• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.347-354
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• 2013

Recently, crushed fine aggregates are being widely used due to the shortage of natural sand. In Korea, the amount of fine particles under 0.08 mm contained in crushed fine aggregates is restricted to be less than 7%, which is similar to the regulations of ASTM but is still very strict compared to the regulations of the other nations. In addition, the crushed aggregates already have in them about 20% of fine particles under 0.08 mm which occurs while they are crushed. The fine particles are not easy to wash out, and also to maximize the use of resources it is deemed necessary to review the possibility of enhancing the limit of the amount of fine particles. Therefore, this study conducted experiments to analyze the characteristics of fine particles under 0.08mm and their influence on the properties of concrete. Experiments using silt and cohesive soil were also done for comparison. In the experiments on fine particles, the methylene blue value was more in the soil dust contained in silt and cohesive soil than in the stone powder contained in crushed fine aggregates. Also, the methylene blue value had a close correlation with packing density and liquid & plastic limit. In the experiments done with concrete, the quantity of high range water reducing agent demanded to obtain the same slump increased as the fine particle substitution rate heightened. However, in the experiment which used stone powder testing the compressive strength and tensile strength of concrete in the same water-cement ratio, there was little change in strength with less than 20% addition of fine particles among the fine aggregates, and no meaningful difference in the amount of drying shrinkage of concrete.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.47-54
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• 2006

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomena are negligible. However, the terms of effective stresses are divided into the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by ${\alpha}$ parameters and ${\beta}$ exponents that are experimentally determined. The ${\beta}$ exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the ${\alpha}$ parameters are changed by contact behaviors among particles, material properties of particles, and type of packing (i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies by using bender elements. Results show the shear wave velocity depends on the stress-induced anisotropy for round particles. Furthermore, the shear wave velocity is dependent on particle alignment under the constant evvective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully estimated and used for the design and construction of geotechnical structures.

• Electrical & Electronic Materials
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• v.10 no.5
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• pp.440-446
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• 1997

This research has been performed for the fabrication of high quality ferrite plastic magnet. The magnetic properties of S $r_{5.9}$F $e_2$ $O_3$ ferrite bonded magnets by injection moulding with a variety of applied magnetic field were investigated. 0.3wt% CaCO3, 0.2wt% $SiO_2$, 0.5wt% $Al_2$ $O_3$and 0.5wt% N $a_2$ $SiO_3$are added in order to improve the magnetic properties of Sr-ferrite plastic magnets during the powder fabrication. For carbon coating on chemical compound specimen, 5wt% polyvinyl alcohol is added, and then calcinated under $N_2$ environment of 12$25^{\circ}C$. The particle size is distributed from 0.9~1.2${\mu}{\textrm}{m}$ which approximates to the single domain. The obtained Sr ferrite powder is well mixed with silane coupling and calcium stearate of 1wt%. Nest, the specimen is pelleted after kneading each of them with polyamidel2 as a binder. When the temperature of injection and mould were 25$0^{\circ}C$ and 8$0^{\circ}C$ respectively at injection pressure of 200kgf/$\textrm{cm}^2$, the degree of orientation was 85.3% under the applied magnetic field of 12kOe. As the results, when the packing density of Sr ferrite powder was 90wt%, the magnetic properties of Sr ferrite bonded magnet were follows : $_{B}$ $H_{c}$=2.41kOe, Br=3.1kG, (BH)$_{max}$=2.21MgOe. Especially, the Sr-ferrite bonded magnet with 10wt% N $d_2$F $e_{14}$B additive were as follows : $_{B}$ $H_{c}$=2.57kOe, Br=3.14kG and (BH)$_{max}$=2.39MGOe.GOe.GOe.GOe.e.

• Journal of the Korean Applied Science and Technology
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• v.29 no.2
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• pp.317-322
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• 2012

The microstructures were examined by SEM, FT-IR spectra, tensible properties mole % of [NCO/OH], and particle size analyzer. Growing concerns in the environment-friendly industries have led to the development of solvent-free formulations that can be cured. We had synthesized the polyurethane resin having the ability to protect stainless steel against corrosion. Compared with general packing materials and coatings, this resin is highly stronger in intensity and longer durability. Polyurethane resins were composed of polyols, IPDI, silicone surfactant, catalyst and crosslink agent. Moreover, thermal fillers such as $Al_2O_3$, fume silica and $ZrO_2$ not only accelerated the curing rate but also improved the physical property as thermal barriers. The rigid segments of polyurethane in mechanical properties were due to crosslink agent and the increase of [NCO/OH]. In conclusion, the polyurethane microstructure with crosslink agent can be good material for themoset coating of metal substrates such as stainless steel.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.17 no.4
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• pp.365-378
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• 1995

Allogeneic bone grafting has recently been used in oral and maxillofacial regions to restore the cosmetic and functional problem. There are several types of allogeneic bone grafts ; bone powder, bone chips, bone blocks. Empirically, it is thought to be better to combine the allogeneic bone chips to any type of tissue adhesive not to displace during packing and condensing. But, there are no reports about using tissue adhesive in allogeneic bone grafting. This experimental study is designed to investigate the effect of the fibrin adhesive on bone healing process after demineralized allogeneic bone grafting in 60 rats. In control groups (30 rats), routine demineralized allogeneic bone grafting were done in 7 ${\times}$ 7mm calvarial bone defects which were drilled intentioally. And we used the fibrin adhesive for holding the bone particle in experimental groups (30 rats). Each experimental specimen was sacrified at 1, 2, 4, 6, 8 weeks postoperatively The results were as follows : 1. The degree of inflammatory cell infiltrations were more prominent in experimental than in control groups till 2 weeks. 2. Early fibroblast proliferation and new capillary proliferation were uncorporated around graft sites in the experimental groups later than in control groups at early stages. 3. Osteoblastic activity in control group was more prominent at 2 weeks. 4. Osteoblastic activity in experimental groups was more prominent than in control group till 4 weeks. 5. New bone formation was more in control group than experimental group till 3 weeks, but similar appearance after that time. As above results, initial bone healing within 2 weeks were more processed in without adhesive group than with adhesive group. But above 4 weeks; similar bone healing were observed.

• Carbon letters
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• v.8 no.4
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• pp.326-334
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• 2007

In this study, graphite composites were fabricated by warm press molding method to realize commercialization of PEM fuel cells. Graphite composites have been considered as alternative economic materials for bipolar plate of PEM fuel cells. Graphite powder that enables to provide electrical conductivity was selected as the main substance. The graphite powder was mixed with phenolic resin and the mixture was pressed using a warm press method. First of all, the graphite powder was pulverized with a ball mill for the dense packing of composite. As the ball milling time increases, the average size of particles decreases and the size distribution becomes narrow. This allows for improvement of the uniformity of graphite composite. However, the surface electrical resistivity of graphite composite increases as the ball milling time increases. It is due to that graphite particles with amorphous phase are generated on the surface due to the friction and collision of particles during pulverizing. We found that the contact electrical resistivity of graphite particles increases as the particle size decreases. The contact electrical resistivity of graphite powders was reduced due to high molding pressure by warm press molding. This leads to improvement of the mechanical properties of graphite composite. Hydrogen gas impermeability was measured with the graphite composite, showing a possibility of the application for bipolar plate in fuel cell. And, I-V curves of the graphite composite bipolar plate exhibit a similar performance to the graphite bipolar plate.

• Journal of the Korean Applied Science and Technology
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• v.31 no.2
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• pp.238-243
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• 2014

The mechanical properties of NATM resin were measured by SEM, FT-IR spectra, tensile properties, mole ％ of [NCO/OH], and particle size analyzer on stainless steel. Growing concerns in the environment-friendly NATM resin, we have synthesized the solvent-free NATM resin to be coating on metals such as stainless. The properties of the synthesized NATM resin to be contained polyols, MDI, silicone surfactant, fillers and crosslink agents(diethyltoluene diamine, anhydrosorbitol), that they have highly stronger in intensity and longer durability than general NATM resin to be contained polyols, IPDI, silicone surfactant, fillers in general packing materials and coatings. The rigid segments of polyurethane in mechanical properties of coatings were due to cross linkage and the increase mole % of [NCO/OH]. In conclusion, the NATM microstructure with cross linkage can be good material for coating of anticorrosion of metal substrates such as stainless steel.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1069-1074
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• 2008

In this work, we made a study for the 3D SAM formation of octanethiol, decanethiol, and dodecanethiol on copper nanoparticles and we verified stability of the copper particle depending on the ratio of dodecanethiol to copper. The reaction was performed in a one-phase system under nitrogen atmosphere and the thiolated copper particles could be obtained by centrifugation. We could confirm that the nanoparticles consisted of a spherical shape of 3~6 nm from TEM images. FT-IR, XPS and TGA results showed that alkanethiols were chemisorbed via thiol group and the packing density of the alkanethiols on copper surface increased with the alkyl chain lengths. XRD patterns gave us useful information about superlattice formations. Finally, $Cu_2O$ was formed when the molar ratio of dodecanethiol to copper is less than unity and copper nanoparticles formed more compact 3D SAMs when the molar ratio of dodecanethiol to copper was 1.25.

• Polymer(Korea)
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• v.27 no.6
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• pp.528-535
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• 2003

The effects of surfactants, organic solvents, and functional monomers on the emulsion polymerization of perfluoroalkyleoylacryaltes and n-alkylacrylates were investigated. In particular, the dependence of the surface properties, contact angle and water repellency on the crystal melting temperature (T$\_$m/) of the fluorocopolymer and the variation of polymer latex particle sizes was investigated. Using WAXD experiments and synthesizing different types of fluorocopolymers which have fallowing fluoroacrylaytes [CH$_2$=CHCO$_2$CH,$_2$(CF$_2$CF$_2$) nH] (n = 4, 5 or 6), the relationship between the molecular packing structure of pendent side groups of fluorocopolymers and the surface properties was also investigated. We observed that the structure of primary carbon atoms of pendent side groups of fluorocopolymers plays key role in determining the surface properties.s.

• Polymer(Korea)
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• v.35 no.4
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• pp.325-331
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• 2011

Molecular simulations via the molecular dynamics method have been carried out to an equation of state of penetrable-sphere model fluids over a wide range of packing fraction ${\phi}$ and finite repulsive energy ${\varepsilon}^*$. The resulting simulation data are compared to theoretical predictions from the two limiting cases of high- and low-penetrability approximations available in the literature. A good agreement between theoretical and simulation results is observed ill the case of ${\varepsilon}^*$ <3.0. However, for the highly repulsive energy systems of ${\varepsilon}^*{\geqq}3.0$, where the potential energy barrier is more than two times higher than the particle kinetic energy, a poor agreement is found due to the clustering formation and the non-continuum size effects in the dense systems of ${\phi}{\geqq}0.7$ and ${\varepsilon}^*$=6.0.