• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.1053-1061
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• 2015

This paper discusses the analysis of the curl deformation behavior when a dynamic force is applied to a tearing tube installed on a flat die to predict the energy absorption capacity and deformation behavior. The deformation of the tips of the curling strips was obtained when the curl tips and tube body are in contact with each other, and a formula describing the energy dissipation rate caused by the deformation of the curl tips is proposed. To improve this formula, we focused on the variation of the curl radius and the reduced thickness of the tube. A formula describing the mean curl radius is proposed and verified using the curl radius measurement data of collision test specimens. These improved formulas are added to the theoretical model previously proposed by Huang et al. and verified from the collision test results of a tearing tube.

• Fire Science and Engineering
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• v.20 no.1 s.61
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• pp.71-76
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• 2006

The major causes of electrical fire are classified to short circuit fault, overload fault, electric leakage and electric contact failure. The occurrence factor of the fire is electric arc or spark accompanied with electrical faults. Residual Current Protective Device(RCD) of high sensitivity type used at low voltage wiring cuts off earth leakage and overload, but the RCD can't cut off electric arc or spark to be a major factor of electrical fire. As the RCDs which are applied low voltage distribution panel are prescribed to rated breaking time about 30[ms](KS C 4613), the RCDs can't perceive to the periodic electric arc or spark of more short wavelength level. To be improved on such problem, this paper is proposed to a auxiliary control apparatus for RCD trip on electric arc or spark due to electrical fire. Some experimental results of the proposed apparatus is confirmed to the validity of the analytical results.

• The Journal of the Convergence on Culture Technology
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• v.6 no.3
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• pp.327-334
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• 2020

Recently, mobile and smart devices are rapidly spreading. As a result, real estate services, which were formerly face-to-face, have now been replaced by mobile environments. This study focuses on the real estate app service and 261 samples were used for the empirical analysis. The results of the hypotheses test using structural equation model are summarized as follows. First, performance expectancy, facilitating conditions, security and aesthetic perceived by users of real estate services have positively influence on positive attitude, but effort expectancy and social influence do not. Second, positive attitude of real estate services have positive effects on service Acceptance. Third, involvement moderated the relationship between positive attitude and service Acceptance. Based on the results of the analysis, it provided meaningful implications for practitioners and researchers in related fields.

• Tribology and Lubricants
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• v.31 no.3
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• pp.109-124
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• 2015

This paper presents a wear analysis procedure for the journal bearings on a stripped-down single-cylinder engine during start-up and coast-down by motoring. A journal bearing is in the mixed elastohydrodynamic (EHL) lubrication region when the shaft speed is less than the corresponding lift-off speed. Below the lift-off speed, a wear scar can form on bearing surfaces. In part 1 of this paper, we develop the appropriate formulations and the calculation procedure for the analysis. Specifically, we formulate an equation for modified film thickness in a journal bearing considering the additional wear volume. In order to obtain the modified specific wear rate induced by the modified Archard’s wear coefficient, we utilized the extended non-dimensional diagram for the specific wear rate, k, the fractional film defect coefficient, Ψ and the asperity load sharing factor, γ₂. This asperity load sharing factor is newly calculated by setting the Zhao-Maietta-Chang (ZMC) asperity contact pressure equation coupled with the central film thickness equation derived by using the ZMC asperity contact model equal to the modified central contact pressure derived by using the central (or maximum) contact pressure at the dry rough line-contact configuration. We can use the procedure introduced in this paper to determine the lifetime (or longterm) linear wear in radial journal bearings that is a result of repeated stop-start cycles.

• Composites Research
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• v.27 no.6
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• pp.213-218
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• 2014

This paper predicted the strength of mechanical joint of composites under bending load by means of the characteristic curve method. The method has been employed only for tensile and compression load conditions, but in this study, this method was extended to the bending load condition. For the finite element analysis (FEA), the nonlinear analysis was conducted considering the contact and friction effects between composite material and pin. The failure strength and mode on characteristic curve were evaluate with Tsai-Wu failure theory. To validate the results of FEA, the experiments were conducted to find out the failure load by applying bending moment on the composite specimens. The results showed reasonable agreements with theoretical results. These results lead to a conclusion that the characteristic curve method can be applied to predict the bending strength of mechanical joint of composites.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.7
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• pp.629-636
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• 2013

Pneumatic levitation is based upon Bernoulli's principle. However, this method is known to require a large gas flow rate that can lead to an increase in the cost of products. In this case, the gas flow rate should be increased, and the compressible effects of the gas may be of practical importance. In the present study, a computational fluid dynamics method has been used to obtain insights into Bernoulli levitation flows. Three-dimensional compressible Navier-Stokes equations in combination with the SST k-${\omega}$ turbulence model were solved using a fully implicit finite volume scheme. The gas flow rate, workpiece diameter,and clearance gap between the workpiece and the circular cylinder were varied to investigate the flow characteristics inside. It is known that there is an optimal clearance gap for the lifting force and that increasing the supply gas flow rate results in a larger lifting force.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.599-607
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• 2004

As buildings become more high-rise and lightweight in recent years, steel has been utilized more frequently. Based on the American AISC standard, all axial loads could be carried through a bearing load in a column splice, but according to Korean codes, the bearing load has constrained the stress that could be carried by only 25% of all axial loads. Thus, new column splice methods that use metal touch have been examined. In this study, the stress path mechanism, as an intermediation parameter in the gap's magnitude, must be determined. Similarly, the behavioral aspect of the metal touch connection must be sought after comparing and analyzing the results of the test.

• Communications of Mathematical Education
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• v.8
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• pp.247-255
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• 1999

대부분의 수학 교사들은 국내외에서 개최되는 많은 학술 행사에 참여하기를 꺼려하고 있으며 수학 교육의 새로운 정보에 접촉하려는 의지가 부족한 실정이다. 이 때문에 세계의 수학 교육의 흐름이 어떤지, 우리 나라의 수학 교육과정이나 교수 ${\cdot}$ 학습법이 외국의 것과는 어떻게 다른지 또는 수준에 차이가 있다면 얼마나 차이가 있는지 별 관심을 갖지 않고 있으며 구태여 많은 노력을 들여 이러한 것을 알려고 하지도 않는다. 필자의 판단으로는 우리 나라의 수학 교육이 당면하고 있는 가장 큰 문제는 수학 교사들은 많으나 우수한 자질을 가진 수학 교사들이 많지 않기 때문에 창의성 교육이 제대로 이루어지지 않는 것과 학교 수학 교육에서 능력별 반 편성이 무엇보다도 필요한 줄 알면서도 수십년 동안 제대로 실행되지 않아 학생들의 수준에 맞도록 효율적으로 수학을 지도할 수 없는 것이라 생각한다. 이 두 문제는 모두 몇몇 수학 교사들의 의지와 노력만으로는 해결할 수 없는 문제들이다. 그러나 많은 교사들이 모여 이러한 문제점들을 공동으로 인식하고 함께 해결하기를 노력한다면 시일이 좀 걸리더라도 언젠가는 해결되리라고 믿는다. 장기적으로 수학 교사의 자질을 향상시키기 위해서는 교사 양성 기관(사범대학과 교육대학교)의 개선이 필요하며, 능력별 반 편성은 교육정책자들이나 교육행정가들이 마음만 먹으면 1${\sim}$2년내에 이룰 수 있다. 이제 전국수학교육연구대회와 같은 행사는 단순한 수학교육이론의 전달이나 현장연구에서 발견한 새로운 사실들만은 발표하는 곳이 아니라, 될 수 있는 데로 많은 수학 교육자들이 모여 수학 교육의 문제점을 찾고, 함께 풀어 나가기 위한 토론의 장(場)이 되어야한다. 또 필요에 따라서는 수학 교육에 관련한 어떤 결의도 하고 교육부 또는 각 교육청이나 교육연구기관에 보내는 건의문도 만들어야 할 것이다. 어떻든 이와 같이 전국 수학교육자들이 모일 때는 꼭 참여하여 우리의 문제를 적극적으로 해결하도록 힘을 합치는 것이 수학교육자의 올바른 태도라고 생각한다.

• Nuclear Engineering and Technology
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• v.23 no.4
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• pp.374-386
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• 1991

Various factors affecting the teachability of Cs-137 in cement matrix have been investigated. Factors investigated include such as pressure curing, vibration curing, pressure leaching, the effect of the clay addition, ion-exchange resin(IRN-77) addition, and $CO_2$or air injection. Leaching experiments were conducted by the method recommended by IAEA. To analyze the experimental results, pore structure analysis of cement matrices was carried out by BET method. Cement matrices may not contact directly with underground water in real repository, since the surroundings of disposed drums are filled with backfill. Thus, the effect of backfill to the teachability has been investigated. The well-known diffusion theory was utilized to predict long term leach rate and cumulative fraction leached of Cs-137 or non-radioactive species.

• Journal of Korean Society of Forest Science
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• v.85 no.4
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• pp.647-655
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• 1996

This paper examined the effects of users' expectations, norms and recreation motives on perceived conflict in a recreation setting. The study used data collected at Second Campground in Chirisan National Park, Korea, during the summer of 1994. Of the total 280 questionnaires distributed, 253 questionnaires(90.4%) were usable. About 82% of the respondents perceived conflict by others' late-night-singing. This study supported the notion that perceived conflict occurs when norms, expectations, and recreation motives are interfered with by others' incompatible behaviors. Solitude/nature motive factor was a better predictor of perceived conflict than norm-interference or expectation-interference. However, the relative predictability of each variable on perceived conflict could be various depending on different kinds of recreation motives, specific ways of measuring norms, expectations and conflict. Management implications were discussed.