• 한국컴퓨터정보학회논문지
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• 제20권12호
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• pp.15-20
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• 2015

In this paper, we propose a modified fuzzy clustering algorithm which can overcome the center deviation due to the Euclidean distance commonly used in fuzzy clustering. Among fuzzy clustering methods, Fuzzy C-Means (FCM) is the most well-known clustering algorithm and has been widely applied to various problems successfully. In FCM, however, cluster centers tend leaning to high density clusters because the Euclidean distance measure forces high density cluster to make more contribution to clustering result. Proposed is an enhanced algorithm which modifies the objective function of FCM by adding a center-scattering term to make centers not to be close due to the cluster density. The proposed method converges more to real centers with small number of iterations compared to FCM. All the strengths can be verified with experimental results.

• 천문학회보
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• 제35권2호
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• pp.82.1-82.1
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• 2010

We have investigated the spatial configuration of stars within the tidal radius of metal poor globular cluster NGC 6626 in the bulge direction. Data were obtained in near-IR J,H,Ks bands with wide-field ($20'\times20'$) detector, WIRCam at CFHT. To trace the stellar density around target cluster, we sorted cluster's member stars by using a mask filtering algorithm and weighting the stars on the color-magnitude diagram. From the weighted surface density map, we found that the stellar spatial distributions within the tidal radius appear asymmetric and distorted features. Especially, we found that more prominent over-density features are extending toward the direction of Galactic plane rather than toward the directions of the Galactic center and its orbital motion. This orientation of the stellar density distribution can be interpreted with result of disk-shock effect of the Galaxy that the cluster had been experienced. Indeed, this over-density feature are well represented in the radial surface density profile for different angular sections. As one of the metal poor globular clusters with extended horizontal branch (EHB) in the bulge direction, NGC 6626 is kinematically decoupled from the normal clusters and known to have disk motion of peculiar motion. Thus, our result will be able to add further constraints to understand the origin of this cluster and the formation of bulge region in early universe.

• 천문학회보
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• 제45권1호
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• pp.48.2-48.2
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• 2020

We present a new void definition that connects voids with clusters, the high-density counterpart. We use a pair of ΛCDM simulations whose initial density fields are sign inverted versions to each other, and study the relation between the effective void volume and the corresponding cluster mass. Massive cluster halos (M ≥ 1013M⊙/h) are identified in one simulation at z=0 by linking dark matter particles. The corresponding void to each cluster is defined in the other simulation as the region occupied by the member particles of the cluster. We find a universal functional form of density profiles at z=0 and 1. We also find a power-law relation between the void effective radius and the corresponding cluster mass. Based on these findings, we identify cluster-counterpart voids directly from a density field without using the pair information by utilizing three parameters such as the smoothing scale, density threshold, and minimum core fraction. We identified voids corresponding to clusters more massive than M ≥ 3 × 1014M⊙/h at approximately 70-74 \% level of completeness and reliability. Our results suggest that we can detect voids comparable to clusters of a particular mass-scale.

• 제어로봇시스템학회논문지
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• 제15권6호
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• pp.619-625
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• 2009

FastSLAM which uses the Rao-Blackwellized particle filter is one of the famous solutions to SLAM (Simultaneous Localization and Mapping) problem that estimates concurrently a robot's pose and surrounding environment. However, the particle depletion problem arises from the loss of the particle diversity in the resampling process of FastSLAM. Then, the performance of FastSLAM degenerates over the time. In this work, DIR (Density Information-based Resampling) technique is proposed to solve the particle depletion problem. First, the cluster is constructed based on the density of each particle, and the density of each cluster is computed. After that, the number of particles to be reserved in each cluster is determined using a linear method based on the distance between the highest density cluster and each cluster. Finally, the resampling process is performed by rejecting the particles which are not selected to be reserved in each cluster. The performance of the DIR proposed to solve the particle depletion problem in FastSLAM was verified in computer simulations, which significantly reduced both the RMS position error and the feature error.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권12호
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• pp.3815-3835
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• 2022

Density-based outlier detection is one of the hot issues in data mining. A point is determined as outlier on basis of the density of points near them. The existing density-based detection algorithms have high time complexity, in order to reduce the time complexity, a new outlier detection algorithm DODMD (Density-based Outlier Detection in Multidimensional Datasets) is proposed. Firstly, on the basis of ZH-tree, the concept of micro-cluster is introduced. Each leaf node is regarded as a micro-cluster, and the micro-cluster is calculated to achieve the purpose of batch filtering. In order to obtain n sets of approximate outliers quickly, a greedy method is used to calculate the boundary of LOF and mark the minimum value as LOF_min. Secondly, the outliers can filtered out by LOF_min, the real outliers are calculated, and then the result set is updated to make the boundary closer. Finally, the accuracy and efficiency of DODMD algorithm are verified on real dataset and synthetic dataset respectively.

• 천문학회보
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• 제36권2호
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• pp.53.1-53.1
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• 2011

We analyze the halo and galaxy catalogs from the Millennium simulations at redshifts z=0, 0.5, 1 to determine the alignment profiles of cluster galaxies in terms of the matter density correlation coefficient and discuss a cosmological implication our result has for breaking parameter degeneracies. For each selected cluster, we measure the alignment between the major axes of the pseudo inertia tensors from all satellites within cluster's virial radius and from only those satellites within some smaller radius. Then we average the measured values over the similar-mass sample to determine the cluster galaxy alignment profile as a function of top-hat scale difference at each redshift. It is shown that the alignment profile of cluster galaxies is well approximated by a power-law of the nonlinear density correlation coefficient that is independent of the power spectrum normalization and bias factor. The alignment profile of cluster galaxies is found to have higher amplitude and lower power-law index when averaged over the larger-mass sample and to have rather weak redshift-dependence. This result is consistent with the picture that the satellite galaxies retain the memory of the external tidal fields right after merging and infalling into the clusters but they gradually lose the initial alignment tendency as the cluster's relaxation proceeds. Demonstrating that the nonlinear density correlation coefficient varies sensitively with the density parameter and neutrino mass fraction, we discuss a potential power of the cluster galaxy alignment profile as an independent probe of cosmology.

• 대한임베디드공학회논문지
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• 제10권6호
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• pp.381-390
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• 2015

The efficient design of a transport protocol contributes to energy conservation as well as performance improvement in wireless sensor networks (WSNs). In this paper, a node-density-aware transport protocol (NDTP) for intra-cluster transmissions in WSNs for monitoring physical attributes is proposed, which takes node density into account to mitigate congestion in intra-cluster transmissions. In the proposed NDTP, the maximum active time and queue length of cluster heads are restricted to reduce energy consumption. This is mainly because cluster heads do more works and consume more energy than normal sensor nodes. According to the performance evaluation results, the proposed NDTP outperforms the conventional protocol remarkably in terms of network lifetime, congestion frequency, and packet error rate.

• 천문학회지
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• 제29권2호
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• pp.269-278
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• 1996

We present the color-magnitude diagrams (CMD) of more than 24,000 stars in the field of an intermediate age open cluster M11, based on wide field CCD imaging. The morphology of the CMDs varies strikingly as the distance from the center of the cluster increases. From the surface number density analysis, we confirm the mass segregation effect in this cluster: the bright, massive stars are centrally more concetrated than the faint, low mass stars. The slope of the field-corrected surface density with respect to magnitude progressively increases as the radius increases, up to r = 5'. Most of the field stars in or near the cluster main sequence band and in the bright part of the red stars in the CMDs appear to be nearly at the same distance as M11, and they are considered to be the major component of disk stars in the Sagittarius-Carina arm.

• 천문학회보
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• 제36권1호
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• pp.62.2-62.2
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• 2011

It is well known that the cluster environment can change the atomic gas properties of galaxies through tidal interactions and/or by the hot cluster medium. Meanwhile, the molecular gas is expected to be less vulnerable to its surroundings due to its higher density, and no obvious influence of the environment on the molecular gas properties had been found among cluster spirals until recently. However, in a recent study by Fumagalli et al. (2009) of a sub-sample of Virgo spirals, it has been suggested that HI deficient galaxies can be also CO deficient. In order to further investigate if the HI deficiency indeed can result in the deficiency in molecular gas content, we compare the global CO and HI gas properties of Virgo spirals with those of galaxies in the Ursa Major cluster and the Pisces cluster, much lower density environments than Virgo. We discuss possible consequences of molecular gas deficiency in star formation activity of spiral galaxies in high density environment.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.34.4-34.4
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• 2010

We present the properties of globular cluster systems for 10 early-type galaxies in low density environments obtained using deep images from the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). Using the ACS Virgo Cluster Survey as a counterpart in high-density environments, we investigate the role of environment in determining the properties of their globular cluster systems. We detect a strong colour bimodality of globular cluster systems in half of our galaxy sample. It is found that there is a strong correlation between the colour and richness of globular cluster populations and their host galaxy luminosities: the less bright galaxies possess bluer and fewer globular clusters as also seen in rich cluster environments. However, the mean colour of globular clusters in our field sample are slightly bluer than those in cluster environments at a given galaxy luminosity, and the colour of the red population has a steeper slope with absolute luminosity. By employing the YEPS simple stellar population model, the colour offset corresponds to metallicity difference of $\Delta$[F e/H ] ~ 0.15 - 1.20 or an age difference of $\Delta$age ~ 2 Gyr on average, implying that GCs in field galaxies appear to be either less metal-rich or younger than those in cluster galaxies. Although we have found that galaxy environment has a subtle effect on the formation and metal enrichment of GC systems, host galaxy mass is the primary factor that determines the stellar populations of GCs and the galaxy itself.