• Membrane Journal
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• v.14 no.2
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• pp.173-184
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• 2004

For the application of direct methanol fuel cell (DMFC), sulfonated polystyrene/teflon (PS/PTFE) composite membranes were developed by changing monomer ratio of styrene and DVB. The composite membranes were prepared as follows: first, the monomer mixtures consisting of styrene, divinyl benzene and AIBN were impregnated in porous PTFE film and then, polymerized under 8$0^{\circ}C$ to give PS/PTFE membranes. Finally, the membranes were reacted with chlorosulfonic acid in 1,2-dichloroethane to give the sulfonated composite membranes. The measurements of ATR-FTIR, SEM, solvent uptake test and ion exchange capacity (IEC) were done for the resulting membranes before or after sulfonation, respectively, which showed the composite membranes with proper crosslinking degree and sulfonic acid content were prepared well as a function of styrene/DVB ratio. ion conductivity and methanol permeability were studied for the sulfonated membranes. It was found that with decreasing the ratio of styrene/DVB, methanol permeability decreased from $6.6{\times}10^{-7}∼1.3{\timas}10^{-7}$ $\textrm{cm}^2$/s, which are much lower values than that of Nafion$^{(R)}$117($1.02{\times}10^{-6}$ $\textrm{cm}^2$/s). Under the same monomer condition, ion conductivity decreased from 0.11 S/cm ($25^{\circ}C$) to 0.08 S/cm ($25^{\circ}C$), which are similar or a little higher values compared with $Nafion^{(R)}117 (1.02{\times}10^{-6}$ $\textrm{cm}^2$/s, 0.0824 S/cm). These two results confirmed the composite membranes prepared could be applied successfully to DMFC.C.

• 전자공학회논문지 IE
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• v.46 no.3
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• pp.6-11
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• 2009

In this paper, manufactured composite nanofiber by electrospinning that make spinning solvent according to weight of PAN/PVdF. PVdF content of composite nanofiber decreases, diameter of fiber decreased. Result that measure contact angle to confirm hydrophile property of PAN/PVdF composite nanofiber, PVdF content increases, could confirm that contact angle with water increases. After leave filter measurement sample for 25 hours in temperature of $40^{\circ}C$, humidity of 85%, result PAN/PVdF composite nanofiber that estimate efficiency could confirm that display performance of HEPA more than 99.95% and ULPA more than 99.999%. And fiber diameter is small, could confirm that filter performance increases. Tensile strength of bulk of PAN/PVdF composite nanofiber was 5-8MPa, expansion 100-300%. And strength and expansion could know that increase according as PVdF's content increases. Tensile strength was 3-8MPa degree after annealing PAN/PVdF composite nanofiber during 2 hours in 120t. Tensile strength was no change almost by annealing, and expansion could know that decrease.

• Restorative Dentistry and Endodontics
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• v.36 no.4
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• pp.324-335
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• 2011

Objectives: This study investigated the effects of the color components of light-cured composite resin before and after polymerization on degree of conversion (DC) and biaxial flexural strength (FS). Materials and Methods: Four enamel shades (A1, A2, A3, A4) and two dentin shades (A2O, A3O) of Premisa (Kerr Co.) and Denfil (Vericom Co.) were evaluated on their CIE $L^*,\;a^*,\;b^*$ color components using the spectrophotometer before curing, after curing and at 7 day. The DC of same specimens were measured with Near-infrared spectrometer (Nexus, Thermo Nicolet Co.) at 2 hr after cure and at 7 day. Finally, the FS was obtained after all the other measurements were completed at 7 day. The correlations between each color component and DC and FS were evaluated. Results: The light-curing of composite resin resulted in color changes of Premisa in red-blue direction and Denfil in green-blue direction. The DC and FS were affected by product, time and shade (3-way ANOVA, p < 0.05) and product and shade (2-way ANOVA, p < 0.05), respectively. Premisa only showed a significant correlation between the DC and CIE $a^*$ component - before and after polymerization (Pearson product moment correlation, p < 0.05). The FS of Premisa showed significant negative correlations with CIE $a^*$ and CIE $b^*$ components. Conclusions: The DC and FS of the light-curing composite resin were affected by the color components of the material before and after polymerization.

• International Journal of Ocean System Engineering
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• v.2 no.3
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• pp.185-194
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• 2012

A Macroscopic combination of two or more distinct materials is commonly referred to as a "Composite Material", having been designed mechanically and chemically superior in function and characteristic than its individual constituent materials. Composite materials are used not only for aerospace and military, but also heavily used in boat/ship building and general composite industries which we are seeing increasingly more. Regardless of the various applications for composite materials, the industry is still limited and requires better fabrication technology and methodology in order to expand and grow. An example of this is that the majority of fabrication facilities nearby still use an antiquated wet lay-up process where fabrication still requires manual hand labor in a 3D environment impeding productivity of composite product design advancement. As an expert in the advanced composites field, I have developed fabrication skills with the use of machinery based on my past composite experience. In autumn 2011, the Korea government confirmed to fund my project. It is the development of a composite sanding machine. I began development of this semi-robotic prototype beginning in 2009. It has possibilities of replacing or augmenting the exhaustive and difficult jobs performed by human hands, such as sanding, grinding, blasting, and polishing in most often, very awkward conditions, and is also will boost productivity, improve surface quality, cut abrasive costs, eliminate vibration injuries, and protect workers from exposure to dust and airborne contamination. Ease of control and operation of the equipment in or outside of the sanding room is a key benefit to end-users. It will prove to be much more economical than normal robotics and minimize errors that commonly occur in factories. The key components and their technologies are a 360 degree rotational shoulder and a wrist that is controlled under PLC controller and joystick manual mode. Development on both of the key modules is complete and are now operational. The Korean government fund boosted my development and I expect to complete full scale development no later than 3rd quarter 2012. Even with the advantages of composite materials, there is still the need to repair or to maintain composite products with a higher level of technology. I have learned many composite repair skills on composite airframe since many composite fabrication skills including repair, requires training for non aerospace applications. The wind energy market is now requiring much larger blades in order to generate more electrical energy for wind farms. One single blade is commonly 50 meters or longer now. When a wind blade becomes damaged from external forces, on-site repair is required on the columns even under strong wind and freezing temperature conditions. In order to correctly obtain polymerization, the repair must be performed on the damaged area within a very limited time. The use of pre-impregnated glass fabric and heating silicone pad and a hot bonder acting precise heating control are surely required.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.774-781
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• 2002

Shear behaviors of eight dapped ends of four full-scale domestic single-tee slabs were evaluated. The dapped ends with 10cm topping concrete were designed based on live load requirements for the domestic parking lot of m 500kgf/㎡ and for the large market of 1,200 kgf/㎡. All specimens were designed by the ACI 318-99 design. The variations of the experiment were the shape of hanger reinforcements as followings: 1) general PCI design method(currently used in domestic), 2) 90 degree bent-up, 3) 60 degree bent-up. All experiments were conducted with 1.2 m shear span. The results obtained in this study were 1) all specimens fully complied with the shear strength requirements as specified by ACI 318-99 except for one strand bond slip specimen, 2)a specimen with the 60 degree bent up hanger reinforcing detail showed the best shear behaviors under full service and ultimate load, and 3)a specimen with the 90 degree bent up hanger reinforcing detail resulted in the worst shear behaviors.

• Restorative Dentistry and Endodontics
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• v.21 no.1
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• pp.254-266
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• 1996

The purpose of this study was to evaluate the degree of marginal leakage that is made by wet bonding to dentin and dissolution of dentinal collagen layer in vivo and in vitro. Class V cavities were prepared to 32 cat's canine teeth and they were randomly assigned into the following 4 groups : Group 1 (not acid conditioned) ; Group 2 (acid-conditioned and blot-dried) ; Group 3 (acid-conditioned and air-dried for 30 seconds) ; Group 4 (acid-conditioned and retreated with 10% NaOCl solution). The acetone-based primer and bonding agent of All Bond 2(Bisco Inc., U.S.A.) and composite resin(Z-100, 3M. Dent. Prod., U.S.A.) were then applied. The resin collar and cap attached to each specimen and 50% silver nitrate solution was placed inside the resin cap for 3 hours. After the canine tooth was resected in level of cervical third, specimens were highly polished and observed the degree of the dye penetration on incisal and gingival margins. The results were as follows ; 1. There was no significant difference of marginal leakage in all the groups between in vivo and in vitro. 2. In vivo, the degree of leakage on the gingival margin showed the lowerest in group 4 and followed by group 2, 3 and group 1 with ascending order. However, there was no statistical difference among all the groups(p>0.05). 3. In vitro, the degree of leakage on the gingival margin showed the lowerest in group 2 and followed by group 4, 3 and group 1 with ascending order. However, there was no significant difference among the experimental groups(p>0.05). 4. The marginal leakage of the incisal margin in vitro was significantly higher in group 1 than the remaining groups(p<0.05).

• Culinary science and hospitality research
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• v.24 no.1
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• pp.140-150
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• 2018

In this study, effects of microground coffee on the quality characteristics and acceptability of instant coffee with probiotics were investigated. A central composite design with two factors (roasting degree and dose of microground coffee) was used and ranges of roasting degree and dose were 30~50 (L value) and 5~10% respectively. Aroma preference, sweetness intensity, bitterness intensity, acidity intensity, body intensity and overall acceptability were evaluated as sensory characteristics and quadratic regression models of all the properties were significant. Especially in aroma preference and overall acceptability, the higher roasting degree and dose of microground coffee, the more aroma preference and overall acceptability of the coffee increased. And this results accorded with the object of this study to increase aroma preference and overall acceptability by blending microground coffee with instant coffee. On the other hand, 129 of aroma compounds were detected in instant coffee with microground coffee but 2,5-dimethyl-pyrazine, ethyl-pyrazine and furfural were significant in quadratic regression models. The optimal conditions were predicted by response surface methodology and desirability function approach and the optimal conditions of roasting degree and dose of microground coffee were 30(L value), 8.4%(w/w) respectively to maximize 2 sensory characteristics (overall preference, aroma preference) and 3 aroma components (2,5-dimethyl-pyrazine, ethyl-pyrazine, furfural).

• Journal of Magnetics
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• v.20 no.4
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• pp.353-359
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• 2015

Dielectric properties of $xBaTiO_3-(1-x)CoFe_2O_4$ composite materials have been investigated. Dielectric properties of $BaTiO_3$, $CoFe_2O_4$ and $0.5BaTiO_3-0.5CoFe_2O_4$ samples show frequency dependence, which is classified as relaxor behavior with different relaxing degree. The relaxor behaviors were described using the modified Curier-Weiss and Vogel-Fulcher laws. Among three above samples, the $BaTiO_3$ sample has highest relaxing degree. Photoluminescence spectral indicated defects, which might in turn control relaxing degree.

• Preventive Nutrition and Food Science
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• v.15 no.4
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• pp.316-321
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• 2010

Krill byproduct was hydrolyzed with Alcalase 2.4L to produce functional ingredients for high antioxidative activities against 1,1-dimethyl-2-picryl-hydrazyl (DPPH) radical and Fe. The objective of this study was to investigate the optimum condition for degree of hydrolysis and antioxidative activity of enzymatic hydrolysate produced with the commercial Alcalase using response surface methodology (RSM) with a central composite rotatable design (CCRD). The ranges of independent variables were pH 7.6~10.4 for initial pH and $50.9{\sim}79.1^{\circ}C$ for hydrolysis temperature and their dependent variables were degree of hydrolysis, Brix, amount of phenolic compounds, DPPH-scavenging activity and Fe-chelating activity. RSM with CCRD was well designed to investigate the optimum condition for functional ingredients with high antioxidative activities using Alcalase 2.4L because of their high $R^2$ values of the range of 0.93~0.99 except the $R^2$ value of 0.50 for the amount of total phenolic compounds. The optimum hydrolysis conditions were pH 9.5 and $62^{\circ}C$ for degree of hydrolysis (DH) and pH 9.1 and $64^{\circ}C$ for DPPH-scavenging activity by response surface methodology. The yield of DH and DPPH-scavenging activity were $14.1{\pm}0.5%$ and $10.5{\pm}0.2%$, respectively. It is advantageous to determine the optimum hydrolysis conditions of krill and its by-products for the creation of different kinds of food products, as well as to increase the usage of marine protein sources.

• Steel and Composite Structures
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• v.25 no.1
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• pp.79-92
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• 2017

Initial damage to a stud due to corrosion, fatigue, unexpected overloading, a weld defect or other factors could degrade the shear capacity of the stud. Based on typical push-out tests, a FEM model and theoretical formulations were proposed in this study. Six specimens with the same geometric dimensions were tested to investigate the effect of the damage degree and location on the static behavior and shear capacity of stud shear connectors. The test results indicated that a reduction of up to 36.6% and 62.9% of the section area of the shank could result in a dropping rate of 7.9% and 57.2%, respectively, compared to the standard specimen shear capacity. Numerical analysis was performed to simulate the push-out test and validated against test results. A parametrical study was performed to further investigate the damage degree and location on the shear capacity of studs based on the proposed numerical model. It was demonstrated that the shear capacity was not sensitive to the damage degree when the damage section was located at 0.5d, where d is the shank diameter, from the stud root, even if the stud had a significant reduction in area. Finally, a theoretical formula with a reduction factor K was proposed to consider the reduction of the shear capacity due to the presence of initial damage. Calculating K was accomplished in two ways: a linear relationship and a square relationship with the damage degree corresponding to the shear capacity dominated by the section area and the nominal diameter of the damaged stud. This coefficient was applied using Eurocode 4, AASHTO LRFD (2014) and GB50017-2003 (2003) and compared with the test results found in the literature. It was found that the proposed method produced good predictions of the shear capacity of stud shear connectors with initial damage.