• Asian Journal of Atmospheric Environment
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• 제6권2호
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• pp.73-82
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• 2012

This study was aimed to thoroughly estimate the characteristics of indoor particulate matter (PM) collected on subway platforms by the cooperative approach of semi-bulk and single particle analyses. The size-resolved PM and its number concentration were measured on the platform in a heavily traveled subway station in Fukuoka, Japan. Particle Induced X-ray Emission (PIXE) and micro-PIXE techniques were applied to the chemical analyses of semi-bulk and single particle, respectively. There was the close resemblance of timely fluctuation between PM number concentration and train service on the third basement floor (B3F) platform compared to the second basement floor (B2F) and its maximum level was marked in rush hour. Higher number counts in large particles ($>1{\mu}m$) and lower number counts in fine particles ($<1{\mu}m$) were shown on the platform compared to an above ground. PM2.5 accounted for 58.2% and 38.2 % of TSP on B3F and on B2F, respectively. The elements that were ranked at high concentration in size-resolved semi-bulk PM were Fe, Si, Ca, S, and Na. The major elements tending to have more elevated levels on B3F than B2F were Fe (4.4 times), Ca (17.3 times), and Si (46.4 times). Although concentrations were very low, Cr ($11.9ng\;m^{-3}$ on B3F, $2.4ng\;m^{-3}$ on B2F), Mn ($3.4ng\;m^{-3}$ on B3F, $0.9ng\;m^{-3}$ on B2F), and Pb ($0.6ng\;m^{-3}$ on B3F, $1.6ng\;m^{-3}$ on B2F) were detected from PM2.5. Individual PM was nearly all enriched in Fe with Si and Ca. Classifying and source profiling of the individual particles by elemental maps and particle morphology were tried and particles were presumably divided into four groups (i.e., train/rail friction, train-rail sparking, ballast/abrasive, and cement).

• 대한기계학회논문집B
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• 제22권11호
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• pp.1571-1581
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• 1998

A flow visualization study was carried out for the branch pipe mixing flow in which a jet was issued normally to the fully developed pipe flow. An instantaneous laser tomographic method was used for cross flow Reynolds numbers based on the cross flow diameter D ranged $Re_{cf}=5.26{\times}10^3{\sim}1.13{\times}10^4$, diameter ratios d/D = 0.1 ~ 0.2 and velocity ratios R = 0.5 ~ 10. Oil mist with the size of about $10{\mu}m$ diameter was used for the scattering particle. The main purpose of this study was to reveal the physical mechanism and the structure of vortices formation with varying the velocity ratios and diameter ratios in the branch pipe flow. It was found that the physical mechanism and the structures of vortices formation were quite different depending on the velocity ratios. Particularly in the case of R < 1, the typical vortex shows single loop shape and that for the case of R > 1 depicts mushroom-like structure in the cross flow jet.

• Computers and Concrete
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• 제33권2호
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• pp.147-162
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• 2024

This study presents a random-aggregate mesoscale model integrating the random distribution of the coarse aggerates and the damage mechanics of the mortar and interfacial transition zone (ITZ). This mesoscale model can generate the random distribution of the coarse aggregates according to the prescribed particle size distribution which enables the automation of the current methodology with different coarse aggregates' distribution. The main innovation of this work is to propose the "correction factor" to eliminate the dimensionally dependent mesh sensitivity of the concrete damaged plasticity (CDP) model. After implementing the correction factor through the user-defined subroutine in the randomly meshed mesoscale model, the predicted fracture resistance is in good agreement with the average experimental results of a series of geometrically similar single-edge-notched beams (SENB) concrete specimens. The simulated cracking pattern is also more realistic than the conventional concrete material models. The proposed random-aggregate mesoscale model hence demonstrates its validity in the application of concrete fracture failure and statistical size effect analysis.

• Journal of Magnetics
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• 제13권3호
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• pp.102-105
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• 2008

This study examined the feasibility of the combining HDDR-process (hydrogenation, disproportionation, desorption and recombination) with mechanical milling to prepare single domain $Nd_2Fe_{14}B$ particles from a Nd-Fe-B alloy ingot. The $Nd_{15}Fe_{77}B_8$ alloy was HDDR-treated and then subjected to a roller-milling. In the HDDR-treated $Nd_{15}Fe_{77}B_8$ alloy, very small $Nd_2Fe_{14}B$ grains comparable to their critical single domain size(0.3 ${\mu}m$) were observed. These fine individual grains were separated successfully along the grain boundaries by a roller-milling. The separated $Nd_2Fe_{14}B$ grains were found to be single domain particles. These results suggest that single domain particles of the $Nd_2Fe_{14}B$ phase can be prepared from a Nd-Fe-B ingot alloy by combining a HDDR-process with mechanical milling.

• 한국분무공학회지
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• 제25권4호
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• pp.154-161
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• 2020

A single spray plume is the basic unit of the entire spray plume and is an important factor in understanding the spray characteristics. However, since the multi-hole GDI injector has a narrow spray angle, the superposition of the spray plumes occurs severely. Therefore, the spray uniformity and the spray atomization characteristics of a single spray plume were analyzed in this study using a single-hole GDI injector. Five single-hole GDI injectors with different nozzle hole diameters were used in the experiment. The uniformity of the spray was evaluated through the analysis of the spray pattern images. In addition, the atomization characteristics were compared using the diameter distribution of the spray droplets obtained using PDPA. As a result, the larger diameter of the nozzle hole, the less uniformity of the spray, and the injection pressure did not have a significant effect on the spray uniformity. It is judged that the surface roughness of the injector has a greater effect on spray uniformity than the diameter of the nozzle hole. Also, the size of the spray droplets increased sharply when the diameter of the nozzle hole was 230 ㎛.

• 설비공학논문집
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• 제4권4호
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• pp.351-359
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• 1992

In order to improve the performance of heat exchanger, fluidized bed is often employed. The experiments are carried out in fluidized double pipe parallel flow heat exchanger in which finned tube is vertically immersed. And the heat transfer coefficients between the heated tube and fluidized bed of alumina beads(dp=0.41, 0.54, 0.65, 0.77mm) are calculated as a function of air fluidized velocity and pumping power. The effects of particle size, static bed height and pumping power on the heat transfer coefficients are investigated. And the heat transfer coefficients are compared with that of single phase forced convection heat exchanger. In particular, the heat transfer performance of each type heat exchanger is evaluated in relation to the pumping power.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.7-10
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• 2001

Orthorhombic type $LiCo_{x}Mn_{1-x}O_{2}$(0 ${\times}$ 0.14) oxides have been synthesized by hydrothermal treatment of $(Co_{x}Mn_{1-x})_{3}O_{4}$ precursors and LiOH aqueous solution at $170^{\circ}C$. As-synthesized powders showed well-ordered ${\beta}-NaMnO_{2}$ structures, and the products were single crystalline particle oxides from TEM observations. The particle size decreased with increasing the amount of Co substituent. Much more improved capacity upon 100 cyclings was clearly seen in orthorhombic $LiCo_{0.1}Mn_{0.9}O_{2}$, comparing to orthorhombic $LiMnO_2$.

• 한국표면공학회지
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• 제29권6호
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• pp.857-861
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• 1996

The influence of rf-plasma operation on the thin film formation containing small particles for Al-Li alloys mainly have been studied as a function of Ar gas pressure and plasma power by means of a 200kV transmission electron microscope (TEM). Under the non-plasma operation, the transition from continuous thin films to clusters of grape-like small particles occurred at Ar gas pressures above 20Pa. Particles were single crystals with clear crystal habit planes. Under the plasma operation, the influence of gas pressures on the film formation at a plasma power of 5W was also examined. Thin films containing particles below 30Pa and the films containing mainly particles above 40Pa were formed. The prominent change of the average particle size was not recognized. The increase of the plasma powers at 20Pa, which formed particles under non-plasma, suppressed growth of particles, and homogeneous films containing very small particles were fabricated. The electric conductivity showed slight decrease with an increase of plasma power.

• E2M - 전기 전자와 첨단 소재
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• 제14권12호
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• pp.7-10
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• 2001

Orthorhombic type LiCo$_{x}$Mn$_{1-x}$ O$_2$(0$\leq$x$\leq$0.14) oxides have been synthesized by hydrothermal treatment of (Co$_{x}$Mn$_{1-x}$ )$_3$O$_4$precursors and LiOH aqueous solution at 17$0^{\circ}C$. As-synthesized powders showed well-ordered $\beta$-MaMnO$_2$structures, and the products were single crystalline particle oxides from TEM observations. The particle size decreased with increasing the amount of Co substituent. Much more improved capacity upon 100 cyclings was clearly seen in orthorhombic LiCo$_{0.1}$Mn$_{0.9}$O$_2$, comparing to orthorhombic LiMnO$_2$./TEX>.EX>.

• 한국응용과학기술학회지
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• 제31권1호
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• pp.59-65
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• 2014

Indoor air quality including metro subway is of recent interests in large cities. Inflow air to the inside of the train and circulating air flow through MVAC of stations contain large amount of iron based fine particles. This paper evaluated the collection of such a dust by magnetic filters as comparing to conventional particle capturing mechanisms such as inertia, direct impaction and diffusion. It was found that filtration velocity, magnetic field intensity, and fiber size were the most important parameters for magnetic filtration. Application of magnetic force obviously enhances the collection efficiency particularly in fine modes smaller than 10 mm. However, its effect was found greater in 2.5 mm than submicron particles.