• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.125-133
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• 2011

The requirement for durability of concrete bridge deck is increasing as the deterioration for the concrete bridge deck exposed to severe environment has been increased. For this reason, the concern about high-durable concrete is being high. Recently, a metakaolin is highly spotlighted as new admixture because its strength and durability are equivalent to silica fume. On the other hands, there are few researches for the metakaolin concrete bridge deck in domestic. So many various long-term data on the mechanical property and durability is needed to apply metakaolin concrete at the concrete bridge deck construction field. This study is aim to evaluate the long-term mechanical properties and durability of metakaolin concrete bridge deck with curing age. Mechanical properties are estimated by the compressive and flexural strength, and the drying shrinkage, the chloride resistance, the scaling, and freezing and thawing characteristics are compared with curing age. According to the results, when the metakaolin concrete is used, the development of compressive and flexural strength proceed in both the early and old ages. It is also improved the resistance of chloride penetration, freezing and thawing in concrete. It was showed that replacement of metakaolin was efficient for the reduction of the drying shrinkage.

• Journal of Ocean Engineering and Technology
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• v.27 no.3
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• pp.61-66
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• 2013

This paper presents the results of finite element simulations of elastic wave propagation in an underwater steel plate and the verification of a proposed method utilizing elastic wave-based damage detection. For the simulation and verification, we carried out the following procedures. First, three-dimensional finite element models were constructed using a general purpose finite element program. Second, two types of damages (mechanical defects and deteriorations) were applied to the underwater steel plate and three parameters (defect location, defect width, and depth) were considered to adjust the severity of the applied damages. Third, elastic waves were generated using the oblique incident method with a Gaussian tone burst, and the response signals were obtained at the receiving point for each defect or deterioration case. In addition, the received time domain signals were analyzed, particularly by measuring the magnitudes of the maximum amplitudes. Finally, the presence and severity of each type of damage were identified by the decreasing ratios of the maximum amplitudes. The results showed that the received signals for the models had the same global pattern with minor changes in the amplitudes and phases, and the decreasing ratio generally increased as the damage area increased. In addition, we found that the defect depth was more critical than the width in the decrease of the amplitude. This mainly occurred because the layout of the depth interfered with the elastic wave propagation in a more severe manner than the layout of the width. An inverse analysis showed that the proposed method is applicable for detecting mechanical defects and quantifying their severity.

• Explosives and Blasting
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• v.30 no.1
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• pp.9-16
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• 2012

With the deterioration and functional loss of structures, there is an increasing demand for demolition and various demolition technologies have been developed. In case of a large-scale concrete foundation, application of some mechanical demolition techniques is limited because of the structural characteristics, and explosive demolition or explosive demolition combined with mechanical demolition is applied recently due to the effect to the surrounding environment by the ground vibration. In this study, we compared peak particle velocity of ground vibration depending on average fragment size in case of explosive demolition design for large-scale concrete foundation using the relation among specific charge, charge constant and transmitting medium constant as well as the relation between average concrete fragment size and specific charge.

• Journal of Biomedical Engineering Research
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• v.36 no.5
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• pp.228-234
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• 2015

The balance ability significantly decreased in the elderly because of deterioration of the neural musculature regulatory mechanisms. Several studies have investigated methods of improving balance ability using real-time systems, but it is limited by the expensive test equipment and specialized resources. Recently, Kinect system based on depth data has been applied to address these limitations. Little information about accuracy/inaccuracy of Kinect system is, however, available, particular in motion analysis for evaluation of effectiveness in rehabilitation training. Therefore, the aim of the current study was to evaluate accuracy/inaccuracy of Kinect system in specific rotational movement for balance rehabilitation training. Six healthy male adults with no musculoskeletal disorder were selected to participate in the experiment. Movements of the participants were induced by controlling the base plane of the balance training equipment in directions of AP (anterior-posterior), ML (medial-lateral), right and left diagonal direction. The dynamic motions of the subjects were measured using two Kinect depth sensor systems and a three-dimensional motion capture system with eight infrared cameras for comparative evaluation. The results of the error rate for hip and knee joint alteration of Kinect system comparison with infrared camera based motion capture system occurred smaller values in the ML direction (Hip joint: 10.9~57.3%, Knee joint: 26.0~74.8%). Therefore, the accuracy of Kinect system for measuring balance rehabilitation traning could improve by using adapted algorithm which is based on hip joint movement in medial-lateral direction.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.7
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• pp.84-93
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• 2007

The pole transformer is one of the most important facility to insure the stability of electric power supply. which distributes electricity to customers directly. However there are a lot of defects which are caused by manufacturing fails(in 3 years) or deterioration (in 13 years), so we need a more improved transformer which insures quality. This thesis talks about the development of the new-type transformer using the hybrid insulation that is durable thermally, mechanically, and electrically. It would show how to lay out and produce the transformer using the hybrid insulation. And finally we are sure that we could increase the utilization rate of a transformer by 160% as compared with its own capacity through the overload test. Also, we carried out the examination about the short-circuit and insulation with a 100[kVA] model transformer, so that we expound the analysis of magnetic-mechanical forces intensity and the measure for improving short-circuit efficiency.

• Polymer(Korea)
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• v.38 no.4
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• pp.525-529
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• 2014

PEDOT-$TiO_2$ hybrid conductive thin film including semiconductive metal oxide was successfully prepared via simultaneous vapor phase polymerization (VPP). The mechanical properties such as pencil hardness and anti-scratch property as well as optoelectrical properties of PEDOT-$TiO_2$ hybrid thin film could be improved as compared with pristine PEDOT thin film. Physicochemically stable crosslinked $TiO_2$ layer derived from a sol-gel process by FTS was generated in the PEDOT thin film layer by simultaneous VPP, resulting in improving mechanical properties of the hybrid thin films without any deterioration of their original optoelectrical properties. PEDOT-$TiO_2$ hybrid thin film showed better electrical conductivity as compared with PEDOT film. It might be due to the fact that the surface morphology of hybrid thin film prepared by simultaneous VPP showed smoother than that of pristine PEDOT thin film.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.811-819
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• 2003

The corrosion of steel reinforcing bar(re-bar) has been the major cause of the reinforced concrete deterioration. FRP(Fiber-reinforced polymer) reinforcing bar has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. However, FRP re-bar is pone to deteriorate due to other degradation mechanisms than those for steel. The high alkalinity of concrete, for instance, is a possible degradation source. Other potentially FRP re-bar aggressive environments are sea water, acid solution and fresh water/moisture. In this study long-term durability performance of FRP re-bar were evaluated. The mechanical and durability properties of two type of CFRP-, GFRP re-bar and one type of AFRP re-bar were investigated; the FRP re-bars were subjected to alkaline solution acid solution, salt solution and deionized water. The mechanical and durability properties were investigated by performing tensile, compressive and short beam tests. Experimental results confirmed the desirable resistance of FRP re-bar to aggressive chemical environment.

• The Journal of Engineering Geology
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• v.14 no.4 s.41
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• pp.381-390
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• 2004

This study was performed to relate the weathering properties of Oyaish tuff from Japan to mechanical properties of rocks in terms of mineralogical alteration and chemistry. The tuff is composed of clinoptilolite, quartz, feldspars, mordenite, opal C-T, and smectite. Since fresh tuff contains approximately $30\~50\%$ zeolite, it is expected that the rock is subjected to weathering process ascribed to water contents on earth surface, significantly reducing mechanical strength of tuff. It is also anticipated that weathering process and properties may be different even in the same rock mass, due to the differences in local mineralogy, chemistry and microtextures in tuff.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.1
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• pp.12-18
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• 2007

As an arc fault interrupter, the AFCI mentioned in this paper has been designed to detect and interrupt arc faults due to wire deterioration, insulation, wire damage, loose connection, and excessive mechanical damage. Since AFCI is digital and uses mechanical and electric stress, the length of interruption against overload and over-current is much shorter than the current bi-metal method. Therefore, the risk of electrical fires has been reduced.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.3
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• pp.146-153
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• 2011

American NREL (National Renewable Energy Laboratory) reported that BDF20 could reduce PM, CO, SOx, and cancerogenic matters by 13.6%, 9.3%, 17.6%, and 13% respectively, compared to diesel fuel. BDF20 has been being tested on garbage trucks and official vehicles at Seoul City, which is positive on air environment, but negative on combustion by higher viscosity in winter season. This study investigated the combustion characteristics by applying pilot injection for improving the deterioration of combustibility caused by the higher viscosity of the BDF20 with the combustion flames taken by a high-speed camera and the cylinder pressure diagram. A 4-cycle single-cylinder diesel engine was remodeled to a visible 2-cycle engine taking the flame photographs, which has a common-rail injection system. The test was done laboratory temperature at $5{\sim}6^{\circ}C$. The results obtained are summarized as follows, (1) In the case of without pilot injection, the flame propagation speed was slowed and the maximum combustion pressure became lower. The phenomena became further aggravated as the fuel viscosity gets higher. (2) In the case of with pilot injection, early stage of combustion such as rapid ignition timing and flame propagation was activated since intermediate products formed by pilot injection act as a catalyst for combustion of main fuel.