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Glass Transition Process of Amorphous Quinidine Studied by Using Brillouin Light Scattering
홍정택,고재현,김태현 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.4
The acoustic properties of amorphous quinidine were investigated by using Brillouin spectroscopy as a function of temperature. The longitudinal sound velocity and the acoustic absorption coefficient showed drastic changes in their slopes at the glass transition temperature of 328 K, which was nearly the same as the thermodynamic and the dielectric glass transition temperatures. The clear difference between the crystalline state and the amorphous state of quinidine, as well as the crystallization process, could be revealed by observing the change in the Brillouin spectrum. Analysis of the lowtemperature absorption coefficient showed that the excess acoustic damping could be attributed to intramolecular relaxation motions, such as side-group rotations.
홍정택,Byoung Wan Lee,Soo Han Oh,Jae-Hyeon Ko,Hunyong Lee,Chulhwa Lee,Doosung Kim 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.7
Acoustic properties of amorphous SiO2 thin films deposited on the Si(100) substrate were investi- gated by using Brillouin spectroscopy. The Brillouin spectrum was obtained by tilting the sample to investigate both the longitudinal acoustic (LA) mode and the surface acoustic wave (SAW) modes. Sound velocities of both modes, the two elastic moduli (longitudinal and shear moduli), and the Poisson ratio of the film could be obtained by combining the Brillouin data and the measured re- fractive index. The longitudinal sound velocity and the longitudinal elastic modulus increased with increasing Ar ratio in the Ar:O2 gas mixture, which was attributed to the better stoichiometry of the film grown at higher Ar ratio.
홍정택,이주은,김재용,김명준,차흥원.Jung Taeck Hong. MD. Jooeun Lee. MD. Jae Yong Kim. MD. Myoung Joon Kim. MD. Hungwon Tchah. MD 대한안과학회 2010 대한안과학회지 Vol.51 No.11
Purpose: To investigate and compare the clinical outcomes of wavefront-guided LASIK performed by 2 different laser platforms. Methods: A retrospective analysis of consecutive cases of eyes that underwent wavefront-guided LASIK by using the VISX S4 CustomVue system and the Zyoptix Z100 system advanced personalized mode. All procedures were performed by one surgeon. Fifty-six eyes of 36 patients were included. Of the 56 eyes, 30 eyes underwent LASIK by using the VISX S4 CustomVue system (CustomVue group), and other 26 eyes underwent LASIK by using the Zyoptix Z100 system (APT group). Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest refraction, contrast sensitivity, total high order aberration (HOA), spherical aberration (SA) and Q-value were recorded preoperatively and at 1 week, 1 and 3 months postoperatively. Results: There was no statistically significant difference between two groups in terms of preoperative UCVA, BCVA, manifest refraction, high order aberrations, Q-value and contrast sensitivity. Induced amount of SA was significantly lower in CustomVue group than in APT group (p = 0.02). Conclusions: Wavefront-guided LASIK performed by 2 different laser platforms caused clinically acceptable outcomes including good visual acuity and contrast sensitivity through 3 months. Furthermore, LASIK performed by VISX S4 CustomVue system caused less SA at three months after operation. J Korean Ophthalmol Soc 2010;51(11):1438-1444
디스플레이 백라이트용 광학 필름에 미치는 자외선과 온도의 영향에 대한 연구
홍정택,고재현 한국물리학회 2018 새물리 Vol.68 No.9
The effects of ultraviolet (UV) irradiation and temperature on the degradation of the optical components in the backlight for liquid crystal displays were investigated. The degrees of degradation of the side molds made of polycarbonate and the multi-layer-type reflective polarizers were estimated for different UV irradiation levels and temperatures by measuring the change in the color coordinates over time. For ambient temperatures, the side mold showed a more substantial degradation at shorter UV wavelengths. The reflective polarizer exhibited accelerated degradation at shorter UV wavelengths at room temperature, but it displayed similar changes in the color coordinates at high temperatures, indicating that the temperature is a more dominant factor from the viewpoint of degradation. Based on this systematic study of the degradation process, we suggest that the long-term reliability of displays may be improved by optimizing the UV shield and by thermal management of the backlight components. 본 연구에서는 액정 표시 장치의 광원인 백라이트 내 부품에 조사되는 자외선과 온도가 일으키는 열화 효과에 대해 조사하였다. 백라이트 유닛 내 폴리카보네이트 (polycarbonate, PC) 재질의 사이드 몰드와 다층박막형 반사형 편광판에 대해 온도 및 자외선 조사 파장을 변화시키며 열화의 진행 정도를 해당 재료의 색좌표의 시간에 따른 변화로 확인하였다. 백라이트 내 일반적인 온도 범위 내에서 PC재질인 사이드 몰드는 자외선 파장이 짧을수록 자외선 열화가 가속화되었다. 반사형 편광판은 실온에서는 조사 자외선 파장이 짧을수록 열화 속도가 증가하지만 고온에서는 조사 자외선 파장과는 무관하게 비슷한 자외선 열화 속도를 보였고 이를 통해 온도가 열화의 주요 요인이라는 것을 알 수 있었다. 열화 과정에 대한 이러한 결과를 기반으로 백라이트 내 부품에 대한 자외선의 차폐 및 효율적인 열방출 설계를 적용하면 디스플레이의 장기 신뢰성을 개선하는데 큰 도움을 줄 것이다.
홍정택,이병완,고재현,Irena Jankowska-Sumara,Maria Podgórna,Andrzej Majchrowski 한국물리학회 2018 Current Applied Physics Vol.18 No.6
The phase transition sequence of a PbHf0.7Sn0.3O3 single crystal was investigated by using Brillouin spectroscopy. The longitudinal acoustic mode showed three distinct changes at ∼370 K, ∼455 K and ∼495 K which corresponded to the antiferroelectric 1 → antiferroelectric 2 → intermediate → paraelectric phase transitions upon heating. The paraelectric phase was characterized by softening acoustic mode, increasing acoustic damping and the appearance of quasielastic central peaks which were observed upon approaching the phase transition temperature. The relaxation times derived from the acoustic mode anomalies and the central peak were consistent with each other and showed a slowing-down behavior. These precursor phenomena were attributed to the polar clusters having broken inversion symmetry. The substitution of Hf with Sn induced a very soft intermediate phase between the paraelectric and the antiferroelectric phases, where the longitudinal acoustic mode exhibited the lowest mode frequency along with substantially high acoustic damping. The transverse acoustic mode, which was observed in the two antiferroelectric phases, did not appear in the intermediate phase. These results indicated that the average symmetry of the intermediate phase may be cubic consisting of fine ferroelastic domains.
홍정택,임현택,Jung Taeck Hong,MD,Hyun Taek Lim,MD 대한안과학회 2010 대한안과학회지 Vol.51 No.11
Purpose: To report a case of prolonged bilateral inferior altitudinal visual field defect in a young migraine patient. Case summary: A 13-year-old female patient presented with bilateral disturbance of visual acuity and visual field, which had begun one month before. She complained of headache, with recently increasing frequency, that occurred 3 or 4 days a week for about 2~3 hours duration, sometimes accompanied by nausea and located in the frontotemporal and retrobulbar area. Brain magnetic resonance imaging showed no abnormal finding in the brain and orbit. Her visual acuity was hand motion in both eyes and Humphrey visual field test showed bilateral inferior altitudinal visual field defect. Pupillary resonse was normal and extraocular muscle movement, anterior segment and fundus were also normal in ophthalmologic examination. Her best corrected visual acuity was 1.0 in both eyes by fogging method, but bilateral inferior altitudinal visual field defect persisted for 6 months follow-up. Conclusions: Bilateral inferior altitudinal visual field defect can be developed in a migraine patient without other causes. Careful examinations to rule out other causes such as ischemic optic neuropathy or brain infarct should be performed in a migraine patient who complains of visual disturbance. J Korean Ophthalmol Soc 2010;51(11):1537-1542
디지털 트윈 & IoT Sensing 융합 기반 전통시장 화재 모니터링 시스템
홍정택 ( Jung-taek Hong ),이규협 ( Kyu-hyup Lee ),송진우 ( Jin-woo Song ),이서준 ( Seo-joon Lee ),장영희 ( Young-hee Chang ),권순욱 ( Soon-wook Kwon ) 한국산업융합학회 2023 한국산업융합학회 논문집 Vol.26 No.6
Traditional markets are infrastructure with facilities and characteristics of very high population density. Recently, arcades have been installed through traditional market modernization policies, and aging infrastructure has been repaired. However, gas and electrical facilities of traditional markets cannot be easily replaced because of its high density. And because regular inspections are not conducted, management of facilities is on very poor condition. In addition, when a fire occurs in a traditional market, the fire easily spreads to nearby stores and is likely to spread to a large fire because of a lot of highly flammable substances. Smoke detectors and heat detectors are installed in most traditional markets to monitor fires, but malfunctions are frequent due to the nature of smoke detectors and heat detectors, and network facilities are not properly maintained. Therefore, in this study, gas detection sensors and flame detectors are additionally installed in Gwangmyeong Traditional Market, and a digital twin-based traditional market fire monitoring system is implemented in conjunction with existing sensors in the market's 3D model. With this digital twin based fire monitoring system, we can reduce the malfunctions of fire detect sensors, and can easily guide the evacuation route.