• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제24권1호
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• pp.1-22
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• 2020

An accurate and efficient gradient estimation method on unstructured grid is presented by proposing a switching process between two Least-Square methods. Diverse test cases show that the gradient estimation by Least-Square methods exhibit better characteristics compared to Green-Gauss approach. Based on the investigation, switching between the two Least-Square methods, whose merit complements each other, is pursued. The condition number of the Least-Square matrix is adopted as the switching criterion, because it shows clear correlation with the gradient error, and it can be easily calculated from the geometric information of the grid. To illustrate switching process on general grid, condition number is analyzed using stencil vectors and trigonometric relations. Then, the threshold of switching criterion is established. Finally, the capability of Switching Weighted Least-Square method is demonstrated through various two- and three-dimensional applications.

• 한국콘텐츠학회논문지
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• 제8권11호
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• pp.1-9
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• 2008

현재 멀티미디어 기술의 발달로 인하여 영상의 전처리 및 후처리 과정을 이용한 수정 작업으로 고품질의 영상 표현 및 다양한 영상 처리가 가능하다. 영상 처리 기법 중에서 이방성 확산의 경우 영상의 스페클 노이즈 제거, 에지 검출, 영상 분할 등에 응용할 수 있는 효과적인 확산 필터링으로 활용되고 있다. 하지만 전통적인 이방성 확산은 십자형 커널을 기반으로 하고 있기 때문에 확산 필터링을 반복 적용하면 영상의 에지가 수평 및 수직 방향으로 집중되는 문제점이 있다. 본 논문에서는 기존의 십자형 커널 기반의 이방성 확산 문제점을 해결하기 위하여 기울기의 방향성에 기반한 새로운 이방성 확산 방식을 제안한다. 제안된 방식은 십자형 커널을 확장하여 대각선 방향 정보를 포함한 8방향의 정방형 커널을 기반으로 작은 기울기를 갖는 방향으로 이방성 확산을 적용한다. 제안된 방식의 실험 결과 에지가 수평 및 수직 방향으로 집중되는 문제점을 해결하면서 임펄스성 노이즈를 제거하여 고품질의 영상을 획득할 수 있었다.

• 한국해양공학회지
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• 제20권6호
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• pp.61-66
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• 2006

Two iterative solvers are applied to solve the modified mild slope equation. The elliptic formulation of the governing equation is selected for numerical treatment because it is partly suited for complex wave fields, like those encountered inside harbors. The requirement that the computational model should be capable of dealing with a large problem domain is addressed by implementing and testing two iterative solvers, which are based on the Stabilized Bi-Conjugate Gradient Method (BiCGSTAB) and Generalized Conjugate Gradient Method (GCGM). The characteristics of the solvers are compared, using the results for Berkhoff's shoal test, used widely as a benchmark in coastal modeling. It is shown that the GCGM algorithm has a better convergence rate than BiCGSTAB, and preconditioning of these algorithms gives more than half a reduction of computational cost.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제15권4호
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• pp.251-259
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• 2015

In this paper, a ship detection method is proposed; this method uses edge-based segmentation and histogram of oriented gradient (HOG) with the ship size ratio. The proposed method can prevent a marine collision accident by detecting ships at close range. Furthermore, unlike radar, the method can detect ships that have small size and absorb radio waves because it involves the use of a vision-based system. This system performs three operations. First, the foreground is separated from the background and candidates are detected using Sobel edge detection and morphological operations in the edge-based segmentation part. Second, features are extracted by employing HOG descriptors with the ship size ratio from the detected candidate. Finally, a support vector machine (SVM) verifies whether the candidates are ships. The performance of these methods is demonstrated by comparing their results with the results of other segmentation methods using eight-fold cross validation for the experimental results.

• Computers and Concrete
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• 제12권2호
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• pp.229-241
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• 2013

The objective of this study is to reveal the sufficiency of neural networks (NN) as a securer, quicker, more robust and reliable method to be used in seismic assessment of existing reinforced concrete buildings. The NN based approach is applied as an alternative method to determine the seismic performance of each existing RC buildings, in terms of damage level. In the application of the NN, a multilayer perceptron (MLP) with a back-propagation (BP) algorithm is employed using a scaled conjugate gradient. NN based model wasd eveloped, trained and tested through a based MATLAB program. The database of this model was developed by using a statistical procedure called P25 method. The NN based model was also proved by verification set constituting of real existing RC buildings exposed to 2003 Bingol earthquake. It is demonstrated that the NN based approach is highly successful and can be used as an alternative method to determine the seismic performance of each existing RC buildings.

• International Journal of Contents
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• 제7권4호
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• pp.24-29
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• 2011

In this paper, we propose a method to segment the bottle label in images taken by mobile phones using multi-gradient approaches. In order to segment the label region of interest-object, the saliency map method and Hough Transformation method are first applied to the original images to obtain the candidate region. The saliency map is used to detect the most salient area based on three kinds of features (color, orientation and illumination features). The Hough Transformation is a technique to isolated features of a particular shape within an image. Therefore, we utilize it to find the left and right border of the bottle. Next, we segment the label based on the gradient information obtained from the structure tensor method and edge method. The experimental results have shown that the proposed method is able to accurately segment the labels as the first step of product label recognition system.

• 디지털콘텐츠학회 논문지
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• 제11권1호
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• pp.39-45
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• 2010

본 논문에서는 기울기 기반 빠른 정상점 탐색 방법론을 제시하고 시뮬레이션 결과를 제시한다. 제안하는 방법론은 유한 구간에서 단봉 그래프를 가지는 함수의 정상점(최대치)을 최대한 적은 수의 함수값을 참조하여 찾는 문제에 대한 솔루션으로, 대표적인 적용분야로는 자동초점이 있다. 우리는 정상점 탐색을 위해 주기적 탐색, 기울기 기반 탐색, 상세 탐색과 같이 세가지 탐색 전략을 통해 정상점을 찾는다. 노이즈가 첨가된 가우시안 함수를 발생시켜 시뮬레이션 한 결과 대략 8번탐색 횟수와 1.04의 오차를 보임을 알 수 있었다.

• Advances in materials Research
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• 제12권2호
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• pp.133-159
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• 2023

In this paper, a size-dependent dynamic investigation of a porous metal foams microbeamsis presented. The novelty of this study is to use a metal foam microbeam that contain porosities based on the refined high order shear deformation beam model, with sinusoidal shear strain function, and the modified strain gradient theory (MSGT) for the first time. The Lagrange's principle combined with differential quadrature hierarchicalfinite element method (DQHFEM) are used to obtain the porous microbeam governing equations. The solutions are presented for the natural frequencies of the porous and homogeneoustype microbeam. The obtained results are validated with the analytical methods found in the literature, in order to confirm the accuracy of the presented resolution method. The influences of the shape of porosity distribution, slenderness ratio, microbeam thickness, and porosity coefficient on the free vibration of the porous microbeams are explored in detail. The results of this paper can be used in various design formetallic foammicro-structuresin engineering.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권11호
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• pp.4355-4371
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• 2020

Phase retrieval, recovering a signal from phaseless measurements, is generally considered to be an NP-hard problem. This paper adopts an amplitude-based nonconvex optimization cost function to develop a new stochastic gradient algorithm, named stochastic reweighted phase retrieval (SRPR). SRPR is a stochastic gradient iteration algorithm, which runs in two stages: First, we use a truncated sample stochastic variance reduction algorithm to initialize the objective function. The second stage is the gradient refinement stage, which uses continuous updating of the amplitude-based stochastic weighted gradient algorithm to improve the initial estimate. Because of the stochastic method, each iteration of the two stages of SRPR involves only one equation. Therefore, SRPR is simple, scalable, and fast. Compared with the state-of-the-art phase retrieval algorithm, simulation results show that SRPR has a faster convergence speed and fewer magnitude-only measurements required to reconstruct the signal, under the real- or complex- cases.

• 한국통신학회논문지
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• 제31권8C호
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• pp.786-794
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• 2006

본 논문에서는 초고해상도 영상을 복원하기 위한 최적화 기법으로 널리 사용되는 PCG(Preconditioned Conjugate Gradient) 기법을 위한 새로운 preconditioner를 제안하였다. 제안된 preconditioner는 기존의 블록 circulant preconditioner를 확장하여 roughness 벌칙 함수에 대해서 효과적인 수렴이 가능하도록 한 것으로써, 잡음에 민감한 기존 방법의 성능을 개선할 수 있는 것이다. 제안된 preconditioner의 성능을 확인하기 위한 실험과 시뮬레이션에서 제안된 PCG 방법은 기존 방법보다 우수한 수렴 속도를 보였다.