• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제3권2호
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• pp.1-4
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• 1999

The Helmholtz equation is very important in physics and engineering. However, solution of the Helmholtz equation is in general known as a very difficult phenomenon. For if the ${\omega}$ is negative, the FDM discretized linear system becomes indefinite, whose solution by iterative method requires a very clever preconditioner. In this paper we assume that ${\omega}$ is nonnegative, and determine the optimal ${\rho}$ parameter for the three dimensional ADI iteration for the Helmholtz equation. The ADI(Alternating Direction Implicit) method is also getting new attentions due to the fact that it is very suitable to the vector/parallel computers, for example, as a preconditioner to the Krylov subspace methods. However, classical ADI was developed for two dimensions, and for three dimensions it is known that its convergence behaviour is quite different from that in two dimensions. So far, in three dimensions the so-called Douglas-Rachford form of ADI was developed. It is known to converge for a relatively wide range of ${\rho}$ values but its convergence is very slow. In this paper we determine the necessary conditions of the ${\rho}$ parameter for the convergence and optimal ${\rho}$ for the three dimensional ADI iteration of the Peaceman-Rachford form for the real Helmholtz equation with nonnegative ${\omega}$. Also, we conducted some experiments which is in close agreement with our theory. This straightforward extension of Peaceman-rachford ADI into three dimensions will be useful as an iterative solver itself or as a preconditioner to the the Krylov subspace methods, such as CG(Conjugate Gradient) method or GMRES(m).

• 한국항행학회논문지
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• 제20권4호
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• pp.361-366
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• 2016

본 논문은 S-파라미터를 어드미턴스 파라미터로 변환하는 것을 바탕으로 비대칭 분배되면서 동시에 임의의 임피던스로 변환시킬 수 있는 임피던스 변환기를 나타내었다. 회로 해석 방법을 우수/ 기수 모드 방법과 비교하면 본 논문의 파라미터 변환을 통한 방법은 위상 지연 정보와 임의의 포트 임피던스 값을 포함시키고 그리고 비대칭 구조등을 해석하는데 간단함을 알 수 있다. 이 설계 방법의 타당성을 확인하기 위해서 중심주파수 1 GHz에서 3:1의 비대칭 분배비율을 갖고 있고 $50{\Omega}$을 $12.5{\Omega}$ 비율로 변환되는 임피던스 변환기를 설계하였다. 임피던스 변환기를 구현하는 방법은 유도된 수식으로부터 계산된 작은 임피던스 선로를 병렬 오픈스터브가 연결된 전송선로를 사용하여 구현하였고, 이것의 실험 결과는 시뮬레이션 결과와 동일하게 나옴을 확인하였다.

• 로봇학회논문지
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• 제4권4호
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• pp.257-264
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• 2009

This paper proposes a novel face detection method that finds tiny faces located at a long range even with low-resolution input images captured by a mobile robot. The proposed approach can locate extremely small-sized face regions of $12{\times}12$ pixels. We solve a tiny face detection problem by organizing a system that consists of multiple detectors including a mean-shift color tracker, short- and long-rage face detectors, and an omega shape detector. The proposed method adopts the long-range face detector that is well trained enough to detect tiny faces at a long range, and limiting its operation to only within a search region that is automatically determined by the mean-shift color tracker and the omega shape detector. By focusing on limiting the face search region as much as possible, the proposed method can accurately detect tiny faces at a long distance even with a low-resolution image, and decrease false positives sharply. According to the experimental results on realistic databases, the performance of the proposed approach is at a sufficiently practical level for various robot applications such as face recognition of non-cooperative users, human-following, and gesture recognition for long-range interaction.

• 한국해양공학회지
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• 제19권6호통권67호
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• pp.58-63
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• 2005

The estimation of springing responses for recent ships is carried out, and application to a ship design is described. To this aim, springing effects on hull girder were re-evaluated, including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder, using the superposition method. The quadratic strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level, and addedasymptotic interpolation along the high frequency range. Several applications were carried out on the following existing ships: The Bishop and Price's container ship, S-175 container ship, large container, VLCC, and ore carrier. One of them is compared with the ship measurement result, while another with that of the model test. The comparison between the analytical solution and the numerical solution for a homogeneous beam-type artificial ship shows good agreement. It is found that Most springing energy comesfrom high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega$$\^{-3}$ instead of $\omega$$\^{-4}$ or $\omega$$\^{-5}$ for the springing calculation.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.173-178
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• 2004

The estimation of springing responses for recent ships are carried out and application to a ship design are described. To this aim, springing effects on hull girder were re-evaluated including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder by the superposition method. The strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level and added asymptotic interpolation along the high frequency range. Several applications to the existing ships were carried out. They are Bishop and Price's container ship, S-175 container ship, large container, VLCC and ore carrier. One of them is compared with ship measurement result while another with that of model test. Comparison between analytical solution and numerical one for homogeneous beam type artificial ship shows good agreement. It is found that most springing energy came from high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega^{-3}\;instead\;of\;\omega^{-4}\;or\;\omega^{-5}$ for springing calculation.

• 대한수학회보
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• 제29권1호
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• pp.31-40
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• 1992

We introduce the generalized Runge-Kutta methods with the exponentially dominant order .omega. in [3], and the convergence theorems of the generalized explicit Euler method are derived in [4]. In this paper we will study the convergence of the generalized implicit Euler method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1842-1846
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• 2008

This work reports development of novel liquid-level sensors based on the $3{\omega}$ method. The sensors determine the liquid level by measuring the thermal response as in the conventional hot-wire technique. However the sensors employ an AC heating method to enhance the sensitivity, noise resistance and time response. Also, the microfabricated thin-film structure of the sensor provides mass-producibility as well as improved sensor performance owing to the increase in the surface-volume ratio of the sensor. Two different types of the sensor are developed: one for point detection of the fluid phase and the other for monitoring continuous variation of liquid level. Notable is that the performance of the sensor is not considerably affected by the liquid flow.

• 센서학회지
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• 제11권6호
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• pp.342-349
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• 2002

본 논문에서는 새로운 방식의 금속 산화물 감지막의 형성 기술에 대해서 제안을 하였다. Sn 증착을 위해 사용된 기판은 Pt 전극을 가진 실리콘 웨이퍼를 이용하였다. 증착 방식은 금속 Sn이 연속적인 막이 아닌 island로만 형성된 상태로 하였다. 제안된 방식의 최적의 Sn 증착 조건을 구하기위해 Pt 전극간의 저항이 $1\;k{\Omega}$, $5\;k{\Omega}$, $10\;k{\Omega}$ 및 $50\;k{\Omega}$이 되도록 Sn을 증착하여 시료를 제작하였다. 또한 일반적인 방식과 새롭게 제안된 방식의 시료를 비교하기 위해서 Sn 막의 두께가 $1,500\;{\AA}$인 시료를 준비하였다. 이것들을 $700^{\circ}C$의 산소분위기에서 3시간 동안 산화를 하여 $SnO_2$를 형성하였다. 산화물 감지막들의 특성 평가를 위해서 SEM, XRD 및 AFM을 이용하였다. 분석을 통하여 $10\;k{\Omega}$의 시료($300\;{\AA}$)가 최적의 감지막 증착 조건임을 알았다. 또한 제조된 감지막을 다양한 농도의 부탄, 프로판 및 일산화탄소에 대해서 동작온도 $250^{\circ}C$, $300^{\circ}C$ 및 $350^{\circ}C$의 경우에 대해서 측정하였다. 그 결과 촉매를 첨가하지 않았음에도 불구하고 모든 가스에 대한 높은 감도 특성을 나타내었다.

• Journal of Animal Science and Technology
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• 제59권8호
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• pp.17.1-17.13
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• 2017

Background: Omega-3 long-chain (${\geq}C_{20}$) polyunsaturated fatty acids (${\omega}3$ LC-PUFA) confer important attributes to health-conscious meat consumers due to the significant role they play in brain development, prevention of coronary heart disease, obesity and hypertension. In this study, the ${\omega}3$ LC-PUFA content of raw and cooked Longissimus thoracis et lumborum (LTL) muscle from genetically divergent Australian prime lambs supplemented with dietary degummed crude canola oil (DCCO) was evaluated. Methods: Samples of LTL muscle were sourced from 24 first cross ewe and wether lambs sired by Dorset, White Suffolk and Merino rams joined to Merino dams that were assigned to supplemental regimes of degummed crude canola oil (DCCO): a control diet at 0 mL/kg DM of DCCO (DCCOC); 25 mL/kg DM of DCCO (DCCOM) and 50 mL/kg DCCO (DCCOH). Lambs were individually housed and offered 1 kg/day/head for 42 days before being slaughtered. Samples for cooked analysis were prepared to a core temperature of $70^{\circ}C$ using conductive dry-heat. Results: Within raw meats: DCCOH supplemented lambs had significantly (P < 0.05) higher concentrations of eicosapentaenoic (EPA, $20:5{\omega}3$) and EPA + docosahexaenoic (DHA, $22:6{\omega}3$) acids than those supplemented with DCCOM or DCCOC; Dorset sired lambs contained significantly (P < 0.05) more EPA and EPA + DHA than other sire breeds; diet and sire breed interactions were significant (P < 0.05) in affecting EPA and EPA + DHA concentrations. In cooked meat, ${\omega}3$ LC-PUFA concentrations in DCCOM (32 mg/100 g), DCCOH (38 mg/100 g), Dorset (36 mg/100 g), White Suffolk (32 mg/100 g), ewes (32 mg/100 g) and wethers (33 mg/100 g), all exceeded the minimum content of 30 mg/100 g of edible cooked portion of EPA + DHA for Australian defined 'source' level ${\omega}3$ LC-PUFA classification. Conclusion: These results present that combinations of dietary degummed crude canola oil, sheep genetics and culinary preparation method can be used as effective management tools to deliver nutritionally improved ${\omega}3$ LC-PUFA lamb to meat consumers.

• 한국전산유체공학회지
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• 제7권4호
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• pp.19-27
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• 2002

An efficient implicit multigrid method is presented for the Navier-Stokes and k-ω turbulence equations. Freezing and limiting strategies are applied to improve the robustness and convergence of the multigrid method. The eddy viscosity and strongly nonlinear production terms of turbulence are frozen in the coarser grids by passing down the values without update of them. The turbulence equations together with the Navier-Stokes equations, however, are consecutively solved on the coarser grids in a loosely coupled fashion. A simple limit for k is also introduced to circumvent slow-down of convergence. Numerical results for the unseparated and separated transonic airfoil flows show that all computations converge well without any robustness problem and the computing time is reduced to a factor of about 3 by the present multigrid method.