• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.77.2-77.2
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• 2015

Galaxies are known to evolve passively in the cluster environment. Indeed, much evidence for HI stripping has been found in cluster galaxies to date, which is likely to be connected to their low star formation rate. What is still puzzling however, is that the molecular gas, which is believed to be more directly related to star formation, shows no significant difference in its fraction between the cluster population and the field galaxies. Therefore, HI stripping alone does not seem to be enough to fully understand how galaxies become passive in galaxy clusters. Intriguingly, our recent high resolution CO study of a subsample of Virgo spirals which are undergoing strong ICM pressure has revealed a highly disturbed molecular gas morphology and kinematics. The morphological and kinematical peculiarities in their CO data have many properties in common with those of HI gas in the sample, indicating that strong ICM pressure in fact can have impacts on dense gas deep inside of a galaxy. This implies that it is the molecular gas conditions rather than the molecular gas stripping which is more responsible for quenching of star formation in cluster galaxies. In this study, using multi transitions of 12CO and 13CO, we investigate the density and temperature distributions of CO gas of a Virgo spiral galaxy, NGC 4402 to probe the physical and chemical properties of molecular gas and their relations to star formation activities.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.9
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• pp.652-662
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• 2001

A WDM/SCM multiple access protocol suitable for optical double star networks is proposed. A node-grouping scheme is employed in the protocol, which is accomplished by connecting some nodes through passive star sub-hubs forming a group. The resulting multiple groups in a network are then connected through a central passive star hub resulting in a passive double star network. Each group is pre-assigned a WDM channel as its home channel, and SCM channels are used to identify the packet reception at each node. [n the proposed protocol, the average packet delay is remarkably reduced since the frame consists of the number of groups rather than the number of network nodes. Furthermore, additional reduction of the average packet delay is achieved by limiting the propagation paths of control packets to the roundtrip between source nodes and sub-hub using a double star network. It is shown in the performance evaluations using analytic and simulation model that the proposed protocol has the advantages of the higher channel utilization and excellent network throughput and average packet delay characteristic.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.84.1-84.1
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• 2012

One of the most intriguing questions regarding black hole (BH)-galaxy co-evolution picture is how the BH accretion, or active galactic nucleus (AGN) activity is linked to star formation (SF) activity. While it is suggested that AGN luminosity of quasars correlates with SF luminosity, it is still unclear how AGN activity is connected to SF activity based on host galaxy properties. Utilizing AKARI's unique slit-less spectroscopic capability and wavelength coverage, we probed star formation activity of several types of AGNs by measuring the PAH 3.3 ${\mu}m$ emission. First, we detected the PAH 3.3 ${\mu}m$ emission from seven out of 27 Seyfert type-1 galaxies at z~0.36. While these galaxies deviate significantly from the local Mbh-${\sigma}$ relation meaning their black holes proceed the host galaxies in terms of evolution, they appear to follow the correlation between nuclear SF and AGN activities of local Seyfert type-1 galaxies. This implies that SF and AGN activities are directly connected at the nuclear region for these Seyfert type-1 AGNs. We also obtained 2-5 ${\mu}m$ spectra for subsamples of Quasar Spectroscopic Observation in Near-infrared Grism (QSONG) which consists of reverberation-mapped AGNs and PG-QSOs. We detected the PAH 3.3 ${\mu}m$ emission from 16 out of 31 reverberation-mapped AGNs and 10 out of 49 PG-QSOs and measured their line strengths. We present the correlations between SF and AGN activities and discuss if there is any dependency of the correlations on properties of host galaxies, such as morphology, or the presence of radio jets.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.37.2-37.2
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• 2012

The A2199 supercluster at z=0.03 is one of the most massive system in nearby universe. In this supercluster, A2199 is kinematically connected to A2197 and several infalling galaxy groups. Thanks to a high-density environment and complex structures around A2199, this supercluster is an excellent laboratory for studying galaxy evolution. We determine the membership of galaxies in the supercluster using radial velocities of galaxies drawn from the SDSS spectroscopic DR7 data. We present an infrared view of this supercluster using AKARI and WISE data. We compare spatial distributions between early- and late-type galaxies, and also AGNs and star-forming galaxies. We also investigate how local and cluster-scale environments affect galaxy properties, such as IR-properties, star formation rates, and morphology transformations.

• International Journal of Aeronautical and Space Sciences
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• v.5 no.1
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• pp.83-93
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• 2004

A new alignment calibration method of attitude sensors for the precisionattitude determination of a spacecraft based on the extended Kalman filter is proposed.The proposed method is divided into two steps connected in series: the gyro and thestar tracker calibration. For gyro calibration, alignment errors and scale factor errorsare estimated during the calibration maneuver under the assumption of a perfect startracker. Estimation of the alignment errors of the star trackers and compensation ofthe gyro calibration errors are then performed using the measurements includingpayload information. Performance of the proposed method are demonstrated bynumerical simulations.

• Journal of the Chungcheong Mathematical Society
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• v.19 no.4
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• pp.403-408
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• 2006

A pebbling move on a connected graph G is taking two pebbles off of one vertex and placing one of them on an adjacent vertex. The domination cover pebbling number ${\psi}(G)$ is the minimum number of pebbles required so that any initial configuration of pebbles can be transformed by a sequence of pebbling moves so that the set of vertices that contain pebbles forms a domination set of G. We determine the domination cover pebbling number for fans, fuses, and pseudo-star.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.33.3-34
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• 2021

In LCDM universe, large, massive structures, like galaxy clusters, grow through the successive accretion/mergers of smaller structures. Therefore, at high redshift, unlike local, it is expected that there would be plenty of galaxy clusters which are still growing. Here, we report the discovery of a high-redshift (z~1) galaxy cluster which is in its active formation stage. This cluster is well connected to the large scale overdense environment and contains high fraction of star-forming galaxies, providing a good example supporting our previously suggested 'Web-feeding model'.

• Journal of the Korean Mathematical Society
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• v.49 no.5
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• pp.1031-1051
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• 2012

In this paper, we will investigate the concept of the torsion-graph of an R-module M, in which the set $T(M)^*$ makes up the vertices of the corresponding torsion graph, ${\Gamma}(M)$, with any two distinct vertices forming an edge if $[x:M][y:M]M=0$. We prove that, if ${\Gamma}(M)$ contains a cycle, then $gr({\Gamma}(M)){\leq}4$ and ${\Gamma}(M)$ has a connected induced subgraph ${\overline{\Gamma}}(M)$ with vertex set $\{m{\in}T(M)^*{\mid}Ann(m)M{\neq}0\}$ and diam$({\overline{\Gamma}}(M)){\leq}3$. Moreover, if M is a multiplication R-module, then ${\overline{\Gamma}}(M)$ is a maximal connected subgraph of ${\Gamma}(M)$. Also ${\overline{\Gamma}}(M)$ and ${\overline{\Gamma}}(S^{-1}M)$ are isomorphic graphs, where $S=R{\backslash}Z(M)$. Furthermore, we show that, if ${\overline{\Gamma}}(M)$ is uniquely complemented, then $S^{-1}M$ is a von Neumann regular module or ${\overline{\Gamma}}(M)$ is a star graph.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.281-284
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• 2012

We utilize AKARI's slitless spectroscopic capability to detect the $3.3{\mu}m$ polycyclic aromatic hydrocarbons (PAHs) emission and measure star formation (SF) activity for various AKARI programs. First, we obtain $2{\sim}5{\mu}m$ spectra of 20 flux-limited galaxies with mixed SED classes in order to calibrate the $3.3{\mu}m$ PAH luminosity ($L_{PAH3.3}$) as a star formation rate (SFR) indicator. We find that $L_{PAH3.3}$ correlates with $L_{IR}$ as well as with the $6.2{\mu}m$ PAH luminosity ($L_{PAH6.2}$). The correlations does not depend on SED classes. We find that ULIRGs deviate from the correlation between PAH luminosities and $L_{IR}$, while they do not for the correlation between PAH luminosities. We suggest possible effects to cause this deviation. On the other hand, how AGN activity is linked to SB activity is one of the most intriguing questions. While it is suggested that AGN luminosity of quasars correlates with starburst (SB) luminosity, it is still unclear how AGN activity is connected to SF activity based on host galaxy properties. We are measuring SFRs for the LQSONG sample consisting of reverberation mapped AGNs and PG-QSOs. This is an extension of the ASCSG program by which we investigated the connection between SB and AGN activities for Seyferts type 1s at z ~ 0.36. While we found no strong correlation between $L_{PAH3.3}$ and AGN luminosity for these Seyferts 1s, $L_{PAH3.3}$ measured from the central part of galaxies correlates with AGN luminosity, implying that SB and AGN activities are directly connected in the nuclear region.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.40.2-40.2
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• 2017

At local, majority of galaxies in the dense environment, such as galaxy cluster, are red and quiescent with little star-formation (SF) activity. However, a different picture emerges as we go to high redshift: (1) there exist non-negligible fraction of galaxies still forming stars actively even in dense environment, and (2) there is a significant cluster-by-cluster variation in the SF properties, such as quiescent galaxy fraction. In this presentation, we show the results of our study about the variation of quiescent galaxy fraction among high-redshift (z~1) galaxy clusters, based on the multi-object spectroscopic (MOS) observation with IMACS on the Magellan telescope. Our main result is that galaxy clusters which are connected with significant large-scale structure (LSS), well beyond the cluster scale, are more active in their SF activity, i.e., the quiescent galaxy fraction for these clusters is lower compared to the clusters which are detached from LSS.