• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.1
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• pp.47-53
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• 2015

In this paper, a novel fluid controlled phase tunable line using inkjet printed microfluidic composite right/left-handed(CRLH) transmission line(TL) is proposed. A CRLH-TL prototype has been inkjet-printed on a paper substrate using silver nano particle ink. In addition, a laser-etched microfluidic channel in poly methyl methacrylate(PMMA) has been integrated with the CRLH TL using inkjet-printed SU-8 as a bonding material. The proposed TL provides excellent phase-tuning capability that is dependent on the different fluidic materials used. As the fluid is changed, the proposed TL can have negative-phase, zero-phase, and positive-phase characteristics at 900 MHz and reflection coefficient is maintained to below -10 dB. The performance of the proposed TL is successfully validated using simulation and measurement results.

• Steel and Composite Structures
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• v.35 no.4
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• pp.463-474
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• 2020

In this paper, the influence of adding multi-walled carbon nanotube (MWCNT) on the pull behavior of steel and GFRP bars in ultra-high-performance concrete (UHPC) was examined experimentally and numerically. For numerical analysis, 3D nonlinear finite element modeling (FEM) with the help of ABAQUS software was used. Mechanical properties of the specimens, including Young's modulus, tensile strength and compressive strength, were extracted from the experimental results of the tests performed on standard cube specimens and for different values of weight percent of MWCNTs. In order to consider more realistic assumptions, the bond between concrete and bar was simulated using adhesive surfaces and Cohesive Zone Model (CZM), whose parameters were obtained by calibrating the results of the finite element model with the experimental results of pullout tests. The accuracy of the results of the finite element model was proved with conducting the pullout experimental test which showed high accuracy of the proposed model. Then, the effect of different parameters such as the material of bar, the diameter of the bar, as well as the weight percent of MWCNT on the bond behavior of bar and UHPC were studied. The results suggest that modifying UHPC with MWCNT improves bond strength between concrete and bar. In MWCNT per 0.01 and 0.3 wt% of MWCNT, the maximum pullout strength of steel bar with a diameter of 16 mm increased by 52.5% and 58.7% compared to the control specimen (UHPC without nanoparticle). Also, this increase in GFRP bars with a diameter of 16 mm was 34.3% and 45%.

• Korean Journal of Materials Research
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• v.28 no.5
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• pp.273-278
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• 2018

Lithium-ion batteries have been considered the most important devices to power mobile or small-sized devices due to their high energy density. $LixCoO_2$ has been studied as a cathode material for the Li-ion battery. However, the limitation of its capacity impedes the development of high capacity cathode materials with Ni, Mn, etc. in them. The substitution of Mn and Ni for Co leads to the formation of solid solution phase $LiNi_xMn_yCo_{1-x-y}O_2$ (NMC, both x and y < 1), which shows better battery performance than unsubstituted $LiCoO_2$. However, despite a high discharge capacity in the Ni-rich compound (Ni > 0.8 in the metal site), poor cycle retention capability still remains to be overcome. In this study, aiming to improve the stability of the physical and chemical bonding, we investigate the stabilization effect of Ca in the Ni-rich layered compound $Li(Ni_{0.83}Co_{0.12}Mn_{0.05})O_2$, and then Ca is added to the modified secondary particles to lower the degree of cationic mixing of the final particles. For the optimization of the final grains added with Ca, the Ca content (x = 0, 2.5, 5.0, 10.0 at.%) versus Li is analyzed.

• Journal of Sensor Science and Technology
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• v.16 no.6
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• pp.457-461
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• 2007

This paper describes the characteristics of poly (polycrystalline) 3C-SiC grown on $SiO_{2}$ and AlN substrates, respectively. The crystallinity and the bonding structure of poly 3C-SiC grown on each substrate were investigated according to various growth temperatures. The crystalline quality of poly 3C-SiC was improved from resulting in decrease of FWHM (full width half maximum) of XRD and FT-IR by increasing the growth temperature. The minimum growth temperature of poly 3C-SiC was $1100^{\circ}C$. The surface chemical composition and the electron mobility of poly 3C-SiC grown on each substrate were investigated by XPS and Hall Effect, respectively. The chemical compositions of surface of poly 3C-SiC films grown on $SiO_{2}$ and AlN were not different. However, their electron mobilities were $7.65{\;}cm^{2}/V.s$ and $14.8{\;}cm^{2}/V.s$, respectively. Therefore, since the electron mobility of poly 3C-SiC films grown on AlN buffer layer was two times higher than that of 3C-SiC/$SiO_{2}$, a AlN film is a suitable material, as buffer layer, for the growth of poly 3C-SiC thin films with excellent properties for M/NEMS applications.

• Restorative Dentistry and Endodontics
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• v.26 no.5
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• pp.399-408
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• 2001

Tooth bleaching has been prevailing recently for its ability to recover the color and shape of natural teeth without reduction of tooth material. However, it has been reported that bleaching procedure adversely affects the adhesive bond strength of composite resin to tooth. At the same time the bond strength was reported to be regained by application of some chemical agents. The purpose of this in vitro study was to investigate the effect of the removal of residual peroxide on the composite- enamel adhesion and also evaluated fracture mode between resin and enamel after bleaching. Sixty extracted human anterior and premolars teeth were divided into 5 groups and bleached by combined technique using of office bleaching with 35 % hydrogen peroxide and matrix bleaching with 10% carbamide peroxide for 4 weeks. After bleaching, the labial surfaces of each tooth were treated with catalase, 70% ethyl alcohol, distilled water and filled with composite resin. Shear bond strength was tested and the fractured surfaces were also examined with SEM. Analysis revealed significantly higher bond strength values. (p＜0.05) for catalase-treated specimens, but water-treated specimens showed reduction of bond strength, alcohol- treated specimens had medium value between the two groups(p＜0.05). The fracture mode was shown that the catalase group and the alcohol group had cohesive failure but the water sprayed group had adhesive failure. It was concluded that the peroxide residues in tooth after bleaching seems to be removed by gradual diffusion and the free radical oxygen from peroxide prevents polymerization by combining catalyst in the resin monomer. Therefore it may be possible to eliminate the adverse effect on the adhesion of composite resin to enamel after bleaching by using water displacement solution or dentin bonding agent including it for effective removal of residual peroxide.

• Clean Technology
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• v.21 no.4
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• pp.235-240
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• 2015

In this study, vanadium dioxide was doped with titanium (0~0.5 at %) to improve thermochromic properties. The titanium doped vanadium dioxide (Ti-VO₂) particles were prepared via thermolysis process using vanadyl sulfate, ammonium bicarbonate and titianium chloride as precursors. The crystal structure, morphology, chemical bonding and thermochromic properties were investigated by using XRD, FE-SEM, XPS, DSC and UV-Vis-NIR spectroscopy. It was found that titanium was successfully doped into the crystal lattice of VO₂ and the obtained Ti-VO₂ particles have monoclinic structure. With increasing Ti concentration, the particle size and phase transition temperature of Ti-VO₂ particles decreased and NIR switching efficiency increased.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1687-1694
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• 2014

Recently FRP of carbon fibers is utilized as a repairing and reinforcing material for concrete structures. In this study, the bond performance between CFRP planks and ductile fiber reinforced cementitious composites was evaluated in order to develop a new system of concrete bridge deck to take advantage of the FRP planks of carbon fiber using as a permanent formwork. In order to strengthen the bonding between the FRP and cast-in-place concrete, an epoxy resin circulated in the market generally was fitted with a silica sand. The bond stress of ordinary concrete appeared in 2.11~5.43MPa and the bond stress of ductile fiber reinforced cementitious composites DC1 (RF4000) and DC2 (PP) respectively were 3.91~5.60MPa, 2.92~5.21MPa and the average bond stress of DC3 (RF4000+RSC15) and DC4 (PP+RSC15) were 4.80~5.58MPa, 5.57~5.89MPa.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.327-341
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• 2017

Openings in slabs are usually required for many different applications such as aeriation ducts and air conditioning. Opening in concrete slabs due to cutouts significantly decrease the member stiffness. There are different techniques to strengthen slabs with opening cutouts. This study presents experimental and numerical investigations on the use of Carbon Fiber Reinforced Polymers (CFRP) as strengthening material to strengthen and restore the load carrying capacity of R.C. slabs after having cutout in the hogging moment region. The experimental program consisted of testing five (oneway spanning R.C. flat slabs) with overhang. All slabs were prismatic, rectangular in cross-section and nominally 2000 mm long, 1000 mm width, and 100 mm thickness with a clear span (distance between supports) of 1200 mm and the overhang length is 700 mm. All slabs were loaded up to 30 kN (45% of ultimate load for reference slab, before yielding of the longitudinal reinforcement), then the load was kept constant during cutting concrete and steel bars (producing cut out). After that operation, slabs were loaded till failure. An analytical study using finite element analysis (FEA) is performed using the commercial software ANSYS. The FEA has been validated and calibrated using the experimental results. The FE model was found to be in a good agreement with the experimental results. The investigated key parameters were slab aspect ratio for the opening ratios of [1:1, 2:1], CFRP layers and the laminates widths, positions for cutouts and the CFRP configurations around cutouts.

• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.253-257
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• 2017

Graphene is a monolayer carbon material which consists of $sp^2$ bonding between carbon atoms. Its excellent intrinsic properties allow graphene to be used in various research fields. Many researchers believe that graphene is suitable for electronic device materials due to its high electrical conductivity and carrier mobility. Through chemical doping, n- or p-type graphene can be obtained, and consequently graphene-based devices which have more comparable structure to common semiconductor-based devices can be fabricated. In our research, we introduced the dielectrophoresis process to the chemical doping step in order to improve the effect of chemical doping of graphene selectively. Under 10 kHz and $5V_{pp}$ (peak-to-peak voltage), doping was conducted and the Au nanoparticles were effectively formed, as well as aligned along the edges of graphene. Effects of the selective chemical doping on graphene were investigated through Raman spectroscopy and the change of its electrical properties were explored. We proposed the method to enhance the doping effect in local region of a graphene layer.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.3
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• pp.379-386
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• 2003

Statement of problem. Resin cements are widely used in adhesive dentistry specially on all ceramic restorations. It is needed to find out adequate bonding strength between different porcelain surface treatments, commercially available porcelains, and different resin cement systems. Purpose. The purpose of this study was to evaluate shear bond strength of resin cements bonded to porcelains in three different modalities; 5 different porcelain surface treatments, 3 different resin cement systems and 3 different commercially available pressable porcelains. Material and Method. This study consisted of 3 parts. Part I examined the effect of five different surface treatments on the pressable porcelain. Fifty discs (5 mm in diameter and 3 mm in height) of Authentic porcelain were randomly divided into 5 groups (n = 10). The specimens were sanded with 320 grit SiC paper followed by 600 grit SiC paper. The specimens were treated as follow: Group 1-Sandblasting (aluminum oxide) only, Group 2 - sandblasting/ silane, Group 3 - sandblasting/ acid etching/ silane, Group 4 - acid etching only, Group 5 - acid etching/ silane. Part II examined the shear bond strength of 3 different resin cement systems (Duolink, Variolink II, Rely X ARC) on acid etching/ silane treated Authentic pressable porcelain. Part 3 examined the shear bond strength of Duolink resin cement on 3 different pressable porcelains (Authentic, Empress I, Finesse). All cemented specimens were stored in distilled water for 2 hours and tested with Ultradent shear bond strength test jig under Universal Instron machine until fracture. An analysis of variance(ANOVA) test was used to evaluate differences in shear bond strength. Result. The shear bond strength test resulted in the following: (1) Acid etched porcelains recorded greater shear bond strength values to the sandblasted porcelains. (2) Silane treated porcelains recorded greater shear bond strength values to non-silane treated porcelains. (3) There was no significant difference between sandblasting/ acid etching/ silane treated and acid etching/ silane treated porcelains. However those values were much higher than other three groups. (4) The shear bond strength with Variolink II was lower than the value of Duolink or Rely X ARC. (5) The shear bond strength of Finesse was lower than the value of Authentic or Empress I.