• Proceedings of the Optical Society of Korea Conference
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• 1991.06a
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• pp.94-97
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• 1991

We have deposited the three kinds of the Langmuir-Blodgett films (Phenylhy drazone, O-stilbazene, N-stilbazene) which have optically nonlinear effect. To study the electro-optic characteristics of these LB films, we performed the differential attenuated total reflection experiment in which the optical properties of the LB films modulated by the electric field(νE = 1KHz). The surface non-linear susceptibilities $\chi$(2) of these LB films obtained, are 1.17$\times$10-10 (m/V), 36.3$\times$10-10 (m/V), and 1.62$\times$10-10 (m/V) for Phenylhydrazone, O-stilbazene, and N-stilbazene, respectively.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.12
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• pp.1219-1226
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• 2011

This paper proposes a novel approach to building an occupancy grid map using sonar data. It is very important for a mobile robot to recognize and construct its surrounding environments for navigation. However, the grid map constructed by ultrasonic sensors cannot represent a realistic shape of given environments due to incorrect sonar measurements caused by specular reflection. To overcome this problem, we propose an advanced sonar sensor model which consists of distance and shape factors used to determine the reliability of sensor data. Through this sensor model, a robot can build a high-quality grid map. The proposed method was verified by various experiments and showed that the robot could build an accurate map with sonar data in various indoor environments.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1744-1746
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• 1996

Surface impedance boundary condition(SIBC) concepts are introduced into the finite-difference time-domain(FDTD) method. Lossy conductors are replaced by surface impedance boundary computations reducing the soluton space and producing significant computational savings. Specifically, a surface impedance boundary condition is developed to reduce a lossy dielectric half-space. Since Maxwell's eqations are solved directly, the reflected and transmitted pulse amplitude demonstrate how the reflection and transmision coefficient determine reflected wave amplitude. In this paper, two implementations of reflection coefficient are presented. One implementation is a standard FDTD technique and the other is a FDTD using surface impedence boundary condition(FDTD-SIBC) that are applicabIe over a very large frequency bandwidth. Particulary, an efficient way to transform the time domain results to frequency domain is presented. Thus, frequency domain results are presented in one dimension and are compared with exact results.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.506-509
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• 2008

Mathematical models have been developed to calculate hydrodynamic characteristics of perforated-wall structures. Most of the models separate the fluid regions into front and back of the wall, assume the solution in each region, and calculate the solution by using the matching condition at the wall. The matching condition involves the permeability parameter, which can be calculated by the methods proposed by Mei et al. or Sollitt and Cross. In this study, we compare these two methods. The former is advantageous because all the related variables are known, but it gives wrong result in the limit of long waves, i.e. zero transmission and perfect reflection of very long waves. In deep water, the latter predicts smaller transmission and larger reflection than the former, and vice versa in shallow water. In the latter method, the friction coefficient decreases as the wall thickness or the porosity of the wall increases.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.3 s.258
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• pp.380-387
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• 2007

We carried out an image analysis of living cells forming their contacts at the bottom of the cell culturing substrate. In order to visualize the contact area selectively, we adopted total-internal-reflection-fluorescence (TIRF) method, which can illuminate the specimen volume within only several hundred nano-meters above the substrate. From the fluorescent intensity of the TRF image, we could calculate the distance of the cell surface from the substrate. As a result, we visualized the origin of cell contacts, their movements, and the change of cell-contact type from the close-contact into focal-contact with information of its vertical displacement representing the temporal evolution process of the three-dimensional cell-surface-profile near the contact area during this metamorphosis.

• Proceedings of the Korea Multimedia Society Conference
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• 2000.11a
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• pp.224-227
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• 2000

본 논문에서는 기준 영상으로부터 면의 반사특성을 검출하고, 구해진 반사특성을 임의의 물체에 적용하여 3매의 명암영상을 얻는다. 이 영상을 측광입체시법(photometric stereo method)에 적용하여 3차원 형상인식하는 방법을 제시한다. 본 연구에서 목적으로 하는 물체의 반사특성은 난반사(diffuse reflection)성분과 전반사(specular reflection)성분이 혼합된 혼합 반사면(hybrid reflectance surface)을 그 대상으로 하며, 이러한 면의 반사특성은 Torrance-sparrow모델로 가정하여 문제를 해결해 나간다. 본 연구에서 목적으로 하는 대상 물체는 동일한 재질로 이루어졌다는 가정 하에서 몇개의 표본점들을 취해 반복수치 계산하기 때문에 계산속도가 빠르며, 각 표본점들로부터 계산된 면특성 파라메터들의 평균값을 취해서 다시 Torrance-sparrow모델에 적용함으로써 측광입체시법의 해석을 가능토록 한다. 즉, 3차원 형상인식 과정시 계산된 면특성 파라메터를 사용해 생성한 참조표와 명암영상과의 비교에 의해 빠른 면방향 복구를 행할 수 있다.

• The Journal of the Acoustical Society of Korea
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• v.18 no.1E
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• pp.37-43
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• 1999

This paper deals with a hybrid finite element method for wave scattering problems in infinite domains. Scattering of waves involving complex geometries, in conjunction with infinite domains is modeled by introducing a mathematical boundary within which a finite element representation is employed. On the mathematical boundary, the finite element representation is matched with a known analytical solution in the infinite domain in terms of fields and their derivatives. The derivative continuity is implemented by using a slope constraint. Drilling degrees of freedom at each node of the finite element model are introduced to make the numerical model more sensitive to the transverse component of the elastodynamic field. To verify the effects of drilling degrees freedom and slope constraints individually, reflection of normally incident P and SV waves on a traction free half spaces is considered. For the P-wave incidence, the results indicate that the use of slope constraint is more effective because it suppresses artificial reflection at the mathematical boundary. For the SV-wave case, the use of drilling degrees freedom is more effective by reducing numerical error at irregular frequencies.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.4
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• pp.669-675
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• 2011

In this paper, we present the AFP(antenna front plate)s which were designed to reduce the reflection for the sake of the improvement of DF(direction finding) accuracy. The AFP consists of front plate, absorber and radome. The AFPs were optimized respectively by real test and we performed the DF test using our AFPs in laboratory. The DF test shows that the DF accuracy is about 2 times better than the requirement capability. Then, the DF field test was executed using the AFPs, which were installed in helicopter in consideration of the reflection by platform. The result of the DF field test is superior to the requirement capability also, which shows the validity of our design method.

• Journal of Power System Engineering
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• v.18 no.3
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• pp.29-35
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• 2014

A new method is presented that uses guided wave techniques for sludge and blockage detection in long-range pipelines. Existing techniques have the limitations that the sludge position needs to be known a priori and the area to be inspected needs to be accessible. A novel guided wave technique has been developed that allow the sludge or blockages to be detected remotely without the need to access the specific location where the pipe is blocked, nor to open the pipe. The technique measures the reflection of guided waves by sludge that can be used to accurately locate the blocked region. The effectiveness of the proposed technique is demonstrated and confirmed by experimental measurements.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.9
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• pp.856-862
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• 2010

In this paper, the power flow analysis(PFA) method was developed to predict the vibrational responses of coupled co-planar orthotropic plates in frequencies ranging from medium to high. To cover the power transmission and reflection at the joint of the orthotropic plates, the wave transmission approach is applied with the assumption that all the incident waves are normal to the joint. Through numerical analyses, the power flow energy density and intensity fields of coupled co-planar orthotropic plates were compared with those of classical modal solutions by changing the frequency and internal loss factor, and they show good agreement in terms of the global decay and the attenuation patterns of the energy density.