• International Journal of Quality Innovation
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• 제4권1호
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• pp.148-159
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• 2003

Variation is the archenemy of quality. To reduce or control the variation in a complex production unit, firstly we need to identify the location of the root cause of the variation. This paper discusses the detection of variability and the techniques used for reduction of variation for a production unit consisting of many processes. In the first part of this paper, the background of variability detection in production systems is introduced which is then followed by a weighted network corresponding to correlation matrix of all processes. Based on the network and clustering criterion of maximum spanning tree, a classification of all processes is derived. Furthermore, the variation of each process in a class is determined by residual analysis. In the last part, the use of methods of robust design for the processes with a larger variability is discussed.

• 한국음향학회지
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• 제31권3호
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• pp.197-204
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• 2012

본 연구에서는 마이크로폰에 입사되는 음성 신호를 거리의 변동에 의해 크기와 주파수 응답특성 변화를 최소화시키는 방법에 대한 연구를 하였다. 우선 마이크로폰과 음성음원 사이의 거리를 변화시키며 거리변화에 따른 응답특성을 측정하였다. 본 연구에 사용된 마이크로폰은 일반적으로 사용되는 마이크로폰 중에 무지향성 마이크로폰과 초단일지향성 마이크로폰, 단일지향성 마이크로폰 등, 3가지 종류의 마이크로폰을 선정하였다. 측정한 이들 마이크의 주파수 응답특성 변화 결과를 기준치와 비교하여 보정치를 구하고 이를 주파수 대역별로 변화된 음성신호를 원음과 근사하게 보상하도록 하였다. 저주파대역은 근접효과에 의한 증폭현상, 그리고 거리에 의한 감쇠효과를 보정하도록 하였다. 중음대역에서는 저음대역보다 거리의 변화에 의한 주파수특성 편차가 비교적 적었지만 음성정보신호에 중요한 영향을 주는 부분이기 때문에 기준신호와 비교하여 복원하도록 하였다. 고주파대역의 음성정보의 변화는 극히 미소하여 고주파대역 조정은 큰 문제가 없이 원음에 가깝게 복원되었다.

• 한국지열·수열에너지학회논문집
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• 제1권2호
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• pp.1-6
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• 2005

Ground water source heat pumps are clean, energy-efficient and environment-friendly systems for cooling and heating. Although the initial cost of ground water source heat pump system is higher than that of air source, it is now widely accepted as an economical system since the installation cost can be returned within a short period of time due to its high efficiency. In a ground water source heat pump system, the variation of the ground water temperature is an important factor that influences the system performance. In this study, variation of the ground water temperature of a single well system is studied experimentally for various operating conditions. When ground water flow exists in the underground, the returned water exchanges heat efficiently with the ground and the temperature of the ground water remains nearly constant. Hence the short circuit problem is minimized. If an active flow of ground water flow exists in the underground, a singe well heat pumps system will be free of short circuit problem and can operate with high performance.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.692-695
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• 1999

A new control scheme is proposed suitable for the three phase PWM converter having abrupt load variation such as a crane. In the converter used in a crane, the peak value of source voltage varies instantaneously due to the abrupt load variations. Such a voltage variation degrades the performance of DC-link control of PWM converter. To overcome this problem, load variations should be detected and compensated properly. We propose a new method for detecting and compensating the load variations without the additional hardware. With the proposed scheme, load variations are detected by estimating the current of DC-link capacitor. The estimated current information is feedbacked to a current controller to improve the performance. Additionally, the variation of source voltage is compensated using feedforward controller. The performance of the proposed scheme has been verified through simulations.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.642-645
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• 2003

We proposed new current source and mirror circuits insensitive to $V_{th}$ variation of poly-Si TFTs. The proposed circuits have been verified by SPICE simulation using poly-Si TFT model. The error currents of the proposed current source and current mirror circuits caused by $V_{th}$ variation reduced less than 6.6% and 4.5% of that of conventional ones, respectively.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2212-2219
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• 2018

This paper describes extended fault location algorithm using estimated remote source impedance. The method uses data only at the local end and the sequence current distribution factors for more accurate estimation. The proposed algorithm can respond to variation of the local and remote source impedance. Therefore, this method is especially useful for transmission lines interconnected to a wind farm that the source impedance varies continuously. The proposed algorithm is very insensitive to the variation in fault distance and fault resistance. The simulation results have shown the accuracy and effectiveness of the proposed algorithm.

• 전기학회논문지
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• 제58권5호
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• pp.885-890
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• 2009

A fault location algorithm using estimated local source impedance after a fault is proposed in this paper. The method uses after fault data only at the local end. It uses the negative sequence current distribution factor for more accurate estimation. The proposed algorithm can keep up with the variation of the local source impedance. Therefore, the proposed algorithm especially is valid for a transmission line interconnected to a wind farm that the equivalent source impedance changes continuously. The performance of the proposed algorithm was verified under various fault conditions using the Simpowersystem of MATLAB Simulink. The proposed algorithm is largely insensitive to the variation in fault distance and fault resistance. The test results show a very high accurate performance.

• 한국전자파학회논문지
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• 제13권9호
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• pp.882-888
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• 2002

본 논문에서는 공정변화와 온도변화에 의한 MMIC의 성능저하를 보상할 수 있는 바이어스 안정화 회로를 제안하였다. 제안된 바이어스 안정화 회로는 기존의 정전류원을 사용하는 바이어스 회로와의 비교를 통하여 그 효과를 검증하였다. 두 구조를 동일한 조건으로 비교하기 위해 하나의 레이아웃에 두 구조를 채택한 증폭기를 동시에 설계 및 제작을 하였다. 공정오차는 세가지 경우 NOM, MIM, MAX로 구분하고 각각에 대해 고주파 특성을 측정하였다. 측정 결과로 정전류원을 가지는 바이어스회로를 채택한 증폭기 의 1.8 GHz에서의 이득변화는 6.4 dB, Ids 변화 7 mA이지만 제안된 바이어스회로를 채택한 증폭기는 이득변화는 2.1 dB, Ids 변화 3 mA로 우수한 특성을 보임을 확인하였다. 따라서, 제안된 바이어스 회로를 적용한 MMIC는 공정상의 변화와 온도 등에 의한 동작점의 변화를 보상하여 고주파특성의 감쇠를 보상할 수 있고 궁극적으로 회로의 수율을 개선할 수 있다. 제작된 회로의 전체크기는 1.2 mm $\times$ 1.4 mm이다.

• 천문학회보
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• 제36권2호
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• pp.60.2-60.2
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• 2011

We introduce the preliminary results of flux monitoring of BL Lac object 0716+714 with the KVN Ulsan 21m radio telescope. This radio source is well known as the intraday variable (IDV) source which is characterized by the rapid flux variation on the time scale of a day or less. In general, the IDV phenomenon is interpreted as the effect of refractive scintillation in the interstellar medium or the evidence of intrinsic flux variation. In previous observations that took a few days, however, it had not been detected the flux variation of short time scale but the monotonic increase and decrease. Therefore, to investigate the longer time scale of 0716+714, we had the flux variation monitoring at 22GHz and 43GHz simultaneously for 9 months from October 2010 to June 2011. We present here the structure functions and the cross correlation functions between different frequencies as well as the light curves.

• Structural Engineering and Mechanics
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• 제73권6호
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• pp.651-666
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• 2020

In this study, the spatial variation mechanisms of large far-field earthquakes at engineering scales are first investigated with data from the 2008 Ms 8.0 Wenchuan earthquake. And a novel 'coherency cut-off frequency' is proposed to distinguish the spatial variations in ground motions in the low-frequency and high-frequency ranges. Then, a practical piecewise coherency model is developed to estimate and characterize the spatial variation in earthquake ground motions, including the effects of source-to-site distances, site conditions and neighboring topography on these variations. Four particular earthquake records from dense seismograph arrays are used to investigate values of the coherency cut-off frequency for different source-to-site distances. On the basis of this analysis, the model is established to simulate the spatial variations, whose parameters are suitable for both near- and far-field earthquake conditions. Simulations are conducted to validate the proposed model and method. The results show that compared to the existing models, the proposed model provides an effective method for simulating the spatial correlations of ground motions at local sites with known source-to-site distances.