• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1700-1711
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• 2015

In the last decade it has been witnessed significant developments in the area of nano particles and nano scale fillers on electrical, thermal, and mechanical properties of polymeric materials such as resins, varnishes, enamel and bakelites. The electric and thermal properties were more important in the electrical equipments for both steady state and transient state conditions. This paper deals with the characterization of the electric and thermal properties of the pure varnish and zirconia (ZrO₂) filler mixed varnish. The electric properties such as dielectric loss (tan δ), dielectric constant (ε), dielectric strength and partial discharge voltage were analyzed and detailed for different samples. It was observed that zirconia nano filler mixed varnish has the superior dielectric and thermal properties when compared to those of standard varnish. It has shown that at power frequency the 1wt% nano composite sample has the higher permittivity value when compared to other samples. It has been examined that the 1wt% sample was having higher inception and extinction voltages when compared to other samples. It has been observed that 1wt% sample has higher dielectric strength when compared with other samples. There has been an improvement of thermal property by adding few weight percent of zirconia nano fillers. There was not much variation in glass transition among the nano mixed composites. The weight loss was improved at 1wt% of the zirconia nano fillers.

• Korean Journal of Food Science and Technology
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• v.23 no.6
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• pp.750-754
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• 1991

The perceived intensities of Cheddar cheese flavor were investigated in terms of cheese processing conditions and types of panels participated. The mean intensities of sensory properties for Cheddar cheese were higher in untrained panels compared to those in trained panels. There are significant differences in Cheddar cheese flavor between six-month and eight-month ripening. Cheddar cheese ripening at 1$13^{\circ}C$ resulted in positive effects on sensory attributes compared to ripening at $8^{\circ}C$. The addition of lactobacilli as starter culture caused an increase of sharpness and a decrease of bitterness. Sharpness and bitterness were not related to other cheese sensory properties, and revealed a positive relationship each other. Cheese acidity was negatively related to rancidity and fruitiness.

• Polymer(Korea)
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• v.37 no.3
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• pp.399-404
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• 2013

In order to develop the blends with good long-term thermal stability and tensile elongation, the blends of polyphenylene sulfide (PPS) and 7 kinds of elastomer were tested. PPS/elastomer (90/10, 80/20, 70/30) blend samples were prepared by compression molding after twin screw extrusion or punching after sheet extrusion. Rheological, mechanical property and morphology of the blends were analyzed by capillary rheometer, UTM, impact tester, and SEM. For long-term thermal stability tests, the mechanical properties were measured again after the samples were stored in a convection oven for a week. The tensile strengths were almost same regardless of kinds of elastomer and the tensile elongation was the maximum for the PPS/m-EVA blend. As the content of elastomer increased, the elongation increased but delamination occurred at 30 wt% of elastomer content. The tensile strength increased but the elongation decreased seriously after thermal aging. Many problems related with PPS processing could be solved by adding a small amount of the elastomers partially compatibile with PPS and it would be applicable to develop various PPS grades.

• The Korea Journal of Herbology
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• v.30 no.4
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• pp.1-9
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• 2015

Objectives : The present study was under taken to characterize chemical composition, antioxidant and cyto-protecting capacity of essential oil obtained from leaves of Liriodendron tulipifera L. Methods : Essential oil from the leafof L. tulipifera L. (EOLL) was extracted by hydro-distillation process and further its chemical composition was evaluated by GC-MS analysis. The in vitro antioxidant potential of the EOLL was determined by DPPH ^●, ABTS ^●+, superoxide and nitric oxide free radical scavenging activity using different concentrations in the range of 50-800 μg/mL. In addition, cyto-protecting property of the EOLLwas determined by MTT assay on Raw 264.7 macrophage cells challenged with hydrogen peroxide (H ₂ O ₂ ). Results : The result of GC-MS analysis showed presence of 34 volatile compounds, principally germacrene D, spathulenol, and α -cadinol in EOLL. The in vitro antioxidant assays of EOLL at the highest used concentration of 800 μg/mL showed 81.62, 84.29, 83.59 and 58.59% inhibition of DPPH ^●, ABTS ^●+, superoxide, and nitric oxide radicals, respectively. It also showed ferric reducing ability with 1310.04 mM Fe (II)/g of essential oil. The EOLL at three different concentrations (200, 400 and 800 μg/mL) protected the cells from H ₂ O ₂ -induced cell damage through scavenging intracellular ROS. Conclusion : The findings from the study suggest that essential oil isolated from leaves of L tulipifera L. is a potent sources of natural antioxidants, which could be used to treat the diseases associated with oxidative stress condition.

• Composites Research
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• v.28 no.3
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• pp.130-135
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• 2015

This study investigates the property of graphene filled polymer nanocomposites in LEO(Low Earth orbit) environment conditions. In order to improve compatibility with polymer matrices and resistance of carbon material against AO(Atomic oxygen) attack, silanization of graphene oxide with organosilane was carried out. The corresponding moieties were characterized through X-ray photoelectron spectroscopy (XPS). Graphene oxide filled nanocomposites were prepared using solution based processing methods. The sets of specimen series were tested in an accelerated LEO simulated space environment facility. Graphene oxide and silane treated graphene oxide reinforced nanocomposites were compared with neat epoxy. The comparison revealed that the silane treated graphene filled polymer composite shows inherent resistance against atomic oxygen attack while the lack of silane treatment resulted in a reduction in performance.

• The Korea Journal of Herbology
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• v.23 no.4
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• pp.81-89
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• 2008

Objectives: In this study, the pharmacological effects of the ethylacetate extract of Ostericum koreanum(North Kangwhal; NK) on allergic inflammation were investigated in activated human mast cells. Methods: North Kangwhal was extracted with 80% methanol for 24 h, and then fractionated with ethylacetate(NK-EtOAc extract). HMC-1 cells, an human mast line, were pre-incubated with different concentrations of NK-EtOAc extract for 30 min, and then stimulated with PMA(50 nM/ml) and A23187($1{\mu}M/ml$) at indicated times. The cell toxicity was determined by MTT assay. The concentrations of prostaglandin E2(PGE2) and cytokines(TNF-${\alpha}$, IL-8) were measured by enzyme-linked immunosorbant assay. Results: NK-EtOAc extract($10{\sim}50{\mu}g/ml$) significantly inhibited the productions of $PGE_2$, TNF-${\alpha}$ and IL-8 in PMA/A23187-stimulated HMC-1 cells without cell toxicity($0{\sim}50{\mu}g/ml$). NK-EtOAc extract also inhibited PMA/A23187-induced phosphorylation of ERK1/2 MAPK and the NF-${\kappa}B$ p65 subunit translocation into the nuclear of HMC-1 cells. Conclusions: This study suggests that NK-EtOAc extract may have an anti-inflammatory property through suppressing the production of inflammatory mediators in activated mast cells and its molecular mechanism underlies the blocking of NF-${\kappa}B$ pathway.

• Journal of the Korean institute of surface engineering
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• v.41 no.4
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• pp.147-155
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• 2008

The dental orthodontic wire provides a good combination of strength, corrosion resistance and moderate cost. The purpose of this study was to investigate the effects of TiN and ZrN coating on corrosion resistance and physical property of orthodontic wire using various instruments. Wires(round type and rectangular type) were used, respectively, for experiment. Ion plating was carried out for wire using Ti and Zr coating materials with nitrogen gas. Ion plated surface of each specimen was observed with field emission scanning electron microscopy(FE-SEM), energy dispersive X-ray spectroscopy(EDS), atomic force microscopy(AFM), vickers hardness tester, and electrochemical tester. The surface of TiN and ZrN coated wire was more smooth than that of other kinds of non-coated wire. TiN and ZrN coated surface showed higher hardness than that of non-coated surface. The corrosion potential of the TiN coated wire was comparatively high. The current density of TiN coated wire was smaller than that of non-coated wire in 0.9% NaCl solution. Pit nucleated at scratch of wire. The pitting corrosion resistance $|E_{pit}-E_{rep}|$ increased in the order of ZrN coated(300 mV), TiN coated(120 mV) and non-coated wire(0 mV).

• Composites Research
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• v.30 no.6
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• pp.371-378
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• 2017

In this study, hygroelastic behavior of thermosetting epoxy is predicted by molecular dynamics simulations. Since consistent exposures to humid environments lead to macroscopic degradation of polymer composite, computational simulation study of the hygroscopically aged epoxy cell is essential for long-time durability. Therefore, we modeled amorphous epoxy molecular unit cell structures at a crosslinking ratio of 30, 90% and with the moisture weight fraction of 0, 4 wt% respectively. Diglycidyl ether of bisphenol F (EPON862) and triethylenetetramine (TETA) are chosen as resin and curing agent respectively. Incorporating equilibrium and non-equilibrium ensemble simulation with a classical interatomic potential, various hygroelastic properties including diffusion coefficient of water, coefficient of moisture expansion (CME), stress-strain curve and elastic modulus are predicted. To establish the structural property relationship of pure epoxy, free volume and internal non-bond potential energy of epoxy are examined.

• The Korean Journal of Applied Statistics
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• v.18 no.1
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• pp.83-98
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• 2005

Exploring distributional patterns of multivariate data is very essential in understanding the characteristics of given data set, as well as in building plausible models for the data. For that purpose, low-dimensional visualization methods have been developed by many researchers along various directions. As one of methods, Kohonen's SOM (Self-Organizing Map) is prominent. SOM compresses the volume of the data, yields abstraction from the data and offers visual display on low-dimensional grids. Although it is proven quite effective, it has one undesirable property: SOM's display is discrete. In this study, we propose two techniques for enhancing quality of SOM's display, so that SOM's display becomes continuous. The proposed methods are demonstrated in two numerical examples.

• Journal of Welding and Joining
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• v.31 no.1
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• pp.58-64
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• 2013

The following results were obtained, microstructures and tensile properties in arc brazed joints of DP(dual phase) steel using Cu-5.3wt%Sn insert metal was investigated as function of brazing current. 1) The Fusion Zone was composed of ${\alpha}Fe+{\gamma}Cu$ and Cu23Sn2. The reason for the formation of these solid solutions. Despite, Fe & Cu were impossible to solid solution at room temperature. It's melting & reaction to something of insert metal & Base Metal (DP Steel) by Arc. Brazing Process has faster cooling rate then Cast Process, Supersaturated solid solution at room temperature. 2) The increase Hardness of Fusion Zone was directly proportional to the rise of welding current. Because, ${\alpha}Fe+{\gamma}Cu$ phase (higher hardness than the Cu23Sn2.(104.1Hv < 271.9Hv)) Volume fraction was Growth, due to increasing the amount of base metal melting by High current. 3) The results of tensile shear test by Brazing, All specimens happen to fracture in Fusion Zone. On the other hand, when Brazing Current increasing tend to rise tensile load. but it was very small, about 26-30% of the base metal. 4) The result of fracture analysis, The crack initiate at Triple Point for meet to Upper B.M/Under B.M/Fusion Zone. This Crack propagated to Fusion zone. So ruptured by tensile strength. The Reason to in the fusion zone fracture, Fusion zone by Brazing of hardness (strength) was very lower then the base metal (DP steel). In addition the Fusion Zone's thickness in triple point was thin than the base metal's thickness in triple point.