• Proceedings of the KSEEG Conference
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• 2001.04a
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• pp.351-353
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• 2001

• Proceedings of the KSEEG Conference
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• 2001.04a
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• pp.115-118
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• 2001

Suppressed Wave equation Estimation of Traveltime (SWEET, Shin et, al., 2000) 알고리즘을 이용하여 등방성 및 이방성 탄성 매질에 대한 ched 주시와 진폭을 계산하는 방법을 개발하였다. SWEET 알고리즘을 2차원 등방성 및 이방성 탄성 매질의 속도 구조에 적용하여 P파의 초동 주시와 진폭을 계산 할 수 있었다. 본 논문에서는 간단한 등방성 균질 탄성 모형, 복잡한 등방성 탄성 모형 및 간단한 이방성 균질 모형에 대한 수치 계산 결과를 보여 줄 것이다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.2
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• pp.437-444
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• 2016

Most methods for detecting arrhythmia require pp interval, diversity of P wave morphology, but it is difficult to detect the p wave signal because of various noise types. Therefore it is necessary to use noise-free R wave. In this paper, we propose algorithm for premature contraction arrhythmia classification through ECG pattern analysis and template threshold. For this purpose, we detected R wave through the preprocessing method using morphological filter, subtractive operation method. Also, we developed algorithm to classify premature contraction wave pattern using weighted average, premature ventricular contraction(PVC) and atrial premature contraction(APC) through template threshold for R wave amplitude. The performance of R wave detection, PVC classification is evaluated by using 6 record of MIT-BIH arrhythmia database that included over 30 PVC and APC. The achieved scores indicate the average of 99.77% in R wave detection and the rate of 94.91%, 95.76% in PVC and APC classification.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.4
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• pp.825-832
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• 2014

Previous works for detecting arrhythmia have mostly used nonlinear method such as artificial neural network, fuzzy theory, support vector machine to increase classification accuracy. Most methods require accurate detection of P-QRS-T point, higher computational cost and larger processing time. Even if some methods have the advantage in low complexity, but they generally suffer form low sensitivity. Also, it is difficult to detect PVC accurately because of the various QRS pattern by person's individual difference. Therefore it is necessary to design an efficient algorithm that classifies PVC based on QRS pattern in realtime and decreases computational cost by extracting minimal feature. In this paper, we propose PVC classification based on QRS pattern using QS interval and R wave amplitude. For this purpose, we detected R wave, RR interval, QRS pattern from noise-free ECG signal through the preprocessing method. Also, we classified PVC in realtime through QS interval and R wave amplitude. The performance of R wave detection, PVC classification is evaluated by using 9 record of MIT-BIH arrhythmia database that included over 30 PVC. The achieved scores indicate the average of 99.02% in R wave detection and the rate of 93.72% in PVC classification.

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.29-36
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• 2007

Recent seismic surveys have shown that the presence of methane hydrate (MH) in sediments has significant influence on seismic attenuation. I have used vertical seismic profile (VSP) data from a Nankai Trough exploratory well, offshore Tokai in central Japan, to estimate compressional attenuation in MH-bearing sediments at seismic frequencies of 30-110 Hz. The use of two different measurement methods (spectral ratio and centroid frequency shift methods) provides an opportunity to validate the attenuation measurements. The sensitivity of attenuation analyses to different depth intervals, borehole irregularities, and different frequency ranges was also examined to validate the stability of attenuation estimation. I found no significant compressional attenuation in MH-bearing sediments at seismic frequencies. Macroscopically, the peaks of highest attenuation in the seismic frequency range correspond to low-saturation gas zones. In contrast, high compressional attenuation zones in the sonic frequency range (10-20 kHz) are associated with the presence of methane hydrates at the same well locations. Thus, this study demonstrated the frequency-dependence of attenuation in MH-bearing sediments; MH-bearing sediments cause attenuation in the sonic frequency range rather than the seismic frequency range As a possible reason why seismic frequencies in the 30-110 Hz range were not affected in MH-bearing sediments, I point out the effect of thin layering of MH-bearing zones.

• Economic and Environmental Geology
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• v.23 no.4
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• pp.393-409
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• 1990

Synthetic seismograms and deduced characteristic properties of the non-geometrical $S^*$ and $P^*$ waves are presented. These waves are excited on the free surface or an interface between two different media by an inhomogeneous P wave from a point source nearby, and propagate as homogeneous waves in the media. Synthetic seismograms are computed using an extended reflectivity method designed for buried source and receiver. An efficient computational procedure for propagator matrices of layers is devised to reduce the computational time and the RAM memory size in the implementation of the reflectivity method. Radiation patterns are obtained from the particle motions of the four types of the "*" waves, i.e., the $S^*$ wave generated near the free surface, and the reflected $S^*$, transmitted $S^*$ and transmitted $P^*$ waves generated near an interface. Some patterns show polarity changes of displacements and others reveal monotonic or non-monotonic variation of amplitude depending on the velocity structure. The decaying trend of amplitude with increasing epicentral distance are also shown for the head wave type of the "*" waves.

• 한국지구물리탐사학회:학술대회논문집
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• 2010.10a
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• pp.55-55
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• 2010

북한 지난 2006년 2009년에 두차례 핵실험을 실시하였다. 이 핵실험은 한국, 일본, 중국에 위치한 지진관측소에 높은 신호대 잡음비를 보이며 관측이 되었다. 북한 핵실험의 지진파형 자료를 분석하여 북한 핵실험 특성 파악을 수행한다. 또한 지역지진파의 전파 경로별 변화 특성을 살펴본다. 한반도의 경우, 동해의 지각구조가 급격하게 변화하므로 동해를 가로지는 경로상에 급격한 지역지진파 변화가 관측된다. 이러한 지역지진파의 경로별 변화로 인해 관측소별 판정에 있어 어려움을 야기한다. 여러 관측소 자료를 종합 분석하는 핵실험 탐지 방법을 제시하며, 이를 북한 핵실험에 적용한다. 과거 구소련과 미국의 핵실험 자료와의 차이점을 살펴보고, 북한 핵실험의 탐지의 효율성을 위해 고려해야 할 사항에 대하여 토론한다. 과거 두 번의 북한 핵실험의 특징인 스펙트럼상의 모서리주파수 부근 에너지 강화 현상이 강하게 관측되며, P파의 상대적 강화 현상이 관측된다. 또한 2010년 천안함 침몰사건에 대하여 지진학적 기법을 활용하여 천암한 침몰 원인에 대하여 추정한다. 침몰 사건시간대에 기록된 지진파형 기록을 수집하여 분석한다. 3개의 관측소 지진파형 자료가 분석에 활용된다. 지진파의 분석을 통해 진앙위치를 추정하며, 지진파형에 드러난 특성을 통해 천암함 침몰과의 연관성을 유추한다. 또한, 지진파 진폭과 주파수 특성을 통해 진원 특성과 침몰 원인등을 추정한다.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.4 no.1
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• pp.17-22
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• 2011

In this study, a P wave emphasizing and detection algorithm from ECG signal was proposed to read arrhythmia. The algorithm uses two slope tracing waveform, the descending slope tracing wave and the ascending slope tracing wave, developed for efficient determination of slope inverting points and sudden slope changing points. The algorithm generates the slope tracing waveform which trace the original ECG wave, and subtracts one tracing wave from the other to detect P and T waves. The algorithm has been applied to MIT/BIH database in order to verify its efficacy and validity in practical applications.

• Journal of the Korean Geotechnical Society
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• v.35 no.11
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• pp.121-129
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• 2019

An Earthquake Early Warning (EEW) system is a technology that alerts people to an incoming earthquake by using P waves that are detected before the arrival of more severe seismic waves. P-wave analysis is therefore an important factor in the production of rapid seismic information as it can be used to quickly estimate the earthquake magnitude and epicenter through the amplitude and predominant period of the observed P-wave. However, when a large-magnitude teleseismic earthquake is observed in a local seismic network, the significantly attenuated P wave phases may be mischaracterized as belonging to a small-magnitude local earthquake in the initial analysis stage. Such a misanalysis may be sent to the public as a false alert, reducing the credibility of the EEW system and potentially causing economic losses for infrastructure and industrial facilities. Therefore, it is necessary to develop methods that reduce misanalysis. In this study, the possibility of seismic misclassifying teleseimic earthquakes as local events was reviewed using the Filter Bank method, which uses the attenuation characteristics of P waves to classify local and outside Korean peninsula (regional and teleseismic) events with filtered waveform depending on frequency and epicenter distance. The data used in our analysis were analyzed for maximum P_v values using 463 events with local magnitudes (2 < M_L ≦ 3), 44 (3 < M_L ≦ 4), 4 (4 < M_L ≦ 5), 3 (M_L > 5), and 89 outside Korean peninsula earthquakes recorded by the KMA seismic network. The results show that local and telesesimic earthquakes can be classified more accurately when combination of filtering bands of No. 3 (6-12 Hz) and No. 6 (0.75-1.5 Hz) is applied.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.6 s.360
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• pp.60-68
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• 2007

A technique is presented to extract differential second harmonic output from common source nodes of a cross-coupled P-& N-FET oscillator. Provided the impedances at the common source nodes are optimized and the fundamental swing at the VCO core stays in a proper mode, it is found that the amplitude and phase errors can be kept within $0{\sim}1.6dB$ and $+2.2^{\circ}{\sim}-5.6^{\circ}$, respectively, over all process/temperature/voltage corners. Moreover, an impedance-tuning circuit is proposed to compensate any unexpectedly high errors on the differential signal output. A Prototype 5-GHz VCO with a 2.5-Hz LC resonator is implemented in $0.18-{\mu}m$ CMOS. The error signal between the differential outputs has been measured to be as low as -70 dBm with the aid of the tuning circuit. It implies the push-push outputs are satisfactorily differential with the amplitude and phase errors well less than 0.34 dB and $1^{\circ}$, respectively.