• 핵의학기술
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• 제15권1호
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• pp.17-24
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• 2011

현재 핵의학 분야에서는 디지털 컴퓨터의 급속한 발전 및 응용으로 인해 FBP 법의 대용으로 OSEM 알고리즘과 같은 고속 영상 재구성 알고리즘이 널리 이용되고 있다. 그 동안 여러 연구에서 파라미터 변경에 따른 OSEM 재구성 영상 질 변화에 대한 평가가 이루어져 왔으나, 어떠한 파라미터를 적용할 지에 관해서는 명확하게 정해진 것은 없다. 본 연구에서는 3D beam modeling을 적용한 3D OSEM 재구성 법에서 iteration 횟수와 subset 개수 변경에 따른 영상의 질 변화를 팬텀 실험과 환자 데이터을 통해 확인하고자 한다. 환자 데이터는 2010년 8월부터 9월까지 본원 핵의학과에서 Brain SPECT를 시행한 환자 5명을 대상으로 연구 분석하였다. 영상은 물과 $^{99m}Tc$ (500 MBq)을 균등하게 혼합한 Jaszczak 팬텀을 이용하여 Siemens사의 이중 헤드 감마 카메라 Symbia T2에서 획득하였다. 환자 데이터는 영상 재구성 시 환자 데이터와 팬텀 데이터 모두 iteration 횟수는 1, 4, 8, 12, 24, 48회, subset 개수는 2, 4, 8, 16, 32개로 변화를 주며 각각의 영상을 재구성하였다. 재구성된 각각의 영상에서 대조도와 영상의 잡음 정도를 가늠하기 위한 변이계수, FWHM을 산출하여 비교하였다. 팬텀 데이터와 환자 데이터에서 영상의 대조도와 공간해상력은 iteration 횟수와 subset 개수의 증가에 따라 모두 선형적으로 증가하는 경향을 나타냈으나 변이계수는 두 파라미터의 증가에 따라 향상되는 경향을 보이지 않았다. Projection 시간에 따른 비교에서도 Projection 당 10초, 20초, 30초 영상에서 모두 영상 대조도와 FWHM은 iteration 횟수와 subset 개수 증가에 따라 선형적으로 향상되는 결과를 나타냈으나 변이계수는 향상되는 경향을 보이지 않았다. 본 실험을 통해 3D beam modeling을 적용한 3D OSEM 재구성 법 영상에서도 기존의 1D와 2D OSEM 재구성 법과 같이 iteration 횟수와 부분집합 개수 증가에 따라 향상하는 영상 대조도의 선형적 관계를 확인할 수 있었다. 하지만 이는 단순한 팬텀 실험과 일부 환자 데이터 만으로 얻은 결과이고, 실제 임상에서는 보다 구조적으로 복잡한 대상과 다양한 변수들이 존재 가능하기 때문에 본 실험의 데이터만을 바탕으로 이를 일반화하기에는 무리가 있으며 차후 실험들을 통해 3D OSEM 재구성 법에 대한 평가가 추가로 이루어져야 할 것이다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.301-305
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• 1996

$\mu$ theory can handle the parametric uncertainty and produces more non-conservative controller than H$_{\infty}$ control theory. However an existing solution of the theory, D-K iteration, creates a controller of huge order and cannot handle the real or mixed real-complex perturbation sets. In this paper, we use genetic algorithms to solve these problems of the D-K iteration method. The Youla parameterization is used to obtain all stabilizing controllers and the genetic algorithms determines the values of the state feedback gain, the observer gain, and Q parameter to minimize $\mu$, the structured singular value, of given system. From an example, we show that this method produces lower order controller which controls a real parameter-perturbed plant than D-K iteration method.

• 전자공학회논문지S
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• 제34S권1호
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• pp.65-71
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• 1997

In this paper, we propose a new .mu.-controller design method using an equivalent weighting function $W_{\mu}$(s). The proposed mehtod is not guaranteed to converge to the minimum as D-K and .mu.-K iteration method. However, the robust performance problem can be converted into an equivalent $H^{\infty}$ optimization problem of unstructured uncertainty by using an equivalent weightng function $W_{\mu}$(s). Also we can find a .mu.-optimal controller iteratively using an error index $d_{\epsilon}$ of differnce between maximum singular value and .mu.-norm. And under the condition of the same order of scaling functions, the proposed method provides the .mu.-optimal controller with the degree less than that obtained by D-K iteration..

• 대한수학회보
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• 제39권3호
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• pp.389-399
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• 2002

We prove that the results of Chang, Park and Cho in ［1］ concerning the iterative approximation of asymptotically pseudocontractive maps with bounded ranges can be extended to a certain class of asymptotically pseudocontractive maps whose ranges need not be bounded.

• 대한수학회지
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• 제36권6호
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• pp.1061-1073
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• 1999

Let X be a real normed linear space. Let T : D(T) ⊂ X \longrightarrow X be a uniformly continuous and ∮-strongly quasi-accretive mapping. Let {${\alpha}$n}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} , {${\beta}$n}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} be two real sequences in [0, 1] satisfying the following conditions: (ⅰ) ${\alpha}$n \longrightarrow0, ${\beta}$n \longrightarrow0, as n \longrightarrow$\infty$ (ⅱ) {{{{ SUM from { { n}=0} to inf }}}} ${\alpha}$=$\infty$. Set Sx=x-Tx for all x $\in$D(T). Assume that {u}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} and {v}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} are two sequences in D(T) satisfying {{{{ SUM from { { n}=0} to inf }}}}∥un∥<$\infty$ and vn\longrightarrow0 as n\longrightarrow$\infty$. Suppose that, for any given x0$\in$X, the Ishikawa type iteration sequence {xn}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} with errors defined by (IS)1 xn+1=(1-${\alpha}$n)xn+${\alpha}$nSyn+un, yn=(1-${\beta}$n)x+${\beta}$nSxn+vn for all n=0, 1, 2 … is well-defined. we prove that {xn}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} converges strongly to the unique zero of T if and only if {Syn}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} is bounded. Several related results deal with iterative approximations of fixed points of ∮-hemicontractions by the ishikawa iteration with errors in a normed linear space. Certain conditions on the iterative parameters {${\alpha}$n}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} , {${\beta}$n}{{{{ { }`_{n=0 } ^{$\infty$ } }}}} and t are also given which guarantee the strong convergence of the iteration processes.

• 한국통신학회논문지
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• 제28권3A호
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• pp.166-170
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• 2003

In this paper, the characteristics of Koch island microstrip patch antenna are investigated by numerical and experimental methods. The Koch patch is fractal shaped antenna which can be characterized by two properties such as space-filling and self-similarity. Due to its space-filling property of fractal structure, the proposed Koch fractal patch antennas are smaller in size than that of conventional square patch antenna. From numerical and experimental results, it is found that as the iteration number and iteration factor of Koch patch increase, its resonance frequency becomes lower than that of conventional patch, thus contributes to antenna size reduction. In particular, when the fractal iteration factor is 1/4, the fractal antenna is 45% smaller in size than that of conventional patch, while maintaining radiation patterns comparable to those of rectangular antenna and cross polarization level is about -20~-14 dB.

• 대한수학회논문집
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• 제25권4호
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• pp.655-669
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• 2010

In this paper we propose new primal-dual interior point methods (IPMs) for $P_*(\kappa)$ linear complementarity problems (LCPs) and analyze the iteration complexity of the algorithm. New search directions and proximity measures are defined based on a class of kernel functions, $\psi(t)=\frac{t^2-1}{2}-{\int}^t_1e{^{q(\frac{1}{\xi}-1)}d{\xi}$, $q\;{\geq}\;1$. If a strictly feasible starting point is available and the parameter $q\;=\;\log\;\(1+a{\sqrt{\frac{2{\tau}+2{\sqrt{2n{\tau}}+{\theta}n}}{1-{\theta}}\)$, where $a\;=\;1\;+\;\frac{1}{\sqrt{1+2{\kappa}}}$, then new large-update primal-dual interior point algorithms have $O((1\;+\;2{\kappa})\sqrt{n}log\;n\;log\;{\frac{n}{\varepsilon}})$ iteration complexity which is the best known result for this method. For small-update methods, we have $O((1\;+\;2{\kappa})q{\sqrt{qn}}log\;{\frac{n}{\varepsilon}})$ iteration complexity.

• International Journal of Precision Engineering and Manufacturing
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• 제1권2호
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• pp.76-83
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• 2000

A study on the robust control of a composite beam with a distributed PVDF sensor and piezo-ceramic actuator is presented in this paper. $1^{st}$ and $2^{nd}$ natural frequencies are considered in the modeling, because robust control theory which has robustness to structured uncertainty is adopted to suppress the vibration. If the controllers designed by $H_{\infty}$ theory do not satisfy control performance, it is improved by $\mu$-synthesis method with D-K iteration so that the $\mu$-controller based on the structured singular value satisfies the nominal performance and robust performance. Simulation and experiment were carried out with the designed controller and the verification of the robust control properties was presented by results.

• Journal of Electrical Engineering and Technology
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• 제9권1호
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• pp.178-183
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• 2014

This paper presents a motor characteristics analysis method using an equivalent circuit. Motor characteristics analysis via equivalent circuit is very important for designing a high efficiency single phase induction motor. The accuracy of the motor characteristics depends on the accuracy of the parameters, especially saturation factor, which determines the cyclical relationship in the analysis process. Therefore, using the proposed method, the saturation factor was calculated using the iteration routine and numerical technique. The proposed method was verified by comparing the finite element method results and the dynamo test results of manufactured prototype model.

• 대한수학회보
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• 제49권4호
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• pp.799-813
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• 2012

In this paper, we first show that the iteration {$x_n$} defined by $x_{n+1}=P((1-{\alpha}_n)x_n +{\alpha}_nTP[{\beta}_nTx_n+(1-{\beta}_n)x_n])$ converges strongly to some fixed point of T when E is a real uniformly convex Banach space and T is a quasi-nonexpansive non-self mapping satisfying Condition A, which generalizes the result due to Shahzad [11]. Next, we show the strong convergence of the Mann iteration process with errors when E is a real uniformly convex Banach space and T is a quasi-nonexpansive self-mapping satisfying Condition A, which generalizes the result due to Senter-Dotson [10]. Finally, we show that the iteration {$x_n$} defined by $x_{n+1}={\alpha}_nSx_n+{\beta}_nT[{\alpha}^{\prime}_nSx_n+{\beta}^{\prime}_nTx_n+{\gamma}^{\prime}_n{\upsilon}_n]+{\gamma}_nu_n$ converges strongly to a common fixed point of T and S when E is a real uniformly convex Banach space and T, S are two quasi-nonexpansive self-mappings satisfying Condition D, which generalizes the result due to Ghosh-Debnath [3].