• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권1호
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• pp.42-46
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• 2003

Arresters are deteriorated by overvoltages or impulse currents, and the resistive leakage current of arresters increases as the deterioration of the arrester progresses, showing an increase in the 3$^{rd}$ harmonic component of the leakage current. In this reason, arrester diagnostic techniques based on the 3$^{rd}$ harmonic leakage current as a reference parameter of deterioration are widely used. The technique, however, includes an error due to the harmonics of power system voltage. Therefore, the influence of the harmonics on arrester diagnostics should be considered. In this paper, we designed a PSpice ZnO arrester model to simulate the influence of the voltage harmonics described above. A pure sinusoidal voltage and its the 3r harmonic voltage were applied to the model, and the leakage current components were analyzed. From the simulation results, it is confirmed that the peak value of resistive leakage current depends not only on the phase of the 3$^{rd}$ harmonic voltage but also on the magnitude of it. Consequently, the errors caused 1)y the harmonic voltage could be minimized by correcting the magnitude of leakage current upon analyzing the harmonics.cs.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마
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• pp.5-12
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• 2000

본 연구에서, Daubechies'Mother Wavelet를 이용한 이산 웨이블렛 변환(Discrete Wavelet Transform)에 기초한 새롭고 효과적인 특정추출방법을 제안하였다. 특정추출을 이용하여 응용방향을 설명하고 또는 통계적 파라메터의 평가를 행하였다. 본 연구에서는 다음과 같은 몇 가지 사실을 알 수 있었다. 1. 시스템에서 발생된 (인가전압이 0[V]) 노이즈라 볼 수 가있는 렌덤노이즈(Random Noise)를 디지털필터인 FIR(Finite Impulse Response)필터를 통하여 상당한 노이즈를 억제할 수가 있었다. 2. 이산 웨이블렛 변환 시 레벨 1~4까지 변환한 결과 최적의 변환상태 Level-3을 기준으로 하였다. 3. 특정추출 파라메터는 음향방출신호의 최대값, 평균값, 분산, 왜도, 첨쇄도를 특정추출파라메터로 이용하였다. 4. 특정추출 결과를 이용하여 전체 열화시간 중 대표적 음향방출신호 중 초기열화신호, 중기열화신호, 말기열화신호를 얻을 수 있었다. 이런 특정추출을 통하여 변압기열화상태를 진단할 수 있는 가능성을 확인 할 수가 있었다.

• Nuclear Engineering and Technology
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• 제34권4호
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• pp.344-357
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• 2002

The present paper reports spontaneous steam explosions observed in fuel coolant interaction experiments using prototypic reactor materials. Pure ZrO$_2$ and a mixture of UO$_2$ and ZrO$_2$ are used. A high temperature molten material in the form of a jet is poured into a subcooled water pool located in a pressure vessel. An induction skull melting technique is used for the melting of the reactor material. In both tests using pure ZrO$_2$ and a mixture of UO$_2$ and ZrO$_2$, either a quenching or a spontaneous steam explosion was observed. The morphology of debris and pressure profile clearly indicate the differences between the qunching cases and explosion cases. The dynamic pressure. dynamic impulse, water temperature, melt temperature, and static pressure Inside the containment chamber were measured . As the spontaneous steam explosion for the reactor material is firstly observed in the present experiments, the results of present experiments could be a siginificant step forward the understanding the explosion of the reactor material.

• 유통과학연구
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• 제20권11호
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• pp.1-9
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• 2022

Purpose: This study determines the effect of spending distribution, namely experiential, impulsive, self-expressive, prosocial, and conspicuous spending, on the financial well-being of young working women in Malaysia. Research design, data and methodology: This study employed a quantitative and deductive approach. A sample of 400 young working women was selected using a systematic sampling technique. Data were collected using a self-administered questionnaire and analysed using Structural Equation Modelling (CB-SEM). Results: The findings revealed prosocial and impulsive spending as the significant spending distribution to affect financial well-being. The effect of prosocial spending is positive on financial well-being, while the effect of impulsive spending is a negative predictor of financial well-being. All other spending distribution - experiential, self-expressive, and conspicuous spending - do not have a significant effect on financial well-being. Conclusion: To achieve financial well-being, young working women need to distribute the spending budget for the happiness of others and reduce impulse buying. The findings provide useful insights on the significant role of spending distribution in influencing, how to fuel young working women to develop good spending habits that consequently improve their financial well-being, for themselves and Malaysian economics, as well as the plausible solution to overcome financial problems and high indebtedness.

• Smart Structures and Systems
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• 제30권4호
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• pp.397-410
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• 2022

It is essential to monitor the working conditions of bolt-connected joints, which are widely used in various kinds of steel structures. The looseness of bolts may directly affect the stability and safety of the entire structure. In this study, a guided wave-based method for bolt looseness detection and localization is presented for a joint structure with multiple bolts. SH waves generated and received by a small number (two pairs) of magnetostrictive transducers were used. The bolt looseness index was proposed based on the changes in the reconstructed responses excited by the time reversal signals of the measured unit impulse responses. The damage locations and local damage severities were estimated using the damage indices from several wave propagation paths. The back propagation neural network (BPNN) technique was employed to identify the local damages. Numerical and experimental studies were conducted on a lap joint with eight bolts. The results show that the total damage severity can be successfully detected under the effect of external force and measurement noise. The local damage severity can be estimated reasonably for the experimental data using the BPNN constructed by the training patterns generated from the finite element simulations.

• 한국정보통신학회논문지
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• 제18권5호
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• pp.1061-1066
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• 2014

천해에서 음파 전달은 매우 복잡하며, sparse한 전달 특성을 갖는다. 이러한 환경에서 수중음향통신 시스템의 성능을 향상시키기 위하여 채널을 추정하기 위한 여러 방법들이 연구되었다. 본 논문에서는 기존의 sparse-aware LMS(Least Mean Square) 알고리즘들보다 빠른 수렴속도를 갖는 LMS 기반 채널 추정 알고리즘을 제안하였다. 제안한 방법은 $L_p$-norm LMS 알고리즘과 soft decision 과정을 결합한 것이다. 모의실험은 실제 해상 실험을 통하여 얻은 수중 음속 데이터를 바탕으로 수행되었다. 그 결과 제안한 방법이 기존의 방법들보다 빠른 수렴속도와 향상된 성능을 보이는 것을 확인하였다.

• Asian Pacific Journal of Cancer Prevention
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• 제16권16호
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• pp.7291-7294
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• 2015

Purpsoe: To investigate the diagnostic value of quantitative analysis of a tissue diffusion and virtual touch tissue imaging quantification (VTIQ) technique with acoustic radiation force impulse (ARFI) elastography for assessing enlarged cervical lymph nodes. Materials and Methods: Fifty-six enlarged cervical lymph nodes confirmed by pathologic diagnoses were covered in the study. According to the results of pathologic diagnosis, patients were classified into benign and malignant groups. All the patients were examined by both conventional ultrasonography and elastography. AREA% and shear wave velocity (SWV) in ROI of different groups were calculated and compared using ROC curves. Cut-off points of AREA% and SWV were determined with receiver operating characteristic curves. Results: Final histopathological results revealed 21 cases of benign and 35 cases of malignant lymph nodes. The mean values of AREA% and SWV in benign and malignant groups were $45.0{\pm}17.9%$ and $2.32{\pm}0.57m/s$, and $61.3{\pm}21.29%$ and $4.36{\pm}1.25$)m/s, respectively. For the parameters of elastography, "AREA%" and SWV demonstrated significant differences between groups (p=0.002). AREA% was positively correlated with SWV with a correlation coefficient of 0.809 (P<0.001). Conclusions: Stiffness of different lymph node diseases in patients may differ. Elastography can evaluate changes sensitively and provide valuable information to doctors. The study proved that the VTIQ elastography technique can play an important role in differential diagnosis of lymph nodes.

• Journal of Electrical Engineering and Technology
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• 제11권2호
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• pp.529-536
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• 2016

In this paper we proposed an unsupervised algorithm to estimate the reverberation time (RT) directly from the reverberant speech signal. For estimation process we use maximum likelihood estimation (MLE) which is a very well-known and state of the art method for estimation in the field of signal processing. All existing RT estimation methods are based on the decay rate distribution. The decay rate can be obtained either from the energy envelop decay curve analysis of noise source when it is switch off or from decay curve of impulse response of an enclosure. The analysis of a pre-existing method of reverberation time estimation is the foundation of the proposed method. In one of the state of the art method, the reverberation decay is modeled as a Laplacian distribution. In this paper, the proposed method models the reverberation decay as a Gamma distribution along with the unification of an effective technique for spotting free decay in reverberant speech. Maximum likelihood estimation technique is then used to estimate the RT from the free decays. The method was motivated by our observation that the RT of a reverberant signal when falls in specific range, then the decay rate of the signal follows Gamma distribution. Experiments are carried out on different reverberant speech signal to measure the accuracy of the suggested method. The experimental results reveal that the proposed method performs better and the accuracy is high in comparison to the state of the art method.

• 한국산학기술학회논문지
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• 제19권7호
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• pp.24-35
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• 2018

무선통신 환경에서 채널상태의 변화에 대응하기 위하여 여러 개의 전송속도 중에서 적합한 하나의 전송속도를 선택하는 링크 적응기법이 사용될 수 있다. 블록부호화방식에서는 채널 상태에 적응하기 위하여 블록의 구조를 결정짓는 프레임 시간과 블록 길이 등을 변화시킬 수 있다. 프레임 타임과 블록 길이의 변화에 따라 프레임 간의 간섭의 크기가 변화하여 시스템의 성능에 영향을 준다. 프레임 시간이 크면 프레임간 간섭이 줄어 비트오율은 감소하나, 비트에 대한 전송시간이 증가하여 전송속도는 감소하게 된다. 따라서, 프레임 시간과 블록 길이는 중요한 설계 요소이다. 본 논문에서는 IEEE 802.15a에서 제안하는 채널모델에 대하여 프레임 시간의 변화에 따른 블록부호의 부호화 이득을 바탕으로 적절한 프레임 시간을 결정하는 방안을 제시한다. 또한 프레임 시간과 블록 길이의 변화가 시스템의 성능에 끼치는 영향을 분석하여 링크 적응 기법에 적용한다. 모의실험을 통하여 CM1~CM4 모델에 대하여 프레임 시간 14~50 nsec 구간에서 변화간격 2~5 nsec를 사용하여 링크 적응을 수행할 수 있다.

• 한국전자파학회지:전자파기술
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• 제10권3호
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• pp.2-17
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• 1999

본 논문에서는 software radio 시스템의 핵심 부 분의 하나인 digital channelizer라고 불리우는 일종 의 programmable downconverter(PDC)를 간단하게 구현하는 방법을 제안한다. 제안하는 방법은 cas-caded integrator-comb(CIC) 여파기에 기초한 POC 를 효과적으로 설계하기 위해 새로운 보간된 2차 다항식 (Interpolated Second Order Polynomial. ISO OP)을 사용하는 것에 근간을 두고 있다. 이러한 ISOP는 매우 간단하면서도 미미하게 aliasing reR jection이 떨어지는 대신 통과대역 dr$\infty$p을 효과적 으로 감소시킨다는 장점을 가지고 있다. 뿐만 아니라 보통 CIC 여파기 다음에 위치 하는 halfband 여 파기를 효과적으로 간단히 만들 수 있도록 하여준 다 본 논문에서는 이러한 ISOP의 장점들을 이용 하여 ISOP여파기 이외에 기존의 halfband 여파기 를 대체할 수 있는 간단한 변형된 halfband 여파기(modified halfband filter. MHBF) 를 제 안한다. 결 국 PDC를 위해 제 안된 decimation 여 파기 는 CIC 여파기, ISOP, MHBF, 프로그램 가능한 FIR (prog grammable FIR. PFIR) 여파기들의 직렬 연결 구 조가 된다. 또한 본 논문에서는 이러한 직렬 연결 된 여러 가지 여파기들을 통시에 최적화하는 기법 을 제안한다. 설계 예제활 통하여 실제로 기존 방 법들보다 본 논문에서 제안하는 방법이 효과적임 을 보인다.