• Journal of KIISE:Information Networking
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• v.36 no.2
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• pp.80-89
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• 2009

A DHT(Distributed Hash Table) based P2P is a method that compensates disadvantages of the existing unstructured P2P method. If a DHT algorithm is used, it can do fast data search and maintain search efficiency independent of the number of peers. The peers in a DHT method send messages periodically to keep the routing table updated. In a mobile environment, the peers in a DHT method should send messages more frequently to keep the routing table updated and reduce the failure of requests. However this results in increasing the overall network traffic. In this paper, we propose a method to reduce the update load of a routing table in the existing DHT by updating it in a reactive way. In the proposed reactive method, a routing table is updated only if a data request is coming whereas it is updated periodically in the existing proactive method. We perform experiments using Chord simulator(I3) made by UC Berkely. The experimental results show the performance improvement of the proposed method compared to the existing method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.7
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• pp.1597-1601
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• 2013

Multiple antenna technique is attracting attention as a core technology for next-generation mobile communication systems to accommodate explosively increasing mobile data traffic. Especially, recent researches focus on multi-user multiple input multiple output (MU-MIMO) system where base stations are equipped with several tens of transmit antennas and transmit data to multiple terminals (users) simultaneously. To enhance the performance of MU-MIMO systems, we, in this paper, propose an adaptive user selection algorithm which adaptively selects a user set according to varying channel states. According to Monte-Carlo based computer simulations, the performance of proposed scheme is significantly improved compared to the conventional scheme without user selection and approaches that of exhaustive search-based optimal scheme. On the other hand, the proposed scheme can reduce the computational complexity to $K/(2^K-1)$ compared to the optimal scheme where K denotes the number of total users.

• KIPS Transactions on Software and Data Engineering
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• v.3 no.5
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• pp.179-186
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• 2014

Current networks such as social network, web page link, traffic network are big data which have the large numbers of nodes and edges. Many applications such as social network services and navigation systems use these networks. Since big networks are not fit into the memory, existing in-memory based analysis techniques cannot provide high performance. Frontier-Expansion-Merge (FEM) framework for graph search operations using three corresponding operators in the relational database (RDB) context. FEM exploits an index table that stores pre-computed partial paths for efficient shortest path discovery. However, the index table of FEM has low hit ratio because the indices are determined by distances of indices rather than the possibility of containing a shortest path. In this paper, we propose an method that construct index table using high degree nodes having high hit ratio for efficient shortest path discovery. We experimentally verify that our index technique can support shortest path discovery efficiently in real-world datasets.

• The Journal of Fisheries Business Administration
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• v.35 no.1
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• pp.57-85
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• 2004

To develop an blue tourism website(BTW) for electronic commerce(EC), information requirements of BTW are defined firstly. We defined information requirements of BTW from two aspects, i.e., front office and back office. Information requirements for front office were derived by consumer purchasing decision process. And information requirements for back office were derived by tourism value chain. Total 29 functions are identified as critical EC related functions of BTW. Among them, 25 functions were investigated into BTW. BTWs were searched by search engines - Yahoo and Empas - to Korean websites. There are 12 specialized BTWs, except one cyber museum website. For 12 websites, 25 functions were probed. By the results, in need recognition stage of blue tourism, only weather information was provided in most websites. In information search stage of blue tourism, package recommendation and various contents were provided in most websites. In consumption stage of blue tourism, traffic information were provided in most websites. And in after - sales service stage of blue tourism, bulletin board function was implemented in most websites. The rest of the functions were scarcely implemented. On the whole, it was concluded that most EC related functions of BTW in Korea were not implemented properly. To improve the status quo, it is expected in the dimension of individual website, that marketing planning, customized service, intelligent service, reinforcing purchasing assistance functions, customer relationship management, and escrow service etc. need to be implemented. And it is expected in the dimension of blue tourism industry, that standardizing product catalog, security assistance policy, information sharing by industrial database, finding referral model of BTW, elevating information mind, revising related laws etc. are needed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.10
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• pp.1309-1316
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• 2016

This paper suggests adjusting TCP for smartphones that often have small size data transmission tendency. Usage of smartphones has been risen dramatically in recent years, including frequent usage of real-time map search, public transportation search, online games, and SNS. Because the small size data transmission ends before the phase of the TCP congestion avoidance, this paper suggests an algorithm that increases the transmission speed ahead of the traffic congestion event. The algorithm reduces unnecessary delay by data size-driven adjustment of the Linux Quick ACK and Nagle's algorithm. Therefore, TCP is improved to maintain a high transmission rate steadily in small data transmission.

• Journal of Information Technology Services
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• v.8 no.3
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• pp.171-184
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• 2009

Since the development of the Distributed Hash Tables (DHTs), the distributed lookup services are one of the hot topics in the networking area. The main reason of this popularity is the simplicity of the lookup structure. However, the simple key based search mechanism makes the so called "keyword" based search difficult if not impossible. Thus, the applicability of the DHTs is limited to certain areas. In this paper. we find that DHTs can be used as the ubiquitous sensor network (USN) metadata lookup service across a large number of sensor networks. The popularity of the Ubiquitous Sensor Network has motivated the development of the USN middleware services for the sensor networks. One of the key functionalities of the USN middleware service is the lookup of the USN metadata, by which users get various information about the sensor network such as the type of the sensor networks and/or nodes, the residual of the batteries, the type of the sensor nodes. Traditional distributed hash table based lookup systems are good for one sensor network. However, as the number of sensor network increases, the need to integrate the lookup services of many autonomous sensor networks so that they can provide the users an integrated view of the entire sensor network. In this paper, we provide a hybrid lookup model, in which the autonomous lookup services are combined together and provide seamless services across the boundary of a single lookup services. We show that the hybrid model can provide far better lookup performance than a single lookup system.

• Archives of Plastic Surgery
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• v.50 no.6
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• pp.550-556
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• 2023

Blunt breast trauma occurs in 2% of blunt chest injuries. This study aimed to evaluate the evidence on breast reconstruction after blunt trauma associated with the use of a seat belt. Also, we describe the first case of breast reconstruction using the Ribeiro technique. In November 2022, a systematic search of MEDLINE, EMBASE, and Google Scholar databases was conducted. The literature was screened independently by two reviewers, and the data was extracted. Our search terms included breast, mammoplasty, blunt injury, and seat belts. In addition, we present the case of a woman with a left breast deformity and her reconstruction using the inferior Ribeiro flap technique. Six articles were included. All included studies were published between 2010 and 2021. The studies recruited seven patients. According to the Teo and Song classification, seven class 2b cases were reported. In five cases a breast reduction was performed in the deformed breast with different types of pedicles (three superomedial flaps, one lower flap, one superior flap). Only one case presented complications. The case here presented was a type 2b breast deformity in which the lower Ribeiro pedicle was used successfully without complications during follow-up. Until now there has been no consensus on reconstructive treatment due to the rarity of this entity. However, we must consider surgical treatment individually for each patient. We believe that the Ribeiro technique is a feasible and safe alternative in the treatment of posttraumatic breast deformities, offering very good long-term results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.12
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• pp.2539-2548
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• 2015

Overcoming inter-cell interference and spectrum scarcity are major issues in heterogeneous cellular networks. Static Frequency reuse schemes have been proposed as an effective way to manage the spectrum and reduce ICI(Inter cell Interference) in cellular networks. In a kind of static frequency reuse scheme, the allocations of transmission power and subcarriers in each cell are fixed prior to system deployment. This limits the potential performance of the static frequency reuse scheme. Also, most of dynamic frequency reuse schemes did not consider small cell and the network environment when the traffic load of each cell is heavy and non-uniform. In this paper, we propose an inter-cell resource allocation algorithm that dynamically optimizes subcarrier allocations for the multi-cell heterogeneous networks. The proposed dynamic frequency reuse scheme first finds the subcarrier usage in each cell-edge by using the exhaustive search and allocates subcarrier for all the cells except small cells. After that it allocates subcarrier for the small cell and then iteratively repeats the process. Proposed dynamic frequency reuse scheme performs better than previous frequency reuse schemes in terms of the throughput by improving the spectral efficiency due to it is able to adapt the network environment immediately when the traffic load of each cell is heavy and non-uniform.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.129-139
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• 2009

The transportation network is a critical infrastructure in the event of natural and human caused disasters such as rainfall, snowfall, and terror and so on. Particularly, the transportation network in an urban area where a large number of population live is subject to be negatively affected from such events. Therefore, efficient traffic operation plans are required to assist rapid evacuation and effective detour of vehicles on the network as soon as possible. Recently, ubiquitous communication and sensor network technology is very useful to improve data collection and connection related emergency information. In this study, we develop a specific algorithm to provide evacuation route and detour information only for vehicles under emergency situations. Our algorithm is based on shortest path search technique and dynamic traffic assignment. We perform the case study to evaluate model performance applying hypothetical scenarios involved terror. Results show that the model successfully describe effective path for each vehicle under emergency situation.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.21 no.1
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• pp.159-181
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• 2022

Today, people in cities use differentthe types of transportation that rangepeople use in cities have diversified from existing public transportation, cars, taxis to shared bicycles and shared electric kickboards. In addition, with the development of mobile platform -based search, order, and payment services, and transportation services have also begun to change into platform-based integrated services. In particular, MaaS, which has emerged as an integrated mobile service and, is currently being studied and operated worldwide., However, MaaS but remains at the level of the integrated provision of the existing public transportation. As a result of Specifically, the results of a literature review on this issue reveal that, the First/Last Mile problem raised at the current level of MaaS is likely to be solved by establishing an improved policy incorporating new means of transportation. Therefore, this study aims to establish a First/Last Mile transportation supply plan for successful MaaS provision. This establishment is realized by analyzing the traffic patterns of urban populations usingbased on the ABATA system,, an activity-based traffic analysis model withevaluated as having higher analysis power on people's traffic.