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Choi, Yoonho,Choi, Myung-Jin,Cha, Song-Hyun,Kim, Yeong Shik,Cho, Seonho,Park, Youmie Springer 2014 NANOSCALE RESEARCH LETTERS Vol.9 No.1
<P>An eco-friendly approach is described for the green synthesis of gold nanoparticles using catechin as a reducing and capping agent. The reaction occurred at room temperature within 1 h without the use of any external energy and an excellent yield (99%) was obtained, as determined by inductively coupled plasma mass spectrometry. Various shapes of gold nanoparticles with an estimated diameter of 16.6 nm were green-synthesized. Notably, the capping of freshly synthesized gold nanoparticles by catechin was clearly visualized with the aid of microscopic techniques, including high-resolution transmission electron microscopy, atomic force microscopy, and field emission scanning electron microscopy. Strong peaks in the X-ray diffraction pattern of the as-prepared gold nanoparticles confirmed their crystalline nature. The catalytic activity of the as-prepared gold nanoparticles was observed in the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH<SUB>4</SUB>. The results suggest that the newly prepared gold nanoparticles have potential uses in catalysis.</P>
Choi, Yoonho,Kang, Sehyeon,Cha, Song-Hyun,Kim, Hyun-Seok,Song, Kwangho,Lee, You Jeong,Kim, Kyeongsoon,Kim, Yeong Shik,Cho, Seonho,Park, Youmie Springer US 2018 NANOSCALE RESEARCH LETTERS Vol.13 No.1
<P>A green synthesis of gold and silver nanoparticles is described in the present report using platycodon saponins from Platycodi Radix (<I>Platycodon grandiflorum</I>) as reducing agents. Platycodin D (PD), a major triterpenoidal platycodon saponin, was enriched by an enzymatic transformation of an aqueous extract of Platycodi Radix. This PD-enriched fraction was utilized for processing reduction reactions of gold and silver salts to synthesize gold nanoparticles (PD-AuNPs) and silver nanoparticles (PD-AgNPs), respectively. No other chemicals were introduced during the reduction reactions, providing an entirely green, eco-friendly, and sustainable method. UV-visible spectra showed the surface plasmon resonance bands of PD-AuNPs at 536 nm and PD-AgNPs at 427 nm. Spherically shaped nanoparticles were observed from high-resolution transmission electron microscopy with average diameters of 14.94 ± 2.14 nm for PD-AuNPs and 18.40 ± 3.20 nm for PD-AgNPs. Minor triangular and other polygonal shapes were also observed for PD-AuNPs along with spherical ones. Atomic force microscopy (AFM) images also demonstrated that both nanoparticles were mostly spherical in shape. Curvature-dependent evolution was employed to enhance the AFM images and precisely measure the sizes of the nanoparticles. The sizes were measured as 19.14 nm for PD-AuNPs and 29.93 nm for PD-AgNPs from the enhanced AFM images. Face-centered cubic structures for both nanoparticles were confirmed by strong diffraction patterns from high-resolution X-ray diffraction analyses. Fourier transform infrared spectra revealed the contribution of –OH, aromatic C=C, C–O, and C–H functional groups to the synthesis. Furthermore, the catalytic activity of PD-AuNPs was assessed with a reduction reaction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride. The catalytic activity results suggest the potential application of these gold nanoparticles as catalysts in the future. The green strategy reported in this study using saponins as reducing agents will pave new roads to develop novel nanomaterials with versatile applications.</P>
Yangsean Choi,Eo-Jin Hwang,Yoonho Nam,Hyun Seok Choi,장진희,정소령,안국진,김범수 대한영상의학회 2019 Korean Journal of Radiology Vol.20 No.7
Objective: To compare apparent diffusion coefficients (ADCs) of brain segments by using two diffusion-weighted imaging acquisition modes, single-shot echo-planar imaging (ss-EPI) and read-out-segmented echo-planar imaging (rs-EPI), and to assess their correlation and agreement in healthy controls. Materials and Methods: T2-weighted (T2W) images, rs-EPI, and ss-EPI of 30 healthy subjects were acquired using a 3T magnetic resonance scanner. The T2W images were co-registered to the rs-EPI and ss-EPI, which were then segmented into the gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) to generate masking templates. ADC maps of rs-EPI and ss-EPI were also segmented into the GM, WM, and CSF by using the generated templates. ADCs of rs-EPI and ss-EPI were compared using Student’s t tests and correlated using Pearson’s correlation coefficients. Bland-Altman plots were used to assess the agreement between acquisitions. Results: ADCs of rs-EPI and ss-EPI were significantly different in the GM (p < 0.001) and WM (p < 0.001). ADCs showed high agreement and correlation in the whole brain and CSF (r > 0.988; p < 0.001). ADC of the WM showed the least correlation (r = 0.894; p < 0.001), and ADCs of the WM and GM showed poor agreement. Pearson’s correlation equations for each brain segment were y = 1.1x - 59.4 (GM), y = 1.45x - 255 (WM), and y = 0.98x - 63.5 (CSF), where x and y indicated ADCs of rs-EPI and ss-EPI, respectively. Conclusion: While ADCs of rs-EPI and ss-EPI showed high correlation and agreement in the whole brain and CSF, ADCs of the WM and GM showed significant differences and large variability, reflecting brain parenchymal inhomogeneity due to different regional microenvironments. ADCs of different acquisition methods should be interpreted carefully, especially in intraindividual comparisons.
최윤호(YoonHo Choi),고창성(Chang-Seong Koh),현범석(Beom-Seok Hyeon),박원배(Won-Bae Park),박준범(Jun-Beom Park) 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10
최근 한라산을 포함한 고지대로부터 저지대까지 제주도의 지질 특성을 재정립하기 위한 연구가 다채롭게 수행되고 있다. 그럼에도 불구하고 아직까지 제주도의 해안선을 따라 상세한 지형분류와 더불어 이와 연계된 지질학적 해석이 제대로 이루어지지 않은 실정이다. 이 연구는 제주도 해안지형의 특징을 지질학적으로 표준화하여 분류하고 해석하기 위한 예비적 연구로서, 제주도 해안지역 중 일부를 선정하여 해안지형의 구성지질과 암상을 토대로 분류한 결과에 대해 소개한다. 제주도의 해안지형 유형은 크게 암석해안과 사질해안으로 나눌 수 있다. 암석해안은 해안경사를 기준으로 완만/평탄형과 해식애형으로 구분된다. 완만/평탄형은 대체로 단일 용암단위의 파호이호이 혹은 아아 용암류가 대지를 이루고 있는 해안에서 관찰된다. 해식애형은 치밀질의 아아 용암류 혹은 복합 용암류 또는 응회퇴적층이 두껍게 발달된 해안에서 확인된다. 특히 해식애형은 기저에 수 m에 달하는 크기의 암괴가 쌓여있는 파석대 또는 표면이 매끄럽고 평탄한 파식대를 이루는데, 보통 파석대는 해식애와 동질의 지질특성을 이루는 반면, 파식대는 이질특성을 보인다. 사질해안은 해안선이 만의 형태를 이루는 곳에 해빈지형을 이루고 있다. 구성입자의 입도를 기준하여 모래해안과 자갈해안으로 구분되며, 입자기원에 따라서 육상기원과 해양기원의 사질해안으로 세분된다. 이러한 제주도 해안지형의 지질학적 분류는 향후 해안선을 따라 발달하는 다양한 지하수 유형을 해석하는데 중요한 기초 자료로서의 역할을 기대한다.
Yangsean Choi,장진희,Yoonho Nam,Na-Young Shin,Hyun Seok Choi,정소령,안국진,김범수 대한영상의학회 2019 Korean Journal of Radiology Vol.20 No.4
Objective: A developmental venous anomaly (DVA) is a vascular malformation of ambiguous clinical significance. We aimed to quantify the susceptibility of draining veins (χvein) in DVA and determine its significance with respect to oxygen metabolism using quantitative susceptibility mapping (QSM). Materials and Methods: Brain magnetic resonance imaging of 27 consecutive patients with incidentally detected DVAs were retrospectively reviewed. Based on the presence of abnormal hyperintensity on T2-weighted images (T2WI) in the brain parenchyma adjacent to DVA, the patients were grouped into edema (E+, n = 9) and non-edema (E-, n = 18) groups. A 3T MR scanner was used to obtain fully flow-compensated gradient echo images for susceptibility-weighted imaging with source images used for QSM processing. The χvein was measured semi-automatically using QSM. The normalized χvein was also estimated. Clinical and MR measurements were compared between the E+ and E- groups using Student’s t-test or Mann-Whitney U test. Correlations between the χvein and area of hyperintensity on T2WI and between χvein and diameter of the collecting veins were assessed. The correlation coefficient was also calculated using normalized veins. Results: The DVAs of the E+ group had significantly higher χvein (196.5 ± 27.9 vs. 167.7 ± 33.6, p = 0.036) and larger diameter of the draining veins (p = 0.006), and patients were older (p = 0.006) than those in the E- group. The χvein was also linearly correlated with the hyperintense area on T2WI (r = 0.633, 95% confidence interval 0.333–0.817, p < 0.001). Conclusion: DVAs with abnormal hyperintensity on T2WI have higher susceptibility values for draining veins, indicating an increased oxygen extraction fraction that might be associated with venous congestion.
최윤호(Choi Yoonho),박혜준(Park Hyejun),송만석(Song Mansuk) 한국정보과학회 1993 한국정보과학회 학술발표논문집 Vol.20 No.1
자연어 처리를 위한 사전을 개발하고자 할 때, 그 방법론의 결정은 매우 중요한 요소이다. 특히, 자연어는 의미적 요소와 구문적 요소, 그리고 공기(collocation) 등 여러가지 요소로 이루어지기 때문에 이런 정보들은 정확하게 추출되어 효율적으로 저장되어야 한다.[7] 그리고 언어란 각 어휘들과 그들의 관계로 정의될 수 있으므로 각 어휘에 대한 용례의 추출은 국어 연구에 있어 가장 기초가 된다.[1] 그러나 지금까지의 용례 추출은 어휘 분석에 많은 시간을 소비함에도 불구하고, 출력된 용례에는 원하지 않는 용례들이 많이 포함되는 비효율성을 내포하고 있었다.[6] 이런 문제점을 해결하기 위해 본 논문은 중의성 해결 논리를 추가하여 보다 진보된 용례 색인기를 개발하고자 한다.
멀티미디어 셀룰러 네트워크상에서 내쉬 협상해법을 이용한 대역폭 관리기법
최윤호(Yoonho Choi),김승욱(Sungwook Kim) 한국정보과학회 2010 정보과학회논문지 : 정보통신 Vol.37 No.6
본 논문에서는 이동 셀룰러 네트워크 환경에서 한정된 자원인 무선대역폭을 효율적으로 사용하기 위해 게임이론을 이용한 대역폭 예약 기법을 제안하였다. 제안된 기법에서는 게임 이론의 협상 해법 중 대표적인 NBS 기법을 이용하여 전체 시스템의 효용을 극대화하는 최적의 대역폭 대여량과 예약량을 계산한다. 성능평가 결과 제안된 기법이 다양한 네트워크의 상황에 탄력적으로 대응할 수 있었기에 기존에 제안된 기법에 비해 뛰어난 성능을 보임을 확인할 수 있었다. Bandwidth is an extremely valuable and scarce resource in a wireless network. Therefore, efficient bandwidth management is necessary in order to provide high quality service to users with different requirements. In this paper, we propose a bandwidth reservation algorithm based on Nash Bargaining Solution. The proposed algorithm has low complexity and are quite flexible in the different situations of network. Simulation results indicate that the proposed scheme has excellent performance than other existing schemes.