• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.16-24
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• 2009

In this study, fatigue crack growth rate of a cracked railway bogie frame under variable amplitude loading is predicted by applying linear elastic fracture mechanics. For this purpose, we find the critical points by reference surveying on cracked railway bogie frames. And we make an effective load history by synthesizing the dynamic load measured from the critical points of railway bogie frame during commercial line operation and the static load calculated from structural analysis. Crack growth analyses are performed at the 3 critical points under the commercial operation loading condition by assuming an initial crack size as 40 mm. and the results are compared with the experimental results from Japanese railway bogie frame crack growth case. From the analysis results, we find that around 500,000 km operating distance is necessary to bring crack growth from the initial crack to unstable crack. And it takes around 3.8 normal operating years. We conclude that it is enough time to detect the crack between normal maintenance period.

• Journal of the Korea Society of Computer and Information
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• v.17 no.11
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• pp.73-81
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• 2012

This paper proposes an ETWAD(Encapsulation and Tunneling Wormhole Attack Detection) design based on positional information and hop count on Ad-Hoc Network. The ETWAD technique is designed for generating GAK(Group Authentication Key) to ascertain the node ID and group key within Ad-hoc Network and authenticating a member of Ad-hoc Network by appending it to RREQ and RREP. In addition, A GeoWAD algorithm detecting Encapsulation and Tunneling Wormhole Attack by using a hop count about the number of Hops within RREP message and a critical value about the distance between a source node S and a destination node D is also presented in ETWAD technique. Therefore, as this paper is estimated as the average probability of Wormhole Attack detection 91%and average FPR 4.4%, it improves the reliability and probability of Wormhole Attack Detection.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.6
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• pp.1-12
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• 2009

Recently, as the importance of Economical Driving has been gradually growing up, the needs for research on automatic analysis of driving patterns that will ultimately provide drivers the methods for Economical Driving have been increasingly risen. Based on this purpose, we have executed two things in this paper. First, we have collected overall driving information such as date, distance, driving time, speed, idle time, sudden acceleration/deceleration count, and the amount of fuel consumption. Second, we have analyzed the influences of driving patterns on economical driving by employing the data mining techniques. These results can be applied in preventing bad driving patterns which will have consequently bad effects on Economical Driving in two aspects: by presenting some information on the terminal of the vehicles such as idle time, over-speed time, sudden acceleration/deceleration count continuously and by providing the drivers with alert information when the idle time ratio and the over-speed time ratio are excessive.

• The Journal of Korean Association of Computer Education
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• v.7 no.1
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• pp.55-66
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• 2004

The Internet today provides group communication model, multicast service. It is important to keep security for multicast communication. Member leaving is associated with scalability problem for group key management. If one member of the group is removed, new group key has to be changed and communicated to all remaining members of group. Modification and distribution of new group keys for rekeying is an expensive operation. Minimizing the number of messages and operation cost for generation of the composite keys are important evaluating criteria of multicast key management scheme. Periodic rekey helps reducing these important parameters rather than removing members sequentially in fashion one after another. In this paper, Hamming distance is calculated between every members to be removed. The members with Hamming distance less than threshold are selected for rekeying procedure. With running the round assignment algorithm, our model has advantages of reducing the number of message and operation cost for generation of the composite keys for rekeying.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.4
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• pp.395-402
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• 2002

In the conventional public switched telephone network(PSTN), there are various types of modulation that can be used in ADSL to offer fast data communication, two of which are CAP(Carrierless Amplitude Phase) and DMT(Discrete MultiTone). As we consider the current situation, DMT is getting more predominant in the market than CAP. One of the reasons is that it gives high performance in spite of its high complexity Since DMT divides the full range of bandwidth into 256 sub-channels, it can be highly adaptive in the circumstances, where the problems of attenuation and noise caused by the propagation distance are very crucial. In this paper, a new bit loading algorithm for DMT modulation is proposed. The proposed algorithm can be efficiently implemented in a way that it requires less computation than the conventional modulation techniques. In contrast to the conventional algorithms which perform sorting processing, the proposed algorithm uses look-up tables to reduce the repetition of calculation. Consequently, it is shown that less processing time and lower complexity can be achieved.

• Journal of Broadcast Engineering
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• v.16 no.5
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• pp.846-860
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• 2011

The binaural auditory system of human has ability to differentiate the direction and the distance of the sound sources by using the information which are inter-aural intensity difference(IID), inter-aural time difference(ITD) and/or the spectral shape difference(SSD). These information is generated from the acoustical transfer of a sound source to pinna, the outer ears. We can create a virtual sound system using the information which is called Head related transfer function(HRTF). However the performance of 3D sound is not always satisfactory because of non-individual characteristics of the HRTF. In this paper, we propose the algorithm that uses human's auditory characteristics for accurate perception. To achieve this, excitation energy of HRTF, global masking threshold and loudness are applied to the proposed algorithm. Informal listening test shows that the proposed method improves the sound localization characteristics much better than conventional methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.10
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• pp.887-894
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• 2016

The CNG pressure vessel is manufactured by a deep drawing and ironing (D.D.I) process for forming cylinder parts, followed by a spinning process for formation of the dome part. However, studies on the buckling phenomenon of the dome part and formation of the inlet part have not been performed yet, and the CNG pressure vessel is produced by the experience of the field engineers and the trial and error method. In this study, buckling phenomenon during the spinning process was predicted by comparing critical buckling loads obtained through theoretical analysis with axial loads from the FEA, and a method for preventing buckling of the dome part was proposed by employing commercial software (Forge NxT 1.0.2). Also, to form the inlet part, forming loads of the roller at contact point between the roller and the dome part were analyzed according to radii of the dome part, and the inlet part was formed by controlling the radius of the dome part.

• Journal of Advanced Navigation Technology
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• v.18 no.4
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• pp.304-311
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• 2014

In this paper, we propose a ultra sound inspection technique for automatic defect detection and classification in aircraft composite materials. Using local maximum values of ultra sound wave, we choose peak values for defect detection. Distance data among peak values are used to construct histogram and to determine surface and back-wall echo from the floor of composite materials. C-scan image is then composed through this method. A threshold value is determined by average and variance of the peak values, and defects are detected by the values. PCA(principal component analysis) and QDA(quadratic discriminant analysis) are carried out to classify the types of defects. In PCA, 512 dimensional data are converted into 30 PCs(Principal Components), which is 99% of total variances. Computational cost and misclassification rate are reduced by limiting the number of PCs. A decision boundary equation is obtained by QDA, and defects are classified by the equation. Experimental result shows that our proposed method is able to detect and classify the defects automatically.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1780-1792
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• 2016

In this paper, we propose an efficient counter-based broadcast scheme for high reachability and energy efficiency. To achieve this, we propose a method to calculate additional coverage when a node receives the same broadcast message from both nodes, in order to rebroadcast by a node who can cover an large area. We also propose a formula to determine random access delay (RAD) considering addition coverage, distance, density, and remaining battery information, and a formula to determine count threshold ($C_{th}$) considering density and remaining battery information. In addition, we evaluate the performance of the proposed broadcast scheme compared with the existing counter-based broadcast schemes through simulation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1404-1411
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• 1993

This study was undertaken to investigate the corrosive wear charateristics upon various transformation condition of austempered low-alloy ductile cast iron in corrosive environments against mating specimen made of the hardened SM45C. The corrosive wear test was carried out by rubbing the annular surface of two test pieces in distilled water and aqueous solution at constant sliding speed of 0.5m/s. In severe wear region, the corrosive wear rate Wc increased hastily with NaCl concentration owing to intermetallic adhesion but Wc went down slowly in mild wear region due to lubricating effect of the corrosion product. The critical sliding distance decreased with increasing NaCl concentration due to increased generation rate of the corrosion product and the specific corrosive wear rate has maximum in 1% NaCl aqueous solution at mild wear region. With the variation of matrix, the corrosive wear resistance of the fine acicular bainite was higher than that of coarse upper bainite because of reducing the local cell reaction by carbides. A growth in volume fraction of retained austenite in matrix increased the Wc due to soften surface, but has a declining tendency of Wc in mild wear region.