• Bulletin of the Korean Chemical Society
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• 제21권4호
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• pp.434-440
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• 2000

We present the results of computer simulation for the steady shear flows of rodlike molecules using nonequi-librium molecular dynamics simulation (NEMD) method. The model particle is a rigid rod composed of lin-early connected 6-sites and the Lennard-Jones 12-6 potential governs interactions between sites in different molecules. The system of rodlike molecules exhibits the change of orientational structure, that is, isotropic-nematic transition at high shear rates. We elucidate the nature of the ordered system developed from an isotro-pic phase by steady shear through an analysis of various quantities: orientational order parameters, orientational pair correlation functions, orientational distribution function, and snapshots of configurations. The effects of temperature and density on the shear rate dependence of orientational structure are described.

• Bulletin of the Korean Chemical Society
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• 제21권3호
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• pp.310-316
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• 2000

Molecular dynamics simulation studies for thermotropic liquid crystalline systems conposed of rodlike molecules with 6 Lennard-Jones interaction sites wre performed in NPT ensemble. Within the range of temperature studied, the system exhibited isotropic and smectic phase. For the characterization of the smectic phase, we examined the structure of the liquid crystalline phase via the radial distribution function, its longitudinal and transverse components to the director, and other orientational correlation function, its longitudinal and transverse components to the director, and other orientational correlation functions. In the smectic A phase, our results showed a large anisotropy in translational motion (i.e.,$D_⊥ >> D_∥$), and the decay of the collective orientational correlation function of rank two became slower than that of the single particle orientational correlation function of rank one. Comments on the spontaneous growth of orientational order directly from the isotropic phase are given.

• Bulletin of the Korean Chemical Society
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• 제12권2호
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• pp.199-206
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• 1991

A statistical thermodynamic theory of thermotropic main-chain polymeric liquid crystalline melts is developed within the framework of the lattice model by a generalization of the well-known procedure of Flory and DiMarzio. According to the results of Vasilenko et al., the theory of orientational ordering in melts of polymers containing rigid and flexible segments in the main chain is taken into account. When the ordering of flexible segments in the nematic melt is correlated with that of rigid mesogenic groups, the former is assumed to be given as a function of the ordering of rigid mesogenic cores. A free energy density that includes short-range packing contributions is formulated. The properties of the liquid-crystalline transiton are investigated for various cases of the system. The results calculated in this paper show not only the order-parameter values but also the first-order phase transition phenomena that are similar to those observed experimentally for the thermotropic liquid-crystalline polymers and show the transitional entropy terms which actually increase upon orientational ordering. In the orientational ordering values, it is shown that mesogenic groups, flexible segments, and gauche energy (temperature) may be quite substantial. Finally, by using the flexibility term, we predict the highly anisotropic mesophase which was shown by Vasilenko et al.

• 한국통신학회논문지
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• 제21권5호
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• pp.1123-1131
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• 1996

Knutsson이 QPS(quadrature polar separable) 필터를 제안한 이후 여러가지 개선된 QPS필터가 발표되고 있으며 질감 영상처리에 응용되고 있다. 이들 필터는 방향각 함수로 Kuntsson의 cosine 함수나 지수감쇠 함수를 이용하고 있으며, 라디엘웨이팅 함수로 FPSS(finite prolate spheroidal sequence)나 점근적 FPSS를 이용하고 있다. 이들 필터는 질감영상 생성이나 방향각평가, 그리고 합성된 질감영상의 영역분할면에서 다른 특성을 나타낸다. 본 논문에서는 2-D QPS 필터를 위한 여러가지 커넬함수를 분석하여 그들의 특성을 고찰하며 푸리에영역내에서 국부조직의 주파수성분과 방향각을 평가한다. 그리고 이들 필터에 의한 질감 영상의 특성추출과 영역분할에 대한 응용상의 문제점에 대해서 고찰한다. 실험결과는 개선된 Knutsson 필터와 점근적 FPSS 필터함수가 합성 질감영샹의 방향각 평가와 영역분할면에서 유용하다는 것을 나타낸다.

• 한국광학회지
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• 제5권4호
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• pp.481-486
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• 1994

높은 정전기장이 인가된 유기용액의 분자배향도를 측정하는 수단으로 z-scan방법을 사용하였다. 무게비로 0.5%의 4-dimethylamino-4'-nitrostilbene을 cyclopentanone에 녹인 혼합용액을 시료로 z-scan실험을 수행하였으며 측정된 등방비선형 굴절율 $n_{2}$값은 $1.064{\mu}m$파장에서 $-0.905\times10^{-8}\textrm{cm}^2/MW$였다. 3.45KV/nm 정전기장을 인가한 경우에 측정된 $n_{2}$의 비등방비 값은 1.34였으며 분자배향도계수 $

_2 및

_4$값은 0.092 및 -0.128이였다.

• 한국진공학회지
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• 제7권s1호
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• pp.149-155
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• 1998

The linear electro-optic (EO) effect is one of the second-order nonlinear optical effects existing in a noncentrosymmetric macroscopic system. In a polymer thin film, the noncentrosymmetry is achieved by electric field poling. The magnitude of the linear EO response is determined through the orientational distribution function of hyperpolarizable molecular dipoles. The relation between the linear EO coefficient and the second-order nonlinear optical susceptibility is explained. Three different methods of measuring the linear EO coefficient of a poled nonliner optical polymer thin film are introduced and discussed. All of them make use of the interferometric technique, the difference being in the optical parameters which are interfering.

• 한국광학회지
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• 제27권6호
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• pp.223-228
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• 2016

액정과 같은 단축 이방성 분자들의 정렬 정도에 따라 달라지는 복굴절으로부터 상대 복굴절 ${\Delta}n_{rel}$를 구하고 ${\Delta}n_{rel}$과 방향질서변수(orientational order parameter) S의 관계를 탐색하였다. 무질서한 분포를 하고 있는 경우를 포함하여 액정의 정렬정도를 달리 표현할 수 있는 분포함수를 도입하고 이 분포함수를 사용하여 질서변수 S가 0부터 1까지 변하도록 액정분자들의 정렬정도를 달리하며 ${\Delta}n_{rel}$과 S를 수치계산 하였다. 이 계산 결과로부터 s와 ${\Delta}n_{rel}$는 $S=(1+a){\Delta}n_{rel}-a{\Delta}n^2_{rel}$와 같이 준선형적인 관계를 만족하며 a는 $n_o{\frac{{\Delta}n}{4}}$으로 근사할 수 있음을 확인하였다. 또한 복굴절으로부터 Vuks의 방법에 따라 구한 분자분극의 이방성과 Neugebauer의 방법에 따라 구한 분자분극의 이방성이 각각 질서변수 S와 또 다른 준선형 관계식들을 따름을 보였다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.256-259
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• 2003

The study of confined liquid crystals flourished in the decade of the nineties. Liquid crystals properties have been probed after confinement in well-defined or interconnected geometries as those available in porous media and in polymer networks. In this work we emphasized the power of the nuclear magnetic resonance technique to determine the confined liquid crystal structures. We also present unexpected results on the dependence of the confined liquid crystal configuration on the chain length.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.1155-1160
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• 1991

Active part mating algorithm using 6-axis force sensor data for the assembly automation and/or teletobotics is presented and experimented. Parts to be mated are cylindrical and have no chamfers. There are basically two modes. One is the normal mode with only a positional error, the other is the tilted mode with an orientational error in addition to a positional error. The used algorithm distinguishes a contact external to the hole from that of internal to the hole in order to perform part-mating in spite of the relative tilt between the hole and the peg.

• Journal of Information Display
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• 제4권1호
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• pp.14-16
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• 2003

The study of confined liquid crystals flourished in the decade of the nineties. Liquid crystals properties have been probed after confinement in well-defined or interconnected geometries as those available in porous media and in polymer networks. In this work we emphasized the power of the nuclear magnetic resonance technique to determine the confined liquid crystal structures. We also present unexpected results on the dependence of the confined liquid crystal configuration on the chain length.