• 조명전기설비학회논문지
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• 제28권10호
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• pp.56-62
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• 2014

When fault currents contain decaying DC offset, the peak value of the fault current in the first cycle of the fault period is higher than the fault current during the steady-state period. To reduce the asymmetric fault current, this paper proposes an operation scheme using the series connection of two hybrid type Superconducting Fault Current Limiters (SFCLs) : an auxiliary SFCL and a main SFCL. The proposed method calculates the fault angle by comparing the zero-crossing time with fault detection time. According to the fault angle calculated, an auxiliary SFCL operates to reduce an asymmetric fault current during half a cycle after fault occurrence. After this process, the fault current is limited by a main SFCL. To confirm the usefulness of the proposed method, case studies using Electro-Magnetic Transients Program (EMTP)/Alternative Transient Program (ATP) Draw are perfomed.

• 대한전기학회논문지:시스템및제어부문D
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• 제54권5호
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• pp.338-347
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• 2005

A computer-based low back muscle evaluation system was designed to simultaneously acquire, process, display, quantify, and correlate electromyographic(EMG) activity with muscle force, and range of motion(ROM) in the lumbar muscle of human. This integrated multi-channel system was designed around notebook PC. Each channel consisted of a time and frequency domain block, and T-F(time-frequency) domain block. The captured data in each channel was used to display and Quantify : raw EMG, histogram, zero crossing, turn, RMS(root mean square), variance, mean, power spectrum, median frequency, mean frequency, wavelet transform, Wigner-Ville distribution, Choi-Williams distribution, and Cohen-Posch distribution. To evaluate the performance of the designed system, the static and dynamic contraction experiments from lumbar(waist) level of human were done. The experiment performed in five subjects, and various parameters were tested and compared. This system could equally well be modified to allow acquisition, processing, and analysis of EMG signals in other studies and applications.

• 대한의용생체공학회:의공학회지
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• 제18권4호
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• pp.413-420
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• 1997

In this paper, we analyzed the contraction patterns of active elbow muscles during isometric, concentric and eccentric contraction. The analysis parameters consist of frequency domain parameters (mean frequency, median frequency, peak frequency, peak power, skewness, kurtosis) and time domain paraseters (zero crossing, positive maxima, integrated EMG). The results of this study were as follows; The BR/BB of isometric contraction appeared to be Venter as the elbow joint was more extended. The BR /BB during concentric and eccentric contraction tended to increase with more extension of the elbow joint angle, but there was no significant difference between concentric and eccentric contraction. Further, the EMG power spectrum due to the type of contraction were different betwen eccentric and concentric contraction. According to the results, it was found that the activation pattern in elbow flexor muscles was different during three different muscle contraction pattern. Therefore, elbow flexor muscles should not be considered a single functioning unit. Especially, at the time domain analysis, IEMG is a dominant parameter for analysis of activation patterns, and the skewness kurtosis can be useful parameters in functional recognition for prosthesis control purpose.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 D
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• pp.3166-3168
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• 2000

This paper proposed variable threshold dual rate ADPCM coding method which is modified from the standard ADPCM of ITU G.726 for speech quality improvement. The speech quality of variable threshold dual rate ADPCM is better than single rate ADPCM at noisy environment without increasing the complexity by using ZCR(Zero Crossing Rate). In this case, ZCR is used to divide input signal samples into two categories(noisy & speech). The samples with higher ZCR is categorized as the noisy region and the samples with lower ZCR is categorized as the speech region. Noisy region uses higher threshold value to be compressed by 16Kbps for reduced bit rates and the speech region uses lower threshold value to be compressed by 40Kbps for improved speech quality. Comparing with the conventional ADPCM, which adapts the fixed coding rate. the proposed variable threshold dual rate ADPCM coding method improves noise character without increasing the bit rate. For real time applications, ZCR calculation was considered as a simple method to obtain the background noise information for preprocess of speech analysis such as FFT and the experiment showed that the simple calculation of ZCR can be used without complexity increase. Dual rate ADPCM can decrease the amount of transferred data efficiently without increasing complexity nor reducing speech quality. Therefore result of this paper can be applied for real-time speech application such as the internet phone or VoIP.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 ICEIC The International Conference on Electronics Informations and Communications
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• pp.237-243
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• 2004

A multichannel smart sound sensor capable to detect and identify sound events in noisy conditions is presented in this paper. Sound information extraction is a complex task and the main difficulty consists is the extraction of high­level information from an one-dimensional signal. The input of smart sound sensor is composed of data collected by 5 microphones and its output data is sent through a network. For a real time working purpose, the sound analysis is divided in three steps: sound event detection for each sound channel, fusion between simultaneously events and sound identification. The event detection module find impulsive signals in the noise and extracts them from the signal flow. Our smart sensor must be capable to identify impulsive signals but also speech presence too, in a noisy environment. The classification module is launched in a parallel task on the channel chosen by data fusion process. It looks to identify the event sound between seven predefined sound classes and uses a Gaussian Mixture Model (GMM) method. Mel Frequency Cepstral Coefficients are used in combination with new ones like zero crossing rate, centroid and roll-off point. This smart sound sensor is a part of a medical telemonitoring project with the aim of detecting serious accidents.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1867-1869
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• 1996

In this paper, in order to obtain the statistic information for parameters of electric and magnetic field waveforms associated with lightning discharges, the electric and magnetic fields produced by lightning discharges in the summer of 1995 were measured by a hemisphere-type electric field sensor and a loop-type magnetic field sensor, which were installed at the campus of Inha University in Inchon. The signals of the electric and magnetic fields were continuously recorded by a transient digitizer having a resolution of 12 bit and a memory capacity of 5000 point. Negative lightning discharges are produced very more than positive lightning discharges in the summer of Korea. The 10 to 90 % rise time of electric and magnetic fields was 2 $2\;{\sim}\;10\;{\mu}s$. And the zero-crossing time of electric field was $15\;{\sim}\;25\;{\mu}s$, whereas that of magnetic field was $20\;{\sim}\;30\;{\mu}s$.

• 대한전자공학회논문지TE
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• 제42권3호
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• pp.39-44
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• 2005

본 논문에서는 견실한 전력선 통신을 위한 5-ary 주파수 편이 키잉 방식을 사용하였다. 5-ary 캐리어중 3 캐리어는 데이터를 송신하기 위해서 사용하는 주파수이며, 115kHz, 120kHz, 125kHz으로, 각각 0.33ms의 송신시간을 할당해 총 영교차점을 기준으로 하여 1ms를 송신을 한다. 수신측에서는 채널 상태를 파악할 수 있는 더미 캐리어를 50kHz, 350kHz를 각각 0.5ms 씩 총 1ms를 추가하였다. 실험 결과 칩 방식과 비교해 볼 때 영 교차점에서의 주파수 천이 키잉 방식이 용량성 부하에 대해 적은 송신 전력으로 더 나은 성능을 가진다.

• 한국통신학회논문지
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• 제26권12A호
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• pp.2000-2011
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• 2001

본 논문에서는 기존 1배속 및 6배속과 같은 저속 DVD 시스템에서 설계되었던 Analog PLL(Phase Locked Loop)을 고배속 동작에 유용하게 디지털화 했으며, 고속인 20배속 DVD 시스템에서의 최적 Digital PLL 모델을 제시하였다. 특히, 고속 DVD 시스템 설계에서 성능 열화의 주요 원인인 bulk delay, 샘플링 클럭 주파수 오타, 비대칭 신호 현상과 같은 채널 영향들을 고려하여 안정적으로 동작할 수 있는 DPLL 설계에 초점을 맞추었다. 우선, DPLL에서는 새로운 타이밍 에러 검출 알고리즘으로 변형된 Early-Late 방법을 제시하였다. 그리고, 비대칭 신호 보정기에는 고속으로 동작하고 안정적으로 보정 역할을 수행하는 영점교차 지점을 이용한 4샘플 신호 보정 알고리즘을 설계하였다. 본 논문에서 제안하는 타이밍 에러 검출기는 기존 방식에 비해 각각, 3dB의 SNR 이득과 지터성능이 4배 향상됨을 볼 수 있었고 또한, 영점교차 지점에서 4샘플 신호를 이용한 보정 알고리즘은 기존 방식에 비해 보상시간의 50% 단축과 2dB의 SNR 이득, 지터 성능의 34% 효율을 볼 수 있었다. 최종적으로 제안된 비대칭 보정기와 DPLL이 통합된 시스템을 BER 성능 평가를 통해서 기존 알고리즘에 비해 제안된 방식이 0.4dB, 2dB 성능 향상을 확인하였다.

• 한국지능시스템학회논문지
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• 제21권4호
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• pp.407-413
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• 2011

본 연구에서는 가정용 전력 모니터링 시스템을 구현하고 실험가구에 적용하여 평가하였으며, 평가과정에서 확보한 기기별 전력 사용 패턴 정보를 이용하여 자동 기기 식별 알고리즘을 개발하였다. 실험가구에 적용해본 결과, 기기별 전력사용 정보와 월별 예상 사용량 정보가 전력 소비 절감에 도움이 된다는 응답을 얻을 수 있었다. 그리고 시스템을 보다 편리하게 사용하기 위해서는 설치의 편의성과 UI를 개선해야한다는 응답을 얻었다. 본 연구에서는 UI 개선을 위하여 일반냉장고, TV, 전기밥솥, 김치냉장고, 세탁기를 자동으로 식별하는 알고리즘을 구현하였다. 자동 장치 식별 알고리즘은 전력 모니터링 과정에서 수집한 전력 소비 패턴을 관찰하여 Zero-Crossing Rate(ZC), Variation of On State(VO), Slope of On State(SO), Duty Cycle(DC) 등 4가지 특징을 규정하여 이용하였으며, 특징을 적용하는 시간 구간은 기기가 동작하는 시간이 25% 이상이 되는 2시간 길이의 구간을 이용하였다. 제안된 알고리즘은 테스트 set에 동일한 기기를 포함하는 경우 82.1%의 성능을 얻을 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제23권2호
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• pp.281-285
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• 2002

The photophysical properties and the singlet oxygen generation efficiencies of meso-tetraphenyl-trithiasapphyrin $(S_3TPS)$ and meso-tetmkis(p-methoxy phenyl)-trithiasapphy rin ((p-MeO)-$S_3TPS$) have been investigated, utilizing steady-state and time-resolved spectroscopic methods to elucidate the possibility of their use as photosensitizers for photodynamic therapy (PDT). The observed photophysical properties were compared with those of other porphyrin-like photosensitizers in geometrical and electronic structural aspects, such as extended ${\pi}$ conjugation, structural distortion, and internal heavy atoms. The steady-state electronic absorption and fluorescence spectra were both red-shifted due to the extended ${\pi}$-conjugation. The fluorescence quantum yields were measured as very small. Even though intersystem crossing rates were expected to increase due to the increment of spin orbital coupling, the triplet quantum yields were measured as less than 0.15. Such characteristics can be ascribed to the more enhanced internal conversion rates compared with the intersystem crossing rates. Furthermore, the triplet state lifetimes were shortened to -1.0 ${\mu}s$ as expected. Therefore, the singlet oxygen quantum yields were estimated to be near zero due to the fast triplet state decay rates and the inefficient energy transfer to the oxygen molecule as well as the low triplet quantum yields. The low efficiencies of energy transfer to the oxygen molecule can be attributed to the lower oxidation potential and/or the energetically low lying triplet state. Such photophysical factors should be carefully evaluated as potential photosensitizers that have extended ${\pi}$-conjugation and heavy core atoms synthesized for red-shifted absorption and high triplet state quantum yields.