• Particle and aerosol research
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• v.10 no.1
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• pp.27-31
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• 2014

A simple bimodal model has been developed to analyze charged particle coagulation by modifying previously suggested bimdal model for evolution of particle generation and growth. In the present model, two monodisperse modes are used and 40 charge nodes are assigned to each mode to account both change of the particle size and charge distribution. In addition, we also implemented the effect of electrostatic dispersion loss in the present model. Based on the developed model, we analyzed coagulation of asymmetric bipolar charged particles by computing evolutions of particle number concentration, geometric mean diameter of particles, charge asymmetric ratio and geometric standard deviation of particle size distribution for various initial charge asymmetric ratios. The number concentration of asymmetric bipolar charged particles decreases faster than that of neutral particles but that does not give faster growth of particles since the electrostatic dispersion loss overwhelms particle growth by coagulation.

• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.190-196
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• 1994

In order to investigate the ball-milling effect on the property changes of UO$_2$ ex-AUC powder, the sinterability of ball -milled powder was studied in terms of the ball -milling time. Spherical shape was found to be kept for ball-milled UO$_2$ powder and the particle size showed a bimodal distribution, which seems to have a higher packing ratio compared with those having monomodal gaussian distribution. The increase of sintered density of the ball -milled UO$_2$ powder is assumed to be mainly affected by the packing ratio, which increase with longer ball -milling time. It is confirmed that the sinterability of UO$_2$ ex-AUC powder is improved by the ball-milling process.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.6
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• pp.475-486
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• 1997

The characteristics of atmospheric aerosols were investigated as a function of particle size and water solubility. The atmospheric aerosols were sampled with classifying into 12 size ranges by the use of Andersen low-pressure impactor. Collected aerosol particles were extracted by ultrapure water and filtered to be separated into water-soluble and insoluble components. The concentrations 12 elements in both components were determined by PIXE analysis. And the concentrations of 8 ions in the soluble component were analyzed by ion chromatography. In general, the mass size distribution of particulate matter was represented as a bimodal distribution. The mass size distributions of S$(SO_4^{2-}), K(K^+), Zn and NH_4^+$ skewed to the smaller size range and those of Si, Ca$(Ca^{2+}), Fe, Na^+ and Mg^{2+}$ skewed to the larger size range. They had roughly one peak in the fine and coarse particle region,respectively. On the other hand, the mass size distribution of Ti, Mn, Ni, Cu, $Cl^- and NO_3^-$ were represented as the bimodal distribution. Fe and Si in the aerosol particles extracted into pure water are existing in high insoluble state. Conversely, almost the whole of S is dissolved in water.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2471-2476
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• 2007

A series of titanium complexes containing terdentate β-ketoiminate ligands were found to be efficient for the ring-opening polymerization of ε-caprolactone (ε-CL), producing poly(ε-caprolactone) (PCL) with bimodal distribution. Steric factors imposed by methyl substituents on the back bone of the alkoxy group affected significantly the polymerization rate and physical properties of the resulting PCL. Intra- and intermolecular transesterifications rather than disproportional rearrangements were responsible for the bimodal behavior and for the change in the molecular weight (Mw). Dilution with toluene reduced yield, and lowered polydispersity (PDI) and Mw of PCL, while the catalytic activities of the dimeric complex, [Ti(Oi-Pr)2(N-alkoxy-β- ketoiminate)]2 and Ti(Oi-Pr)4 were not sensitive to the added solvent. The dimeric complex showed living character, while other catalysts suffered from chain termination reactions.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.32.2-32.2
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• 2016

The globular cluster (GC) systems in most elliptical galaxies show bimodal color distributions. This phenomenon has been generally regarded as a bimodal metallicity distribution, indicating the presence of two sub-populations in a GC system. However, since a new explanation on the bimodality was introduced where the nonlinear metallicity-to-color conversion can cause bimodal color distributions, the origin of this phenomenon has been under hot debate. In this presentation, we briefly review the ten-year debate on the origin of GC color bimodality, and present our recent pieces of evidence on the nonlinear nature of GC color-metallicity relations.

• Journal of Korean Society for Atmospheric Environment
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• v.14 no.3
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• pp.191-208
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• 1998

Estimations of dry and wet depositions in Korea and the size distributions of yellow sand above Korea have been carried out using the Eulerian aerosol model with the simulated meteorological data from the SNU mesoscale meteorological model. The estimated particle size distribution in Korea shows a bimodal distribution with peak values at 0.6 pm and 7 pm and a minimum at 2 pm in the lower layer However, as higher up, the bimodal distribution becomes an unimodal distribution with a peak value at 4∼5mm. Among the total amount of yellow sand deflated in the source regions , the dry and wet deposition fluxes were about 92%, and about 1.3∼0.5%, repectively, and the rest(5∼6%) is suspended in the air, Most of dust lifted in the air during the clear weather is deposited in the vicinity of the source regions by dry deposition and the rest undergoes the long -range transport with a gradual removal by the wet deposition processes. Over Korean peninsula, the total amount of yellow sand suspended in the air was about 6∼8% of the emissions in the source region and the dry and wet deposition fluxes were about 0.005∼0.7% and 0.003∼0.051% of the total emitted amount, repectively. It is estimated that 2.7∼8.9 mesa-tons of yellow sand is transported annually over the Korean peninsula with the annual mean dry deposition of 2.1∼490 kilo-tons and the annual mean wet deposition of 1.5∼65 kilo-tons.

• Journal of Astronomy and Space Sciences
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• v.29 no.2
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• pp.191-194
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• 2012

The observed distribution of a blending-corrected sample of Einstein ring crossing times, $t_E$, for microlensing events toward the galactic bulge/bar are analyzed. An inspection of the distribution of crossing times suggests that it may be bimodal, indicating that two populations of lenses could be responsible for observed microlensing events. Given the possibility that microlensing in this direction can be due to the two most common classes of stars, main-sequence and white dwarf, we analyze and show via Monte Carlo simulations that the observed bimodality of $t_E$ can be derived from their accepted mass functions, and the density distributions of both stellar populations in the galactic disk and bulge/bar, with a transverse velocity distribution that is consistent with the density distribution. Kolmogorov-Smirnov (KS) one sample tests shows that a white dwarf population of about 25% of all stars in the galaxy agrees well with the observed bimodality with a KS significance level greater than 97%. This is an expanded and updated version of a previous investigation (Wickramasinghe, Neusima, & Struble, in Mao 2008). A power-point version of the talk, with introductory figures, is found at: https://sites.google.com/site/rhkochconference/agenda-1/program.

• Journal of Preventive Medicine and Public Health
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• v.17 no.1
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• pp.95-106
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• 1984

To acquire the essential basic data to the establishment of control measure for the hazardous health effect that could be caused by harmful metals, the author measured the concentrations of trace metals in whole blood of women of $20{\sim}39$ years old living in urban and rural area using atomic absorption spectrophotometer. The summarized results were as follows; 1. The mean concentration of zinc in whole blood was $10.69{\pm}8.07{\mu}g/ml$ in rural area. The frequency distribution by zinc concentration level was nearly L-type and the cumulative frequency distribution was showed bimodal type in both area. 2. The mean iron concentration in whole blood was $323.09{\pm}87.15{\mu}g/ml$ and $322.07{\pm}104.74{\mu}g/ml$ in urban and rural area, respectively. The frequency distribution was similar to normal distribution type in both area, but the cumulative distribution was unimodal type in urban area and bimodal type in rural area. 3. The mean magnesium concentration was $41.08{\pm}19.58{\mu}g/ml$ and $40.28{\pm}16.82{\mu}g/ml$ in the area, respectively. The frequency distribution type had skewness to the right and the cumulative frequency distribution was unimodal type in both area. 4. The mean copper concentration was $1.417{\pm}0.761{\mu}g/ml$ and $1.375{\pm}0.743{\mu}g/ml$ in the area, respectively. The frequency distribution type had skewness to the right and the cumulative frequency distribution was bimodal type in both area. 5. The mean manganese concentration was $0.079{\pm}0.039{\mu}g/ml$ and $0.07{\pm}0.058{\mu}g/ml$ in the area, respectively. The frequency distribution type had skewness to the right in both area but slight irregular in rural area and the cumulative distribution was unimodal and bimodal type in urban and rural area, respectively. 6. The mean cadmium concentration in whole blood was $0.031{\pm}0.026{\mu}g/ml$ in urban and $0.028{\pm}0.023{\mu}g/ml$ in rural area. The frequency distribution type had skewness to the right and cumulative frequency distribution was bimodal type in both area.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.50.1-50.1
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• 2015

The origin of globular cluster (GC) color bimodality, which is one of the salient phenomena observed in most large galaxies, has not yet been fully resolved. The phenomenon has conventionally been interpreted as a bimodal metallicity distribution based on an assumption of linear GC color-metallicity relations (CMRs). Recent studies however suggest that nonlinear GC CMRs can cause a bimodal color distribution even from a single-peaked metallicity spread. Using photometric and spectroscopic data on GCs in NGC 5128 (Cen A) and NGC 4594 (Sombrero), we investigate the nonlinearity of GC CMRs and compare the observed GC CMRs with the predictions of stellar population simulation models. Our careful selection of old GCs effectively reduces the scatter and reveals the nonlinear nature of the GC CMRs for various colors. The overall shape of the observed CMRs agrees well with that of the modeled CMRs, while offsets are present for some colors. We discuss the implications of our results in terms of the GC color bimodality and GC formation in NGC 5128 and NGC 4594.

• Journal of the Korean Ceramic Society
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• v.32 no.6
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• pp.653-658
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• 1995

Directional effect of applied pressure during sintering on the microstructure and fracture toughness of the heat-treated silicon nitride ceramics has been investigated. The specimens with a composition of 92Si3N4-8Y2O3(in wt%) were sintered at 172$0^{\circ}C$ by a hot press (HP ) and a hot isostatic press (HIP) and heat-treated for grain growth at 1800~20$0^{\circ}C$. The fracture toughness of the HP samples increased with the grain size while the fracture toughness of the HIP treated samples remained the same even though the grain growth occurred. This discrepancy was explained by a bimodal grain size distribution and large aspect ratio of the HPed samples and a monomodal grain size distributjion and samll aspect ratio of the HIP treated samples.