• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.12
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• pp.597-600
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• 2002

Film Bulk Acoustic wave Resonator (FBAR) using thin piezoelectric films can be made as monolithic integrated devices with compatibility to semiconductor process, leading to small size and low cost, high Q RF circuit elements with wide applications in communications area. This paper presents a MMIC compatible suspended FBAR using surface micromachining. Membrane is composed $Si_3N_4SiO_2Si _3N_4$ multi layer and air gap is about 50${\mu}{\textrm}{m}$. Firstly, We perform one dimensional simulation applying transmission line theorem to verify resonance characteristic of the FBAR. Process of the FBAR is used MEMS technology. Fabricated FBAR resonate at 2.4GHz, $K^2_{eff}$ and Q are 4.1% and 1100.

• Journal of the Korean Mathematical Society
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• v.47 no.5
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• pp.967-983
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• 2010

Let M be an n-dimensional complete simply connected Riemannian manifold with sectional curvature bounded above by a nonpositive constant $-{\kappa}^2$. Using the cone total curvature TC($\Gamma$) of a graph $\Gamma$ which was introduced by Gulliver and Yamada [8], we prove that the density at any point of a soap film-like surface $\Sigma$ spanning a graph $\Gamma\;\subset\;M$ is less than or equal to $\frac{1}{2\pi}\{TC(\Gamma)-{\kappa}^2Area(p{\times}\Gamma)\}$. From this density estimate we obtain the regularity theorems for soap film-like surfaces spanning graphs with small total curvature. In particular, when n = 3, this density estimate implies that if $TC(\Gamma)$ < $3.649{\pi}\;+\;{\kappa}^2\inf\limits_{p{\in}F}Area(p{\times}{\Gamma})$, then the only possible singularities of a piecewise smooth (M, 0, $\delta$)-minimizing set $\Sigma$ are the Y-singularity cone. In a manifold with sectional curvature bounded above by $b^2$ and diameter bounded by $\pi$/b, we obtain similar results for any soap film-like surfaces spanning a graph with the corresponding bound on cone total curvature.

• The Journal of Advanced Prosthodontics
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• v.4 no.1
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• pp.24-29
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• 2012

PURPOSE. To compare the effect of sodium hypochlorite and microwave disinfection on the dimensional stability of denture bases without and with relining. MATERIALS AND METHODS. A brass die was prepared by simulating an edentulous maxillary arch. It was used to fabricate 1.5 mm and 3 mm of thickness denture bases (n = 40). The 1.5 mm of thickness-specimens (n = 20) were relined with 1.5 mm of autopolymerizing relining resin. Five holes were prepared over crest of ridge of brass die with intimately fitting stainless steel pins which were transferred to the intaglio surface of specimens during fabrication of denture bases. For calculation of dimensional changes in denture bases, differences between the baseline area before and after disinfection of the specimens were used. The denture bases without and with relining were divided into 2 groups (each n =20). Data were analyzed using student paired 't'and unpaired 't'test. RESULTS. Microwave disinfection produces significant shrinkage in both denture bases without relining (t =17.16; P<.001) and with relining (t = 14.9; P<.001). Denture bases without relining showed more shrinkage when compared with relined denture bases after microwave disinfection (t = 6.09; P<.001). The changes in dimensional stability after sodium hypochlorite disinfection were not significant for both denture bases without relining (t = 2.19; P=.056) and denture bases with relining (t = 2.17; P=.058). CONCLUSION. Microwave disinfection leads to increased shrinkage of denture bases without and with relining. Chemical disinfection with sodium hypochlorite seems to be a safer method of disinfection with regards to physical properties such as changes in dimensional stability.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.634-638
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• 2011

We report growth of epitaxial AlN thin films on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. To achieve two-dimensional growth the substrates were nitrided by nitrogen plasma prior to the AlN growth, which resulted in the formation of a two-dimensional single crystalline AlN layer. The formation of the two-dimensional AlN layer by the nitridation process was confirmed by the observation of streaky reflection high energy electron diffraction (RHEED) patterns. The growth of AlN thin films was performed on the nitrided AlN layer by changing the Al beam flux with the fixed nitrogen flux at 860$^{\circ}C$. The growth mode of AlN films was also affected by the beam flux. By increasing the Al beam flux, two-dimensional growth of AlN films was favored, and a very flat surface with a root mean square roughness of 0.196 nm (for the 2 ${\mu}m$ ${\times}$ 2 ${\mu}m$ area) was obtained. Interestingly, additional diffraction lines were observed for the two-dimensionally grown AlN films, which were probably caused by the Al adlayer, which was similar to a report of Ga adlayer in the two-dimensional growth of GaN. Al droplets were observed in the sample grown with a higher Al beam flux after cooling to room temperature, which resulted from the excessive Al flux.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.4
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• pp.405-420
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• 2003

Purpose : The purpose of this study was to compare the fracture resistance of the IPS Empress ceramic crown with 1.0mm width rounded shoulder, which is usually recommended in all ceramic crown. and 0.5mm width chamfer finish lines on the maxillary central incisor. Material and method : After 15 metal dies were made for each group, the IPS Empress all ceramic crowns were fabricated and cemented with resin cement(Bistite resin cement, Tokuyama Soda Co. LTD., Japan) on the metal die. The cemented crowns were mounted on the positioning jig and the universal testing machine(Zwick Z020, Zwick Co. Germany)was used to measure the fracture strength with loading on the incisal edge. And also, three-dimensional finite element stress analysis was used to measure the stress distribution with the various types of the finish lines(1.0mm width rounded shoulder, 0.5mm width chamfer), the loading site(incisal edge, incisal $\frac{1}{3}$) and the type of loading(concentration loading, distribution loading). Results and conclusion : 1. In the fracture resistance experiment according to the finish line, the mean fracture strength of rounded shoulder(876N) and the mean fracture strength of chamfer(882N) did not skew any significant difference between each other(p>0.05). 2. The stress distribution of all ceramic crown in three dimensional finite element analysis showed concentration aspect at loading point and cervical area or labial surface. 3. In metal die, there were no differences in stress distribution between finish lines, but in natural teeth model, chamfer finish line showed higher stress than rounded shoulder finish line. 4. When force was loaded on the incisal edge the stress was concentrated on the incisal edge and the cervical area of labial surface. When force was loaded on the incisal $\frac{1}{3}$, the stress concentrated on the cervical area of labial surface and the cingulum area. 5. Generally, natural teeth model showed higher and various stress than the metal die.

• Economic and Environmental Geology
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• v.13 no.3
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• pp.141-158
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• 1980

A geologic structure could be formed through various processes, because there are a number of factors which control the deformation of the Earth's crust. In geology, we could call it geological epistemology to describe exactly a geologic structure, and call it geological logics to infer logically the deforming process through which the geologic structure had been formed. Degree of legitimacy of geological logics depends upon the degree of exactness of geological epistemology. This study described quantitatively 3-dimensional Hambaek Syncline through computer analysis, and examined qualitatively into its deforming mechanism based on the results of 3-dimensional analysis of the structure. Input data for the computer analysis are dips and dip directions of bedding planes of the structure. The Hambaek Syncline disclose a minor fold group of NE-SW or NNE-SSW trend and a large scale fold of E-W trend. The conclusions of this study are as follows: (1) The fold of E-W trend is primary fold $(F_1)$ and the minor fold group of NE-SW or NNE-SSW trend secondary fold $(F_2)$. (2) Hambaek Syncline is cylindrical type fold. (3) Apparent axial trace of Hambaek syncline does not coincide with true axial trace. The apparent axial trace is $N70^{\circ}-80^{\circ}W$ in Gohan and Sabuk area, and changes to $N70^{\circ}-80^{\circ}E$ in the westward of the area, while the true axial trace is $N40^{\circ}-70^{\circ}W$ in the former, and $N60^{\circ}-80^{\circ}E$ in the latter area. (4) Westward dipping of axial plane of the minor fold group of NE-SW or NNE-SSW trend can be attributed to simple shear movements along overthrusts. (5) Angle between axial trace and the directional trace of the maximum principal compressive stress $({\sigma}_1)$ may not be perpendicular each other. The angle between them is governed by the following factors; 1) the plunge of fold axis 2) the dip of axial surface 3) cylindrisity (6) The mean axial trace of Hambaek Syncline $(F_1)$ is $N45.6^{\circ}W$, and the directional trace of ${\sigma}_1$ is $N52.4^{\circ}E$ (7) The mean axial trace of the minor fold group of NE-SW or NNE-SSW trend $(F_2)$ is $N21^{\circ}E$, and the directional trace of ${\sigma}_1$ is $N22^{\circ}W$.

• Nuclear Engineering and Technology
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• v.39 no.4
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• pp.313-326
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• 2007

In this paper, an algorithm to reconstruct two orthogonal images into a three-dimensional image is developed in order to measure the bubble size and volume in a two-phase boiling flow. The central-active contour model originally proposed by P. $Szczypi\'{n}ski$ and P. Strumillo is modified to reduce the dependence on the initial reference point and to increase the contour stability. The modified model is then applied to the algorithm to extract the object boundary. This improved central contour model could be applied to obscure objects using a variable threshold value. The extracted boundaries from each image are merged into a three-dimensional image through the developed algorithm. It is shown that the object reconstructed using the developed algorithm is very similar or identical to the real object. Various values such as volume and surface area are calculated for the reconstructed images and the developed algorithm is qualitatively verified using real images from rubber clay experiments and quantitatively verified by simulation using imaginary images. Finally, the developed algorithm is applied to measure the size and volume of vapor bubbles condensing in a subcooled boiling flow.

• Bulletin of the Korean Chemical Society
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• v.16 no.6
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• pp.493-498
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• 1995

Ultrathin networks of itaconic acid copolymers and poly(allylamine) were produced by a Langmuir-Blodgett (LB) technique employing a double-chain amine as a monolayer template which was subsequently removed by extraction after thermal crosslinking. Itaconic acid copolymers used were copoly (itaconic acid-ethyl vinyl ether) and copoly (itaconic acid-n-butyl vinyl ether). The polyion-complexed monolayers of three components consisting of template amine, itaconic acid copolymer and poly (allylamine) were formed at the air-water interface. The Langmuir film properties have been studied by the surface pressure-area isotherm and fluorescence microscopy. The monolayers were transferred on solid substrates and were characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy (SEM). Two-dimensional polymer networks were formed through imide or amide linkages by heat treatment under vacuum. The heat-treated films were extracted with chloroform after immersion in aq. sodium chloride to remove the template amines. SEM observation of a LB film on a porous fluorocarbon membrane filter with pore diameter of 0.1 μm showed covering of the pores by six layers in the polyion complex state.

• Membrane Journal
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• v.29 no.1
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• pp.30-36
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• 2019

In this study, we reported a solid-state supercapacitor consisting of titanium nitride (TiN) nanofiber and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS) conducting polymer electrode and poly(vinyl alcohol) (PVA)-based polymer electrolyte membrane. The TiN nanofiber was selected as electrode materials due to high electron conductivity and 2-dimensional structure which is beneficial for scaffold effect. PEDOT-PSS is suitable for organic/inorganic composites due to good redox reaction with hydrogen ions in electrolyte and good dispersion in solution. By synergetic effect of TiN nanofiber and PEDOT-PSS, the PEDOT-PSS/TiN electrode showed higher surface area than the flat Ti foil substrate. The PVA-based polymer electrolyte membrane could prevent leakage and explosion problem of conventional liquid electrolyte and possess high specific capacitance due to the fast ion diffusion of small $H^+$ ions. The specific capacitance of PEDOT-PSS/TiN supercapacitor reached 75 F/g, which was much higher than that of conventional carbon-based supercapacitors.

• Korean Journal of Materials Research
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• v.19 no.10
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• pp.562-568
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• 2009

Electrospinning is a technique that produces sub-micron sized continuous fibers by electric force from polymer solutions or melts. Due to its versatile manufacturability and the cost effectiveness, this method has been recently adopted for the fabrication of one-dimensional materials. Here, we fabricated polyacrylonitrile (PAN) polymer fibers, from which uniform carbon fibers with diameters of 100-200 nm were obtained after carbonization at 800 $^{\circ}C$ in N$_2$. Special emphasis was directed to the influence of the phase separated polymer solution on the morphology and the microstructure of the resulting carbon fiber. The addition of poly(stylene-co-acrylonitile) (SAN) makes the polymer solution phase separated, which allows for the formation of internal pores by its selective elimination after electrospinning. XPS and Raman Spectroscopy were used to confirm the surface composition and the degree of carbonization. At the PAN:SAN = 50:50 in vol%, the uniform carbon fibers with diameters of 300$\sim$500 nm and surface area of 131.6 m$^2$g$^{-1}$ were obtained.