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허승헌,조광연,김창열,구은해 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.6
Electron-beam irradiation (EBI) on a graphene oxide (GO) film resulted in the stepwise growth of carbon nanostructures from a few-layered graphitic- and stripes-like nucleation to embedded onions; the formation mechanism of these embedded onions is different from that of free onions. Further, EBI-induced reduction and size-dependent onion and nanodiamond formations were also observed. The detailed in-situ observations reveal that the formation of unique carbon nanostructures results from a GO film's intrinsic properties related to slow reactivity with heat generation, thermodynamic stability, and a physically well-bound flat reaction surface.
김영대,허지회,이경열,남효석,한상원,이종윤,조한진,김규식,김서현,차명진,안성환,오승헌,이기욱,정요한,최혜연,한상돈,이혜선,남정모,김은혜,이기정,송동범,박희남 연세대학교의과대학 2015 Yonsei medical journal Vol.56 No.2
Purpose: In this study, we investigated the stroke mechanism and the factors associatedwith ischemic stroke in patients with nonvalvular atrial fibrillation (NVAF) who were on optimal oral anticoagulation with warfarin. Materials and Methods: This was a multicenter case-control study. The cases were consecutive patients with NVAF who developed cerebral infarction or transient ischemic attack (TIA) while on warfarin therapy with an international normalized ratio (INR) ≥2 between January2007 and December 2011. The controls were patients with NVAF without ischemicstroke who were on warfarin therapy for more than 1 year with a mean INR ≥2 during the same time period. We also determined etiologic mechanisms of stroke in cases. Results: Among 3569 consecutive patients with cerebral infarction or TIA who had NVAF, 55 (1.5%) patients had INR ≥2 at admission. The most common stroke mechanism was cardioembolism (76.0%). Multivariate analysis demonstrated that smoking and history of previous ischemic stroke were independently associated with cases. High CHADS2 score (≥3) or CHA2DS2-VASc score (≥5), in particular, with previous ischemic stroke along with ≥1 point of other components of CHADS2 score or ≥3 points of other components of CHA2DS2-VASc score was a significant predictor for development of ischemic stroke. Conclusion: NVAF patients with high CHADS2/CHA2DS2-VASc scores and a previous ischemic stroke or smoking history are at high risk of stroke despite optimal warfarin treatment. Some other measures to reduce the risk of stroke would be necessary in those specific groups of patients.
소수의 층을 갖는 환원 graphene oxide(rGO) 표준화를 위한 물성분석
안해준,허승헌,지영호,이병우 한국결정성장학회 2022 한국결정성장학회지 Vol.32 No.6
Reduced graphene oxide (rGO) has attracted many attention and applications due to its excellent electrochemical ability. Therefore, standardization of rGO through structural and thermal analysis facilitates quality improvement and management, enabling users to increase efficiency and reduce relevant costs. For rGO and graphene-related materials, it is very important to determine the number of layers and define the resulting difference in physical properties. In this study, 3~4 layers of rGO-1 and 9~10 layers of rGO-2 were obtained from graphene oxide (GO) through a hydrazine reduction process. For the prepared rGOs, X-ray diffraction (XRD) pattern obtained a diffraction peak at 2θ≈25° related to (002) reflection was used to calculate the layer numbers by determining interlayer distance and FWHM value. To reduce the angular uncertainty, XRD data analysis was performed with angle correction using standard reference materials for X-ray powder diffraction analysis. Precise interlayer distance and number of layers were determined using OriginLab and opensource XRD diffraction analysis programs using the angle-corrected diffraction data. TG-DSC thermal analysis was performed to further standardize the physical properties of rGO samples. 환원그래핀옥사이드(rGO)는 우수한 전기 화학적 능력으로 많은 응용과 관심이 집중되고 있어, 이에 대한 구조 및 열분석을 통한 rGO의 표준화는 품질개선과 관리를 용이하게 하여 사용자가 효율성을 높이고 비용을 절감할 수 있도록 할 수 있다. rGO 및 그래핀 관련 재료의 경우 레이어 층수의 결정과 그에 따른 물성의 차이를 정의하는 것이 매우 중요하다. 본 연구에서는 하이드라진 환원공정을 통해 그래핀옥사이드(GO)로부터 3~4층의 rGO-1과 9~10층의 rGO-2를 얻었다. 이렇게 준비된 rGO에 대해 X선 회절(XRD) 패턴인 (002) 반사와 관련된 2θ≈25°에서 회절 피크를 얻어 층간 거리와 FWHM 값을 얻어 층수(layer number)를 결정하였다. 이때 XRD 데이터 분석은 회절분석용 표준물질들을 사용하여 각도 보정을 수행하였다. 정밀한 층간거리와 FWHM 값은, 각도 보정된 회절 데이터를 이용하여 OriginLab 및 오픈 소스 XRD 회절분석 프로그램들을 사용하여 결정하였다. rGO 샘플들의 추가적인 물성 표준화 분석을 위해 TG-DSC 열분석을 수행하였다.
조광연,류도형,허승헌,신동근,김현이,최종화,정해원,Cho, Kwang-Youn,Riu, Doh-Hyung,Huh, Seung-Hun,Shin, Dong-Geun,Kim, Hyoun-Ee,Choi, Jong-Hwa,Cheong, Hae-Won 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.7
Ceramic Fiber separator is the promising material for thermal battery system because it reduces the production cost and offers the potential to a new application compared to a pellet type electrolyte. The molten salt electrolytes for thermal battery were prepared by the impregnation of the commercial glass filters such as GF-A, C and F (Whatman, USA) with two types of molten-lithium salts, LiCl-KCl and LiK-LiBr-LiF. The wetting properties were evaluated by wetting balance test and wetting angle measurement. The wetting behaviors were strongly affected by the composition of the molten salts and the pore structure of the glass separators. The optimum wetting conditions for maximum loading and effective retention of the molten electrolyte were also studied.
분무열분해법에 의하여 제조한 FTO 투명전도막의 F/Sn 비율에 따른 전기, 광학적 특성과 XPS 분석
송철규,김창열,허승헌,류도형,좌용호,Song, Chul-Kyu,Kim, Chang-Yeoul,Huh, Seung-Hun,Riut, Doh-Hyung,Choa, Yong-Ho 한국재료학회 2007 한국재료학회지 Vol.17 No.7
Fluorine-doped tin oxide (FTO) thin film was coated on aluminosilicate glass at $450^{\circ}C$ by spray pyrolysis method. In the range of 0-2.7 molar ratio of F/Sn, the variations of electrical conductivity and visible light transmission were investigated. At the F/Sn ratio of 1.765, the film showed the lowest electrical resistivity value of $3.0{\times}10^{-4}{\Omega}\;cm$, the highest carrier concentration of $2.404{\times}10^{21}/cm^3$, and about $8\;cm^2/V{\cdot}sec$ of electronic mobility. The FTO film showed a preferred orientation of (200) plane parallel to the substrate. X-ray photoelectron spectroscopy analysis results indicated that the contents of $Sn^{4+}-O$ bonding are the highest at 1.765 of F/Sn molar ratio.