• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.5
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• pp.421-427
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• 2014

Most of the structure of the real world is influenced under dynamic loads. However, when structure analysis and the structural optimization is performed, it is assumed that the static load acts on structure. When considering the actual load of dynamic loads in order to take into account a variety of loads, computational resources and time becomes a big burden in terms of cost. However, considering only the simple static load condition is not preferable for structural safety. For this reason, a lot of studies have been conducted trying to compensate this trouble by applying weight factor or replacing dynamic load with the equivalent static load. In this study, structural optimization techniques for structures under dynamic loads is proposed by applying the equivalent static load. From previous study, after determining the positions of equivalent static load based on primary degrees of freedom, the equivalent static load is calculated through the optimization process. In this process, the equivalent static load optimization of previous research is complemented by adding constraints to avoid excessively large load extraction. In numerical examples, dynamic load is applied to the truss structure and the plate. Then, the reliability of the proposed optimization technique is verified by carrying out size optimization with the equivalent static load.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.266-271
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• 2004

A very small amount of SiO$_2$ was locally added in sintered BaTiO$_3$ ceramics and then heat-treated at 135$0^{\circ}C$. In the region where SiO$_2$ was not added, grain growth occurred very slowly. In the region where a very small amount of SiO$_2$ was added, however, grain growth occurred very actively. After long time annealing at 135$0^{\circ}C$, abnormal grains appeared only in the part where SiO$_2$ was added and grew up to 2 cm in size. In the grown abnormal grains or single crystals, (111) double or single twins were not observed. The growth of abnormal grains or single crystals was explained by formation of liquid phase in the region where SiO$_2$ was added. These results showed that centimeter-sized BaTiO$_3$ single crystals without (111) double or single twins could be fabricated by using abnormal grain growth.

• Journal of the Korean Magnetics Society
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• v.17 no.1
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• pp.43-46
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• 2007

The samples were synthesized by using a solid state reaction. The X-ray diffraction pattern for $Ti_{0.96}Co_{0.02}Fe_{0.02}O_2$ showed a pure rutile phase with tetragonal structures. Mixtures of the proper proportions of the elements sealed in evacuated quartz ampoule were heated at $870{\sim}930^{\circ}C$ for one day and then slowly cooled down to room temperature at a rate of $10^{\circ}C/h$. In order to obtain single phase material, it was necessary to grind the sample after the first firing and to press the powders into pellets before annealing them for a second time in evacuated and sealed quartz ampoule. Magnetic properties have been investigated using the vibrating sample magnetometer(VSM). Room temperature magnetic hysteresis(M-H) curve showed an obvious ferromagnetic behavior and the magnetic moment per Fe atom under the applied of 0.8T was estimated to be about $1.3{\mu}_B/CoFe$. But the magnetic moment per Fe atom under the applied of 0.8T was estimated to be about $0.02{\mu}_B/CoFe$ without Ti-getter.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.7
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• pp.1-9
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• 2012

In this paper, resistance temperature detector (RTD) integrated into the LED package is proposed in order to solve the temperature dependence of LED's optical properties. To measure the package temperature in real time, the RTD type temperature sensor having excellent accuracy and linearity between temperature change and resistance change was adopted. A stable metallic film is required for long term reliability and stability of the RTD type temperature sensor. Therefore, deposition and annealing condition for the film were determined. Based on the determined condition, the RTD type temperature sensor with the sensitivity of about $1.560{\Omega}/^{\circ}C$ was fabricated inside the LED package. In order to configurate the LED package system keeping the constant brightness regardless of the temperature, additional conversion circuit and control circuit boards were fabricated and added to the fabricated LED package. The proposed system was designed to compensate the light intensity caused by temperature change using the variable duty rate of driving current. As a result, the duty rate of PWM signal which is the output signal of the configurated system was changed with the temperature change, and the duty rate was similarly varied with the target duty rate. Consequently, it was focused the fabricated RTD can be used for compensating the optical properties of LED and the LED package which exhibits constant brightness regardless of the temperature change.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.425-431
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• 2015

LNG (liquefied natural gas) is considered the best alternative eco-fuel, and many studies on the LNG fuel system have been performed to use LNG as the fuel for ships. For the LNG fuel supply system, natural gas transfers from the vaporizer to the engine in the gaseous state with a temperature of $50^{\circ}C$ and a pressure of 35MPa. Therefore, a structural safety evaluation of the double-walled pipelines considering thermal load is essential. In this article, an uniaxial tensile test for super duplex stainless steel, material for double-walled pipe, according to the annealing time was carried out to analyze the thermal effect. In addition, thermo-structural analysis of the high temperature-high pressure double-walled pipe with fixed supports that are now used widely was carried out to evaluate the structural safety. To minimize stress concentration of the connection point between the support and inner pipe, the shapes of the new type support that can slip through inner pipe were proposed, and the supports which has best structural performance was selected using the results from the thermo-structural analyses of new supports and an analysis of the whole double-walled pipeline was performed to ensure structural safety. These results can be used as a database for the design of double-walled pipelines and sliding support.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.829-834
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• 2002

Ferroelectric properties of $ErMnO_3$ thin films deposited on Si(100) substrate using Sol-gel process with metal salts were investigated. $ErMnO_3$ thin films with a (001) preferred orientation were crystallized at 800$^{\circ}C$. The $ErMnO_3$ thin film post-annealed at 800$^{\circ}C$ for 1 h showed the dielectric constant(k) of 26 and the dielectric loss(tan ${\delta}$) of 0.032 at the frequency range from 1 to 100 KHz. The grain size of $ErMnO_3$ thin film post-annealed at 800 for 1 h was 10∼30 nm. The remanent polarization($P_r$) of the $ErMnO_3$ thin films increased with increasing (001) preferred orientation. The $ErMnO_3$ thin films post-annealed at 800$^{\circ}C$ for 1 h showed the remanent polarization($P_r$) of 400 nC/$cm^2$, with the increase of post-annealing time at 800$^{\circ}C$, the coercive field($E_c$) of thin films was lowered because the dense and homogeneous thin films were obtained.

• Journal of Sensor Science and Technology
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• v.8 no.3
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• pp.283-290
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• 1999

The $n^+/p/p^+$ junction PERL solar cell of $0.1{\sim}2{\Omega}{\cdot}cm$ (100) p type silicon wafer was fabricated through the following steps; that is, wafer cutting, inverted pyramidally textured surfaces etching by KOH, phosphorus and boron diffusion, anti-reflection coating, grid formation and contact annealing. At this time, the optical characteristics of device surface and the efficiency of doping concentration for resistivity were investigated. And diffusion depth and doping concentration for n+ doping were simulated by silvaco program. Then their results were compared with measured results. Under the illumination of AM (air mass)1.5, $100\;mW/cm^2$ $I_{sc}$, $V_{oc}$, fill factor and the conversion efficiency were 43mA, 0.6 V, 0.62. and 16% respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.131-131
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• 2013

A single-layer graphene has been uniformly grown on a Cu surface at elevated temperatures by thermally processing a poly(methyl methacrylate) (PMMA) film in a rapid thermal annealing (RTA) system under vacuum. The detailed chemistry of the transition from solid-state carbon to graphene on the catalytic Cu surface was investigated by performing in-situ residual gas analysis while PMMA/Cu-foil samples being heated, in conjunction with interrupted growth studies to reconstruct ex-situ the heating process. The data clearly show that the formation of graphene occurs with hydrocarbon molecules vaporized from PMMA, such as methane and/or methyl radicals, as precursors rather than by the direct graphitization of solid-state carbon. We also found that the temperature for vaporizing hydrocarbon molecules from PMMA and the length of time the gaseous hydrocarbon atmosphere is maintained, which are dependent on both the heating temperature profile and the amount of a solid carbon feedstock are the dominant factors to determine the crystalline quality of the resulting graphene film. Under optimal growth conditions, the PMMA-derived graphene was found to have a carrier (hole) mobility as high as ~2,700 cm2V-1s-1 at room temperature, superior to common graphene converted from solid carbon.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.288-294
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• 1999

In the flip chip interconnection using solder bump, the Under Bump Metallurgy (UBM) is required to perform multiple functions in its conversion of an aluminum bond pad to a solderable surface. In this study, various UBM systems such as $Al 1\mu\textrm{m} / Ti 0.2\mu\textrm{m} / Cu 5\mu\textrm{m}, Al 1\mu\textrm{m} / Ti 0.2\mu\textrm{m} / Cu 1\mu\textrm{m}, al 1\mu\textrm{m}/Ni 0.2\mu\textrm{m} / Cu 1\mu\textrm{m} and Al 1\mu\textrm{m}/Pd 0.2\mu\textrm{m} / Cu 1\mu\textrm{m}$ for flip chip interconnection using the low melting point eutectic 63Sn-37Pb solder were investigated and compared to their metallurgical properties. $100\mu\textrm{m}$ size bumps were prepared for using an electroplating process. The effects of the number of reflows and aging time on the growth of intermetallic compounds(IMC) were investigated. $Cu_6Sn_5$ and $Cu_3Sn$ IMC were abserved after aging treatment in the UBM system with thick coper $(Al 1\mu\textrm{m}/Ti 0.2\mu\textrm{m}/Cu 5\mu\textrm{m})$. However only the $Cu_6Sn_5$ was detected in the UBM system with $1\mu\textrm{m}$ thick copper even after 2 reflow and 7 day aging at $150^{\circ}C$. Complete Cu consumption by Cu-Sn IMC growth gives rise to a direct contact between solder inner layer such as Ti, Ni and Pd, and hence to possibly cause reactions between two of them. In this study, however, only for the Pd case, IMC of PdSn. was observed by Cu consumption. UBM interfacial reactions with s이der affected the adhesion strength ot s이der balls after s이der reflow and annealing treatment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.6
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• pp.496-500
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• 2019

In this study, we investigate the effect of an Sb-deficiency on the thermoelectric properties of double-filled n-type skutterudite ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$). Samples were prepared by encapsulated induction melting, consecutive long-time annealing, and finally spark plasma sintering processes. The Sb-deficient sample contained a $CoSb_2$ secondary phase. Both the double-filled n-type skutterudite pristine and Sb-deficient samples showed metallic behavior in electrical conductivity with increasing temperature. The carrier concentration of the Sb-deficient sample decreased compared with that of the pristine sample. Due to a decrease in carrier concentration, the Sb deficient sample showed decreased electrical conductivity and an increased Seebeck coefficient compared with the conductivity and coefficient of the pristine sample. Furthermore, the Sb deficient sample showed an increase in the power factor (${\sigma}{\cdot}S^2$); the power factor maximum shifted to athe lower temperature side than ones of the pristine sample. As a result, the Sb-deficient sample represents an improved average figure of merit (ZT) and a $ZT_{max}$ temperature lower than that of the pristine sample. Therefore, we propose that Sb-deficient double-filled n-type skutterudite thermoelectric material ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$) be used in the 573~673 K temperature range.