• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.343-346
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• 1998

잡음환경에서의 음성인식 성능향상을 위하여 본 논문에서는 스펙트럼 차감법 이후에 남아 있는 잔여 잡음으로 인한 mismatch를 극복하는 수단으로 기존의 스펙트럼 차감법에서의 flooring factor를 사용하는 대신에 target 잡음레벨을 이용하여 잡음 마스킹을 적용하는 스펙트럼 차감법과 잡음 마스킹의 hybrid 방식을 사용한다. 이 방법은 낮은 SNR에서 개선되지 않는 기존의 잡음 마스킹이 가지는 약점을 극복하고 동시에 스펙트럼 차감버에서의 잔여 잡음 문제를 완화시킬 수 있었다. 특히 시간/주파수 영역 smoothing을 적용함으로써 스펙트럼 차감법과 잡음 마스킹의 hybrid 방식의 적용 이후에도 여전히 남아 있는 일부 잡음을 추가적으로 감소시켰으며, 더욱 향상된 인식성능을 얻을 수 있었다.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.169-172
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• 2000

본 논문에서는 차량 환경에서 핸즈프리 단말기를 위한 잔향반향제거 방법을 제안한다. 제안된 방법은 기존의 음향반향제거와 잡음제거의 결합구조에 근거하며, 음성신호의 스펙트럼 특성을 배경잡음화함으로써 잔여 반향제거 성능을 향상시킨다. 일반적으로 음향반향제거에서 실제 충격응답보다 적은 차수의 적응필터를 이용할 경우 잔여반향의 전력이 증가하며, 잡음제거기법을 적용하여 잔여반향성분을 줄일 수 있다. 음성신호가 입력되는 음향반향제거기의 잔여반향을 효과적으로 제거하기 위해 음성신호의 AR 스펙트럼에 따른 역필터링을 수행함으로써 잡음제거기에 의한 잔여반향제거 성능을 향상시킬 수 있다. 제안된 기법은 현재 상용화되고 있는 이동통신용 음성부호화기에 포함된 잡음제거기법과 결합하여 사용할 경우 매우 적은 부가 계산량만으로 구현할 수 있다.

• Progress in Medical Physics
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• v.23 no.4
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• pp.285-291
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• 2012

In the present study, we measured the pure beta particle energy spectra of $^{147}Pm$, $^{85}Kr$, $^{90}Sr+^{90}Y$ radionuclide sources. We confirmed the residual maximum energies of KRISS sources meet the requirement of ISO 6980 and calculated mass collision stopping power ratio, which is essential for absolute measurement of absorbed dose from the reference ${\beta}$-rays. The residual maximum energies of KRISS $^{147}Pm$, $^{85}Kr$, $^{90}Sr+^{90}Y$ sources are 0.14, 0.57 and 0.93 MeV, respectively and the mass collision stopping power ratios are 1.123, 1.120 and 1.109, respectively.

• Journal of Advanced Navigation Technology
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• v.27 no.1
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• pp.111-118
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• 2023

For the implementation of a smart factory, it is necessary to collect data by connecting various sensors and devices in the manufacturing environment and to diagnose or predict failures in production facilities through data analysis. In this paper, to predict the residual useful lifetime of milling insert used for machining products in CNC machine, weight k-NN algorithm, Decision Tree, SVR, XGBoost, Random forest, 1D-CNN, and frequency spectrum based on vibration signal are investigated. As the results of the paper, the frequency spectrum does not provide a reliable criterion for an accurate prediction of the residual useful lifetime of an insert. And the weighted k-nearest neighbor algorithm performed best with an MAE of 0.0013, MSE of 0.004, and RMSE of 0.0192. This is an error of 0.001 seconds of the remaining useful lifetime of the insert predicted by the weighted-nearest neighbor algorithm, and it is considered to be a level that can be applied to actual industrial sites.

• Composites Research
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• v.14 no.2
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• pp.50-59
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• 2001

The predictions of residual strength evolution and fatigue life of full scale composite rotor blade for multipurpose helicopter were studied using a strength degradation model. Flight-by-flight load spectrum was developed on the basis of FELIX standard spectrum data. The laminated structural analysis was also performed to obtain corresponding local stress and/or strain spectra for each ply of laminate skin and glass roving spar structures around the blade root where fatigue damage was severely anticipated.

• Journal of Korea Multimedia Society
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• v.4 no.1
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• pp.56-66
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• 2001

The spectral subtraction algorithm using a criterion based on the human perception has been recently developed. The speech processed with Virag's algorithm sounds more pleasant to a human listener than those obtained by the classical methods. However, Virag's algorithm requires a robust voice activity detector (VAD). In the ESS (extended spectral subtraction) algorithm without VAD, the residual noise becomes more noticeable as the SNR decrease. In this paper we propose a new speech enhancement method, the combination of Wiener filter and spectral subtraction based on noise masking characteristics in the human auditory system. There is no need of VAD because the noise can be successively updated even during speech activity using Wiener filter. The adjustment of the subtraction parameter based on the masking threshold makes the residual noise inaudible. The proposed method has been compared with conventional spectral subtraction algorithms. Objective and subjective evaluation of the proposed system is performed with several noise types having different time-frequency distributions. The application of objective measures, the study of the speech spectrograms, as well as subjective listening tests, confirm that the enhanced speech with proposed algorithm is more pleasant to a human listener.

• Composites Research
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• v.23 no.6
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• pp.26-31
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• 2010

This research work contributes to a study for the procedure and methodology to assess the fatigue durability for a composite torque link for helicopter landing gear, which was newly developed and fabricated by the resin transfer moulding technique to interchange with metal component. The simulated load spectrum anticipated to be applied to the torque link during its operation life was generated using an advanced method of probabilistic random process, and the fatigue durability was evaluated by the residual strength degradation approach on the basis of material test data. The full scale fatigue test was performed and compared with the analysis results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1819-1830
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• 1991

The problems associated with noise/energy source identification using multiple input/single output model in linear systems are investigated. Partial coherence function is formulated for the model introducing a virtual force and extraneous noises into the conventional two input/single output system. The analytical results show that the partial coherence function in two input/single output linear system is the function of noise/signal ratios when multiple inputs are mutually coherent and extraneous noises exist. Parametric studies for ordinary and partial coherence functions are carried out to demonstrate the effects of noise/signal ratios for these functions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.11
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• pp.1056-1063
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• 2007

Recently, there has been a growing consumer interest in the amount of noise produced by household electrical appliances. The designer of the product must identify the source of the noise, in order to reduce the noise. In the case of a household electric appliance such as the washing machine, there is consumer's complaint about the noise that is generated during the dehydrating condition. Because of several noise sources combined each other. It is difficult to identify the noise sources that contribute to the noise output. Multi-Dimensional Spectral Analysis (MDSA) is a method that can remove the correlation between different noise sources, and it expresses the key contributing factor as a unique output. This study utilized MDSA to analyze the contribution of each input in the noise output during the dehydrating condition.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.9A
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• pp.1451-1458
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• 2001

디지털 이동통신 시스템에서 가장 빈번하게 발생하는 음성 서비스의 궁극적인 목표는 양호한 음성 품질과 높은 주파수 효율의 제공에 있다. 음성은 묵음 구간에 의하여 구분되어진 짧고 간헐적인 음성 에너지의 반복으로 표현 가능하며 실제 음성 통화중 활성 음성이 존재하는 구간은 약 40%, 나머지 60% 구간은 묵음 또는 상대방의 음성을 듣는 구간이다. 이 묵음 구간을 효율적으로 활용함에 의해 시스템의 스펙트럼 이득을 얻을 수 있다. 본 논문에서는 디지털 이동통신 시스템과 같이 다양하게 변화하는 주변 잡음 환경에서도 강건하게 동작 가능하여 10msec 프레임 크기를 갖는 음성부호화기에 적용 가능한 음성 활성도 측정 방안을 설계하였다. 설계된 알고리즘은 음성에너지, 스펙트럼 분포, 영교차율, 그리고 LPC 잔여신호의 Peakiness 측정값을 이용하였다.