• Corrosion Science and Technology
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• v.9 no.4
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• pp.147-152
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• 2010

Conventional paints for conversion coating applications in steel production derived mainly from water-based polymer dispersions containing several additives actually show good general performance, but suffer from poor scratch and abrasion resistance during use. The reason for this is because the relatively soft organic binder matrix dominates the mechanical surface properties. In order to maintain the high quality and decorative function of coated steel sheets, the mechanical performance of the surface needs to be improved significantly. In fact the wear resistance should be enhanced without affecting the optical appearance of the coatings by using appropriate nanoparticulate additives. In this direction, nanocomposite coating compositions (Nanomer$^{(R)}$) have been derived from water-based polymer dispersions with an increasing amount of surface-modified nanoparticles in aqueous dispersion in order to monitor the effect of degree of filling with rigid nanoparticles. The surface of nanoparticles has been modified for optimum compatibility with the polymer matrix in order to achieve homogeneous nanoparticle dispersion over the matrix. This approach has been extended in such a way that a more expanded hybrid network has been condensed on the nanoparticle surface by a hydrolytic condensation reaction in addition to the quasi-monolayer type small molecular surface modification. It was expected that this additional modification will lead to more intensive cross-linking in coating systems resulting in further improved scratch-resistance compared to simple addition of nanoparticles with quasi-monolayer surface modification. The resulting compositions have been coated on zinc-galvanized steel and cured. The wear resistance and the corrosion protection of the modified coating systems have been tested in dependence on the compositional change, the type of surface modification as well as the mixing conditions with different shear forces. It has been found out that for loading levels up to 50 wt.-% nanoparticles, the mechanical wear resistance remains almost unaffected compared to the unmodified resin. In addition, the corrosion resistance remained unaffected even after $180^{\circ}$ bending test showing that the flexibility of coating was not decreased by nanoparticle addition. Electron microscopy showed that the inorganic nanoparticles do not penetrate into the organic resin droplets during the mixing process but rather formed agglomerates outside the polymer droplet phase resulting in quite moderate cross linking while curing, because of viscosity. The proposed mechanisms of composite formation and cross linking could explain the poor effect regarding improvement of mechanical wear resistance and help to set up new synthesis strategies for improved nanocomposite morphologies, which should provide increased wear resistance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1438-1443
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• 2001

The significance of the casting/forging process for reducing the production cost of large components is being noted in these days. This casting/forging process is a method of forging a workpiece preformed by casting into the final shape. In this study, the casting/forging process has been applied in manufacturing a large aluminum flange in order to reduce press capacity and material cost. Firstly, a hot compression test was performed with cast cylindrical billets in order to determine the optimum forging condition of the aluminum flange. The optimum range of forging temperature of Al 5083 was from 420$\^{C}$ to 450$\^{C}$. The suitable strain rate was 1.5 sec(sup)-1. The deformation amount of a preform of a preform in a forging process is a key role in the mechanical properties of casting/forging products. In order to find the change of mechanical properties according to effective stain of cast aluminum billets, a hot upsetting test were performed with rectangular blocks and then a uniaxial tensile test was performed with specimens cut from the upsetted billets. The tensile strength and the elongation of cast/upsetted aluminum billets were increased largely until the effective strain was 0.7. FE analysis was performed to determine the configurations of case preform and die for an aluminum flange. In the FE analysis, the forging load-limit was fixed 1500ton for low equipment cost. The cast preform was designed so that the effective stain around the neck of a flange exceeded 0.7. From the result of FE analysis, optimal configurations of the cast preform and the die were designed for a large flange. The filling and solidification analysis for a sound cast-preform was carried out with MAGMA soft. In the forging experiment for an aluminum flange, it was confirmed that the optimal configuration of the cast preform predicted by FE analysis was very useful. The cast/forged products using designed preform were made perfectly without any defects.

• Membrane Journal
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• v.28 no.5
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• pp.307-319
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• 2018

Ion-exchange membrane (IEM) has fixed charge groups and is a separation membrane which is capable of selectively transporting ions of the opposite polarity. Recently, the interest in IEMs has been increasing as the importance of the desalination and energy conversion processes using them as the key components has increased. Since the IEMs determine the efficiency of the above process, it is necessary to improve the separation performance and durability of them and also to lower the expensive membrane price, which is a hindrance to the widening application of the IEM process. Therefore, it is urgent to develop high-performance and low-cost IEMs. Among various types of IEMs, pore-filled membranes prepared by filling ionomer into a porous polymer substrate are intermediate forms of homogeneous membranes and heterogeneous membranes. The production cost would be cheap like the case of heterogeneous membranes because of the use of inexpensive supports and the reduction of the amount used of raw materials, and at the same time, they exhibit excellent electrochemical characteristics close to homogeneous membranes. In this review, major research and development trends of pore-filled IEMs, which are attracting attention as high-performance and low-cost IEMs, have been summarized and reported according to the application fields.

• Atmosphere
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• v.16 no.2
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• pp.97-110
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• 2006

This study investigates the response of a typhoon model to the change of the sea surface temperature (SST) throughout the model integration. The SST change is parameterized as a formulae of which the magnitude is given as a function of not only the intensity and the size but the moving speed of tropical cyclone. The formulae is constructed by referring to many previous observational and numerical studies on the SST cooling with the passage of tropical cyclones. Since the parameterized cooling formulae is based on the mathematical expression, the resemblance between the prescribed SST cooling and the observed one during the period of the numerical experiment is not complete nor satisfactory. The agreements between the prescribed and the observed SST even over the swath of the typhoon passage differ from case to case. Numerical experiments are undertaken with and without prescribing the SST cooling. The results with the SST cooling do not show clear evidence in improving the track prediction compared to those of the without-experiments. SST cooling in the model shows its swath along the incomplete simulated track so that the magnitude and the distribution of the sea surface cooling does not resemble completely with the observed one. However, we have observed a little improvement in the intensity prediction in terms of the central pressure of the tropical cyclone in some cases. In case where the model without the SST treatment is not able to yield a correct prediction of the filling of the tropical cyclone especially in the decaying stage, the pulling effect given by the SST cooling alleviates the over-deepening of the model so that the central pressure approaches toward the observed value. However, the opposite case when the SST treatment makes the prediction worse may also be possible. In general when the sea surface temperature is reduced, the amount of the sensible and the latent heat from the ocean surface become also reduced, which results in the weakening of the storms comparing to the constant SST case. It turns out to be the case also in our experiments. The weakening is realized in the central pressure, maximum wind, horizontal temperature gradient, etc.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.1
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• pp.19-29
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• 2002

The purpose of this study was to compare the polymerization shrinkage and the compressive strength of composite and compomer cured with two different light sources ; conventional halogen-light curing unit and recently-developed plasma arc curing unit. The 'strain gauge method' was used for determination of polymerization shrinkage and the compressive strength was measured by universal testing machine. The results of the present study can be summarized as follows: 1. Filling materials in polyethylene molds showed the initial expansion in the early phase of polymerization. This was followed by the rapid contraction in volume during the first 60 seconds and gradually diminished as curing process continued. 2. The polymerization shrinkage in tooth samples was generally lower than in the mold samples. 3. The generally lower amount of linear polymerization shrinkage was observed in compomer and plasma arc curing unit group when compared to composite and conventional curing unit. 4. The higher compressive strength values was found in composite groups regardless curing methods. The results of this study strongly support the application of plasma arc system and fluoride-containing compomer in the field of clinical pediatric dentistry claiming its effectiveness in curing the esthetic dental materials and the anticariogenic capacity.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.1
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• pp.1-10
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• 2002

The purpose of this study was to evaluate the fluoride release and anticariogenic effect of two compomers which is known to have been developed to improve the weak properties of glass ionomer cement and composite resin. Z-100 as composite resin(Group I), Dyract AP(Group II) and F-2000(Group III) as compomer, and Fuji II LC as glass ionomer cement(Group IV) were used as test materials and evaluations were peformed by pH/ISE meter far analyses of fluoride and polarizing microscope for analyses of anticariogenicity. The results can be summarized as follows: 1. The amount of fluoride release in compoite resin and compomer groups showed general pattern of decline during test period. Z-100 showed no fluoride release during test period. Fuji II LC showed the highest fluoride release among test groups and then F-2000 were followed. 2. The least resistance to dimineralization was observed microscopically in Z-100 group which has no fluoride in it. The best resistance to dimineralization was observed microscopically in Fuji II LC group and then compomer groups were followed. 3. Significant difference in lesion area was found between Fuji II LC group and another groups. Significant difference in lesion area was found between compomer groups and Z-100 group. No significant difference in lesion area was found between Dyract AP group and F-2000 cup. 4. Two compomers showed continual fluoride release and anticariogenic effect around filling materials. therefore, compomer was evaluated very attractive restorative material in pediatric dentistry.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.6
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• pp.485-493
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• 2017

In this study, the collision analysis of SCP(Sandwich Concrete Panel) composing the outer tank of LNG storage was performed and its collision behavior was analyzed. For the same collision energy value proposed in BS7777 code, the collision conditions are composed by using two types of missiles and various collision speeds. Nonlinear dynamic analysis models were constructed to perform numerical analysis on the various collision conditions. Also, the collision behavior was analyzed assuming that the second collision with the same collision energy occurs at the same point after the first collision. As a result of the analysis, it was found that with smaller missile and low collision speed had caused larger deformation. The collision energy dissipated in ratio of about 6: 4 in the outer steel plate and the inner filling concrete. In the results of double collision analysis, the final collisional deformation was dominated by the size of the second missile, and the amount of deformation due to the second collision was smaller than that of the first collision because of the membrane behavior of the steel plates. In the offset double collision cases, the largest deformation occurs at the secondary collision point regardless of the offset distance.

• Land and Housing Review
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• v.1 no.1
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• pp.35-42
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• 2010

Most of the dredged sand generated from the sewage pipe maintenance project and the government's four-river project are disposed depending on abandonment and filling-up. This is caused by the lack of related recycling technology using dredged sand appropriately and high absorption rate and micro-particles of dredged sand producted from existing sand production system. Thus, this study carried out a quality assessment for the dredged sand produced through the optimum washing and sorting system supplementing problems of existing dredged sand production system as a part of research to examine performance of removing micro-particles and foreign substances. As a result of the assessment, the dredged sand produced through the cleaning and sorting system showed a wide quality improvement effect in absorption rate, 0.08 mm sieve pass amount, clay lump volume and organic impurity content, and it turned out to satisfy both the quality standards of this study, KS F 2573(recycled aggregate for concrete) and KS F 2526(aggregate for concrete) so it could be confirmed that it would be able to be used as an aggregate for concrete in the future.

• Korean Journal of Medicinal Crop Science
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• v.5 no.2
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• pp.108-112
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• 1997

This experiment was carried out to clarify the effect of cultural years on the growth and yield of Fritillaria thunbergii. It was planted on Middle September, with high ridge between $100cm\;(2 lines){\times}interrow 9cm$ and N-P-K=8.1-11.2-8kg/10a of fertilizers treated basal application. Cultural years were 1, 2 and 3 years, the block of 2 or 3 years was additional same amount of fertilizers at early spring. The results were summarized are as follows. Rapid bulb filling stage was begun 32 days after sprouting, and completed bulb growth needed 72 days. Dry weight/fresh ratio of bulb was ranged from $27.2{\sim}30.3$%. Rate of over 5g bulb weight was 89% at 1 year, 87% at 2 years and 77% at 3 years and bulb yield were 638kg/10a at 1 year. Compared with yield at 1 year, the yield increased 88% at 2 years and 189% at 3 years.

• The Journal of the Petrological Society of Korea
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• v.27 no.4
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• pp.195-205
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• 2018

Noerok is a green pigment made of mineral used the Gachil(priming coat) of wooden architecture in Chosun Dynasty era. It has been reported that various Noerok are discovered in Janggimyeon, Pohang. In this study, The Noerok from two places is compared and discussed. Noerok in the two places has blulsh-green to green color, and it is similar to their occurrences on fracture filling, vein and dike on outcrop. However, there are differences between two sites according to its petrological feature, mineral composition and geochemistry. While the Noeseongsan sample is mostly celadonite, Gwangjeongsan samples are characterized by celadonite with varying contents of cristobalite, tridymite, feldspar, along with some vitrified contents. In terms of major elements, the amount of $Al_2O_3$, $Fe_2O_3$, MgO and $K_2O$ decreases linearly with increasing $SiO_2$, whereas $Fe_2O_3$ is linearly proportional to MgO. In summary, Noerok in the study areas can be classified into 4 types (type 1, type 2, type 3-1, type 3-2) base on color, mineral composition, elemental composition, and vitrification grade.