Enhanced Electrochemical Stability of Quasi-Solid-State Electrolyte Containing SiO₂ Nanoparticles for Li-O₂ Battery Applications

Kim, Hyunjin,Kim, Tae Young,Roev, Victor,Lee, Heung Chan,Kwon, Hyuk Jae,Lee, Hyunpyo,Kwon, Soonchul,Im, Dongmin American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.2

<P>A stable electrolyte is required for use in the open-packing environment of a Li-O-2 battery system. Herein, a gelled quasi-solid-state electrolyte containing SiO2 nanoparticles was designed, in order to obtain a solidified electrolyte with a high discharge capacity and long cyclability. We successfully fabricated an organic-inorganic hybrid matrix with a gelled structure, which exhibited high ionic conductivity, thereby enhancing the discharge capacity of the Li-O-2 battery. In particular, the improved electrochemical stability of the gelled cathode led to long-term cyclability. The organic-inorganic hybrid matrix with the gelled structure played a beneficial role in improving the ionic conductivity and long-term cyclability and diminished electrolyte evaporation. The experimental and theoretical findings both suggest that the preferential binding between amorphous SiO2 and polyethylene glycol dimethyl ether (PEGDME) solvent led to the formation of the solidified gelled electrolyte and improved electrochemical stability during cycling, while enhancing the stability of the quasi-solid state Li-O-2 battery.</P>

Flexible free-standing air electrode with bimodal pore architecture for long-cycling Li-O₂ batteries

Kim, Hyunjin,Lee, Hyunpyo,Kim, Mokwon,Bae, Youngjoon,Baek, Woonjoong,Park, Kwangjin,Park, Seongyong,Kim, Taeyoung,Kwon, Hyukjae,Choi, Wonsung,Kang, Kisuk,Kwon, Soonchul,Im, Dongmin Elsevier 2017 Carbon Vol.117 No.-

<P>Li-O-2 batteries have been proposed as next-generation energy-storage devices, but this technology is hindered by serious problems including parasitic reactions, degradation, and leakage of the electrolyte. Li-O-2 batteries are also currently designed to have a rigid bulky structure, which cannot satisfy the flexibility demands of modern electronics. Herein, we report the significant enhancement of the electrochemical performance and flexibility of a Li-O-2 battery by introducing a free-standing, binder-free carbon nanotube cathode with a bimodal pore architecture. This electrode structure imparted stability to active sites during the recovery of discharge products to the initial state, providing long-term cyclability of more than 100 cycles in a tetraethylene glycol dimethyl ether electrolyte system. The O-2 transportation and conductivity were also improved, yielding an increased discharge capacity of 5500 mAh g(-1) (nearly twice that of a non-porous cathode) and minimizing parasitic reactions. This novel bimodal-pore cathode exhibited an increased tri-phase boundary for the Li-O-2 reactive zone in the interconnected CNT network. The small pore structures (similar to 50 nm) accommodated Li2O2, and the large pore structures (similar to 385 nm) enabled effective oxygen diffusion without clogging the pores. Moreover, Li+ and oxygen diffusion were facilitated by the two independent channels provided by the pore structures. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Stiffness Enhancement of a Redundantly Actuated Parallel Machine Tool by Dual Support Rims

Shin, Hyunpyo,Kim, Sunho,Jeong, Jayil,Kim, Jongwon 한국정밀공학회 2012 International Journal of Precision Engineering and Vol.13 No.9

A novel kinematic structure called as the Eclipse-IA is suggested for an application to the parallel machine tools. The stiffness enhancement design based on the Eclipse-IA structure is also introduced with its stiffness analysis for redundantly actuated parallel mechanisms. Relationship between the new structure and the stiffness properties including determinant and isotropy of the corresponding stiffness matrix is examined. Moreover, the design parameters are optimized to maximize the stiffness properties for the application of the Eclipse-IA as a multi-functional machine tool. By various simulation cases, the suggested parallel mechanism and the redundant actuation are verified to increase the stiffness properties against arbitrary external forces.

판매관리비의 비중이 주가폭락에 미치는 영향

김현표 ( Hyunpyo Kim ),정준희 ( Joonhei Cheung ) 한국회계학회 2017 회계학연구 Vol.42 No.3

일반적으로 판매관리비는 부정적인 측면과 긍정적인 측면이 모두 존재하여, 판매관리비 정보의 해석은 투자자간 비대칭적으로 나타난다. 주가폭락의 주요원인이 정보비대칭에 기인한 결과로 볼 때 판매관리비의 속성은 주가폭락과 관련성을 가지게 될 것이다. 이에 본 연구는 판매관리비의 정보가 주가폭락에 미치는 영향에 대해 알아보았다. 실증분석결과, 판매관리비의 비중이 높아질수록 주가폭락현상이 덜 발생하는 것으로 나타났다. 또한, 경쟁이 낮은 시장에서는 판매관리비는 주가폭락에 부정적인 영향이 있음을 보여주었다. 위 결과는 전통적인 견해와 달리 판매관리비는 대리인비용보다 미래가치로써 자본적 속성이 있음을 보여주는 것이다. 그렇지만 독점적 시장에서는 판매관리비는 주가폭락과 정(+)의 관련성을 가지는 것으로 나타났는데 이는 경쟁이 낮을 경우 판매관리비 비중은 경영자의 비효율성을 나타내는 지표가 됨을 의미한다. 본 연구는 재무제표 기본분석이 주가폭락을 예측할 수 있음을 보여주는 연구로서 회계정보와 함께 이를 분석할 수 있는 능력이 필요함을 보여준다. 나아가 자본시장의 정책 및 제도와 함께 회계교육이 중요함을 제시해주고 있다. SG&A costs ratio has two perspectives on firm`s value or performance. On the one hand, the SG&A costs ratio gives negative signal about future profitability. Traditionally, this ratio is perceived as the operating efficiency. Therefore, the increase of the SG&A costs ratio suggests the inefficiency or lack of ability of managers regarding control costs or operations. On the other hand, the SG&A costs ratio indicates the signal as future performance. Thus, this ratio is considered as important signal because the SG&A costs ratio is monitored by stakeholder for future operating. Overall, this ratio provides information asymmetry because of two conflicting perspectives on the SG&A costs to sales. Therefore, this paper empirically examines whether SG&A costs ratio is associated with the future stock price crash risk. Also, the relation between the SG&A costs ratio and stock price crash risk is likely to incrementally differ based on firm`s competitive environment. Using a large sample of 61,710 firm-year observations from 1991 to 2013, we find that the SG&A costs ratio is significantly negative associated with stock price crash risk. Also, we find that the association between the SG&A costs ratio and stock price crash risk is less pronounced for firms in less competitive industry. These findings are contrary to traditional evidence that SG&A costs ratio is a proxy for agency costs. Also, for firms with less competitive industry, the SG&A costs ratio is perceived as inefficiency of managers.

Improvement of occupational exposure assessment in Korea from the evaluation of ECETOC TRA according to PROCs

Ki Eun Kim(김기은),Hyunpyo Jeon(전현표),Jang Pyo Cheong(정장표),Sanghun Kim(김상헌) 환경독성보건학회 2019 한국독성학회 심포지움 및 학술발표회 Vol.2019 No.4

MPI의 지속 통신 메커니즘을 이용한 병렬 유한차분시간영역 전산모사 프로그램의 통신 성능 향상에 관한 연구

김희운 ( Huioon Kim ),전경원 ( Kyungwon Chun ),김형규 ( Hyeong-gyu Kim ),홍현표 ( Hyunpyo Hong ),정영주 ( Youngjoo Chung ) 한국정보처리학회 2009 한국정보처리학회 학술대회논문집 Vol.16 No.1

유한차분시간영역 방법은 전자기파 관련 분야의 전산모사에 많이 사용되는 수치해석기법이다. 이 방법을 이용하여 구현한 전산모사 프로그램은 많은 계산 자원 필요로 하기 때문에 병렬 계산 환경을 이용하게 되는 경우가 많다. 병렬 계산 환경에서 전산모사를 수행할 경우, 병렬로 수행되는 각 프로세스 간의 통신 속도와 네트워크의 지연 시간은 계산의 병목 현상을 초래하여 전체적인 성능을 저하시키는 원인이 된다. 따라서, 본 논문에서는 MPI의 지속 통신 메커니즘을 이용하여 병렬 프로세스 간 동기화 속도를 증가시킴으로써 유한차분시간영역 전산모사 프로그램에서의 MPI 통신 성능의 향상을 꾀하고, 그 결과를 그래프로 도시하였다. 또한 기존의 양방향 통신과 단방향 통신 메커니즘을 사용했을 때의 성능과 비교/분석하여, 병렬 유한차분시간영역 전산모사 프로그램에 있어서 지속 통신 메커니즘의 장/단점을 제시하고, 그 효용성에 관해 논의한다.

Carrier Transport Properties of MoS ₂ Asymmetric Gas Sensor Under Charge Transfer-Based Barrier Modulation

Kim, Sun Jun,Park, Jae Young,Yoo, SangHyuk,Umadevi, Palanivel,Lee, Hyunpyo,Cho, Jinsoo,Kang, Keonwook,Jun, Seong Chan Springer US 2018 NANOSCALE RESEARCH LETTERS Vol.13 No.1

<P>Over the past few years, two-dimensional materials have gained immense attention for next-generation electric sensing devices because of their unique properties. Here, we report the carrier transport properties of MoS<SUB>2</SUB> Schottky diodes under ambient as well as gas exposure conditions. MoS<SUB>2</SUB> field-effect transistors (FETs) were fabricated using Pt and Al electrodes. The work function of Pt is higher than that of MoS<SUB>2,</SUB> while that of Al is lower than that of MoS<SUB>2</SUB>. The MoS<SUB>2</SUB> device with Al contacts showed much higher current than that with Pt contacts because of its lower Schottky barrier height (SBH). The electrical characteristics and gas responses of the MoS<SUB>2</SUB> Schottky diodes with Al and Pt contacts were measured electrically and were simulated by density functional theory calculations. The theoretically calculated SBH of the diode (under gas absorption) showed that NO<SUB><I>x</I></SUB> molecules had strong interaction with the diode and induced a negative charge transfer. However, an opposite trend was observed in the case of NH<SUB>3</SUB> molecules. We also investigated the effect of metal contacts on the gas sensing performance of MoS<SUB>2</SUB> FETs both experimentally and theoretically.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (10.1186/s11671-018-2652-9) contains supplementary material, which is available to authorized users.</P>

Antagonistic Stiffness Optimization of Redundantly Actuated Parallel Manipulators in a Predefined Workspace

Hyunpyo Shin,Sungcheul Lee,Jeong, J. I.,Jongwon Kim IEEE 2013 IEEE/ASME transactions on mechatronics Vol.18 No.3

<P>An optimization procedure regarding shape of usable workspace and antagonistic stiffness is developed for a redundantly actuated parallel manipulator. The kinematic parameters such as configuration of the mechanism and length of linkages are optimized to maximize and equal out antagonistic stiffness of the redundantly actuated manipulator when the shape of usable workspace is given as a rectangle. The proposed procedure is verified by simulation and experiment with a 2-DOF planar manipulator. In the experiment, the principal axes of displacements of ellipses are measured when the corresponding external forces are imposed on the end-effector. The simulation and experimental results show that the proposed procedure is valid for designing the redundantly actuated parallel manipulator with maximum antagonistic stiffness.</P>

6-자유도 Eclipse-II 모션 시뮬레이터의 최적 원점 복귀 알고리즘

신현표(Hyunpyo Shin),김종원(Jongwon Kim) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.4

This paper describes the optimal home positioning algorithm of Eclipse-II, a new conceptual parallel mechanism for motion simulator. Eclipse-II is capable of translation and 360 degrees continuous rotation in all directions. In unexpected situations such as emergency stop, riders have to be resituated as soon as possible through a shortest translational and rotational path because the return paths are not unique in view of inverse kinematic solution. Eclipse-II is man riding. Therefore, the home positioning is directly related to the safety of riders. To ensure a least elapsed time, ZYX Euler angle inverse kinematics is applied to find an optimal home orientation. In addition, the subsequent decrease of maximum acceleration and jerk values is achieved by combining the optimal return path function with cubic spline, which consequently reduces delivery force and vibration to riders.

A new prenylated flavanone from the roots of Sophora flavescens

Kang, SamSik,Kim, JuSun,Son, KunHo,Chang, HyeunWook,Kim, HyunPyo 영남대학교 약품개발연구소 2000 영남대학교 약품개발연구소 연구업적집 Vol.10 No.-

A new prenylated flavanone was isolated from the roots of Sophora flavescens. The structure of the new compound was elucidated as (2S)-7,4'-dihydroxy-5-methoxy-8-(r,r-di-methylallyl)-flavanone(1) on the basis of chemical and spectral evidence. ⓒ 2000 Elsevier Science B.V. All rights reserved.