• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.1
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• pp.310-317
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• 1995

Crack detection technique by ultrasonics in structures and components made of austenitic stainless steel often loses its reliability due to the material characteristics during inservice inspection of nuclear power plants, especially in the area of detection and sizing in centrifugally cast stainless steel pipings. In order to understand and overcome this problem, computer program for tracing the ultrasonic rays within material has been developed to simulate the process of defect detection within weld. The program simulates through transmission and reflection technique in crack detection of austenitic stainless steel as well as ultrasonic beam propagation through multiple media including stainless steel cladding interface.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.5
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• pp.8-14
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• 2008

For nondestructive inspection of electron beam (EB) welding part in automotive power transmission assembly, a pulse-echo ultrasonic testing apparatus in water immersion has been applied using the ultrasonic waves with a frequency of 10MHz. However various problems have appeared during the ultrasonic inspection, which led to some significant mistakes in automatic quality evaluation of the welding parts. Experimental study showed that the state of water couplant medium containing some amount of contaminants, rusts and anti-corrosion agents had considerable influences on the reduction of ultrasonic amplitudes during wave propagation. The amplitude reduction depending on the coupling medium state could bring about some mis-diagnoses for defects in the welding parts. The results proposed that for a reliable inspection of defects in welds the state of water medium should be kept in about 15 volume fractions (vol.%) of anti-corrosion agents and in minimized contaminants.

• Journal of Korea Foundry Society
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• v.29 no.4
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• pp.176-180
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• 2009

Effect of matrix microstructure on creep behaviors of squeeze cast magnesium matrix composites was investigated. Aluminum borate whisker was used as reinforcement and AZ31, AS52 and Sr added AS52 Mg alloys were used for matrix alloys. The reinforcement was distributed homogeneously and defect-free composite was manufactured. Creep tests were carried out at the temperature of $150^{\circ}C$ under the applied stress of 50 and 100 MPa for Mg alloys and Mg MMCs, respectively. The creep resistance of Mg MMCs was in this order: AS52-Sr > AS52 AZ31 MMCs. Void initiation during creep mainly occurred at $Mg/Mg_{17}Al_{12}$ interface and propagation went along grain boundaries. On the other hand, $Mg_2Si$ phase was not attributed to the creep void initiation.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.8
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• pp.742-747
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• 2015

The quality of steel plate products is determined by the number of defects and the process problems are estimated by shapes of defects. Therefore pinholes defects of cold rolled steel have to be controlled. In order to improve productivity and quality of products, within each production process, the product is inspected by an adequate inspection system individually in the lines of steelworks. Among a number of inspection systems, we focus on the pinholes detection system. In this paper, we propose an embedded system using FPGA which can detect pinholes defects. The proposed system is smaller and more flexible than a traditional system based on expensive frame grabbers and PC. In order to detect consecutive defects, FPGAs acquire two dimensional image and process the image in real time by using correlation of lines. The proposed pinholes detection algorithm decreases arithmetic operations of image processing and also we designed the hardware to shorten the data path between logics due to decreasing propagation delay. The experimental results show that the proposed embedded system detects the reliable number of pinholes in real time.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.12
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• pp.2313-2321
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• 2008

In order to develop reliable on-site partial discharge(PD) pattern recognition algorithm, the fuzzy neural network based on fuzzy set(FNN) and the polynomial network pattern classifier based on fuzzy Inference(PNC) were investigated and designed. Using PD data measured from laboratory defect models, these algorithms were learned and tested. Considering on-site situation where it is not easy to obtain voltage phases in PRPDA(Phase Resolved Partial Discharge Analysis), the measured PD data were artificially changed with shifted voltage phases for the test of the proposed algorithms. As input vectors of the algorithms, PRPD data themselves were adopted instead of using statistical parameters such as skewness and kurtotis, to improve uncertainty of statistical parameters, even though the number of input vectors were considerably increased. Also, results of the proposed neuro-fuzzy algorithms were compared with that of conventional BP-NN(Back Propagation Neural Networks) algorithm using the same data. The FNN and PNC algorithms proposed in this study were appeared to have better performance than BP-NN algorithm.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.771-772
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• 2010

X-ray equipment used to diagnose a patient has a big defect of a patient's exposure to radiation caused in irradiating X-ray to the human body, ICRP restricts the permissible exposure dose of the human body. A number of studies has been proceeded to reduce these exposures. In this study the high voltage generator with inverter system, which is possible to increase the generation efficiency of X-ray and to control the precise output power was produced. Also, to minimize the ripple which is possible to occur in the direct voltage that is applied to X-ray tube the propagation rectification method was applied and the radiation reproducibility and properties were evaluated to use this for the diagnosis of patient.

• Journal of the Korean Society for Railway
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• v.11 no.6
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• pp.524-529
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• 2008

The damaged wheel in railway vehicle would cause a poor ride comfort, a rise in the maintenance cost and even fracture of the wheel, which then leads to a tremendous social and economical cost. The defect initiation and crack propagation in wheel may result in the damage of the railway vehicle or derailment. Therefore, it is important to evaluate the characteristics of the wheel tread. In the present paper, the characteristics of wheel tread based on contact positions, running distance and brake pattern are evaluated. The result shows that the damaged wheel tread is remarkably depended on the contact positions between wheel and rail.

• Structural Engineering and Mechanics
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• v.90 no.6
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• pp.591-600
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• 2024

This study investigated the acceleration response and shape change characteristics of a gravity quay wall according to the magnitude of the applied acceleration. The quay wall was defined as a port facility damaged by the Kobe earthquake. Four experimental scenarios were established based on the inclination condition grades, considered to be a significant defect factor in the quay wall. Then, the shaking table test was conducted using scaled-down quay wall models constructed per each scenario. The ground acceleration was gradually increased from the peak ground acceleration (PGA) of 0.1 g to 0.7 g. After each ground acceleration test, acceleration installed on the wall and backfill ground and inclination on the top of the wall were measured to assess the amplification of peak response acceleration and maximum response amplitude and the change in the inclination of the quay wall. This study also analyzed the separation of the quay wall from the backfill and the crack pattern of the backfill ground according to PGA values and inclination condition grades. The result of this study shows that response acceleration could provide a reasonable prediction for the changes in the inclination of the quay wall and the crack generation and propagation on the backfill from a current inclination condition grade.

• The Journal of the Acoustical Society of Korea
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• v.29 no.5
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• pp.314-324
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• 2010

In waveguide structures, waves may be partially reflected by local non-uniformities. The effects of local non-uniformities has been previously investigated by means of a combined spectral element and finite element (SE/FE) method at relatively low frequencies. However, since the SE is formulated based on a beam theory, the SE/FE method is not appropriated for analysis at higher frequencies where complex deformation of the waveguide occurs. So it is necessary to extend this approach for high frequencies. For the wave propagation at higher frequencies, a combined spectral super element and finite element (SSE/FE) method is introduced in this paper. As an example of the application of this method, wave reflection and transmission due to a local defect in a rail are simulated at frequencies between 20kHz and 30kHz. Also numerical errors are evaluated by means of the conservation of the incident power.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.246-246
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• 2016

Tungsten-nitrogen (W-N) co-doping has been known to enhance the photocatalytic activity of anatase titania nanoparticles by utilizing visible light. The doping effects are, however, largely dependent on calcination or annealing conditions, and thus, the massive production of quality-controlled photocatalysts still remains a challenge. Using density functional theory (DFT) thermodynamics and time-dependent DFT (TDDFT) computations, we investigate the atomic structures of N doping and W-N co-doping in anatase titania, as well as the effect of the thermal processing conditions. We find that W and N dopants predominantly constitute two complex structures: an N interstitial site near a Ti vacancy in the triple charge state and the simultaneous substitutions of Ti by W and the nearest O by N. The latter case induces highly localized shallow in-gap levels near the conduction band minimum (CBM) and the valence band maximum (VBM), whereas the defect complex yielded deep levels (1.9 eV above the VBM). Electronic structures suggest that substitutions of Ti by W and the nearest O by N improves the photocatalytic activity of anatase by band gap narrowing, while defective structure degrades the activity by an in-gap state-assisted electron-hole recombination, which explains the experimentally observed deep level-related photon absorption. Through the real-time propagation of TDDFT (rtp-TDDFT), we demonstrate that the presence of defective structure attracts excited electrons from the conduction band to a localized in-gap state within a much shorter time than the flat band lifetime of titania. Based on these results, we suggest that calcination under N-rich and O-poor conditions is desirable to eliminate the deep-level states to improve photocatalysis.