• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.16-19
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• 2001

Rapid Prototyping (RP) and Rapid Tooling (RT) were introduced to reduce time-to-market and cost by shortening not only the development phase but also the production phase of the manufacturing process. RP generally builds up a prototype layer by layer, rapidly generating a fully three-dimensional free form shape. RT enables the manufacture of production tools. The integration of RP and RT has the potential for rapid net shaping of thee-dimensional parts, which have geometrical complexity. In this study, net shaping techniques for making three-dimensional parts using RP and RT are described and a sample part are shown. A three-dimensional metal part is manufactured by a new RP process, Variable Lamination Manufacturing by using Expandable Polystyrene Foam (VLM-S), and its application to RT for making a clover punch. In addition, we discussed the technology fusion between metal forming md RP/RT.

• Journal of Power Electronics
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• 제16권3호
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• pp.1176-1189
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• 2016

In this paper, a novel quasi-direct power control (Q-DPC) scheme based on a resonant frequency adaptive proportional-resonant (PR) current controller with a variable frequency resonant phase locked loop (RPLL) is proposed, which can achieve a fast power response with a unity power factor. It can also adapt to variations of the generator frequency in T-type Three-level shaft synchronous generator (SSG) converters. The PR controller under the static α-β frame is designed to track ac signals and to avert the strong cross coupling under the rotating d-q frame. The fundamental frequency can be precisely acquired by a RPLL from the generator terminal voltage which is distorted by harmonics. Thus, the resonant frequency of the PR controller can be confirmed exactly with optimized performance. Based on an instantaneous power balance, the load power feed-forward is added to the power command to improve the anti-disturbance performance of the dc-link. Simulations based on MATLAB/Simulink and experimental results obtained from a 75kW prototype validate the correctness and effectiveness of the proposed control scheme.

• 항공우주기술
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• 제12권1호
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• pp.64-72
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• 2013

본 논문에서는 GPS 수신기의 반송파 추적루프를 3차 PLL로 구성하고 대역폭을 변화시켰을 때 발사체 시나리오를 이용한 시뮬레이션에서 GPS 수신기의 추적 및 항법성능을 분석한다. 시험에 사용된 GPS 수신기는 발사체가 가지는 동특성으로 인해 3차 PLL로 구성된 추적루프의 대역폭에 따라 추적 및 항법성능에 차이가 나타났으며, 특히 대역폭이 좁게 설정된 경우에는 신호추적을 놓쳐 항법 계산을 하지 못하는 경우도 발생하였다.

• The Journal of Korean Physical Therapy
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• 제14권2호
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• pp.74-85
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• 2002

The purpose of this study was to investigate the effect of static balance performance on gait in elderly. Subjects were twenty four members living in Gwangju(12males, 12females), between 65 and 81 years of age. The Force platform was used to measured static balance performance and gait analyzed the 3-D Motion Analysis The results of this study were as follow ; 1. The postural sway showed, The mean value of toe-heel was $1.41\pm0.51cm$ and left-right was $063\pm0.20cm$. In gait analysis, the mean value of each variable were swing phase $40.5\pm9.65\%$, stance phase $59.5\pm9.65\%$, stride length 0.79m, cadence $0.83\pm0.44step/sec$, velocity $0.57\pm0.32m/sec$, Knee up $34.7\pm31.0^{\circ}$, Knee down $-53.6\pm40.14^{\circ}$. Ankle up $12.14\pm13.94^{\circ}$, Ankle down $-16.8\pm25.0^{\circ}$ showed. 2. The correlation matrix between L-R sway and Toe-heel sway and gait variables was not showed. 3. In multiple regression test, there were no related variable.

• Nuclear Engineering and Technology
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• 제39권4호
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• pp.313-326
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• 2007

In this paper, an algorithm to reconstruct two orthogonal images into a three-dimensional image is developed in order to measure the bubble size and volume in a two-phase boiling flow. The central-active contour model originally proposed by P. $Szczypi\'{n}ski$ and P. Strumillo is modified to reduce the dependence on the initial reference point and to increase the contour stability. The modified model is then applied to the algorithm to extract the object boundary. This improved central contour model could be applied to obscure objects using a variable threshold value. The extracted boundaries from each image are merged into a three-dimensional image through the developed algorithm. It is shown that the object reconstructed using the developed algorithm is very similar or identical to the real object. Various values such as volume and surface area are calculated for the reconstructed images and the developed algorithm is qualitatively verified using real images from rubber clay experiments and quantitatively verified by simulation using imaginary images. Finally, the developed algorithm is applied to measure the size and volume of vapor bubbles condensing in a subcooled boiling flow.

• 천문학회보
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• 제46권2호
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• pp.49.2-49.2
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• 2021

We present the results of long-term simultaneous monitoring observations (~ 12 years) of H²O (22 GHz) maser and several vibrationally excited lines of SiO J = 1-0, 2-1, 3-2 masers (43, 86, 129 GHz) carried out with the 21-m antennas of the Korean VLBI Network (KVN) toward a sample of three AGB stars (RT Vir, RR Aql, IRC-10151) that are believed to be semiregular variable star, Mira variable star, and OH/IR star, respectively, according to a sequential evolutionary phase of AGB star. A total 10 transitions were observed, of which we detected H²O, SiO 𝝊 = 1 and 2, J = 1-0, SiO 𝝊 = 1, J = 2-1 and J = 3-2 maser lines in all three target objects, depending on the observational epochs. In this study, we scrutinize the evolutionary traits of each target object based on the maser line profiles, flux/velocity variations, and phase lags with the optical light curves. The IRAS two color diagram and the infrared spectral energy distributions (SEDs) in the wavelength range from 1.2 to 240 ㎛ of three observed sources were also analyzed.

• 아태비즈니스연구
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• 제14권3호
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• pp.221-240
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• 2023

Purpose - This paper investigates how business cycle impacts on corporate credit spreads since global financial crisis. Furthermore, it tests how the impact changes by the phase of the cycle. Design/methodology/approach - This study collected dataset from Barclays Global Aggregate Bond Index through the Bloomberg. It conducted multi-regression analysis by projecting business cycle using Hodrick-Prescott filtering and various cyclical variables, while ran dynamic analysis of 5-variable Vector Error Correction Model to confirm the robustness of the test. Findings - First, it proves to be statistically significant that corporate credit spreads have moved countercyclicaly since the crisis. Second, It indicates that the corporate credit spread's countercyclicality to the macroeconomic changes works symmetrically by the phase of the cycle. Third, the VECM supports that business cycle's impact on the spreads maintains more sustainably than other explanatory variable does in the model. Research implications or Originality - It becomes more appealing to accurately measure the real economic impact on corporate credit spreads as the interaction between credit and business cycle deepens. The economic impact on the spreads works symmetrically by boom and bust, which implies that the market stress could impact as another negative driver during the bust. Finally, the business cycle's sustainable impact on the spreads supports the fact that the economic recovery is the key driver for the resilience of credit cycle.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 추계학술대회 논문집 학회본부
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• pp.340-343
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• 1990

Recently, Power Electronics system increase makes harmonics and low input power factor problem. In this paper present new analysis method of PWM Boost AC/DC Converter. This PWM AC/DC Converter is capability of unity power factor, control of DC side voltage level, generation, and near sinusoidal current in 3-phase line. The control of this type of converter is widely discussed. And this paper propose new phase convert function and analysis in steady state of system to obtain amplitude and phaser of switching function. This switching function is general solution and it can use in high power approach. And this control method show the clear meaning of control variable. This paper propose new analysis method of Boost AC/DC Converter of steady state and 3-phase 2KW experimental system show its validity.

• 대한전기학회논문지
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• 제33권8호
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• pp.289-298
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• 1984

The single phase induction motor is recently requested to meet a broad speed control and smooth forward and reverse operation due to the multifarious usages. This paper deals with two phase operation of a two winding motor by reference current adaptive inverter which can supply the currents to satisfy the balanced oeration into the main and auxiliary winding through the entire operational region. According to the roposed system, the starting, forward and reverse and variable speed control of a two winding motor eliminated the capacitor from the capacitor-run motor is also possible. The formation and its principle of the reference current adaptive inverter and characteristic analysis of the motor fed by this apparatus are described in this paper. Excellent agreement with the measured results and calculated values by computer simulation is obtained.

• 대한전기학회논문지
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• 제40권1호
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• pp.39-46
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• 1991

In the VSS control, the trajectories with a conventional sliding surface have a reaching phase which is an interval from the initial state to the first touching of the sliding surface. Since the sliding mode control can not be realized in a reaching phase, the trajectories may be sensitive to the disturbances and parameter variations. A simple nonlinear sliding surface is proposed to improve the robustness in a reaching phase. The position control of a PM DC servo motor using a new sliding surface is carried out and is compared to the one using the conventional surface. The sliding mode occurs in entire trajectories with the proposed new sliding surface and the improved robustness is obtained.