골관절 결핵에 대한 연구

고재현,최영건,안재인,박병문 최신의학사 1980 最新醫學 Vol.23 No.10

Sound Propagation in 5CB Liquid Crystals Homogeneously Confined in a Planar Cell

고재현,황윤홰,김종현 한국정보디스플레이학회 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±7 m/s at 300 K. The attenuation coefficient  was estimated to be approximately 1.9ⅹ10⁶m⁻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.

Cyclosporine에 의한 가역적 피질 실명 1례

고재현,이홍기,정윤재,배상수,기현균,서대원,윤혜영,이종태,정현식 大韓血液學會 1997 大韓血液學會誌 Vol.32 No.3

Elastic Properties of Bismuth Layer-Structure Perovskite Single Crystals Studied by Brillouin Scattering

고재현,Anwar Hushur,Bryan C. Sih,Do Han Kim,Jong Pil Kim,Min-Su Jang,Seiji Kojima,Zuo-Guang Ye 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV

Elastic properties of bismuth layered perovskite compounds, LaxBi4..xTi3O12 (LBT-x) and SrBi2Ta2O9 (SBT), were examined at room temperature by Brillouin scattering. Elastic stiness coecients, c33 and c44, dened in the pseudotetragonal symmetry, were obtained. The longitudinal sound velocities propagating along the c axis, were 3985 m/s and 3118 m/s for the pure bismuth titanate (BTO) and SBT, respectively. The sound velocity of SBT is very slow and is believed to be related with the weak interlayer bonding of this layer-structure compound. A simple linear chain model showed that the dierence in the sound velocity between BTO and SBT is mainly due to the dierence in the c axis lattice constant. The sound velocity of LBT-x increased slightly with the increase of x, while c33 seems to be insensitive to x.

고효율 LDC용 Diode Module 개발 (LDC : Low DC-DC Converter)

고재현 전력전자학회 2011 전력전자학술대회 논문집 Vol.2011 No.11

(+)-데커시놀 (Decursinol)의 비정질화 가능성 및 단결정의 상전이에 대한 연구

고재현,김태현,정세훈,전종갑 한국물리학회 2013 새물리 Vol.63 No.4

(+)-Decursinol is a linear dihydrocoumarin isolated from the root of Angelica gigas Nakai (Umbelliferae) and is known to have cytotoxic activity, anti-Helicobacter pylori activity, and strong antinociceptive activity. The elastic properties of a (+)-decursinol single crystal were investigated by using a Brillouin light scattering technique. The acoustic phonons exhibited anomalous behaviors at about 65 $^\circ$C indicating the existence of structural phase transition at that temperature. The low-temperature elastic property of the (+)-decursinol single crystal could be explained by using two models based on normal lattice anharmonicity. The melted (+)-decursinol was quenched at liquid-nitrogen temperature to check whether it could be transformed into an amorphous state, but the quenched sample was crystallized even at the lowest temperature, indicating a high tendency for crystallization. 당귀에서 추출되는 물질 중 하나인 (+)-데커시놀은 항암, 항헬리코박터파이롤리 및 강력한 진통작용을 나타내는 약제물질이다. 본 연구에서는(+)-데커시놀 단결정의 탄성특성을 브릴루앙 분광법을 이용해조사하였다. 그 결과 측정된 음향포논의 주파수 및 반치폭이 섭씨 65도부근에서 비정상성을 보임을 확인하였고 이를 통해 (+)-데커시놀이 상온이상에서 구조상전이를 보임을 알 수 있었다. (+)-데커시놀의종음향포논이 저온 영역에서 보이는 탄성특성은 격자 비조화성에 기반한이론적 모델로 설명할 수 있었다. (+)-데커시놀이을 녹인 후에 10$^\circ$C/min의 냉각속도로 급냉하여 비정질상을 얻고자 하였으나 이물질은 액체질소 온도에서도 결정화가 일어나는 등 높은 결정화 경향성을가짐을 알 수 있었다.

브릴루앙 광산란 분광법을 이용한 응집물질의 탄성 특성 및 상전이 거동 연구

고재현 한국물리학회 2018 새물리 Vol.68 No.1

Brillouin spectroscopy is one of the inelastic laser-light scattering spectroscopies and is used to probe long-wavelength low-energy excitation processes in the characteristic frequency range of a few tens of gigahertz. Based on this technique, the velocities of acoustic waves in amorphous materials, such as polymers and liquids, and the energies and the elastic constants of acoustic phonon modes in crystals can be determined accurately. The elastic property is one of the fundamental physical properties in condensed matter, and it is sensitive to phase transitions and to changes in structure or composition. In this paper, we review the principles and the measurement methods of Brillouin spectroscopy and their main applications. Especially, we discuss property data and related physics obtainable from Brillouin spectroscopy by investigating several application examples, such as perovskite-structured oxide materials showing ferroelectricity or a relaxor state and amorphous materials including polymers. 브릴루앙 분광법은 비탄성 레이저 광산란 분광법의 하나로써 수십 GHz 정도의 특성 진동수를 가지는 장파장, 저에너지의 여기 과정을 연구하는데 활용된다. 이를 통해 고분자나 액체와 같은 비정질 물질 내 음향파의 속도와 탄성 모듈러스, 그리고 단결정 내 음향 포논의 에너지와 탄성계수를 정확히 결정할 수 있다. 응집물질의 탄성 특성은 물질의 구조나 조성 변화 혹은 상전이에 따라 민감하게 변하는 근본적인 물성 중 하나이다. 우리는 이 연구에서 브릴루앙 분광법의 원리 및 측정법, 그리고 주요 적용 분야에 대해 개괄하고자 한다. 특히 강유전 상전이 혹은 릴랙서 특성을 보이는 페로브스카이트 구조의 산화물과 폴리머를 포함한 비정질 물질에 대한 연구 사례를 검토함으로써 브릴루앙 분광법을 통해 얻을 수 있는 물성 데이터 및 이에 관련된 물리에 대해 논의한다.

Polarization Rotations in the Relaxor Ferroelectric Pb[(Zn$_{1/3}$Nb$_{2/3}$)$_{0.91}$Ti$_{0.09}$]O$_3$ Studied by Micro-Brillouin Scattering

고재현,Seiji Kojima 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV

Brillouin spectra of a relaxor-based ferroelectric Pb[(Zn1=3Nb2=3)0:91Ti0:09]O3 (PZN-9%PT) single crystal have been examined under an electric eld oriented along the pseudocubic [001] direction. One longitudinal and two transverse modes are softened along with the increase of the Brillouin linewidth during the polarization reversal. The eld-induced changes in the frequency shift of the three modes are maximum at the coercive eld of about 2.5 kV/cm, and then they recover their initial values with further increasing the electric eld. In particular, one transverse mode, which corresponds to the (c11 .. c12)=2 elastic stiness coecient, shows the most drastic changes at two electric elds. This seems to indicate the existence of intermediate monoclinic phases during the eld-induced transformation. Our results demonstrate that Brillouin scattering is a powerful tool in investigating elastic properties of ferroelectric relaxors during the polarization reversal.

고효율 고연색 양자점 조명 시뮬레이션

고재현,이정균,고영욱,김용득,Go, Jae-Hyeon,Lee, Jeong-Gyun,Go, Yeong-Uk,Kim, Yong-Deuk 한국정보디스플레이학회 2020 인포메이션 디스플레이 Vol.21 No.2

Effects of oxygen deficiency on the acoustic anomalies and phase transition behaviors of barium titanate single crystals

고재현,신선협,장문규,원충재,허남정 한국물리학회 2018 Current Applied Physics Vol.18 No.1

The acoustic behaviors of oxygen-reduced barium titanate (BaTiO3-d) single crystals with d~0.04 were investigated as a function of temperature by using Brillouin spectroscopy. The longitudinal acoustic mode of the moderately-reduced BaTiO3 (BTO) showed two pronounced anomalies at approximately 112 C and 11 C, which correspond to the cubic-tetragonal and tetragonal-orthorhombic phase transition temperature, respectively. These temperatures were lower by more than 10 C compared to those of the pure BaTiO3 suggesting that the disorder introduced by oxygen vacancies lowers the phase transition temperatures. The paraelectric phase of the reduced BaTiO3 were characterized by substantial softening of the longitudinal acoustic mode and the growth of central peaks centered at zero frequency. These anomalies were observed in a certain temperature range above the Curie temperature, indicating that pretransitional precursor polar clusters exist in the cubic phase and that their dynamics are responsible for the acoustic anomalies caused by electrostrictive coupling between the strain and the polarization. The relaxation time of the precursor polar clusters derived from the central peak exhibited a critical slowing-down behavior showing that their dynamics becomes more sluggish as temperature approaches the Curie point.