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        검색결과 16

        1.
        2019.02 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        The KVN(Korean VLBI Network)-style simultaneous multi-frequency receiving mode is demonstrated to be promising for mm-VLBI observations. Recently, other Very long baseline interferometry (VLBI) facilities all over the globe start to implement compatible optics systems. Simultaneous dual/multi-frequency VLBI observations at mm wavelengths with international baselines are thus possible. In this paper, we present the results from the first successful simultaneous 22/43 GHz dualfrequency observation with KaVA(KVN and VERA array), including images and astrometric results. Our analysis shows that the newly implemented simultaneous receiving system has brought a significant extension of the coherence time of the 43 GHz visibility phases along the international baselines. The astrometric results obtained with KaVA are consistent with those obtained with the independent analysis of the KVN data. Our results thus confirm the good performance of the simultaneous receiving systems for the non-KVN stations. Future simultaneous observations with more global stations bring even higher sensitivity and micro-arcsecond level astrometric measurements of the targets.
        4,000원
        9.
        2015.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) is the rst international VLBI array dedicated to high-frequency (23 GHz (K-band) and 43 GHz (Q-band)) observations in East Asia. To evaluate the imagine capability of KaVA, we performed imaging observations of three bright active galactic nuclei (AGNs) known for their complex morphologies: 4C 39.25, 3C 273, and M87 by KaVA at K-/Q-band. Our KaVA images reveal extended out ows with complex substructure such as knots and limb brightening, in agreement with previous observations by other VLBI facilities. Angular resolutions are better than 1.4 and 0.8 milliarcsecond (max) at K-/Q-band, respectively. KaVA achieves a high dynamic range of ~1000, more than three times the value achieved by VERA. We conclude that KaVA is a powerful array with a great potential for the study of AGN out ows, at least comparable to the best existing radio interferometric arrays.
        3,000원
        10.
        2015.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        KaVA (KVN and VERA Array) is a new combined VLBI array composed of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). Here, we report the following two issues. (1) We review the initial results of imaging observations of M87 at 23 GHz following Niinuma et al. (2014). The KaVA images reveal extended out ows including complex substructures such as knots and limb-brightening, in agreement with previous VLBI observations. KaVA achieves a high dynamic range of ~1000, more than three times better than that achieved by VERA alone. (2) Based on subsequent observations and discussions led by the KaVA AGN SubWorking Group, we set monitoring observations of Sgr A* and M87 as our Key Science Project (hereafter KSP) because of the closeness and largeness of their central super-massive black holes. The main science goals of the KSP are (i) testing the magnetically- driven-jet paradigm by mapping velocity fields of the M87 jet, and (ii) obtaining tight constraints on physical properties of the radio emitting region in Sgr A*. Towards KSP, we show the first preliminary images of M87 at 23 GHz and Sgr A* at 43 GHz with the bandwidth of 256 MHz.
        3,000원
        11.
        2015.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this paper we introduce the Plasma Physics of Active Galactic Nuclei project, which is an ongoing experiment with Korean VLBI Network (KVN) and KVN and VERA Array (KaVA) to study multi- frequency polarimetric properties on parsec scales of active galaxies. The goal of the project is to improve our understanding of fundamental jet physics, especially evolution of the relativistic out ow coupled with the large-scale magnetic field. We selected six radio-loud AGN as our targets. So far we (i) detected resolved emissions regions at 86 and 129 GHz on VLBI scales, (ii) constructed 2D spectral index maps of the out ows, and (iii) found polarizations at 22 and 43 GHz for a few targets. Here we present spectral index distributions of 3C 120 between 22 and 43 GHz and a linear polarization map of BL Lac at 43 GHz obtained with KVN.
        3,000원
        16.
        2016.12 KCI 등재 서비스 종료(열람 제한)
        카바(Piper methysticum, P. methysticum)는 비뇨생식기 질환, 류머티즘, 위장 장애, 호흡기 자극 및 폐 통증에 대해 전통적으로 사용되는 것으로 알려져 있다. 본 연구에서는 카바에서 분리된 flavokavain C (FKC)가 염증성 유전자의 발현에 관여하는 전사인자인 핵요소-κB (NF-κB) 의존성 산화 질소(NO) 생산 및 산화 질소 합성 효소(iNOS)의 발현에 리포폴리사카라이드(LPS) 처리된 대식세포에서 항 염증 활성을 나타 낸다는 것을 확인하였다. FKC는 과산화수소와 같은 반응성 산소 종(ROS)의 축적을 억제하고, LPS로 유도된 NO 생성 및 각종 염증 관련 유전자(iNOS, IL-1β, IL-6)의 발현을 NF-κB 및 MAPKs (ERK 및 JNK)의 억제를 통해 농도 의존적으로 줄일 수 있었다. 결론적으로, 이러한 결과는 FKC가 NF-κB 경로와 MAPKs 포 함한 염증 프로세스를 억제하는 능력을 가지고 있음을 나타내며, 이는 항 염증 및 항산화 효능 기반 기능성 화장 품에 적용될 수 있음을 암시한다.