• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 춘계종합학술대회
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• pp.1113-1116
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• 2005

본 논문에서는 다중빔 스위칭 기능을 갖는 Ka 대역 통신해양기상위성의 통신 중계기를 이용한 고속통신 서비스를 위한 링크 설계와 양질의 전송 서비스를 제공할 수 있는 최적의 전송 채널을 제안한다. 다양한 전송 서비스를 제공하는 Ka 대역 통신 중계기의 열화 요인으로 작용하는 군 지연 및 비선형 그리고 이득 평탄도에 대한 채널 모델링과 성능 열화를 해석한다. 전송 데이터가 증가함에 따라 군지연과 비선형에 의한 영향은 증가하며, 군지연의 선형 성분과 비선형의 AM-AM 성분이 시스템 성능 열화에 지배적으로 작용하는 것을 알 수 있었다. 고속 데이터에 따른 광대역 전송 대역폭으로 낮은 군지연과 이득 평탄도를 얻기가 어려우므로 주요 열화 요소를 등화하여 수십 Mbps에서부터 수백 Mbps의 넓은 범위의 서비스를 동일 시스템에서 효과적으로 제공하여야 한다. 분석된 결과는 통신해양기상위성을 이용한 최적의 고속 위성전송 시스템을 설계하고 운용하는데 활용될 수 있다.

• Tribology and Lubricants
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• 제30권6호
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• pp.323-329
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• 2014

The friction-reducing properties of lubricants containing ionic liquids based on ammonium dithiocarbamate are studied. The ionic liquids are produced through the following two steps: the synthesis of sodium alkyl dithiocarbamates via the substitution reaction of dialkylamine and carbon disulfide and their subsequent conversion into ammonium dithiocarbamate-based ionic liquids through an ion-exchange reaction with a quaternary alkyl ammonium halide salt. The structures of the ionic liquids are characterized by NMR spectroscopy and Fourier transform infrared spectroscopy. The isolated yields of the ionic liquids, which are viscous and pale yellow, are approximately 92%. The Brookfield viscosities and pour points of the ionic liquids are determined. Further, their wear resistances are measured through the four-ball wear test and the Schwingung Reibung Ver-schleiss (oscillation, friction, wear) test. The wear scar diameter of the lubricants containing 1 wt of the quaternary alkyl ammonium dithiocarbamate-based ionic liquids (0.475-0.631 mm) is significantly lower than that of the base oil (0.825 mm), proving that the ammonium dithiocarbamate-based ionic liquids have good friction-reducing characteristics. However, these friction-reducing characteristics fade significantly after long-term storage, owing to the degradation of the ionic liquids.

• 한국재료학회지
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• 제22권10호
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• pp.562-568
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• 2012

Metal nanowires can be coated on various substrates to create transparent conducting films that can potentially replace the dominant transparent conductor, indium tin oxide, in displays, solar cells, organic light-emitting diodes, and electrochromic windows. One issue with these metal nanowire based transparent conductive films is that the resistance between the nanowires is still high because of their low aspect ratio. Here, we demonstrate high-performance transparent conductive films with silver nanofiber networks synthesized by a low-cost and scalable electrospinning process followed by two-step sequential thermal treatments. First, the PVP/$AgNO_3$ precursor nanofibers, which have an average diameter of 208 nm and are several thousands of micrometers in length, were synthesized by the electrospinning process. The thermal behavior and the phase and morphology evolution in the thermal treatment processes were systematically investigated to determine the thermal treatment atmosphere and temperature. PVP/$AgNO_3$ nanofibers were transformed stepwise into PVP/Ag and Ag nanofibers by two-step sequential thermal treatments (i.e., $150^{\circ}C$ in $H_2$ for 0.5 h and $300^{\circ}C$ in Ar for 3 h); however, the fibrous shape was perfectly maintained. The silver nanofibers have ultrahigh aspect ratios of up to 10000 and a small average diameter of 142 nm; they also have fused crossing points with ultra-low junction resistances, which result in high transmittance at low sheet resistance.

• Molecules and Cells
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• 제38권1호
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• pp.20-25
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• 2015

TGF-${\beta}$ regulates pleiotropic cellular responses including cell growth, differentiation, migration, apoptosis, extracellular matrix production, and many other biological processes. Although non-Smad signaling pathways are being increasingly reported to play many roles in TGF-${\beta}$-mediated biological processes, Smads, especially receptor-regulated Smads (R-Smads), still play a central mediatory role in TGF-${\beta}$ signaling for epithelial-mesenchymal transition. Thus, the biological activities of R-Smads are tightly regulated at multiple points. Inhibitory Smad (I-Smad also called Smad7) acts as a critical endogenous negative feedback regulator of Smad-signaling pathways by inhibiting R-Smad phosphorylation and by inducing activated type I TGF-${\beta}$ receptor degradation. Roles played by Smad7 in health and disease are being increasingly reported, but the molecular mechanisms that regulate Smad7 are not well understood. In this study, we show that E3 ubiquitin ligase Itch acts as a positive regulator of TGF-${\beta}$ signaling and of subsequent EMT-related gene expression. Interestingly, the Itch-mediated positive regulation of TGF-${\beta}$ signaling was found to be dependent on Smad7 ubiquitination and its subsequent degradation. Further study revealed Itch acts as an E3 ubiquitin ligase for Smad7 polyubiquitination, and thus, that Itch is an important regulator of Smad7 activity and a positive regulator of TGF-${\beta}$ signaling and of TGF-${\beta}$-mediated biological processes. Accordingly, the study uncovers a novel regulatory mechanism whereby Smad7 is controlled by Itch.

• Korean Journal of Geomatics
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• 제2권1호
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• pp.37-46
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• 2002

Accurate classification of water area is an preliminary step to accurately analyze the flooded area and damages caused by flood. This step is especially useful for monitoring the region where annually repeating flood is a problem. The accurate estimation of flooded area can ultimately be utilized as a primary source of information for the policy decision. Although SAR (Synthetic Aperture Radar) imagery with its own energy source is sensitive to the water area, its shadow effect similar to the reflectance signature of the water area should be carefully checked before accurate classification. Especially when we want to identify small flood area with mountainous environment, the step for removing shadow effect turns out to be essential in order to accurately classify the water area from the SAR imagery. In this paper, the flood area was classified and monitored using multi-temporal RADARSAT SAR images of Ok-Chun and Bo-Eun located in Chung-Book Province taken in 12th (during the flood) and 19th (after the flood) of August, 1998. We applied several steps of geometric and radiometric calculations to the SAR imagery. First we reduced the speckle noise of two SAR images and then calculated the radar backscattering coefficient $(\sigma^0)$. After that we performed the ortho-rectification via satellite orbit modeling developed in this study using the ephemeris information of the satellite images and ground control points. We also corrected radiometric distortion caused by the terrain relief. Finally, the water area was identified from two images and the flood area is calculated accordingly. The identified flood area is analyzed by overlapping with the existing land use map.

• 미술이론과 현장
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• 제3호
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• pp.173-192
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• 2005

Yoo Youngkuk started his career as an artist when he entered Bunkagakuin of Tokyo in 1935 he actively participated in the Japanese art scene as a young Korean artist until 1943. In his earliest works, Rhapsody and Work B, Surrealist and abstract influences are manifested as these were prevalent in Japan at the time. With the exception of Rhapsody and Work B, all works available that were executed between 1937 and 1940 are abstract, which points to the fact that Yoo intended abstraction from the beginning. Surviving works in relief suggest his early style was founded on the abstractions similar to Russian Avant-Garde, Neo-plasticism and Bauhaus simplicity. His early abstractions were not the ideational images derived in the process of the abstraction of the representational image, but they arose from the constructive attitude in composing the already stylized non-representational geometries. It is worth noting that his early emphasis was on the pure and absolute geometric abstraction, rather than the images motivated from the figurative representation. Yoo differentiates himself from Kim Whan Ki in the following aspects: one, he eliminated the subject matter i.e. human figures and the nature; two, he maintained the constructivist attitude in creating a strict and absolute abstraction; three, he experimented with different styles without combining them. He manifests direct influences from the prevalent Western art influences, such as Futurism and Russian Avant-Garde, unlike Kim who vaguely references. In both paintings and reliefs, Yoo's attempt in the realization of the pictorial depth and space seems cerebral and conceptualized compared with the other artists of the time who resolved abstraction via the constructive dimension. Uemura, a contemporary critic to the geometric abstractions in Japan, disapproves the stylistic bent in the adaptation of the abstract painting without the comprehension of its spiritual movement. As witnessed in other criticisms as well, contemporary Japanese critics' interest lie mainly in the superficial observation such as the presence of representational elements, composition and use of color. Such formal and superficial understanding of the geometric abstraction resulted in

• 한국지진공학회논문집
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• 제7권4호
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• pp.81-87
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• 2003

본 논문에서는 Shannon의 샘플링 이론을 이용하여 제한된 수의 센서에서 얻은 모드형상으로 정확한 모드형상을 재생성하고, 이렇게 재생성한 모드형상을 이용하여 구조물에 발생한 손상을 탐지할 수 있는지의 가능성에 대해 조사하였다. 우선 시간 영역에서의 Shannon의 샘플링 이론을 검토하였고, 이를 공간영역으로 확대하였다. 공간영역으로 확대한 Shannon의 샘플링 이론은 그 효용성을 확인하기 위하여 단순보의 모드형상을 해석적으로 구한 후 최소한으로 제한된 수의 샘플 데이터로 모드형상을 재생하였고 이를 원래의 모드형상과 비교하였다. 이렇게 하여 얻은 결과를 바탕으로 구조물의 모드형상을 추출하는 동적실험에서 필요한 최적 가속도계의 위치를 구할 수 있는 간단한 관계식을 제안하였다. 제안된 관계식과 공간영역으로 확대한 Shannon의 샘플링 이론의 실용성은 연속 2스팬으로 구성된 실험실 빔 구조물의 손상 전과 후의 모드형상에 적용하여 손상을 탐지함으로써 입증하였다.

• Bulletin of the Korean Chemical Society
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• 제7권5호
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• pp.395-399
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• 1986

Intramolecular proton transfer equilibria of acetamide and methyl carbamate have been studied theoretically by MNDO MO method. For both substrates, carbonyl-O protonated tautomer was found to be the most stable form, the next most stable one being N-protonated form. Gas phase proton transfers take place by the 1,3-proton rearrangement process and in all cases have prohibitively high activation barriers. When however one solvate water molecule participates in the process, the barriers are lowered substantially and the process proceeds in an intermolecular manner through the intermediacy of the water molecule via a triple-well type potential energy surface; three wells correspond to reactant(RC), intermediate(IC) and product complex(PC) of proton donor-acceptor pairs whereas two transition states(TS) have proton-bridge structure. General scheme of the process can be represented for a substrate with two basic centers(heteroatoms) of A and B as, $$ABH\limits^+\;+\;H_2O\;{\to}\;ABH\limits^+{\cdots}{\limits_{RC}}OH_2\;{\to}\;AB{\cdots}H\limits_{TS}^+{\cdots}{\limits_{1}}OH_2\;{\to}\;AB{\cdots}{\limits_{IC}}H\limits^+OH_2\;{\to}\;BA{\cdots}H\limits_{TS}^+{\cdots}{\limits_{2}}OH_2\;{\to}\;BA H\limits^+{\cdots}{\limits_{PC}}OH_2\;{\to}\;BAH\limits^+\;+\;H_2O$$ Involvement of a second solvate water had negligible effect on the relative stabilities of the tautomers but lowered barrier heights by 5∼6 Kcal/mol. It was calculated that the abundance of the methoxy-O protonated tautomer of the methyl carbamate will be negligible, since the tautomer is unfavorable thermodynamically as well as kinetically. Fully optimized stationary points are reported.

• 한국IT서비스학회지
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• 제18권3호
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• pp.53-74
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• 2019

In this paper, a theoretical measurement model for comparing cultural power of nations as a form of national power is built and applied to the G20 nations. The measurement model is drawn from the literature of the state theories regarding culture, theories of epistemology, and debates about the sources of national power. Taking the multiple indicator approach, indicators reflecting diverse aspects of cultural power are developed are developed. Examined with empirical data, this model is proved as appropriate as a tool for measuring and comparing the cultural power of nations. Diverse aspects of the cultural power of the G20 nations are ranked and interesting points regarding the state and potential of Korean culture and her cultural governance in these respects are elaborated. The overall ranking of the cultural power of Korea is found as the $11^{th}$ while the U.S., U.K. and France respectively as the $1^{st}$, the $2^{nd}$, and the $3^{rd}$. The U.S. is ranked as the 1st in all three aspects of the cultural power of nation: cultural attractiveness, efforts to enhance the national cultural power, and cultural base of a nation. Korea is ranked as $14^{th}$, $11^{th}$, and $6^{th}$ respectively in these three respects of the national cultural power. Based upon typological analysis of the cultural power of Korea, it is found that Korea belongs to Type III. Trying to move eventually toward Type I state via Type II is suggested as a strategy movement for future cultural governance by Korean government and people to enhance her national cultural power.

• 한국기계가공학회지
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• 제20권9호
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• pp.1-10
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• 2021

Recently, the repair and recycling of damaged mechanical parts via metal additive manufacturing processes have been industrial points of interest. This is because the repair and recycling of damaged mechanical parts can reduce energy and resource consumption. The directed energy deposition(DED) process has various advantages such as the possibility of selective deposition, large building space, and a small heat-affected zone. Hence, it is a suitable process for repairing damaged mechanical parts. The shaft is a core component of various mechanical systems. Although there is a high demand for the repair of the shaft, it is difficult to repair with traditional welding processes because of the thermal deformation problem. The objective of this study is to propose a repair procedure for a damaged shaft using the DED process and discuss its applications. Three types of cases, including a small shaft with a damaged surface, a medium-size shaft with a worn bearing joint, and a large shaft with serious damage, were repaired using the proposed procedure. The microstructure and hardness were examined to discuss the characteristics of the repaired component. The efficiency of the repair of the damaged shaft is also discussed.