• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.410-415
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• 2002

In this article, spatial filtering procedures with application to spherical acoustical holography are discussed. Planar and cylindrical holography are the most widely used amongst the various nearfield acoustical holography techniques. However, when the geometry of a source is similar to a sphere, spherical holography may yield better results than other types of holography since there are no errors due to truncation of the sound field in the spherical case. Spatial filtering affects the accuracy of spherical acoustical holography critically, especially in the case of backward projection. Thus spatial filtering is essential for successful application of spherical holography. In the present work, various filtering methods were evaluated in simulations made using sound pressure fields of various types and with different levels of random spatial noise. It was found that a procedure based on eliminating spherical harmonic coefficients that contribute insignificantly to the total sound power of the source gave the best results on average of the different procedures considered here. Spherical holography procedures were also verified experimentally. Reliable results were obtained using the power filtering algorithm. Thus it was concluded that spherical holography combined with power filtering may prove to be a useful tool for noise source identification.

• Journal of the Optical Society of Korea
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• 제7권4호
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• pp.216-223
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• 2003

We report a technique that improves the spatial resolution of optical coherence tomography (OCT) by utilizing fiber-based spectral filtering. The proposed technique improves the resolution by filtering out the erbium’s characteristic peak from the amplified spontaneous emission (ASE) source spectrum, and reshaping the spectrum to Gaussian-like. We used a long period fiber grating (LPG) and an erbium doped fiber (EDF) absorber for the spectral filtering. An in-house made ASE source as well as a commercial ASE source [ASE-FL7002] was used as the OCT sources to study the proposed technique. The resolution of the OCT based on an in-house made ASE source is enhanced from 200 to 40 ㎛ with an LPG. While, the resolution of the OCT based on a commercial ASE source is enhanced from 25 to 19 ㎛ with the aid of an EDF absorber. However, sidelobes still exist in the interferogram due to imperfect spectral filtering, which limited the resolution. Further enhancement in the spatial resolution of the OCT system using the ASE source is possible with the aid of cascaded LPGs and/or carefully designed EDF absorber.

• 대한의용생체공학회:의공학회지
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• 제20권3호
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• pp.291-297
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• 1999

다채널의 심전도 신호에서, 소수의 리이드에 만 잡음이 유기되고 나머지 대부분의 리이드 신호들은 이 잡음과 통계적인 상관 관계가 없을 때, source consistency filtering(SCF) 은 이러한 잡음의 감쇄에 매우 효과적이다. 특히, SCF는 원래 신호의 왜곡을 최소화하면서 , 선택적으로 잡음 만을 제거하는 매우 우수한 특성을 가진다. 이러한 특성은 하나의 신호원에서 기인하는 다채널 신호들의 공간적 및 시간적 상관관계를 모두 이용함으로서 가능하다. 본 논문에서는 SCF의 원리 및 구현 방법을 구체적으로 기술하여 이 방법에 대한 이해를 증진하고자 한다. 또한 기존의 방법을 개선한 새로운 SCF를 제안하였으며 , 이의 효과적인 구현에 필요한 알고리즘의 상세한 설계 지침을 제시하였다. 다채널의 심전도 신호를 대상으로 하여 그 성능을 검증하였고, 현재의 SCF 가 가지는 한계를 명확히 하며, 개선의 방향을 제시하였다.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2005년도 하계학술대회
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• pp.313-317
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• 2005

고정된 호스트의 출발지 주소 변조(IP Source Address Spoofing)를 막는 가장 단순하면서도 효과적인 해결방법으로 네트워크 진입여과(Network Ingress Filtering)가 있다. 이동(Mobile) IPv4 네트워크에서는 이러한 네트워크 진입 여과가 설정될 경우 이동 호스트의 통신이 불가능해지기 때문에 이를 피하기 위한 방법으로 역터널링(Reverse Tunneling)이 고안되었지만 이에 따라 이동 호스트의 출발지 주소 변조를 통한 서비스 공격을 막을 수가 없게 되었다. 본 논문에서는 이동 IPv4 네트워크에서 외부 에어전트에 이동 호스트들만이 연결되고 각각의 외부 에이전트(Foreign Agent)가 관리하는 네트워크가 작다는 가정하에, 이동 호스트의 출발지 주소 변조를 효과적으로 막는 방법에 대해 제안하고자 한다.

• 한국환경과학회지
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• 제17권10호
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• pp.1147-1154
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• 2008

Road runoff, one of non-point source pollutants, contains various heavy metals, most of which flow into discharge waters without being treated. The mechanism of removing the heavy metals in water is similar to that of removing micro-particles. Therefore, it is considered that it is possible to remove a lot of the heavy metals contained in the road runoff by filtering or absorbing them. In this paper, performed has been a basic study on the characteristics of UNFS (Up Flow Non-Point Source Filtering System) using carbide pellet and zeolite pellet as double-layer filtering mediums to treat the road runoff. The removal rate with filtering and absorption time has been shown as follows: 29.0% for Cr; 27.8% for Cd; 25.7% for Fe; 25.4% for Co; 21.2% for Pb; ]9.6% for Zn; 18.2% for Al; 17.0% for Mn; 11.3% for Ni; 7.5% for Cu. The overall removal rate according to influx change has been shown to be approximately 30%, and the load of heavy metals flowing out in initial precipitation could be reduced by using carbide as a recycling filtering medium. When the removal as coarse particles settle is added up, it is expected that UNFS will result in a higher removal rate.

• 대한의용생체공학회:의공학회지
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• 제29권5호
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• pp.355-363
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• 2008

In order to extract only the alpha activity related signals from EEG recordings, we have applied Constrained Independent Component Analysis (cICA), a new extension of ICA in which some a priori knowledge of the alpha activity is utilized to extract only desired components. Its extraction (or filtering) performance has been compared to that of the conventional band-pass filtering via the scalp alpha power maps and cortical source maps of the alpha activity. Our results demonstrate that the alpha power maps and cortical source maps from the cICA-extracted alpha signals reveal more focalized alpha generating regions of the brain than those from the band-pass filtered alpha EEG signals. Furthermore they match more closely the activated regions of the brain mapped using fMRI, validating our results. We believe that the cICA-based filtering approach of EEG signals is a more effective means of extracting a specific brain activity reflected in EEG signals that will result in more accurate source localization or imaging maps.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.344.2-344
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• 2002

In this presentation, a power-based spatial filtering procedure with application to spherical acoustical holography is presented. Planar and cylindrical holography are the most widely used amongst the various nearfield acoustical holography techniques. However, when the geometry of a source is similar to a sphere. spherical holography may yield better results than other types of holography since there are no errors due to truncation of the sound field in the spherical case. (omitted)

• 한국멀티미디어학회논문지
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• 제24권2호
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• pp.274-284
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• 2021

Customized services to a sleep induction for better sleepcare are more effective because of different satisfaction levels to users. The EOG data measured at the frontal lobe when a person blinks his eyes can be used as biometric data because it has different values for each person. The accuracy of measurement is degraded by a noise source, such as toss and turn. Therefore, it is necessary to analyze the noisy data and remove them from normal EOG by filtering. There are low-pass filtering and high-pass filtering as filtering using a frequency band. However, since filtering within a frequency band range is also required for more effective performance, we propose a machine learning model for the filtering of EOG data in this paper as the second filtering method. In addition, optimal values of parameters such as the depth of the hidden layer, the number of nodes of the hidden layer, the activation function, and the dropout were found through experiments, to improve the performance of the machine learning filtering model, and the filtering performance of 95.7% was obtained. Eventually, it is expected that it can be used for effective user identification services by using filtering model for EOG data.

• The Journal of the Acoustical Society of Korea
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• 제23권2E호
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• pp.56-67
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• 2004

Despite abundant research outcomes of blind source separation (BSS) in many types of simulated environments, their performances are still not satisfactory to be applied to the real environments. The major obstacle may seem the finite filter length of the assumed mixing model and the nonlinear sensor noises. This paper presents a two-step speech enhancement method with multiple microphone inputs. The first step performs a frequency-domain BSS algorithm to produce multiple outputs without any prior knowledge of the mixed source signals. The second step further removes the remaining cross-channel interference by a spectral cancellation approach using a probabilistic source absence/presence detection technique. The desired primary source is detected every frame of the signal, and the secondary source is estimated in the power spectral domain using the other BSS output as a reference interfering source. Then the estimated secondary source is subtracted to reduce the cross-channel interference. Our experimental results show good separation enhancement performances on the real recordings of speech and music signals compared to the conventional BSS methods.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 컴퓨터소사이어티 추계학술대회논문집
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• pp.77-80
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• 2003

Complying with highly demand of information through internet. the utility of computer and network is rapidly provided with to schools. This situation brings about many problems. For example, the stolen information through false identification(Hacking) is the most greatest concern. In this paper it tells that the efficient way of preservating computer use is by using operating system of Open Source, which is Linux system. Further more, it shows the system which was organized by IP-Tabling (offered service-Packet Filtering method from the Linux system) functions well as a security system.