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Daejeon, South Korea

Ji S.-C.,Chungnam National University | Lee J.-S.,Hanhwa Corporation | Kim D.-H.,KCC Corporation | Kang C.-H.,Hankook Tire Randnter | And 2 more authors.
Polymer (Korea)

Dipyridine-terminated polystyrenes and polybutadienes were synthesized by the chain end-functionalization reaction of polystyryllithium (PSLi) and polybutadienyllithium (PBDLi) with di(2-pyridyl) ketone (DPK) using a living anionic polymerization method in the Ar-glove box. Living polymeric lithiums with low molecular weights (Mw=1000-2000 g/mol) were used to investigate the chain end-functionalization yield with DPK and the degree of coupling reaction by the attack of organolithium to the pyridine ring in the presence of TMEDA using GPC, 1H-NMR, 13C-NMR analysis. DPK-terminated PBD exhibited much higher functionalization yield and less amount of coupling reaction compared with DPK-terminated PS. 86% functionalization yield with 9% degree of coupling was obtained when the PBDLi was added dropwise to DPK solution at room temperature. The functionalization yield was increased as the reaction temperature decreased, however, no LiCl effect was observed in this chain end-functionalization reaction with DPK. Source

Woo J.-H.,Yonsei University | Yoon J.-H.,Yonsei University | Hur Y.J.,Hanhwa Corporation | Park N.-C.,Yonsei University | And 2 more authors.
IEEE Transactions on Magnetics

In this study, we propose the optimal shape of a ferromagnetic yoke intended to reduce the crosstalk that occurs because of fringe effects at the edge of the magnet used in optical image stabilization (OIS) actuators. Topology optimization was performed with finite element (FE) analysis to determine the optimal shape of the ferromagnetic yoke without degrading the performance of the actuator. To promote the effective use of the topology optimization, the problem was simplified into a 2-D FE analysis, and finite difference approximation was used in the sensitivity analysis. The closest objective function to the special reference value was defined to minimize both the standard deviation and the average magnetic flux density in the y-direction for the Hall effect sensor. Consequently, the optimal shape of the ferromagnetic yoke, obtained by using topology optimization under various volume fraction constraints, was verified using 3-D FE analysis. The results demonstrate that the suggested design method is useful and effective. © 2011 IEEE. Source

Kim M.T.,Yonsei University | Song S.,Yonsei University | Yim Y.J.,Hanhwa Corporation | Jang M.W.,Hanhwa Corporation | Baek G.,Agency for Defense Development
Propellants, Explosives, Pyrotechnics

The infrared irradiance signature from exhaust plume is essential for the design of solid rocket motors. To overcome the difficulty of conducting experiments using real rocket motors, experimental studies were carried out to compare standard rocket motors and real rocket motors of the same propellant. The static firing tests on standard and real rocket motors of NEPE and HTPB propellants were conducted. Despite different rocket motor size and methodology of spectro-radiometric measurement, the spectral characteristics of the infrared irradiance signature for both rocket motors were quite similar. The standard and real rocket motors of HTPB propellant showed similar tendency of steady infrared irradiance emission throughout the combustion, whereas both rocket motors of NEPE propellant showed a rapid emission in the midstream of combustion. The total infrared irradiance of NEPE was about 55% less than that of HTPB propellant for both standard and real rocket motor experiments. Additionally, the relative amounts of chemical products produced during propellant combustion came out to be similar for both rocket motors. The experimental results indicated that the spectral characteristics of infrared irradiance and combustion products were quite similar for different sized rocket motors of same propellant and that a correlation of infrared irradiance signature exists between small-sized standard rocket motors and real rocket motors. Thus, the spectral characteristics of real rocket motors could be reasonably estimated from the results of standard rocket motors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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