• Journal of Korean Society of Environmental Engineers
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• v.27 no.6
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• pp.581-589
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• 2005

Recently, membrane processes have been replacing the conventional processes for waste water treatment to produce better quality of effluent and to meet more stringent regulations because of water shortage. However, using membrane processes for water treatment has confronted with fouling and difficulty in treating dissolved organic pollutants. In this study, membrane process equipped with crossflow microfiltration is combined with coagulation process using alum and PAC to improve permeability and treatment efficiency. The effects of coagulant dosage and optimum membrane operating conditions were investigated from measurement of permeate flow, cumulative volume, total resistance, particle size, dissolved organic pollutant, dissolved aluminium and quality of effluent. Characteristic of PAC coagulation was compared with that of alum coagulation. PAC coagulation reduced membrane fouling because of forming larger particle size and increased permeate velocity and cumulative volume. Less dissolved organic pollutants and dissolved aluminum made decreasing-rate of permeate velocity being lowered. At using $0.2\;{\mu}m$ membrane, cake filtration observed. At using $0.45\;{\mu}m$ membrane, there was floc breakage due to shear stress occurred born circulating operation. It made floc size smaller than membrane pore size, which subsequently to decrease permeate velocity and to increase total resistance. The optimum coagulation dosage was $300{\pm}50\;mg/L$ for both alum and PAC. PAC coagulation was more efficiently used with $0.2\;{\mu}m$ membrane, and the highest permeate flux was in using $0.45\;{\mu}m$membrane. The greatest efficiency of treatment was as follows; turbidity 99.8%, SS 99.9%, $BOD_5$ 94.4%, $COD_{Cr}$ 95.4%, T-N 54.3%, T-P 99.8%.

• Journal of Korea Foundry Society
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• v.41 no.5
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• pp.434-444
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• 2021

This study investigated the overall dependence of the tensile properties of Al-Si alloys on the distribution aspect of a eutectic Si particle in terms of defect susceptibility to the effective void area fraction, referring to the sum of pre-existing microvoids and the damage evolution of the Si particle. The network morphology of as-cast Al-xSi (x=2,5,8,11) alloys was modified to a granular type via a T4 treatment, after which a computational topography (CT) analysis and scanning electron microscope (SEM) observations were utilized to evaluate the size and distribution of the microvoids. The CT and SEM analyses indicated that the main cracks grow along local regions that possess the highest porosity level. The local plastic deformation around the microvoids and the distribution aspect of the microvoids induced a practical difference between the iso-volumetric CT measurement and the SEM fractography outcomes. The results demonstrated that the overall dependence of the ultimate tensile strength (UTS) and elongation on the effective void area fraction is more sensitive to the variation of the area fraction of the Si particle in the network morphology than in the granular type; this is due to the sequential damage evolution of the neighboring Si particles in the eutectic Si colony.

• Journal of Korea Water Resources Association
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• v.32 no.3
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• pp.215-223
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• 1999

Recently, measurement of soil moisture contents using TDR (time domain reflectometry) has been proven to be viable technique. The first empirical model proposed by Topp et al. (1980) has been widely used to determine moisture contents of soils from the TDR-measured dielectric constants. However, applicability of the model was limited to medium-textured soils. In this study, we investigate the applicability of the model to sandy-gravelly soils. Calibration experiments consisted of measurement on travel time of electromagnetic waveform along the parallel TDR rods inserted into samples and gravimetric determination of soil moisture contents. The experiments are performed for two sets of samples different in the length and each set consisted of seven different particle size distributions with various gavel contents. The calibration results show that the Topp equation overestimated the measured moisture content for a given dielectric constant by 3 to 8%. We therefore propose new empirical relationships valid for sandy-gravelly soils.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.6
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• pp.642-647
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• 2018

Gas compressors are mostly driven by motors. It is important to measure the power of motors to evaluate their power efficiency, because the mechanical loads of gas compressors are always varied. In order to measure the power given to the driving motors, the torque should be measured. Manufacturers of compressors usually use the torque data to calculate the compressors qualities such as power consumption, efficiencies and failures. In general, measurements for the shaft torque of the compressors have been based upon contact types, strain gauges. In the cases of larger compressors, the contact type of strain gauges have several disadvantages such as large size and high cost. In this study, a relatively inexpensive and simple torque sensing technique that is not restricted to shaft diameter is introduced using visualization technique. Particle image velocimetry (PIV) has been adopted to complete non-contact torques measurements for rotating motors. In order to compare the performance of the newly constructed torque measurement technique, torque measurement by a transducer based on MEMS technology has been performed simultaneously during experiments.

• Resources Recycling
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• v.27 no.1
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• pp.55-63
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• 2018

Physical property changes of printed circuit board (PCB) according to heat treatment conditions were investigated. The heat treatment was carried out in air and nitrogen atmosphere at temperature range from $200^{\circ}C$ to $325^{\circ}C$. Thermogravimetric analysis showed that the PCB was pyrolyzed in two steps. The thickness of PCB expanded by 11~28% at about $300^{\circ}C$ in both air and nitrogen atmosphere as layer disintegration occurred. Mechanical strength of PCB decreased from 338.4 MPa to 20.3~40.2 MPa due to the delamination caused by the heat treatment. The heated printed circuit boards were crushed and sieved for analysis of density distribution and liberation degree of copper according to particle size. As a result of the density distribution measurement, non metallic particles and copper particles were concentrated into different size range, respectively. The liberation degree of copper was improved from 9.3% to 100% at size range of $1,400{\sim}2,000{\mu}m$ by heat treatment.

• Applied Chemistry for Engineering
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• v.28 no.2
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• pp.177-185
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• 2017

In the present work, the interaction of fatty acid with vesicle membrane of phospholipids was investigated using 3 different kinds of fatty acids such as stearic acid (SA), oleic acid (OA) and linoleic acid (LA). Basically, the same trend has been found in 3 fatty acid systems. The addition of fatty acid produced a close packing of liposome due to the penetration of fatty acid molecules into liposome vesicles, which resulted in a decrease in size and an increase in zeta potential of liposome. However, excessive addition of fatty acid produced a transition from liposomes to aggregates of lipid particles having polymorphic structure. The membrane fluidity, characterized by measuring membrane deformability and fluorescence anisotropy ratio of liposomes, was in good agreement with measurement results of transmission electron microscopy (TEM) and particle size. The minimum size and closest packing of liposome with SA, OA and LA were found when the molar ratios of fatty acid to lecithin were 0.70, 0.50, and 0.25 respectively.

• Korean Journal of Soil Science and Fertilizer
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• v.17 no.3
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• pp.212-217
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• 1984

Spatial variabilities of particle size distribution of 96 samples from Hwadong SiCL and Jungdong Sl were studied by using geostatistical concepts. The measurement was made at the nodes of the regular grid consisting of 12 rows and 8 columns. Sample spacing within rows and columns was 3 and 2 meters, respectively. The results are summarized as follows. 1. Variograms of Hwadong SiCL were fitted for the linear model and those of Jungdong SL for the spherical model. 2. Variograms of properties for Hwadong and clay for Jungdong showed the pure nugget effect. Those of silt and clay for Jungdong, however, appeared the nugget effect. 3. The minimum number of samples necessary to reproduce results similar to the true mean of the 96 measured values was approximately estimated. The minimum sample sizes of silt, clay, and sand in Hwadong SiCL were 27, 13, and 6, respectively. And the minimum sample size of clay in Jungdong SL was 17. 4. The approximate number of samples required to detect the difference of 5% of the true mean with 0.95 confidence level was estimated. The resulting number of samples for silt and sand in Jungdong was 14, and 26, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.5
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• pp.255-264
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• 2013

Cobalt aluminate ($CoAl_2O_4$) is a highly stable pigment with excellent resistance to light, weather, etc., which has resulted in widespread use as a ceramic pigment. Due to the unique optical characteristics, $CoAl_2O_4$ is generally used as a coloring agent to decorate porcelain products, glass, paints and plastics. Here, $CoAl_2O_4$ pigments were synthesized by polymerized complex method and solid state reaction. Then $CoAl_2O_4$ pigment were grinded using the attrition milling with 1 mm size zirconia ball for 3 hours. The attrition milling process was performed at the constant speed of 800 rpm and ball to powder weight ratio (BPR) was 100 : 1. The characteristics of synthesized pigment were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), particle size analyser (PSA) and CIE $L^*a^*b^*$. The XRD patterns of $CoAl_2O_4$ show single phase spinel structure. The particle size of $CoAl_2O_4$ measured by FE-SEM, TEM and PSA analysis was in the range of 100~200 nm. The blue color of obtained $CoAl_2O_4$ pigments could be confirmed through CIE $L^*a^*b^*$ measurement.

• Electrical & Electronic Materials
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• v.10 no.2
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• pp.141-149
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• 1997

L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ powders were prepared by both GNP(Glycine-Nitrate Process) and solid state reaction method in various of calcination temperature(800-1000.deg. C) and time in air. Also, L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ cathode contacts on YSZ(Yttria-Stabilized Zirconia) substrate were prepared by screen printing and sintering method as a function of sintering temperature(1100-1450.deg. C) in air. Sintering behaviors have been investigated by SEM(Scanning Electron Microscope) and porosity measurement. Compositional and structural characterization were carried out by X-ray diffractometer and ICP AES(Inductively Coupled Plasma-Atomic Emission Spectrometry) analysis. Electrical characterization was carried out by the electrical conductivity with linear 4 point probe method. As the calcination period increased in solid state reaction method, L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ phase increased. Although L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ single phase was obtained only for 48hrs at 1000.deg. C, in GNP method it was easy to get single and ultra-fine L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ powders with submicron particle size at 650.deg. C for 30min. The particle size and thickness of L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ cathode contact by solid state reaction method did not change during the heat treatment, while those by GNP method showed good sintering characteristics because initial powder size fabricated from GNP method is smaller than that fabricated from solid state reaction method. Based on enthalpy change from thermodynamic data and ICP-AES analysis, it was suggested to make cathode contact in composition of (L $a_{0.7}$S $r_{0.3}$)$_{0.91}$ Mn $O_{3}$ which have little second phase (L $a_{2}$Z $r_{2}$ $O_{7}$) for high efficient solid oxide fuel cells applications. As (L $a_{0.7}$S $r_{0.3}$)$_{0.91}$Mn $O_{3}$ cathode contact on YSZ substrate was sintering at 1250.deg. C the temperature that liquid phase sintering did not occur. It was possible to obtain proper cathode contacts with electrical conductivity of 150(S/cm) and porosity content of 30-40%.m) and porosity content of 30-40%.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.6
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• pp.24-32
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• 2012

A large fraction of urban $PM_{10}$ concentrations is due to non-exhaust traffic emissions including road dust, tire wear particles, and brake lining particles. Although potential health and environmental impacts associated with tire wear debris have been increased, few environmentally and biologically relevant studies of actual tire wear debris have been conducted. Tire wear particles (TWP) are released from the tire tread as a result of the interaction between the tire and the pavement. Roadway particles (RP), meanwhile, are particles on roads composed of a mixture of elements from tires, pavements, fuels, brakes, and environmental dust. The main objective of present study is to identify the contribution of tires to the generation of RP and to assess the potential environmental and health impacts of this contribution. First, a mobile measurement system was constructed and used to measure the roadway particles on asphalt road according to vehicle speed. The equipment of the mobile system provides $PM_{10}$ concentrations by Dusttrak DRX and number density & size distribution measurements of fine and ultra-fine particles by a fast mobility particle sizer (FMPS) and an aerosol particle sizer (APS). When traveling on an asphalt road at constant speed, there is a clear tendency for PM10 concentration to increase slightly in accordance with an increase in the vehicle speed. It was also found that considerable brake wear particles and particles from tire/road interface were generated by rapid deceleration of the vehicle. The morphology and elements of the roadway particles were also analyzed using SEM-EDX technique.