• 대한수학회논문집
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• 제26권1호
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• pp.135-149
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• 2011

Using (r, s)-preopen sets [14] and pre-${\omega}_t$-closures [6], a new kind of covering property $P^t_{({\omega}_r,s)}$-closedness is introduced in a bitopological space and several characterizations via filter bases, nets and grills [30] along with various properties of such concept are investigated. Two new types of cluster sets, namely pre-(${\omega}_r$, s)t-${\theta}_f$-cluster sets and (r, s)t-${\theta}_f$-precluster sets of functions and multifunctions between two bitopological spaces are introduced. Several properties of pre-(${\omega}_r$, s)t-${\theta}_f$-cluster sets are investigated and using the degeneracy of such cluster sets, some new characterizations of some separation axioms in topological spaces or in bitopological spaces are obtained. A sufficient condition for $P^t_{({\omega}_r,s)}$-closedness has also been established in terms of pre-(${\omega}_r$, s)t-${\theta}_f$-cluster sets.

• 보건교육건강증진학회지
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• 제10권2호
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• pp.86-99
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• 1993

본 연구의 목적은 한국청소년들의 건강행동실태를 파악하기 위한 것이다. 본 연구의 의의는 미국에서 행해지고 있는 청소년의 건강유지 및 증진과 아울러 성인병이나 조기사망에 대한 역학적인 접근방식을 한국청소년을 대상으로 하여 응용하는 데 있다. 이 연구에 사용된 연구도구는 미국의 Centers for Disease Control에서 청소년의 건강행동을 역학적으로 연구하기 위해 개발한 Youth Risk Behavior Survey를 한국 사회환경의 요구도에 맞게 수정한 것이다. 본 연구는 한국인 청소년들의 건강행동을 조사하기 위한 타당성있는 연구도구를 개발하기 위해 4개의 단계로 구성되어 있다. 두번의 focus group discussion과 pilot test, 그리고 실제조사로 이루어져 있다. 서울지역의 중.고등학생을 대표할 표본추출은 cluster sampling을 사용하였다. Cluster는 본 연구에서 구분한 서울의 지리적인 구역들, 즉 북부, 남부, 그리고 산업지역을 포함했고, 남자학교, 여자학교, 남녀공학학교를 포함했다. 총38개 중.고교 학생 4,747명이 조사되었다. 약 52.4%의 응답자가 심각하게 자살을 생각해본 적이 있다고 답했다. 그리고 23.6%가 설문조사전 30일 중에 담배를 피운 적이 있다고 응답했으며 49.7%는 설문조사전 30일중에 술을 마신 적이 있다고 답했다. 약 29%가 설문조사전 30일 중에 싸움에 가담한 적이 있다고 응답했다. 본 연구에서 조사된 건강관련행동 (건강위험행동 포함)들은 성, 연령, 성적, 사회경제적 위치, 학교 종류, 그리고 서울의 지리적인 구역에 따라 다양하게 나타났다. 남학생이 여학생보다 더 간강위험행동을 나타내었다. 건강위험행동은 나이가 증가함에 따라 증가했다. 사회경제적 위치가 낮다고 응답한 학생들과 학급에서 성적이 하위라고 응답한 학생들의 경우 건강위험행동은 더 많이 나타났다.

• 한국경제지리학회지
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• 제25권3호
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• pp.420-450
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• 2022

최근 테슬라나 삼성전자 등 글로벌 기업들이 미국 텍사스 주로 본사를 이전하거나, 기존 생산시설의 확장 또는 신규 지역거점본부를 설립하는 현상이 두드러지게 나타나고 있다. 이른바 '텍시트(Texit)'로까지 명명되는 텍사스를 향한 기업들의 투자 행렬은 2000년대부터 가속화되어 오고 있는 현상이며, 지리적으로 댈러스-포트워스, 휴스턴, 오스틴, 샌안토니오를 중심으로 하는 대도시권 산업클러스터에 집중되어 있다. 이를 배경으로 본 논문은 텍사스 대도시권 산업클러스터의 부문별 현황과 지리적 특징을 고찰하고, 강력한 제도적 행위자로서 텍사스 주정부가 어떠한 산업클러스터 발전 정책을 추진해 왔는지를 살펴본다. 연구 결과, 텍사스의 시장자유주의 정책, 다각화된 인센티브 프로그램, 대도시권별 특성화 등이 주정부 발전 전략의 핵심을 이루고 있는 것으로 파악되었다. 텍사스는 실리콘밸리와 같이 보헤미안적 자유주의에 바탕을 둔 국지화된 기업가주의와 그에 따른 창업이 활발하지는 않지만, 강력한 주정부의 리더십 하에서 낮은 세율과 규제완화, 저렴한 토지와 인프라, 우수한 교육제도와 인적자본 등에서 경쟁우위를 형성하여 이를 외부 투자유치에 적극적으로 활용하고 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권1호
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• pp.168-186
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• 2016

In this paper, we investigate the degrees of freedom (DoF) of a two-cluster multiple-input multiple-output (MIMO) multiway relay interference channel (mRIC), where there are two relays and two users per cluster. In this channel, users within the same cluster exchange messages among themselves with the help of two relays.We first obtain the DoF upper bound of the considered MIMO mRIC based on cut-set bound. Then, we propose a novel transmission strategy, blind interference neutralization (BIN), to approach the DoF upper bound. This new method utilizes the overheard information at two relays and focuses on the beamforming matrix designs at two relays so that the channel state information (CSI) at users is not required. Through theoretical analysis and numerical simulations, we show that the DoF upper bound can be obtained by using the BIN scheme. From simulation results, we show that the proposed BIN scheme can provide significant performance gain over the conventional time division multiple access (TDMA) scheme in terms of DoF. In addition, we show that the BIN scheme is a superior approach to the existing signal space alignment (SSA) schemes for the considered mRIC.

• 천문학회보
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• 제42권1호
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• pp.51.2-51.2
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• 2017

Diffuse radio relics are often detected in merging galaxy clusters and are emitted by synchrotron process. Radio relics are believed to trace the shock waves in the intracluster medium induced by ram pressure during a major cluster merger. Radio halos and relics are found in approximately 50 galaxy clusters to date that are all in a state of merging. The rarest of these galaxy clusters contain pairs of relics of similar brightness as well as a radio halo. The massive galaxy cluster PLCKG287.0+32.9 belongs to this rare population and is the second most significant detection from the Planck SZ All-sky Survey. Perhaps even more intriguing is that the radio relics are observed at vastly different distances from the X-ray peak requiring a complex merging scenario. In this study, we use weak-lensing to peer deeper into the merging scenario by reconstructing the dark matter distribution. We relate the mass distribution to the radio, X-ray, and optical emissions to provide constraints for future simulations of the merger. Fitting an NFW profile to the tangential shear we infer the mass of the cluster and discuss its implications for the merging scenario.

• 한국진공학회지
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• 제1권1호
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• pp.139-144
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• 1992

Ionized Cluster Beam(ICB) 방법을 이용하여 Polyimide(PI) 박막을 증착시켰다. 증 착된 PI 박막의 결정성과 이미드화의 정도를 투과전자현미경(TEM)과 적외선 분광 스펙트럼 (FT-IR)을 이용하여 분석하였다. 최적의 조건에서 증착된 PI 박막은 이미드화가 최대로 증 가하였고 결정구조를 가짐을 관찰할 수 있었다. 이것은 다른 방법으로 제작된 PI 박막과 비 교할 때 훨씬 우수한 것이다.

• 동아시아식생활학회지
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• 제26권4호
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• pp.285-296
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• 2016

This study was conducted to obtain a better understanding of American green tea consumers for increasing Korean green tea sales in the US market. In doing so, this study investigated green tea choice attributes of US consumers and segmented them based upon their perceptions about important attributes of green tea. A factor-cluster segmentation approach was used for this study. An exploratory factor analysis identified five green tea choice motives: 'Sensory', 'Diet', 'Price', 'Health', and 'Brand'. Based upon these five choice attributes, cluster analyses classified all respondents into four homogeneous subgroups: 'Highly motivated', 'Taste/Price oriented', 'Health oriented', and 'Brand oriented'. Cross-tab tests proved that green tea consumption and purchasing patterns were significantly different among the four clusters. In particular, two cluster groups representing 'Highly motivated' and 'Health oriented' groups were found to offer the most utility for further American green tea market segmentation research. Findings show that American green tea consumers include a wide range of age groups and they usually buy green tea at grocery markets. Managerial implications for all cluster groups based upon their unique characteristics are provided. Korean green tea companies can apply these findings in order to develop more effective and efficient marketing strategies to attract American consumers to buy more Korean green tea.

• 천문학회보
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• 제41권1호
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• pp.68.4-69
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• 2016

We report preliminary results of KaVA observations of central galaxies in cool-core and non cool-core clusters. The main goal is to study how cooling environments of galaxy clusters affect the central AGN activities especially at its innermost region. For KaVA observations, 7 radio bright AGNs have been selected from the extended Highest Flux Galaxy Cluster Sample (eHIFLUGCS; the X-ray flux limited & all sky galaxy cluster catalog) with various cooling timescales. In our previous KVN study, we have found that most AGNs in the cool-core clusters show the hint of pc-scale jet-like features while the ones in the non cool-core clusters do not. Using the KaVA 22/43 GHz data of a much higher resolution than the KVN resolution, we have investigated detailed pc-scale jet properties such as physical size, morphology, and radiative age. Based on the KaVA data, we discuss the effect of cluster cooling environment on the evolution of AGNs in the cluster center.

• 한국IT서비스학회지
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• 제9권3호
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• pp.95-106
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• 2010

Many researches have been performed to increase energy-efficiency in wireless sensor networks. One of primary research topics is about clustering protocols, which are adopted to configure sensor networks in the form of hierarchical structures by grouping sensor nodes into a cluster. However, legacy clustering protocols do not propose detailed methods from the perspective of implementation to determine a cluster's boundary and configure a cluster, and to communicate among clusters. Moreover, many of them involve assumptions inappropriate to apply those to a sensor field. In this paper, we have designed and implemented a new T-Clustering (Top-down Clustering) protocol, which takes into considerations a node's density, a distance between cluster heads, and remained energy of a node all together. Our proposal is a sink-node oriented top-down clustering protocol, and can form uniform clusters throughout the network. Further, it provides re-clustering functions according to the state of a network. In order to verify our protocol's feasibility, we have implemented and experimented T-Clustering protocol on Crossbow's MICAz nodes which are executed on TinyOS 2.0.2.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2469-2490
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• 2019

A low-energy adaptive clustering hierarchy (LEACH) protocol is a low-power adaptive cluster routing protocol which was proposed by MIT's Chandrakasan for sensor networks. In the LEACH protocol, the selection mode of cluster-head nodes is a random selection of cycles, which may result in uneven distribution of nodal energy and reduce the lifetime of the entire network. Hence, we propose a new selection method to enhance the lifetime of network, in this selection function, the energy consumed between nodes in the clusters and the power consumed by the transfer between the cluster head and the base station are considered at the same time. Meanwhile, the improved FTBA algorithm integrating the curve strategy is proposed to enhance local and global search capabilities. Then we combine the improved BA with LEACH, and use the intelligent algorithm to select the cluster head. Experiment results show that the improved BA has stronger optimization ability than other optimization algorithms, which the method we proposed (FTBA-TC-LEACH) is superior than the LEACH and LEACH with standard BA (SBA-LEACH). The FTBA-TC-LEACH can obviously reduce network energy consumption and enhance the lifetime of wireless sensor networks (WSNs).