• Communications for Statistical Applications and Methods
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• 제30권4호
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• pp.369-388
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• 2023

In this paper, we develop the two-step procedure that detects and estimates the position of structural changes for multivariate nonstationary time series, either on mean parameters or second-order structures. We first investigate the presence of mean structural change by monitoring data through the aggregated cumulative sum (CUSUM) type statistic, a sequential procedure identifying the likely position of the change point on its trend. If no mean change point is detected, the proposed method proceeds to scan the second-order structural change by modeling the multivariate nonstationary time series with a multivariate locally stationary Wavelet process, allowing the time-localized auto-correlation and cross-dependence. Under this framework, the estimated dynamic spectral matrices derived from the local wavelet periodogram capture the time-evolving scale-specific auto- and cross-dependence features of data. We then monitor the change point from the lower-dimensional approximated space of the spectral matrices over time by applying the dynamic principal component analysis. Different from existing methods requiring prior information on the type of changes between mean and covariance structures as an input for the implementation, the proposed algorithm provides the output indicating the type of change and the estimated location of its occurrence. The performance of the proposed method is demonstrated in simulations and the analysis of two real finance datasets.

• 한국정보과학회논문지:정보통신
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• 제36권3호
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• pp.173-183
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• 2009

본 논문에서는 엔트로피에 기반한 이상징후 탐지 시스템을 제안한다. 엔트로피는 시스템의 무질서정도를 측정하는 지표로써, 이상징후 출현 시 네트워크의 엔트로피는 급증한다. 네트워크를 IP와 포트번호를 기준으로 분류하여, 패킷별로 역학을 관찰하고 엔트로피를 각각 측정한다. 분산서비스거부공격이나 웜, 스캐닝 등의 네트워크 공격 출현 시 패킷 교환과정이 정상적일 때와는 다르므로 엔트로피를 통하여 기존기법 보다 높은 탐지율로 이상징후를 탐지할 수 있다. 본 논문에서는 다수의 원과 서비스거부공격을 포함한 데이터 셋을 수집하여 제안기법을 검증하였다. 또한 지수평활법, Holt-winters 등의 시계열예측 기법과 주성분분석을 이용한 이상징후 탐지 기법과 정확도 측면에서 비교한다. 본 논문에서 제안한 기법으로 웜, 서비스거부공격 등의 이상징후 탐지에 있어 오탐지율을 낮출 수 있다.

• ETRI Journal
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• 제39권3호
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• pp.326-335
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• 2017

In the uplink transmission of massive (or large-scale) multi-input multi-output (MIMO) systems, large dimensional signal detection and its hardware design are challenging issues owing to the high computational complexity. In this paper, we propose low-complexity hardware architectures of Richardson iterative method-based massive MIMO detectors. We present two types of massive MIMO detectors, directly mapped (type1) and reformulated (type2) Richardson iterative methods. In the proposed Richardson method (type2), the matrix-by-matrix multiplications are reformulated to matrix-vector multiplications, thus reducing the computational complexity from $O(U^2)$ to O(U). Both massive MIMO detectors are implemented using a 65 nm CMOS process and compared in terms of detection performance under different channel conditions (high-mobility and flat fading channels). The hardware implementation results confirm that the proposed type1 Richardson method-based detector demonstrates up to 50% power savings over the proposed type2 detector under a flat fading channel. The type2 detector indicates a 37% power savings compared to the type1 under a high-mobility channel.

• 한국측량학회지
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• 제9권1호
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• pp.47-54
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• 1991

본 연구에서는 사진측량에서의 관측값을 대상으로 과대오차 검출을 용이하게 할 수 있도록 잔차들의 상관관계를 고려하고 최신 분산값(updated reference variance)을 채택하여 기각역을 설정함으로써 여러개의 과대오차를 검출할 수 있고 이들 과대오차를 소거한 후 자체검정 번들 조정법에 정오차 보정을 위한 부가매개변수를 도입하여 3차원 위치결정 정확도를 향상시키고자 하였다. 본 연구에서는 근거리 사진측량의 3차원 위치결정에 있어서 관측값에 대해 순차적 data-snooping 법을 적용하여 과대오차를 제거하고 종래의 번들조정법들과 정확도를 비교 분석한 결과, 과대오차를 제거한 이후에 정오차를 보정하는 것이 바람직함을 알 수 있었으며, 관측값에 두개 이상의 과대오차가 포함되면 최소제곱법의 masking효과에 의해 과대오차가 잔차의 상관성이 가장 큰 점의 검정통계량에 영향을 주기 때문에 상관성이 가장 큰 점을 먼저 탐색하고, 제거한 후 실제 과대오차를 제거하여야 함을 알 수 있었다.

• Current Optics and Photonics
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• 제6권2호
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• pp.151-160
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• 2022

Fundus images can reflect ocular diseases and systemic diseases such as glaucoma, diabetes mellitus, and hypertension. Thus, research on fundus-detection equipment is of great importance. The fundus camera has been widely used as a kind of noninvasive detection equipment. Most existing devices can only obtain two-dimensional (2D) retinal-image information, yet the fundus of the human eye also has spectral characteristics. The fundus has many pigments, and their different distributions in the eye lead to dissimilar tissue penetration for light waves, which can reflect the corresponding fundus structure. To obtain more abundant information and improve the detection level of equipment, a snapshot nonmydriatic fundus imaging spectral system, including fundus-imaging spectrometer and illumination system, is studied in this paper. The system uses a microlens array to realize snapshot technology; information can be obtained from only a single exposure. The system does not need to dilate the pupil. Hence, the operation is simple, which reduces its influence on the detected object. The system works in the visible and near-infrared bands (550-800 nm), with a volume less than 400 mm × 120 mm × 75 mm and a spectral resolution better than 6 nm.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2016년도 추계학술대회
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• pp.942-943
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• 2016

스테레오 감마선 탐지장치는 감마선을 신호를 측정하여 위치값을 통한 2차원의 감마선 영상을 생성 한후, 가시광영상과 중첩하여 실제 공간상의 감마선 분포를 나타낸다. 스테레오 감마선 탐지장치는 감마선 탐지센서를 포함하는 탐지부와 감마선 신호를 검출하는 신호측정부 그리고 탐지부의 위치를 제어하기 위한 모션제어부로 구성된다. 본 논문에서는 개별적으로 구성된 각각의 모듈을 효율적으로 운용하기 위한 시스템 운용 알고리즘을 개발하였고, 이를 통해 감마선 조사시험장에서 감마선에 대한 영상화 및 분포정보 출력을 확인하였다.

• 한국정보기술응용학회:학술대회논문집
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• 한국정보기술응용학회 2005년도 6th 2005 International Conference on Computers, Communications and System
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• pp.65-68
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• 2005

In this paper, an algorithm to extract bar-space area is suggested. In a section of bar-code space area the threshold value is computed, and bar and space are extracted according to threshold value. PDF417 is used everyday life and printed in many different materials. The printed PDF417 is especially influenced by various light source. The decision of bar and space is very hard under the change of illumination. The fixed threshold value to distinguish the bar and space can not be applied. in these cases, The proposed algorithm is developed to investigate variable threshold. The variable threshold can be obtained by simple calculation.

• Structural Engineering and Mechanics
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• 제50권4호
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• pp.441-457
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• 2014

This paper presents a finite element based numerical model to solve two dimensional bi-material problems. A bi-material beam consisting of two phase materials ceramic and metal is modelled by finite element method. The beam is subjected simultaneously to mechanical and thermal loadings. The main objective of this study is the analysis of crack deviation located in the brittle material near the interface. The effect of temperature gradient, the residual stresses and applied loads on crack initiation, propagation and deviation are examined and highlighted.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(II)
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• pp.1383-1386
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• 1987

This paper concerns, the method for velocity of dynamic Image on two dimensional sequence Image which can be obtained from two sample lines on the street. The velocity of a single moving object Is measured by the number of total frame which Is required when an automobile passes over the second sample line through the first sample line. The measured results show that the velocity error Is less than 5% comparing with the value measured by X-band speed gun.

• Journal of Radiation Protection and Research
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• 제26권3호
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• pp.231-236
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• 2001

A brief introduction is presented on the radiation safety studies at Tohoku University Cyclotron & Radioisotope Center. Studies on two subject are described; (1) measurement of the thick target neutron yield and radioisotope production / activation cross section for ten's of MeV neutrons and ions using K=110 Tohoku University cyclotron to provide basicdata for accelerator shielding, and (2) development of techniques for high sensitive radiation detection and profile measurement using an Imaging Plate which is a high sensitive two-dimensional radiation sensor. Application of the Imaging Plate techniques to localization of very weak radioactivity and to neutron profile measurement is described.