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Optically Induced Anisotropy in Photoresponsive Sol-Gel Matrix Bearing a Silylated Disperse red 1
최동훈,조강진,차영관,오상준,Choe, Dong Hun,Jo, Gang Jin,Cha, Yeong Gwan,O, Sang Jun Korean Chemical Society 2000 Bulletin of the Korean Chemical Society Vol.21 No.12
We synthesized the simple triethoxysilanes (SGDR1) bearing a disperse red 1 for thin film fabrication. The thin films were prepared using the solution of SGDR1 after hydrolysis and condensation. The films were annealed at two different temperatures such as $150^{\circ}C$ and $200^{\circ}C$. Trans-to-cis photoisomerization was observed under the exposure of 532 nm light with UV-Vis absorption spectroscopy. The kinetic study of photoisomerization was performed in the film. Reorientation of the polar azobenzene molecules induced optical anisotropy under a linearly polarized light at 532 nm. The effect of aggregation of the chromophores and annealing of the silicon oxide in the matrix were studied on the dynamic properties of isomerization and induced birefringence.
최동훈,김민수,김종립,전재영,Choe, Dong-Hun,Kim, Min-Su,Kim, Jong-Rip,Jeon, Jae-Yeong 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.9
Based on the exponential intervening variable, a new two-point approximation method is presented. This introduces the shifting level into each exponential intervening variable to avoid the lack of def inition of the conventional exponential intervening variables due to zero-or negative-valued design variables. Then a new quadratic approximation whose Hessian matrix has only diagonal elements of different values is proposed in terms of these intervening variables. These diagonal elements are determined in a closed form that corrects the typical error in the approximate gradient of the TANA series due to the lack of definition of exponential type intervening variables and their incomplete second-order terms. Also, a correction coefficient is multiplied to the pre-determined quadratic term to match the value of approximate function with that of the previous point. Finally, in order to show the numerical performance of the proposed method, a sequential approximate optimizer is developed and applied to solve six typical design problems. These optimization results are compared with those of TANA-3. These comparisons show that the proposed method gives more efficient and reliable results than TANA-3.
Effect of Photopolymerization on the Rate of Photocrosslink in Chalcone-based Oligomeric Compounds
최동훈,오상준,반시영,오광용,Choe, Dong Hun,O, Sang Jun,Ban, Si Yeong,O, Gwang Yong Korean Chemical Society 2001 Bulletin of the Korean Chemical Society Vol.22 No.11
A new photochemically bifunctional epoxy and dimethacrylate compounds were synthesized for investigating the photosensitivity under UV irradiation. Photosensitivity of the synthesized chalcone-based compounds was investigated by using UV-visible absorption and Fourier transformed infrared (FT-IR) spectroscopies. The result of spectroscopic analysis substantiated that the two chalcone-based compounds have functions of both photocrosslinking and photopolymerization by UV exposure in the presence of photoinitiator. Two kinds of photochemical reactions proceeded competitively during UV exposure. Particularly, we studied the effect of photopolymerization on the rate of photocrosslink due to cycloaddition in the two oligomeric compounds.
부상특성 향상을 위한 극소 공기윤활막을 지닌 헤드 슬라이더의 형상 최적 설계
강태식,최동훈,정태건,박노열,이성창,Gang, Tae-Sik,Choe, Dong-Hun,Jeong, Tae-Geon,Park, No-Yeol,Lee, Seong-Chang 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.4
Flying attitudes of the slider, which are flying height, pitch and roll, are affected by the air flow velocity, the skew angle, and the manufacturing tolerances. Traditional designs of the air bearing surface have considered only the flying performances for the variations in the air flow velocity and the skew angle, which are determined by the radial position. In this study, we present the new shape design of the air bearing surface by considering the track seek performance and the air bearing stiffness as well as the traditional design requirements. The optimization technique is used to improve the dynamic characteristics and operating performance of the newly proposed air bearing surface shape design further. The optimized configuration is obtained automatically and the optimally designed sliders show the enhanced flying and dynamic characteristics.
윤기찬,최동훈,Yun, Gi-Chan,Choe, Dong-Hun 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.2
This paper presents a new design method of the 1 generation wheel bearing unit using a numerical optimization technique in order to increase bearing fatigue life. For calculating the fatigue life, a method of load analysis is studied on the automotive wheel bearing system. The design variables selected are ball size, initial contact angle, number of balls, pitch diameter, pre-load, and distance between ball centers. The method of feasible directions in ADS (Automated Design Synthesis) is utilized to automatically find the optimum design variables. To validate the design method, a computer program is developed and applied to a practical passenger car model. The optimum design results demonstrated the effectiveness of the proposed design method showing that the system life of the optimally designed wheel bearing unit is enhanced in comparison with that of the initial ones within the given available design space.
섭동법을 이용한 공기윤활 슬라이더 베어링의 동특성 해석
강태식,최동훈,정태건,Gang, Tae-Sik,Choe, Dong-Hun,Jeong, Tae-Geon 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.6
This study presents a method for determining bearing stiffness and damping coefficients of air-lubricated slider bearing, and shows influences of air-bearing surface geometry(recess depth, crown an d pivot location) on flying attitude and dynamic characteristics. To derive the dynamic lubrication equation, the perturbation method is applied to the generalized lubrication equation which based on linearized Boltzmann equation. The generalized lubrication equation and the dynamic lubrication equation are converted to a control volume formulation, and then, the static and dynamic pressure distributions are calculated by finite difference method. The recess depth and crown of the slider show significantly influence on flying attitude and dynamic characteristics comparing with those of pivot location.
김두인,최동훈,안효석,Kim, Du-In,Choe, Dong-Hun,An, Hyo-Seok 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.4
Gerotor is a planar mechanism consisting of a rotor and lobes which form a closed space, namely a chamber. As active contact points between a rotor and lobes are subjected to very high contact stresses, wear in one or both of the rotor and lobe cannot be avoided. Therefore, in the design of Gerotor used in hydraulic motors a compromise between high torque output and contact stress is of great importance and a thorough analysis of design parameters should be conducted to achieve this compromise. In this study, a contact point is modelled as a linear spring in consideration of equivalent curvature to analyze the contact stress. As the contact stress calculation in this problem is a statically indeterminate type, a numerical iterative scheme has been adopted to obtain the solution. To fully understand the influence of design parameters on the contact stress, the relationship between pressure force, equivalent curvature, contact force and contact stress are analyzed. It is shown that the equivalent curvature of the contact point is a dominant factor that affects the maximum contact stress.