• 한국통신학회논문지
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• 제27권4B호
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• pp.298-307
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• 2002

본 논문에서는 향후 이동 통신 시스템의 표준안으로 고려되는 WCDMA의 순방향 링크에서 성능 향상된 시공간 다중 사용자 수신기를 제안하고 성능을 분석한다. 제안한 수신기는, 이동 통신 환경에서 다중 경로 및 다중 사용자 간섭에 대한 분석과 시공간 다이버시티에 대한 고찰을 통해 오류 확률을 개선하고자 하는 기법으로 조건부 적응 시공간 간섭 제거기 (Constrained Adaptive Space-time Interference Canceller; C-ASTIC) 라 부른다. 논문에서는 비교를 위해 단일 사용자 및 다중 사용자 WCDMA 시스템에 대한 수식적인 성능을 분석하여 결과에 반영하였다. 또한, 제안한 C-ASTIC를 기존의 단일 안테나 간섭 제거 시스템, 최대 결합비 RAKE 수신기, 그리고 시공간 전송 다이버시티 결합 RAKE 수신기와 컴퓨터 시뮬레이션을 통해 그 성능을 비교하였다. 마지막으로 본 논문에서는 멀티미디어 환경에서의 유용성을 검증하기 위해 다중 전송률 시스템에서의 성능을 실험하였다. 결과로부터 C-ASTIC가 50% 이상의 시스템 용량 환경에서 $10^{-3}$의 BER에서 4 dB 이상의 성능 이득을 보였다.

• 천문학회보
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• 제44권1호
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• pp.35.3-35.3
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• 2019

Blazars are a subclass of active galactic nuclei (AGNs) with relativistic jets aligned with our line of sight. The jet physics is yet to be understood, but can be studied with blazar variability (e.g., flares). The highly variable blazar 3C 279 has shown a general decline of its radio flux density since 2013, but the flux density has been increasing since 2017. To better understand physical properties of 3C 279 related with the flux variations, we analyze multi-frequency new radio data obtained with Korean VLBI Network (KVN), as well as archival data from Owens Valley Radio Observatory (OVRO) and Submillimeter Array (SMA). We measure the radio spectral variability and infer the relativistic jet properties of 3C 279. The high-cadence OVRO and SMA observations are used to construct detailed light curves of the source, and KVN data supplement the spectral coverage and allow us to locate the spectral break frequencies precisely. In this talk, we present our analysis results and interpret them using a blazar jet model.

• International Journal of Aeronautical and Space Sciences
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• 제13권4호
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• pp.421-427
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• 2012

Solar Sail propulsion has been validated in space (IKAROS, 2010) and soon several more solar-sail propelled spacecraft will be flown. Using sunlight for spacecraft propulsion is not a new idea. First proposed by Frederick Tsander and Konstantin Tsiolkovsky in the 1920's, NASA's Echo 1 balloon, launched in 1960, was the first spacecraft for which the effects of solar photon pressure were measured. Solar sails reflect sunlight to achieve thrust, thus eliminating the need for costly and often very-heavy fuel. Such "propellantless" propulsion will enable whole new classes of space science and exploration missions previously not considered possible due to the propulsive-intense maneuvers and operations required.

• 대한수학회지
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• 제45권4호
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• pp.977-991
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• 2008

We characterize the boundedness and compactness of the weighted composition operator $uC_{\psi}$ from the general function space F(p, q, s) into the logarithmic Bloch space ${\beta}_L$ on the unit disk. Some necessary and sufficient conditions are given for which $uC_{\psi}$ is a bounded or a compact operator from F(p,q,s), $F_0$(p,q,s) into ${\beta}_L$, ${\beta}_L^0$ respectively.

• 천문학논총
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• 제30권2호
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• pp.629-631
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• 2015

In this proceedings, preliminary results of the KVN Source-Frequency Phase-Referencing (SFPR) observation of 3C 66A and 3C 66B are presented. The motivation of this work is to measure the core-shift of these 2 sources and study the temporal evolution of the jet opacity. Two more sources were observed as secondary reference calibrators and each source was observed at 22, 43, and 86 GHz simultaneously. Our preliminary results show that after using the observations at the lower frequency to calibrate those at the higher frequency of the same source, the residual visibility phases for each source at the higher frequencies became more aligned, and the coherence time became much longer; also, the residual phases for different sources, within 10 degrees angular separations, follow similar trends. After reference to the nearby calibrator, the SFPRed maps were obtained as well as the astrometric measurements, i.e. the combined coreshift. The measurements were found to be affected by structural blending effects because of the large beamsize of KVN, but this can be corrected with higher resolution maps (e.g. KAVA maps).

• Journal of Astronomy and Space Sciences
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• 제16권2호
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• pp.115-130
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• 1999

We report the discovery of 17 new RR Lyrae variables in the central region ($\rleq1'$) of the globular cluster M53. There candidates were identified by using the Welch & Stetson (1993) technique and confirmed by checking individual light curves in both B and V bands. The color-magnitude diagram of the horizontal-branch stars in the central region is compared with that for stars observed in the outer region by Rey et al. (1998). Including the new data from this study, we estimate the fraction of c typeRR Lyrae variables, n(c)/n(ab + c), to be 0.43 which agrees well with the valuse of other Oosterhoff group II clusters.

• Journal of Astronomy and Space Sciences
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• 제38권4호
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• pp.193-202
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• 2021

We present analysis results of Korean VLBI Network (KVN) four-band data for the highly variable blazar 3C 279. We measured the 22, 43, 86, and 129 GHz flux densities and spectral indices of the source using contemporaneous data taken over 5.6 years. We used the discrete correlation function to investigate correlations between the radio emission properties and those measured in the optical (2 × 10¹⁴ - 1.5 × 10¹⁵ Hz), X-ray (0.3-10 keV), and gamma-ray (0.1-300 GeV) bands. We found a significant correlation between the radio spectral index and gamma-ray flux without a time delay and interpreted the correlation using an extended jet scenario for blazar emission.

• Korean Journal of Mathematics
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• 제12권1호
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• pp.41-47
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• 2004

We introduce the $K_0$-proximity space as a generalization of the Efremovi$\check{c}$-proximity space. We try to show every ultrafilter in $K_0$-proximity space generates a cluster and every Cauchy cluster is a point cluster.

• Korean Journal of Mathematics
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• 제14권2호
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• pp.169-183
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• 2006

In this paper, we define and study the C-integral and the strong C-integral of functions mapping an interval [a,b] into a Banach space X. We prove that the C-integral and the strong C-integral are equivalent if and only if the Banach space is finite dimensional, We also consider the property of primitives corresponding to Banach-valued functions with respect to the C-integral and the strong C-integral.

• 교육녹색환경연구
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• 제9권1호
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• pp.41-51
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• 2010

It is high level of management activity for the fixed property of building to operating spaces for education in university campus. Therefore, this study is focused on definition of the factors for analyzing the actual conditions of space operation and application of them to C university campus in Gyeongbuk in the aspect of infrastructure of university and efficiency of space operation. These analytical factors are the rate of lecture and experimentation room, the rate of theoretical and experimental subject in curriculum and unit area for infrastructure and the rate of use, turnover rate and occupation rate per lecture for space operation. If the analytical factors of space operation are systemized as program module for space operation, the space management system of university campus will be characterized on the foundation of university information system. And it will be able to support the decision making about space management. It needs to integrate various type of information and data of university to increase the efficiency of decision making.