• 전자공학회논문지
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• 제52권3호
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• pp.162-170
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• 2015

BPS(bandpass sampling) 기술은 입력 신호보다 낮은 주파수로 표본화하는 것으로서, 표본화 처리만으로 기저 대역 신호를 얻을 수 있다. 이 덕분에 별도의 주파수 하향 변환기를 사용하지 않아도 되어, 수신기 회로 구현이 간소화 된다. 2차 BPS 방식은 표본화 장치를 2개 사용하는 것이며, 표본화로 인하여 aliasing 간섭이 발생하더라도 두 가지 BPS 신호를 결합함으로써 간섭 성분을 제거할 수 있다. 본 논문에서는 여러 개의 간섭이 한꺼번에 신호 성분에 aliasing 되는 경우에 대한 2차 BPS 시스템의 설계 문제를 다루었다. 신호 대 간섭 비를 극대화시키도록 interpolant 필터의 최적 위상값을 구하는 방법을 분석하였고, BPS 입력단의 전력밀도 스펙트럼 자료를 이용하여 준최적 위상값을 구하는 실용적인 공식을 도출하였다. 제안된 시스템에 대하여 컴퓨터 시뮬레이션을 수행하였고, 다중 aliasing을 고려함으로써 신호 대 간섭 비가 증가되는 것을 확인하였다.

• Communications for Statistical Applications and Methods
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• 제26권1호
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• pp.11-25
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• 2019

The present paper utilizes auxiliary information to neutralize the effect of non-response for estimating the population mean. Improved ratio type estimators for population mean have been proposed and their properties are studied. These estimators are suggested for both single phase sampling and two phase sampling in presence of non-response. Empirical studies are conducted to validate the theoretical results and demonstrate the performance of the proposed estimators. The proposed estimators are shown to perform better than those used by Cochran (Sampling Techniques (3rd ed), John Wiley & Sons, 1977), Khare and Srivastava (In Proceedings-National Academy Science, India, Section A, 65, 195-203, 1995), Rao (Randomization Approach in Incomplete Data in Sample Surveys, Academic Press, 1983; Survey Methodology 12, 217-230, 1986), and Singh and Kumar (Australian & New Zealand Journal of Statistics, 50, 395-408, 2008; Statistical Papers, 51, 559-582, 2010) under the derived optimality condition. Suitable recommendations are put forward for survey practitioners.

• 대한의용생체공학회:의공학회지
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• 제10권1호
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• pp.33-42
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• 1989

도플러 효과는 혈관의 혈류속도를 측정하는데 이용된다. 대부분의 도플러 시스템은 측정위치에 대한 정보를 제공하는 펄스 도플러 시스템이다. 본 논문에서는 2차 샘플링 방식과 직렬 신호 처리를 이용한 새로운 2차원 펄스 도플러 시스템을 제안한다. 제안된 시스템은 직각 위상 검파 방식에서 동상과 $90^{\circ}$ 지연된 위상신호의 불평형성을 해결하고, 또한 직렬 신호 처리를 사용하므로서 2차원 도플러 시스템에서의 채널 간의 평형성 문제를 해결했다.

• Journal of Power Electronics
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• 제4권2호
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• pp.102-111
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• 2004

This paper is concerned with a deadbeat current control implementation of shunt-type three-phase active power filter (APF). Although the one-dimensional deadbeat control method can attain time-optimal response of APF compensating current, one sampling period is actually required fur its settling time. This delay is a serious drawback for this control technique. To cancel such a delay and one more delay caused by DSP execution time, the desired APF compensating current has to be predicted two sampling periods ahead. Therefore an adaptive predictor is adopted for the purpose of both predicting the control error of two sampling periods ahead and bringing the robustness to the deadbeat current control system. By adding the adaptive predictor output as an adjustment term to the reference value of half a source voltage period before, settling time is made short in a transient state. On the other hand, in a steady state, THD (total harmonic distortion) of the utility grid side AC source current can be reduced as much as possible, compared to the case that ideal identification of controlled system could be made.

• 대한의용생체공학회:의공학회지
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• 제19권2호
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• pp.143-152
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• 1998

In this paper, we present the performances of a Doppler system using single channel RF(Radio Frequency) sampling. This technique consists of undersampling the ultrasonic blood backscattered RF signal on a single channel. Conventional undersampling method in Doppler imaging system have to use a minimum of two identical parallel demodulation channels to reconstruct the multigate analytic Doppler signal. However, this system suffers from hardware complexity and problem of unbalance(gain and phase) between the channels. In order to reduce these problems, we have realized a multigate pulsed Doppler system using undersampling on a single channel, It requires sampling frequency at $4f_o$(where $f_o$ is the center frequency of the transducer) and 12bits A/D converter. The proposed " single-Channel RF Sampling" method aims to decrease the required sampling frequency proportionally to $4f_o$/(2k+1). To show the influence of the factor k on the measurements, we have compared the velocity profiles obtained in vitro and in vivo for different intersequence delays time (k=0 to 10). We have used a 4MHz center frequency transducer and a Phantom Doppler system with a laminar stationary flow. The axial and volumetric velocity profiles in the vessel have been computed according to factor k and have been compared. The influence of the angle between the ultrasonic beam and the flow axis direction, and the fluid viscosity on the velocity profiles obtained for different values of k factor is presented. For experiment in vivo on the carotid, we have used a data acquisition system with a sampling frequency of 20MHz and a dynamic range of 12bits. We have compared the axial velocity profiles in systole and diastole phase obtained for single channel RF sampling factor.ng factor.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 F
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• pp.1937-1939
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• 1998

This paper presents a simple switching method to generate a PWM pattern mostly relevant to signle-phase three-level PWM rectifier. The adopted PWM switching pattern is performed in a manner similar to the space vector PWM method, which is popularly used in the three-phase rectifier and inverter. A set of possible voltages has been selected so that an equation with a time integral considered within a sampling period should be satisfied every sampling time. The simulation result shows that the proposed control scheme is good in some performance criteria such as unity power factor, low harmonic distortion of input current, dynamic response and voltage balancing of two series-connected DC capacitors.

• 한국전자파학회논문지
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• 제17권12호
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• pp.1249-1258
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• 2006

ISAR 자동 초점(autofocus) 기법이란 움직이는 표적에 대한 2차원 레이더 영상인 ISAR 영상을 얻을 때 표적에 의한 doppler-shift 때문에 발생하는 위상 오차를 예측, 제거하는 기법이다. 이러한 자동 초점 기법이 수행되지 않은 ISAR 영상은 위상 오차(phase ewer)에 의한 왜곡이 포함되기 때문에 초점이 맞지 않는 것처럼 흐린(blurred) 영상이 된다. 이러한 영상은 추후에 구분기(classifier)를 이용하여 표적 구분 시 올바른 구분을 보장할 수 없으므로 반드시 자동 초점 기법이 수행되어야 하며, 본 논문에서는 이를 위해 영상의 엔트로피(entropy)를 최소화시키는 알고리즘을 이용한다. ISAR 자동 초점 기법은 크게 range alignment 과정과 phase adjustment 과정으로 나뉘는데, range alignment 과정에서 샘플링 포인트(sampling point)의 수와 그에 따른 영상 품질과의 관계를 분석하고, phase adjustment 과정 을 수행하기 위한 알고리즘인 SSA(Stage-by-Stage Approaching)의 계산시간 단축을 위한 방법을 분석한다.

• Journal of the Optical Society of Korea
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• 제14권3호
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• pp.240-244
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• 2010

In this work, we used PWM sampling for demodulation of a fiber-optic interferometric current transformer. The interference signal from a fiber-optic CT is sampled with PWM triggers that produce a 90-degree phase difference between two consecutively sampled signals. The current-induced phase is extracted by applying an arctangent demodulation and a phase unwrapping algorithm to the sampled signals. From experiments using the proposed demodulation, we obtained phase measurement accuracy and a linearity error, in AC current measurements, of ~2.35 mrad and 0.18%, respectively. The accuracy of the proposed method was compared with that of a lock-in amplifier demodulation, which showed only 0.36% difference. To compare the birefringence effects of different fiber-optic sensor coils, a flint glass fiber and a standard single-mode fiber were used under the same conditions. The flint glass fiber coil with a Faraday rotator mirror showed the best performance. Because of the simple hardware structure and signal processing, the proposed demodulation would be suitable for low-cost over-current monitoring in high voltage power systems.

• Journal of Power Electronics
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• 제19권5호
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• pp.1162-1170
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• 2019

Finite-control-set model predictive control (FCS-MPC) is a promising control scheme for two-level voltage-source inverters (TL-VSIs). However, two main issues arise in the classical FCS-MPC method: an exponentially-increasing computational time and a low steady-state performance. To solve these two issues, a novel FCS-MPC method has been proposed for n-phase TL-VSIs in this paper. The basic idea of the proposed method is to carry out the FCS-MPC scheme of TL-VSIs for one leg by one leg, like a "pipeline". Based on this idea, the calculations are reduced from exponential time to linear time and its current waveforms are improved by applying more switching states per sampling period. The cases of three-phase and five-phase TL-VSIs were tested to verify the effectiveness of proposed method.

• Nuclear Engineering and Technology
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• 제42권6호
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• pp.690-703
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• 2010

Sampling based uncertainty analysis was carried out to quantify uncertainty in predictions of best estimate code RELAP5/MOD3.2 for a thermal hydraulic test (10% hot leg break LOCA) performed in the Large Scale Test Facility (LSTF) as a part of an IAEA coordinated research project. The nodalisation of the test facility was qualified for both steady state and transient level by systematically applying the procedures led by uncertainty methodology based on accuracy extrapolation (UMAE); uncertainty analysis was carried out using the Latin hypercube sampling (LHS) method to evaluate uncertainty for ten input parameters. Sixteen output parameters were selected for uncertainty evaluation and uncertainty band between $5^{th}$ and $95^{th}$ percentile of the output parameters were evaluated. It was observed that the uncertainty band for the primary pressure during two phase blowdown is larger than that of the remaining period. Similarly, a larger uncertainty band is observed relating to accumulator injection flow during reflood phase. Importance analysis was also carried out and standard rank regression coefficients were computed to quantify the effect of each individual input parameter on output parameters. It was observed that the break discharge coefficient is the most important uncertain parameter relating to the prediction of all the primary side parameters and that the steam generator (SG) relief pressure setting is the most important parameter in predicting the SG secondary pressure.