• 응용통계연구
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• 제21권3호
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• pp.537-546
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• 2008

시계열자료 분석에 있어 주요 목적 중에 하나는 미래에 대한 예측 값을 추정하는 것이다. 이 논문에서는 정상자기회귀이동평균 모형에서 변환-역변환 방법을 이용하여 예측값을 구하는 과정에서 발생하는 문제에 대해 알아보고 회귀분석에서 제안되었던 smearing 추정방법을 시계열분석에서 사용할 수 있도록 붓스트랩을 이용하여 수정한 추정법을 소개한다. Yeo-Johnson 변환 (2000)을 이용한 KOSDAQ지수의 수익률 실증분석을 통해 기존에 사용되고 있는 방법의 문제점과 제안된 방법의 적절성에 대해 고찰해 보았다.

• 천문학회보
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• 제40권2호
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• pp.38.3-38.3
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• 2015

Recently, the Pierre Auger Observatory (PAO), the largest ground-based project for detecting ultra-high-energy cosmic rays (UHECRs), published their 10-year data. We can access an unprecedented number of UHECR data observed by the project, which give us a possibility to get an accurate statistical test result. In this work, we investigate the influence of the galactic magnetic field (GMF) on the distribution of UHECRs by searching the correlation with the large-scale structure (LSS) of the universe. We simulate the mock UHECR events whose trajectories from the sources would be deflected by the Gaussian smearing angle which reflects the influence by the GMF. By the statistical test, we compare the correlation between the expected/observed distribution of UHECRs and the LSS of the universe in the regions of sky divided by the galactic latitude, varying the smearing angle. Here, we assume the deflections by the GMF are mainly dependent on the galactic latitude. Using the maximum likelihood estimation, we find the best-fit smearing angle in each region. If we get a trend that best-fit smearing angles differ from each region, the influence of GMF may be stronger than that of intergalactic magnetic fields (IGMF) because it is known that the distribution of IGMF follows the LSS of the universe. Also, we can estimate the strength of the GMF using the best-fit parameter by the maximum likelihood.

• 대한원격탐사학회지
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• 제36권4호
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• pp.535-544
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• 2020

In synthetic aperture radar (SAR) based ship detection application, false alarms frequently occur due to various noises caused by the radar imaging process. Among them, radio frequency interference (RFI) and azimuth smearing produce substantial false alarms; the latter also yields longer length estimation of ships than the true length. These two noises are prominent at cross-polarization and relatively weak at co-polarization. However, in general, the cross-polarization data are suitable for ship detection, because the radar backscatter from background sea surface is much less in comparison with the co-polarization backscatter, i.e., higher ship-sea image contrast. In order to improve the ship detection accuracy further, the RFI and azimuth smearing need to be mitigated. In the present letter, Sentinel-1 VV- and VH-polarization intensity data are used to show a novel technique of removing these noises. In this method, median image intensities of noises and background sea surface are calculated to yield arithmetic tendency. A band-math formula is then designed to replace the intensities of noise pixels in VH-polarization with adjusted VV-polarization intensity pixels that are less affected by the noises. To verify the proposed method, the adaptive threshold method (ATM) with a sliding window was used for ship detection, and the results showed that the 74.39% of RFI false alarms are removed and 92.27% false alarms of azimuth smearing are removed.

• 천문학회보
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• 제39권2호
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• pp.73.1-73.1
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• 2014

We investigate the influence of the galactic magnetic field (GMF) on the arrival direction (AD) of ultra-high energy cosmic rays (UHECRs) by searching the correlation with the large-scale structure (LSS) of the universe. The deflection angle of UHECRs from sources by the GMF is reflected in a source model by introducing the Gaussian smearing angle as a free parameter. Assuming the deflections by the GMF are mainly dependent on the galactic latitude, b, we divide the regions of sky by b and analyze the correlation between the AD of UHECRs and the LSS of the universe in each region varying the smearing angle. We find the deflection is strongly dependent on the galactic latitude by the maximum likelihood estimation. Specifically, the best-fit smearing angles are $9^{\circ}$ and $84^{\circ}$ in the high galactic latitude (HGL), $-90^{\circ}$ < b < $-60^{\circ}$, and in the low galactic latitude (LGL), $-30^{\circ}$ < b < $30^{\circ}$, respectively. The strength of GMF becomes stronger from the HGL to the LGL. From the results, we can estimate the strength of GMF in each region. In the LGL, for example, if we assume UHECRs are protons, we have the order of $100{\mu}G$ GMF, which is much stronger than the expected value of conventional GMF model. However, if the primaries are heavy nuclei, which is consistent with the observational result of mass composition analysis, the order of GMF strength is a few ${\mu}G$. More data from the future experiments make it possible to study the GMF between the source of UHECRs and Earth more accurately.

• 한국전자파학회논문지
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• 제23권4호
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• pp.491-498
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• 2012

최근 OFDM 시스템의 T-DMB 동일 채널 중계기에서 궤환 신호를 제거하여 송신 출력을 증강시키고, 등화기를 사용하여 ICI(Inter Carrier Interference)를 제거함으로써 시스템 성능을 개선하기 위하여 노력하였다. 그러나 T-DMB 동일 채널 중계기의 경우, 성상도 번짐 현상으로 수신 단말기에서 완벽하게 신호 품질이 개선되지 않고 있다. 그러므로 본 논문에서는 성상도 번짐 현상을 억압하기 위하여 파일럿(PRS)을 이용하여 주파수 영역에서의 ICI를 고려한 적응형 채널 추정과 결정지향 잡음 제거 기법을 제안함으로써 단말기에서 수신 품질을 확보한다. T-DMB 단말기에서 요구되는 QoS(Quality of Service)를 확보하기 위하여 동일 채널 중계기에서 SNR과 BER을 평가하고, 시뮬레이션을 통하여 검증하였다. 시뮬레이션 결과를 통하여 back-off=9 dB 상태에서 위상 잡음 -18 dBc의 경우, 위상 잡음을 보상하여 수신기에서 SNR=14 dB 이하에서 BER=$10^{-5}$의 성능을 만족할 수 있다.