• Nuclear Engineering and Technology
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• 제53권1호
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• pp.79-92
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• 2021

Venturi tube is based on turbulent flow, whereby the microbubbles can be generated by the turbulent fragmentation. This phenomenon is common in several venturi bubblers used by the nuclear, aerospace and chemical industries. The first objective of this paper is to study the liquid-phase velocity field experimentally and develop correlations for the turbulent quantities. The second objective is to research velocity field characteristics theoretically. Stereoscopic PIV measurements for the velocity field have been analyzed and utilized to develop the turbulent kinetic energy in the venturi tube. The tracking properties of the tracer particles have been verified enough for us to analyze the turbulence field. The turbulence kinetic energy has a bimodal distribution trend. Also, the results of turbulence intensity along the horizontal direction is gradually uniform along the downstream. Both the mean velocity and the fluctuation velocity are proportional to the Reynolds number. Besides, the distribution trend of the mean velocity and the velocity fluctuation can be determined by the geometric parameters of the venturi tube. An analytical function model for the flow field has been developed to obtain the approximate analytical solutions. Good agreement is observed between the model predictions and experimental data.

• 대한수의학회지
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• 제6권1호
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• pp.82-91
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• 1966

Studies On the myelinated fibers of the recurrent laryneal nerves were made in five, species of domestic animals namely dog, pig, goat, horse and Korean ox. Throughout the studies, the following characteristics of the myelinated fibers were obtained. 1. The number, size and cross sectional area of the myelinated fibers seemed to be proportionally related to the animal body weights. 2. The highest peak of diameter size frequency distribution of the myelinated fibers, observed at the right cranial level, in dog, goat and horse were 4-6 micron group, while in the case of Korean ox, 10-12 micron group was the highest. 3. The highest peak of diameter size frequency distribution of the myelinated fibers, observed at the right caudal level of Korean ox was 6-8 micron group, and 4-6 micron group was the highest in the other animals. 4. The highest peak of diameter size frequency distribution of the myelinated fibers obsered at the left cranial level was same to that of right cranial level. 5. The highest peak of diameter size frequency distribution of the myelinated fibers, observed at the left caudal levels in dog, goat, horse and Korean ox was 4-6 micron group, while in case of pig, $14-16{\mu}$ group was the highest. 6. The largest cross sectional areas were found in the group of 10-16 micron in all species of animals. 7. The fiber diameter size frequency distribution of recurrent laryngeal nerves of dog, goat, pig and horse were bimodal and Korean ox seemed to be a unimodal.

• 한국환경보건학회지
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• 제32권6호
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• pp.543-555
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• 2006

During a twenty-day period in 2005, a nine-stage Andersen cascade impactor was used to determine the seasonal size distribution of atmospheric particles and its inorganic ion species sampled for 24hr in Iksan city, located southwest of the Korean peninsula. Samples were analyzed for major water-soluble ion species using Dionex-100 ion chromatograph. Average fine and coarse mass concentrations of atmospheric particles were, respectively, 31.4 and $82.6{\mu}g\;m^{-3}$ in spring and 35.8 and $73.4{\mu}g\;m^{-3}$ in fall-winter during the sampling period of 2005, while measurements of 69.8 and 9.9 were obtained in the sampling period of summer, The size distribution of particulate mass concentration during the non-Asian dust period was generally bimodal, whereas the size distribution of particulate mass concentration during the Asian dust period was unimodal due to the significant increase of coarse particles, which originated from long-range transport of soil dust particles from loess regions of the Asian continent. Among ionic species, $SO{_4}^{2-},\;NH{_4}^+,\;K^+$ were mainly distributed in fine particles due to their characteristics of emission sources and gas-to-particle conversion, while $Na^+,\;Mg^{2+}\;and\;Ca^{2+}$ were dominantly in coarse particles. However, $NO_3{^-}\;and\;Cl^-$ were distributed in both coarse particles and fine particles. Although $SO{_4}^{2-}$ was mainly distributed in fine particles, the size distributions of $SO{_4}^{2-}$ in coarse mode were significantly increased during the Asian dust events compared to those during the non-Asian dust period. $Ca^{2+}$ showed the most abundant species in the atmospheric particles during the Asian dust period. $NH{_4}^+$ was found to mainly exist as $(NH_4)_2SO_4$ in fine particles.

• Advances in nano research
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• 제7권2호
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• pp.125-134
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• 2019

The Origanum vulgare L.-mediated synthesis of Ag nanoparticles was successfully realized within the present study. Various concentrations of the $AgNO_3$ used as a silver precursor (1, 2.5, 5, 10 and 100 mM) were used. Very rapid formation of Ag nanoparticles was observed, as only minutes were necessary for the completion of the reaction. With the increasing concentration, red shift of the surface plasmon resonance peak was observed in the Vis spectra. According to photon cross-correlation spectroscopy results, the finest grain size distribution was obtained for the 2.5 mM sample. The transmission electron microscopy analysis of this sample has shown bimodal size distribution with larger crystallites with 100 nm size and smaller around 10 nm. The antibacterial activity was also the best for this sample so the positive correlation between good grain size distribution and antibacterial activity was found. The in-depth discussion of antibacterial activity with related works from the materials science point of view is provided, namely emphasizing the role of effective nanoparticles distribution within the plant extract or matrix. The antibacterial activity seems to be governed by both content of Ag nanoparticles and their effective distribution. This work contributes to still expanding environmentally acceptable field of green synthesis of silver nanoparticles.

• 한국재료학회지
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• 제34권1호
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• pp.27-33
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• 2024

Al₂O₃ has excellent sintering properties and is important in semiconductor manufacturing processes that require high-temperature resistance and chemical inertness in a plasma environment. In this study, a comprehensive analysis of the chemical characteristics, physical properties, crystal structure, and dispersion stability of three commercially available Al₂O₃ powders was conducted. The aim was to provide a technological foundation for selecting and utilizing appropriate Al₂O₃ powders in practical applications. All powders exhibited α-Al₂O₃ as the main phase, with the presence of beta-phase Na₂O-11Al₂O₃ as the secondary phase. The highest Na⁺ ion leaching was observed in the aqueous slurry state due to the presence of the secondary phase. Although the average particle size difference among the three powders was not significant, distinct differences in particle size distribution were observed. ALG-1SH showed a broad particle size distribution, P162 exhibited a bimodal distribution, and AES-11 displayed a uniform unimodal distribution. High-concentration Al₂O₃ slurries showed differences in viscosity due to ion release when no dispersant was added, affecting the electrical double-layer thickness. Polycarboxylate was found to effectively enhance the dispersion stability of all three powders. In the dispersion stability analysis, ALG-1SH exhibited the slowest sedimentation tendency, as evidenced by the low TSI value, while P162 showed faster precipitation, influenced by the particle size distribution.

• 한국진공학회지
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• 제10권2호
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• pp.275-281
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• 2001

플라즈마 반응기 내에서 입자 전하 분포가 Gaussian형태로 표현될 때 전하 분포를 가지는 입자들의 충돌에 의한 입자 성장을 discrete-sectional 모델을 사용하여 이론적으로 고찰하였다. 플라즈마 반응기 내에서 입자 성장을 분석하기 위해 monomer크기, monomer생성 속도 등의 공정 변수들을 변화시켰다. 입자 크기가 40 m이상인 큰 입자들은 플라즈마 반응기내에서 대부분이 음으로 존재하였으며 40 m이하인 작은 입자들은 음성, 중성 혹은 양으로 존재하였다 입자 충돌에 의해 입자 크기가 증가함에 따라 입자 표면적의 증가와 더불어 입자가 가지는 평균 음전하수도 증가하였다. 입자 충돌에 의해 큰 입자들이 생성됨에 따라 입자크기분포는 2개의 모드로 양분화 됐다. 본 연구의 이론 결과와 Shiratani 등 [3]의 실험결과가 비교적 잘 맞았으며 본 연구에서 사용한 모델식은 플라즈마 반응기 내에서 수 나노 크기의 입자 성장 연구에도 활용될 수 있을 것으로 기대된다.

• Journal of Korean Society for Atmospheric Environment
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• 제17권E1호
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• pp.1-7
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• 2001

The elemental characteristics of atmospheric aerosols were investigated as a function of particle size and water solubility. The aerosol particles were samples at 12 individual size ranges between 0.01 and 30㎛. Collected aerosol particles were separated into both soluble and insoluble components. The concentrations of 15 elements in both components were determined by a PIXE analysis using a 2.0 MeV-proton beam. In general, the mass size distribution of particulate matter was represented as a bimodal distribution. The maximum rations of S in July and December were 5.5 and 3.8 %, and they appeared in the size range of 0.47∼1.17㎛(stage No. 6 or 7) . The ratios of a S at non-separated size were 3.1 and 2.2 % in July and December, respectively, On the other hand, the maximum rations of Si in July and December were 7.0 and 5.4% and they appeared in the size range of 5.1∼30㎛(stage No. 0∼2). The ratios of Si at the non-separated size were 2.1 and 1.8% in July and December, respectively, The mass diameter of 12 elements ranged between 0.59㎛ of S and 3.20 of Fe. More than 90% of atmospheric aerosols consisted of the light elements such as C, N, O, H and Al. The soluble component was dominant in the smaller size range and the insoluble component in the larger size range. Large portions of Si. Ti and Fe existed in insoluble state. By contrast, S, Cl, Ca, Zn and Br were dissolved in water.

• 한국환경과학회지
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• 제13권4호
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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.

• 한국산업보건학회지
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• 제26권1호
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• pp.30-37
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• 2016

Objectives: This study was performed to measure and evaluate the concentration, size distribution and fugitive emission of particulate matter from process operations at foundries. Methods: Particle matter was collected from three foundries, and samples were also collected from a background site for calculating the fugitive emission concentration of the foundries. For the collection of the samples, a Nanosampler cascade impactor was used. Results: The concentration of TSP in the samples collected from the three foundries was $0.675{\sim}1.222mg/m^3$, $PM_{10}$ was $0.525{\sim}1.018mg/m^3$ and $PM_{2.5}$ was $0.192{\sim}0.615mg/m^3$. The mass size distribution was bimodal or monomodal with maximum peak at two stage(size $2.5{\sim}10{\mu}m$). The mass median aerodynamic diameter(MMAD) was $1.80{\sim}3.98{\mu}m$. The fugitive emission concentration of TSP varies in the range of 0.65 to $1.21mg/m^3$, which exceeds the emission standard of fugitive dust($0.5mg/m^3$). Conclusions: Particle concentration and size is an important industrial hygiene factor to protect foundry workers. Furthermore, the presence of high emission of particulate pollutants has a significant negative impact on the ambient air of the study area. Therefore, it is important to improve both the process and prevention facility in oder to reduce particulate pollutants in foundries.

• 천문학회지
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• 제29권2호
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• pp.119-136
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• 1996

To examine the effect of neighboring galaxies on the gravitational lensing statistics, we performed numerical simulations of lensing by many galaxies. The models consist of a galaxy in the rich cluster like Coma, or a galaxy surrounded by field galaxies in $\Omega_0 = 1$ universe with $\Omega_{gal} = 0.1,\;\Omega_{gal} = 0.3\;or\;\Omega_{gal}=1.0\;,\;where\;\Omega_{gal}$ is the total mass in galaxies. Field galaxies either have the same mass or follow Schechter luminosity function and luminosity-velocity relation. Each lensing galaxy is assumed to be singular isothermal sphere (SIS) with finite cutoff radius. In most simulations, the lensing is mainly due to the single galaxy. But in $\Omega_{gal} = 3$ universe, one out of five simulations have 'collective lensing' event in which more than two galaxies collectively produce multiple images. These cases cannot be incorporated into the simple 'standard' lensing statistics calculations. In cases where 'collective lensing' does not occur, distribution of image separation changes from delta function to bimodal distribution due to shear induced by the surrounding galaxies. The amount of spread in the distribution is from a few $\%\;up\;to\;50\%$ of the mean image separation in case when the galaxy is in the Coma-like cluster or when the galaxy is in the field with $\Omega_{gal} = 0.1\;or\;\Omega_{gal}=0.3.$ The mean of the image separation changes less than $5\%$ compared with a single lens case. Cross section for multiple image lensing turns out to be relatively insensitive to the presence of the neighboring galaxies, changing less than $5\%$ for Coma-like cluster and $\Omega_{gal}=0.1,\;0.3$ universe cases. So we conclude that Coma-like cluster or field galaxies whose total mass density $\Omega_{gal}<0.3$ do not significantly affect the probability of multiple image lensing if we exclude the 'collective lensing' cases. However, the distribution of the image separations can be significantly affected especially if the 'collective lensing' cases are included. Therefore, the effects of surrounding galaxies may not be negligible when statistics of lensing is used to deduce the cosmological informations.