• Journal of KIISE:Software and Applications
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• v.27 no.4
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• pp.432-440
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• 2000

In this study, a new algorithm for canceling MRI artifact due to translational motion in image plane is described. Unlike the conventional iterative phase retrieval algorithm, in which there is no guarantee for the convergence, a direct method for estimating the motion is presented. In previous approaches, the motions in the x(read out) direction and the y(phase encoding) direction are estimated simultaneously. However, the features of x and y directional motions are different from each other. By analyzing their features, each x and y directional motion is canceled by different algorithms in two steps. First, it is noticed that the x directional motion corresponds to a shift of the x directional spectrum of the MRI signal, and the non-zero area of the spectrum just corresponds to the projected area of the density function on the x-axis. So the motion is estimated by tracing the edges between non-zero area and zero area of the spectrum, and the x directional motion is canceled by shifting the spectrum in inverse direction. Next, the y directional motion is canceled by using a new constraint condition, with which the motion component and the true image component can be separated. This algorithm is shown to be effective by using a phantom image with simulated motion.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.1
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• pp.18-23
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• 2013

Omni-directional robot is a typical holonomic constraint robot that has three degrees of freedom movement in 2D plane. In this study, a new omni-directional robot whose wheels are arranged in radial directions was proposed to improve driving performance of the robot. Unlike a general omni-directional robot whose wheels were arranged in a circumferential direction, moments do not arises in the proposed robot when the robot travels in a straight line. To analyze driving performance, dynamic modeling of the omni-directional robot, which considers friction and slip, was carried out. By friction measurement experiments, the relationship between dynamic friction coefficient and relative velocity was derived. Dynamic friction coefficient according to the angle difference between robot travel direction and wheel rotation direction was also obtained. By applying these results to the dynamic model, driving performance of the robot was calculated. As a result, the proposed robot was 1.5 times faster than the general robot.

• Plant Journal
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• v.5 no.3
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• pp.66-73
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• 2009

This study aims to develop a strategy for South Korean companies to penetrate into the global NPP(nuclear power plant) market with their strength as the sixth biggest nuclear power generator in the world. With 20 nuclear plants in commercial operation and 6 more in construction, South Korea has the best technology in construction and operation of NPP. Despite these capabilities as demonstrated on its domestic market, Korean companies' constraint to enter and play a key role in global NPP market would be the lack of experience in overseas NPP projects, original technologies, and diplomatic effectiveness. This study analyzes the competitiveness of Korean standardized nuclear power plant, construction management skills, construction technologies, manufacturing equipment and materials and operation skills. In this research the current status of existing NPP and the forecast of building NPP according to countries was analyzed in order to work out strategies with technology, cost-effectiveness, and diplomatic consideration.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.60-65
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• 2004

Kim et al. described and compared other methods of measuring stress triaxiality using the displacements near the side necking, proved the validities of these models and explored the effect of location where the displacements are measured using three-dimensional finite element analysis for a standard CT specimen with 20% side-grooves. In this paper, the applicability of these models to various specimen and materials are examined in detail. To consider the effects of side groove, thickness of specimen, crack length, specimen geometry and strain hardening exponents, three-dimensional finite element simulation has been performed for various specimen geometries. For a case without a side groove, in the whole the difference between the stress triaxilaity analytically evaluated and directly determined is similar. For a case with a 20% side groove the stress triaxiality is measured at the area where ${\theta}$ is smaller than $60^{\circ}$, which excludes a side grooved area.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.300-305
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• 2003

Reduced activation ferritic (JLF-1) steel is leading candidates for blanket/first-wall structures of the D-T fusion reactor. In fusion application, structural materials will suffer effects of repeated changes of temperature. Therefore, the data base of tensile strength and fracture toughness at operated temperature $400^{\circ}C$ are very important. Fracture toughness ($J_{IC}$) and tensile tests were carried out at room temperature and elevated temperature ($400^{\circ}C$). Fracture toughness tests were performed with two type size to investigate the relationship between the constraint effect of a size and the fracture toughness resistance curve. As the results, the tensile strength and the fracture toughness values of the JLF-1 steel are slightly decreased with increasing temperature. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. The fracture toughness values of JLF-1 steel at room temperature and at $400^{\circ}C$ shows an excellent fracture toughness ($J_{IC}$) of about $530kJ/m^2\;and\;340kJ/m^2$, respectively.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.4 no.1
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• pp.101-110
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• 2004

The robots that will be needed in the near future are human-friendly robots that are able to coexist with humans and support humans effectively. To realize this, humans and robots need to be in close proximity to each other as much as possible. Moreover, it is necessary for their interactions to occur naturally. It is desirable for a robot to carry out human following, as one of the human-affinitive movements. The human-following robot requires several techniques: the recognition of the moving objects, the feature extraction and visual tracking, and the trajectory generation for following a human stably. In this research, a predictable intelligent space is used in order to achieve these goals. An intelligent space is a 3-D environment in which many sensors and intelligent devices are distributed. Mobile robots exist in this space as physical agents providing humans with services. A mobile robot is controlled to follow a walking human using distributed intelligent sensors as stably and precisely as possible. The moving objects is assumed to be a point-object and projected onto an image plane to form a geometrical constraint equation that provides position data of the object based on the kinematics of the intelligent space. Uncertainties in the position estimation caused by the point-object assumption are compensated using the Kalman filter. To generate the shortest time trajectory to follow the walking human, the linear and angular velocities are estimated and utilized. The computer simulation and experimental results of estimating and following of the walking human with the mobile robot are presented.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.441-449
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• 2015

In this paper we perform a linearized buckling analysis using the Kirchhoff plate theory and the von Karman nonlinear strain-displacement relation. Design sensitivity analysis(DSA) expressions for plane elasticity and buckling problems are derived with respect to Young's modulus and thickness. Using the design sensitivity, we can formulate the topology optimization method for minimizing the compliance and maximizing eigenvalues. We develop a topology optimization method applicable to plate buckling problems using the prestress for buckling analysis. Since the prestress is needed to assemble the stress matrix for buckling problem using the von Karman nonlinear strain, we introduced out-of-plane motion. The design variables are parameterized into normalized bulk material densities. The objective functions are the minimum compliance and the maximum eigenvalues and the constraint is the allowable volume. Through several numerical examples, the developed DSA method is verified to yield very accurate sensitivity results compared with the finite difference ones and the topology optimization yields physically meaningful results.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.37 no.3
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• pp.70-78
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• 2000

In this study, a new method for canceling MRI artifacts through the motion translation of image plane is presented Breathing often makes problems in a clinical diagnosis. Assuming that the head moves up and down due to breathing, rigid translational motions in only y(phase encoding axis) direction are treated Unlike the conventional Iterative phase retrieval algorithm, this method is based on the MRI imaging process and analyzing of Image property A new constraint condition with which the motion component and the true image component in the MRI signal can be separated by a simple algebraic operation is extracted After the x(read out) directional Fourier transformation of MRI signal is done, the y(phase encoding) directional spectrum phasing value is Just an algebraic sum of the Image component and the motion component Meanwhile, as It is known that the density of subcutaneous fat area is almost uniform in the head tomographs, the density distribution along a y directional line on this fat area is regarded as symmetric shape If the density function is symmetric, then the phase of spectrum changes linearly with the position Hence, the departure component from the linear function can be separated as the motion component Based on this constrant condition, the new method of artifact cancellation is presented Finally, the effectiveness of this algorithm IS shown by using a phantom with simulated motions.