• Journal of Powder Materials
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• v.2 no.1
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• pp.29-35
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• 1995

In this study the calcined condition and characteristic of Cu-Ni-Zn ferrite powder were investigated. The Cu-Ni-Zn ferrite powder has been synthesized by the thermal decomposition of the organic acid salt. This process did not require a strict pH control and provided the uniform composition and fine powder with about 0.3 $\mu\textrm{m}$. The XRD diffraction pattern of this powder showed about 50% spinel phase. The optimum calcination was found to be done at $700^{\circ}C$ for one hour. After the calcination, the amount of spinel increased to 90%. The distribution of the particle size showed bimodal peaks, one was about 0.5 $\mu\textrm{m}$ and the other was about 20 $\mu\textrm{m}$. The large particles of 20 $\mu\textrm{m}$ were the agglomeration of fine Particles. The mean Particle size of the powder was about 0.4 $\mu\textrm{m}$. The powder was compacted under 100 MPa pressure and sintered at 1100~ $1250^{\circ}C$ for one hour in air. The density of ferrites specimen was a function of the sintering temperature. The higher the temperature, the denser the ferrite. The maximum relative density of the sintered ferrite was about 93% at $1250^{\circ}C$. The grain size of sintered specimen at $1200^{\circ}C$ was 5 $\mu\textrm{m}$ and homogeneous.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.189-212
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• 2003

I review the current status of understanding when, how long, and how giant elliptical galaxies formed, focusing on the globular clusters. Several observational evidences show that massive elliptical galaxies formed at z > 2 (> 10 Gyr ago). Giant elliptical galaxies show mostly a bimodal color distribution of globular clusters, indicating a factor of $\approx$ 20 metallicity difference between the two peaks. The red globular clusters (RGCs) are closely related with the stellar halo in color and spatial distribution, while the blue globular clusters (BGCs) are not. The ratio of the number of the RGCs and that of the BGCs varies depending on galaxies. It is concluded that the BGCs might have formed 12-13 Gyr ago, while the RGCs and giant elliptical galaxies might have formed similarly 10-11 Gyr ago. It remains now to explain the existence of a gap between the RGC formation epoch and the BGC formation epoch, and the rapid metallicity increase during the gap (${\Delta}t{\approx}$ 2 Gyr). If hierarchical merging can form a significant number of giant elliptical galaxies > 10 Gyr ago, several observational constraints from stars and globular clusters in elliptical galaxies can be explained.

• Polymer(Korea)
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• v.36 no.6
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• pp.693-698
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• 2012

In this study aluminum isopropyl oxide ($Al(O-i-Pr)_3$) was supported on the amine-functionalized surface of silica to synthesize high molecular weight (MW) polylactide (PLA), and it was tested for PLA polymerization behaviors. A silica was funtionalized with silane compound having amine groups, then in-situ treated with $Al(O-i-Pr)_3$. $Al(O-i-Pr)_3$ attached to amine group on silica showed activity only in the presence of MAO (methyl aluminoxane). At the polymerization temperature of $115^{\circ}C$, the conversion and the MW of PLA were increased as the amount of silane was increased. At the polymerization temperature of $130^{\circ}C$, the conversion was decreased while the MW was increased drastically and reached to MW 44000 g/mol when the amine concentration was 3.0 mmol/g. A bimodal type GPC curve was shown at the polymerization temperature of $115^{\circ}C$. As the amount of amine group increased, the peaks of GPC curve were merged. At the polymerization of $130^{\circ}C$, a unimodal GPC curve was shown. $Al(O-i-Pr)_3$ supported on amine-functionalized silica was able to produce higher MW PLA with enhanced activity compared to homogeneous $Al(O-i-Pr)_3$.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.6
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• pp.675-688
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• 2007

To characterize organic and elemental carbon (OC and EC), and water-soluble organic carbon (WSOC) contents, daily $PM_{2.5}$ measurements were performed in August 2006 (summer) and Jan $11{\sim}Feb$ 12 2007 (winter) at an urban site of Gwangju. Daily size-segregated aerosol samples were also collected for WSOC analysis. No clear seasonal variations in EC and WSOC concentrations were observed, while seasonal differences in OC concentration, and OC/EC and WSOC/EC ratios were shown. The WSOC/OC ratio showed higher value in summer (0.56) than in winter (0.40), reflecting the greater enhancement of secondary WSOC formation at the site in summer. Secondary WSOC concentrations estimated using EC tracer method were in the range $0.0{\sim}2.1\;{\mu}g/m^3$ (average $0.42\;{\mu}g/m^3$) and $0.0{\sim}1.1\;{\mu}g/m^3\;(0.24\;{\mu}g/m^3)$, respectively, accounting for $0{\sim}51.6%$ (average 16.8%) and $0{\sim}52.5%$ (average 13.1 %) of the measured WSOC concentrations in summer and winter. Sometimes higher WSOC/OC ratio in winter than that in summer could be attributed to two reasons. One is that the stable atmospheric condition often appears in winter, and the prolonged residence time would strengthen atmospheric oxidation of volatile organic compounds. The other is that decrease of ambient temperature in winter would enhance the condensation of volatile secondary WSOC on pre-existing aerosols. In summertime, atmospheric aerosols and WSOC concentrations showed bimodal size distributions, peaking at the size ranges $0.32{\sim}0.56\;{\mu}m$ (condensation mode) and $3.2{\sim}5.6\;{\mu}m$ (coarse mode), respectively. During the wintertime, atmospheric aerosols showed a bimodal character, while WSOC concentrations showed a unimodal pattern. Size distributions of atmospheric aerosols and WSOC with a peak in the size range $0.32{\sim}0.56\;{\mu}m$ were observed for most of the measurement periods. On January 17, however, atmospheric aerosols and WOSC exhibited size distributions with modal peaks in the size range $1.0{\sim}1.8\;{\mu}m$, suggesting that the aerosol particles collected on that day could be expected to be more aged, i.e, longer residence time, than the aerosols at other sampling periods.

• Korean Journal of Food Science and Technology
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• v.19 no.4
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• pp.371-376
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• 1987

The structral properties of rice starch and its components were investigated. The intrinsic viscosities of rice starch, amylose and amylopectin solutions were 1.053, 1.772 and 1.596 ml/g, respectively. ${\beta}-amlolysis$ limits of rice starch was 73% and those of amylose and amylopectin were 106 and 56%, respectively. The outer chain length $({\overline{OCL}})$ and inner chain length $({\overline{ICL}})$ of amylopectin were 1.56 and 7.7, respectivety. Debranching of rice starch with pullulanase yield two peaks on Sephadex G-75. The peak I at void volume was principally amylose components and peak II at ${\overline{dp}}$ 25-10, constituted of branched amylopectin. However, the elution profile of debranched amylopectin by pullulanase revealed a bimodal peak distribution at ${\overline{dp}}$ 35-25 hydrolyers and ${\overline{dp}}$ 25-10, and no distinct peak at void volume. The elution profile of the debranched, ${\beta}-amylase$ hydrolyrates of starch and amylopectin yielded major peak at ${\overline{dp}}$ 2-10.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.525-535
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• 2023

In thi study, we unveil the intricate interplay among picophytoplankton (0.2-2 ㎛) communities, warming surface water temperatures, and major inorganic nutrients within the southwestern East Sea from 2003-2022. The observed surface temperature rise, reflecting global climate trends, defies conventional seasonal patterns in temperate seas, with highest temperatures in summer and lowest in spring. Concurrently, concentrations of major dissolved inorganic nutrient display distinct seasonality, with peaks in winter and gradually declining thereafter during spring. The time course of chlorophyll-a concentrations, a proxy for phytoplankton biomass, reveals a typical bimodal pattern for temperate seas. Notably, contributions from picophytoplankton exhibited a steady annual increase of approximately 0.5% over the study period, although the total chlorophyll-a concentrations declined slightly. The strong correlations between picophytoplankton contributions and inorganic nutrient concentrations is noteworthy, highlighting their competitively advantageous responsiveness to the shifting nutrient regime. These findings reflect significant ecological implications for the scientific insights into the marine ecosystem responses to changing climate conditions.

• Journal of Korean Society for Atmospheric Environment
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• v.25 no.6
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• pp.550-561
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• 2009

This study is to investigate the air pollution characteristics of an industrialized midsize west-coastal city by comparing air quality to a neighboring inland city. The hourly averaged data of $O_3$, $SO_2$, $NO_2$, CO, and $PM_{10}$ measured from continuous air quality monitoring sites in Gunsan (coastal) and Jeonju (inland) were analyzed. The data set covers the period from 2004 to 2006. The annual average concentrations of the air pollutants in two cities were compared in their abundances and temporal trends as well. $O_3$ and $SO_2$ in Gunsan were relatively higher than those in Jeonju, while vice versa in case of $NO_2$ and $PM_{10}$. It seems that heavy automobile emissions from Jeonju mainly bring on higher $NO_2$ and $PM_{10}$ than those in Gunsan on annual base. $NO_2$ concentrations in both cities showed bimodal diurnal variations with peaks in the morning and in the late evening. These peaks correspond to the coupled effects of rush hour traffic and meteorological conditions (i.e., variation of mixing height and dispersion conditions). Maximum hourly averages of $NO_2$ ranged from 18 ppb to 28 ppb at Jeonju, and from 12 ppb to 20 ppb at Gunsan. $O_3$ showed typical diurnal variation with a maximum in the afternoon between 14:00 and 16:00 LST. Diurnal variations of CO and $PM_{10}$ were similar to $NO_2$ while $SO_2$ was similar to $O_3$. Seasonal variations of $PM_{10}$ in both cities indicated that their concentrations during spring season were significantly high. Asian dust storms occur frequently during spring and seem to affect increase in $PM_{10}$. High $O_3$ and $PM_{10}$ days were selected from both cities. The analyses based on the HYSPLIT trajectory model during the high $O_3$ and $PM_{10}$ showed these episodes (six cases) were mostly coincident with Asian dust storm originated from northern China and Mongolia. However, these high air pollution episodes in the west coastal cities may not only be caused by the Asian dust but also affected by other air pollutants transported from China accompanying the Asian dust.

• Journal of the Korean Geographical Society
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• v.49 no.5
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• pp.779-793
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• 2014

This study was aimed at examining the recent and the future changes of tourism climatic conditions for Chiaksan national park using TCI(Tourism Climate Index). The distribution type of daily mean of TCI showed the bimodal-shoulder peaks for all periods of the past and the future. Therefore, Chiaksan national park showed affordable climate of touring in spring and autumn due to temperature and relative humidity constituting Cid and Cia. Summer tourism climatic conditions of Chiaksan national park has become worse recently. In the future, these trends are projected more stronger. Also, the lowest TCI in the year is projected to shift from winter to summer due to a decrease of Cid.

• Journal of Environmental Science International
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• v.13 no.4
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• pp.377-387
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• 2004

This study has been performed to clarify the characteristics of temporal and spatial distribution of surface ozone concentration over Jeju Island, one of the cleanest areas in Korea with low emissions of air pollutants. Ozone data are monitored at four sites in Jeju Island. These monitoring sites are located at two urban area(referred to Ido and Donghong), coastal area(Gosan site) and forest site(Chuna site). Ozone data has been routinely collected at these sites for the late four years. The patterns of seasonal cycle of ozone concentrations at all stations show the bimodal with the peaks on spring and autumn and a significant summer minimum. However, the patterns of diurnal variations at rural station, i.e., Gosan and Chuna sites are considerably different to those at urban stations such as Ido and Donghong sites. The patterns of $\DeltaO_3$ variations are very similar with those of monthly mean ozone concentrations and $\DeltaO_3$ values are exceeded 30 ppb, at urban stations. This may be that urban stations are more influenced by local photochemical reactions rather than rural stations. In order to assess the potential roles of meteorological parameters on ozone formation, the meteorological parameters, such as radiation, temperature, and wind are monitored together with ozone concentrations at all stations. The relationships of meteorological parameters to the corresponding ozone concentration are found to be insignificant in Jeju Island. However, at Gosan and Donghong stations, when the sea breeze blew toward the station, the ozone concentration is considerably increased.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.E1
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• pp.35-43
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• 2006

Ambient particle size distributions of PCBs and their dry deposition fluxes were measured at a site in Seoul to quantify dry deposition fluxes of PCBs and size characteristics of PCBs in the air, and to estimate ambient concentrations of gaseous PCBs and dry deposition fluxes. The dry deposition plate was used to measure dry deposition fluxes of particulate mass and PCBs and a cascade impactor and rotary impactor were used to measure ambient particle size distributions for small ($D_p<9{\mu}m$) and large ($D_p>9{\mu}m$) particles, respectively. Six sample sets were collected from April to July 1999. The fluxes of particulate total PCBs (the sum of 43 congeners) ranged from 160 to $607ng\;m^{-2}day^{-1}$. The size distribution of total PCBs was bimodal with two peaks in small particle size ($D_p{\sim}0.6\;and\;6{\mu}m$, respectively) and, thus, mass concentration being dominant in small particles. The mean particulate PCBs concentration was $6.9{\mu}g$ PCBs/g. The concentrations of PCB homologues in the gas phase were estimated based on the particle/gas partition coefficient ($K_p$) with the measured values of particulate PCBs in this study and they were comparable to those observed in other previous studies. Dry deposition fluxes were estimated by calculating dry deposition velocities.