• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.50.2-50.2
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• 2021

There is increasing evidence that the convective mixing length (α) in stellar evolution models depends on metallicity of stars. In order to confirm a more precise metallicity-dependent mixing length trend, we investigate the effective temperature and metallicity of 14 red supergiant stars (RSGs) in the irregular dwarf galaxy IC 1613 using the near-infrared spectra observed with the MMIRS on the MMT telescope. From the synthetic spectral fitting to the observed spectra, we find that the mean metallicity is about [Fe/H]=0.69 with a weak bimodal distribution. We also find that the effective temperature of RSGs in IC 1613 is higher by about 250 K than that of the SMC on average. We compare the RSG position with stellar evolutionary tracks on the HR diagram, finding that models with α = 2.2-2.4 H_p can best reproduce the effective temperatures of the RSGs in IC 1613. It is evident that the mixing length values for IC 1613 is lower than that of the Milky Way. This result supports our previous study on a metallicity-dependent mixing length: mixing length decreases with decreasing metallicity of host galaxies. However, this dependency becomes relatively weak for RSGs having a metallicity equal to or less than the SMC metallicity.

• Journal of Environmental Science International
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• v.33 no.2
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• pp.113-119
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• 2024

In this study, the most suitable sampling methods for the bimodal mass distribution characteristics and individual particle analysis of atmospheric aerosols were investigated. Samples collected in Quartz, Teflon, and Nuclepore filters were analyzed for individual particles using scanning electron microscopy with an energy-dispersive X-ray spectrometer (SEM/EDS). Then, the pore diameter of the filter and the collection flow rate were determined using the theoretical collection efficiency calculation formula for two-stage separation sample collection of coarse and fine particles. The Nuclepore filter was found to be the most suitable filter for identifying the physical and chemical characteristics of atmospheric aerosols since it was able to separate the sample and count the different sized particles better than either Quartz or Teflon. Nuclepore filters with 8.0 ㎛ and 0.4 ㎛ pores were connected in series and exposed to a flow rate of 16.7 L/min for two-stage separation sampling. The results show that it is possible to separate and collect both coarse and fine particles. We expect that the proposed methodology will be used for future individual particle analysis of atmospheric aerosols and related research.

• Journal of Korean Society for Atmospheric Environment
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• v.18 no.3
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• pp.213-221
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• 2002

The emission characteristics of particulate matter (PMs) and heavy metals from hazardous industrial wast incinerators were investigated. The particle size distribution (PSD) of PM-10 showed different patterns for two tripes of incinerators; stoker and rotary kiln. However both types showed bimodal form at inlet of air pollution control devices (APCD) and each peak (mode) is located at smaller than 1 ${\mu}{\textrm}{m}$ and near 10 ${\mu}{\textrm}{m}$. It could explain the growth of fine PM by nucleation/coagulation/condensation of metal vapors for fine mode. The PSD of PM-10 after APCD was also influenced by APCD types that had different collection mechanism, and both electrostatic precipitator and bag filter showed less collection efficiency for particles ranged from 0.2 to 0.4 ${\mu}{\textrm}{m}$ and led to a mode in the range of 0.2 to 0.8 ${\mu}{\textrm}{m}$. However the hag filter showed two modes of PSD, while the electrostatic precipitator had one peak. The PMs and heavy metals emission factors, the representative value of emission quantity for sources, for tested facilities were developed. The emission factor of uncontrolled total PM and PM-10 were 14.7 and 7.05 kg/ton waste, respectively. The emission factors from this study were a little bit different with those from US EPA AP-42. It may thus be appropriate to use these results in the course of developing national emission factors.

• Analytical Science and Technology
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• v.11 no.4
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• pp.260-265
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• 1998

Spherical, ${\mu}m$-sized particles of barium titanyl oxalate were prepared by thermal decomposition of dimethyl oxalate in acidic barium and titanium solutions. Precipitation was carried out in the presence of several supporting anions. Spherical particles having a specific type of particle size distribution. i.e., unimodal or bimodal distribution, with mean size in the range of $0.2{\sim}3{\mu}m$, were formed depending on the supporting anions, oxalate ion generation rate and aging time. Particles of barium titanyl oxalate settled on the bottom of the beaker at the aging time of 120 min grew to the critical monosize of about $1.5{\sim}3{\mu}m$. XRD spectra and chemical analyses of barium titanate showed that barium titanyl oxalate with high qualities could be synthesized by choosing chloride ion as a supporting anion and increasing the reaction temperatures.

• Journal of Korean Society for Atmospheric Environment
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• v.8 no.1
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• pp.20-28
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• 1992

The x-ray fluorescence(XRF) is one of the most convenient and widely used techniques for analyzing trace elements in ambient particulate matters. The objects of the study were to estimate the optimum exposure time using the XRF, to investigate the distributions of heavy metal levels in particulate matters, and finally to study seasonal variation for the concentrations of total suspended particulate matters(TSP) and size fractionated particulate matters. The suspended particulate matters had been collected by a cascade impactor having 9 size fragnated stages for 3 years(Dec. 1988 to Nov. 1991) in Kyung Hee University-Suwon Campus. The particulate matters were then collected on each stage by membrane filters. The weight concentrations were determined by the XRF system. Thus, seasonal variations and relationship between concentration and particle size could be investigated. Resulting distribution was bimodal with the coarse and the fine particle groups minimum occurring around 2.1 to 3.3 $\mu$m as an aerodynamic diameter. To determine optimum exposure time of the XRF for various trace inorganic elements, membrane filters and the NIST standard filters were extensively studied. Using a statistical technique, optimum exposure time was estimated for each trace element and overall elements. The time was then determined as 20 seconds for the XRF system. The concentration of TSP was 123.9$\mum/m^3$ on an arithmatic average. The levels of each inorganic metal were Si 2420.0ng/$m^3$, Fe 977.1ng/$m^3$, and so on. The Pb. Zn, and Cu abounded in the fine mode group, while Ca, Fe, Si, Al, and K in the coarse group. Marked seasonal variation of TSP and metal concentrations was observed. The concentration of heavy metals in the fine mode was highest in winter : on the other hand, that in the coarse mode was highest in spring.

• Journal of Pharmaceutical Investigation
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• v.38 no.6
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• pp.393-398
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• 2008

A propofol delivery system was prepared using two biocompatible polymeric surfactants, poloxamer 407 and PEG 400. The nanoparticular stability of the micellar system was evaluated in terms of temperature change, storage time and composition. The particle size of the system was slightly increased with elevating temperature from $4^{\circ}C$ to $25^{\circ}C$, but its distribution was unimodal. At $40^{\circ}C$, the system presented a bimodal particle size distribution and the increase in the fraction of particles larger than 15 nm. This result might be due to the expansion of the nanoparticles through micellar swelling at the high temperature. It was found that propofol was gradually come out of the system, stored for a month at three different temperatures (4, 25 and $40^{\circ}C$). The drug loss was apparently dependent on temperature and the system composition. Increasing temperature induced the acceleration of the drug loss of $7{\sim}10%$ at $4^{\circ}C$ and $14{\sim}16 %$ at $40^{\circ}C$. This may be owing to the high diffusivity resulting from the swelling of the hydrophilic surface of the nanoparticle at high temperature. However, the addition of PEG 400 to the system led to the reduction of the drug loss. This result is associated with the previous investigation that PEG coverage decreased diffusion coefficient because of the formation of the denser structure on the surface of nanoparticulate. Nevertheless, the limited amount of PEG, less than 2% (w/v), should be used to prevent the precipitation and discoloration of the system.

• International Journal of Concrete Structures and Materials
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• v.11 no.1
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• pp.59-68
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• 2017

Mercury intrusion and nitrogen sorption porosimetry were employed to investigate the pore structure of calcium sulfoaluminate ($C{\bar{S}}A$) and portland cement pastes with cement-to-water ratio (w/c) of 0.40, 0.50, and 0.60. A unimodal distribution of pore size was drawn for $C{\bar{S}}A$ cement pastes, whereas a bimodal distribution was established for the portland cement pastes through analysis of mercury intrusion porosimetry. For the experimental results generated by nitrogen sorption porosimetry, the $C{\bar{S}}A$ cement pastes have a smaller and coarser pore volume than cement paste samples under the same w/c condition. The relative dynamic modulus and percentage weight loss were used for investigation of the concrete durability in freeze-thaw condition. When coarse aggregate with good freeze-thaw durability was mixed, air entrained portland cement concrete has the same durability in terms of relative dynamic modulus as $C{\bar{S}}A$ cement concrete in a freeze-thaw environment. The $C{\bar{S}}A$ cement concrete with poor performance of durability in a freeze-thaw environment demonstrates the improved durability by 300 % over portland cement concrete. The $C{\bar{S}}A$ concrete with good performance aggregate also exhibits less surface scaling in a freeze-thaw environment, losing 11 % less mass after 297 cycles.

• Particle and aerosol research
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• v.9 no.1
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• pp.7-21
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• 2013

Twelve-hour size-resolved atmospheric aerosols were measured to determine size distributions of water-soluble organic carbon(WSOC) during daytime and nighttime, and to investigate sources and formation pathways of WSOC in individual particle size classes. Mass, WSOC, ${NO_3}^-$, $K^+$, and $Cl^-$ at day and night showed mostly bimodal size distributions, peaking at the size range of $0.32-0.55{\mu}m$(condensation mode) and $3.1-6.2{\mu}m$(coarse mode), respectively, with a predominant condensation mode and a minor coarse mode. While ${NH_4}^+$ and ${SO_4}^{2-}$ showed unimodal size distributions which peaked between 0.32 and $0.55{\mu}m$. WSOC was enriched into nuclei mode particles(< $0.1{\mu}m$) based on the WSOC-to-mass and WSOC-to-water soluble species ratios. The sources and formation mechanisms of WSOC were inferred in reference to the size distribution characteristics of inorganic species(${SO_4}^{2-}$, ${NO_3}^-$, $K^+$, $Ca^{2+}$, $Na^+$, and $Cl^-$) and carbon monoxide. Nuclei mode WSOC was likely associated with primary combustion sources during daytime and nighttime. Among significant sources contributing to the condensation mode WSOC were homogeneous gas-phase oxidation of VOCs, primary combustion emissions, and fresh(or slightly aged) biomass burning aerosols. The droplet mode WSOC could be attributed to aqueous oxidation of VOCs in clouds, cloud-processed biomass burning aerosols, and small contributions from primary combustion sources. From the correlations between WSOC and soil-related particles, and between WSOC and sea-salt particles, it is suggested that the coarse mode WSOC during daytime is likely to condense on the soil-related particles($K^+$ and $Ca^{2+}$), while the WSOC in the coarse fraction during nighttime is likely associated with the sea-salt particles($Na^+$).

• Resources Recycling
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• v.14 no.1
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• pp.26-32
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• 2005

A study on the preparation of Ag fine particles was performed through a reduction reaction using ascorbic acids as a reductant, which is one of the indispensable processes for the recycling of silver-bearing wastes. Silver nitrate solution in the range of 10~120 mmole/l was used and Tamol NN8906 or PVP was also used as a dispersant in the preparation of Ag fine particles size analyze, SEM, and TEM to determine the particle size and morphology of them. As a result, the reduction reaction of silver ions with ascorbic acid reached equilibrium within 10 min. It was found that about 60% excess of ascorbic acid was required in order to reduce completely silver ions in the solution. The particle size distribution of Ag particles prepared through the reduction reaction showed typically biomodal or trimodal distribution. Especially, initial Ag concentration in the solution, the type and amount of dispersant added during the reduction reaction played an important role in determining the mean particle size of Ag particles.

• Korean Journal of Materials Research
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• v.10 no.1
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• pp.55-61
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• 2000

The sintering characteristics of PVA-Al(III) complex added $UO_2$ pellet and AlOOH added $UO_2$pellet were compared. The major phase of PVA-Al(III) complex and AlOOH decomposed at $1000^{\circ}C$ in $H_2$atmosphere was $\theta-Al_2O_3$. Compared with the apparent density of pure $UO_2$, that of AlOOH added $UO_2$ powder was higher but that of PVA-Al(III) complex was lower. the densification of AlOOH added $UO_2$ pellet was initiated at about $800^{\circ}C$, the densification of PVA-Al(III) complex added $UO_2$ pellet was initiated at about $900^{\circ}C$ respectively. In a view of pore size distribution, the PVA-Al(III) complex added $UO_2$ pellet appeared as monomodal type, whereas the AlOOH added $UO_2$ pellet appeared as bimodal type. The grain size of AlOOH added $UO_2$ pellet was about $13\mu\textrm{m}$ but the grain size of PVA-Al(III) complex added $UO_2$ pellet was increased up to about $36\mu\textrm{m}$.