• 천문학회지
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• 제38권2호
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• pp.223-226
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• 2005

We present the results of a 21cm radio continuum aperture synthesis mosaic of the Large Magellanic Cloud (LMC), made by combining data from 1344 separate pointing centers using the Australia Telescope Compact Array (ATCA) and the 64-m Parkes single-dish telescope. The resolution of the mosaicked images is 55' ( 10 pc, using a distance to the LMC) and a region $10^{\circ}{\times}12^{\circ}$ is surveyed.

• 천문학회보
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• 제46권2호
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• pp.71.2-71.2
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• 2021

Using multi-epoch spectra of active galactic nuclei (AGN) obtained from the Sloan Digital Sky Survey, we identify 16 spectrally variable sources, for which the spectral shapes of broad emission lines significantly vary with a time scale of yrs. Out of them, 3 AGNs are already known as changing-look (CL) AGNs by previous studies. 6 AGNs are newly identified as CL AGNs from our study. A majority of these AGNs are relatively faint and their variability in the continuum is small, which may explain their non-detection in the previous studies. 7 sources are known as binary AGN candidates based on the systematic velocity offset between broad emission lines and narrow emission lines. For those sources and 3 CL AGNs, we find that the peak of broad emission lines had been shifted up to a few thousands km/s for ~10 years, implying that those can be promising candidates for pc-scale binary AGNs or recoiling black holes. We plan to conduct multiwavelength follow-up studies to nail down the physical origin of the velocity shift.

• 대한전자공학회논문지TC
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• 제43권1호
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• pp.9-18
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• 2006

본 논문에서는 몬테카를로(Monte-Carlo) 방법을 이용해서 900MHz 수동형 RFID 시스템간의 간섭확률(Probability of Interference)을 획득하는 방법을 제시한다. 간섭원으로 동작하는 RFID 리더 방사 마스크 (emission mask)가 주워졌을 때 방사 마스크로부터 수신기 필터로 수신되는 in-band 간섭전력을 적은 계산 량으로 계산하는 방법을 제시하며 또한 수신 필터의 특성이 주워졌을 때 블로킹에 의한 out-of-band 간섭전력을 계산하는 방법도 제시한다. 제시된 방법에 근거해서 900MHz 대역에서 FHSS 시스템을 사용하는 RFID시스템의 경우와 채널을 센싱 후 송신을 시작하는 LBT 기능이 있는 FHSS 시스템 두 경우에 대해서 간섭확률을 계산한다. ERO에서 개발한 SEAMCAT 소프트웨어로 시뮬레이션하고 SEAMCAT 알고리즘을 MATLAB 툴로 구현 후 MATLAB으로 시뮬레이션 하여 결과가 거의 유사함을 보인다.

• 천문학회보
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• 제20권
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• pp.33.1-33.1
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• 1995

• 천문학회보
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• 제21권
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• pp.10.1-10.1
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• 1996

• 천문학회지
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• 제48권2호
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• pp.155-164
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• 2015

In Kang (2015) we calculated the acceleration of cosmic-ray electrons at weak spherical shocks that are expected to form in the cluster outskirts, and estimated the diffuse synchrotron radiation emitted by those electrons. There we demonstrated that, at decelerating spherical shocks, the volume integrated spectra of both electrons and radiation deviate significantly from the test-particle power-laws predicted for constant planar shocks, because the shock compression ratio and the flux of inject electrons decrease in time. In this study, we consider spherical blast waves propagating through a constant density core surrounded by an isothermal halo with ρ ∝ r⁻ⁿ in order to explore how the deceleration of the shock affects the radio emission from accelerated electrons. The surface brightness profile and the volumeintegrated radio spectrum of the model shocks are calculated by assuming a ribbon-like shock surface on a spherical shell and the associated downstream region of relativistic electrons. If the postshock magnetic field strength is about 0.7 or 7 µG, at the shock age of ∼ 50 Myr, the volume-integrated radio spectrum steepens gradually with the spectral index from α_inj to α_inj + 0.5 over 0.1–10 GHz, where α_inj is the injection index at the shock position expected from the diffusive shock acceleration theory. Such gradual steepening could explain the curved radio spectrum of the radio relic in cluster A2266, which was interpreted as a broken power-law by Trasatti et al. (2015), if the relic shock is young enough so that the break frequency is around 1 GHz.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2021년도 추계학술대회
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• pp.119-120
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• 2021

국내 어선의 해상업무용 무선설비 및 항해 장비는 IEC 60945를 준용한 KN60945_60533의 성능기준을 따르도록 규정하고 있다. LTE-M 송수신기는 해상업무용 무선설비에 포함되지 않아 기존 선박용 장비들과 동일한 기준을 적용받지 않기 때문에, 방사 방출 또는 전도 방출에 의한 간섭으로 기존 해상업무용 무선설비에 가청 소음을 발생하는 원인이 되고 있다. 본 논문에서는 초고속해상무선통신망 무선설비를 소형선으로 확대보급하기 위해 선결 사항으로 위와 같은 간섭 영향의 원인을 분석하고 관련 대책을 검증 제안한다.

• 천문학회지
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• 제37권2호
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• pp.61-77
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• 2004

We have searched for HI 21 cm line emission from shocked atomic gas associated with southern supernova remnants (SNRs) using data from the Southern Galactic Plane Survey. Among the 97 sources studied, we have detected 10 SNRs with high-velocity HI emission confined to the SNR. The large velocity and the spatial confinement suggest that the emission is likely from the gas accelerated by the SN blast wave. We also detected 22 SNRs which show HI emission significantly brighter than the surrounding regions over a wide ($>10 km\;s^{-1}$) velocity interval. The association with these SNRs is less certain. We present the parameters and maps of the excess emission in these SNRs. We discuss in some detail the ten individual SNRs with associated high-velocity HI emission.

• 천문학회보
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• 제40권2호
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• pp.30.1-30.1
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• 2015

Radio relics are diffuse radio sources found in the outskirts of galaxy clusters and they are thought to trace synchrotron-emitting relativistic electrons accelerated at shocks. We explore a diffusive shock acceleration (DSA) model for radio relics in which a spherical shock with the parameters relevant for the Sausage radio relic in cluster CIZA J2242.8+5301 impinges on a magnetized cloud containing fossil relativistic electrons. This model is expected to explain some observed characteristics of giant radio relics such as the relative rareness, uniform surface brightness along the length of thin arc-like radio structure, and spectral curvature in the integrated radio spectrum. We find that the observed surface brightness profile of the Sausage relic can be explained reasonably well by shocks with speed $u_s{\sim}3{\times}10^3km/s$ and sonic Mach number $M_s{\sim}3$. These shocks also produce curved radio spectra that steepen gradually over $(0.1-10){\nu}_{br}$ with a break frequency ${\nu}_{br}{\sim}1GHz$, if the duration of electron acceleration is ~60-80 Myr. However, the abrupt increase in the spectral index above ~1.5 GHz observed in the Sausage relic seems to indicate that additional physical processes, other than radiative losses, operate for electrons with the Lorentz factor, ${\gamma}_e$ > $10^4$.

• 천문학회지
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• 제29권spc1호
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• pp.261-262
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• 1996

Nearly simultaneous observations for $^{28}SiO$ v=0, 1, 2, J =3-2 transitions in 39 late-type stars have been carried out in February 1995 and 1996 with the 14 m radio telescope at Taeduk Radio Astronomy Observatory (TRAO). Observations for $^{28}SiO$ v=0, 1, 2, J=2-1 lines in the same objects have been also carried out in March 1995 and March-April 1996. The detection rate of $^{28}SiO$ v=l, J=3-2 line for the $^{28}SiO$ v=l, J=2-1 sources was $59\%$. Seventeen new detections in the $^{28}SiO$ v=l, J=3-2 transition and 4 new detections in the $^{28}SiO$ v=2, J=3-2 transition have been reported including the intensity ratios within the vibrational ladders and rotational states.