• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.409-412
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• 2006

In process of reinforced concrete(RC) box structure, the heat of hydration may cause serious thermal cracking problems. In order to eliminate hydration heat of mass concrete, this paper reports results of hydration heat control in mass concrete using the OCHP(Oscillating Capillary tube Heat Pipe). Recently OCHP is drawn special attention from these points of low cost as well as short construction schedule for the manufacturing of heat exchanger, flexibility, simplification and high performance. There were three RC box molds$(1.2{\times}1.2{\times}1.2m)$ which shows a difference as compared with each other. One was not equipped with OCHP. While others were equipped with OCHP and these were cooled with air natural convection and spraying water respectively. The OCHP was composed of copper pipe with 12 turns(O.D : 4mm, I.D : 2.8mm). The working fluid was R-22 and its charging ratio was 30(Vol. %). In order to analyze the distribution of temperature and index figure of thermal crack in sequential placement of mass concrete, we used HYCON of computer program. As a result of the experiment, the peak temperature decreased about $15.6\sim23.4^{\circ}C$ than the general specimen and the probability of thermal crack generated in mass concrete decreased up to 0%.

• Journal of Power Electronics
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• v.13 no.5
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• pp.737-745
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• 2013

Offshore wind farms are rapidly growing owing to their comparatively more stable wind conditions than onshore and land-based wind farms. The power capacity of offshore wind turbines has been increased to 5MW in order to capture a larger amount of wind energy, which results in an increase of each component's size. Furthermore, the weight of the marine turbine components installed in the nacelle directly influences the total mechanical design, as well as the operation and maintenance (O&M) costs. A reduction in the weight of the nacelle allows for cost-effective tower and foundation structures. On the other hand, longer transmission distances from an offshore wind turbine to the load leads to higher energy losses. In this regard, DC transmission is more useful than AC transmission in terms of efficiency because no reactive power is generated/consumed by DC transmission cables. This paper describes some of the challenges and difficulties faced in designing high-power-density power conversion systems (HPDPCSs) for offshore wind turbines. A new approach for high gain/high voltage systems is introduced using transformerless power conversion technologies. Finally, the proposed converter is evaluated in terms of step-up conversion ratio, device number, modulation, and costs.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.4
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• pp.565-578
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• 2012

Integrated watershed sewage works program(IWSWP) is defined as implementing, by one of local governments or central government, sewage facilities planning, installation and management for a certain watershed in which criteria of water quality is established and two or more local governments are involved. It is shown that IWSWP is more efficient for the improvement of water quality of water body than conventional local sewage works program(CLSWP) and besides, economical benefits can be achieved by integration of facilities and M&O. In this research, case study for 8 watershed area were investigated to evaluate the difference of effect between IWSWP and CLSWP. The research shows that IWSWP has the money saving result of approximately 12 % by cost reduction for sewage works investment. B/C analysis result shows that B/C ratio of IWSWP was 1.749 and it is higher than B/C ratio of 1.439 for CLSWP. At the same time, the B/C sensitivity analysis is carried out for the rate of discount and the recreational use benefit.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.530-534
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• 2017

Chitosan is a promising flocculant for microalgae harvesting, but its scale-up application is not economically supported yet. Low solubility of chitosan in microalgae suspension demands high dosage (as a flocculant) to destabilize the cells, and thus, increases the cost of microalgae harvesting. This study identifies efficient solvents for the chitosan, and optimizes the concentration of solvents and chitosan dose to improve the harvesting efficiency. Chitosan was dissolved in different acids, and subsequently used as a flocculant. The flocculant efficacy was measured in terms of harvesting efficiency and reduction in chemical oxygen demand (COD) of the microalgae suspension. It was found that chitosan dissolved in 0.05 M HCl showed the highest harvesting efficiency ($89{\pm}0.87%$) at only 30 mg/L of dosage. In comparison, 270 mg/L of $FeCl_3{\cdot}6H_2O$ was required to attain $86{\pm}0.083%$ of the harvesting efficiency. $H_2SO_4$ dissolved chitosan required high flocculant dose (150 mg/L) and resulted in relatively low harvesting efficiency ($77{\pm}0.11%$). It was concluded that the efficacy of chitosan is solvent dependent, and the selection of proper solvent can decrease the dosage requirement for microalgae harvesting.

• Journal of Korean Vacuum Science & Technology
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• v.3 no.1
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• pp.79-84
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• 1999

the photolithographic patterning on an indium-tin oxide (ITO) glass and the electro-phoretic deposition were combined for preparing the screen of the full-color field emission display(FED). the patterns with a pixel of 400$\mu\textrm{m}$ on the ITO-glass were made by etching the ITO with well-prepared etchant consisting of HCL, H2O, and HNO3. Electrophoretic method was carried out in order to deposit each spherical red (R), green(G), and blue (B) phosphor on the patterned ITO-glass. The process parameters such as bias voltage, salt concentration, and deposition time were optimized to achieve clear boundaries. It was found that the etching process of ITO combined with electrophoretic method was cost-effective, provided distinct pattern, and even reduced process steps compared with conventional processes. The application of reverse bias to the dormant electrodes while depositing the phosphors on the stripe pattern was found to be very critical for preventing the cross-contamination of each phosphor in a pixel.

• 한국태양에너지학회:학술대회논문집
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• 2011.04a
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• pp.101-104
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• 2011

Many studies in crystalline silicon solar cell fabrication have been focused on high efficiency and low cost. In this paper, we carried out the doping procedure by varying the silicon wafer thicknesses and sheet resistance. The silicon wafers with various thicknesses were obtained by shiny etching and texturing. The thicknesses of wafers were 100, 120, 150, and $180{\mu}m$. The emitter layer formed by $POCl_3$ doping process had sheet resistance with 40 and $80{\Omega}/sq$ for selective emitter application. This experiment indicated wafer thickness did not influence sheet resistance but lifetime was strongly effected.

• Journal of the Semiconductor & Display Technology
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• v.10 no.4
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• pp.61-64
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• 2011

In order to grow the crystalline solar cells industry continuously, development of alternate low-cost manufacturing processes is required. Plasma doping system is the technique for introducing dopants into semiconductor wafers in CMOS devices. In photovoltaics, plasma doping system could be an interesting alternative to thermal furnace diffusion processes. In this paper, plasma doping system was applied for phosphorus doping in crystalline solar cells. The Plasma doping was carried out in 1~4 KV bias voltages for four minutes. For removing surface damage and formation of pn junction, annealing steps were carried out in the range of $800{\sim}900^{\circ}C$ with $O_2$ ambient using thermal furnace. The junction depth in about $0.35{\sim}0.6{\mu}m$ range have been achieved and the doping profiles were very similar to emitter by thermal diffusion. So, It could be confirmed that plasma doping technique can be used for emitter formation in crystalline solar cells.

• Korean Journal of Materials Research
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• v.16 no.8
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• pp.479-484
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• 2006

Highly c-axis oriented poly-crystalline GaN with a dimension of $1{\sim}3\;{\mu}m$ was deposited on $c-Al_2O_3$ substrate by vapor transport epitaxy (VTE) method at the temperature range of $900{\sim}1150^{\circ}C$. XRD intensities from (00'2) plane of grown GaNs were increased with reaction conditions which indicate the improvement of the crystal quality. In the PL spectra measured at 10 K, the spectrum composed with the neutral-donor bound exciton-related emission at 3.47 eV, crystal defect-related emission band at 3.42 eV and with its phonon replicas. The fact that intensity of $I_2$ were increased and FWHM were decreased with growth conditions means that the quality of GaN crystals were improved. With this simple VTE technology, we confirm that the GaNs were simply deposited on sapphire substrate and crystal quality related to optical properties of GaN grown by VTE were relatively good. PL emission without deep level emission in spite of polycrystalline structure can be applicable to the fabrication of large area and low cost optical devices using poly-GaN grown by VTE.

• Journal of Biosystems Engineering
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• v.25 no.3
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• pp.203-212
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• 2000

One of the obstructing factors against managing large-scaled dairy farm in Korea has been heavy labor requirement for feeding dairy cows. A tractor attached TMR mixer was developed to reduce the cost and to provide economic benefit in this research. The TMR mixer was designed to have a feeding capacity of 35 heads at a batch with various functioning systems of paddle type mixer, cutter and grinder, delivery conveyor, weighing console, power transmission train, and mounting trailer. The maximum power required during the mixing operarion was 26.3 kw(P.T.O), readily available from 32kw-rated tractors, which had been widely used in Korea. Low coefficient of variation(14.0%) revealed an uniform mixing performance of the mixer. The mixer can also be used in compost mixing as well as concentrates and roughage.

• Journal of Electrochemical Science and Technology
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• v.10 no.1
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• pp.1-13
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• 2019

Na-ion batteries are being considered as promising cost-effective energy storage devices for the future compared to Li-ion batteries owing to the crustal abundance of Na-ion. However, the large radius of the Na ion result in sluggish electrode kinetics that leads to poor electrochemical performance, which prohibits the use of these batteries in real time application. Therefore, identification and optimization of the anode, cathode, and electrolyte are essential for achieving high-performance Na-ion batteries. In this context, the current review discusses the suitable high-voltage cathode materials for Na-ion batteries. According to a recent research survey, sodium vanadium fluorophosphate (NVPF) compounds have been emphasized for use as a high-voltage Na-ion cathode material. Among the fluorophosphate groups, $Na_3V_2(PO_4)_2F_3$ exhibited the high theoretical capacity ($128mAh\;g^{-1}$) and working voltage (~3.9 V vs. $Na/Na^+$) compared to the other fluorophosphates and $Na_3V_2(PO_4)_3$. Here, we have also highlighted the classification of Fluorophosphates, NVPF composite with carbonaceous materials, the appropriate synthesis methods and how these methods can enhance the electrochemical performance. Finally, the recent developments in NVPF for the application in energy storage devices and its outlook are summarized.