• Geophysics and Geophysical Exploration
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• v.20 no.2
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• pp.96-99
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• 2017

Virtual source data were produced by applying the seismic interferometry to the 2002 experimental seismic refraction data. Using the data, moveout velocities and effective anellipticity were experimentally computed for the crust at eight sites in the Korean peninsula. The moveout velocities of reflection events at approximate Moho depths were yielded to be $6.30{\pm}0.25km/s$ using near-offset traveltimes. Expanding the Taylor approximation to the $3^{rd}$ term for far-offset traveltimes, the effective anellipticity parameters were computed to be $0.18{\pm}0.07$ for the crust material.

• Korean Journal of Optics and Photonics
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• v.26 no.2
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• pp.115-120
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• 2015

Explicit expressions are derived for the effective reflection coefficients of obliquely incident light on a multilayered substrate coated with two uniaxially anisotropic films. Based on these reflection coefficients, ellipsometric constants are obtained as function of the tilt and azimuthal angles of the optical axes of the uniaxial films. Explicit expressions are provided, which can be used to separate the effects of surface anisotropy for anisotropic film from that of its bulk anisotropy, so that these expressions may be utilized in characterizing the surface anisotropy of alignment layers.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2415-2423
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• 2015

Experiments were conducted on sine wave fin-and-tube heat exchangers having oval tubes under wet condition. Oval tubes having an aspect ratio of 0.6 were made, by deforming 12.7mm round tubes. Twelve samples, having different fin pitch and tube row, were tested. Results showed that, for oval tube samples, the effect of fin pitch on j and f factor was not significant. As for the effect of tube row, the lowest j factor was obtained for one row configuration(81% of two row configuration), which is clear contrast to round tube samples, where the highest j factor was obtained for one row configuration. Possible reasoning is provided considering the flow and heat transfer characteristics of sine wave channel combined with connecting oval tubes. Comparison of $j/f^{1/3}$ with plain fin-and-tube heat exchanger having 15.9mm O.D. round tube reveals that present oval fin-and-tube heat exchanger shows superior thermal performance except for one row configuration. In other words, $j/f^{1/3}$ of the two row oval tube heat exchanger was 1.6~2.5 times larger than those of round tube heat exchanger, 1.4~2.4 times larger for three row configuration and 1.2~2.8 times for four row configuration.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.31-36
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• 1997

We measured refractive indices and thicknesses of SiO$_2$ thin films that have been plated on LCD glass substrate for the purpose of preventing the out-diffusion of sodium ions. The best experimental condition to determine refractive index and thickness of SiO$_2$ thin film by using ellipsometry is searched for, where ⅰ) the film thickness is increased uniformly by 20 $\AA$ from 0 $\AA$ to the period thickness while the angle of incidence is fixed and ⅱ) the angle of incidence is increased uniformly by 1$^{\circ}$ from 45$^{\circ}$ to 70$^{\circ}$ while the film thickness is fixed. We estimated the errors in determining the refractive index and thickness by comparing the measurement error of $\Delta$ and Ψ with the calculated one. The ellipsometric constants of SiO$_2$ thin film on LCD glass substrate are measured at several angle of incidence around the Brewster angle, which is the best angle if the experimental error of ellipsometer is not sensitive to the incident angle. Also the best fit refractive index and thickness of SiO$_2$ thin film to these ellipsometric constants measured at several angle of incidenc eas well as the best fit ones to the SE data are obtained using regressional analysis.

• Composites Research
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• v.24 no.6
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• pp.37-48
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• 2011

A volume integral equation method (VIEM) is introduced for the solution of elastostatic problems in an unbounded isotropic elastic solids containing interacting multiple isotropic or anisotropic elliptical inclusions subject to remote uniaxial tension. The method is applied to two-dimensional problems involving long parallel elliptical cylindrical inclusions. A detailed analysis of stress field at the interface between the matrix and the central inclusion is carried out for square and hexagonal packing of the inclusions. Effects of the number of isotropic or anisotropic elliptical inclusions and various fiber volume fractions for the circular inclusion circumscribing its respective elliptical inclusion on the stress field at the interface between the matrix and the central inclusion are also investigated in detail. The accuracy and efficiency of the method are examined through comparison with results obtained from analytical and finite element methods. The method is shown to be very accurate and effective for investigating the local stresses in composites containing isotropic or anisotropic elliptical fibers.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.49 no.4
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• pp.23-35
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• 2012

This paper presents a 3-D pose (position and orientation) estimation method for an elliptic object in 3-D space. It is difficult to resolve the problem of determining 3-D pose parameters with respect to an elliptic feature in 3-D space by interpretation of its projected feature onto an image plane. As an alternative, we propose a two points-based pose estimation algorithm to seek the 3-D information of an elliptic feature. The proposed algorithm determines a homogeneous transformation uniquely for a given correspondence set of an ellipse and two coplanar points that are defined on model and image plane, respectively. For each plane, two triangular features are extracted from an ellipse and two points based on the polarity in 2-D projection space. A planar homography is first estimated by the triangular feature correspondences, then decomposed into 3-D pose parameters. The proposed method is evaluated through a series of experiments for analyzing the errors of 3-D pose estimation and the sensitivity with respect to point locations.

• Journal of Astronomy and Space Sciences
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• v.22 no.1
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• pp.21-34
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• 2005

The initial conditions that generate bounded motion in eccentric reference orbit are determined for satellite formation flying. Because Hill's equations cannot describe the relative motion between two satellites in eccentric orbit, a new relative dynamics utilizing the nonlinearity and eccentricity correction for Hill's initial conditions is implemented. The constraint that matches angular rates of chief and deputy satellites is used to obtain the bounded motion between them. The constraint can be applied to satellite formation motions in eccentric orbit, since it implicates J2 perturbation due to the central body's aspherical gravitational forces. The periodic bounded motions are analyzed for the orbit with the eccentricity of less than 0.05 and about 0.5 km relative distance between chief and deputy satellites. It is mainly illustrated that the satellite formations in small eccentric orbits can have hounded motions; consequently, the formation can be kept by matching angular rates of the satellites. These results demonstrate an useful method that reduces the cost for operating satellites by providing effective initial conditions for satellite formation flying in eccentric orbit.

• Journal of the Korean Vacuum Society
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• v.2 no.1
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• pp.92-98
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• 1993

Si 기판 위에 증착된 Al 박막을 질소 ECR 플라즈마에 노출시켜 시료를 제작하고 분광타원해석법으로 분석한 결과 Al박막에 질화층이 형성되었음을 확인하였다. 사용한 질소 ECR 플라즈마의 전자온도와 전자밀도는 챔버내의 위치에 따라 각각 10~20eV, 0.9~1.2$\times$1011/㎤의 값을 보였다. 질소 ECR 플라즈마에 노출된 기판은 급격한 온도상승을 보였으며 노출시킨 뒤 5~6분이 지나면 $500^{\circ}C$ 근처에서 포화상태를 이루었다. 분광타원해석상수인 $\Delta$와 Ψ를 분석한 결과 증착된 Al의 두께는 시료에 따라 $140~160AA$이었고 표면에 형성된 AIN 층의 두께는 질소 ECR 플라즈마에 노출된 시간이 길수록 그리고 시료의 위치가 공명지점에 가까울수록 증가하였다. AlN층의 두께가 노출시간의 제곱근에 비례하는 것으로부터 AlN층은 Al의 표면에 흡착된 질소가 Al속으로 확산하여 이루어진 것으로 설명하였다.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 1998.12a
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• pp.455-468
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• 1998

암호해독법은 암호시스템의 안전성을 논하는데 필수적이다. 본 논문에서는 ECDLP 공격법인 Pollard-$\rho$와 그 변형들간의 성능을 유한체 GF(2$^{19}$ ) ~ GF(2$^{41}$ ) 상의 타원곡선에서 측정 비교하였다. 또한 이 공격법을 네트웍을 통해 10대의 컴퓨터로 병렬처리해 공격시간을 1/10로 단축시켰으며 실험 데이타를 토대로 GF(2$^{163}$ )상에서 공격시간 및 저장용량을 예측하였다.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10a
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• pp.604-606
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• 2001

타원 곡선이 정의되는 유한체외 연산 중 곱셈에 대한 역원을 빠르게 구하는 것은 타원 곡선 암호시스템의 성능 향상에 있어 중요한 요소이다. 본 논문에서는 이진체 $F_{2m}$ 상에서 다항식 기저를 사용하는 경우 곱셈에 대한 역원을 빠르게 구하는 알고리즘을 제시한다. 이 알고리즘은 기약 다항식으로부터 미리 계산 가능한 테이블을 만들어 테이블 참조 방식으로 속도 향상을 꾀한다. 이 방법을 사용할 경우 이전에 알려진 가장 빠른 방법보다 10~20% 정도 성능 향상이 있다.다.