• Journal of Korean Society of Environmental Engineers
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• v.30 no.1
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• pp.85-89
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• 2008

The purpose of this study is to understand the removal possibility of microalgae using inorganic coagulants in coagulation and sedimentation process for water treatment. Removal of microalgae was studied according to coagulant type(Alum and PAC), coagulation factors(alkalinity, coagulant dosage, and setting time), and size fraction of microalgae. The contribution of applied coagulants for removal of microalgae was also examined. The removal rate of the microalgae by change of alkalinity was most high in 25 mg/L of alkalinity(Alum) as 87.2% and 30 mg/L of that(PAC) as 90.1%. Optimal coagulant dosage to remove the microalgae was 40 mg/L(removal effi.; 88.1%), and PAC was 50 mg/L(removal effi.; 90.1%). Alum was better than the PAC to remove the microlgae. In the water treatment processes such as rapid slow mixing and sedimentation the removal efficiency of microalgae with coagulants was 2 times higher than that of without. In optimal condition, the removal efficiencies of microalgae were nanoplankton > microplankton > picoplankton. Especially, the removal efficiency of the picoplankton was very low as below 30%.

• Economic and Environmental Geology
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• v.30 no.1
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• pp.61-65
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• 1997

Cadmium occurs as a minor element in sphalerite ((Zn, Fe)S) from the Boseong-Jangheung gold-silver mine district. We analyzed the abundance of cadmium in sphalerite using an electron probe micro analyzer (EPMA) and discussed the natural sources of cadmium in terms of bedrock geochemistry, in order to preliminarily reconnoiter the potential cadmium contamination in mine districts. Cadmium contents of sphalerites from the Au-Ag mines (Bodeok, Mundeok, Jeonbo, Boknae, Keumsan) in the Boseong-Jangheung district are considerably high, compared with cadmium contents of sphalerites (average = 0.5 wt.% Cd, maximum = 4.4 wt.% Cd) in the world. Sphalerites from the Keumsan mine (average = 9.49 wt.% Cd, maximum=11.22 wt. Cd) are highly enriched in cadmium. Our data suggest that the Boseong-Jangheung area is an important potential site of cadmium contamination in Korea. Based on bedrock geochemistry, natural causes of cadmium enrichment in sphalerite from the mine district are thought to be the mixing of cadmium leached from organic-rich, metasedimentary rocks (including coal) and/or black shales. From this study, we propose that the pinpointing of potential sites of pollution by toxic heavy metals can be done effectively through detailed reconnaisance study on mineralogical compositions of ore minerals such as sphalerite from the mine area.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.3
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• pp.101-105
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• 2006

We fabricated the nano $TiN_x$ by making of reaction between titanium powder and $Si_3N_4$ during planetary milling. The $TiN_x$ powder was sintered by spark plasma sintering machine after mixing with 50 wt% of titanium powder, and the sintered body was heat-treated at $850^{\circ}C$ in order to investigate its hardness property at the elevated temperature. We analyzed crystal structure by XRD. We observed the peaks of $TiN_{0.26}$ and TiN after 10 hours milling, and we observed TiN peak mainly after 20 hours milling. The reacted particle size distribution was investigated by FE-SEM. Increase of milling time, the size of reacted particles was decreased and the $10{\sim}20nm$ size of $TiN_x$ on the surface of titanium and $TiN_x$ was observed after 20 hours milling. The micro-Vickers hardness of mixed sintered body was about $1050kgf/mm^2$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.1
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• pp.7-12
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• 2017

3YSZ + (x) $Al_2O_3$ composites (x = 20, 40, 60, 80 wt%) were fabricated and the influences of particle sizes of $Al_2O_3$ on their microstructures and mechanical properties were investigated with XRD, SEM, vickers hardness and fracture toughness. $Al_2O_3$-3YSZ composites containing $Al_2O_3$ powder of a $0.3{\mu}m$ and an $1.0{\mu}m$, which are here in after named as $Al_2O_3$($0.3{\mu}m$)-3YSZ and $Al_2O_3$($1.0{\mu}m$)-3YSZ, respectively, were made by mixing raw materials, uni-axial pressing and sintering at $1,400^{\circ}C$, $1,500^{\circ}C$, and $1,600^{\circ}C$. $Al_2O_3$($0.3{\mu}m$)-3YSZ composites show the higher density and the better mechanical properties than $Al_2O_3$($1.0{\mu}m$)-3YSZ composites. The Vickers hardness of the $Al_2O_3$($0.3{\mu}m$)-3YSZ composites show a peak value of 1,997 Hv at the content of 60 wt% $Al_2O_3$, which is a slightly higher value in comparison with 1,938 Hv of the $Al_2O_3$($1.0{\mu}m$)-3YSZ composite. However, the fracture toughness of $Al_2O_3$-3YSZ composites monotonically increases with decreasing the content of $Al_2O_3$ without any peak values. $Al_2O_3$($0.3{\mu}m$)-3YSZ and $Al_2O_3$($1.0{\mu}m$)-3YSZ composites sintered at $1,600^{\circ}C$ have a maximum value of a $6.9MPa{\cdot}m^{1/2}$ and a $6.2MPa{\cdot}m^{1/2}$, respectively at the composition of containing 20 wt% $Al_2O_3$. It should be noticed that the mechanical properties and the sintering density of the $Al_2O_3$-3YSZ composites can be enhanced by using more fine $Al_2O_3$ powder due to their denser microstructure and smaller grain size.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.5
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• pp.475-479
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• 2012

We present a novel polymer fabrication process involving direct UV patterning of a hyperbranched polymer, AEO3000. Compared to PDMS, which is the most widely used polymer in bioMEMS devices, the present polymer has advantages with regard to electrode integration and fast fabrication. We designed a four-chip microelectrofluidic bench having three electrical pads and two fluidic I/O ports. We integrated a microfluidic mixer and a cell separator on the bench to characterize the interconnection performance and sample manipulation. Electrical and fluidic characterization of the microfluidic bench was performed. The measured electrical contact resistance was $0.75{\pm}0.44{\Omega}$, which is small enough for electrical applications, and the pressure drop was 8.3 kPa, which was 39.3% of the value in the tubing method. By performing yeast mixing and a separation test in the integrated module on the bench, we successfully showed that the interconnected chips could be used for bio-sample manipulation.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.1
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• pp.52-60
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• 2005

Purpose. The intent of this study was to evaluate the effects of curing conditions on self-curing denture base resins to find out proper condition in self-curing resin polymerization. Materials and methods, In this study, 3 commercial self-curing denture base resins are used Vertex SC, Tokuso Rebase and Jet Denture Repair Acrylic. After mixing the self curing resin, it was placed in a stainless steel mold(3$\times$6$\times$60mm). The mold containing the resin was placed under the following conditions: in air at 23$^{\circ}C$; or in water at 23$^{\circ}C$; or in water at 23$^{\circ}C$ under pressure(20psi); or in water at 37$^{\circ}C$ under pressure(20psi) or in water at 50$^{\circ}C$ under pressure(20psi) , or in water at 65$^{\circ}C$ under pressure(20psi), respectively. Also heat-curing denture base resin is polymerized according to manufactures' instructions as control. Fracture toughness was measured by a single edge notched beam(SENB) method. Notch about 3mm deep was carved at the center of the long axis of the specimen using a dental diamond disk driven by a dental micro engine. The flexural test was carried out at a crosshead speed 0.5mm/min and fracture surface were observed under measuring microscope. Results and conclusion . The results obtained were summarized as follows : 1. The fracture toughness value of self-curing denture base resins were relatively lower than that of heat-curing denture base resin. 2. In Vertex SC and Jet Denture Repair Acrylic, higher fracture toughness value was observed in the curing environment with pressure but in Tokuso Rebase, low fracture toughness value was observed but there was no statistical difference. 3. Higher fracture toughness value was observed in the curing environment with water than air but there was no statistical difference. 4. Raising the temperature in water showed the increase of fracture toughness.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.3
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• pp.345-350
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• 2006

This study investigated the removal of recalcitrant organics in dyeing wastewater using a fluidized bed reactor(FBR) that contained cell-immobilized pellets. The pellets were manufactured and condensing the gel phase by mixing PEG-polymer and cells to form micro-porous PEG-polymer pellets whose size were ${\Phi}\;4mm{\times}H\;4mm$ on average. An industrial activated sludge without any pre-adaptation was used for the cell immobilization because it gave an equivalent removal efficiency to a pre-adapted sludges. The feed was obtained from an effluent of a biological treatment plant, which contained $SCOD_{Cr}$ of 330 mg/L and $SBOD_5$ of 20 mg/L. The $SCOD_{Cr}$ removal efficiency was over 45% and the effluent $COD_{Mn}$ concentration was less than 100 mg/L at HRTs from 6 to 24 hrs. The optimum HRT in the FBR was determined as 12 hrs considering the removal efficiency and cost. When a raw wastewater containing 768 mg/L of $COD_{Cr}$ was fed to the FBR, the effluent $COD_{Cr}$ concentration increased only slightly, giving a 70% of $COD_{Cr}$ removal or a 97% of $BCOD_5$ removal. This indicated that the FBR had an excellent capability of biodegradable organics removal also. In conclusion, the FBR could be applied to textile wastewater treatment in place of an activated sludge process.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.157-167
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• 2015

Cement composites subjected to high-velocity projectile shows local failure and it can be suppressed by improvement of flexural toughness with reinforcement of fiber. Therefore, researches on impact resistance performance of cement composites are in progress and a number of types of fiber reinforcement are being developed. Since bonding properties of fiber with matrix, specific surface area and numbers of fiber are different by fiber reinforcement type, mechanical properties of fiber reinforced cement composites and improvement of impact resistance performance need to be considered. In this study, improvement of flexural toughness and failure reduction effect by impact of high-velocity projectile have been evaluated according to fiber type by mixing steel fiber, polyamide, nylon and polyethylene which are have different shape and mechanical properties. As results, flexural toughness was improved by redistribution of stress and crack prevention with bridge effect of reinforced fibers, and scabbing by high-velocity impact was suppressed. Since it is possible to decrease scabbing limit thickness from impact energy, thickness can be thinner when it is applied to protection. Scabbing of steel fiber reinforced cement composites was occurred and it was observed that desquamation of partial fragment was suppressed by adhesion between fiber and matrix. Scabbing by high-velocity impact of synthetic fiber reinforced cement composites was decreased by microcrack, impact wave neutralization and energy dispersion with a large number of fibers.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.5
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• pp.272-279
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• 2003

This study was performed to develop a more rapid and simple nutrient diagnosis method of plants than the conventional leaf analysis method. Cucumber (Cucumis sativus L. cv. jangil banbaek) was planted in the mixed media produced by mixing perlite and rock wool at 1:1 (v/v) ratio. The Yamazakki nutrient solution for cucumber was supplied to the media using micro-drip irrigation system. Experimental plots were consisted of no fertilization, deficient fertilization, adequate fertilization, and surplus fertilization for N, P and K. Specific color difference sensor value (SCDSV) measured by chlorophyll meter was closely related to total-N concentration in leaves measured by the conventional method. Nitrate, $PO_4$ and K concentration in petiole sap measured by test strips showed a significant relationship with total-N, P and K concentration in leaves. Linear regression equations between $NO_3$, $PO_4$ and K concentration in petiole sap and total-N, P and K concentration in the leaves were prepared. Optimum levels of $NO_{3}$, $PO_{4}$ and K in petiole sap were obtained by plugging the optimum concentrations of total-N, P and K in the leaves by other researchers into the equations. In conclusion, the SCDSV measured by chlorophyll meter and the concentration of $NO_3$, P and K in petiole sap measured by the test strips would be suitable for rapid estimation of plant nutrient status.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.213-213
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7NO1 spot-welded by pulse Nd: YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed: center line crack($C_{C}$), diagonal crack($C_{D}$), and U shape crack($C_{U}$). Also, HAZ crack($C_{H}$), was observed in the HAZ region, furthermore, mixing crack($C_{M}$), consisting of diagonal crack and HAZ crack was observed.White film was formed at the hot crack region in the fractured surface after it was immersed to 10%NaOH water. In the case of A5083 alloy, white films in C crack and $C_D crack region were composed of low melting phases, Fe₂Si$Al_8$ and eutectic phases, Mg₂Al₃ and Mg₂Si. Such films observed near HAZ crack were also consist of eutectic Mg₂Al₃. In the case of A7N01 alloy, eutectic phases of CuAl₂, $Mg_{32}$ (Al,Zn) ₃, MgZn₂, Al₂CuMg and Mg₂Si were observed in the whitely etched films near $C_{C}$ crack and $C_{D}$ crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Si in the case of A7N01 aooly, respectively.The $C_{D}$ and $C_{C}$ cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of $C_{M}$ crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The $C_{U}$ crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification. (Received October 7, 1999)