• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.5
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• pp.179-190
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• 2020

This research analyses the financial characteristics of corporate R&D intensity in the Korean capital market. It is important to pay greater attention to this subject, given the current situation of the shortage of core components domestically in Korea. Three hypotheses are postulated to investigate the financial factors of R&D investments for KOSDAQ-listed firms during the post-era of the global financial turmoil. By applying a conditional quantile regression (CQR) model, three variables included R&D intensity in the previous year (Lag_RD), the squared term of Lag_RD, and interaction between the high-tech sector and Lag_Rd, reveal significant effects on the current R&D ratio. Whereas more than half of the total variables show variable impacts between firms with higher and lower R&D intensity, only Lag_RD and squared term of Lag_RD were found to be significant. It is expected that these results may contribute to being financial catalysts for an optimal level of R&D expenditures, thereby maximizing firm value for shareholders in KOSDAQ-listed firms.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.5
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• pp.648-655
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• 2020

The firing pin of modern automatic rifles detonates the primer of loaded ammunition via a hammer. During this process, the firing pin receives an impact load and repetitive force throughout the life of the rifle. An endurance test of a rifle showed that the firing pin breaks prematurely at 96.26% of life. Accordingly, a case study was conducted through cause analysis and a reconstruction test. Optical microscopy and scanning electron microscopy of the broken surface of the firing pin showed that a crack began in the circumferential direction of the surface, resulting in a fatigue crack to the core after repeated impact. Crack growth and fatigue destruction occurred at the end due to the repetitive impact and was estimated using a notch. For verification, a sample that produced a 0.03mm circumferential notch was broken at 64.25% of life in the reconstruction test. A test of breakage according to the notch types showed that a 0.3mm and a 0.5mm one-side notch were broken at 66.53% and 50.76%, respectively, and a 0.03mm six-point notch was broken at 85.65%. The endurance life of a sample firing pin with a rough surface and tool mark was examined, but an approximately 381 ㎛ internal crack formed. Through this study, failure for each notch type was considered. These results show that quality control of the notch and surface roughness is essential for ensuring the reliability of a component subjected to repeated impact.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.4
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• pp.393-399
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• 2017

In a reciprocating compressor, the piston and connecting rod are important parts. Excess mechanical stress on these parts may cause damage, and broken parts are expensive and difficult to replace. Therefore, it is necessary to analyze the mechanical stress affecting durability and longevity. The main purpose of this study was to identify locations of maximum stress on pistons and connecting rods. Based on dynamic calculation of the working process of a specific air compressor, an analysis of piston and connecting rod performance has been completed. A three-dimensional model for the air compressor's pistons and connecting rods was built separately, and FEM analysis of these components was carried out using a numerical method. The pistons were loaded by pressure which was changed according to crankshaft angle without thermal boundary conditions. The simulation results were used to predict and estimate stress concentration as well as the value of this stress on pistons and connecting rods. The maximum equivalent stress calculated are over 190 MPa on pistons and 123 MPa on connecting rods at crank angle $135^{\circ}$ and $225^{\circ}$ but these are under tensile yield strength. Besides, the calculated safety factors of connecting rods and pistons is higher than 1. Moreover, the results obtained can be used to provide manufacturers with references to optimize the design of pistons and connecting rods for reciprocating compressors.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.77-84
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• 2018

As the application of BIM (Building Information Modeling) to the civil sector has become practical, and mandatory for road projects, the standardization, development of systems, etc. for the application and operation of BIM are required. In particular, it is important to develop BIM data standards for producing, sharing and managing the lifecycle data of civil facilities because they are commonly national public facilities. The BIM data standards have been developed by utilizing or extending IFC (Industry Foundation Classes), which is an international standard, but schema extensions of river facilities has not been developed thus far. This study proposes an approach to an IFC extension for river facilities using the WBS (Work Breakdown Structure) as a fundamental study for IFC-based schema extension in the river field. For this purpose, the research was carried out as follows. First, the IFC extension development method was selected to represent the river facilities by analyzing the existing IFC structure and previous research cases for the IFC extension. Second, extended elements of the river facilities were identified through an analysis of the WBS and classified according to the high-level structure of the IFC schema. Third, the classified elements were arranged based on the IFC hierarchy and the IFC schema extension for river facilities was established. Based on the suggested extension method of IFC schema, this study developed the schema by defining the element components and parts of river facilities, such as distribution flow elements and deriving their detailed types and properties.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1789-1793
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• 2008

전자파표면유속계는 홍수유속측정을 위하여 개발된 기기로 평 갈수기에는 유속측정이 불가하여 프로펠러 유속계를 이용하고 있다. 현재 보급된 전자파표면유속계는 하천의 흐름방향에 나란하게 설치하였을 때에만 유속을 측정할 수 있는 기기의 구조상의 한계성 때문에 교량이 없는 지점에서는 유속측정이 불가하여 유량산정을 할 수가 없다. 또한 편각측정이 불가능하여 기기를 각 측선마다 이동 설치하여야 하기 때문에 유속측정시 효율성 떨어진다. 이에 홍수시 유량측정의 효율성을 증대시키고 전자파표면유속계의 활용도를 높이고자 편각측정이 가능하도록 전자파표면유속계의 성능을 개선하는 것이 본 연구의 주된 목적이다. 전자파표면 유속계에서의 편각 측정은 하천의 유속방향을 기준으로 정면에서 측정하면 수평 편각이 0도가 되며 좌우로 안테나를 회전하여 움직인 각도가 측정 편각으로 결정된다. 현장에서 전자파표면유속계의 사용시 편의성을 높이고 유량측정을 효율적으로 하기 위해서는 가급적 편각을 크게 해서 측정을 해야 하지만, 편각이 증가하면 전자파의 물리적 특성 때문에 반사된 신호의 수신 크기가 감소하여 측정이 불가능하게 된다. 이러한 문제를 해결하기 위해서는 유속 측정시 전자파 출력을 기존의 시스템보다 높게 물표면에 발사하여야 하며 안테나를 포함한 RF 모듈의 수신감도 및 지향성이 개선되어야 한다. 이에 편각측정이 가능하도록 이러한 사항에 주안점을 두어 새로운 시스템을 구성하였다. 수신감도 향상을 위해서는 물표면에 반사되어 돌아오는 신호를 가장 먼저 수신하는 안테나의 특성이 중요하며 그 다음 수신용 증폭기, IF 증폭기 순으로 개선이 필요하다. 본 연구에서는 안테나의 형태를 기존 파라볼릭 안테나에서 위상 배열 평면안테나로 변경하였으며, 이에 따른 이점으로는 송수신부를 분리하여 하나의 평면에 두 개의 안테나를 구성할 수 있다는 사항이다. 즉 외형적으로는 하나의 안테나로 보이지만 두 개의 안테나가 하나로 구성된 것이다. 송수신부를 분리하는 형태는 기존 파라볼릭 안테나에선 불가능한 구조로 변경에 따른 수신감도 향상은 수치적으로 10dB 이상 개선하였다. 송수신부 분리가 수신감도에 영향을 미치는 이유는 물표면으로 발사된 송신 신호의 일부가 수신단으로 유입되는 현상으로 누설되는 송신 신호를 최대한 차단하는 분리도가 수신 신호 검출에 직접적인 양향을 주기 때문에다. 평면 안테나를 적용하면 기존 파라볼릭 안테나에서 사용하던 써큘레이터라는 부품을 삭제할 수 있으며, 안테나의 구조적인 분리를 통해서 수신감도를 개선할 수 있었다. 안테나의 지향성은 발사하는 전자파의 빔폭 성능과 일치하며 각도 단위로 표시한다. 각도 값이 작을수록 전자파의 에너지가 한 곳에 집중된다고 말할 수 있다. 즉 빔폭이 크면 측정시 반사면적이 커져 정확한 지점의 유속을 측정하기 어려운 문제가 발생한다. 본 연구를 통해 빔폭은 기존 안테나 대비2도를 개선하였으며 25%의 개선 효과를 얻었다. 또한 수신감도 및 지향성 개선과 더불어 전자파의 출력을 기존 장비 대비하여 1.6배를 증가하여 편각측정을 위한 전자파표면 유속계의 성능을 개선하였다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.1
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• pp.10-19
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• 1992

Mn - Zn Ferrite has physical properties of the high initial permeability, saturation magnetic flux density, and low loss factor as a representative magnetic material of soft ferrites, in addition the mechanical property is excellent as a single crystal. Therefore it is important electronic components and used for VTR Head. Mn - Zn Ferrite single crystals with the diameter 8mm were grown in atmosphere mixed with $O_2$ and Ar gas by the Floating Zone(FZ) method that impurities can not be incorporated to the crystals because of not-using the crucible to put in the melt, and the sharp temperature gradient results from making a focus at one point utilizing the infrared ray emitted from the halogen lamp as a heat source. During the crystal growing, the highest temperature of melting area was maintained to be $1650^{\circ}C$, growth rate and rotation rate were 10 mm/hr, 20 rpm respectively. The phases and the growth directions of crystals were determined from the analysis of X RD patterns, Laue, TEM diffraction patterns and etch pit shapes were observed by the optical microscope through the chemical etching. The corelation of optimum conditions for acquiring the better crystals was found out with the growth rate, the length and diameter of melt at the interface according to the diameter of feed rod, and the patterns of growing interface also studied.

• Journal of the Korean Magnetics Society
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• v.21 no.3
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• pp.116-119
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• 2011

A Chinese shipping boat collided with two Japanese coast guard boats in waters near the disputed Senkaku islands (known as Diaoyudao in China) in the East China Sea on September 7th last year. The boat was held and captain was arrested by Japanese Government. The incident soon turned into a big political and economic conflict between the two countries. Japan's intention was to show her tight control over Senkaku, whereas China's intention was to make it a disputed territory in the eyes of international politics. While the conflict was going on, a top-rank bilateral talk between the two countries was suspended, boycott of Japanese goods was suggested, numerous rallies were held in both countries. This situation lasted for several months until China used an extreme card of "Cutting Supply of Rare Earth to Japan". Under this pressure, Japan instantly released the captain and closed the case. Over this incident, public noticed the importance of rare earth and its impact on the global economy. Since then, the policy of Chinese Government for the rare earth has created more confusion and turmoil in the global market. The purpose of this article is to overview the price rally and future of the rare earth.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.2
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• pp.128-139
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• 2017

Railway is one of the public transportation systems along with shipping and aviation. With the recent introduction of high speed train, its proportion is increasing rapidly, which results in the higher risk of catastrophic failures. The wheel bearing to support the train is one of the important components requiring higher reliability and safety in this aspect. Recently, many studies have been made under the name of prognostics and health management (PHM), for the purpose of fault diagnosis and failure prognosis of the bearing under operation. Among them, the most important step is to extract a feature that represents the fault status properly and is useful for accurate remaining life prediction. However, the conventional features have shown some limitations that make them less useful since they fluctuate over time even after the signal de-noising or do not show a distinct pattern of degradation which lack the monotonic trend over the cycles. In this study, a new method for feature extraction is proposed based on the observation of relative frequency energy shifting over the cycles, which is then converted into the feature using the information entropy. In order to demonstrate the method, traditional and new features are generated and compared using the bearing data named FEMTO which was provided by the FEMTO-ST institute for IEEE 2012 PHM Data Challenge competition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.2 s.72
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• pp.195-202
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• 2006

Thin-walled structures are efficiently utilized an automobiles, aircraft, satellite and ship as well as needed light weight simultaneously. This paper presents new shape of automobile hood reinforcement that rotating parts as engine, transmission are protected by thin-walled structures. The automobile hood is concerned about the resonance occurs due to the frequency of the rotating parts. The hood must be designed by supporting the stiffness of design loads and considering the natural frequencies. Hence, it is sustained the stiffness and considered the vibration by resonance. It is deep related to ride. Therefore, the topology, shape and size optimization methods are used to design the automobile hood. Topology technique is applied to determine the layout of a structural component optimum size with maximized natural frequency by volume reduction. In this research, The optimal structure layout of an inner reinforcement of an automobile hood for the natural frequency of a designated mode is obtained by using topology optimization method. The optimum size and the optimum shape are determined by PLBA(Pshenichny-Lim-Belegundu-Arora) algorithm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1307-1313
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• 2011

The mechanical limited slip differential (LSD) in vehicles is being replaced by the electromagnetic LSD because of its fast response and better active control characteristics. The coil housing made of STS 304 is one of the most important parts in the solenoid assembly of the electromagnetic LSD. High geometrical accuracy is a prerequisite for the manufacture of such coil housings, but precision machining is difficult because of the use of STS 304 thin plate and the variance in machining variables. The aim of this study is to optimize the mean and variance of the shape accuracy in the coil housing by finding a robust solution for the machining process conditions. The mean and standard deviation of the jaw contact pressure, cutting speed, and feed rate are considered to be the major parameters for minimizing the geometrical mean and variance. The response surface model based on the second-order Taylor series is combined together to minimize the mean and variance of the shape accuracy of the coil housing.