• Atmosphere
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• v.22 no.3
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• pp.321-330
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• 2012

Generation mechanisms of the three moderate-or-greater (MOG)-level clear-air turbulence (CAT) encounters over South Korea are investigated using the Weather Research and Forecasting (WRF) model. The cases are selected among the MOG-level CAT events occurred in Korea during 2002-2008 that are categorized into three different generation mechanisms (upper-level front and jet stream, anticyclonic flow, and mountain waves) in the previous study by Min et al. For the case at 0127 UTC 18 Jun 2003, strong vertical wind shear (0.025 $s^{-1}$) generates shearing instabilities below the enhanced upper-level jet core of the maximum wind speed exceeding 50 m $s^{-1}$, and it induces turbulence near the observed CAT event over mid Korea. For the case at 2330 UTC 22 Nov 2006, areas of the inertia instability represented by the negative absolute vorticity are formed in the anticyclonically sheared side of the jet stream, and turbulence is activated near the observed CAT event over southwest of Korea. For the case at 0450 UTC 16 Feb 2003, vertically propagating mountain waves locally trigger shearing instability (Ri < 0.25) near the area where the background Richardson number is sufficiently small (0.25 < Ri < 1), and it induces turbulence near the observed CAT over the Eastern mountainous region of South Korea.

• KCID journal
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• v.11 no.2
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• pp.72-81
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• 2004

In this study, the runoff characteristic of nutrients in the small sized stream was investigated with seasonal change. The area considered was greenhouse site situated near Nam river, Jinju, Korea. In this site, groundwater was used for the irrigation and

• ALGAE
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• v.23 no.4
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• pp.257-268
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• 2008

Species composition, standing crop and dominant species of phytoplankton were investigated at 6 sites of Galgok stream and Incheon river which run into Gomso Bay, Jeollanam-do in April, August and November 2007. Total of 210 taxa were found which were classified as 6 classes, 12 orders, 25 families, 66 genera, 177 species, 27 varieties, 5 forms and 1 unidentified species. These river and stream had lower concentration of T-N and T-P compared to that of others; however, the site 2 of Galgok stream in summer was hypertrophic in T-P and also near hypertrophic in TN, and the site 1 in Incheon river during fall appeared to be hypertrophic in T-N, and the site 3 in summer showed near hypertrophic level in T-P. Determining the trophic status of the water quality based on chlorophyll a (chl-a), the site 3 of Galgok stream in spring and the site 3 of Incheon river in fall were oligotrophic; moreover, 6 sites including the site 2 and 3 of Galgok stream in summer were mesotrophic, and 9 sites including all sites of Galgok stream in fall turned out to be eutrophic. Particularly, the site 1 of Galgok stream in summer was hypertrophic, having 58.19 mg chl-a m$^{-3}$. There was a conspicuous difference between two values of standing crops based on chl-a and cell counting. This discrepancy may have occurred because of abundant cyanophytes and exclusion of picoplankton cells in cell counting. In the study, 5 cyanophytes, Synechocystis aquatilis, Microcystis aeruginosa, M. flos-aquae, Oscillatoria angustissima, O. limnetica and 2 diatoms, Thalassiosira bramaputrae and Navicula viridula var. rostellata were abundant. Based on the T-N, T-P values, standing crops and cell counting in Galgok stream and Incheon river were between mesotrophic and eutrophic conditions.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1192-1192
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• 2001

Usually there are many furnaces in a ethylene plant and the performance of total furnaces can be improved if that of each furnace is monitored and controlled. For this purpose real-time data for the effluent of each furnace is necessary. However, it is very difficult to analyze the total effluent stream of a ethylene furnace by real-time because it is composed of so many components including heavy hydrocarbons. Fortunately, component data for lighter hydrocarbons is much more important than that of heavier ones for ethylene furnace. In ordinary case, the on-line measurement of light hydrocarbons is performed by on-stream gas chromatography, after separating gas-phase part from effluent. The main and important components of gas-phase are Methane, Ethane, Ethylene, and Propylene. If we can use Near-infrared spectroscopy for measuring those components within good reproducibility, shorter analysis time, better repeatability, easier maintenance and lower cost will make Near-infrared (NIR) analyzer replace on-stream gas chromatography in this process. Although it is known to be very difficult to measure gas components because of very weak absorption in Near-infrared region, we have studied the feasibility of the application of NIR for the measurement of gas-phase hydrocarbon in the effluent of ethylene furnace. The samples were obtained from actual process and NIR spectra were collected over 1100 to 2500nm range. NIR spectra and calibrations showed and demonstrated the possibility of extending NIR spectroscopy to the measurement of gas-phase hydrocarbon in the effluent of ethylene furnace.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.44.2-45
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• 2021

As implied by the zodiacal light and spacecraft impact measurements, the space between large bodies in our Solar System is filled with interplanetary dust particles (IDPs). IDPs give us deeper insight into the composition and evolution of the Solar System, as well as being a crucial reference for extrasolar research. IDPs can be interpreted as bearers of carbon and organic materials, and thus, their interaction with Earth can be considered as important factors for the birth of terrestrial life. One of the key routes of IDPs entering Earth is via meteoroid streams (Love and Brownlee 1993). The Geminid meteoroid stream is a notable example. Together with its source asteroid (3200) Phaethon, the Phaethon-Geminid stream complex (PGC) (Whipple 1983; Gustafson 1989) can potentially provide information on the properties and evolution of IDPs in near-Earth space. DESTINY+* is a JAXA/ISAS spacecraft planned to launch in 2024 to explore the physical and chemical features of near-Earth IDPs and uncover the dust ejection mechanism of active near-Earth asteroids, especially Phaethon (Arai et al. 2018). Previous studies on the dust ejection mechanism of Phaethon have various degrees of success in explaining the ejection of submillimeter particles and try to recreate the dust replenishment rate of the Geminid stream. However, none of them are satisfactory for explaining the observed Geminid stream, especially for larger particles of a millimeter and centimeter scales. Inspired by the discovery of rotational mass shedding in the Main Belt region (Jewitt et al., 2014), we investigate a dust ejection scenario by rotational instability on Phaethon. Using the N-body integrator MERCURY6 (Chambers 1999; modified by Jeong 2014), we performed a long-term integration of dust particles of various sizes ejected at ~1 m/s. Through this process, we discuss the implications Phaethon's rotation may have on its ejection, the formation and evolution of IDP by this mechanism, and contribute to the DESTINY+ mission.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.628-636
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• 1997

Flow visualization technique incorporating photochromic dye is used to study the flow characteristics of the gravity driven laminar wavy film. The film thickness and wave speed are successfully measured by flow visualization. As the inclination angle increases, the waves have higher peaks and lower substrate thickness. The measured cross stream velocity at the free surface is up to 10% of stream wise velocity, which shows enhanced mixing in the lump of the film. The measured stream wise velocity profiles are close to parabolic profile near the substrate and the peak but show significant velocity defect near the rear side of the wave. The measured wall shear rate distributions show good agreement with the previous workers' numerical results.

• Journal of Mechanical Science and Technology
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• v.19 no.6
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• pp.1347-1357
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• 2005

Effects of combustor-level high free-stream turbulence on the blade-surface heat/mass transfer have been investigated in the three-dimensional flow region near the endwall within a high-turning turbine rotor cascade passage. Free-stream turbulence intensity and integral length scale in the high turbulence case are 14.7 percents and 80 mm, respectively. The result shows that there is no considerable discrepancy in the blade heat/mass transfer near the endwall between the low and high turbulence cases. As departing from the endwall, however, the deviation between the two cases becomes larger, particularly in the region where flow separation and re-attachment occur. Under the high turbulence, flow disturbances such as boundary-layer separation and re-attachment seem to be suppressed, which makes the blade heat/mass transfer more uniform. Moreover, there are some evidences that endwall vortices tend to be weakened under the high turbulence.

• Journal of the Korean Society of Combustion
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• v.17 no.4
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• pp.60-65
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• 2012

The MILD combustion and pollutant emission characteristics were investigated computationally. The temperature of supplying air-stream and mixing rate (${\Omega}$) of exhaust gas in the air-stream were adjusted to investigate the effects of those parameters on the MILD combustion in jet flow field. The emission indices for NO (EINO) and CO (EICO) were introduced to quantify the amount of those species emitted from the combustion. The high-temperature region disappeared gradually as the mixing rate increased for fixed air-stream temperature. The EINO increased as the air-stream temperature became higher for fixed mixing rate, and the EINO decreased dramatically with increasing the mixing rate for each air-stream temperature condition. The EICO also decreased with increasing the mixing rate and it was nearly independent of air-stream temperature except for near ${\Omega}$ = 0.7. It was found that the CO supplied in the air-stream can be destroyed in the MILD combustion over the certain mixing rate.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.35-41
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• 2012

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to complement the previous experimental results of the bluff body stabilized flames [1]. For both fuel ejection configurations against an oxidizer stream, the flame stability was affected mainly by vortex structure and mixing field near bluff body. FDS(Fire Dynamic Simulator) based on the LES(Large Eddy Simulation) was employed to clarify the isothermal mixing characteristic and wake flow pattern around bluff body. The air used atmosphere and the fuel used methane. The result of counter flow configuration shows that the flow field depends on air velocity but the mixing field is influenced on the fuel velocity. At low fuel velocity the fuel mole fraction is below the flammable limit and hence the mixing is insufficient to react. Therefore, as the result, the flame formed at low fuel velocity is characterized by non-premixed flames. For the flow field of co-flow configuration, flame stability was affected by fuel velocity as well as air velocity. the vortex generated by fuel stream has counter rotating direction against the air stream. Therefore, the momentum ratio between air and fuel stream was important to decide the flame blow out limit, which is result in the characteristic of the partially premixed reacting wake near extinction.

• Journal of Environmental Science International
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• v.11 no.9
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• pp.881-895
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• 2002

Sediments and river waters form the channel of Hwasun-cheon were studied in sedimentological size and geochemical analyses of metallic elements for the purposes of identification of depositional environments and geochemical characteristics. The sizes of sediments are assigned to pebble to coarse sand in mean size and polymodal in distribution. And the sediments are poorly to very poorly sorted and positively skewed. According to the grain size distributions of the sediments, the Hwasun-cheon belongs to gravel-bed river on the basis of the grain size distribution of the sediments. The behaviors of metallic elements in the sediments mainly depend on not grain size distribution but the geology connected with geomorphological reliefs near the stream. Contamination indices(CI) of Zn, Cu and Pb are 2.83 to 6.96 with average 4.31 in the sediments. Hwasun-cheon is assigned to general stream type in accordance with water quality of physical factors and chemical characteristics by Piper's diagram. Though meaningful values of BOD, T-N, T-P were locally depicted near Masan-ri, Hwasun-eup and Jiseok-cheon areas, artificial metal concentration do not represent in the most area of the stream. Sediments and river water are considered that the relatively more or less high metallic contents in the stream are originated from coal mine and urban area.