• Advances in materials Research
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• v.6 no.2
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• pp.155-168
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• 2017

The terrorist attacks and dangers by bomb blast have turned into an emerging issue throughout the world and the protection of the people and structures against terrorist acts depends on the prediction of the response of structures under blast and shock load. In this paper, behavior of aluminum and unidirectionally reinforced E-Glass Epoxy composite plates with and without focal circular holes subjected to shock loading has been identified. For isotropic and orthotropic plates (with and without holes) the classical normal mode approach has been utilized as a part of the processing of theoretical results. To obtain the accurate results, convergence of the results was considered and a number of modes were selected for plate with and without hole individually. Using a shock tube as a loading device, tests have been conducted to composite plates to verify the theoretical results. Moreover, peak dynamic strains, investigated by experiments are also compared with the theoretical values and deviation of the results are discussed accordingly. The strain-time histories are likewise indicated for a specific gauge area for aluminum and composite plates. Comparison of dynamic-amplification factors between the isotropic and the orthotropic plates with and without hole has been discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.229.1-229.1
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• 2014

Tactile sensors have widely been researched in the areas of electronics, robotic system and medical tools for extending to the form of bio inspired devices that generate feeling of touch mimicking those of humans. Recent efforts in adapting the tactile sensor have included the use of novel materials with both scalability and high sensitivity [1]. Graphene, a 2-D allotrope of carbon, is a prospective candidate for sensor technology, having strong mechanical properties [2] and flexibility, including recovery from mechanical stress. In addition, its truly 2-D nature allows the formation of continuous films that are intrinsically useful for realizing sensing functions. However, very few investigations have been carrier out to investigate sensing characteristics as a device form with the graphene subjected to strain/stress and pressure effects. In this study, we present a sensor of vertical forces based on single-layer graphene, with a working range that corresponds to the pressure of a gentle touch that can be perceived by humans. In spite of the low gauge factor that arises from the intrinsic electromechanical character of single-layer graphene, we achieve a resistance variation of about 30% in response to an applied vertical pressure of 5 kPa by introducing a pressure-amplifying structure in the sensor. In addition, we demonstrate a method to enhance the sensitivity of the sensor by applying resistive single-layer graphene.

• Journal of the Korean Society of Clothing and Textiles
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• v.25 no.7
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• pp.1303-1313
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• 2001

This study was performed to develop a mobile functional pattern reflecting the characteristics of the middle aged women's lower body types based on the slacks construction components. The results and procedures obtained from this study were as follows; 1. The bodys measurement of the 252 middle aged women of 45∼59 years old were used to analyze the size and somato type. 2. For multiple analysis of the lower body types, horizontal and vertical section maps were obtained by sliding gauge method and extracted constructional factors of slacks. 3. The following condition was determined with both standing and moving position of body: (gradient of C.B.L/2)+3°and (back crotch extention)+2cm. 4. Development of new slacks pattern drafting was based on the result of data analysis. Trough the wearing test by the sensory evaluation, It showed that developed slacks pattern was judged better than existing patterns in items of comfort of comfort of silhouette and moving.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.256-261
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• 2004

Due to the problems of global warming, the frequency of meteorological extremes such as droughts, floods and the annual rainfall amount are suddenly increasing. Even though the increase of greenhouse gases, for example, is thought to be the main factor for global warming, its impact on global climate has not yet been revealed clearly in rather quantitative manners. Therefore, tile objective of this study is to inquire the change of precipitation condition due to climate change by global warming. In brief, this study want to see its assumption if rainfall quantile estimates are really changing. In order to analyze the temporal change, the rainfall quantile estimates at the Seoul rain gauge stations are estimated for the 21-year data period being moved from 1908 to 2002 with 1-year lag. The main objective of this study is to analyze the variability of rainfall quantile estimates using four methods. Next, The changes in confidence interval of rainfall quantile are evaluated by increasing the data period. It has been found that confidence interval of rainfall quantile estimates is reduced as the data period increases. When the hydraulic structures are to be designed, it is important to select the data size and to re-estimate the flood prevention capacity in existing river systems.

• Smart Structures and Systems
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• v.5 no.4
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• pp.345-355
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• 2009

This article describes the development of a fiber optic accelerometer based on Fiber Bragg Gratings (FBG). The accelerometer utilizes the stiffness of the optical fiber and a lumped mass in the design. Acceleration is measured by the FBG in response to the vibration of the fiber optic mass system. The wavelength shift of FBG is proportional to the change in acceleration, and the gauge factor pertains to the shift in wavelength as a function of acceleration. Low frequency version of the accelerometer was developed for applications in monitoring bridges. The accelerometer was first evaluated in laboratory settings and then employed in a demonstration project for condition assessment of a bridge. Laboratory experiments involved evaluation of the sensitivity and resolution of measurements under a series of low frequency low amplitude conditions. The main feature of this accelerometer is single channel multiplexing capability rendering the system highly practical for application in condition assessment of bridges. This feature of the accelerometer was evaluated by using the system during ambient vibration tests of a bridge. The Frequency Domain Decomposition method was employed to identify the mode shapes and natural frequencies of the bridge. Results were compared with the data acquired from the conventional accelerometers.

• East Asian Journal of Business Economics (EAJBE)
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• v.6 no.4
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• pp.13-24
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• 2018

Purpose - This study investigates the moderation effect of internal factor, a firms size, on the external knowledge sourcing strategy and its effectiveness in generating radical innovation. We incorporate concepts of breadth and depth as two measures to gauge the degree of openness in firms external search Research design and methodology - The dependent variable in the regression model is the percentage of innovative sales and therefore, Tobit regression is employed for estimating significant factors affecting on the ratio of first-to-market by breadth and depth in external knowledge, internationalization, and size. Results - The results show that the external knowledge, in terms of both breadth and depth, has a positive relationship with radical innovation. However internationalization as external knowledge resources is not statistically accepted. Firm size has moderating effect on innovation negatively only in case of using external knowledge resources to a high degree. Conclusions - Firms obtain external information mostly from customers, competitors, and suppliers etc. empirical knowledge in terms of scope and intensity is an important contributor to innovation. And intensity use of external knowledge and information resources can work in favor of smaller firms rather than larger ones. Internationalization seems to have little effect on innovation but it requires further researches with clear criteria and more data.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.91.1-91.1
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• 2012

그래핀의 우수한 기계적 물성에 관한 연구가 보고된 이후 그래핀의 기계적 특성을 이용한 다양한 어플리케이션에 관한 연구가 진행되고 있다. 기계적 특성을 이용한 다양한 어플리케이션 중 가장 대표적인 것은 발생한 스트레인을 측정하는 스트레인 게이지일 것이다. 때문에 본 연구에서는 다양한 기계적 활용 방안 중 스트레인 게이지를 목표로 그래핀을 이용한 스트레인 게이지의 가능성에 관한 실험을 진행하였다. 먼저 그래핀 내에서의 Piezo-resistive 효과에 관한 기초 테스트를 진행을 통해 그래핀의 gauge factor 수치가 2.5가량이 나옴을 확인하였다. 이 때 사용된 그래핀의 경우 Ni 촉매층을 이용하여 CVD 장비를 이용하여 사용되었고 7%의 투과도를 보였다. 추가적으로 이 같은 그래핀의 Piezo-resistive 특성을 이용하여 우리는 두 종류의 변형률 센서를 제작하였다. 한 가지는 기존의 단일 게이지의 경우 미리 지정된 방향의 변형률 정도만을 측정할 수 있다는 단점을 극복하기 위한 rosette 형태의 스트레인 게이지를 제작함으로써 변형률 뿐만 아니라 표면에서 발생하는 주변형률의 방향을 측정할 수 있었다. 또한 제작된 스트레인 센서를 장갑위에 부착 함으로써 다가올 입는 형태의 전사소자에 응용이 가능한 모양의 변형률 센서 제작에 성공하였다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.561-571
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• 1997

In this paper, the fundamental equations are developed for the pulsatile laminar flow generated by changing the oscillatory flow with $0{\leq}f{\leq}48Hz$ into a steady one with $0{\leq}Re{\leq}2500$ in a rigid circular pipe. Analytical solutions for the wave propagation factor k, the axial distributions of cross-sectional mean velocity $u_m$ and pressure p are schematically derived and confirmed experimentally. The axial distributions of centerline velocity and pressure were measured by using Pitot-static tubes and strain gauge type pressure transducers, respectively. The cross-sectional mean velocity was calculated from the centerline velocity by applying the parabolic distribution of the laminar flow and it was confirmed by using the ultrasonic flowmeter. It was found that the axial distributions of cross-sectional mean velocity and pressure agree well with theoretical ones and depend only on the Reynolds number Re and angular velocity $\omega$.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.150-153
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• 2001

In this paper, the tensile test of three kinds of the specimens was performed. Type I specimen is without notch and type II, III specimens have a radius of semi-circular edge crack of 2.5mm, 4.0mm. The tensile load(20kN and 30kN) was applied to the specimen by Universal Testing Machine. 3D-ESPI system and strain gauge measured simultaneously the strain in the center of the specimen and near the edge crack. The test results were compared with each other. Moreover, the stress concentration factor based on geometric information was calculated to confirm the accuracy of the strain measured by 3D-ESPI system. The calculated strain was compared with the measured one by 3D-ESPI system. As a result, it was confirmed that 3D-ESPI system measured the right strain near the semi-circular edge crack of the specimens.

• International Journal of Railway
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• v.3 no.2
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• pp.60-67
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• 2010

This paper deals with an experimental study on the wheel flange climbing of railway vehicles, which is a major factor leading to derailment. An experiment is carried out on a 1/5-scale model wheelset of a truck used on a standard-gauge track, which is placed on a roller rig. The lateral external force acting on the wheelset is ramped up until derailment occurs under the condition of a fixed attack angle and wheel-load unbalance ratio. Three parameters, the height of wheel lift, the lateral force, and the wheel load acting on the outer rail, are measured until derailment occurs. From these measurements, it is possible to observe the behavior of the wheelset and to elucidate how the attack angle, the wheel-load unbalance ratio and the lateral external force affect flange-climb derailment. Then, a numerical simulation is carried out using an analytical model based on a single wheelset. As a result, the flange-climb behavior observed in the experiment can be explained theoretically on the bases of the analytical results, although further improvement of the model is desired.