• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.370-376
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• 2016

Corrosion on the surface of a structure can generate cracks or cause walls to thin. This can lead to fracturing, which can eventually lead to fatalities and property loss. In an effort to prevent this, laser imaging technology has been used over the last ten years to detect thin-plate structure, or relatively thin piping. The most common laser imaging was used to develop a new technology for inspecting and imaging a desired area in order to scan various structures for thin-plate structure and thin piping. However, this method builds images by measuring waves reflected from defects, and subsequently has a considerable time delay of a few milliseconds at each scanning point. In addition, the complexity of the system is high, due to additional required components, such as laser-focusing parts. This paper proposes a laser imaging method with an increased scanning speed, based on excitation and the measurement of standing waves in structures. The wavenumber of standing waves changes at sections with a geometrical discontinuity, such as thickness. Therefore, it is possible to detect defects in a structure by generating standing waves with a single frequency and scanning the waves at each point by with the laser scanning system. The proposed technique is demonstrated on a wall-thinned plate with a linear thickness variation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.12
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• pp.7292-7301
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• 2014

With the development of IT Info-Communications technology, the vehicle with a combination of wireless-communication technology has resulted in significant research into the convergence of the component of existing traffic with information, electronics and communication technology. Intelligent Vehicle Communication is a Machine-to-Machine (M2M) concept of the Vehicle-to-Vehicle. The Vehicle-to-Infrastructure communication consists of safety and the ease of transportation. Security technologies must precede the effective Intelligent Vehicle Communication Structure, unlike the existing internet environment, where high-speed vehicle communication is with the security threats of a wireless communication environment and can receive unusual vehicle messages. In this paper, the Vehicle Identification number between the V2I and the secure message communication protocol was proposed using hash functions and a time stamp, and the validity of the vehicle was assessed. The proposed system was the performance evaluation section compared to the conventional technique at a rate VPKI aspect showed an approximate 44% reduction. The safety, including authentication, confidentiality, and privacy threats, were analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2B
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• pp.302-312
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• 2010

Internet Protocol Television (IPTV) service is the convergence service of the telecommunication and broadcasting that provides various bidirectional multimedia contents by IPTV service subscribe's request through the high-speed internet. However, the proposed technologies current do not guarantee the security such as authentication between Set-Top-Box (STB) and the user mobile devices available IPTV service at home domain, and authentication of mobile user device at out of door. This paper proposes the authentication protocol for distributing content securely from STB to the users' mobile devices at home domain and authentication for network access and IPTV service access when the user's mobile device is moved out of the house. The proposed scheme using the proxy signature enables to distribute and protect securely the contents protected through an underlying Conditional Access System (CAS) without re-encrypting then that the existing scheme should employ. Then this protocol supports the authentication scheme to get service access authentication based on network access authentication using the signature, which the STB issued on behalf of the trust authority of IPTV service provider. Also the proposed authentication protocol reduces the total communication overhead and computation time comparing to the other authentication protocol.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.6
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• pp.436-449
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• 2013

In this paper, a numerical analysis is carried out to study the characteristics of supercavitating flows and the drag of relatively simple two-dimensional and axisymmetric bodies which can be used for supercavity generation device, cavitator, of a high-speed underwater vehicle. In order to investigate the suitability of numerical models, cavity flows around the hemispherical head form and two-dimensional wedge are calculated with combinations of three turbulence models(standard $k-{\epsilon}$, realizable $k-{\epsilon}$, Reynolds stress) and two cavitation models(Schnerr-Sauer, Zwart-Gerber-Belamri). From the results, it is confirmed that the calculated cavity flow is more affected by the turbulence model than the cavitation model. For the calculation of steady state cavity flows, the convergence in case of the realizable $k-{\epsilon}$ model is better than the other turbulence models. The numerical result of the Schnerr-Sauer cavitation model is changed less by turbulence model and more robust than the Zwart-Gerber-Belamri model. Thus the realizable $k-{\epsilon}$ turbulence model and the Schnerr-Sauer cavitation model are applied to calculate supercavitating flows around disks, two dimensional $10^{\circ}$ and $30^{\circ}$ wedges. In case of the disk, the cavitation number dependences of the cavity size and the drag coefficient predicted are similar to either experimental data or Reichardt's semi-empirical equations, but the drag coefficient is overestimated about 3% higher than the Reichardt's equation. In case of the wedges, the cavitation number dependences of the cavity size are similar to experimental data and Newman's linear theory, and the agreement of the cavity length predicted and Newman's linear theory becomes better as decreasing cavitation number. However, the drag coefficients of wedges agree more with experimental data than those of Newman's analytic solution. The cavitation number dependences of the drag coefficients of both the disk and the wedge appear linear and simple formula for estimating the drag of supercavitating disks and wedges are suggested. Consequently, the CFD scheme of this study can be applied for numerical analysis of supercavitating flows of the cavitator and the cavitator design.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2
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• pp.101-112
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• 1995

In order to construct a feature map-based phoneme classification system for speech recognition, two procedures are usually required. One is clustering and the other is labeling. In this paper, we present a phoneme classification system based on the Kohonen's Self-Organizing Feature Map (SOFM) for clusterer and labeler. It is known that the SOFM performs self-organizing process by which optimal local topographical mapping of the signal space and yields a reasonably high accuracy in recognition tasks. Consequently, SOFM can effectively be applied to the recognition of phonemes. Besides to improve the performance of the phoneme classification system, we propose the learning algorithm combined with the classical K-mans clustering algorithm in fine-tuning stage. In order to evaluate the performance of the proposed phoneme classification algorithm, we first use totaly 43 phonemes which construct six intra-class feature maps for six different phoneme classes. From the speaker-dependent phoneme classification tests using these six feature maps, we obtain recognition rate of $87.2\%$ and confirm that the proposed algorithm is an efficient method for improvement of recognition performance and convergence speed.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2
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• pp.121-128
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• 2003

Acoustic Echo Cancellation(m) is very active research topic having many applications like teleconference and hands-free communication and it employs Double Talk Detector(DTD) to indicate whether the near-end speaker is active or not. However. the DTD is very sensitive to the variation of acoustical environment and it sometimes provides wrong information about the near-end speaker. In this paper, we are focusing on the development of robust DTD algorithm which is a basic building block for reliable AEC system. The proposed AEC system consists of delayless subband AEC and narrow-band DTD. Delayless subband AEC has proven to have excellent performance of echo cancellation with a low complexity and high convergence speed. In addition, it solves the signal delay problem in the existing subband AEC. On the other hand, the proposed narrowband DTD is operating on low frequency subband. It can take most advantages from the narrow subband such as a low computational complexity due to the down-sampling and the reliable DTD decision making procedure because of the low-frequency nature of the subband signal. From the simulation results of the proposed narrowband DTD and wideband DTD, we confirm that the proposed DTD outperforms the wideband DTD in a sense of removing possible false decision making about the near-end speaker activity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.7176-7181
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• 2015

This thesis is about the system where the solar module is attached to the high functional guardrail posts with anti-weed, anti-plant, and road-kill applied to produce internal power, enabling the integrated control and real-time monitoring of appearance of wildlife and road conditions using the USN. The whole system consists of a photovoltaic module(PV), a detection sensor(pyroelectric), a controller(operation select and motion sensor), the USN system, the DB(sound and flash), an output unit of sound and flash, and the control system of road-kill prevention and safety induction for vehicles. Thus this study aims to address the remote control and monitoring system of multipurpose guardrails to improve road environment, prevent road-kills, protect wild animals, and guide cars safely by using the USN which is combined with new renewable energy and IT convergence technology. As a result of the study on the remote control and monitoring system using the USN, it was ascertained that the response time of the unmanned sensing system was within 5.1 ms with the current consumption of 0.328 mA, and the data transmission speed of the remote control system was 250 kbps with the current consumption of 0.283 mA.

• Clean Technology
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• v.23 no.2
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• pp.133-139
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• 2017

Bio-based plastics containing the biomass content higher than 25 wt% have been considered as environment-friendly materials due to their effects on the reduction in the $CO_2$ emission and petroleum consumption as well as biodegradability after use. In this study, poly vinyl chloride, plant-derived plasticizers, by adding a biodegradable catalyst was observed a change in the biodegradability and physical properties. To produce the oxidative decomposition transparent bio film, which is broken down in the initial percent elongation and physical properties such as tensile strength, it was to test the safety of the product as a food packaging material. Poly vinyl chloride, primary plasticizer, secondary plasticizer, anti fogging agent, the combined stabilizer were mixed in a high speed mixer, then extruded using an extrusion molding machine, after cooling, winding, to produce a oxidative decomposition transparent bio film and the control film, with a thickness of $12{\mu}m$ through winder role. Mechanical properties tensile strength, elongation, and the maximum load elongation and biodegradation test. Transparent bio film produced by biodegradation catalyst is compared with the control film. Tensile strength and elongation of films were found to be no significant difference. Further, as a result of the biodegradation test for 45 days based on the ASTM D6954-04 method, biodegrability of film is 61.4%.

• Journal of Digital Convergence
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• v.14 no.9
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• pp.73-87
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• 2016

The purpose of this study is to investigate the cultural difference between eastern and western culture in the online community in view of Hofstede dimensions of national culture through social network analysis. And this study tries to interpret the cultural dimensions by using social network indexes. The results show every cultural dimension offered conflicting results except uncertainty avoidance. The eastern culture shows individualism, and low power distance compared to western culture in the online community. Moreover the communication speed of eastern culture is faster than western culture. But eastern culture shows high uncertainty avoidance in the online community similar to an offline culture. This results of this study show that because of certain differences between the offline and online culture, the typical framework we use to analyze offline culture should not be applied to analyze online culture. Therefore we believe that the most important contribution of this study should be related with the finding that we need very different approach to be able to correctly understand the prevalent culture in the online community than the one that we use in the offline community.

• Journal of IKEEE
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• v.18 no.2
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• pp.272-281
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• 2014

In electrical impedance tomography (EIT), modified Newton Raphson (mNR) method is widely used inverse algorithm for static image reconstruction due to its convergence speed and estimation accuracy. The unknown conductivity distribution is estimated iteratively by minimizing a cost functional such that the residual error namely the difference in measured and calculated voltages is reduced. Although, mNR method has good estimation performance, EIT inverse problem still suffers from ill-conditioned and ill-posedness nature. To mitigate the ill-posedness, generally, regularization methods are adopted. The inverse solution is highly dependent on the choice of regularization parameter. In most cases, the regularization parameter has a constant value and is chosen based on experience or trail and error approach. In situations, when the internal distribution changes or with high measurement noise, the solution does not get converged with the use of constant regularization parameter. Therefore, in this paper, in order to improve the image reconstruction performance, we propose a new scheme to determine the regularization parameter. The regularization parameter is computed based on residual error and updated every iteration. The proposed scheme is tested with numerical simulations and laboratory phantom experiments. The results show an improved reconstruction performance when using the proposed regularization scheme as compared to constant regularization scheme.