• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.1
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• pp.8-14
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• 2004

Model-based inversion tools for eddy current signals have been developed by combining neural networks and finite element modeling, for quantitative flaw characterization in steam generator tubes. In the present work, interpretation of experimental eddy current signals was carried out in order to validate the developed inversion tools. A database was constructed using the synthetic flaw signals generated by the finite element model. The hybrid neural networks composed of a PNN classifier and BPNN size estimators were trained using the synthetic signals. Experimental eddy current signals were obtained from axisymmetric artificial flaws. Interpretation of flaw signals was conducted by feeding the experimental signals into the neural networks. The interpretation was excellent, which shows that the developed inversion tools would be applicable to the Interpretation of real eddy current signals.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4313-4319
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• 2013

The purpose of our study is to shorten the scanning time and minimize the inconveniences of the patients in acquisition of the black blood images using the signal void effect in the fast spin echo technique while keeping the diagnostic value of the test. Thirty-two consecutive patients who underwent black blood MR imaging were examed with additional double inversion recovery (DIR) sequence and the conventional fast spin echo (FSE) sequence. Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) of the internal carotid arteries' lumen were compared in T1 and T2 weighted images to determine whether there are differences between the two techniques for depiction of the signal void effect inside the vessel wall. The FSE images showed lower SNR values than the DIR images in both of the T1 and T2 weighted images (11.49% and 13.66% respectively). While the CNR values were higher in the FSE images than in the DIR images in both of the T1 and T2 weighted images (8.69% and 7.55% respectively).There was no significant difference between the two techniques for either of the SNR or CNR (p>0.05, p>0.05 respectively). The DIR and the FSE images demonstrated almost identical imaging patterns. Therefore, it is anticipated that the use of FSE technique in acquisition of the black blood imaging could reduce the inconveniences of the patients during the scanning and minimize exam time while keeping the diagnostic value of the test.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.1
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• pp.161-174
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• 1996

Addressed in this paper is performance analysis of the maximum-likelihood code acquisition technique for slotted-mode preamble search in the CDMA reverse link. The probabilities of detection, miss, and false alarm are derived analytically for a multiple $H_{1}$ cell case in a frequency-selective Rayleigh fading channel, based on the statics of the CDMA noncoherent demodulator output. the probability density function of the decision variable consisting of successive demodulator outputs is also derived by considering the fading characteristics of the received signal for both single and dual antenna cases. The performance of the code acquisition technique is evaluated numerically with an emphasis on investigating the effects of post-detection integration, fading rate, and antenna diversity on the detection performance.

• Journal of Biomedical Engineering Research
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• v.25 no.3
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• pp.227-233
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• 2004

In this paper, it is proposed that the four channel electrode arrangement at a frontal lobe and the noise reduction method using a JADE for the EEG biofeedback system. The proposed electrode arrangement is based on the retina-cornea dipole model. Using JADE and signals which are acquired by the proposed arrangement, four independent components are separated. To estimate a pure EEG component among four components, it is measured that a ratio of alpha wave to the whole signal and then the component that has a maximum value is considered as a pure EEG which the noise is eliminated. As a result of experiments, the proposed methods are effective in reduction of noises during acquisition of the EEG.

• Journal of the Korean Institute of Intelligent Systems
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• v.10 no.5
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• pp.459-465
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• 2000

In this paper, we propose a method for controlling camera focus in the short distance by analyzing NTSC signal of a CCD camera. When the distance between a camera and an object is less than about 1 meter, the existing CCD cameras with auto-focusing function are hard to acquire the proper images because they focus on the protruding minute parts ofthe object without taking into account the whole state of the object. To solve such a problem, we use an annealing algorithm to control the motor of a camera by analyzing the overall signal obtained from the camera. By doing so, we can acquire the adequate images at the near distance. The proposed method will be used for a personal identification system by human iris patterns.

• The Magazine of the IEIE
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• v.33 no.1 s.260
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• pp.35-45
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• 2006

최근 휴대폰에서 개인 정보 보안의 중요성이 대두되고 있으며, 이에 따라 생체인식 기능을 내장한 휴대폰에 관심이 집중되고 있으므로, 본 논문에서는 휴대용 기기에 홍채인식기술을 적용하기 위한 방법을 제안하고 하다. 기존의 홍채인식 알고리즘은 인식을 위해 확대된 홍채영상을 사용하여 처리하였고, 이러한 홍채영상을 획득하기 위해서 고 배율의 줌 렌즈(zoom lens)와 초점 렌즈(focus lens)를 사용하였다. 그런데, 휴대폰에서의 홍채인식을 시도하기 위해 줌렌즈와 초점렌즈를 장착하게 되면 가격이 상승하고 부피가 증가되어, 작고 휴대하기 편리한 휴대폰의 특징에 맞지 않아 사용하기 어려운 문제가 있다. 그러나 최근 휴대폰의 멀티미디어 기기 융복합 추세로 인해 휴대폰 내에 장착된 메가 픽셀 카메라(Mega-pixel Camera)의 성능이 급속히 발전함에 따라, 고 배율의 줌, 초점 렌즈 없이도 확대된 홍채영상의 획득이 가능하게 되었다. 즉, 메가 픽셀 카메라 폰을 사용하여 사용자로부터 원거리에서 취득한 얼굴영상에서 홍채 영역이 홍채인식을 위해 충분한 픽셀정보를 가지게 된다. 그러나 이러한 경우 입력 얼굴영상에서 눈 영역을 먼저 찾는 과정이 요구된다. 본 논문에서는 이러한 얼굴영상에서 각막에 의해 반사되는 조명 반사광을 기반으로 휴대폰에서의 홍채인식을 위한 고속 동공검출 방법을 제안한다. 또한 입력 영상 신호를 디지털 신호로 변환하는 과정에서 밝기와 대조 값을 조정하여 동공의 검은 영역과 조명 밝은 반사 위치를 추출함으로써, 정확한 홍채 영역을 보다 빠르고 쉽게 추출할 수 있는 방법 역시 제안한다. 그리고 일반적으로 휴대폰에서 홍채 인식의 경우 손으로 들고 사용하므로, 손 흔들림에 의한 영상 흐림 현상이 빈번하게 발생하게 된다. 이러한 문제를 해결하기 위하여 본 연구에서는 영상 복원 기법을 적용하여 흐려진 홍채 영상을 복원하는 기법을 제안한다. 마지막으로, 휴대폰의 경우 실외에서 사용이 빈번함으로, 입력 홍채 영상에서 태양광에 의한 영향을 많이 받게 된다. 이러한 문제를 해결하여 홍채 인식 성능을 개선할 수 있는 방법 역시 소개하고자 한다.

• The Journal of the Acoustical Society of Korea
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• v.24 no.6
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• pp.303-308
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• 2005

In this paper, the acoustic properties of the light bulb are presented based on a new light bulb source system of continuously transmitting implosive signal . We describe the results of analysis of bulb signals and comparison with Previous works. The results show that Peak-source-level and Primary resonant frequency are increasing with increasing source depth. This bulb source can be used for the purpose of geoacoustic parameter inversion and source tracking in sha]low water via matched field processing.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.9
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• pp.702-708
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• 2002

The spectrum of impulse response signal from an impulse hammer testing is widely used to obtain frequency response function(FRF). However the FRFs obtained from impact hammer testing have not only leakage errors but also finite record length errors when the record length for the signal processing is not sufficiently long. The errors cannot be removed with the conventional signal analyzer which treats the signals as if they are always steady and periodic. Since the response signals generated by the impact hammer are transient and have damping, they are undoubtedly non-periodic. It is inevitable that the signals be acquired for limited recording time, which causes the errors. This paper makes clear the relation between the errors of FRF and the length of recording time. A new method is suggested to reduce the errors of FRF in this paper. Several numerical examples for 1-dof model are carried out to show the property of the errors and the validity of the proposed method.

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.202-208
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• 1999

We introduce a new acoustic parameter for the classification of seafloor sediments from chirp sonar acoustic profiling data. The acoustic parameter is defined as a derivative of the unwrapped phase of the Fourier transform of acoustic profiling data. Consequently, it represents the characteristics of attenuation by dissipative dispersion in sediments. And we estimated acoustic properties by geoacoustic modeling using Chirp data obtained from the different sedimentary facies. Our classification results, when compared with the results of analysis of sampled sediments, show that the acoustic parameter discriminates sedimentary facies and bottom hardness. Thus the method in this paper is expected to be an effective means of geoacoustic modeling of the seafloor.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.7 s.361
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• pp.88-95
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• 2007

In this paper, we suggest the novel MIMO-UWB transceiver structure which can easily be adapted for various MIMO schemes and presents MIMO channel model for obtaining correlation characteristics among channels to analyze the performance. From the indoor channel modeling, we obtain the interferences among antennas due to the MIMO channel formation through numerical simulation and analyze the performance of MIMO-UWB system under frequency selective fading. Especially, to reduce the excessive computational complexity due to the inverse matrix computation of channel transfer function, we take the scheme combining the transmitting signals estimated from each receiving antenna after recovering each transmitting antenna signal from a receiving antenna.