Search results for: Soo Yeol Lee

Authors: Oh-Yeol Kwon, Sung-Il Chien

Abstract:

A conventional image posterization method occasionally fails to preserve the shape and color of objects due to the uneffective color reduction. This paper proposes a new image posterizartion method by using modified color quantization for preserving the shape and color of objects and color contrast enhancement for improving lightness contrast and saturation. Experiment results show that our proposed method can provide visually more satisfactory posterization result than that of the conventional method.

Keywords: Color contrast enhancement, color quantization, color segmentation, image posterization

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Authors: Yong Seo Koo, Jong Ho Nam, Yong Nam Choi, Dae Yeol Yoo, Jung Woo Han

Abstract:

This paper presents a silicon controller rectifier (SCR) based ESD protection circuit for IC. The proposed ESD protection circuit has low trigger voltage and high holding voltage compared with conventional SCR ESD protection circuit. Electrical characteristics of the proposed ESD protection circuit are simulated and analyzed using TCAD simulator. The proposed ESD protection circuit verified effective low voltage ESD characteristics with low trigger voltage and high holding voltage.

Keywords: ESD (Electro-Static Discharge), SCR (Silicon Controlled Rectifier), holding Voltage.

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Authors: Hyunhee Ryu, Young Ju Jeon, Jaeuk U. Kim, Hae Jung Lee, Yu Jung Lee, Jong Yeol Kim

Abstract:

The aim of this study was to investigate the effect of blood viscosity on the radial pulse wave. For this, we obtained the radial pulse wave of 15 males with abnormal high hematocrit level and 47 males with normal hematocrit level at the age of thirties and forties. Various variables of the radial pulse wave between two groups were analyzed and compared by Student's T test. There are significant differences in several variables about height, time and area of the pulse wave. The first peak of the radial pulse wave was higher in abnormal high hematocrit group, but the third peak was higher and longer in normal hematocrit group. Our results suggest that the radial pulse wave can be used for diagnosis of high blood viscosity and more clinical application.

Keywords: Radial pulse wave, Blood viscosity, Hematocrit.

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Authors: Sang-Yoon Lee, Jung-Mi Lee, Hyeong-Yeol Kim, Jae-Joon Song

Abstract:

In this study, a longitudinal joint connection was proposed for the short-span slab-type modular bridges with rapid construction. The slab-type modular bridge consists of a number of precast slab modules and has the joint connection between the modules in the longitudinal direction of the bridge. A finite element based parameter analysis was conducted to design the shape and the dimensions of the longitudinal joint connection. Numbers of shear keys within the joint, height and depth of the shear key, tooth angle, and the spacing were considered as the design parameters. Using the local cracking load at the corner of the shear key and the cross-sectional area of the joint, an efficiency factor was proposed to evaluate the effectiveness of the longitudinal joint connection. The dimensions of shear key were determined by comparing the cracking loads and the efficiency factors obtained from the finite element analysis.

Keywords: precast, slab bridge, modular bridge, shear key

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Authors: Dong-Hyun Kim, Jin-Woong Choi, Hyeong-Yeol Kim, Sun-Kyu Park

Abstract:

This study is to evaluate the behavior of integral and segmental specimens through static and cyclic tests. Integral specimens were made with the same size to be compared with segmental specimens that were made by connected precast members. To evaluate its bending performance and serviceability, 1 integral and 3 segmental specimens were tested under static load. And 1 integral and 2 segmental specimens were tested under cyclic load, respectively. Different load ranges were considered in the cyclic tests to evaluate the safety and serviceability. The test results showed that under static loading, segmental specimens had about 94% of the integral specimen's maximum moment, averagely. Under cyclic loading, the segmental specimens showed that had enough safety in the range of higher than service load and enough serviceability. In conclusion, the maximum crack width (0.16mm) satisfied the allowable crack width (0.30mm) in the range of service load.

Keywords: Modular bridge, Transverse connection, Precast concrete, Static and cyclic test.

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Authors: Kyoungwoo Park, Byeong Sam Kim, Hyo-Jae Lim, Ji Won Han, Park Kyoun Oh, Juhee Lee, Keun-Yeol Yu

Abstract:

Predictions of flow and heat transfer characteristics and shape optimization in internally finned circular tubes have been performed on three-dimensional periodically fully developed turbulent flow and thermal fields. For a trapezoidal fin profile, the effects of fin height h, upper fin widths d1, lower fin widths d2, and helix angle of fin ? on transport phenomena are investigated for the condition of fin number of N = 30. The CFD and mathematical optimization technique are coupled in order to optimize the shape of internally finned tube. The optimal solutions of the design variables (i.e., upper and lower fin widths, fin height and helix angle) are numerically obtained by minimizing the pressure loss and maximizing the heat transfer rate, simultaneously, for the limiting conditions of d1 = 0.5~1.5 mm, d2 = 0.5~1.5 mm, h= 0.5~1.5mm, ? = 10~30 degrees. The fully developed flow and thermal fields are predicted using the finite volume method and the optimization is carried out by means of the multi-objective genetic algorithm that is widely used in the constrained nonlinear optimization problem.

Keywords: Computational fluid dynamics, Genetic algorithm, Internally finned tube with helix angle, Optimization.

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Authors: Mohamed K. Metwally, Sherif H. El-Gohary, Kyung Min Byun, Seung Moo Han, Soo Yeol Lee, Min Hyoung Cho, Gon Khang, Jinsung Cho, Tae-Seong Kim

Abstract:

Photoacoustic imaging (PAI) is a non-invasive and non-ionizing imaging modality that combines the absorption contrast of light with ultrasound resolution. Laser is used to deposit optical energy into a target (i.e., optical fluence). Consequently, the target temperature rises, and then thermal expansion occurs that leads to generating a PA signal. In general, most image reconstruction algorithms for PAI assume uniform fluence within an imaging object. However, it is known that optical fluence distribution within the object is non-uniform. This could affect the reconstruction of PA images. In this study, we have investigated the influence of optical fluence distribution on PA back-propagation imaging using finite element method. The uniform fluence was simulated as a triangular waveform within the object of interest. The non-uniform fluence distribution was estimated by solving light propagation within a tissue model via Monte Carlo method. The results show that the PA signal in the case of non-uniform fluence is wider than the uniform case by 23%. The frequency spectrum of the PA signal due to the non-uniform fluence has missed some high frequency components in comparison to the uniform case. Consequently, the reconstructed image with the non-uniform fluence exhibits a strong smoothing effect.

Keywords: Finite Element Method, Fluence Distribution, Monte Carlo Method, Photoacoustic Imaging.

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Authors: Apirak Sombat, Teerapol Saleewong, Poom Kumam, Parin Chaipunya, Wiyada Kumam, Anantachai Padcharoen, Yeol Je Cho, Thana Sutthibutpong

Abstract:

This research is aimed to study a two-step iteration process defined over a finite family of σ-asymptotically quasi-nonexpansive nonself-mappings. The strong convergence is guaranteed under the framework of Banach spaces with some additional structural properties including strict and uniform convexity, reflexivity, and smoothness assumptions. With similar projection technique for nonself-mapping in Hilbert spaces, we hereby use the generalized projection to construct a point within the corresponding domain. Moreover, we have to introduce the use of duality mapping and its inverse to overcome the unavailability of duality representation that is exploit by Hilbert space theorists. We then apply our results for σ-asymptotically quasi-nonexpansive nonself-mappings to solve for ideal efficiency of vector optimization problems composed of finitely many objective functions. We also showed that the obtained solution from our process is the closest to the origin. Moreover, we also give an illustrative numerical example to support our results.

Keywords: σ-asymptotically quasi-nonexpansive nonselfmapping, strong convergence, fixed point, uniformly convex and uniformly smooth Banach space.

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Authors: Won Yeol Choi, Sangmo Kang

Abstract:

The propulsion of a bacterial flagellum in a viscous fluid has attracted many interests in the field of biological hydrodynamics, but remains yet fully understood and thus still a challenging problem. In this study, therefore, we have numerically investigated the flow around a steadily rotating micro-sized spring to further understand such bacterial flagellum propulsion. Note that a bacterium gains thrust (propulsive force) by rotating the flagellum connected to the body through a bio motor to move forward. For the investigation, we convert the spring model from the micro scale to the macro scale using a similitude law (scale law) and perform simulations on the converted macro-scale model using a commercial software package, CFX v13 (ANSYS). To scrutinize the propulsion characteristics of the flagellum through the simulations, we make parameter studies by changing some flow parameters, such as the pitch, helical radius and rotational speed of the spring and the Reynolds number (or fluid viscosity), expected to affect the thrust force experienced by the rotating spring. Results show that the propulsion characteristics depend strongly on the parameters mentioned above. It is observed that the forward thrust increases in a linear fashion with either of the rotational speed or the fluid viscosity. In addition, the thrust is directly proportional to square of the helical radius and but the thrust force is increased and then decreased based on the peak value to the pitch. Finally, we also present the appropriate flow and pressure fields visualized to support the observations.

Keywords: Fluid viscosity, hydrodynamics, similitude, propulsive force.

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