• Structural Engineering and Mechanics
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• v.66 no.5
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• pp.557-568
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• 2018

An investigation is made in the present work on the post-buckling and geometrically nonlinear behaviors of moderately thick perfect and imperfect rectangular plates made-up of functionally graded materials. Spectral collocation approach based on Legendre basis functions is developed to analyze the functionally graded plates while they are subjected to end-shortening strain. The material properties in this study are varied through the thickness according to the simple power law distribution. The fundamental equations for moderately thick rectangular plates are derived using first order shear deformation plate theory and taking into account both geometric nonlinearity and initial geometric imperfections. In the current study, the domain of interest is discretized with Legendre-Gauss-Lobatto nodes. The equilibrium equations will be obtained by discretizing the Von-Karman's equilibrium equations and also boundary conditions with finite Legendre basis functions that are substituted into the displacement fields. Due to effect of geometric nonlinearity, the final set of equilibrium equations is nonlinear and therefore the quadratic extrapolation technique is used to solve them. Since the number of equations in this approach will always be more than the number of unknown coefficients, the least squares technique will be used. Finally, the effects of boundary conditions, initial geometric imperfection and material properties are investigated and discussed to demonstrate the validity and capability of proposed method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1186-1189
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• 2005

Focused Ion Beam machining is an attractive approach to produce nano-scale 3D structures. However, like other beam-based manufacturing processes, the redeposition of the sputtered material during the machining deteriorates the geometric accuracy of ion beam machining. In this research a new approach to reduce the geometric error in FIB machining is introduced. The observed redeposition phenomena have been compared with existing theoretical model. Although the redeposition effect has good repeatability the prediction of exact amount of geometric error in ion beam machining is difficult. Therefore, proposed method utilizes process control approach. Developed algorithm measures the redeposition amount after every production cycle and modifies next process plan. The method has been implemented to a real FIB machine and the experimental results demonstrated considerable improvement of five micrometer-sized pocket machining.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.4
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• pp.680-686
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• 2006

Document images captured by scanners have only skewing distortion. But camera captured document images have not only skew but also vignetting effect and geometric distortion. Vignetting effect, which makes the border areas to be darker than the center of the image, make it difficult to separate characters from the document images. But this effect has being decreased, as the lens manufacturing skill is developed. Geometric distortion, occurred by the mismatch of angle and center position between the document image and the camera, make the shape of characters to be distorted, so that the character recognition is more difficult than the case of using scanner. In this paper, we propose a method that can increase the performance of character recognition by correcting the geometric distortion of document images using a linear approximation which changes the quadrilateral region to the rectangle one. The proposed method also determine the quadrilateral transform region automatically, using the alignment of character lines and the skewed angles of characters located in the edges of each character line. Proposed method, therefore, can correct the geometric distortion without getting positional information from camera.

• Carbon letters
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• v.26
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• pp.61-65
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• 2018

Comprehensive calculations of the Rh decoration effect on zigzag CNTs with n ranging from 7 to 12 were conducted in this work to understand the effect of Rh doping on geometric structures and electronic behaviors upon metallic and semiconducting CNTs. The obtained results indicated that Rh dopant not only contributes to the deformation of C-C bonds on the sidewall of CNTs, but also transforms the electron distribution of related complexes, thereby leading to a remarkable increase of the conductivity of pure CNTs given the emerged novel state within the energy gap for metallic CNTs and the narrowed energy gap for semiconducting CNTs. Our calculations will be meaningful for exploiting novel CNT-based materials with better sensitivity to electrons and higher electrical conductivity compared with pure CNTs.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.2
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• pp.248-255
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• 2009

We proposed a power line channel model. We adopted advantages of other power line channel models to calculate channel responses correctly and simply. Infinite geometric series reduced the calculation complexity of the multipath signal propagation. Description Matrices were also adopted to handle the network topology easily. It represents complex power line network precisely and simply. Newly proposed model considered the effect of the adjacent nodes to channel responses, which have been not considered so far. Several simulations were executed to verify the effect of the adjacent nodes. As a result we found out that it affected channel responses but its effect was limited within certain degree.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.670-676
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• 2004

In this paper, a modeling method for the vibration analysis of rotating structures composed of beams and shells employing multi-reference frames is presented. The rotary inertia effect and the geometric stiffening effect that results from centrifugal inertia force we considered for beams and shells with lumped mass model. In most previous studies, single reference frame has been employed for the vibration analysis. In the present study, a modeling method employing multi-reference frames is presented and the effects of employing multi-reference frames on the analysis accuracy are investigated through solving numerical examples.

• Steel and Composite Structures
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• v.30 no.4
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• pp.305-313
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• 2019

Creating different cutout shapes in order to make doors and windows, reduce the structural weight or implement various mechanisms increases the likelihood of buckling in thin-walled structures. In this study, the effect of cutout shape and geometric imperfection (GI) is simultaneously investigated on the critical buckling load and knock-down factor (KDF) of composite cylindrical shells. The GI is modeled using single perturbation load approach (SPLA). First, in order to assess the finite element model, the critical buckling load of a composite shell without cutout obtained by SPLA is compared with the experimental results available in the literature. Then, the effect of different shapes of cutout such as circular, elliptic and square, and perturbation load imperfection (PLI) is investigated on the buckling behavior of cylindrical shells. Results show that the critical buckling load of a shell without cutout decreases by increasing the PLI, whereas increasing the PLI does not have a great impact on the critical buckling load in the presence of cutout imperfection. Increasing the cutout area reduces the effect of the PLI, which results in an increase in the KDF.

• Proceedings of the KWS Conference
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• 1994.05a
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• pp.232-234
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• 1994

• Proceedings of the KWS Conference
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• 1995.04a
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• pp.160-163
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• 1995

• Proceedings of the KWS Conference
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• 1993.10a
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• pp.125-128
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• 1993