극저탄소강에서의 탄소분포 및 Cu 첨가의 영향 (초)

유대황,서정화,동계령,박대영,이찬규,이봉호,윤정봉,홍문희,백두진,박찬경,신기삼 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속재료학회 학술대회 개요집 Vol.2008 No.1

양끝이 열린 단층 탄소 나노튜브에 흡착된 질소에 대한 연구

유대황,김청식,황윤희,김형국,류기홍 한국물리학회 2002 새물리 Vol.45 No.1

The adsorption of N$_2$ on the open-ended single-walled carbon nanotube bundles was studied. The amount corresponding to the first coverage adsorbed on open-ended carbon nanotube bundles was three times larger than the amount adsorbed on close-ended nanotube bundles. The isosteric heat of adsorption was obtained from adsorption isotherm measurements performed at different temperatures ranging from 117 K to 130 K. The estimated heat of adsorption of nitrogen on the open-ended nanotube bundles was about twice that on the close-ended nanotube bundles. This directly leads to the conclusion that the binding energy of nitrogen on open-ended nanotubes is greater than that of nitrogen on close-ended nanotube bundles. 열린 단층 나노튜브에 흡착된 질소의 흡착에 대한 연구를 하였다. 열린 나노튜브에서 흡착된 첫 번째 층에 대응하는 질소 양의 크기는 닫힌 튜브에 흡착한 경우에 비하여 약 3배정도 증가하였다. 그리고 117 K에서 130 K 의 영역에서 등온 흡착 실험을 하여 얻은 등적 흡착열은 닫힌 나노튜브의 경우에 비해 약 두 배 더 큼을 알 수 있었다. 이것은 탄소 나노튜브의 내부에서 결합 에너지가 더 클 것이라는 이론적 예상과 일치한다.

Thermal Conductivity of Al2O3/water Nanofluids

유대황,양호순,J. A. Eastman,K. S. Hong,T. E. Hong 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.II

Nanofluids, fluids with suspended nanoparticles, are of interest as a novel material for improving heat transfer efficiency. The conventional theory of two-component mixtures cannot explain the large enhancement of thermal conductivity of nanofluids. It is to be expected that the thermal conductivity of nanofluids is related with many factors, such as that effect of surfactants, dispersion of particles, convection or Brownian motion of nanoparticles, \emph{etc.} but the mechanism is not known. Thermal conductivity of Al$_{2}$O$_{3}$ nanofluids is studied in this work and compared with that of Fe nanofluids. To study the effect of pH of the base fluid on thermal conductivity, we measured the thermal conductivity of Al$_{2}$O$_{3}$ nanofluids with different pH values. Al$_{2}$O$_{3}$ nanoparticles were dispersed in water of pH values such as 7.0, 9.65 and 10.94. Nanoparticles have a tendency to form clusters, due to van der Waals interaction resulting in reduction of thermal conductivity. It is understood from the variation of thermal conductivity as the pH value of base fluids varies that the pH of base fluids affects clustering of nanoparticles.

Quick Phase Search Method on an Adsorbed System

유대황,김형국,류기홍,이호섭,백현종,황윤회 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I

The desorption rate of adsorbed nitrogen on planar graphite was measured as the change in the adsorbed amount with increasing temperature. There exist regions in which the desorption rate changes with increasing temperature, and the regions coincide with the phase boundaries of nitrogen on graphite. These regions are caused by changes in the binding energy and the heat of adsorption under a phase transition in the adsorbed system, which affects the interaction between an adsorbed particle and either neighboring particles or the substrate. Those results show that this temperature scanning adsorption method is useful for a rough search of phases and phase boundaries in an adsorbed system without the help of other auxiliary measurements such as heat capacity measurements. This method is different from the traditional isothermal adsorption process in which much effort is needed to follow measurements repeated at different temperatures and in which other experimental methods are needed to obtain information for phases and phase changes related to the phase diagram for the adsorbed system. Through this experimental method, we can easily find the phases and the phase boundaries needed to complete the phase diagram of the adsorbed system, so the method saves much time for traditional isothermal adsorption experiments.

Enhanced photocatalytic activity of graphene oxide decorated on TiO_2 films under UV and visible irradiation

유대황,Tran Viet Cuong,Viet Hung Pham,정진석,Nguyen Tri Khoa,김의정,한성홍 한국물리학회 2011 Current Applied Physics Vol.11 No.3

Photocatalytic TiO_2 films were prepared using RF magnetron sputtering and three kinds of graphene oxide (GO) solutions with different concentration of 0.05 mg GO, 0.03 mg GO, and 0.01 mg GO in 10 ml ethanol were coated on TiO_2 films, respectively. Structures and morphologies of the samples were examined by AFM, SEM, and Raman and photocatalytic properties under UV and visible irradiation were examined respectively. The efficiency of the photodegradation is enhanced when TiO_2 thin film was coated with GO, it is related to its giant π-conjugation system and two-dimensional planar structure and efficient charge separation by coating GO. The maximum photodegradation rate was observed for TiO_2thin film coated with 0.03 mg GO. It is attributed to the increase of absorbance and scattering of photons through excess carbon in the photosystem.

Effect of Ultrasonic and Air Blast Shot Peening on the Microstructural Evolution and Mechanical Properties of SUS304

유대황,J. L. Dong,D. H. Yoo,조인식,Y. Pyoun,I. Cho,신기삼 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.3

The effects of the process parameters of shot peening on the microstructural evolution and resulting mechanical property of SUS304 were investigated with microscopic analyses and mechanical tests. Shot peening on SUS304 was carried out with different impact energies and ball diameters (2.3 - 6 mm). In the deformed layer of 80 220 with a high dislocation density, the top layer of in thickness was found to have nanostructures of 20 100 nm with mechanical twins, which decreased with increasing depth. Deformation-induced martensite, whose volume fraction increased as the total energy deposition increased and/or as the ball diameter decreased, even at the same impact energy. The density of the multi-directional mechanical twins gradually decreased and single-directional mechanical twins gradually appeared instead. In addition, the average distance of twins increased with increasing depth in all of the shot-peened specimens. When processed by air blast shot peening, a few precipitates were additionally observed on the grain boundaries and are attributed to the conceivably higher temperature reached during the processing.

Effect of copper oxide on the resistive switching responses of graphene oxide film

유대황,TRANVIET CUONG,한성홍 한국물리학회 2014 Current Applied Physics Vol.14 No.9

The role of CuO films in meliorating resistive switching behavior of graphene oxide (GO) in CuO/GO/CuO memory structure was investigated. An increase in the set voltage from 1.3 to 3.0 V and a step-like switching current was clearly observed when the GO film was sandwiched between two CuO layers. It is attributed to the fact that the set voltage of GO is lower than that of CuO and accumulated charge carriers located at the interface of GO and CuO can pass through CuO abruptly at set voltage of 3.0 V. Our results suggested that designed sandwich structure of materials with different set voltage enables to amend resistive switching response characteristics.

나노표면개질(UNSM) 처리를 한 SUS304의 표면 및 깊이에 따른 미세 구조 및 기계적 특성 분석 (초)

유대황,요언군,조인식,이창순,박인규,신기삼 대한금속ㆍ재료학회 2009 대한금속재료학회 학술대회 개요집 Vol.2009 No.-

Antiaging Effects of Musa sapientum L. (Banana) Leaf Extract

유대성,장수진,박윤정,김승회,황형서,Yoo, Dae Sung,Jang, Su Jin,Park, Yun Jeong,Kim, Seung Hoi,Hwang, Hyung-seo The Korean Society for Biotechnology and Bioengine 2016 KSBB Journal Vol.6 No.2

To examine the possibility of using Musa sapientum L. (Banana) leaf extract as a cosmetic raw material, banana leaves grown in Jeju Island were extracted with 70% ethanol. Polysaccharides present in banana leaf extract were discarded by precipitation with cold ethanol. Polysaccharide-discarded banana leaf extract promoted procollagen and COL1A1 gene expression, but inhibited matrix metalloproteinase (MMP)-1 and MMP-2 gene expression in human skin fibroblasts when examined by real-time reverse-transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). The active compound in banana leaves was identified by fractionation with various solvents. The chloroform fraction showed the highest anti-wrinkle efficacy and the active compound of chloroform fraction was identified as corosolic acid by NMR, FT-IR, EA, and HPLC-MS. In addition, banana leaf extract showed anti-oxidative efficacy with an IC50 value of 67.91 ppm, as determined by DPPH free radical scavenging assay. Finally, the anti-wrinkle efficacy of banana leaf extract-containing cream was confirmed by clinical tests. Based on these results, banana leaves could have an application as a cosmetic raw material with anti-wrinkle efficacy.

바나나잎 추출물의 미백 개선 효과

황형서 ( Hyung Seo Hwang ),유대성 ( Dae Sung Yoo ),심중현 ( Joong Hyun Shim ) 대한화장품학회 2016 대한화장품학회지 Vol.42 No.1

바나나잎의 기능성화장품 소재로써 응용 가능성을 규명하고자 바나나잎 추출물이 피부 미백에 미치는 효과를 B16F10 세포주를 활용하여 cell viability, mRNA 발현 및 tyrosinase (Tyr) 활성 저해 실험을 통하여 알아보았다. 10%의 바나나잎 추출물은 tyrosinase 활성을 저해하고, 멜라닌 합성을 65% 감소시키는 것을 확인하였다. 정량적 real-time RT-PCR을 수행한 결과 바나나잎 추출물이 tyrosinase related protein 1 (TRP1)/ tyrosinase related protein 2 (TRP2) / tyrosinase mRNA 발현을 각각 20 / 40 / 60% 가량 억제하는 효과를 확인하였다. 또한 바나나잎 추출물이 함유된 크림제형의 임상시험을 수행하여 자외선 조사 직후 바나나잎 추출물이 함유된 크림의 육안평가 결과 유의한 미백효과가 있는 것을 확인하였다. 본 연구 결과는 바나나잎 추출물이 미백 기능성 화장품 소재 뿐 아니라 향후 기전 연구 수행을 통해 다양한 산업화 소재로 개발될 수 있음을 시사한다. This research was carried out to identify the whitening effect of Banana leaf extract. B16F10 cells were used to measure cell viability, mRNA expression, and tyrosinase activity inhibition assay from B16F10 cell. We also carried out clinical test of the cream product containing banana leaf extract. In this study, we elucidated the effects of banana leaf extract on TRP1 / TRP2 / Tyr mRNA expression and tyrosinase activity inhibition. Quantitative real-time PCR showed that banana leaf extract decreased mRNA level of TRP1, TRP2 and Tyr gene and tyrosinase activity inhibition assay also revealed that banana leaf extract 65% decreased melanin production in B16F10 cell. Banana leaf extract cream can whiten the skin darkness induced by ultraviolet. Therefore, we successfully identified the whitening effect of banana leaf extract, and this finding suggested the banana leaf extract is a considerable potent cosmetic ingredient for skin whitening. Based on this, we anticipated further researches about banana leaf extract for mechanism to develop not only cosmetics but healthcare food or medicines.