• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.1013-1017
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• 2012

Advanced composite-sintered bushings are widely utilized in the areas of excavators and injection molding machines as a journal bearing. Since the bearings are mainly used under high loads, service life should be long and the stored oil of inner bushings has to be continually fed into the bearing. The composite-sintered bushings are consisted of the two different materials; outer steel materials and inner porous sintered materials respectively. High temperature diffusion bonding has been applied for holding the both materials of the bushing together. Therefore, it is very important that the bonding reliability has to be assured and evaluated in manufacturing process. Finite element method (FEM) is performed in order to evaluate the minimum allowable flaw sizes that are possibly generated in the composite-sintered bushings. Additionally, the composite-sintered bushings were undergone ultrasonic C-scan tests to find out the size of inherent flaws through artificially simulated UT signal analysis.

• Journal of the Korean Electrochemical Society
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• v.3 no.2
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• pp.109-114
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• 2000

The relation between the phase-shift profile fur the intermediate frequencies and the Langmuir adsorption isotherm at the poly-Ir/0.1 M $H_2SO_4$ aqueous electrolyte interface has been studied using ac impedance measurements, i.e., the phase-shift methods. The simplified interfacial equivalent circuit consists of the serial connection of the electrolyte resistance $(R_s)$, the faradaic resistance $(R_F)$, and the equivalent circuit element $(C_P)$ of the adsorption pseudoca-pacitance $(C_\phi)$. The comparison of the change rates of the $\Delta(-\phi)/{\Delta}E\;and\;\Delta{\theta}/{\Delta}E$ are represented. The delayed phase shift $(\phi)$ depends on both the cathode potential (E) and frequency (f), and is given by $\phi=tan^{-1}[1/2{\pi}f(R_s+R_F)C_P]$. The phase-shift profile $(-\phi\;vs.\;E)$ for the intermediate frequency (ca. 1 Hz) can be used as an experimental method to determine the Langmuir adsorption isotherm $(\theta\;vs.\;E)$. The equilibrium constant (K) for H adsorption and the standard free energy $({\Delta}G_{ads})$ of H adsorption at the poly-Ir/0.1 M $H_2SO_4$ electrolyte interface are $2.0\times10^{-4}$ and 21.1kJ/mol, respectively. The H adsorption is attributed to the over-potentially deposited hydrogen (OPD H).

• Journal of Astronomy and Space Sciences
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• v.24 no.3
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• pp.227-234
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• 2007

A comet that passes extremely close to the Sun at perihelion is called a sungrazing comet (of sungrazer). Around 1270 sungrazing comets have been discovered on coronagraph images from the SOHO (SOlar and Heliospheric Observatory) spacecraft since 1996 up to April, 2007. The major groups orbiting around the Sun in similar orbits are named as Kreutz, Meyer, Marsden, and Kracht 1&2 families. About 85% of SOHO comets belong to the Kreutz family with perihelion on distances of less than about $2{\sim}3R_{\bigodot}$. The distributions of perihelia and the orbital elements of SOHO sungrazing comets are analyzed. We investigated closely spaced pairs and clusters in the orbital element space. Here, we suggest three prospective groups of the sungrazing cornets: [(C/2000 Y6, C/2000 Y7), (C/2000 V4, C/2001 T5), (C/2003 H6, C/2003 H7)].

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.957-959
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• 2005

A noise reduction equipment in power systems was device combined in a passive element such as the form of L, R and C. A analysis of frequency characteristics for the transformer models shall be considered the additional capacitance between the windings($C_{ps}$), terminals($C_s$), and winding-ground($C_g$). A noise in transformer is modeled by take account into the different frequency. In case of the high frequency, transformer windings with stray capacitance have lower impedance. Therefore a noise is transferred from primary winding to secondary winding. Noise Cut Transformer(NCT) was the noise reduction device and was normally single phase two-winding type transformer. We analyzed frequency characteristics using the nodal network analysis with the equivalent circuit and the simulation of the MATLAB.

• Proceedings of the PSK Conference
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• 2003.10b
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• pp.85.3-86
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• 2003

Oltipraz, a cancer chemopreventive agent, induces CYP1A1 to a certain extent by transactivation of the gene via the Ah receptor (AhR)-xenobiotic response element (XRE) pathway. Previously, we showed that oltipraz promoted CCAAT/enhancer binding protein (C/EBP ) activation, which leads to the induction of glutathione S-transferase. Given that oltipraz activates C/EBP for gene transactivation and that the putative C/CBP binding site is located in CY)1A1 promoter region, this study investigated the effect of oltipraz on CYP1A1 induction by 3-methylcholanthrene (3-MC). (omitted)

• Transactions of Materials Processing
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• v.20 no.2
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• pp.146-153
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• 2011

This study aimed at providing an experimental database for the mechanical properties of AZ31B magnesium alloy sheet such as stress-strain curve, yield stress, R-value and forming limit diagram(FLD) at various strain-rates and temperatures. Tensile tests were carried out on specimens having the orientations of $0^{\circ}$, $45^{\circ}$ and $90^{\circ}$ to the rolling direction with different crosshead speeds in the range between 0.008 and 8 mm/s at temperature from 25(room temperature) to $300^{\circ}C$. The influence of the specimen gage length on the tensile properties was investigated. FLD tests were performed at punch speed of 0.1 and 1.0 mm/s in the same temperature range as that of the tensile tests. Swift cup tests were conducted to verify the usefulness of the material database and the reliability of the finite element analysis(FEA). The effects of strain-rate as well as temperature were taken into account in these simulations. It was shown that the FLD-based failure was reasonably well predicted by the thermal-deformation coupled analysis for this rate-sensitive material.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.119-125
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• 2003

A way to measure the second parameter $A_2$of CT specimens is described. The displacement $\delta$$_{5}$ which is measured continuously from visual images of the lateral surface during crack growth is used to calculate the A, as a function of crack growth. The crack length is measured by DCPD(Direct Current Potential Drop) method and the J-resistance curve is determined according to ASTM standard E1737-96. To prove the validity of this method, three dimensional finite element analyses were performed, and variations of the displacements $\delta$$_{5}$ and $A_2$along the thickness were explored. As the result, it has been shown that the $\delta$$_{5}$ measured from the visual images of the lateral surface and the corresponding $A_2$can be regarded as the average through the thickness for 1T and 1/2T specimens of SA106Gr.C steel.steel.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.990-1001
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• 2015

This paper presents analysis of Switched Reluctance Machine (SRM) using Geometry Based Analytical Model (GBAM), Finite Element Analysis (FEA) and Fourier Series Model (FSM) with curve fitting technique. Further a Transient Analysis (TA) technique is proposed to corroborate the analysis. The main aim of this paper is to give in depth procedure in developing a Geometry Based Analytical Model of Switched Reluctance Machine which is very accurate and simple. The GBAM is developed for the specifications obtained from the manufacturer and magnetizing characteristic of the material used for the construction. Precise values of the parameters like Magneto Motive Force (MMF), flux linkage, inductance and torque are obtained for various rotor positions taking into account the Fringing Effect (FE). The FEA model is developed using MagNet7.1.1 for the same machine geometry used in GBAM and the results are compared with GBAM. Further another analytical model called Fourier Series Model is developed to justify the accuracy of the results obtained by the methods GBAM and FEA model. A prototype of microcontroller based SRM drive system is constructed for validating the analysis and the results are reported.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.2
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• pp.289-295
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• 2001

The aim of this study is to investigate the ductile fracture behaviour under pure Mode II loading using A533B pressure vessel steel. Single punch shear(SPS) test was performed to obtain the J-R curve under pure Mode II loading which was compared with that of the Model I loading. Simulation using Rousellier Ductile Damage Theory(RDDT) was carried out with 4-node quadrilateral element(L(sub)c=0.25mm). For the crack advance, the failed element removal technique was adopted with a $\beta$ criterion. Through the $\beta$ value tuning-up procedures, $\beta$(sub)crit(sup)II was determined as 1.5 in contrast with $\beta$(sub)crit(sup)I=5.5. In conclusion, it was found that the J-R curve under Mode II loading was located at lower part than that under Mode I loading obtained from the previous study and that the $\beta$ values strongly depended on the loading type. In addition, the predicted result using RDDT showed a good agreement with the SPS experimental one under pure Mode II loading.

• Bulletin of the Korean Mathematical Society
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• v.54 no.3
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• pp.875-894
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• 2017

Let $[n]=\{1,2,{\ldots},n\}$. A set ${\mathbf{A}}=\{A_1,A_2,{\ldots},A_l\}$ is a minimal cover of [n] if ${\cup}_{1{\leq}i{\leq}l}A_i=[n]$ and $$\bigcup_{{1{\leq}i{\leq}l,}\\{i{\neq}j_0}}A_i{\neq}[n]\text{ for all }j_0{\in}[l]$$. Let ${\mathcal{C}}(n)$ denote the collection of all minimal covers of [n], and write $C_n={\mid}{\mathcal{C}}(n){\mid}$. Let ${\mathbf{A}}{\in}{\mathcal{C}}(n)$. An element $u{\in}[n]$ is critical in ${\mathbf{A}}$ if it appears exactly once in ${\mathbf{A}}$. Two minimal covers ${\mathbf{A}},{\mathbf{B}}{\in}{\mathcal{C}}(n)$ are said to be restricted t-intersecting if they share at least t sets each containing an element which is critical in both ${\mathbf{A}}$ and ${\mathbf{B}}$. A family ${\mathcal{A}}{\subseteq}{\mathcal{C}}(n)$ is said to be restricted t-intersecting if every pair of distinct elements in ${\mathcal{A}}$ are restricted t-intersecting. In this paper, we prove that there exists a constant $n_0=n_0(t)$ depending on t, such that for all $n{\geq}n_0$, if ${\mathcal{A}}{\subseteq}{\mathcal{C}}(n)$ is restricted t-intersecting, then ${\mid}{\mathcal{A}}{\mid}{\leq}{\mathcal{C}}_{n-t}$. Moreover, the bound is attained if and only if ${\mathcal{A}}$ is isomorphic to the family ${\mathcal{D}}_0(t)$ consisting of all minimal covers which contain the singleton parts $\{1\},{\ldots},\{t\}$. A similar result also holds for restricted r-cross intersecting families of minimal covers.