• Composites Research
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• v.23 no.3
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• pp.58-63
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• 2010

Tensile and flexural properties and electrical conductivity of MWCNT/epoxy composites with different aspect ratios of MWCNTs were compared. The MWCNT/epoxy mixtures were prepared by mechanical dispersion methods using a homomixer and a three-roll mill, and then composite samples were fabricated by compression molding process. The fractured surfaces of the samples were observed by SEM in order to evaluate the degree of dispersion of MWCNTs. The addition of MWCNTs into epoxy resin improved its tensile strength by 7.0% while its flexural strength increased slightly as compared with the one without MWCNTs. In the case of MWCNTs having highest aspect ratio, the mechanical properties of the composites were decreased. When the contents of CM-95 MWCNTs were varied, maximum of tensile and flexural strengths occurred at 1wt% and 0.5wt%, respectively. From the higher contents than these, tensile and flexural strengths of the composites decreased. Electrical conductivities of in-plane and thought-the-thickness directions of MWCNT/epoxy composites were measured using a two-point probe method. They increased with the increase of the aspect ratios and concentrations of MWCNTs in the epoxy matrix.

• Composites Research
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• v.33 no.1
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• pp.1-6
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• 2020

Dispersion and electrical resistance (ER) properties of polyurethane (PU) type topcoat were evaluated using carbon nanotube (CNT) with different CNT weight fraction. CNT was dispersed in PU type topcoat using ultra sonication dispersion method. CNT/PU topcoat was coated on carbon fiber reinforced epoxy composite (CFRC) surface using gravity feed spraying method. Static contact angles of CFRC and CNT/PU topcoat were performed using 4 types of solvents to calculate the work of adhesion between CNT/PU topcoat and CFRC surface. Surface resistance of CNT added PU topcoat was measured to determine CNT dispersion. Adhesion property between CNT/PU topcoat and CFRC was determined via cross hatch cutting test based on ASTM D3359. The optimized condition of CNT weight fraction was found.

• Journal of Environmental Science International
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• v.23 no.4
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• pp.715-722
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• 2014

Effects of coagulation types on flocculation were investigated by using a photometric dispersion analyzer (PDA) as an on-line monitoring technique in this study. Nakdong River water were used and alum and ferric chloride were used as coagulants. The aim of this study is to compare the coagulation characteristics of alum and ferric chloride by a photometric dispersion analyzer (PDA). Floc growing rates ($R_v$) in three different water temperatures ($4^{\circ}C$, $16^{\circ}C$ and $30^{\circ}C$) and coagulants doses (0.15 mM, 0.20 mM and 0.25 mM as Al, Fe) were measured. The floc growing rate ($R_v$) by alum was 1.8~2.8 times higher than that of ferric chloride during rapid mixing period, however, for 0.15 mM~0.25 mM coagulant doses the floc growing rate ($R_v$) by ferric chloride was 1.1~2.3 times higher than that of alum in the slow mixing period at $16^{\circ}C$ water temperature. Reasonable coagulant doses of alum and ferric chloride for turbidity removal were 0.1 mM (as Al) and 0.2 mM (as Fe), respectively, and the removal efficiency of those coagulant doses showed 94% for alum and 97% for ferric chloride. The appropriate coagulant dose of alum and ferric chloride for removing dissolved organic carbon (DOC) showed about 0.3 mM (as Al, Fe) and at this dosage, DOC removal efficiencies were 36% and 44%, and ferric chloride was superior to the alum for removal of the DOC in water.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.1
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• pp.1-15
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• 2008

Chemical Accident Response Information System (CARIS) which has been designed for the efficient emergency response of chemical accidents produces the real-time atmospheric fields through the Regional Atmospheric Modeling System, RAMS. The previous studies were emphasized that improving an initial input data had more effective results in developing prediction ability of atmospheric model. In a continuous effort to improve an initial input data, we replaced the land-use dataset using in the RAMS, which is a high resolution USGS digital data constructed in April, 1993, with the latest land-use data of the Korea Ministry of Environment over the South Korea and simulated atmospheric fields for developing a real-time prediction in dispersion of chemicals. The results showed that the new land-use data was written in a standard RAMS format and shown the modified surface characteristics and the landscape heterogeneity resulting from land-use change. In the results of sensitivity experiment we got the improved atmospheric fields and assured that it will give more reliable real-time atmospheric fields to all users of CARIS for the dispersion forecast in associated with hazardous chemical releases as well as general air pollutants.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2B
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• pp.161-170
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• 2006

A tracer test technique using a radioisotope was proposed to investigate pollutant mixing characteristics in rivers. The main advantages of radioisotope as a tracer in field tests are that it can be detected easily, and that its detection range is quite large. Also, using the radioisotope, the amount sorbed by the bed material and the biota may be a minimum. Field tracer tests were conducted at seven different sites in natural rivers with various meandering pattern. Based on the acquired data, the behavior of the tracer cloud in the intermediate-field was examined two-dimensionally, and dispersion coefficients were calculated using several evaluation methods. Results revealed that the tracer cloud was transported skewed to the outer bank and dispersion coefficients in bends were larger than those in straight reaches.

• Journal of Korean Society of Water and Wastewater
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• v.13 no.4
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• pp.62-71
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• 1999

The containment retardation capacities of four different aquifers were evaluated in a preliminary study for development of bank filtration in the Young San river area. $NO_3-N$, $NO_2-N$, $NH_4^+-N$, Fe, Mn, phenol, and chloride were selected as the target contaminants and a nonreactive tracer, respectively. Batch isotherm tests were conducted to measure the partition coefficients of the target contaminants. The mass transport parameters of nonreactive tracer were estimated from column tests. From the results of bath isotherm tests, it was shown that lower stream aquifer materials have greater partition coefficients of $NO_3-N$, $NH_4^+-N$, Mn, and phenol than the upper stream aquifer materials; however, there was no significant position-dependent trend for Fe. All aquifer materials tested have the same range of partition coefficients for $NO_2-N$. Column tests showed that the molecular diffusion of Cl- was much less than the mechanical dispersion; and there was no significant difference between the estimated dispersivities of tested aquifer materials. Consequently, it seems that the difference in the containment retardation capacities between four aquifers tested in this study would primarily result not from hydrodynamic dispersion but from partitioning.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.343-345
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• 2017

We present the development of a spectral dispersion device for wideband spectroscopy for which the primary scientific objective is the characterization of transiting exoplanets. The principle of the disperser is simple: a grating is fabricated on the surface of a prism. The direction of the spectral dispersion power of the prism is crossed with the grating. Thus, the prism separates the spectrum into individual orders while the grating produces a spectrum for each order. In this work, ZnS was selected as the material for the cross disperser, which was designed to cover the wavelength region, ${\lambda}=0.6-13{\mu}m$, with a spectral resolving power, $R{\geq}50$. A disperser was fabricated, and an evaluation of its surface was conducted. Two spectrometer designs, one adopting ZnS (${\lambda}=0.6-13{\mu}m$, $R{\geq}300$) and the other adopting CdZnTe (${\lambda}=1-23{\mu}m$, $R{\geq}250$), are presented. The spectrometers, each of which has no moving mechanical parts, consist simply of a disperser, a focusing mirror, and a detector.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.1
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• pp.61-67
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• 2016

The airbag is a widely accepted device for occupant protection in the automotive industry. As the injuries induced by airbag deployment have become a critical issue, revisions to Federal Motor Vehicle Safety Standard (FMVSS) 208 were required to create advanced airbags that can protect occupants of varying statures. In this paper, we developed a new low-risk deployment passenger airbag by adding the Passenger Protection Wrap (PPW). The PPW reduces the cushion impact force to the occupant in order to ensure pressure dispersion. A series of tests were conducted by using FMVSS 208 test procedures to demonstrate the proposed system. It was found that the system not only satisfied the injury criteria of FMVSS 208 but was also effective for protecting passengers of all sizes (male, small female, 3-year-old, 6-year-old).

• Journal of Korean Society of Water and Wastewater
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• v.22 no.1
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• pp.49-63
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• 2008

The objectives of this research were to evaluate the pressurized/the main inlet water flowrate ratio which have been used as the most important parameter for operating the pump diffusion mixer until now, to suggest the alternative operating parameter and the relating criteria if the flowrate ratio was not inadequate. For the objectives of this research, computational fluid dynamics (CFD) simulation was conducted for 21 cases of flowrate ratio in full-scaled pump diffusion mixer. From the results of CFD simulation, the local velocity gradient values were calculated in each case in order to analyze the simulation results in more detail. For verifying CFD simulation, wet test was conducted. The wet test was to measure the factual coagulant dispersion distribution at a distance of 5.4m from deflector. From both results of CFD simulation and wet test, flowrate ratio was inadequate as operating parameter or criteria, on the other hand the pressurized/the main inlet velocity ratio(dimensionless) was useful in predicting the performance of pump diffusion mixer. Also, the injected coagulant could be dispersed evenly in overall cross section on the condition that pressurized/the main inlet velocity ratio(dimensionless) is over at least 20.

• Journal of Pharmaceutical Investigation
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• v.41 no.4
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• pp.211-215
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• 2011

The aim of this study was to develop a stable enteric coated diclofenac sodium (DFS) tablets using Aqua-Polish E without using a subcoat. DFS uncoated tablets were manufactured through the non direct compression process. AquaPolish E white aqueous coating dispersion was used as enteric coating material. This film forming polymer is a mixture of selected polymethacrylic/ethylacrylate copolymers. The stability of the obtained enteric coated tablets was evaluated according to ICH guidelines. No signs of disintegration or cracking was observed when they placed in 0.1N HCl solution (pH1.2), but they were completely disintegrated within 10 minutes when they placed in buffered solution at pH6.8. Dissolution test was also conducted by placing tablets in 0.1 N HCl for 2 hours and then 1 hour in phosphate buffer at pH 6.8. Less than 0.9 % of drug was released in the acidic phase and up to 97% in the basic medium. These findings suggest that aqueous enteric coating with AquaPolish E system is an easy and economical approach for preparing stable DFS enteric coat without the use of a subcoating layer.