• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.406-413
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• 2011

This paper presents the shape optimization of a nonaxisymmetric endwall and endwall boundary layer fence which improve the aerothermal environment of a gas turbine passage. The endwall and fence methods were used simultaneously. The turbine passage was simulated by a $90^{\circ}$ turning duct ($Re_D$=360,000). The main purpose of the present investigation was to focus on finding a nonaxisymmetric endwall and boundary layer fence with minimum total pressure loss in the passage and heat transfer coefficient on the endwall of the duct. An approximate optimization method was used for the investigation to secure the computational efficiency. Results indicated that a significant improvement in aerothermal environment can be achieved through the application of a nonaxisymmetric endwall and boundary layer fence.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.4
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• pp.276-280
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• 2019

In this study, we investigated the crystal defects and grain boundary properties in a ZZCCC ($ZnO-Zn_2BiVO_6-Co_3O_4-Cr_2O_3-CaCO_3$) varistor, with the liquid-phase sintering aid $Zn_2BiVO_6$ developed by our laboratory. The ZZCCC varistor sintered at $1,200^{\circ}C$ exhibited excellent nonlinear current-voltage characteristics (${\alpha}=63$), with oxygen vacancy ($V_o^*$ ; 0.35 eV) as a main defect, and an apparent activation energy of 1.1 eV with an electrically single grain boundary. Therefore, among the various additives to improve the electrical properties of ZnO varistors, if $Zn_2BiVO_6$ is used as a liquid phase sintering aid, it will be ideal to use Co for the oxygen vacancy and Ca for the electrically single grain boundary. This will allow the good properties of ZnO varistors to be maintained up to high sintering temperatures.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.4
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• pp.663-670
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• 2019

The modified Canny edge detection algorithm that can detect the boundary between screen door and platform in the subway is proposed in this paper. Generally, in the subway, the boundary line between the platform and the screen door is darker than the surrounding area. Therefore, an edge image is using the modified bottom-hat transform by considering its characteristics. Double thresholded images with strong edge and weak edge through double thresholding are obtained. An algorithm that detects the boundary invasion between the platform and the screen door is proposed by calculating the length by applying the Hough transform to the double thresholded image and comparing the boundary line length between when there is an object such as a person and when there is no object. In this paper, the results of the proposed modified Canny edge detection algorithm using two different input images according to camera height position are shown by computer simulation.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.6
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• pp.1049-1056
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• 2023

The height of the atmospheric boundary layer indicates the peak developed when turbulence is generated by mixing heat and water vapor, and is generally determined through thermodynamic methods. Wind profilers produce atmospheric information from the scattering of signals sent into the atmosphere. A method for making the spectrum of turbulent components, turbulent kinetic energy dissipation rate, and refractive index structure coefficient was presented to determine the atmospheric boundary layer depth. Compared with the vertical distribution characteristics of potential temperature and specific humidity based on radiosonde data, the determination method of the atmospheric boundary layer height from wind profiler output was evaluated as very useful.

• The Journal of the Acoustical Society of Korea
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• v.26 no.6
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• pp.293-300
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• 2007

Turbulent boundary layer over an underwater vehicle is formed when it moves underwater and wall pressure fluctuation within the turbulent boundary layer generates flow-induced noise by exciting the elastic hull of the underwater vehicle. One of the methods to reduce this flow noise is to attach a compliant layer on the surface of the vehicle. In order to observe the possibility of noise reduction in the water when the compliant layer treatments are applied on the surface, three types of specimens those are a bare steel plate, a steel plate coated with neoprene and a steel plate with polyurethane coating material are tested at various flow speeds in a low noise cavitation tunnel. This paper presents the results of measurements and analysis of wall pressure fluctuations which is a main source of flow noise, within the turbulent boundary layer on three specimens. Its results could be shown that about 10dB reduction of wall fluctuation pressure at high frequencies was achieved due to the dissipation of turbulent energy by the compliant coating while it makes the turbulent boundary layer thicker and changes the behavior of turbulent flow in the layer.

• Coupled systems mechanics
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• v.1 no.4
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• pp.381-395
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• 2012

Dynamic response of Pile Supported Structures is highly depended on Soil Pile Structure Interaction. In this paper, by comparison of experimental and numerical dynamic responses of a prototype jacket offshore platform for both hinge based and pile supported boundary conditions, effect of soil-pile-structure interaction on dynamic characteristics of this platform is studied. Jacket and deck of a prototype platform is installed on a hinge-based case first and then platform is installed on eight skirt piles embedded on continuum monolayer sand. Dynamic characteristics of platform in term of natural frequencies, mode shapes and modal damping are compared for both cases. Effects of adding and removing vertical bracing members in top bay of jacket on dynamic characteristics of platform for both boundary conditions are also studied. Numerical simulation of responses for the studied platform is also performed for both mentioned cases using capability of ABAQUS and SACS software. The 3D model using ABAQUS software is created using solid elements for soil and beam elements for jacket, deck and pile members. Mohr-Coulomb failure criterion and pile-soil interface element are used for considering nonlinear pile soil structure interaction. Simplified modeling of soil-pile-structure interaction effect is also studied using SACS software. It is observed that dynamic characteristics of the system changes significantly due to soil-pile-structure interaction. Meanwhile, both of complex and simplified (ABAQUS and SACS, respectively) models can predict this effect accurately for such platforms subjected to dynamic loading in small range of deformation.

• Journal of IKEEE
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• v.27 no.4
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• pp.464-471
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• 2023

In this paper, we propose a method to reduce age distortion in facial expression image generation using StyleGAN Encoder. The facial expression image generation process first creates a face image using StyleGAN Encoder, and changes the expression by applying the learned boundary to the latent vector using SVM. However, when learning the boundary of a smiling expression, age distortion occurs due to changes in facial expression. The smile boundary created in SVM learning for smiling expressions includes wrinkles caused by changes in facial expressions as learning elements, and it is determined that age characteristics were also learned. To solve this problem, the proposed method calculates the correlation coefficient between the smile boundary and the age boundary and uses this to introduce a method of adjusting the age boundary at the smile boundary in proportion to the correlation coefficient. To confirm the effectiveness of the proposed method, the results of an experiment using the FFHQ dataset, a publicly available standard face dataset, and measuring the FID score are as follows. In the smile image, compared to the existing method, the FID score of the smile image generated by the ground truth and the proposed method was improved by about 0.46. In addition, compared to the existing method in the smile image, the FID score of the image generated by StyleGAN Encoder and the smile image generated by the proposed method improved by about 1.031. In non-smile images, compared to the existing method, the FID score of the non-smile image generated by the ground truth and the method proposed in this paper was improved by about 2.25. In addition, compared to the existing method in non-smile images, it was confirmed that the FID score of the image generated by StyleGAN Encoder and the non-smile image generated by the proposed method improved by about 1.908. Meanwhile, as a result of estimating the age of each generated facial expression image and measuring the estimated age and MSE of the image generated with StyleGAN Encoder, compared to the existing method, the proposed method has an average age of about 1.5 in smile images and about 1.63 in non-smile images. Performance was improved, proving the effectiveness of the proposed method.

• Journal of Sensor Science and Technology
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• v.1 no.1
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• pp.67-75
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• 1992

PTC thermistor has been fabricated with as-received $BaTiO_{3}$ powder and its electrical properties were investigated. The resistivity of the PTC thermistor was measured at $20^{\circ}C$ intervals from $20^{\circ}C$ to $200^{\circ}C$. The electrical characteristics of the PTC thermistor are determined by the ac complex impedance analysis. The average grain size measured with a scanning electron microscope increased from $3.8{\mu}m$ to $8.8{\mu}m$ with increasing sintering temperature between $1280^{\circ}C$ and $1400^{\circ}C$. The maximum resistivity jump was $4{\times}10^{5}$. The bulk resistivity of the thermistor sintered above $1340^{\circ}C$ decreased with increasing temperature of the measurement. The grain boundary resistance increased exponentially, the grain boundary capacitance decreased, and the built-in potential at the grain boundary increased with increasing temperature of the measurement. The charge densiy at the grain boundary increased with increasing temperature up to $110^{\circ}C$, which leveled off with further increase in measuring temperature.

• Structural Engineering and Mechanics
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• v.16 no.6
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• pp.655-674
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• 2003

Investigated in this study are the natural vibration characteristics of the coaxial cylindrical shells coupled with a fluid. Theoretical method is developed to find the natural frequencies of the shell using the finite Fourier series expansion, and their results are compared with those of finite element method to verify the validation of the method developed. The effect of the fluid-filled annulus and the boundary conditions on the modal characteristics of the coaxial shells is investigated using a finite element modeling.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1988.10a
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• pp.122-125
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• 1988

The radiation characteristics of corrugated conical horn antenna is calculated. The electromagnetic field equations which are satisfied with boundary conditions in courrugated horn are derived. Using the eqvivalent principle, the formularsof radiation pattern are obtaind. The experiments on 8.0 ~ 13.8 GHz frequency range agree well with the theoretical results.