• 한국경영과학회지
• /
• 제18권3호
• /
• pp.35-49
• /
• 1993

The node coloring problem is a problem to color the nodes of a graph using the minimum number of colors possible so that any two adjacent nodes are colored differently. This problem, along with the edge coloring problem, has a variety of practical applications particularly in item loading, resource allocation, exam timetabling, and channel assignment. The node coloring problem is an NP-hard problem, and thus many researchers develop a number of heuristic algorithms. In this paper, we survey and classify those heuristics with the emphasis on how an algorithm orders the nodes and colors the nodes using a determined ordering.

• 대한전자공학회논문지
• /
• 제25권7호
• /
• pp.734-745
• /
• 1988

In this paper, it is tried to improve efficiency of the D-algorithm by assigning the logic values effectively on the nodes related to the critical path for back tracing to reduce the number of search nodes when acyclic combinational logic circuits are composed of NAND gates only. For that purpose, LASAR algorithm which is suitable for determining a critical path for back tracing is applied to the D-algorithm and it is implemented by IBM-PC with APL language. The test results on a number of NAND circuits which have multi-fanout, reconvergent and symetric characteristics show that the modified D-algorihtm reduces the number of search nodes in forward and backward tracing and decreases the run time of CPU about 10 percents.

• ETRI Journal
• /
• 제36권4호
• /
• pp.564-571
• /
• 2014

Sphere decoding (SD) for multiple-input and multiple-output systems is a well-recognized approach for achieving near-maximum likelihood performance with reduced complexity. SD is a tree search process, whereby a large number of nodes can be searched in an effort to find an estimation of a transmitted symbol vector. In this paper, a simple and generalized approach called layer pruning is proposed to achieve complexity reduction in SD. Pruning a layer from a search process reduces the total number of nodes in a sphere search. The symbols corresponding to the pruned layer are obtained by adopting a QRM-MLD receiver. Simulation results show that the proposed method reduces the number of nodes to be searched for decoding the transmitted symbols by maintaining negligible performance loss. The proposed technique reduces the complexity by 35% to 42% in the low and medium signal-to-noise ratio regime. To demonstrate the potential of our method, we compare the results with another well-known method - namely, probabilistic tree pruning SD.

• 한국컴퓨터정보학회논문지
• /
• 제23권9호
• /
• pp.43-50
• /
• 2018

In this paper, we propose a hexagon model-based efficient beacon frame scheduling approach for wireless sensor networks. The existing beacon frame scheduling approaches use a lot of slots and subslots for the beacon frame scheduling. Thus, the data from source nodes are not efficiently delivered to a sink node. Also in case a sink node needs to broadcast a beacon frame to the nodes in the network, delivering the beacon frame to the network nodes is not efficient as well. Thus, to solve the problem, we use a hexagon model to find the number of slots and subslots for the beacon frame scheduling. By using them for the beacon frame scheduling, the proposed approach performs better than other approaches in terms of the data transmission delay, the number of received data, the beacon transmission delay and the number of relaying the beacon frames.

• 대한산업공학회지
• /
• 제24권3호
• /
• pp.407-416
• /
• 1998

For fast Cholesky factorization, it is most important to reduce the number of nonzero elements by ordering methods. Generally, the minimum deficiency ordering produces less nonzero elements, but it is very slow. We propose an efficient implementation method. The minimum deficiency ordering requires much computations related to adjacent nodes. But, we reduce those computations by using indistinguishable nodes, the clique storage structures, and the explicit storage structures to compute deficiencies.

• 대한두경부종양학회지
• /
• 제37권2호
• /
• pp.25-31
• /
• 2021

Background/Objectives: Although thyroid lobectomy recently is considered as sufficient for low-risk papillary thyroid carcinoma (PTC), completion thyroidectomy is required due to the insufficiency of the preoperative evaluation. The aim of this study was to investigate recurrence rate and disease free survival depending on the gross extrathyroidal extension (gETE) or the number of metastatic lymph node identified in patients with PTC. Materials & Methods: We assessed 3373 patients with PTC who underwent lobectomy at Seoul St. Mary's Hospital (Seoul, Korea) between January 2009 and December 2014. Clinicopathological characteristics and long-term surgical outcomes were retrospectively analyzed through complete chart reviews. The mean follow-up duration was 97.1 ± 21.4 months. Results: The rate of recurrence was higher in gETE group (1.8% vs. 6.0%, p=0.004), leading to decreased disease free survival in Kaplan-Meier analysis (log-rank p<0.001). N1 group (n=1389) was analyzed into two groups whether the number of positive nodes is more than 5 or less. For the group of the more metastatic nodes, the recurrence rate higher compared to the other group (3.0% vs. 9.3%, p<0.001). DFS was longer in the group that had lesser metastatic nodes (log-rank p<0.001). However, in terms of N1 group over 1cm (n=492), No statistical difference was observed according to the number of positive lymph nodes (4.5% vs. 9.1%, p=0.092) Conclusion: When it comes to node positive PTC, Despite the number of positive lymph nodes was over 5, follow-up with no further surgery can be an option.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제12권9호
• /
• pp.4228-4247
• /
• 2018

Many methods have been developed for the vehicles to create clusters in vehicular ad hoc networks (VANETs). Usually, nodes are vehicles in the VANETs, and they are dynamic in nature. Clusters of vehicles are made for making the communication between the network nodes. Cluster Heads (CHs) are selected in each cluster for managing the whole cluster. This CH maintains the communication in the same cluster and with outside the other cluster. The lifetime of the cluster should be longer for increasing the performance of the network. Meanwhile, lesser the CH's in the network also lead to efficient communication in the VANETs. In this paper, a novel algorithm for clustering which is based on the social behavior of Gray Wolf Optimization (GWO) for VANET named as Intelligent Clustering using Gray Wolf Optimization (ICGWO) is proposed. This clustering based algorithm provides the optimized solution for smooth and robust communication in the VANETs. The key parameters of proposed algorithm are grid size, load balance factor (LBF), the speed of the nodes, directions and transmission range. The ICGWO is compared with the well-known meta-heuristics, Multi-Objective Particle Swarm Optimization (MOPSO) and Comprehensive Learning Particle Swarm Optimization (CLPSO) for clustering in VANETs. Experiments are performed by varying the key parameters of the ICGWO, for measuring the effectiveness of the proposed algorithm. These parameters include grid sizes, transmission ranges, and a number of nodes. The effectiveness of the proposed algorithm is evaluated in terms of optimization of number of cluster with respect to transmission range, grid size and number of nodes. ICGWO selects the 10% of the nodes as CHs where as CLPSO and MOPSO selects the 13% and 14% respectively.

• 디지털콘텐츠학회 논문지
• /
• 제14권1호
• /
• pp.41-50
• /
• 2013

소셜 네트워크 분석은 1개의 연결을 가지는 n개의 노드를 대상으로 한다. 노드 수 n이 수십 또는 수백 정도의 소셜 네트워크를 분석할 때는 전체 데이터를 대상으로 분석이 가능하지만, 그 이상이 되면 육안으로 분석하기는 어렵다. 따라서 전체 소셜 네트워크를 분리할 필요가 있는데 이 때 사용할 수 있는 방법이 군집화이다. 군집화를 통해 전체 노드를 하위 그룹으로 구성하면, 소셜 네트워크의 특징 분석이나 노드간의 관계 분석을 쉽게 수행할 수 있게 된다. 군집화 기법은 하위 그룹의 개수를 미리 설정해야 하기 때문에 사용자와의 상호 작용이 필요하고, 이렇게 생성된 하위 그룹이 최적의 결과라는 것을 보증할 수 없다. 본 논문에서는 외부 커뮤니티 연관도를 활용한 동적인 하위 그룹 생성 방법을 제안한다. 발견된 하위 그룹의 개수와 하위 그룹 순도를 기준으로 기존의 연구들과 비교하였고, 실험 결과 제안하는 방법의 우수성을 확인할 수 있었다.

• Journal of Information Processing Systems
• /
• 제14권3호
• /
• pp.694-708
• /
• 2018

China possesses a passenger dedicated line system of large scale, passenger flow intensity with uneven distribution, and passenger nodes with complicated relations. Consequently, the significance of passenger nodes shall be considered and the dissimilarity of passenger nodes shall be analyzed in compiling passenger train operation and conducting transportation allocation. For this purpose, the passenger nodes need to be hierarchically divided. Targeting at problems such as hierarchical dividing process vulnerable to subjective factors and local optimum in the current research, we propose a clustering approach based on self-organizing map (SOM) and k-means, and then, harnessing the new approach, hierarchical dividing of passenger dedicated line passenger nodes is effectuated. Specifically, objective passenger nodes parameters are selected and SOM is used to give a preliminary passenger nodes clustering firstly; secondly, Davies-Bouldin index is used to determine the number of clusters of the passenger nodes; and thirdly, k-means is used to conduct accurate clustering, thus getting the hierarchical dividing of passenger nodes. Through example analysis, the feasibility and rationality of the algorithm was proved.

• 대한전자공학회논문지TC
• /
• 제49권8호
• /
• pp.84-97
• /
• 2012

무선 센서 네트워크에서 클러스터 구조는 부하균형, 에너지 절약, 분산 키 관리와 같은 중요한 이점들을 유발한다. 네트워크를 클러스터 구조로 변경하기 위해서 센서들은 배치된 후에 클러스터 구성 프로토콜을 실행해야 한다. 이때 일부 노드들이 공격자에 의해 오염될 수 있으며 이들이 클러스터 구성 프로토콜에 따르지 않으면 임의의 클러스터에서 멤버십의 비일치가 발생한다. 이러한 경우에 클러스터들은 분할되게 되며 이에 따라 클러스터 수는 증가하고 클러스터내의 멤버수가 줄어드는 문제점이 발생한다. 본 논문에서는 오염노드들의 프로토콜 비협조에 잘 대처하는 기법을 제안한다. 먼저, 제안방법은 클러스터 내에서 임의의 두 노드 간에 거리가 최대 2홉이 되는 2홉 클러스터들을 생성한다. 게다가 제안방법은 오염노드에 의한 클러스터들의 분할을 막기 위해 2홉 거리의 노드에 의한 검증을 이용한다. 또한 제안방법은 노드들의 에너지 소모를 감소시키기 위하여 주로 방송전송들을 이용한다. 실험결과들은 제안방법이 다른 방법에 비해 클러스터 수를 감소시키며 좀 더 안전하고 에너지 효율적임을 보여주었다.