• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2018년도 춘계학술대회
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• pp.131-134
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• 2018

구조방정식 모델링은 경로분석 및 확인적 요인분석을 동시에 수행해 주는 통계적 절차를 따르고 있다. 오늘날이 통계적 절차는 사회과학 분야의 연구자에게 필수적인 도구이다. 구조방정식 모델링 분석을 해주는 대표적인 도구로는 (AMOS, LISREL and PLS)가 있다. AMOS는 초보자가 사용할 수 있도록 편리한 그래픽 사용자 인터페이스를 제공해 주고 있다. PLS는 그래픽 사용자 인터페이스뿐만 아니라 정규분포에 대한 제약조건도 없다는 장점을 가지고 있다. 또한 사회과학 분야에서 가장 많이 사용하는 3가지 도구(Applications)를 비교분석 하였다. 이러한 결과를 바탕으로 연구의 한계와 시사점을 제시하고자 한다.

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.681-688
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• 2020

The telegrapher's theory was used to develop a new formulation for the neutron noise equation. Telegrapher's equation is supposed to demonstrate a more realistic approximation for neutron transport phenomena, especially in comparison to the diffusion theory. The physics behind such equation implies that the signal propagation speed is finite, instead of the infinite as in the case of ordinary diffusion. This paper presents the theory and results of the development of a new method for calculation of the neutron noise using the telegrapher's equation as its basis. In order to investigate the differences and strengths of the new method against the diffusion based neutron noise, a comparison was done between the behaviors of two methods. The neutron noise based on SN transport considered as a precision measuring point. The Green's function technique was used to calculate the neutron noise based on telegrapher's and diffusion methods as well as the transport. The amplitude and phase of Green's function associated with the properties of the medium and frequency of the noise source were obtained and their behavior was compared to the results of the transport. It was observed, the differences in some cases might be considerable. The effective speed of propagation for the noise perturbations were evaluated accordingly, resulting in considerable deviations in some cases.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.362-369
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• 2005

Studying unsaturated soil mechanics, determination of soil water characteristic curve and permeability equation is an essential factor but it is not easy. In this research a new testing apparatus was developed to determine soil water characteristic curve and permeability equation. The testing to get saturated permeability coefficients and soil water characteristic curves for two soils was performed by using the developed testing apparatus. First, a saturated permeability testing was performed and then the testing to get soil water characteristic curve of a drying process was performed. Next, the testing to get soil water characteristic curve of a wetting process was performed. Testing results showed hysteresis phenomena between soil water characteristic curve of a drying process and soil water characteristic curve of a wetting process. The permeability equations were determined by a theoretical method where a saturated permeability coefficient and a soil water characteristic curve were used.

• Advances in materials Research
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• 제1권4호
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• pp.285-297
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• 2012

The present study addresses the problem of quantitative prediction of effective complex relative permittivity of Barium Titanate/Polyvenylidene Fluoride (PVDF) and $(Bi_{0.5}Na_{0.5})_{0.94}Ba_{0.06}TiO_3$/Poly(VDF-TrFE) biphasic ceramic-polymer composites. Theoretical results for effective relative permittivity derived from several dielectric mixture equations were fitted to the experimental data taken from the works of Prasad et al. (2010), Wang et al. (2004), Takenaka et al. (1991) and Yamada et al. (1982). The study revealed that out of the different test equations, only a few equations like modified Rother-Lichtenecker equation, Dias-Dasgupta equation or Rao equation for the real part and Bruggeman equation for the imaginary part of complex permittivity well fitted the corresponding experimental results. In the present study, some of the equations were used in their original forms, while some others were modified by choosing suitable shape-dependent parameters in order to get reasonably good agreement with experimental results. Besides, the experimental results have been proposed in the form of a mathematical model using first order exponential growth, which provided excellent fits.

• 한국정밀공학회지
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• 제31권2호
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• pp.171-178
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• 2014

In this study, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micropillars was studied. The previous researches showed that the Wenzel equation and the Cassie-Baxter equation were thermodynamically derived for the rough hydrophilic/hydrophobic surfaces and generally referenced on the field of wetting phenomena. For the verification of both equations, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micro-pillars was measured. In the comparison between the measured and estimated apparent contact angles with the equations, the differences between the apparent contact angles were analyzed. Conclusively, the available range and limitation of theoretical equations were investigated and further researches about the apparent contact angle on the rough surfaces were proposed.

• 대한기계학회논문집B
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• 제27권7호
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• pp.956-962
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• 2003

The Lippmann-Young equation has been widely used in electrowetting to predict the contact-angle change of a droplet on a insulating substrate with respect to the externally-applied electrical voltage. The Lippmann-Young equation is derived by assuming a droplet as a perfect conductor, so that the effect of the electrical double layer and the line tension are not taken into account. The validity of the assumption has never been checked before, systematically. In the present investigation, a modified Lippmann-Young equation is derived taking into account of the effect of the electrical double layer and the line tension. To assess their influence on contact-angle change in electrowetting, the electrostatic field around the three-phase contact line is analyzed by solving the Poisson-Boltzmann equation numerically. The validity of the numerical methods is verified by using the past theoretical results on the electrostatic field around a wedge-shaped geometry, which shows fairly good agreement. The results of the present investigation clearly indicate that the effect of the electrical double layer and the line tension is negligible for a millimeter-sized droplet. On the other hand, for a micron-sized droplet, the effect of the line tension can become a dominating factor which controls the contact-angle change in electrowetting.

• 한국세라믹학회지
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• 제35권11호
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• pp.1162-1170
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• 1998

PbO-TiO2-B2O3-BaO 계 유리상에서 PbTiO3의 결정화 메커니즘에 대한 이론적 고찰 및 전자현미경 관찰 그리고 결정화 기구의 열시차 분석에 대한 응용성을 조사하였다. 열시차 분석에 대한 Kissinger 식의 응용은 DTA 분석시 시료내 핵밀도가 변하지 않을 때 적용할 수 있으며, 표면결정화를 유도하기 위해 분말시료를 사용하는 경우도 활성화 에너지를 시료의 결정화 메커니즘에 크게 영향을 받는다. Ozawa 식에 의한 Avrami parameter n은 전자현미경 관찰에 의해 파악된 결정화메커니즘과 잘 일치하고 있었으며, 수정 Kissinger 식은 시료의 결정화 메커니즘을 반영하고 있어 시료의 전처리와 관계없이 참값의 활성화에너지를 구할 수 있다.

• 전기학회논문지P
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• 제56권1호
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• pp.1-5
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• 2007

Study on the electron transport coefficient in mixtures of CF4 and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for $CF_4$ and Ar, were used. The differences of the transport coefficients of electrons in $CF_4$ mixtures of Ar, have been explained by the deduced energy distribution functions for electrons and the complete collision cross-sections for electrons. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in $CF_4-Ar$ mixtures shows the Maxwellian distribution for energy. That is, $f({\varepsilon})$ has the symmetrical shape whose axis of symmetry is a most probably energy. The proposed theoretical simulation techniques in this work will be useful to predict the fundamental process of charged particles and the breakdown properties of gas mixtures. A two-term approximation of the Boltzmann equation analysis and Monte Carlo simulation have been used to study electron transport coefficients.

• Elastomers and Composites
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• 제45권4호
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• pp.250-255
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• 2010

비뉴톤 점탄성 Maxwell 요소와 탄성 스프링으로 이루어진 3 요소 비뉴톤 모델로부터 응력완화 식을 유도하였다. 이 식을 응력완화 실험 결과에 적용하여 여러 가지 모델 파라메타를 계산하였다. 모델 파라메타로부터 계산한 이론 곡선은 실험적인 응력완화 곡선과 잘 일치하였다. 비선형 점탄성 모델 파라메타로부터 섬유고분자 물질의 홀부피, 미세구조, 점탄성성질, 역학적인 성질 등을 연구하였다. 응력완화 실험은 용매기를 부착한 인장 시험기를 사용하였으며, 시료는 두 종류의 polyacrylonitrile-polyvinylchloride 공중합체와 또 다른 두 종류의 PVC 모노 필라멘트 섬유를 여러 온도의 공기와 물속에서 응력완화 실험을 하였다.

• Bulletin of the Korean Chemical Society
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• 제17권3호
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• pp.262-268
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• 1996

Flow properties of all suspensions are controlled by their flow units. The factors effecting on the flow units are the characteristics of the particle itself (surface properties, particle sizes, particle shapes and etc.), the electrostatic interactions among the particles and the influences of the medium in the suspensions. Here, we studied the transition between the flow units with shear rate which can be added to the above factors. For the concentrated starch-water suspensions, by using the Couette type rotational viscometer, we confirmed that at low shear rate, dilatancy is appeared, but it is transformed to thixotropy with increasing shear rate. In order to explain this fact, we derived the following flow equation, representing the transition from dilatancy to thixotropy with shear rate, by assuming the equilibrium between the flow units. f = X1β1s./α1 + 1/(1+Kexp(c0s.2/RT))((1-X1)/α2)sinh-1{(β2)0 s. exp(c2s.2/RT)} + K exp(c0s.2/RT)/(1+K exp(c0s.2/RT))((1-X1)/α3)sinh-1{(β3)0 s. exp(-c3s.2/RT)} By applying this flow equation to the experimental flow curves for the concentrated starch-water suspensions, the flow parameters were obtained. And, by substituting the obtained flow parameters to the flow equation, the theoretical flow curves were reproduced. Also, Ostwald curve was represented by applying the flow equation, and the applicability for stress relaxation was discussed.