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고재용,윤순동,박성현 木浦海洋大學校 2000 論文集 Vol.8 No.1
In the ship structure, the stress concentration is to be occured at the corner of hatch opening under static and dynamic loading conditions. Recently, the ship structure design based on the fatigue strength analysis is increasingly demanded. Therefor, we analyzed the main deck hatch corner which was representative discontinuty of ship structure with ANSYS. According to the results, the stress concentration factor is lied from 1.68 to 6.41.
Ko, Jae-Hyeon,Kim, Tae Hyun,Kojima, Seiji,Bokov, Alexei A,Ye, Zuo-Guang IOP Pub 2010 Journal of Physics, Condensed Matter Vol.22 No.48
<P>A Brillouin spectroscopic investigation was carried out on PMN–55%PT single crystals, which are known to have no chemically ordered regions and undergo a well-defined structural phase transition at <I>T</I><SUB>C</SUB> ∼ 521 K. The longitudinal and transverse sound velocities probed on a right-angle scattering geometry exhibited a remarkable softening and increasing hypersonic damping on approaching <I>T</I><SUB>C</SUB> from <I>T</I><SUB>B</SUB> ∼ 610 K that was characterized by the deviation of the dielectric permittivity from the high-temperature Curie–Weiss behavior. The acoustic anomalies of the longitudinal acoustic mode at the backward scattering were more substantial than those observed at the right-angle scattering, which could be understood in the framework of normal acoustic dispersion considering the difference in the acoustic frequency. The softening of the transverse sound velocity was more significant than that of the longitudinal one upon cooling toward <I>T</I><SUB>C</SUB>, suggesting that this acoustic anomaly may be related to the local rhombohedral transformation, occurring in polar nano-regions (PNRs). The observed acoustic behaviors combined with the central peak dynamics clearly indicated the existence of dynamic polar nano-regions in PMN–55%PT where there are no chemically ordered regions, and seem to suggest that the order parameter fluctuations due to two kinds of coupling contribute to the acoustic anomalies in the temperature range of <I>T</I><SUB>C</SUB> ∼ <I>T</I><SUB>B</SUB>: electrostrictive coupling between the acoustic waves and the dynamic PNRs, and linear coupling between the acoustic waves and the precursor polar clusters, i.e., the ordering unit responsible for the order–disorder-type slowing down behavior probed by the central peak. </P>
Sound Propagation in 5CB Liquid Crystals Homogeneously Confined in a Planar Cell
Ko, Jae-Hyeon,Hwang, Yoon-Hwae,Kim, Jong-Hyun The Korean Infomation Display Society 2009 Journal of information display Vol.10 No.2
The Brillouin spectrum of 4'-n-pentyl-4-cyano-biphenyl (5CB) liquid crystals homogeneously confined in a planar liquid crystal (LC) cell was measured using a 6-pass tandem Fabry-Perot interferometer. By adopting a special right-angle scattering geometry, the sound velocity of 5CB was estimated from the Brillouin shift without knowing the refractive index. The sound velocity of the longitudinal wave propagating along the direction of the directors aligned parallel to the glass plates of the LC cell was 1784${\pm}$7 m/s at 300 K. The attenuation coefficient $\alpha$ was estimated to be approximately $1.9{\times}10^6m^{-1}$, which is about twice as large as that of the longitudinal sound wave propagating along the direction perpendicular to the directors. The present method may be very useful in the evaluation of the elastic properties of the materials used in display devices, whose refractive indices are not known.
Ko, Jae-Hyeon,Jeong, Min-Seok,Lee, Byoung Wan,Kim, Jae Hyun,Ko, Young Ho,Kim, Kwang Joo,Kim, Tae Hyun,Kojima, Seiji,Ahart, Muhtar Optical Society of Korea 2013 한국광학회지 Vol.24 No.5
Brillouin spectroscopy has been widely used for the investigation of acoustic properties of condensed matters in the hypersonic region. A high-pressure Brillouin spectrometer was set up by combining a diamond anvil cell and a tandem multi-pass Fabry-Perot interferometer. It was successfully applied to liquid ethanol, and the pressure dependence of the sound velocity, the refractive index and other acoustic properties were derived based on the measurements. The detailed optical setup and experimental procedure are described.
Ko, Jae-Hyeon,Ryu, Jin-Sun,Yu, Mi-Yeon,Park, Seung-Mi,Kim, Su-Jin The Korean Institute of IIIuminating and Electrica 2010 조명·전기설비학회논문지 Vol.24 No.3
For better picture quality in LCD TVs, it is important to reach a steady emitting state within as short a time as possible in the initial stage after the TV is turned on. The initial characteristics of LCD TVs are mainly determined by the properties of the backlight. In the present study, the photometric and spectroscopic properties of a 55-inch Cold Cathode Fluorescent Lamp (CCFL) and Light Emitting Diode (LED) backlights were investigated. The measured properties include time dependence of the spectrum, luminance, and color coordinates. The results show that the change in the spectroscopic properties of the LED backlight is smaller than that of the CCFL backlight. This indicates that the initial picture quality of the LCD TV with the LED backlight is superior to that with the CCFL backlight. The origins of this difference were discussed in relation to the inherent characteristics of the two light sources.
Jae-Hyeon Ko,Jin-Sun Ryu,Mi-Yeon Yu,Seung-Mi Park,Su-Jin Kim 한국조명·전기설비학회 2010 조명·전기설비학회논문지 Vol.24 No.3
For better picture quality in LCD TVs, it is important to reach a steady emitting state within as short a time as possible in the initial stage after the TV is turned on. The initial characteristics of LCD TVs are mainly determined by the properties of the backlight. In the present study, the photometric and spectroscopic properties of a 55-inch Cold Cathode Fluorescent Lamp (CCFL) and Light Emitting Diode (LED) backlights were investigated. The measured properties include time dependence of the spectrum, luminance, and color coordinates. The results show that the change in the spectroscopic properties of the LED backlight is smaller than that of the CCFL backlight. This indicates that the initial picture quality of the LCD TV with the LED backlight is superior to that with the CCFL backlight. The origins of this difference were discussed in relation to the inherent characteristics of the two light sources.