similar performance of single cell with and without humudification at cathode points out an adequate transport of water through the microporous membrane.

• Biotechnology and Bioprocess Engineering:BBE
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• v.5 no.3
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• pp.207-210
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• 2000

When endothelial cells isolated isolated from human umbilical venis were cultred for 6dary using 96-well microplates, the final cell density in each was fiund not to be the same although the medium composition of each well was exactly the same. Cell growth in the wells located at the periphery of a microplate was low, while that in the central area of the plate was high. A possible cause for different rate of growth was proposed as the uneven concentration of oxygen in the culture medium of each well.

• Journal of Microbiology and Biotechnology
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• v.27 no.7
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• pp.1316-1323
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• 2017

Geosmin and 2-methylisoborneol (2-MIB), responsible for earthy or musty smell, are a major concern for safe drinking water supplies. This study investigated the effects of environmental factors on odorous compound production and cell growth in cyanobacterial strains. Anabaena sp. FACHB-1384, a 2-MIB producer, was sensitive to low temperature (<$20^{\circ}C$). However, geosmin producers, Anabaena sp. Chusori and Anabaena sp. NIER, were sensitive to high light intensity (>$100{\mu}mol/m^2/sec$), but not to low temperature. Geosmin concentrations increased under higher nitrate concentrations, being linearly proportional to cell density. A P-limited chemostat showed that P-stress decreased the geosmin productivity and extracellular geosmin amount per cell in Anabaena sp. NIER. However, only 2-MIB productivity was reduced in Planktothrix sp. FACHB-1374 under P-limitation. The extracellular 2-MIB amount per cell remained constant at all dilution rates. In conclusion, high light intensity and P-stress can contribute to the lower incidence of geosmin, whereas 2-MIB reduction could be attainable at a lower temperature.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.4
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• pp.291-296
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• 2020

The high power of a shingled photovoltaic module can be attributed to its low cell-to-module loss. The production of high power modules in limited area requires high efficiency solar cells. Shingled photovoltaic modules can be made by divided solar cells, which can be produced by the laser scribing process. After dividing the 21% PERC cell using laser scribing, the efficiency decreased by approximately 0.35%. However, there was no change in the efficiency of the solar cell having relatively lower efficiency, because the laser scribing process induce higher heat damages in solar cells with high efficiency. To prove this phenomena, the J₀ (leakage current density) of each cell was analyzed. It was found that the J₀ of 21% PERC increased about 17 times between full and divided solar cell. However, the J₀ of 20.2% PERC increased only about 2.5 times between full and divided solar cell.

• Korean Journal of Materials Research
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• v.29 no.5
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• pp.317-321
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• 2019

We investigated the characteristics of nano crystalline silicon(nc-Si) thin-film solar cells on graphite substrates. Amorphous silicon(a-Si) thin-film solar cells on graphite plates show low conversion efficiency due to high surface roughness, and many recombination by dangling bonds. In previous studies, we deposited barrier films by plasma enhanced chemical vapor deposition(PECVD) on graphite plate to reduce surface roughness and achieved ~7.8 % cell efficiency. In this study, we fabricated nc-Si thin film solar cell on graphite in order to increase the efficiency of solar cells. We achieved 8.45 % efficiency on graphite plate and applied this to nc-Si on graphite sheet for flexible solar cell applications. The characterization of the cell is performed with external quantum efficiency(EQE) and current density-voltage measurements(J-V). As a result, we obtain ~8.42 % cell efficiency in a flexible solar cell fabricated on a graphite sheet, which performance is similar to that of cells fabricated on graphite plates.