• Korean Chemical Engineering Research
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• v.43 no.5
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• pp.609-615
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• 2005

$TiO_2$ particles, 30-300 nm in diameter, were prepared by thermal decomposition of titanium tetraisopropoxide (TTIP) using an aerosol microreactor, by which about $1{\mu}l$ of the liquid precursor is injected into an evaporator, 1 cc in volume, and vaporized precursor is then transported by nitrogen as a bolus to a tubular reactor 4 mm in diameter and 35 cm in length. Investigated were the effects of the reactor temperature and the concentration of TTIP vapor on the morphology, particle size distribution and crystalline structure of produced $TiO_2$ particles. With TTIP vapor concentration kept constant at 1 mol%, the reactor temperature was varied from 300 to 500 and $700^{\circ}C$. The primary particle size decreased with increasing the temperature, and the size distributions were mono-modal at 300 and $500^{\circ}C$, but bi-modal at $700^{\circ}C$. The TTIP vapor concentration was increased from 1 to 3.5 and 7 mol%, holding the reactor temperature at $700^{\circ}C$. The bi-modal distribution seen at the concentration of 1 mol% disappeared and the number of particles composing an agglomerate increased at the higher concentrations. These effects of the reactor temperature and the precursor concentration were discussed in comparison with experimental results reported earlier.

• Elastomers and Composites
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• v.45 no.4
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• pp.256-262
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• 2010

Dispersion polymerization of methyl acrylate, ethyl acrylate, butyl acrylate, and glycidyl methacrylate were performed in supercritical $CO_2$ at $80\;^{\circ}C$ and 346 bar. Glycidyl methacrylate linked poly(dimethylsiloxane) (GMS-PDMS) surfactant, which was prepared by linking glycidyl methacrylate to monoglycidyl ether terminated PDMS with amino-propyltriethoxysilane, was used as surfactant for the dispersion polymerization in $CO_2$. The yield of the poly(alkyl acrylate) polymers, synthesized in $CO_2$ medium, decreased as the alkyl tail of the acrylate monomers increased. Poly(glycidyl methacrylate) and poly(methyl acrylate) were produced in bead form whereas poly(ethyl acrylate) and poly(butyl acrylate) were viscous liquid. The poly(glycidyl methacrylate) particles had a number average diameter of 2.45 ${\mu}m$ and monodisperse distribution. The poly(methyl acrylate) had a number average diameter of 0.52 ${\mu}m$ and the particle size distribution was bimodal. The glass transition temperatures ($T_g$) of the poly(glycidyl methacrylate) and the poly(alkyl acrylate) products were 4~9 K higher than the $T_g$ of the corresponding acrylate polymers synthesized in conventional processes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.1
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• pp.11-19
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• 2013

As the temperature data show a distribution pattern with a number of peaks, assumption of normal distribution will result in a serious bias in the analysis. In this study, the Gaussian Mixture Distribution (GMD), a type of bimodal distribution, is presumed as a frequency distribution for the water temperature, in order to estimate the optimal parameter and to carry out the relation analysis between the optimal parameter and the basic statistical information such as mean and variance on the data. By the way, an estimation formulae to compute the frequency distribution of the data is developed by computing the parameters of GMD (i.e. ${\alpha}_1$, ${\mu}_1$, ${\sigma}_1$, ${\alpha}_2$, ${\mu}_2$, ${\sigma}_2$) by means of the major characteristic values, such as mean, standard deviation and skewness of the data. The formulae shows an excellent coincidence with the result from the observation data, in the RMS limit accuracy of 5%.

• 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.

• Journal of the Korean Society for Railway
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• v.17 no.5
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• pp.336-341
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• 2014

The articulated structures seen in train or tram applications are being applied in road transportation systems, for use in mass passenger transit. When articulated vehicles are driven on public roads, they no longer follow a guided track. Therefore, there are a lot of control elements that need to be considered, such as turning radius, swept path width, off-tracking, and swing-out. Some of the currently available articulated vehicles on roads are equipped with an independent drive system; a system that has one motor at each wheel. Through this drive system, each wheel can be independently controlled, making precise and quick dynamic stability control possible. In this paper, we propose a torque distribution algorithm that can reduce the overall turning radius of the articulated vehicle, which has been verified through dynamic simulation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.5
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• pp.278-284
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• 2014

Water temperature due to climate change can be estimated using the air temperature because the air and water temperatures are closely related and the water temperatures have been widely used as the indicators of the environmental and ecological changes. It is highly necessary to estimate the frequency distribution of the air and water temperatures, for the climate change derives the change of the coastal water temperatures. In this study, the distribution function of the air temperatures is estimated by using the long-term coastal air temperature data sets in Korea. The candidate distribution function is the bi-modal distribution function used in the previous studies, such as Cho et al.(2003) on tidal elevation data and Jeong et al.(2013) on the coastal water temperature data. The parameters of the function are optimally estimated based on the least square method. It shows that the optimal parameters are highly correlated to the basic statistical informations, such as mean, standard deviation, and skewness coefficient. The RMS error of the parameter estimation using statistical information ranges is about 5 %. In addition, the bimodal distribution fits good to the overall frequency pattern of the air temperature. However, it can be regarded as the limitations that the distribution shows some mismatch with the rapid decreasing pattern in the high-temperature region and the some small peaks.

• Journal of Plant Biology
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• v.24 no.1
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• pp.47-57
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• 1981

Girth at breast height was measured to test skewness ($g_1$) and kurtosis ($g_2$) of frequency distribution of the basal area in terms of t-test and Kolmogorov-Smirnov test for a total of forty six monocultures within Sudong and Kwhangnung area in central part of Korean peninsula in 1979 and 1980. The monocultures are about 10 to 50 years old, and four kinds: Pinus koraiensis, Larix kaempferi, Abies holophylla and Pinus rigida. Most of the sample sizes per site were ranged 70 to 110 excluding 4 sites. The number of classes interval was based on Sturges rule for each monoculture and was ranged from 5 to 10. In Sudong the range of age(yr) and basal area (($cm^2$)/tree) of the monocultures were from 10 to 20 and from 27.60 to 383. for Kwhangnung they were from 15 to 47 and mostly 102.15 to 619.14, respectively. All 43 monocultures except 1 showed +$g_1$, which ranged from 0.3 to 2.2 except six sites. Of the total 46 sites, 23 sites showed significant +$g_1$ which includes about 10 year-old monoculture. The number of classes interval with significant positive skewness ranged from 6 to 9. The data suggest that intraspecific competition in terms of stand structure seems to appear from about 10 year-old monocultures, and it may even last to about 50 year-old one. Around 24 monocultures showed nonsignificant -$g_2$ except one. Most -$g_2$ ranged from -0.12 to -0.83. Around 20 monocltures showed positive $g_2$ ranging from +0.13 to +3.841. Of the 22 +$g_1$, majority of 11 were very highly significant. Of all monocultures only 5 showed significant result from Kolmogorov-Smirnov test. Of the 4 species, Larix kaempferi seems to show density stress first then Abies holophylla, and Pinus koraiensis last. Data of this study indicate that adequate number of classes intervals and sample sizes for studying intraspecific competition in terms of basal area are 6 to 9 and 80 trees rather than 12 and 100 trees, respectively. It also suggests that most of the frequency distribution of basal area class are trimodal rather than bimodal under density stress. It is proposed that the leptokurtic distribution appears before normal distribution rather than direct change from platykurtic to normal distribution of basal area for selected stages in the development of stands.

• Journal of Environmental Health Sciences
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• v.35 no.1
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• pp.21-35
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• 2009

The Asian dust storms which originated in the deserts of Mongolia and China transported particles to Korea and led to a high concentration of atmospheric particulate matters (PM) of more than $1000{\mu}g/m^3$ throughout the country in the spring, of 2007. Public concern, in Korea, about the possible adverse effects of these dust events has increased, as these dust storms can contain various air pollutants emitted from heavily industrialized eastern China. The objectives of this study were to understand the concentration characteristics of PM as a function of particle size between the Asian dust storm episodes and non-Asian dust period and to consider the mass size distribution of PM in the Asian dust storms and their water soluble ion species on the potential, possible effects on deposition levels in the three regions (nasopharyngeal, tracheobronchial, and alveolar) of the human respiratory system. The size distribution of PM mass concentration during the Asian dust storms showed a peak in the coarse particle region due to the long-range transport of soil particles from the deserts of Mongolia and China, which was identified by HYSPLIT-4 model for backward trajectory analysis of air arriving in the sampling site of Iksan. During the non-Asian dust period, there were two different types in PM size distribution: bimodal distribution when low concentrations of $PM_{2.5}$ were observed, while unimodal distribution having a peak in fine particle region when high concentrations of $PM_{2.5}$ were showed. This unimodal distribution with high concentrations of fine particulate and secondary air pollutants such as ${SO_4}^{2-}$, ${NO_3}^-$, ${NH_4}^+$ was found to be due to the long-range transport of air pollutants from industrialized eastern China. During the Asian dust storms, the mean concentrations of PM that can be deposited in the nasopharyngeal, tracheobronchial, and alveolar region were $128.8{\mu}g/m^3$, $216.5{\mu}g/m^3$, and $89.6{\mu}g/m^3$, respectively. During the non-Asian dust period, the mean concentrations of PM that can be deposited in the nasopharyngeal, tracheobronchial, and alveolar region were $8.4{\mu}g/m^3$, $9.5{\mu}g/m^3$ and $38.5{\mu}g/m^3$, respectively.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.E2
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• pp.78-88
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• 2006

In order to study the characteristics of cloud, a real-scale experiment for cloud generation was carried out using an extinct vertical mine (430 m height) located in the northeastern Honshu, Japan. The dry particles generated from the three-step concentrations of NaCl solutions were used for cloud generation. The number size distributions of initial dry particles and cloud droplets were monitored by Scanning Mobility Particle Sizer (SMPS) and Forward Scattering Spectrometer Probe (FSSP) at bottom and upper sites of pit, respectively. The polymeric water absorbent film (PWAF) method was employed to measure liquid water content ($W_L$) as a function of droplet size. Moreover the chemical properties of individual droplet replicas were determined by micro-PIXE. The CCN number concentration shows the lognormal form in dependence of the particle size, while the number size distributions of droplets are bimodal showing the peaks around $9{\mu}m$ and $20{\mu}m$ for every case. In comparison to background mineral particles, right shifting of size distribution line for NaCl particles was occurred. When NaCl solutions with three-step different concentrations were neulized, $W_L$ shows the strong droplet size dependence. It varied from $10.0mg\;m^{-3}$ up to $13.6mg\;m^{-3}$ with average $11.6mg\;m^{-3}$. A good relationship between $W_L$ and cloud droplet number concentration was obtained. Both chemical inhomogeneities (mixed components with mineral and C1) and homogeneities (only mineral components or C1) in individual droplet replicas were obviously observed from micro-PIXE elemental images.

• Clinical and Experimental Pediatrics
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• v.51 no.2
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• pp.116-121
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• 2008

Unintentional injuries are the most important cause of morbidity and mortality in the pediatric population, and the home is the most common site of injury for children in Korea. The most common cause of injury was slip down. Fall down and burn were frequent in infant/toddlers group, automobile and bicycle accident more frequent in preschool children. Findings from the survey could then be used to provide targets for direct educational efforts by medical services and to direct environmental safety modifications tailored to the unique situation of each family. Pediatric toxic ingestions are treated commonly by pediatricians and emergency physicians. Significant injury after these ingestions is infrequent, but identifying the dangerous ingestion is sometimes a difficult task. By performing a detailed history, focused physical examination, and directed laboratory evaluation, an estimation of risk can be developed. According to recent Korean poison papers, there were bimodal peak of age distribution in poisoned children patient on the whole: infant and adolescents group. Various types of materials belonged the classes of drugs, household products, and industrial solvents. Most of the poisoned children patients had been poisoned accidentally, while most cases of adolescents poisoning had been intentional. More than half of the adolescents group had a suicidal purpose in Korea, so an understanding of the demographic factors associated with self-harm poisoning may provide useful information to improve prevention and treatment strategies.