• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.749-761
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• 2014

Improving spectrum utilization efficiency is a fundamental goal of dynamic spectrum access technology. The definition of spectrum holes determines how to detect and exploit them. Current definitions of spectrum holes are ineffective in exploiting spatial-temporal spectrum holes. In this paper, a novel definition of spectrum holes is proposed, in which throughput loss indicates the impact of secondary users on primary users. The definition specifies spectrum holes, unifies the impact of secondary users on primary users and is effective exploiting spatial-temporal spectrum holes. Theoretical analysis and numerical simulations show that the new definition proposed in this paper significantly improves the spectrum utilization efficiency.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(4)
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• pp.93-96
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• 2002

This paper presents robust and efficient scene-based video watermarking method using visual rhythm (spatio-temporal slice) in compressed domain. Scene change can be detected easily using visual rhythm and video sequences are conveniently edited at the scene boundaries. Therefore, scene-based watermark embedding Process it a natural choice. Temporal spread spectrum can be achieved by applying spread spectrum methods to visual rhythm. Additive Gaussian noise, low-pass filtering, median filtering and histogram equalization attack are simulated for all frames. Frame sub-sampling is also simulated as a typical video attack Simulation results show that proposed algorithm is robust and efficient in the presence of such kind of attacks.

• 한국통신학회논문지
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• 제21권2호
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• pp.347-356
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• 1996

In this paper, we present the circular array structure for estimating the temporal and spatial specturm of multiple narrowband incoherent signals which have different frequencies. The conventional linear array is computationally demanding for simultaneously estimating the spatial and temporal spectrum since it requires the tapped delay line filer. The statistical performance of the circular array is never deteriorated eve though it requires much less computational load than the uniform linear array. Especially, it is shown that the circular array resolves the direction-of-arrivals of the multiple signals without the spatial and temporal aliasing the fundamental nonuniform-sampling property prossessed by it. Computer simulation results are shown to demonstrate the better performance achieved with the circular array geometry relative to that obtained with a uniform linear array with taps.

• 한국위성정보통신학회논문지
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• 제12권2호
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• pp.65-70
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• 2017

The structure of MMSE receiver front-ended by CMA(Constant Modulus Array) array working in CDMA forward link which is applicable to LEO spread spectrum satellite communication system is proposed. By using the despreaded pilot signal of forward link as a reference signal, the CMA array can capture multi-path signals securely even in severely faded LEO satellite channel. The remaining MAI (Multiple Access Interference) is cancelled by the cascaded MMSE receiver. Besides theoretical development, through relevant computer simulation, it is proved that the proposed system shows much better BER performance than any other possible candidate systems. As a spatio-temporal receiver mounted on a mobile vehicle, the proposed system also reduces implemental cost and complexity by adopting the simplest algorithm for its spatial and temporal domain processing.

• 한국지구과학회지
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• 제25권7호
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• pp.604-614
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• 2004

경기도 이천에서 2002년 7월부터 12까지 총 6개월 동안 측정된 지자기 3성분 자료를 이용하여 일별 각 성분의 스펙트럼, 지자기 전달함수의 크기, 위상, 오차 등을 계산하였다. 지자기 스펙트럼은 관측기간 동안 태양활동에 의한 무작위적 강약이 반복되는 형태를 보여주었고, 유의미한 시간적 변동은 존대하지 않았다. 지자기 전달함수의 크기, 위상, 오차의 경우, 주기 100초 이하와 주기 1000초 이상에서 부분적으로 무작위적인 경향을 확인할 수 있었으나, 시간에 따른 증감추세 없이 대체로 안정적인 값을 보였다. 이와 더불어, 전기장의 P$_{1}\;^{0}$ 소스(zonal harmonics) 가정을 통하여 시간에 따른 근사적인 겉보기 전기비저항의 변동을 조사하였는데, 근사된 전기비저항의 변화는 지각의 자체적인 물성 변화보다는 수평 자기장 성분의 시간적 강약에 지배적임을 확인할 수 있었다.

• Journal of Oral Medicine and Pain
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• 제20권2호
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• pp.269-281
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• 1995

To study the characteristics of EMG power spectrum of masticatory muscles during sustained isometric contraction and recovery at various contraction times, the author analysed the EMG signals of anterior temporal and masseter muscles before, during, and after sustained isometric contraction at 50% level of maximum voluntary contraction (MVC) for 15,30,60 seconds. Twelve normal subjects were included in this study. The author came to following conclusions from the results. 1. MMF of anterior temporal muscle in the contraction period was significantly higher than that of masseter muscle during sustained isometric contraction regardless of isometric contraction times (p<0.05). 2. MMF in the contraction period decreased as the contraction time increased during sustained isometric contraction in both temporal and masseter muscles(p<0.05). 3. SMF in the contraction period increased as the contraction tie increased during sustained isometric contraction in both temporal and masseter muscles(p<0.01). 4. MMF in the first part of recovery period (20 seconds) decreased as the contraction time increased during sustained isometric contraction(p<0.05). However, MMF in the later parts of recovery period (20-120 seconds) showed no significant differences. 5. MMF of anterior temporl muscle in the recovery period was significantly higher than that of masseter muscle after sustained isometric contraction regardless of isometric contraction times (p<0.05). 6. The recovery rate of MF reached 100% in 100 seconds after the isometric contraction regardless of isometric contraction times.

• 한국통신학회논문지
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• 제18권11호
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• pp.1645-1654
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• 1993

본 논문에서는 기존의 잡음 제거용 순환 filter와 달리 시간축 대역제한을 통해 시각특성의 개선과 영상데이타 압축 효과를 개선시키는데 그 목적을 두고 있다. 일반적으로 시간축 대역제한을 수행하려면 시간방향으로의 aliasing을 고려해야 한다. 신호 처리 관점에서 보면 신호에 aliasing이 생긴다면 이의 영향을 받지않고 (de-aliasing) filtering하는 것은 불가능하다고 알려져있다. 그러나 영상신호에서는 baseband spectrum 구조를 예측할 수 있고, 이를 토대로 aliasing의 영향을 받지않는 대역제한 방안을 생각할 수 있다. 이는 이동벡터의 궤적을 따라 공간 영역에서 대역제한(Motion Adaptive Spatial Filter)을 하는 것으로서 이들의 특성 및 구성방안으 제안한다. 이렇게 구성된 filter는 aliasing의 제기 뿐만아니라 시간축 잡음의 제거에도 기여를 하게 된다. 실험에서는 제안방법의 de-aliasing 특성과 영상부호화기로의 적용결과를 알아본다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권7호
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• pp.1756-1776
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• 2012

Wireless sensor networks (WSNs) are likely to be more prevalent as their cost-effectiveness improves. The spectrum of applications for WSNs spans multiple domains. In environmental sciences, in particular, they are on the way to become an essential technology for monitoring the natural environment and the dynamic behavior of transient physical phenomena over space. Existing sensor network query processors (SNQPs) have also demonstrated that in-network processing is an effective and efficient means of interaction with WSNs for performing queries over live data. Inspired by these findings, this paper investigates the question as to whether spatio-temporal and historical analysis can be carried over WSNs using distributed query-processing techniques. The emphasis of this work is on the spatial, temporal and historical aspects of sensed data, which are not adequately addressed in existing SNQPs. This paper surveys the novel approaches of storing the data and execution of spatio-temporal and historical queries. We introduce the challenges and opportunities of research in the field of in-network storage and in-network spatio-temporal query processing as well as illustrate the current status of research in this field. We also present new areas where the spatio-temporal and historical query processing can be of significant importance.

• Journal of Astronomy and Space Sciences
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• 제24권4호
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• pp.261-268
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• 2007

We have studied the temporal variation in the North-South asymmetry of the sunspot area during the period from 1874 to 2007. Though the 9-year periodicity is commonly reported, shorter periodicities is still under study. We employ the cepstrum analysis method to analyze the noisy power spectrum of the North-South asymmetry. We demonstrate that the cleaned power spectrum shows reduction of the spurious back-ground noise level. Some of short period peaks in the power spectrum disappear after deconvolution. It should be, however, pointed out that power spectrum might look less noisy because of a filtering process during deconvolution. We conclude by pointing out that a more sophisticate filtering algorithm is required to produce a precise and reliable periodicity estimate.

• 한국소음진동공학회논문집
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• 제26권3호
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• pp.270-280
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• 2016

노치가 있는 보에 부착된 압전소자의 전기역학적 어드미턴스 전이과정을 파전달 관점에서 규명한다. 유한요소 해석을 통해 노치가 있는 보에서 잔향하는 램파에 대한 수치해를 구한다. 보에 병치된 압전소자의 분극을 이용하여 노치에 의해 발생하는 모드변환된 램파 신호를 추출한다. 전기역학적 어드미턴스의 전이과정을 보여줄 수 있는 일련의 템포럴 스펙트럼은 모드변환된 램파 신호들을 시간영역에서 순차적으로 절단한 후, 고속 푸리에 변환을 적용하여 계산한다. 절단 시간이 상대적으로 작을 때 이에 대응되는 템포럴 스펙트럼은 입력 주파수 대역의 특성이 지배적이다. 그러나, 절단 시간이 증가함에 따라 입력 주파수 대역 내에 존재하는 보의 모달 특성이 템포럴 스펙트럼에 중대한 영향을 준다. 이는 보에서 잔향하는 모드변환램파가 보의 공진에 기여함을 의미한다. 각 공진주파수 부근에서 템포럴 스펙트럼에 대한 제곱평균제곱근을 계산한다. 모든 공진주파수 부근에서 절단시간에 따라 제곱평균제곱근은 증가한다. 마지막으로, 보의 손상 진단 측면에서 수치해석 결과의 시사점에 대해 논의한다.