• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.6
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• pp.687-692
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• 2004

In this paper, we proposed an efficient cache hoarding method in mobile computing environments using collaborative filtering. This method is used for solving the difficult problem of mobile computing, which is the vacuum of information service depending on low bandwidth, long delay, and frequent network disconnection. Many previous researches have been studied a cache hoarding approach for solving these problems of mobile client. But, the research of history information of mobile client did not support all informative requests for mobile clients. In our research, collaborative filtering model using history information and location data of mobile client is proposed. This proposed model supports an efficient service of necessary items for client's requirement. For the performance evaluation of proposed model, we make an experiment of simulation data using SAS enterprise miner. According to objective evaluation using cache hit ratio, we show that our model has a good result.

• The Journal of the Convergence on Culture Technology
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• v.6 no.3
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• pp.211-216
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• 2020

The purpose of this study is to discover about the parenting anxiety of working mother and full-time mother with elementary school children, and to find ways to support them. All the study participants were 20 mothers with elementary school children. Data was collected from June 23, 2017 to July 8, 2017. Data was collected using in-depth group interviews. Parenting anxiety felt by working mothers is 'sorry about the child', 'burden on the role of parents', and 'difficulty in caring', 'Reemployment and career disconnection'. The conclusion is as follows. First, it is necessary to reduce the burden of raising children on elementary school children of both working and full-time mothers. Second, practical support plans are needed for working mothers and full-time mothers of elementary school children. Third, practical support plans are needed for working mothers and full-time mothers with elementary school children.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.48 no.4
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• pp.142-152
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• 2011

In general, existing emergency evacuation guiding systems depend on visual techniques like emergency lights or LEDs. Actually people in the case of fire emergency condition may not obtain a range of view because of smoke from the fire. This paper introduces a technique to design an emergency guiding system using directivity sound to cope with this problem. In this case all speakers are serially connected for audio signal transmission in a serial fashion to achieve convenient speaker installation. Floyd algorithm is used to find shortest evacuation paths. Because serially connected multi-channel speakers are weak in case of disconnection, this paper uses a technique to solve the diagnostic problem. In the proposed system, a PC based on the USB protocol is used for control and observation. The system has achievements, such as increasing evacuation rate under emergency conditions, and serial transmission of audio signal for easy maintenance and low installation cost.

• Journal of the Korea Society of Computer and Information
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• v.15 no.11
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• pp.135-142
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• 2010

QoS in the proxy system are under heavy influence from interferences such as congestion, latency, and retransmission. Also, multi-level streaming services affects from temporal synchronization, which lead to degrade the service quality. This paper proposes a new segment-based buffer management mechanism which reduces performance degradation of streaming services and enhances throughput of streaming due to drawbacks of the proxy system. The proposed paper optimizes streaming services by: 1) Use of segment-based buffer management mechanism, 2) Minimization of overhead due to congestion and interference, and 3) Minimization of retransmission due to disconnection and delay. This paper utilizes fuzzy value $\mu$ and cost weight $\omega$ to process the result. The simulation result shows that the proposed mechanism has better performance in buffer cache control rate, average packet loss rate, and delay saving rate with stream relevance metric than the other existing methods of fixed segmentation method, pyramid segmentation method, and skyscraper segmentation method.

• Journal of the Korea Society of Computer and Information
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• v.19 no.12
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• pp.71-80
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• 2014

Recently, most mobile nodes, such as smartphones, will have multiple wireless radio interfaces. This feature allows a mobile node to access a multi-network through multiple wireless radio interfaces simultaneously. Accordingly, various networking technology has been studied to use wireless multi-interface more efficiently. In this paper, MPTCP based handover scheme is proposed to reduce data loss and end-to-end latency during the handover in PMIPv6 domain. The proposed scheme performs 2-step flow mobility on the multi-path established through the multi-interface of mobile node in the handover procedure and uses MPTCP subflow function to overcome end-to-end disconnection during the handover. Therefore, the proposed scheme takes the advantage of being able to minimize data loss and a latency generated during performing the handover of mobile node.

• Safety and Health at Work
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• v.10 no.4
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• pp.400-408
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• 2019

The "fourth industrial revolution" (FIR) is an age of advanced technology based on information and communication. FIR has a more powerful impact on the economy than in the past. However, the prospects for the labor environment are uncertain. The purpose of this study is to anticipate and prepare for occupational health and safety (OHS) issues. In FIR, nonstandard employment will be common. As a result, it is difficult to receive OHS services and compensation. Excessive trust in new technologies can lead to large-scale or new forms of accidents. Global business networks will cause destruction of workers' biorhythms, some cancers, overwork, and task complexity. The social disconnection because of an independent work will be a risk for worker's mental health. The union bonds will weaken, and it will be difficult to apply standardized OHS regulations to multinational enterprises. To cope with the new OHS issues, we need to establish new concepts of "decent work" and standardize regulations, which apply to enterprises in each country, develop public health as an OHS service, monitor emerging OHS events and networks among independent workers, and nurture experts who are responsible for new OHS issues.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.49 no.4
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• pp.82-88
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• 2012

A VANET (Vehicular Ad Hoc Network), a subclass of MANET (Mobile Ad Hoc Network), is an ad hoc network using wireless communication between vehicles without fixed infrastructure such as base station. VANET suffers a frequent link breakage and network topology change because of the rapid movement of vehicles and the density change of vehicles. From these characteristics of VANET, geographical routing protocols such as GPSR (Greedy Perimeter Stateless Routing) using only the information of neighbor nodes are more suitable rather than AODV and DSR that are used in existing MANETs. However, GPSR may have a transmission delay and packet loss by frequent link disconnection and continual local maxima under the low vehicle density conditions. Therefore, in this paper, we propose a DTVR (Delay Tolerant Vehicular Routing) algorithm that perform a DTN-based routing scheme if there is no 2-hop neighbor nodes for efficient routing under the low vehicle densities in VANETs. Simulation results using ns-2 reveal that the proposed DTVR protocol performs much better performance than the existing routing protocols.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.1
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• pp.130-135
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• 2005

The electrical fire frequently happens through careless use such as poor contact, mechanical stress on power cord sets. In this paper, we simulated a wall-model in order to investigate the patterns of fire dispersion on power cord sets which consists of vinyl cord and rubber cord, etc. The fire progress and dispersive patterns were measured by a high speed imaging system(HG-100K, REDLAKE, USA). From the results, the fire pattern of power cord sets was progressed in order of flashover, scattering and disconnection. The short-circuit of the vinyl cords happened easier than the rubber cords by the external flame. In case vinyl cord is disconnected. the fire progress is not observed because the ignition energy decreases. Whereas, the fire progressed continuously in case of the rubber cord.

• Journal of the Korean Society of Safety
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• v.32 no.2
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• pp.27-33
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• 2017

This study is intended to identify issues on the basis of investigating the actual state of laboratory environment and outlet circuit, and derive end states by expressing sequences from the initiating event of disaster to accident in leakage current, poor contact and overload through ETA(event tree analysis). To this end, this study investigated the actual state of electric equipment of laboratory at universities in all parts of country. And it is shown that most of them are failure in electric work and user negligence in the investigation of actual state. It is found that there is earth fault and defect in wire diameter in the failure of electric work and the problem of partial disconnection due to wire bundling and poor contact in user negligence. Outlet-related component, failure rate and initiating events are composed of a total of 41 initiating events, i.e., 30 internal initiating events and 11 external initiating events. And end states are composed of a total of 15 parts, i.e., 3 electric power parts and 12 safety parts. Earthing class 3 is the most important safety device against leakage current (initiating event). And in case of poor contact, it is necessary for manager to check thoroughly because there is no safety device. In case of overload/overcurrent, when high-capacity equipment is connected, a molded case circuit breaker, safety device, worked. However, in most cases, it is verified that this doesn't work. This study can be utilized as electric equipment safety guide for laboratory safety manager and managers.

• Journal of Korea Multimedia Society
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• v.11 no.1
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• pp.106-116
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• 2008

It is difficult to provide Web services on a mobile environment because of the intermittent disconnection of a wireless network and the frequent change of context information. To resolve this, Web services must be migrate to devices, which can provide services to users seamlessly. However, researches on hosting, migrating, and replicating Web services on mobile devices are still in an early stage. This paper presents a lightweight Web service framework and an efficient method for establishing a policy of migrating Web services. Based on the WS-Policy standard, the proposed method defines a policy schema, which provides constructs for describing various kinds of contextual information. Specifically, the schema is designed to be extensible enough for different service providers to use different vocabularies to describe their policies. To show the validity, the proposed method for establishing a migration policy has been applied to our mobile Web services framework, resulting in a seamless provisioning of services.