• Smart Structures and Systems
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• 제9권4호
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• pp.335-353
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• 2012

This study suggests a simple two-step method for structural vibration-based health monitoring for beam-like structures which only utilizes mode shape curvature and few natural frequencies of the structures in order to detect and localize cracks. The method is firstly based on the application of wavelet transform to detect crack locations from mode shape curvature. Then particle swarm optimization is applied to evaluate crack depth. As the Rayleigh quotient is introduced to estimate natural frequencies of cracked beams, the relationship of natural frequencies and crack depths can be easily obtained with only a simple formula. The method is demonstrated and validated numerically, using the numerical examples (cantilever beam and simply supported shaft) in the literature, and experimentally for a cantilever beam. Our results show that mode shape curvature and few estimated natural frequencies can be used to detect crack locations and depths precisely even under a certain level of noise. The method can be extended for health monitoring of other more complicated structures.

• 대한수학회보
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• 제53권5호
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• pp.1531-1548
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• 2016

Let C[0, t] denote the space of real-valued continuous functions on [0, t] and define a random vector $Z_n:C[0,t]{\rightarrow}\mathbb{R}^n$ by $Z_n(x)=(\int_{0}^{t_1}h(s)dx(s),{\ldots},\int_{0}^{t_n}h(s)dx(s))$, where 0 < $t_1$ < ${\cdots}$ < $ t_n=t$ is a partition of [0, t] and $h{\in}L_2[0,t]$ with $h{\neq}0$ a.e. Using a simple formula for a conditional expectation on C[0, t] with $Z_n$, we evaluate a generalized analytic conditional Wiener integral of the function $G_r(x)=F(x){\Psi}(\int_{0}^{t}v_1(s)dx(s),{\ldots},\int_{0}^{t}v_r(s)dx(s))$ for F in a Banach algebra and for ${\Psi}=f+{\phi}$ which need not be bounded or continuous, where $f{\in}L_p(\mathbb{R}^r)(1{\leq}p{\leq}{\infty})$, {$v_1,{\ldots},v_r$} is an orthonormal subset of $L_2[0,t]$ and ${\phi}$ is the Fourier transform of a measure of bounded variation over $\mathbb{R}^r$. Finally we establish various change of scale transformations for the generalized analytic conditional Wiener integrals of $G_r$ with the conditioning function $Z_n$.

• 한국통신학회논문지
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• 제32권2C호
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• pp.113-123
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• 2007

유비쿼터스 통신 환경에서는 영상의 다양한 형태의 변환이 필수적인데, 대부분의 디지털 영상은 DCT (Discrete Cosine Transform)를 기반으로 한 JPEG, MPEG 등의 표준 기법을 이용하여 압축되어 저장되어 있다. 본 논문에서는 DCT 영역에서 영상의 크기를 변환시키는 기존의 여러 가지 알고리즘들을 고찰하고 그 성능을 분석하며, 기존의 방법보다 더 우수한 성능을 보이는 DCT 영역에서의 영상 크기 변환 알고리즘을 제안한다. 제안하는 알고리즘은 DCT 영역에서 영상의 임의 크기 변환을 위해 여러 개의 $8{\times}8$ DCT 계수 블록을 변환 비율에 따라 변환식을 통하여 하나의 블록으로 변환하고 최적의 zero-padding 및 truncating을 위한 IDCT의 크기를 정하는 방법을 이용하여 영상 크기 변환의 성능을 높인다. 이것은 화소간의 상관도를 최대한 이용하여 DCT 계수를 구하고, 여기서 얻어진 DCT 계수 블록에서 원하는 비율에 따라 최적의 크기를 구함으로써 성능을 높이는 알고리즘이다. 그 성능을 원 영상과 축소하여 다시 확대시킨 영상의 PSNR 비교를 통하여 확인하였고, 제안하는 알고리즘은 특정 비율의 변환에 있어서 기존의 알고리즘을 포괄할 수 있는 방법임을 확인할 수 있었다.

• 한국시뮬레이션학회논문지
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• 제33권1호
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• pp.19-26
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• 2024

단계형 확률분포는 마코프 체인이 특정 상태로 흡수되는 시점까지 거쳐가는 여러 단계에서 체재하는 시간들의 합으로 정의되며 대기행렬 시스템과 신뢰성 분석 모형 등에 광범위하게 사용된다. 연속적 단계형 분포의 경우 흡수 상태로 진입하기까지 거쳐가는 각각의 단계에서의 체재 시간이 지수분포를 따르므로 연속적 단계형 분포는 다양한 지수분포들의 합 또는 볼록 결합으로 나타낼 수 있다. 단계형 분포를 생성하는 가장 일반적이면서도 직관적인 방법은 마코비안 표현방법이라 불리는 초기 확률벡터와 전이 생성행렬에 의해 주어지는 조건부 확률을 이용하는 것이다. 적률이 주어진 상황에서 단계형 변수를 생성하는 방법에 대한 기존의 연구들은 대부분 적률을 마코비안 표현방법으로 변환하는 것을 전제로 하고 있다. 본 연구에서는 적률을 마코비안 표현방법으로 변환하지 않고 확률 분포함수를 결정하여 단계형 확률변수를 생성하는 방법에 대해 살펴보고 마코프 표현을 사용하는 기존의 방법 대신에 조단 분해법과 최소 표현 라플라스 변환을 이용하여 2계 단계형 확률변수를 분포함수를 결정하는 공식과 절차를 제시한다. 이러한 접근 방법은 고차원의 단계형 확률분포를 이용하여 대기행렬의 시뮬레이션을 하는 경우에 마코비안 표현방법의 전이행렬을 결정하여 변수를 생성하는 경우보다 효율적이다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.91-94
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• 2005

A numerical formula that presents relationship between a point of a satellite image and its ground position is called a sensor model. For precise geolocation of satellite images, we need an error-free sensor model. However, the sensor model based on GOES ephemeris data has some error, in particular after Image Motion Compensation (IMC) mechanism has been turned off. To solve this problem, we investigate three sensor models: Collinearity model, Direct Linear Transform (DLT) model and Orbit-based model. We apply matching between GOES images and global coastline database and use successful results as control points. With control points we improve the initial image geolocation accuracy using the three models. We compare results from three sensor models that are applied to GOES-9 images. As a result, a suitable sensor model for precise geolocation of GOES-9 images is proposed.

• 대한수학교육학회지:학교수학
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• 제3권2호
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• pp.447-473
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• 2001

Since the greater part of mathematical concepts have been developed in the direction of “from the concrete and realistic aspects to the abstract level”, children should be secured to learn mathematics genetically with various manipulative materials. The aim of this study is to instigate the active use of geoboards in mathematics classroom. To achieve this arm, we first embodied the several significances on the use of geoboards in mathematics instruction. And we then performed an instruction that children discover and justify the formula related to the area of trapezoid by exploring with geoboards, and analyzed the instructional episode to support our assertion about some secure merit accompanied by using geoboards. From this study, we obtained the conclusion that geoboard activity contains many significances such as children can explore congruence, symmetry, similarity, fundamental properties of figures, and pattern. Futhermore, geoboard activity enable children to transform a figure into other equivalently, develop spatial sense, have basic experiences for coordinate geometry, build a concrete model to explain abstract ideas, and foster the ability of problem solving and mathematical thinking.

• 한국경영과학회지
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• 제40권1호
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• pp.1-4
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• 2015

This paper presents a heuristic approach to derive the Laplace-Stieltjes transform (LST) and the probability generating function (PGF) of the waiting time distributions of a continuous- and a discrete-time GI/G/1 queue, respectively. This is a new idea to derive the well-known results, the waiting time distribution of GI/G/1 queue, in a different way.

• 대한수학회지
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• 제50권2호
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• pp.259-274
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• 2013

In this paper, we consider the Fourier-type functionals on Wiener space. We then establish the analytic Feynman integrals involving the ${\diamond}$-convolutions. Further, we give an approach to solution of the Schr$\ddot{o}$dinger equation via Fourier-type functionals. Finally, we use this approach to obtain solutions of the Schr$\ddot{o}$dinger equations for harmonic oscillator and double-well potential. The Schr$\ddot{o}$dinger equations for harmonic oscillator and double-well potential are meaningful subjects in quantum mechanics.

• 호남수학학술지
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• 제36권2호
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• pp.357-385
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• 2014

Recently several authors have extended the Gamma function, Beta function, the hypergeometric function, and the confluent hypergeometric function by using their integral representations and provided many interesting properties of their extended functions. Here we aim at giving further extensions of the abovementioned extended functions and investigating various formulas for the further extended functions in a systematic manner. Moreover, our extension of the Beta function is shown to be applied to Statistics and also our extensions find some connections with other special functions and polynomials such as Laguerre polynomials, Macdonald and Whittaker functions.

• 한국공작기계학회논문집
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• 제10권1호
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• pp.101-111
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• 2001

Recursive formulas have been effective in solving the equations of motion for large scale constratined mechanical sys-tems. However, derivation of the formulas has been limited to individual terms in the equations of motion, such as veloci-ty, acceleration. and generalized forces. The recursive formulas are generalized in this paper. The velocity transformation method is employed to transform the equations of motion from Cartesian to the joint spaces. Computational structure of the equations of motion in the joint space is carefully examined to classify all necessary computational operations into sev-eral categories. The generalized recursive formula for each category is then developed and applied whenever such a cate-gory of computation is encountered. Since the velocity transformation method yields the equations of motion in a compact form and computational efficiency is achieved by generalized recursive formulas, the proposed method is not only easy to implement but is also efficient. A library of generalized recursive formulas is developed to implement a dynamic analysis algorithm using backward difference.