• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.3
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• pp.608-614
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• 2009

In wireless sensor networks, there are hundreds to thousands of small battery powered devices which are called sensors. As sensors have a limited energy resources, there is a need to use it effectively. A clustering based routing protocol forms clusters by distributed algorithm. Member nodes send their data to their cluster heads then cluster heads integrate data and send to sink node. In this paper we propose an energy efficient cluster-head selection algorithm. We have used some factors(a previous cluster head experience, a existence of data to transmit and an information that neighbors have data or not) to select optimum cluster-head and eventually improve network lifetime. Our simulation results show its effectiveness in balancing energy consumption and prolonging the network lifetime compared with LEACH and HEED algorithms.

• Journal of Periodontal and Implant Science
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• v.26 no.3
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• pp.725-734
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• 1996

The present study has been performed to revise the forms of early-onset periodontitis(EOP) into the homogeneous phenotypic subsets by cluster analysis using sets of clinical parameters. Retrospective radiographic interproximal alveolar bone levels were measured from cemento-enamel junctions on patients who have previously been diagnosed as having one of EOP during last 5 years. Mean interproximal bone levels(BL) and mesial bone level(Ratio) of 1st molars relative to mean interproximal bone levels of adjacent teeth(lst and 2nd premolars and canines)were calculated on each patient. Using parameters BL and Ratio(BR group) or BL, Ratio and age(BRA group), cluster analysis was performed to revise EOP patients into homogeneous subsets. At least three or four cluster could be homogeneously formed both in BR or BRA groups with statistically significant differences in parameters used among clusters as evidenced by MANOVA test. It was shown that the greater the BL, the smaller the Ratio was. It was also evident that mean interproximal bone levels were lowest aroud 1st molars and/or incisors regardless of cluster types. The results has provided cluster-based studies for identifying laboratory markers responsible for the development of EOP subsets.

• Journal of the Korean Academic Society of Industrial Cluster
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• v.3 no.1
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• pp.11-25
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• 2009

Wind power is the most rapidly growing energy source in the world. Increased focus on climate changes and renewable energy is supporting the wind power industry in gaining momentum. Noksan wind cluster in Busan has been a major area in manufacturing the elementary parts of wind turbine. Despite growing recognition of the significance of Noksan, there has been only limited attention paid and in recent years. This paper reviews the literature of the current burning issues in wind turbine industries in the western countries. In addition, it describes the present state of Noksan wind power generation cluster and suggests the future plans to make it more effective complex.

• Publications of The Korean Astronomical Society
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• v.15 no.spc1
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• pp.15-30
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• 2000

A large scatter of the chemical abundances among globular cluster red giants has been observed. Especially the chemical elements C, N, O, Na, Mg, and Al vary form star to star within globular clusters. Except for $\omega$ Cen and M22, most globular clusters could be considered to be monometallic of their iron peak elements within error ranges. The variations in light elements among globuar cluster giants appear much more pronounced than in field halo giants of comparable Fe-peak metallicity. It has been found that in general the nitrogen abundance is anticorrelated with both carbon and oxygen, while it is correlated with Na and AI. These intracluster abundance inhomogeneities can be interpreted either by mixing of nucleosythesized material from the deep stellar interior during the red giant branch phase of evolution or by inhomogeneities of primordially processed material, from which the stars were formed. The simple way of distingushing between two senarios is to obtain the element abundances of main-sequence stars in globular clusters, which are too faint for high resolution spectroscopic studies until now. Both 'evolutionary' and 'primodial' origins are accepted for explanations of abundance variations among red giants and CN-CH anticorrelations among main-sequence stars in globular clusters. This paper reviews chemical abundances of light elements among globular cluster giants, with brief reviews of cannonical stellar evolution of low mass stars after main-sequence and deep mixing for abundance variations of cluster giants, and a possible connection between deep mixing and second parameter.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.49 no.1
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• pp.8-15
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• 2012

In this paper, we propose a new monitor for collecting job information from Hadoop clusters in real time. This monitor is made of two programs called Collector and Agent. Agent collects Hadoop cluster's node information and job information, and Collector analyzes the collected information and saves it in a database. Also, Collector was placed in a new node outside the Hadoop cluster so that it does not affect Hadoop's work and will not cause overload. When the proposed monitor was implemented and applied, the testbed cluster was able to detect the occurrence of dead nodes immediately. In addition, we were able to find Hadoop jobs which were inefficient and when we modified such jobs to further enhance the performance of Hadoop.

• International Journal of Advanced Culture Technology
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• v.4 no.2
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• pp.19-26
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• 2016

The most important factor in the wireless sensor network is the use of effective energy and increase in lifetime of the individual nodes in order to operate the wireless network more efficiently. For this purpose, various routing protocols have been developed. The LEACH such a protocol, well known among typical cluster routing protocols. However, when a cluster head is selected, the energy consumption may not be equal because it does not take into account the energy of the nodes. In this paper, we seek to improve the cluster head selection method according to residual energy of each sensor node. This method then adaptively applies the LEACH algorithm and the cluster head section algorithm with consideration of node energy in accordance with the energy of the whole sensor field. Through the simulation, it was found that this proposed algorithm was effective.

• Journal of Korea Multimedia Society
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• v.20 no.4
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• pp.640-648
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• 2017

Sensors have limited resources in sensor networks, so efficient use of energy is important. In order to use the energy of the sensor node efficiently, researches applying mobile sink to the sensor network have been actively carried out. The sink node moves the sensor network, collects data from each sensor node, which spread the energy concentrated around the sink node, thereby extending the entire life cycle of the network. But, when the sink node moves, it requires a reset of the data transmission path, which causes a lot of control messages and delays. In this paper, we propose a CMS(Cluster-based Mobile Sink) method to support the movement of mobile sink in a cluster sensor environment. The proposed scheme minimizes an amount of control messages without resetting the routing paths of entire sensor networks by supporting the sink mobility path using the neighbor cluster list. And, it simplifies the routing path setup process by setting a single hop path between clusters without a gateway. The experiment results show that the proposed scheme has superior energy efficiency in processing and network structure, compared with existing clustering and mesh routing protocols.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.117.2-117.2
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• 2011

We probe 12CO J=2-1 and 13CO J=1-0 properties of a Virgo disk galaxy, NGC 4402 which is located near the cluster center. Our goal is to study the impact of intra cluster medium (ICM) on the molecular gas of a galaxy in the cluster environment. It has been believed that cluster galaxies are deficient in atomic hydrogen gas (HI gas) compared to their field counterparts and now there is much evidence that low density ISM can be easily removed by ram pressure caused by ICM wind. Meanwhile, no significant molecular gas deficiency of the cluster galaxy population has been found yet they show overall lower star formation rate than galaxies in the field, and it is still controversy whether dense ISM can be also stripped by the ICM wind or not. NGC 4402 with truncated HI disk($D_{HI}/D_{opt}$ ~ 0.75 and only 36%of HI gas compare to field galaxies of a similar size) and a disturbed gas morphology, appears to have strong ongoing ram pressure. Using high resolution 12 and 13CO data of NGC 4402 from a Sub Millimeter Array (SMA), we probe the molecular gas properties under strong ICM pressure. We discuss how its star formation activity and hence the global color of NGC4402 would be changed in the future.

• Journal of the Korean Chemical Society
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• v.61 no.6
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• pp.311-319
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• 2017

By using Density Functional Theory (DFT), we have performed alkali metal and alkaline earth metal inside fullerene-like BeO cluster (FLBeOC) in terms of energetic, geometric, charge transfer, work function and electronic properties. It has been found that encapsulated processes of the alkali metal are exothermic and thermodynamically more favorable than alkaline earth metal encapsulation, so that interaction energy ($E_{int}$) of the alkali metal encapsulation FLBeOC is in the range of -0.02 to -1.15 eV at level of theory. It is found that, the electronic properties of the pristine fullerene-like BeO cluster are much more sensitive to the alkali metal encapsulation in comparison to alkaline earth metal encapsulation. The alkali and alkaline earth metal encapsulated fullerene-like BeO cluster systems exhibit good sensitivity, promising electronic properties which may be useful for a wide variety of next-generation nano-sensor device components. The encapsulation of alkali and alkali earth metal may increase the electron emission current from the FLBeOC surface by reducing of the work function.

• Journal of information and communication convergence engineering
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• v.11 no.3
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• pp.153-166
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• 2013

A hierarchical time division multiple access (HTDMA) medium access control (MAC) protocol is proposed for clustered mobile underwater acoustic networks. HTDMA consists of two TDMA scheduling protocols (i.e., TDMA1 and TDMA2) in order to accommodate mobile underwater nodes (UNs). TDMA1 is executed among surface stations (e.g., buoys) using terrestrial wireless communication in order to share mobility information obtained from UNs which move cluster to cluster. TDMA2 is executed among UNs, which send data to their surface station as a cluster head in one cluster. By sharing mobility information, a surface station can instantaneously determine the number of time slots in a TDMA2 frame up to as many as the number of UNs which is currently residing in its cluster. This can enhance delay and channel utilization performance by avoiding the occurrence of idle time slots. We analytically investigate the delay of HTDMA, and compare it with that of wellknown contention-free and contention-based MAC protocols, which are TDMA and Slotted-ALOHA, respectively. It is shown that HTDMA remarkably decreases delay, compared with TDMA and Slotted-ALOHA.