• ETRI Journal
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• 제39권1호
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• pp.30-40
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• 2017

In this study, we investigate topology control as a means of obtaining the best possible compromise between the conflicting requirements of reducing energy consumption and improving network connectivity. A topology design algorithm capable of producing network topologies that minimize energy consumption under a minimum-connectivity constraint is presented. To this end, we define a new topology metric, called connectivity efficiency, which is a function of both algebraic connectivity and the transmit power level. Based on this metric, links that require a high transmit power but only contribute to a small fraction of the network connectivity are chosen to be removed. A connectivity-efficiency-based topology control (CETC) algorithm then assigns a transmit power level to each node. The network topology derived by the proposed CETC heuristic algorithm is shown to attain a better tradeoff between energy consumption and network connectivity than existing algorithms. Simulation results demonstrate the efficiency of the CECT algorithm.

• Investigative Magnetic Resonance Imaging
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• 제15권2호
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• pp.110-122
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• 2011

목적 : 본 연구의 목적은 확산텐서영상에 기반하여 한국 아동 집단의 해부학적 뇌연결성 지도를 확립하고 뇌신경망의 효율성을 평가하는 기법을 개발하는 것이다. 대상 및 방법 : 건강한 아동 12명에서 얻은 확산텐서영상과 뇌구획영상을 바탕으로 구조 연결 행렬을 구하여 집단의 구조 연결성을 평가하였다. 일표본 t-검정을 시행하여 평균적인 구조 연결성을 파악하였고 이 때 얻은 각 피험자의 백질 다발을 표준공간으로 정규화하여 집단의 해부학적 뇌연결망 지도를 확립했다. 뇌신경망의 군집정도(clustering coefficient), 평균이동거리(characteristic path length), 전체/부분 연결망 효율성(global/local efficiency) 등 연결망 속성을 계산한 후 시각화 하였다. 결과 : 연결망 측면에서 한국 아동 집단의 뇌연결성이 작은세상속성을 가짐을 밝혔다. 또한 해부학적 뇌연결망 지도를 얻었는데 대뇌 반구 내의 연결성이 높게 나타남과 뇌간과 운동/감각 영역간에 많은 신경 연결이 집중되어 있음을 확인하였다. 결론 : 한국 아동 집단의 해부학적 뇌연결망 지도를 작성하는 방법론을 제시하여 뇌를 연결성 측면에서 이해하고 발달 장애와 성인 뇌신경망의 효율성을 평가할 수 있는 기본 도구를 확립하게되었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권9호
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• pp.3335-3356
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• 2015

In this paper, we analyze the connectivity of cognitive radio ad-hoc networks in a log-normal shadow fading environment. Considering secondary user and primary user's locations and primary user's active state are randomly distributed according to a homogeneous Poisson process and taking into account the spectrum sensing efficiency of secondary user, we derive mathematical models to investigate the connectivity of cognitive radio ad-hoc networks in three aspects and compare with the connectivity of ad-hoc networks. First, from the viewpoint of a secondary user, we study the communication probability of that secondary user. Second, we examine the possibility that two secondary users can establish a direct communication link between them. Finally, we extend to the case of finding the probability that two arbitrary secondary users can communicate via multi-hop path. We verify the correctness of our analytical approach by comparing with simulations. The numerical results show that in cognitive radio ad-hoc networks, high fading variance helps to remarkably improve connectivity behavior in the same condition of secondary user's density and primary user's average active rate. Furthermore, the impact of shadowing on wireless connection probability dominates that of primary user's average active rate. Finally, the spectrum sensing efficiency of secondary user significantly impacts the connectivity features. The analysis in this paper provides an efficient way for system designers to characterize and optimize the connectivity of cognitive radio ad-hoc networks in practical wireless environment.

• 한국통신학회논문지
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• 제37B권9호
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• pp.767-777
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• 2012

Topology control increases channel efficiency by controlling transmission power of a node, and as a result, network lifetime and throughput are increased. However, reducing transmission range causes a network connectivity problem, especially in mobile networks. When a network loses connectivity, the network topology should be re-configured. However, topology re-configuration consumes lots of energy because every node need to collect neighbor information. As a result, network lifetime may decrease, even though topology control is being used to prolong the network lifetime. Therefore, network connectivity time needs to be increased to expend network lifetime in mobile networks. In this paper, we propose an Adaptive-Redundant Transmission Range (A-RTR) algorithm to address this need. A-RTR uses a redundant transmission range considering a node status and flexibly changes a node's transmission range after a topology control is performed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권12호
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• pp.4372-4388
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• 2014

Robotic sensor network (RSN) contains mobile sensors and robots providing feasible solution for many multi-agent applications. One of the most critical issues in RSN and its application is how to effectively assign tasks. This paper presents a novel connectivity preserving hybrid task allocation strategy to answer the question particularly for RSN. Firstly, we model the task allocation in RSN to distinguish the discovering and allocating processes. Secondly, a fully distributed simple Task-oriented Unoccupied Neighbor Algorithm, named TUNA, is developed to allocate tasks with only partial view of the network topology. A connectivity controller is finally developed and integrated into the strategy to guarantee the global connectivity of entire RSN, which is critical to most RSN applications. The correctness, efficiency and scalability of TUNA are proved with both theoretical analysis and experimental simulations. The evaluation results show that TUNA can effectively assign tasks to mobile robots with the requirements of only a few messages and small movements of mobile agents.

• 한국IT서비스학회지
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• 제15권4호
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• pp.125-151
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• 2016

In recent years, O2O (Online to Offline) services get a lot of attention to improve the trust in online shopping and minimize the inconvenience and the cost burden in offline shopping as the number of consumers, who do not show concern about the purchase platform like online or offline, increases. Even though the services have been getting the spotlight as a strong business platform for next generation commerce, there have been only a few studies on the O2O services. The purpose of this research is to investigate the factors which affect the consumer's intention to use location-based O2O services. The study is based on VAM (Value-based Adoption Model) which is able to analyze those factors from the aspects of benefit and sacrifice. We used the partial least squares (PLS) method for empirical analysis, and the result shows that contextual offers, instant connectivity, webrooming and economic efficiency, which fall under the benefit, affect perceived value positively while annoyance and face consciousness, which fall under the sacrifice, do not affect perceived value significantly. In addition, contextual offers and instant connectivity affect trust positively. Location accuracy, which falls under the benefit of location-based O2O service, do not significantly affect perceived value and trust while security risk affects trust and use intention negatively. It appears that trust affects perceived value and use intention positively.

• 한국컴퓨터그래픽스학회논문지
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• 제26권1호
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• pp.17-25
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• 2020

본 논문은 비정렬 격자에 대한 광선투사 수행의 전처리 과정 중 하나인 셀 사이 연결정보 추출에 대한 멀티코어 CPU 기반 병렬처리 알고리즘을 제안한다. 본 연구는 기존의 직렬처리 알고리즘을 단순히 병렬화하였을 때 발생하는 동기화 문제를 확인하고, 이를 해결할 수 있는 3-단계 병렬처리 알고리즘을 제안한다. 제안하는 알고리즘은 각 단계 내에서의 스레드 간 동기화를 제거함으로서 병렬처리 효율을 높인다. 또한, 연결정보 추출 알고리즘의 핵심 연산인, 삼각형 중복 검사 과정의 메모리 접근에 대한 공간적 지역성을 높이고 캐시 활용 효율을 향상시킨다. 본 연구는 나아가, 스레드 마다 자체 메모리 풀을 사용하게 함으로서 병렬처리 효율을 더욱 높인다. 본 연구의 효용성을 확인하기 위해, 제안하는 알고리즘을 두 개의 옥타코어 CPU를 가지는 시스템에 구현하고 세 개의 비정렬 격자 데이터에 적용하였다. 그 결과, 제안하는 병렬처리 알고리즘은 스레드 수 증가에 따라 지속적으로 성능 향상을 보여주었다. 또한, 32개 스레드(물리코어 16개)를 사용하여 기존 직렬처리 알고리즘 대비 최대 82.9배 높은 성능을 보여주었다. 이는 제안하는 알고리즘의 높은 병렬처리 확장성 및 캐시 활용 효율 개선 효과를 증명하며, 대용량 비정렬 격자 처리에 대한 적합성을 보여주는 결과다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.462-465
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• 2000

It is important to compress three dimensional (3D) data efficiently, since 3D data are too large to store or transmit in general. In this paper, we propose a lossless compression algorithm of the 3D mesh connectivity, based on the vertex degree. Most techniques for the 3D mesh compression treat the connectivity and the geometric separately, but our approach attempts to exploit the geometric information for compressing the connectivity information. We use the geometric angle constraint of the vertex fanout pattern to predict the vertex degree, so the proposed algorithm yields higher compression efficiency than the conventional algorithms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제2권5호
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• pp.222-238
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• 2008

In this paper, the random key pre-distribution scheme introduced in ACM CCS'02 by Eschenauer and Gligor is reexamined, and a generalized form of key establishment is introduced. As the communication overhead is one of the most critical constraints of any successful protocol design, we introduce an alternative scheme in which the connectivity is maintained at the same level as in the original work, while the communication overhead is reduced by about 40% of the original overhead, for various carefully chosen parameters. The main modification relies on the use of a two-level key pool design and two round assignment/key establishment phases. Further analysis demonstrates the efficiency of our modification.

• 감성과학
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• 제21권3호
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• pp.83-102
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• 2018

The process model of emotion regulation suggests that cognitive reappraisal and expressive suppression engage at different time points in the regulation process. Although multiple brain regions and networks have been identified for each strategy, no articles have explored changes in network characteristics or network connectivity over time. The present study examined (a) the whole-brain network and six other resting-state networks, (b) their modularity and global efficiency, which is an index of the efficiency of information exchange across the network, (c) the degree and betweenness centrality for 160 brain regions to identify the hub nodes with the most control over the entire network, and (d) the intra-network and inter-network functional connectivity (FC). Such investigations were performed using a traditional large-scale FC analysis and a relatively recent sliding window correlation analysis. The results showed that the right inferior orbitofrontal cortex was the hub region of the whole-brain network for both strategies. The present findings of temporally altering functional activity of the networks revealed that the default mode network (DMN) activated at the early stage of reappraisal, followed by the task-positive networks (cingulo-opercular network and fronto-parietal network), emotion-processing networks (the cerebellar network and DMN), and sensorimotor network (SMN) that activated at the early stage of suppression, followed by the greater recruitment of task-positive networks and their functional connection with the emotional response-related networks (SMN and occipital network). This is the first study that provides neuroimaging evidence supporting the process model of emotion regulation by revealing the temporally varying network efficiency and intra- and inter-network functional connections of reappraisal and suppression.