• Asian Journal of Atmospheric Environment
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• v.6 no.4
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• pp.288-303
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• 2012

In this study, real time measurements of particle number size distribution in urban Gwangju, coastal Taean, and industrial Yeosu in Korea were conducted in 2008 to understand the occurrence of ultrafine particle (UFP) (<100 nm) events, the variation of its concentration among different sampling sites, and UFP formation pathways. Also, to investigate seasonal and long-term variation of the UFP number concentration, data were collected for the period of 5 years (2007, 2008, 2010, 2011, and 2012) in urban Gwangju. Photochemical and combustion events were found to be responsible for the formation of UFP in the urban Gwangju site, whereas only photochemical event led to the formation of UFP in the coastal Taean site. The highest UFP concentration was found in industrial Yeosu (the average UFP number fractions were 79, 59 and 58% in Yeosu, Gwangju, and Taean, respectively), suggesting that high amount of gas pollutants (e.g., $NO_2$, $SO_2$, and volatile organic carbon (VOC)) emitted from industries and their photochemical reaction contributed for the elevated UFP concentration in the industrial Yeosu site. The UFP fraction also showed a seasonal variation with the peak value in spring (61.5, 54.5, 50.5, and 40.7% in spring, fall, summer, and winter, respectively) at urban Gwangju. Annual average UFP number concentrations in urban Gwangju were $5.53{\times}10^3\;cm^{-3}$, $4.68{\times}10^3\;cm^{-3}$, $5.32{\times}10^3\;cm^{-3}$, $3.99{\times}10^3\;cm^{-3}$, and $2.16{\times}10^3\;cm^{-3}$ in the year 2007, 2008, 2010, 2011, and 2012, respectively. Comparison of the annual average UFP number concentration with urban sites in other countries showed that the UFP concentrations of the Korean sites were lower than those in other urban cities, probably due to lower source strength in the current site. TEM/EDS analysis for the size-selected UFPs showed that the UFPs were classified into various types having different chemical species. Carbonaceous particles were observed in both combustion (soot and organics) and photochemical events (sulfate and organics). In the photochemical event, an internal mixture of organic species and ammonium sulfate/bisulfate was identified. Also, internal mixtures of aged Na-rich and organic species, aged Ca-rich particles, and doughnut shaped K-containing particles with elemental composition of a strong C with minor O, S, and K-likely to be originated from biomass burning nearby agricultural area, were observed. In addition, fly ash particles were also observed in the combustion event, not in the photochemical event.

• Analytical Science and Technology
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• v.13 no.5
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• pp.584-591
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• 2000

The separation of Nd from the simulated $U_3Si/Al$ spent fuel solution with sequential two-step anion exchange separation has been studied. To prepare the simulated $U_3Si/Al$ spent nuclear fuel, unirradiated $U_3Si/Al$ whose composition consists of small $U_3Si$ particle dispersed in an Al matrix with Al cladding was dissolved with a mixture of 4 M HCl and 10 M $HNO_3$ and 8 or 15 fission product elements were added to the dissolved solution. The trace amount of silica in the solutions was removed by evaporating to dryness with HF and the U was adsorbed on the first anion exchange resin. Neodymium can be purely isolated from the fission product elements with a methanol-nitric acid eluent using the second anion exchange resin. A large excess of Al didn't influence on the elution velocity of Nd, but reduced the eluted contents of Nd, Al, Eu, Gd, Sm and Sr, A large amount of Al was removed first from the column with 3 mL of loading solution (0.8 M $HNO_3$/99.8% MeOH) before Nd elution by the eluent [0.04 M $HNO_3$-99.8% MeOH(1:9)]. The recovery of Nd was more than 94%, regardless of Al contents. Taking the 9 to 13 mL fraction of eluate was effective to purely isolate Nd.

• Journal of the Korean Geotechnical Society
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• v.27 no.12
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• pp.17-25
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• 2011

A fabric of soil media may change due to certain factors such as dissolution of soluble particles, desiccation, and cementation. The fabric changes affect the mechanical behavior of soils. The purpose of this study is to investigate the effects of geo-material dissolution on shear strength. Experiments and numerical simulations are carried out by using a conventional direct shear and the discrete element method. The dissolution specimens are prepared with different volumetric salt fraction in sand soils. The dissolution of the specimens is implemented by saturating the salt-sand mixtures at different confining stresses in the experimental study or reducing the sizes of soluble particles in the numerical simulations. Experimental results show that the angle of shearing resistance decreases with the increase in the soluble particle content and the shearing behavior changes from dilative to contractive behavior. The numerical simulations exhibit that macro-behavior matches well with the experimental results. From the microscopic point of view, the particle dissolution produces a new fabric with the increase of local void, the reduction of contact number, the increase of shear contact forces, and the anisotropy of contact force chains compared with the initial fabric. The shearing behavior of the mixture after the particle dissolution is attributed to the above micro-behavior changes. This study demonstrates that the reduction of shearing resistance of geo-material dissolution should be considered during the design and construction of the foundation and earth-structures.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.40 no.5
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• pp.600-607
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• 1995

Orostachys japonicus, called Wasong and used as anti-tumor medicinal plant, was cultivated in plastic house. The experiment was done to clarify the effect of long-day and night-break treatment at the timing of bolting on its morphological characters, organ dry weight and flowering of florets. After grown in 15cm plastic boxes containing 2:1 soil:peat moss mixture for about 4 months, long-day of 16 hours and night-break of 2 hours around midnight were treated from Sept. 9. The plants were sampled 5 times at 2-week interval after the treatments. Long-day and night-break treatment delayed the growth of inflorescence and showed greater stem diameter on the last sampling and no. of leaves and bracts than the natural daylength. The treatments also had greater leaf and bract dry weight since 2 weeks, and the other fraction and total dry weights since 4 weeks but less floret dry weight from 4 to 6 weeks after the treatments than the natural daylength. The treatments, however, decreased no. of flowered florets and ratio of flowering plants although all the treatments showed nearly the same no. of total florets per plant until 6 weeks after the treatments, late October, which resulted in the modification of source to sink or vice versa. In the natural daylength, the florets were functioned as sink, while root, leaf and bract as source, but in the long-day and night-break treatments stem and florets were done as sink.

• Journal of the Korean Society of Combustion
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• v.20 no.4
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• pp.34-41
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• 2015

Oxy-methane nonpremixed flames diluted with $CO_2$ were investigated to clarify impact of radiation heat loss and chemical effects of additional $CO_2$ to oxidizer stream on flame extinction. Flame stability maps were presented with functional dependencies of critical diluents mole fraction upon global strain rate at several oxidizer stream temperatures in $CH_4-O_2/N_2$, $CH_4-O_2/CO_2$, and $CH_4-O_2/CO_2/N_2$ counterflow flames. The effects of radiation heat loss on the critical diluent mole fractions for flame extinction are not significant even at low strain rate in nonpremixed $CH_4-O_2/N_2$ diffusion flame, whereas those are significant at low strain rate and are negligible at high strain rate (> $200s^{-1}$) in $CH_4-O_2/CO_2$ and $CH_4-O_2/CO_2/N_2$ counterflow flames. Chemical effects of additional $CO_2$ to oxidizer stream on the flame extinction curves were appreciable in both $CH_4-O_2/CO_2$ and $CH_4-O_2/CO_2/N_2$ flames. A scaling analysis based on asymptotic solution of stretched flame extinction was applied. A specific radical index, which could reflect the OH population in main reaction zone via controlling the mixture composition in the oxidizer stream, was identified to quantify the chemical kinetic contribution to flame extinction. A good correlation of predicted extinction limits to those calculated numerically were obtained via the ratio between radical indices and oxidizer Lewis numbers for the target and baseline flames. This offered an effective approach to estimate extinction strain rate of nonpremixed oxy-methane flames permitting air infiltration when the baseline flame was taken to nonpremixed $CH_4-O_2/N_2$ flame.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.5
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• pp.511-521
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• 2006

Homologue and isomer patterns of polychlorinated dibenzo-p-dioxins(PCDDs) and polychlorinated dibenzofurans(PCDFs) congeners formed from phenols in the gas-phase at $600{\sim}700^{\circ}C$ and via particle-mediated reactions at $400^{\circ}C$ were studied in an isothermal flow reactor. A mixture of 20 phenols in relative concentrations found in a municipal waste incinerator(MWI) stack gas was used for this study. PCDDs and PCDFs homologue and isomer patterns obtained from the phenol. From the phenol experiments, gas-phase formation at $600{\sim}700^{\circ}C$ favors PCDFs formation whereas particle-mediated formation at $400^{\circ}C$ favors PCDDs formation. DD and DF were most abundant homologue groups, PCDDs and PCDFs homologue fraction decreased with increasing number of chlorine substituents. PCDDs and PCDFs homologue and isomer fractions were almost constant from gas-phase formation and particle-mediated formation. Unsubstituted phenol, which was present in high concentration, played a significant role in the formation of PCDD/Fs congeners under both sets of experimental conditions.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.10
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• pp.933-940
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• 2009

To evaluate characteristics in spray flame, laminar counterflow is investigated on the effects of equivalence ratio and fuel by a two-dimensional DNS (direct numerical simulation). For the gaseous phase, Eulerian mass, momentum, energy, and species conservation equations are solved. For the disperse phase, all individual droplets are calculated by the Lagrangian method without the parcel model. n-Decane ($C_{10}H_{22}$) and n-heptane ($C_7H_{16}$) is used as a liquid spray fuel, and a one-step global reaction is employed for the combustion reaction model. As equivalence ratio increases, the fuel ignites early and the high temperature region spreads wider. The peak value of temperature, however, tends to once increase and then decreases with increasing equivalence ratio. The decrease in the peak value of temperature for the higher equivalence ratio condition is caused by the cooling effect associated with droplet group combustion. Since the evaporation of n-heptane is early, the high temperature region spreads wider than ndecane, but the peak values of temperature for both n-heptane and n-decane is almost same.

• Korean Journal of Food Science and Technology
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• v.30 no.3
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• pp.697-701
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• 1998

Two major flavonoid compounds having inhibition activity of xanthine oxidase from onion skin were separated, isolated and identified by ODS chromatography, Sephadex LH-20 chromatography, UV/visible absorption spectroscopy and FAB Mass. Spectral analyses indicated that $F_1$ was a flavonol having 3,5,7,3'-OH and 4'-glucoside (quercetin 4'-glucoside), and $F_2$ was a flavonol having 3(5),7,3',4'-OH (quercetin). FAB-Mass of fraction $F_1\;and\;F_2$ in positive-ion-mode produced a spectra containing main ions at m/z 465, corresponding to the $(M＋H)^+$ ion of quercetin 4'-glucoside, and m/z 303, corresponding to the $(M＋H)^+$ ion of quercetin. The inhibition mechanisms of $F_1\;and\;F_2$ were a mixture of the uncompetative and non-competative modes, with respect to xanthine as a substrate.

• Journal of the Korean Society of Food Science and Nutrition
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• v.13 no.2
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• pp.175-180
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• 1984

Lipids in oyster mushroom (Pleurotus florida) were extracted by the mixture of chloroform-methanol (2: 1, v/v) and fractionated into neutral lipids, glycolipids and phospholipids by silicic acid column chromatography. Components and fatty acid composition of each fraction were deter- mined by thin-layer and gas-liquid chromatographies. Fresh oyster mushroom contained 0.5% total lipid in which the contents if neutral lipids, glycolipids and phospholipids were 33.8%, 19.7% and 45. 6%, respectively, Triglycerides(38.2%), free fatty acids (20%) and free sterol (10%) were the major components among the neutral lipids. Diglycerides, monoglycerides, sterol esters and three unidentified neutral lipids were the minor components. Major components of glycolipids were steryl glycosides(35.9%) and esterified steryl glycosides (23.7%). Digalactosyl diglycerides, mono-galactosyl diglycerides and two unknown components were also present. Of the phospholipids, phosphatidyl cholines and serines (48.2%), and phosphatidyl ethanolamines(44.4%) were the major components. On the other hand, the major fatty acids of neutral lipids we.e linoleic, palmitoleic, oleic and palmitic acid. Linoleic and palmitic acid were the predominant fatty acids of both glycolipids and phospholipids.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.8
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• pp.17-27
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• 2000

This paper presents deposition and characterization of hydrogenated microcrystalline silicon (${\mu}c$ -Si:H) films on low cost glass substrate by Hot Wire CVD(HWCVD). The HWCVD ${\mu}c$ -Si:H films had deposition rates ranging from 2${\AA}$/sec to 35${\AA}$/sec with the variations of preparation conditions, which was 10 times higher than that of the films obtained from the conventional PECVD method. From the Raman spectroscopy, the prepared silicon films were found to be composed of the mixture of crystalline and amorphous phases. The crystalline volume fraction and average crystallite size, obtained from the Raman To mode peak near 520cm$^{-1}$, were 37-63% and 6-10 nm, respectively. The conductivity activation energy($E_a$) of the ${\mu}c$ -Si:H films, representing the difference of conduction band and Fermi level in an intrinsic semiconductors, increased from 0.22eV to 0.68eV with increasing pressure from 30mTorr to 300mTorr. The increase of $E_a$ with pressure indicates that the deposited films have properties close to intrinsic semiconductors, which is also proved with low dark conductivity of the ${\mu}c$ -Si:H deposited at 300mTorr. The tungsten concentration incorporated into films was about $6{\times}10^{16}atoms/cm^3$ in the samples prepared at wire temperature of 1800$^{\circ}C$.