• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.125-135
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• 2008

Rigid-soft particle mixtures, which consist of sand and rubber, are investigated for the understanding of the stress-deformation and elastic moduli. Specimens are prepared with various size ratio sr between sand and rubber particles, and different volumetric sand fraction sf. Small strain shear waves are measured under $K_o$-loading condition incorporated with the stress-deformation test by using oedometer cell with bender elements. The stress-deformation and small strain shear wave characteristics of rigid-soft particle mixtures show the transition from a rigid particle behavior regime to a soft particle behavior regime under fixed size ratio. A sudden rise of $\Lambda$ factor and the maximum value of the $\zeta$ exponent in $G_{max}=\;{\Lambda}({\sigma}'_{o}/kPa)^{\zeta}$ are observed at $sf\;{\approx}\;0.4{\sim}0.6$ regardless of the size ratio sf. Transition mixture shows high sensitivity to confining stress. The volume fraction for the minimum porosity may depend on the applied stress level in the rigid-soft particle mixtures because the soft rubber particles easily distort under load. In this experimental study, the size ratio and volumetric sand fraction are the important factors which determine the behavior of rigid and soft particle mixtures.

• Journal of the Korean Geosynthetics Society
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• v.6 no.4
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• pp.29-37
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• 2007

Reduction Factor for Installation Damage required for calculation of design strength of geogrid used in MSEW(mechanically stabilized earth wall) design is usually obtained in the field test simulating real construction condition. However, damages occurred in geogrid during backfill work are influenced by many factors such as polymer types, unit weight per area, backfill construction method and gradation of backfill material and field test considering these factors demands lots of time and costs. In this study, factors affecting installation damage are analyzed and empirical method for evaluating reduction factor for installation damage using maximum particle size in backfill material is suggested.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.10 s.253
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• pp.982-986
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• 2006

It is well known that the surface tension forces can make a particle denser than water float when the size of the particle is of the order of 1 mm. This is deeply related to the basic mechanism enabling small insects to wander around on the pond surface and also to a newly emerging technology of self-assembly using capillary forces. For the quantitative understanding of this effect, we experimentally study the maximum density of a cylinder that can float on water and how fast the cylinder sinks when the density exceeds the maximum value. We compare our experimental results with the theoretical prediction and find good agreement between them.

• Korea-Australia Rheology Journal
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• v.13 no.1
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• pp.47-54
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• 2001

Prediction of the maximum packing volume fraction with non-spherical particles has been one of the important problems in powder technology. The sphericity of fly ash particles depending on the particle diameter was measured by means of a CCD image processing instrument. An algorithm to predict the maximum packing volume fraction with non-spherical particles is proposed. The maximum packing volume fraction is used to predict the slurry viscosity under well dispersed conditions. For this purpose, Simha's cell model is applied for concentrated slurry with wide particle size distribution. Also, Usui's model developed for aggregative slurries is applied to predict the non-Newtonian viscosity of dense fly ash - water slurry. It is certified that the maximum packing volume fraction for non-spherical particles can be successfully used to predict slurry viscosity. The pressure drop in a pipe flow is predicted by using the non-Newtonian viscosity of dense fly ash-water slurry obtained by the present model. The predicted relationship between pressure drop and flow rate results in a good agreement with the experimented data obtained for a test rig with 50 mm inner diameter tube. Base on the design procedure proposed in this study, a feasibility study of fly ash hydraulic transportation system from a coal-fired power station to a controlled deposit site is carried out to give a future prospect of inexpensive fly ash transportation technology.

• Asian Journal of Atmospheric Environment
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• v.6 no.1
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• pp.14-22
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• 2012

This paper is focused on the comprehensive and detailed interpretation for the chemical transformation of individual Asian dust (hereafter called "AD") particles during long-range transport from source regions to receptor area. A multi-stage particle sampler was operated at a ground-based site in Taean, Korea directly exposed to the outflow of air masses from China during AD period in April 2003. Both quantitative and qualitative analyses for size-classified individual particles were carried out by a microbeam X-ray fluorescence (XRF) method and a microbeam Particle Induced X-ray Emission (micro-PIXE), respectively. Among major characteristic elements, the elemental masses of soil derived components, sulfur, and chloride varied as a function of particle size showing the monomodal maximum with a steeply increasing at 3.3-4.7 ${\mu}m$ particle size. Although the details on chemical composition of AD particle collected on a straight line from source area to our ground-based site are needed, a large amount of Cl coexisted in and/or on AD particles suggests that AD particles collected in the present study might be actively engaged in chemical transformation by sea-salt and other Cl containing pollutants emitted from the China's domestic sources. Through the statistical analyses it was possible to classify individual AD particles into six distinct groups. The internally mixed AD particles with Cl, which has various sources (e.g., sea-salt, coal combustion origin HCl, gaseous HCl derived from the adsorption of acids to sea-salt, and Cl containing man-made particles) were thoroughly fractionated by the elemental spectra drivened by the double detector system of micro-PIXE.

• Korean Journal of Metals and Materials
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• v.50 no.9
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• pp.685-690
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• 2012

Decalcomania is a new method for SOFCs (solid oxide fuel cells) unit cell fabrication. A tight and dense $5{\mu}m$ Yttria-stabilized zirconia (8YSZ) electrolyte layer on anode substrate was fabricated by the decalcomania method. After 8YSZ as the electrolyte starting material was calcined at $1200^{\circ}C$, the particle size was controlled by the attrition mill. The median particle size (D50) of each 8YSZ was $39.6{\mu}m$, $9.30{\mu}m$, $6.35{\mu}m$, and $3.16{\mu}m$, respectively. The anode substrate was coated with decalcomania papers which were made by using 8YSZ with different median particle sizes. In order to investigate the effect of median particle sizes and sintering conditions on the electrolyte density, each sample was sintered for 2, 5 and 10 h, respectively. 8YSZ with a median particle size of $3.16{\mu}m$ which was sintered at $1400^{\circ}C$ for 10 had the highest density. With this 8YSZ, a SOFCs unit cell was manufactured with a $5{\mu}m$ layer by the decalcomania method. Then the unit cell was run at $800^{\circ}C$. The Open Circuit Voltage (OCV) and Maximum power density (MPD) was 1.12 V and $650mW/cm^2$, respectively.

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.E2
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• pp.53-59
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• 2004

The roadway tunnels in urban areas give rise to problems such as a localized air pollution. Here, we report the results of a case study of an urban roadway tunnel measurement. The size-resolved particle sampling was carried out with a two 2-stage filter pack samplers and an Andersen impactor sampler at the center of Buk-Ak tunnel in November 2001. Particle Induced X-ray Emission (PIXE) was applied to determine the elemental composition of size-resolved particles divided into soluble and insoluble fractions. The Thermal/Optical Reflectance (TOR$^{(R)}$) method was also employed in analyzing of elemental carbon (EC) and organic carbon (OC). Mass concentrations of fine (< 1.2 ${\mu}{\textrm}{m}$) and coarse (> 1.2 ${\mu}{\textrm}{m}$) particles are 165 and 48 $\mu\textrm{g}$ m$^{-3}$ , respectively. Total elemental mass concentration (the sum of insoluble coarse, soluble coarse, insoluble fine, and soluble fine) is found to be 24$\mu\textrm{g}$ m$^{-3}$ and comprises only 11 % of total particle mass concentration. The concentrations of EC, OC, and mass show the clear dependency on particle size with the maximum between 0.1 and 0.43 ${\mu}{\textrm}{m}$ aerodynamic diameters. Total carbon (sum of EC and OC) accounts for approximately 70% of mass concentration.n.

• Journal of the Korean Institute of Gas
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• v.17 no.4
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• pp.33-38
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• 2013

A study was carried out on the effect of particle size (mean diameter) on magnesium dust explosion. Experimental investigations were conducted in a 20-L explosion sphere, using 10 kJ chemical ignitors. Explosion tests were performed with three different dusts having mean diameter (38, 142, $567{\mu}m$) and the dust concentrations were up to $2250g/m^3$. The lower explosion limits(LEL) of magnesium dusts were about $30g/m^3$ at $38{\mu}m$ and $40g/m^3$ at $142{\mu}m$. LEL tended to increase with particle size and this means that the explosion probability of magnesium dust decreased with increase of particle size. The maximum explosion presssure ($P_m$) and $K_{st}$ (Explosion index) decreased with the increase of particle size. For magnesium powder of $567{\mu}m$, however, the explosive properties were not observed in the 5 kJ ignition energy.

• Journal of Korean Society for Atmospheric Environment
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• v.29 no.1
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• pp.10-26
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• 2013

To understand the traffic emissions with high temporal and spatial resolutions on road, a mobile laboratory was developed. The objective of this study is to characterize on-road air pollution on Naebu express way surrounding the northern area of Seoul, Korea. We measured the number concentration of ultrafine particles larger than 5 nm and particle size distribution using a condensation particle counter and a fast mobility particle sizer, respectively on 3, 7, and 8 December 2009. The average ultrafine particle number concentration on the Naebu express way excluding tunnels was 126,000 particles/$cm^3$ and 4.2 times higher than that on internal road at Korea Institute of Science and Technology in Seoul, and more than twice higher than that measured on and at the arterial roads of Seoul in previous studies. The maximum ultrafine particle number concentration was observed at the tunnel sections. It was 232,000 particles/$cm^3$ and 1.8 times higher than average ultrafine particle number concentration for the other sections on Naebu express way. The ultrafine particle number concentration on the wider roads with higher traffic volume along the Han River was similar to that in the residential section, probably because of enhanced dilution effect in widely open environment. The size distribution of particles on the Naebu express way was highly fluctuated for a short duration. Ultrafine particles measured at the tunnel showed a bimodal size distribution with mode diameters of ~10 nm and ~50 nm. At the Han riverside section, ~10 nm particles appeared significantly compared with size distribution at the tunnel. This on-road measurement approach can be utilized to manage vehicle-related air pollution in urban area.

• Journal of the Korean Ceramic Society
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• v.25 no.4
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• pp.397-407
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• 1988

Spinel, mullite and cordierite powders have synthesized from Mg(NO3)2.6H2O, Al(NO3).9H2O and SiCl4 solution by spray pyrolysis method. The two-fluid nozzle was used as an atomizer. The powders of sinel and mullite were synthesized above 80$0^{\circ}C$, but the cordierite composition was noncrystalline for all synthersizing temperature. Those noncrystalline powders were crystallized to $\alpha$-cordierite during calcining at 130$0^{\circ}C$ for 2hrs. The synthesized spinel, mullite and cordierite powders seem to be consisted of agglomerated hollow spherical particles. For all powders, the particle size ranged from submicron to about 3${\mu}{\textrm}{m}$ and mean particle size was about 1.4${\mu}{\textrm}{m}$ in diameter. The specific surface area values of spinel, mullite and cordierite powders were maximum for powders prepared at 100$0^{\circ}C$, and those were 45.9, 25.8 and 13.6$m^2$/gr, respectively.