• Ocean and Polar Research
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• 제42권4호
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• pp.271-281
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• 2020

We investigated mesozooplankton in the Yellow Sea in spring to understand its community structure and relationship with environmental factors. Total mesozooplankton density ranged from 1,542 to 7,367 ind. m-3 and the biomass ranged from 3 to 42 mg C m-3. The total density and biomass had a positive relationship with chlorophyll-a (chl-a) concentration. The mesozooplankton community was divided into two groups at 125.5 E by cluster analysis: one was an inshore group and the other was an offshore group. The inshore group of mesozooplankton was of high density but low diversity, while the offshore group was of high diversity but low density. Copepod Acartia hongi and its copepodites were the most abundant species, comprising 27.8% of the total mesozooplankton density. A. hongi was especially abundant at the inshore, serving as the indicator species of the inshore group. Redundancy analysis found a positive relationship between the density of A. hongi and chl-a concentration. Oithona similis and Centropages abdominalis were 2nd and 3rd dominant species comprising 9 and 7% of the total density, respectively. The density of O. similis was positively related to water depth, but C. abdominalis was related to chl-a concentration. Chl-a concentration seems to influence significantly the mesozooplankton community structure in the Yellow Sea in spring, rather than water temperature or salinity.

• 한국도로학회논문집
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• 제14권4호
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• pp.133-140
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• 2012

PURPOSES : Traffic situation of Seoul City is different each administrative district. because each administrative district population, average travel speed, etc are different. thus, regionally differentiated policy is necessary. METHODS : In this study, first, it is to implement the cluster analysis using the traffic factor of twenty-five administrative districts in Seoul, categorize it into the cluster and understand the properties. second, related factors of speed were derived. and method to increase the speed was investigated. we choose the eleven traffic factors such as the number of traffic accident cases, total length, speed, the number of cross section, the number of cross section per km, the rate of roads, registered cars, population attending office and school, population density, area. RESULTS : In the results, first, we could categorize the Seoul-City administrative district into three clusters. in order to find Factors associated with speed a simple regression analysis was performed. and the number of intersections per km is closely related to the speed. CONCLUSIONS : Through this study, transportation policies reflecting local traffic-related characteristics are required.

• 한국지능시스템학회논문지
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• 제17권2호
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• pp.196-201
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• 2007

Fuzzy C-Means (FCM) 알고리즘은 probabilitic 멤버쉽을 사용하는 클러스터링 방법으로서 널리 쓰이고 있다. 하지만 이 방법은 노이즈에 대하여 민감한 성질을 가진다는 단점이 있다. 따라서 본 논문에서는 이러한 노이즈에 민감한 성질을 보완하기 위해서 데이터의 밀도추정을 이용하여 새로운 FCM 알고리즘을 제안한다. 본 논문에서 제안된 알고리즘은 FCM과 비슷한 성능의 클러스터링 수행이 가능하며, 노이즈가 포함된 데이터에서는 FCM보다 더 나은 성능을 보여준다.

• Ocean Science Journal
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• 제40권3호
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• pp.119-125
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• 2005

Qualitative and quantitative composition of meiobenthos was studied in Amursky Bay (Peter the Great Bay, the East Sea). Ten taxonomic groups were found, where nematodes were dominant. Density of meiobenthos in ground sediments of the Bay were not uniform, and the average density was measured at $126.4{\pm}62.3ind.mo^{-2}$. 56 species of nematodes were detected, and dominant species were Sabatieria palmaris, Paracanthonchus macrodon, Sphaerolaimus limosus, S. gracilis and Oncholaimium ramosum. Five taxocenes of nematodes were allocated based on the results of cluster analysis and species domination according to density. Low diversity in species composition of nematodes was noted in the northwestern part of the Bay, which is a zone of desalination, and in the eastern part, which is exposed to household drains.

• Bulletin of the Korean Chemical Society
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• 제27권9호
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• pp.1453-1455
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• 2006

• 천문학회지
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• 제29권2호
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• pp.119-136
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• 1996

To examine the effect of neighboring galaxies on the gravitational lensing statistics, we performed numerical simulations of lensing by many galaxies. The models consist of a galaxy in the rich cluster like Coma, or a galaxy surrounded by field galaxies in $\Omega_0 = 1$ universe with $\Omega_{gal} = 0.1,\;\Omega_{gal} = 0.3\;or\;\Omega_{gal}=1.0\;,\;where\;\Omega_{gal}$ is the total mass in galaxies. Field galaxies either have the same mass or follow Schechter luminosity function and luminosity-velocity relation. Each lensing galaxy is assumed to be singular isothermal sphere (SIS) with finite cutoff radius. In most simulations, the lensing is mainly due to the single galaxy. But in $\Omega_{gal} = 3$ universe, one out of five simulations have 'collective lensing' event in which more than two galaxies collectively produce multiple images. These cases cannot be incorporated into the simple 'standard' lensing statistics calculations. In cases where 'collective lensing' does not occur, distribution of image separation changes from delta function to bimodal distribution due to shear induced by the surrounding galaxies. The amount of spread in the distribution is from a few $\%\;up\;to\;50\%$ of the mean image separation in case when the galaxy is in the Coma-like cluster or when the galaxy is in the field with $\Omega_{gal} = 0.1\;or\;\Omega_{gal}=0.3.$ The mean of the image separation changes less than $5\%$ compared with a single lens case. Cross section for multiple image lensing turns out to be relatively insensitive to the presence of the neighboring galaxies, changing less than $5\%$ for Coma-like cluster and $\Omega_{gal}=0.1,\;0.3$ universe cases. So we conclude that Coma-like cluster or field galaxies whose total mass density $\Omega_{gal}<0.3$ do not significantly affect the probability of multiple image lensing if we exclude the 'collective lensing' cases. However, the distribution of the image separations can be significantly affected especially if the 'collective lensing' cases are included. Therefore, the effects of surrounding galaxies may not be negligible when statistics of lensing is used to deduce the cosmological informations.

• 천문학회보
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• 제41권1호
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• pp.33.1-33.1
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• 2016

Dwarf elliptical galaxies (dEs), the most abundant galaxy type in clusters, were recently shown to exhibit a wide variety in their properties. Particularly, the presence of blue cores in some dEs, what we call dE(bc), supports the scenario of late-type galaxy infall and subsequent transformation into red, quiescent dEs. While several transformation mechanisms for these dE(bc)s within cluster environment have been proposed, all these processes are able to explain only some of the observational properties of dEs. In this context, internal kinematic properties of dE(bc)s provide the most crucial evidence to discriminate different processes for the formation of these galaxies. We present Gemini Multi Object Spectrograph (GMOS) long-slit spectroscopy of two dE(bc)s in the Virgo cluster. We obtained radial profiles of velocity and velocity dispersion out to ~1.3 effective radius. We found that two dE(bc)s exhibit kinematically decoupled components as well as distinct peculiar features in velocity profiles, supporting the scenario of mergers. We also found that these galaxies are structurally compatible with low surface brightness component of blue compact dwarf galaxies. We suggest that a part of dE(bc)s in the Virgo Cluster were formed through galaxy merger in low density environment such as galaxy group or outskirt of the cluster, and then were quenched by subsequent effects within cluster environment.

• 한국콘텐츠학회논문지
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• 제22권5호
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• pp.26-36
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• 2022

최근 운전자의 안전과 원활한 교통을 위하여 VANET 환경에서 차량들을 클러스터로 구축하고 안전 메시지를 배포하는 연구들이 진행되고 있다. 본 논문에서 제안하는 기법은 차량의 밀도와 이동성이 높은 VANET 환경에서 V2V 통신과 V2I 통신을 통해 안전 메시지 배포를 배포하기 위한 클러스터 관리 기법을 제안한다. 제안하는 기법은 메시지 수 감소와 수신율을 높이기 위해 수신 품질, 차량이 보유한 전체 데이터 수, 이동속도, 연결된 차량 수 등을 고려한 클러스터 헤드(CH) 선출과 기존 클러스터 안전 메시지 배포 환경에서 고려하지 못했던 클러스터의 잦은 이탈과 가입을 고려하여 메시지 배포의 주체인 클러스터 헤드 후보를 유지함으로써 패킷 손실을 감소시킨다. 또한, 제안하는 기법은 RSU(Road Side Unit)와 협업하여 동작함으로써 클러스터를 활용하여 중복 메시지를 추가적으로 감소시킨다. 제안한 기법의 우수성을 입증하기 위해 메시지 패킷 손실과 RSU 처리 요청 수 관점에서 다양한 성능평가를 수행한다. 성능평가 결과 본 논문에서 제안한 클러스터 관리 기법이 기존 기법보다 우수한 성능을 보인다.

• Korean Chemical Engineering Research
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• 제56권6호
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• pp.909-913
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• 2018

A hydrocarbon trap (HT) plays an important role of controlling vehicle emissions in the so-called cold emission period by holding hydrocarbons until three way catalysts (TWCs) are thermally activated. In this study, we have investigated the adsorption characteristics of cation (H, La, K, and Ag)-exchanged ZSM-5 zeolites for hydrocarbons (propylene, n-butane, and toluene) by DFT (density functional theory)-based computational chemistry. Cation exchange is to improve the hydrothermal stability of zeolites and their adsorption capacity, thereby rendering cation-exchanged zeolites promising materials for HT. The idea of cluster approximation makes the calculation of adsorption energies superbly efficient in computation. The results showed that Ag-exchanged ZSM-5 would be the best for the adsorption of all three adsorbates, without often encountered Ag oxidation in experiments. Besides, the hydrothermal stability of La-exchanged ZSM-5 was confirmed from the change of geometrical parameters by cation exchange, and it showed good adsorption capacity for propylene and toluene. Hydrogen-exchanged ZSM-5 was also good for hydrogen adsorption, but had poor hydrothermal stability.

• 대한화학회지
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• 제67권5호
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• pp.333-338
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• 2023

In this study, the H₂O reaction with SiO clusters was investigated using ab initio Monte Carlo simulations and density functional theory calculations. Three chemistry models, PBE1/DGDZVP (Model 1), PBE1/DGDZVP (Si atom), and aug-cc-pVDZ (O and H atoms), (Model 2) and PBE1/aug-cc-pVDZ (Model 3), were used. The average bond lengths, as well as the relative and reaction energies, were calculated using Models 1, 2, and 3. The average bond lengths of Si-O and O-H are 1.67-1.75 Å and 0.96-0.97 Å, respectively, using Models 1, 2, and 3. The most stable structures were formed by the H transfer from an H₂O molecule except for Si₃O₃-H₂O-1 cluster. The Si₃O₃ cluster with H₂O exhibited the lowest reaction energy. In addition, the Bader charge distributions of the Si_nO_n and (SiO)_n-H₂O clusters with n = 1-7 were calculated using Model 1. We determined that the reaction sites between H₂O and the SiO clusters possessed the highest fraction of electrons.