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Extraordinary Off-Stoichiometric Bismuth Telluride for Enhanced n-Type Thermoelectric Power Factor
Park, Kunsu,Ahn, Kyunghan,Cha, Joonil,Lee, Sanghwa,Chae, Sue In,Cho, Sung-Pyo,Ryee, Siheon,Im, Jino,Lee, Jaeki,Park, Su-Dong,Han, Myung Joon,Chung, In,Hyeon, Taeghwan American Chemical Society 2016 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.138 No.43
<P>Thermoelectrics directly converts waste heat into electricity and is considered a promising means of sustainable energy generation. While most of the recent advances in the enhancement of the thermoelectric figure of merit (ZT) resulted from a decrease in lattice thermal conductivity by nanostructuring, there have been very few attempts to enhance electrical transport properties, i.e., the power factor. Here we use nanochemistry to stabilize bulk bismuth telluride (Bi2Te3) that violates phase equilibrium, namely, phase-pure n-type K0.06Bi2Te3.18. Incorporated potassium and tellurium in Bi2Te3 far exceed their solubility limit, inducing simultaneous increase in the electrical conductivity and the Seebeck coefficient along with decrease in the thermal conductivity. Consequently, a high power factor of similar to 43 mu W cm(-1) K-2 and a high ZT > 1.1 at 323 K are achieved. Our current synthetic method can be used to produce a new family of materials with novel physical and chemical characteristics for various applications.</P>
Characteristic research of pellet injection system in KSTAR
Park, SooHwan,Kim, HongTack,Song, JaeIn,Woo, InSik,Lee, KunSu,Lee, HyunMyung,Kim, YoungOk,Yonekawa, Hirofumi,Kim, KwangPyo,Chu, Yong,Oh, YeongKook Elsevier 2018 Fusion engineering and design Vol.136 No.2
<P><B>Abstract</B></P> <P>20 Hz pellet injection system was installed for improving a fueling system of KSTAR (Korea Superconducting Tokamak Advanced Research) in 2016. Several things of hardware such as a liquid helium transfer line, an extruder nozzle and an extension part of pellet guide tube are changed for 2017 campaign. For plasma experiments, the pellet injection system uses the smallest pellet (1.5 mm of length, 2 mm of diameter). The pellet velocity can be variable from 150 m/s to over 200 m/s by controlling of propellant gas pressure. The clear increase of plasma density observed during KSTAR experiments is also presented in this paper.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The smallest pellet (1.5 mm of length, 2 mm of diameter) injection is successful. </LI> <LI> Slower pellet injection less than 150 m/s is achieved. </LI> <LI> Pellet trajectory is closer to plasma by straight extension part. </LI> </UL> </P>
김건수(Kunsu Kim),이동훈(Dong-hoon Lee),박두경(Doo-Kyung Park),이지형(Jee-Hyong Lee) 한국지능시스템학회 2008 한국지능시스템학회논문지 Vol.18 No.2
웹서비스와 상황인식서비스는 사용자의 요구에 따라 많은 종류의 서비스를 제공할 수 있어야 한다. 사용자의 요구는 날로 다양해지고 있고 그에 발맞추어 다양한 종류의 서비스들이 서비스 제공 업체에 의해 새롭게 시장에 등장하고 있다. 하지만 사용자의 새로운 요청에 맞추어 새로운 서비스를 생산하거나 일부 사용자의 요구때문에 새로운 서비스를 만드는 것은 비효율적이다. 그래서 최근에는 유저의 다양한 요청에 보다 유연하게 대응할 수 있는 기술들에 대한 연구가 이루어지고 있다. 그 중 단일 서비스의 조합을 통해 복합서비스를 제공할 수 있는 서비스 컴포지션이라는 기술이 주목을 받고 있다. 하지만, 기존 연구들은 다소 늦은 처리속도로 인해 빠른 응답이 필요한 실시간 상황인식서비스에는 부적합하다. 그래서 본 논문은 사례기반추론을 이용하여 기존 방법보다 빠른 서비스 컴포지션을 구현하는 방법을 제안한다. 그리고 제안하는 알고리즘을 검증하기 위해 사용자에게 이동서비스와 구매정보서비스를 이용하여 사용자의 이동 및 구매 요구를 만족하는 조합을 찾아주는 물건 구매 서비스 서비스를 구현하고 이 구현된 물건 구매 도우미 서비스에 제안하는 알고리즘과 기존 서비스 컴포지션 기법을 적용하여 각 알고리즘의 성능을 비교분석 한다. Context-aware service environment should provide many kinds of services according to users' requests. Users want a great variety of services. In response to their demands the service provider should make a new service every time. But making a new service every time may be inefficient even for a small number of users' requests. So, there are studies on how to efficiently support various and complex requests from users. In many researches, service compositions have lately attracted considerable attention. However, existing researches have mainly focused on Web services. So they are not proper to rapidly providing services in response to users' requests, especially in context-aware service environment. This paper proposes a rapid service composition using case-based reasoning. For evaluating the proposed algorithm we implement 'purchasing service agent'. With this system, we compare our algorithm and the existing service composition algorithms.
Foreign Currency Denominated Debt and Dividend Policy
Youngmok Choi,Kunsu Park 한국재무학회 2015 한국재무학회 학술대회 Vol.2015 No.05
We examine whether foreign currency denominated debt affects corporate dividend policy. Specifically, this study tests the prediction that foreign currency denominated debt ratio is negatively related to the likelihood of paying dividends and the levels of dividends. Consistent with our prediction, we find that firms with a higher foreign currency debt ratio are less likely to pay dividends, and pay lower levels of dividends when they do. These findings indicate that foreign currency debt ratio is one of the important factors that affect corporate dividend policy. Our results provide evidence that foreign creditors have the potential in determining corporate dividend policy.
Foreign Currency Denominated Debt and Corporate Dividend Policy
Youngmok Choi(최영목),Kunsu Park 대한경영학회 2016 대한경영학회 학술발표대회 발표논문집 Vol.2016 No.1
We examine whether foreign currency denominated debt affects corporate dividend policy. Specifically, this study hypothesizes that foreign currency denominated debt ratio is negatively related to the likelihood of paying dividends and the level of dividends. For the hypothesis, we provide the following two rationales, one based on foreign currency risk and the other based on agency costs. Consistent with our hypothesis, we find that a firm with a higher foreign currency debt ratio is less likely to pay dividends and pays a lower level of dividends. These findings suggest that foreign currency debt can be an important determinant of corporate dividend policy. Our results are robust to endogeneity concerns, to alternative measures of the level of dividends, and to change regressions. We also find that the negative relation between foreign currency debt ratio and the level of dividends is more pronounced in firms with lower cash flow uncertainty and higher free cash flows. Overall, our empirical evidence suggests that foreign creditors have the potential to determine corporate dividend policy.
사례기저 수치화와 트리구조 관리를 이용한 서비스 컴포지션의 속도 향상 연구
이승훈(Seunghoon Lee),김건수(Kunsu Kim),윤태복(Taebok Yoon),박두경(Dookyung Park),이지형(Jee-Hyung Lee) 한국정보과학회 2008 한국정보과학회 학술발표논문집 Vol.35 No.1
유비쿼터스 컴퓨팅의 목표 중 하나는 사용자의 직접적이거나 은연중에 내포된 요청에 따라 적절한 서비스를 제공하는 것이다. 최근에는 사용자의 다양한 요청에 보다 유연하게 대응할 수 있는 연구가 이루어지고 있으며 그 중 단일서비스의 조합을 통해 복합서비스를 제공할 수 있는 서비스 컴포지션(Service Composition)이 주목을 받고 있다. 하지만 기존 연구들은 늦은 처리속돌 인해 실시간 상황인식 서비스에서 빠른 응답을 바라는 사용자의 요구사항을 만족시키기 어렵다. 또한 사례기반추론은 사례기저에 쌓인 사례의 수가 늘어감에 따라 속도가 저하되는 단점이 있다. 이러한 단점을 최소화 하기 위하여 클러스터링 기법이 사용되고 있다. 그러나 클러스터링 기법은 사례기저의 수를 줄여가면서 속도를 유지하기 때문에 기존의 사례가 다시 발생하였을 경우에도 새로운 문제로 인식하게 되는 문제를 가지고 있다. 이러한 문제점을 해결하기 위해서 본 논문에서는 사례기저의 수를 유지하면서 사례기저의 수치화 및 트리구조 관리를 이용하여 기존방법보다 빠른 서비스 컴포지션을 구현하는 방법을 제안한다. 그리고 기존의 서비스 컴포지션 기법과 비교 분석을 통하여 제안하는 기법의 유효함을 확인하였다.
Son, Jae Sung,Park, Kunsu,Han, Mi‐,Kyung,Kang, Chanyoung,Park, Sung‐,Geun,Kim, Jae‐,Hee,Kim, Woochul,Kim, Sung‐,Jin,Hyeon, Taeghwan WILEY‐VCH Verlag 2011 Angewandte Chemie Vol.123 No.6
<P><B>Gepresste Bi‐Nanokristalle</B>, die durch eine einfache Kolloidmethode erhalten wurden, zeigten sehr hohe elektrische Leitfähigkeiten von 10<SUP>4</SUP>–10<SUP>5</SUP> S m<SUP>−1</SUP> bei einer extrem niedrigen thermischen Leitfähigkeit von 0.35 W m<SUP>−1</SUP> K<SUP>−1</SUP>. Die Synthesemethode kann für die kostengünstige Herstellung von hoch effizienten thermoelektrischen Materialien durch gezielten Größenzuschnitt der Nanokristalle genutzt werden (siehe Bild; Skalierung 50 nm; <I>ZT</I>=Gütezahl).</P>
Hedging with Property-Liability Insurance and Corporate Dividend Policy
Young Mok Choi,Kunsu Park 대한경영학회 2016 대한경영학회 학술발표대회 발표논문집 Vol.2016 No.2
Using a sample of 617 Korean firms between 2002 and 2015, we examine the extent to which property-liability insurance has an effect on a firm’s dividend payout. We find that firms with a higher extent of property-liability insurance use pay more dividend payouts, consistent with our central hypothesis. Furthermore, our main result is robust to endogeneity problems, alternative estimation methods, and different measures for the level of dividends. Overall, our study suggests that hedging with property-liability insurance is one of the potential determinants of corporate dividend policy.
전자기적 발열에서의 KSTAR In-Vessel Control Coil의 열 및 기계적 거동
강진구(Jin Gu Kang),박성현(Sunghyun Park),장민용(Minyoung Jang),이현정(Hyunjung Lee),김현욱(Hyun Wook Kim),이근수(KunSu Lee),김광표(Kwang Pyo Kim),박갑래(Kaprai Park),김범석(Beom Seok Kim) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11
To settle fusion technology, technical- and engineering challenges should be solved to control unstable fusion plasma. In-vessel control coil (IVCC) in Korea Superconducting Tokamak Advanced Research (KSTAR) has been implemented for plasma control. We characterize the mechanical behaviors of IVCC under high heat-generation environments due to electrically induced eddy currents. Numerical evaluations reveal electromagnetic-, thermal- and mechanical responses under operating conditions. Thermal stability is assessed in terms of transient temperature variations and consequent thermal stress distributions. Experimental approaches using IVCC mock-up models are employed to validate the numerical results. We suggest candidates reduce eddy current and guarantee heat-dissipating performance via tailored methods with an upgrade of the IVCC case. The preliminary results will be the fundamental data for feasible upgrade of IVCC in KSTAR.
전자기적 발열에서의 KSTAR In-Vessel Control Coil의 열 및 기계적 거동
강진구(Jin Gu Kang),박성현(Sunghyun Park),장민용(Minyoung Jang),이현정(Hyunjung Lee),김현욱(Hyun Wook Kim),이근수(KunSu Lee),김광표(Kwang Pyo Kim),박갑래(Kaprai Park),김범석(Beom Seok Kim) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11
To settle fusion technology, technical- and engineering challenges should be solved to control unstable fusion plasma. In-vessel control coil (IVCC) in Korea Superconducting Tokamak Advanced Research (KSTAR) has been implemented for plasma control. We characterize the mechanical behaviors of IVCC under high heat-generation environments due to electrically induced eddy currents. Numerical evaluations reveal electromagnetic-, thermal- and mechanical responses under operating conditions. Thermal stability is assessed in terms of transient temperature variations and consequent thermal stress distributions. Experimental approaches using IVCC mock-up models are employed to validate the numerical results. We suggest candidates reduce eddy current and guarantee heat-dissipating performance via tailored methods with an upgrade of the IVCC case. The preliminary results will be the fundamental data for feasible upgrade of IVCC in KSTAR.