• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.166-173
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• 2007

A numerical study was conducted to have the effect of $CO_2$ addition to fuel on the chemical reaction mechanism with the change of the initial concentration of $CO_2$ and the axial velocity gradient. From this study, it was found that there were two serious effects of $CO_2$ addition on a non-premixed flame ; a diluent effect by the reactive species reduction and chemical effect of the breakdown of $CO_2$ by the third-body collision and thermal dissociation. Especially, the chemical effect was serious at the lower velocity gradient of the axial flow. It was certain that the mole fraction profile of $CO_2$ was deflected and CO was increased with the initial concentration of $CO_2$. It was also ascertained that the breakdown of $CO_2$ would cause the increasing of CO mole fraction at the reaction region. It was also found that the addition of $CO_2$ did not alter the basic skeleton of $H_2-O_2$ reaction mechanism, but contributed to the formation and destruction of hydrocarbon products such as HCO. The conversion of CO was also suppressed and $CO_2$ played a role of a dilution in the reaction zone at the higher axial velocity gradient.

• Mass Spectrometry Letters
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• v.1 no.1
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• pp.17-20
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• 2010

As background significantly affects measurement accuracy and a detection limit in determination of the trace amounts of uranium, it is necessary to minimize the impurities in the filaments used for thermal ionization mass spectrometry (TIMS). We have varied the degassing condition such as the heating currents and duration times to reduce the backgrounds from the filaments prepared with zone-refined rhenium tape. The most efficient degassing condition of the heating current and the duration time was determined as 3.5 A and 60 min, respectively. The TIMS measurement combined with the isotope dilution mass spectrometry (IDMS) technique showed that the uranium backgrounds were determined to be in a few fg level from blank rhenium filaments. The background minimized filaments were utilized to measure the uranium isotope ratios of a U030 (NIST) standard sample. The excellent agreement of the measurement with the certified isotope ratios showed that the degassing procedure optimized in this study efficiently reduced the impurity signals of uranium from blank rhenium filaments to a negligible level.

• Journal of Soil and Groundwater Environment
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• v.18 no.6
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• pp.18-31
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• 2013

This study was performed to examine use of the pump-and-treat method for remediation of TCE, CF and CT in groundwater contaminated by DNAPL. The Woosan industrial complex is located in Wonju, about 120 km east of Seoul, Korea. Two pumping wells (KDPW7 and KDPW8) and five monitoring wells (KDMW7, KDMW8, KDMW9, KDMW10, and SKW2) were installed for the test. An asphalt laboratory is a main source of the extensive subsurface contamination at this site. To evaluate change in the concentrations of TCE, CF, and CT in groundwater in the study area, three rounds of pump-and-treat pilot tests were performed (6 July to 6 August, 22 August to 6 September, and 19 September to 2 December in 2011). The groundwater levels and the concentrations of TCE, CF, and CT exhibited negative correlations in the wet season but positive correlations in the dry season, which suggests that the TCE concentrations were mainly controlled by dilution through rainfall during the wet season and by residual TCE, CF, and CT in the unsaturated zone during the dry season. These possibilities should be considered in the full-scale remediation plan.

• Food Science and Biotechnology
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• v.17 no.4
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• pp.850-856
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• 2008

White, red, and extruded ginsengs were studied against 8 strains of food-borne pathogens and/or food spoilage microorganisms. The ginseng powders were extracted with different extractants and screened for antimicrobial activity using the disc diffusion and broth dilution techniques. The results showed that the yield of extraction was higher with increase of aqueous solution content and temperature. Preliminary screening revealed that the red ginseng extracts were most active, that has been found to be highly effective against all tested microbe except Listeria monocytogenes. Moreover, Bacillus subtilis has shown highly susceptible, which the diameters of inhibition zone values of 28 extracts were between 7 and 14 mm. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) recorded for the different crude ginseng extracts against microorganism using ranged from 6.25 to 100 mg/mL, indicated that the methanol extract of ginseng were more effective than ethanol and water extracts. The 60% methanol extract of red ginseng had the greatest effects against B. subtilis with MIC and MBC values at 6.25 mg/mL.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.64-72
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• 2011

The spot weldability of dissimilar metal joints between austenitic stainless steels (STS316)/IF steels and ferritic stainless steels (STS430)/IF steels was investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint's weldability, including its welding nugget shape, tensile-shear strength, hardness, and microstructure. The comparison of these results was described in terms of fracture behavior. Compared with the weld lobe of similar metal joints, dissimilar metal joints (STS430/IF) had reduced weld current range. However, the weld lobe of STS316/IF steel joint showed increased weld current range. This is because the dilution of chemical composition in the molten weld pool suppressed the heat input being caused by Joule heat with current flow through the samples. The microstructure of the fusion zone was fully martensite and mixture of ferrite and martensite for austenitic stainless steel/IF steel and ferritic stainless steel/IF steel combination, respectively. The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the austenitic and ferritic stainless steel sheet was larger due to the higher bulk-resistance. The predicted microstructure by using the Schaeffler diagram was well matched with experimental results. After peel test, the fracture was initiated from heat affected zone of ferritic stainless steel sheet side, however the final fracture was propagated into the IF steel sheet side due to its lower strength.

• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.4
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• pp.12-20
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• 2001

The temporal variability in near-field mixing characteristics of discharging plumes in oceanic environment was investigated using the time series data of the buoyant jet parameters. Based on the currents and density profiles observed in Masan outfall site and effluent discharge flowrates for 63days of summer season, the temporal variabilities and those occurrence frequency were obtained by line plume equations. The results show that wide range of variability in Masan outfall's mixing characteristics was found due to the temporal changes of effluent flowrates and ambient oceanic conditions. The near-field dilution was in the range of 30~71 with the averaged dilution of 34, which was a good agreement with field measurements of salinity deficit. The length of mixing zone was in the range of 5.4~36.2 m with the average of 9.5 m, and the plume rise height was in the range of 8.1~10.2 m with the average of 8.9 m. However, only the 30~44% of the whole results are higher than the averages, which indicates the necessity of this frequency analysis with the continuously measured data for designing and managing the ocean outfall system.

• Journal of Navigation and Port Research
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• v.32 no.8
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• pp.637-643
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• 2008

When planning outfall system, the first target cif design is to maximize initial dilution of discharge effluent. To achieve the target effectively, the characteristics of mixing phenomenon between ambient and discharged water should be analyzed. Especially the analysis at the Near-Field-Region(NFR) as initial dilution zone should be preceded. Usually, the initial behavior of effluent through outfall system is rising toward the surface due to mixing with ambient water for heat discharge and sinking toward the bottom due to the difference of density for brine discharge. After mixed with eddies accompanied by the ambient water, the plumes are showing the same density and internal current pattern by advection and diffusion. Until recently, lots of studies are being carried out for the optimum design of outfall system. but it is difficult to find any studies of heat and brine discharge at the same time. Therefore, this study is hoped to provide some basic data for optimum design of outfall system.

• Journal of the Korean Institute of Gas
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• v.25 no.2
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• pp.1-12
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• 2021

MILD(Moderate or Intense Low-oxygen Dilution) combustion has attracted attention as the clean thermal energy technology due to the lower emissions of unburnt carbon and NO_x. MILD combustion aims to enlarge the combustion reaction zone using the spontaneous ignition phenomenon of the reactants. In this study, the ignition delay time of CH₄ according to the initial temperature of reactants and the addition of CO, H₂ was investigated using a numerical approach. Ignition delay time became shorter as the increases of initial temperature and H₂ addition. But, CO addition to the fuel increase the ignition delay time. In case of H₂ addition to the fuel, the ignition delay time decreased because the higher fraction of HO₂ promotes the decomposition of methyl radical(CH₃) and produce OH radical. However, in case of CO addition to the fuel, ignition delay time inceased because a high proportion of HCO consumes H radical. There was no significant effect of HCO on the reduction of ignition delay time. Also, the increase rates of NO emissions by the addition of CO and H₂ were approximately 7% and 1%, respectively. A high proportion of NCO affects the increase in NO production rate.

• Korean Journal of Food Science and Technology
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• v.49 no.2
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• pp.146-150
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• 2017

Staphylococcus aureus is a pathogenic bacterium that causes food poisoning, exhibits a strong capacity to form biofilm, and is highly resistant to antimicrobial agents. The purpose of this study was to investigate the antimicrobial characteristics of corosolic acid against S. aureus. S. aureus showed high susceptibility to corosolic acid in a concentration-dependent manner. The minimum inhibitory concentration and colony-forming ability determined by the broth microdilution method showed that corosolic acid had strong antimicrobial activity against the bacteria. The diameters of the inhibition zone and numbers of colony forming units at each concentration of corosolic acid were also measured. In addition, corosolic acid displayed potent biofilm inhibition activity against S. aureus at concentrations below its minimum inhibitory concentration. These results suggest that corosolic acid can be used to effectively prevent biofilm formation by S. aureus, thereby making S. aureus more susceptible to the action of antimicrobials.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.39-47
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• 2008

Automatic landing performance of UAV can be enhanced by adding Pseudolite(PL) to GPS. However, it is very hard to install and operate PL with confidence because GPS satellites are moving and the landing zone are usually changeable. The coverage and accuracy of combined GPS and PL can be estimated by using simulator and the correct information is very crucial to UAV operation. In this paper, design, implementation and evaluation of GPS/PL simulator for UAV landing are given. A very realistic coverage estimation is obtained using GIS data and ray launching method with considerations of the transmitter power level, altitude of UAV, number and location of PL. The expected accuracy is estimated using DOP and NSP computed using both GPS and PL. The performance of simulator is evaluated by comparing with the results of a real GPS receiver, and the certified simulator shows the required accuracy for UAV landing can be easily met by proper installation of at least 2 PLs.