• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.63-63
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• 2003

• Journal of Korea Multimedia Society
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• v.3 no.4
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• pp.347-355
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• 2000

This paper presents an adaptive AEC(acoustic echo canceller) based on the wavelet transform using M-channel subband QMF filter banks. The proposed algorithm improves the performance of AEC with a realtime process by a low complexity of wavelet transform filter banks, a subband processing and a orthogonality of wavelet subband filter. Adaptive filter coefficients of each subband are updated using LMS algorithm with a low complexity and a easy realization for a realtime processing and a reduction of hardware cost. For a input signal, a white Gaussian noise and a real speech signal with a environment noises are used for a performance estimation of the proposed algorithm. As a result of computer simulation, the proposed AEC has a low asymptotic error, a low computation complexity and a robust performance.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.08a
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• pp.161-164
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• 2000

본 논문에서 제안한 동시통화 검출기는 기존의 전대역에서 이루어지던 상호상관계수를 이용한 동시통화 검출기의 검출성능을 향상시키기 위하여 웨이브릿변환된 각각의 서브밴드 내에서 동시통화 및 반향경로를 구별하여 효율적으로 검출할 수 있도록 구성하였다. 서브밴드 동시통화 검출기 사용으로 동시통화 시에 발생하는 적응필터의 계수 발산을 막음으로써 시스템의 안정성을 높이고, 근단화자 신호가 원단화자에게 더 유쾌하게 들릴 수 있게 함으로써 원활한 통화환경을 제공할 수 있도록 구현하였다.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.73-76
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• 2000

본 논문에서는 음향반향제거기를 구현하기 위한 적응알고리즘을 제안한다 특히 긴 임펄스 응답을 가지는 시스템의 식별을 위해 웨이블릿 필터를 사용하여 입력신호를 서브밴드로 분해함으로써 기존의 RLS알고리즘의 계산량을 줄여 수렴속도를 향상시켰다. 이 과정에서 적응필터를 다위상 구조로 구성하여 컨벌루션 과정을 병렬처리가 가능하도록 하였다. 제안된 알고리즘의 성능분석을 위하여 실제 음성신호를 입력신호로 하여 컴퓨터 모의실험을 수행하였으며 전대역 RLS알고리즘과 비교하였다.

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.43-49
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• 1997

Generally, echo cancelers of a TV conference system or a audio conference system are to carry out a real time processing in the case of the closed room having long reverberation time because the system requires much time to modify filter coefficients to environmental changes. Therefore this paper proposes a new subband adaptive filtering method using polyphase filter banks of MPEG(Moving Picture Experts Group) audio system to solve the problems. This method divides signal spectra of input and output into several frequency bands, and each band is adaptively filtered by using ES-NLMS (Exponential Step-Normalized Least Mean Square) algorithm. The optimal number of subband is determined by computational simulations. According to the results of simulation, ERLE of the subband model is 2dB smaller than general full band, calculation rate's of the subband model is decreased about 88%.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.81-89
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• 2022

It is necessary to increase the surface hardness and improve the wear resistance and peeling resistance through the surface treatment and performance evaluation of the mold steel. As a result of vacuum heat treatment analysis, residual austenite measurement and surface treatment wear test, retained austenite should be removed by sub-zero treatment, and retained austenite was completely removed by treatment at -196℃. The TiMon film coated on the sub-zero treated STD11 specimen showed the lowest coefficient of friction.

• Proceedings of the Korean Information Science Society Conference
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• 2000.04b
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• pp.514-516
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• 2000

본 논문은 조영제를 사용하지 않은 정상인의 신장의 추출에 관한 연구로서 복구 CT 영상의 특성을 파악하고 신장부분을 분석함으로서 신장의 자동적인 추출을 시행하였다. 처리과정에서 기준값에 의한 이진영상에서 각 장기의 서로 다른 화소분포의 특징을 이용하여 장기추출을 시행하였고 템플리트를 이용한 서브트랙션과 채우기 과정을 거쳐 단일 슬라이스에서 신장을 추출한 후 추출된 신장영상의 슬라이스들을 겹친 영상을 생성하여 단일 슬라이스 내에서 제거되지 못한 노이즈들을 제거하였다.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.3
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• pp.295-300
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• 2021

This study investigated the dominant frequency of the elastic waves from the tensile test. The specimen was rolled with five different rolling degrees (10, 22, 33, 42 and 50%), which was treated subzero. The specimen was rolled at room temperature, which was transformed from austenite to martensite (only α'-martensite). The dominant frequency increased with an increase in the rolling degree regardless of the subzero temperature, and decreased after 33% of the rolling degree. On the other hand, higher frequency band was obtained at lower temperature and long time. The dominant frequency increased when the amount of α'-martensite increased and decreased with the α'-martensite amount between 50-65%. The lower subzero treatment temperature increased the amount of α'-martensite, which resulted in the higher dominant frequency. The longer treatment time at the same subzero temperature led to an increase in the amount of α'-martensite, leading to high dominant frequency.

• Korean Journal of Metals and Materials
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• v.47 no.3
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• pp.169-174
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• 2009

The effect of sub zero treatment on the damping capacity in austempered ductile cast iron investigated. Austenite transformed in to martensite by subzero treatment, and with the decrease of subzero treatment temperature, volume fraction of martensite increased. Damping capacity of austempered ductile cast iron was highly increased by subzero treatment, with the decrease of subzero treatment temperature, damping capacity was slowly increased. With the decrease of subzero treatment time, damping capacity was rapidly increased to 30 min. and then slowly increased. With the increase of volume fraction of martensite, damping capacity rapidly increasing to 5% and then slowly increased.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.2
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• pp.124-131
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• 1989

This paper showed that the system reliability optimization problem with sereval failure modes at each subsystem can be treated as efficient computational algorithm proposed here. This algorithm was developed by considering a generalized upper bounding which always exists in constraints when the system reliability optimization problem may be reformulated as 0-1 integer programming problem. We demonstrated the optimal allocation of redundant units for system reliability by using the proposed algorithm. Our algorithm is superior to others in terms of number of iterations and variables used.