• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.27-33
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• 1995

The microwave absorbing characteristics and complex permeability of $Ni_{2-x}Zn_{x}Y$ - rubber composites with variation of composition and particle size were investigated. With a ferrite particle with a diameter of about $1\mu\textrm{m}$, only spin rotational resonance was observed. This behavior probably due to the particle being sufficiently small to approach single domain characteristics so that only spin rotations can occur. The first matching frequency, found in $Ni_{2-x}Zn_{x}Y$ - rubber composites, which was higher than that of spin rotational resonance, increased with spin rotational resonance frequency. It is also found that the second matching frequency is independent of spin rotational resonance frequency. Based on these findings, it could be concluded that the microwave absorbing characteristics were caused by only one type of resonance, the spin rotational resonance.

• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.252-256
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• 2007

A series of spherical porous carbons were prepared via resorcinol-formaldehyde (RF) sol-gel polymerization in the presence of cationic surfactant (CTAB, cetyltrimethylammonium bromide), wherein the carbon sphere size was controlled by varying the CTAB introduction time after a pre-determined period of addition reaction (termed as "pre-curing"). The sphere size gradually decreases with an increase in the pre-curing time within the range of 30-150 nm. The carbons possess two types of pores; one inside carbon spheres (intra-particle pores) and the other at the interstitial sites made by carbon spheres (inter-particle pores). Of the two, the surface exposed on the former was dominant to determine the electric double-layer capacitor (EDLC) performance of porous carbons. As the intra-particle pores were generated inside RF gel spheres by gasification, the pore diameter was similar for all these carbons, thereby the pore length turned out to be a decisive factor controlling the EDLC performance. The charge-discharge voltage profiles and complex capacitance analysis consistently illustrate that the smaller-sized RF carbons deliver a better rate capability, which must be the direct result of facilitated ion penetration into shorter pores.

• Journal of Environmental Health Sciences
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• v.47 no.4
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• pp.366-377
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• 2021

Background: Polycyclic aromatic hydrocarbons (PAHs) are generated in petrochemical complexes, can spread to residential areas and affect the health of residents. Although harmful PAHs are mainly present in particle phase, gas phase PAHs can generate stronger toxic substances through photochemical reaction. Therefore, the risk assessment for PAHs around the petrochemical complex should consider both particle and gas phase concentrations. Objectives: This study aimed to investigate the concentration characteristics of particle and gas phase PAHs by season in residential areas around petrochemical complexes, and to assess the risk of PAHs. Methods: Samples were collected for 7 days by seasons in 2014~2015 using a high volume air sampler. Particle and gas phase PAHs were sampled using quartz filter and polyurethane foam, respectively, analyzed by GC-MS. Chronic toxicity and probabilistic risk assessment were performed on 14 PAHs. For chronic toxicity risk assessment, inhalation unit risk was used. Monte-Carlo simulation was performed for probabilistic risk assessment using the mean and standard deviation of measured PAHs. Results: The concentration of particle total PAHs was highest in autumn. The gas phase concentration was highest in autumn. The average gas phase distribution ratio of low molecular weight PAHs composed of 2~3 benzene rings was 85%. The average of the medium molecular weight composed of 4 benzene rings was 53%, and the average of the high molecular weight composed of 5 or more benzene rings was 9%. In the chronic toxicity risk assessment, 7 of the 14 PAHs exceeded the excess carcinogenic risk of 1.00×10^-6. In the Monte-Carlo simulation, Benzo[a]pyrene had the highest probability of exceeding 1.00×10^-6, which was 100%. Conclusions: The concentration of PAHs in the residential area around the petrochemical complex exceeded the standard, and the excess carcinogenic risk was evaluated to be high. Therefore, it is necessary to manage the air environment around the petrochemical complex.

• Journal of Environmental Science International
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• v.16 no.12
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• pp.1355-1367
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• 2007

This study summarizes the relations among $PM_{2.5}$ concentration, water-soluble ions concentration, metallic element Components characteristics and SPSS in negative ion and metallic element of $PM_{2.5}$ particle in Miryang.(By the urban area, the industrial complex area and the suburban area according to the season) $PM_{2.5}$ concentration of total 72 samples collected from 3 sites turned out to range from 3.47 to 34.7 ${\mu}g/m^3$, and the average concentration was the suburban area-the kin nup(16.00 ${\mu}g/m^3$) > the urban area-the roof of the old Miryang university(10.32 ${\mu}g/m^3$) > the industrial complex-Sapo industrial complex(10.29 ${\mu}g/m^3$). In particular, the suburban area had $PM_{2.5}$ concentration 1.5 times those of urban area, industrial complex. It was thought although the site was suburban and farm-side without pollutants around, it had a higher concentration value influenced by external factors including the brickyard, small-scale incinerator, driving range construction, construction on the Daegu-Busan express and the widening of the four-lane road between Miryang-Anyang nearby. As for water-soluble ions among $PM_{2.5}$ particle collected in Miryang area, $SO4_{2^-}$ accounted for 60% and $NO_{3^-}$, was 30% in spring and summer. And $NO_{3^-}$ accounted for 50% and $SO4_{2^-}$ was 35% in fall and winter. The AI value of metallic Components among $PM_{2.5}$ particle collected in Miryang area had a high value influenced by the apartment complex construction and the extension work of road. The industrial complex area had Zn concentration 3 times, and Fe concentration 2 times those of urban area and suburb area. When it comes to the relation with metallic elements in urban area, the highest coefficient of correlation was between Cr-Fe with 0.85, and Pb-Cd turned out in the reverse correlation. Among metallic elements, the coefficients of correlation between Zn and Cr, Mn, Fe, NI were high in industrial complex area. The highest coefficient of correlation was between Mn-Zn with 0.88, meanwhile Ni and Cu, Cd turned out in the reverse correlation in the suburb area. These coefficients of correlation are attributed to the difference in pollutant sources, rather than difference in pollutant and non-pollutant.

• Journal of Welding and Joining
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• v.26 no.1
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• pp.76-82
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• 2008

The effect of Nb addition on the precipitation and precipitate coarsening behavior was investigated in Ti and Ti + Nb steel weld HAZ. A dilatometer equipped with a He-quenching system was used to simulate the weld thermal cycle. Compared to $TiC_yN_{1-y}$ precipitate in a Ti containing steel, $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle with addition of Nb is precipitated in a Ti + Nb containing steel. Meanwhile, precipitate coarsening occurred more easily in Ti + Nb steel, which may be because the high temperature stability of $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle is deteriorated by the Nb addition.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.151-157
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• 2005

In the chemical, mineral and electronics industries, mechanically stirred tanks are widely used for complex liquid and particle mixing processes. In order to understand the complex phenomena that occur in such tanks, it is necessary to investigate flow field in the vessel. Most difficulty on the numerical analysis of stirred tank flow field focused particularly on free surface analysis. In order to decrease the dead zone and improve the flow efficiency of a system with free surface, this paper presents a new method that overcomes free surface effects by properly combining the benefits of using experiment and 3-D CFD. This method is applied to study the mixing flow in an agitated tank. From the results of experimental studies using the PIV (particle image velocimetry) system, the distribution of mixing flow including free surface are obtained. And these values that are expressed as a velocity vector field have been patched for simulating the free surface. The results of velocity distribution obtained by 3-D CFD are compared with those of experimental results. The experimental data and the simulation results are in good agreement.

• Geomechanics and Engineering
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• v.15 no.1
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• pp.669-676
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• 2018

The "pseudo-wedge" failure is a name for a complex instability occurring at the Sarcheshmeh open-pit mine (Iran). The pseudo-wedge failure contains both the rock bridge failure and sliding along pre-existing discontinuities. In this paper, a cross section of the failure area was first modeled using a bonded-particle method. The results indicated development of tensile cracks at the slope toe which explains the freedom of pseudo-wedge blocks to slide. Then, a three-dimensional discrete element method was used to perform a block analysis of the instability. The technique of shear strength reduction was used to calculate the factor of safety. Finally, the influence of geometrical characteristics of the mine wall on the pseudo-wedge failure was investigated. The safety factor significantly increases as the dip and dip direction of the wall decrease, and reaches an acceptable value with a 10-degree decrease of them.

• Bulletin of the Korean Chemical Society
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• v.30 no.11
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• pp.2669-2674
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• 2009

Controlled reduction of silver alkylcarbamate complexes with hydrogen gas was investigated as a facile synthetic method for high concentrations of silver nanocolloids in organic solvent. Polyvinylpyrrolidone (PVP) was used to stabilize the silver colloids obtained from the chemical reduction. To determine optimum conditions for preparation of the stable and controlled silver colloids with the narrowest particle size and distribution, a large number of experiments were carried out involving variations in the concentrations of the silver 2-ethylhexylcarbamate (Ag-EHCB) complex, PVP, and 2-propanol. The initial colloid had a mean particle diameter between 5$\sim$50 nm, as measured by transmission electron microscopy, and exhibited a sharp absorption band in the UV region with a maximum size near 420 nm. After treatment with a reducing agent, the colloids were characterized by ultraviolet-visible spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy.

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.384-386
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• 2009

This paper introduces an effectively optimized Fuzzy model identification by means of complex and nonlinear system applying PSO algorithm. In other words, we use PSO(Particle Swarm Optimization) for identification of Fuzzy model structure and parameter. PSO is an algorithm that follows a collaborative population-based search model. Each particle of swarm flies around in a multidimensional search space looking for the optimal solution. Then, Particles adjust their position according to their own and their neighboring-particles experience. This paper identifies the premise part parameters and the consequence structures that have many effects on Fuzzy system based on PSO. In the premise parts of the rules, we use triangular. Finally we evaluate the Fuzzy model that is widely used in the standard model of gas data and sew data.

• Structural Engineering and Mechanics
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• v.70 no.5
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• pp.513-524
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• 2019

This study proposed an improved particle swarm optimization (IPSO) method ensemble with kriging model for model updating. By introducing genetic algorithm (GA) and grouping strategy together with elite selection into standard particle optimization (PSO), the IPSO is obtained. Kriging metamodel serves for predicting the structural responses to avoid complex computation via finite element model. The combination of IPSO and kriging model shall provide more accurate searching results and obtain global optimal solution for model updating compared with the PSO, Simulate Annealing PSO (SimuAPSO), BreedPSO and PSOGA. A plane truss structure and ASCE Benchmark frame structure are adopted to verify the proposed approach. The results indicated that the hybrid of kriging model and IPSO could serve for model updating effectively and efficiently. The updating results further illustrated that IPSO can provide superior convergent solutions compared with PSO, SimuAPSO, BreedPSO and PSOGA.