• The Journal of the Korea Contents Association
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• v.18 no.1
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• pp.465-475
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• 2018

Recently, as the use of social media and IoT has increased, large graph streams has been generating and studies on real-time processing for them have been actively carrying out. In this paper we propose a incremental graph stream processing scheme that reuses previous result data when the graph changes continuously. We also propose a cost model to selectively perform incremental processing and static processing. The proposed cost model computes the predicted value of the detection cost and the processing cost of the recalculation area based on the actually processed history and performs the incremental processing when the incremental processing is more profit than the static processing. The proposed incremental processing increases the efficiency by processing only the part that changes when the graph update occurs. Also, by collecting only the previous result data of the changed part and performing the incremental processing, the disk I/O costs are reduced. It is shown through various performance evaluations that the proposed scheme outperforms the existing schemes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1619-1627
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• 2014

Wearable computer systems can use the wireless universal serial bus (WUSB) that refers to USB technology that is merged with WiMedia PHY/MAC technical specifications. In this paper, we focus on an integrated system of the wireless USB over the IEEE 802.15.6 wireless body area networks (WBAN) for wireless wearable computer systems supporting U-health services. And a communication structure that performs the time-synchronization is proposed for WUSB over IEEE 802.15.6 hierarchical protocol. Proposed time-synchronization mechanisms adopt the WBAN Polling Access and combine it with a time-synchronization middleware using time stamps. In our performance evaluations, time-synchronization performances with only WBAN Polling Access scheme are analyzed first. After that, performances combined with the time-synchronization middleware are analyzed to evaluate the effectiveness of proposed time-synchronization structure in WUSB over IEEE 802.15.6.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1610-1618
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• 2014

Wearable computer systems can use the wireless universal serial bus (WUSB) that refers to USB technology that is merged with WiMedia PHY/MAC technical specifications. In this paper, we focus on an integrated system of the wireless USB over the IEEE 802.15.6 wireless body area networks (WBAN) for wireless wearable computer systems supporting U-health services. And a communication structure that performs the hibernation for low power consumption is proposed for WUSB over IEEE 802.15.6 hierarchical protocol. In the proposed hibernation mechanisms, WUSB communications are permitted at each m-periodic inactive periods of WBAN superframes by using the WBAN information of Wakeup Period and Wakeup Phase message fields. In our performance evaluations, performances according to amount of WUSB traffic and Wakeup Periods are analyzed respectively to evaluate the effectiveness of proposed hibernation structure in WUSB over IEEE 802.15.6.

• Journal of the Korean Institute of Gas
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• v.15 no.2
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• pp.15-20
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• 2011

Although CNG is able to meet the current emission standards, it is expected to be impossible to satisfy the requirements of the next EURO-6 emission regulation without an additional after-treatment device. Hydrogen is known to be a gaseous fuel which features the wide flammability limit and the fast reactivity. A certain amount of hydrogen addition to CNG is able to extend the lean combustion range and produce lesser amounts of harmful emissions. In this research, the combustion and emission characteristics of HCNG(mixture of Hydrogen and CNG) fuel were experimented in an 11-liter heavy duty lean burn engine varying hydrogen contents, air-to-fuel ratio and spark timing. The optimization of this HCNG engine for a city bus was performed through the evaluations of oxidation catalyst characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.10
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• pp.2035-2046
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• 2015

Recently, researches on resource allocation algorithms operating in a distributed way are widely conducted because of the increasing number of network nodes and the rapidly changing the network environment. In this paper, we propose Multi-Hop DESYNC(MH DESYNC), that is bio-inspired TDMA-based resource allocation scheme operating in a distributed manner in multi-hop networks. In this paper, we define a frame structure for the proposed MH DESYNC algorithm and firing message structure which is a reference for resource allocation and propose the related operating procedures. We show that MH DSYNC can resolve the hidden-node problem effectively and verify that each node shares resources fairly among its neighboring nodes. Through simulation evaluations, it is shown that MH DESYNC algorithm works well in a multi-hop networks. Furthermore, results show that MH DESYNC algorithm achieves better performance than CSMA/CA algorithm in terms of throughput.

• Wind and Structures
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• v.21 no.3
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• pp.353-367
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• 2015

As concrete wind-turbine towers are increasingly being used in wind-farm construction, there is a growing need to understand the behavior of concrete wind-turbine towers. In particular, experimental evaluations of concrete wind-turbine towers are necessary to demonstrate the dynamic characteristics and load-carrying capacity of such towers. This paper describes a model test of a prestressed concrete wind-turbine tower that examines the dynamic characteristics and load-carrying performance of the tower. Additionally, a numerical model is presented and used to verify the design approach. The test results indicate that the first natural frequency of the prestressed concrete wind turbine tower is 0.395 Hz which lies between frequencies 1P and 3P (0.25-0.51 Hz). The damper ratio is 3.3%. The maximum concrete compression stresses are less than the concrete design compression strength, the maximum tensile stresses are less than zero and the prestressed strand stresses are less than the design strength under both the serviceability and ultimate limit state loads. The maximum displacement of the tower top are 331 mm and 648 mm for the serviceability limit state and ultimate limit state, respectively, which is less than L/100 = 1000 mm. Compared with traditional tall wind-turbine steel towers, the prestressed concrete tower has better material damping properties, potential lower maintenance cost, and lower construction costs. Thus, the prestressed concrete wind-turbine tower could be an innovative engineering solution for multi-megawatt wind turbine towers, in particular those that are taller than 100 m.

• Journal of the Korean Society for Railway
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• v.18 no.2
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• pp.111-116
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• 2015

LED luminaires as a lighting system have attracted much research attention due to their high efficiency and long lifetimes. However, disappointing outcomes have been noted in terms of performance levels and lifetimes as compared to desired system requirements in practice due to certain electrical and thermal characteristics of LEDs. LM-80 and TM-21 established by IESNA are the best known standards for lifetime test procedures and estimation techniques. However, they only handle LED light sources without guaranteeing the LED luminaire in a reliability test. They also operate for more than 6,000 hours and undergo various stresses, such as the operating current and temperature. Therefore, a lifetime standard for LED luminaires has not yet been established. This paper proposes a conceptual design of a lifetime test system for LED headlamps depending on the operating environment. Eventually, this method can assist with evaluations of the validity of lifetime standard tests of LED headlamps.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.6
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• pp.58-64
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• 2009

For the success of the reconfigurable computing, the algorithm for mapping operations onto coarse-grained reconfigurable architecture is very important. This paper proposes a resource-aware mapping system for the coarse-grained reconfigurable architecture and its own underlying heuristic algorithm. The operation assignment and the routing path allocation are simultaneously performed with a cycle-accurate time-exclusive resource model. The proposed algorithm minimizes the communication resource usage and the global memory access with the list scheduling heuristic. The operation to be mapped are prioritized with general properties of data flow. The evaluations of the proposed algorithm show that the performance is significantly enhanced in several benchmark applications.

• Journal of The Korean Association For Science Education
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• v.21 no.2
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• pp.255-263
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• 2001

The purpose of this study is to analyse the eighth grade students' performance of open investigations for two kinds of tasks: the qualitative one which involves the descriptive approach through observation, and the quantitative one which involves the quantitative data processing through control of variables. Researcher's observation, interview data as well as students' investigation reports, self-evaluations were analysed. The difficulties of qualitative open investigation lie in detecting and dealing with unexpected observations, of which the acceptance and interpretation were influenced by preconceptions. On the other hand, managing several variables, making reliable and valid measures, and quantitative data processing constituted main difficulties of quantitative open investigation. Some students could recognize the deficiencies of their methods and findings in qualitative one, but few in quantitative one. These results suggest the teaching point for each task of open investigations.

• Journal of the Korea Society of Computer and Information
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• v.13 no.2
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• pp.67-78
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• 2008

The purpose of this paper is to discuss the design and implementation of a WCBT(Web and Computer based Test). The WCBT combines the strengths of both a WBT(Web-based test) and a CBT(Computer-based test) on the basis of efficiency and stability. The current assessment system, considered an important management tool in the construction and operation of a total management system for the national technical qualification, has some unstable elements with regard to system load and stability. The proposed system's technological aspects have been tested through a basic simulation pilot program. The pilot program will be expanded to include the local Chamber of Commerce and Industry because the stability of the system was proved through its application to the real-time national technical examination of KCCI (Korea Chamber of Commerce and Industry). The WCBT system has shown great efficiency in terms of system load, and has solved frequent communication problems which have occurred through the use of foreign qualifying examinations. The server and client systems of the WCBT have been given good evaluations with regard to the convenience of their use and the management system for operators and supervisors.