• Composites Research
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• v.30 no.6
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• pp.350-355
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• 2017

The new liquid crystalline (LC) epoxy was designed by substituting the phenylcyclohexyl (PCH) mesogen moiety with an alkyl chain at the 2,5 position of the diglycidyl terephthalate. The mesomorphic properties were evaluated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). All LC epoxy derivatives exhibited an enantiotropic smectic phase upon heating and cooling process. The LC phase temperature range was widened by mixing the eutectic mixture of LC epoxies. Interestingly, the cured LC epoxy exhibited the highest thermal conductivity of $0.4W{\cdot}m^{-1}{\cdot}K^{-1}$. The novel LC epoxy with high thermal conductivity might be used as a composite material for electronic and display devices.

• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.215-220
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• 2015

Phase evolution, microstructure, and microwave dielectric properties of $Li_2O$ and $Al_2O_3$ doped $Zn_{1.9}Si_{1.05}O_4$, i.e., $Zn_{1.9-2x}Li_xAl_x-Si_{1.05}O_4$, ceramics (x = 0.02 ~ 0.10) were investigated. The ceramics were densified by $SiO_2$-rich liquid phase composed of the Li-Al-Si-O system, indicating that doped Li and Al contributed to the formation of the liquid. As the secondary phase, ${\beta}$-spodumene solid solution with the composition of $LiAlSi_3O_8$ was precipitated from the liquid during the cooling process. The dense ceramics were obtained for the specimens of $$x{\geq_-}0.06$$ showing the rapid densification above $1000^{\circ}C$, implying that a certain amount of liquid is necessary to densify. The specimen of x = 0.06 sintered at $1050^{\circ}C$ exhibited good microwave dielectric properties; the dielectric constant and the quality factor ($Q{\times}f_0$) were 6.4 and 11,213 GHz, respectively.

• Journal of Navigation and Port Research
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• v.33 no.5
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• pp.303-308
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• 2009

Recently, unmanned systems have been studied and developed in various areas including aircrafts, automobiles and vessels. In addition, many researches about unmanned systems in Korea have been studying actively with the advancement of IT However, it is not satisfied with the result of the researches and developments. Bemuse of the reason we've here tried to make a very small USV which is a barge type. We applied the Great circle navigation calculation based on GPS to the autonomous navigation algorithm and used the LabVIEW 8.2 developed by NI corp. for programming The engine and rudder were controlled by pulse width modulation method. The engine system was composed of the DC motor and ESC(Electronic Speed Controller). It was also applied by the direct cooling system using DC motor pump. A very small USV was designed and made by ourself and it was verified the effectiveness of autonomous navigation algorithm through the tests at the sea.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.6
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• pp.183-190
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• 2004

This paper proposes a methodology to solve problems upon the circuit design applied to inductor load by applying a circuit to improve power factor with is partial switching PFC module to the power supply system for cooling/heating inverter air conditioner and by designing an input power section in compliance with IEC555-2 on the basis of better input power factor and minimized harmonic components of current. On the other hand, this paper suggested how to control the increase of output voltage along with tぉw current waves and partial switching PFC circuit as well, which can provide the output as twice as input voltage This study applied a method to control the compressors of air conditioner by means of increased the voltage applicable to compressor motor by lowering switching number conclusively, it could solve questions about efficiency, economics, electronic noise and so forth. and so that the reasonable voltage for running moor could be set up along with lower power consumption of air conditioner than estimated It was demonstrated that total sum of energy efficiency to operate system was increased to the extent of valid level. And all this merits and appropriateness was proved by computer simulation and experience.

• Reproductive and Developmental Biology
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• v.35 no.1
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• pp.55-60
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• 2011

The objective of this study was carried out to evaluate the efficiency of sperm collection methods on the post-thaw viability of cat semen. The cat semen was collected by artificial virginal (AV) and electronic ejaculate (EE) methods. The composition of semen extender was consisted of Tris-buffer supplemented with 20% egg yolk and 1% P/S antibiotics in Ext I, and more added 8% glycerol, 1.0% Equex STM paste of total volume in Ext II. The collected semen was adjusted the concentration and then diluted in Ext I for optimal concentration. The diluted semen was cooling to $5^{\circ}C$ temperature in refrigerator for at least 2 hrs and then diluted stepwise with Ext II for at least 1 hrs. After an equilibration for 1 hrs, the cooled semen was packaged in 0.5 ml straw and then freezing on the $LN_2$ vapor over 5 cm above from $LN_2$ and then immersed directly in $LN_2$ for cryopreservation. The frozen semen was thawed in $38^{\circ}C$ water for 15 sec and then evaluated the motility, viability, and morphology. Post-thaw semen were calculated the motility by SMI (sperm motility index). The live-dead sperm was evaluated by Eosin-B and morphological evaluation was by Diff-quik kit staining. The post-thaw concentration ($89{\times}10^6$ /ml vs. $128{\times}10^6$ /ml), viability ($22.6{\pm}10.6%$ vs. $37.1{\pm}26.1%$), morphological normality ($27.0{\pm}50.2%$ vs. $45.6{\pm}123.0%$) of EE and AV groups were not significant different, but the post-thaw motility was significant lower in EE than that in AV group ($53.1{\pm}3.6$ vs. $73.6{\pm}5.7$) (p<0.05). In conclusion, semen collection methods did not significant different between EE and AV groups except of post-thaw motility and so both semen collection methods could be applied in feline semen collection methods.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.942-948
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• 2010

In this study we aims to examine the effects of 0.5 mol% $Cr_2O_3$ addition on the reaction, microstructure development, resultant electrical properties, and especially the bulk trap and interface state levels of ZnO-$Bi_2O_3-Sb_2O_3$ (Sb/Bi=0.5, 1.0, and 2.0) systems (ZBS). The samples were prepared by conventional ceramic process, and characterized by XRD, density, SEM, I-V, impedance and modulus spectroscopy (IS & MS) measurement. The sintering and electrical properties of Cr-doped ZBS (ZBSCr) systems were controlled by Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$) was decomposed more than $100^{\circ}C$ lowered on heating in ZBS (Sb/Bi=1.0) by Cr doping. The densification of ZBSCr (Sb/Bi=0.5) system was retarded to $800^{\circ}C$ by unknown Bi-rich phase produced at $700^{\circ}C$. Pyrochlore on cooling was reproduced in all systems. And $Zn_7Sb_2O_{12}$ spinel ($\alpha$-polymorph) and $\delta-Bi_2O_3$ phase were formed by Cr doping. In ZBSCr, the varistor characteristics were not improved drastically (non-linear coefficient $\alpha$ = 7~12) and independent on microstructure according to Sb/Bi ratio. Doping of $Cr_2O_3$ to ZBS seemed to form $Zn_i^{..}$(0.16 eV) and $V^{\bullet}_o$ (0.33 eV) as dominant defects. From IS & MS, especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one (1.1 eV) and electrically inactive intergranular one (0.95 eV) with temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.52-52
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• 2008

The positive temperature coefficient of resistivity (PTCR) effect in (1-x)$BaTiO_3$ - $x(Bi_{0.5}K_{0.5})TiO_3$ doped with $Nb_2O_5$ was investigated. $(Bi_{1/2}K_{1/2})TiO_3$ (BKT) is more environment-friendly than $PbTiO_3$ in order to use in PTC thermistors. The incorporation of 1 mol% BKT to $BaTiO_3$ increased the Curie temperature (Tc) to $148^{\circ}C$. Doping of $Nb_2O_5$ to $Ba_{0.99}(Bi_{0.5}K_{0.5})_{0.01}TiO_3$ (BaBKT) ceramic has enhanced its PTCR effects. For the sample containing 0.025 mol% $Nb_2O_5$, it showed good PTCR properties; low resistivity at room temperature (${\rho}_r$) of 30 $\Omega{\cdot}cm$, a high PTCR intensity of approximately $3.3\times10^3$, implying the ratio of maximum resistivity to minimum resistivity (${\rho}_{max}/{\rho}_{min}$) in the measured temperature range, and a large resistivity temperature factor (a) of 13.7%/$^{\circ}C$ along with a high Curie temperature (Tc) of $167^{\circ}C$. In addition, the cooling rate of the samples during the sintering process had an influence on their PTCR behavior. All the samples showed the best ${\rho}_{max}/{\rho}_{min}$ ratio when they have cooled down at a rate of $600^{\circ}C$/min.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.11
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• pp.878-885
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• 2012

In this study we aims to examine the co-doping effects of 1/3 mol% $Mn_3O_4+Co_3O_4$ (1:1) on the reaction, microstructure, and electrical properties such as the bulk defects and grain boundary properties of $ZnO-Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi=0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Mn,Co-doped ZBS, ZBS(MCo) varistors were controlled by Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$) was decomposed and promoted densification at lower temperature on heating in Sb/Bi=1.0 by Mn rather than Co. Pyrochlore on cooling was reproduced in all systems however, spinel (${\alpha}$- or ${\beta}$-polymorph) did not formed in Sb/Bi=0.5. More homogeneous microstructure was obtained in $Sb/Bi{\geq}1.0$ In ZBS(MCo), the varistor characteristics were improved drastically (non-linear coefficient, ${\alpha}$=30~49), and seemed to form $Zn_i^{..}$(0.17 eV) and $V_o^{\bullet}$(0.33 eV) as dominant defects. From impedance and modulus spectroscopy (IS & MS), the grain boundaries have divided into two types, i.e. the one is tentatively assign to $ZnO/Bi_2O_3(Mn,Co)/ZnO$ (0.47 eV) and the other ZnO/ZnO (0.80~0.89 eV) homojunctions.

• Journal of Climate Change Research
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• v.1 no.3
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• pp.189-203
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• 2010

The objective of this study is the estimate of $CO_2$ emissions by the energy consumption of functional technology introduced by classifying energy use in households according to functions as well as energy resources. This study also intends to provide the practical basis data in order to establish specific alternatives for GHG mitigation in residential sector with examining the cause analysis affecting $CO_2$ emission increases from 1995 to 2007. The results of this study show a 6.6% increase in the total $CO_2$ from 60,636 thousand tons in 1995 to 64,611 thousand tons in 2007 by using energy in residential sector. Heating is the greatest $CO_2$ emission sector by use, followed electric appliances, cooking, lighting and cooling. Heating sector shows 56.6% reductions from 71.5% in 1995 and as do cooling and electric home appliances, with a 2.4% increase from 0.6% and a 21.8% increase from 14.2% respectively. To analyze factors resulted in $CO_2$ emissions in residential sector, the relevant indicator change rate from 2005 to 2007 was examined. The results find that population, the number of household, housing areas, family patterns, and family income resulted in the $CO_2$ emissions increase in residential sector from 1995 to 2007. On the other hand, carbon intensity and energy intensity contribute to $CO_2$ reduction in residential sector with -2% and -38.7% respectively because of the energy conversion and the improvement of energy efficiency in electronic appliances. This study can be used as a reference when taken account of the reality and considered the introduction of highly effective measures to increase the possibility of mitigation potential in residential sector hereafter.

• Corrosion Science and Technology
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• v.12 no.1
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• pp.1-6
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• 2013

Recently Digital TV industry has drastically been moving the illuminating system, which causes an obvious product change from PDP and LCD to LED model to provide high-definition image. Due to strong competition in the digital industry, TV manufacturers make a great efforts to reduce production cost by using low-priced materials such as steels instead of aluminum and plastic etc. In this paper we have developed a new low-priced electrogalvanized steel sheet, which has a black resin composite layer, to substitute conventional high-priced PCM steel and plastic mold for rear cover panel in the digital TV. The black resin composite was prepared by mechanical dispersion of the mixture solution that consists of high solid polyester resin, melamine hardener, black pigment, micronized silica paste, polyacrylate texturing particle and miscellaneous additives. The composite solution was coated on the steel sheet using roll coater followed by induction furnace curing and cooling. Although the coated layer has a half thickness compared to the conventional PCM steels having $23{\mu}m$ thickness, it exhibits excellent quality for the usage of rear cover panel. The new steel sheet was applied to test products to get quality certification from worldwide electronic appliance customers. Detailed discussion provides in this paper including preparation of composite solution, roll coating technology, induction curing technology and quality evaluation from customers.