• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.5
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• pp.521-526
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• 2014

In this study, closed-cell aluminum foam with an initial crack was investigated to produce an axial load-time graph. Using the 10-kN Landmarks of MTS Corporation, a 15-mm/min velocity of mode I shape was applied to the aluminum foam specimen using the displacement control method. ABAQUS 6.10 simulation was used to model and analyze the identical model in three dimensions under conditions identical to those of the experiment. The energy release rate was calculated on the basis of an axial load-displacement graph obtained from the experiment and a transient image of the crack length, and then an FE model was analyzed on the basis of this fracture energy condition. The relation between load and displacement was discussed; it was found that the aluminum foam deformed somewhat less than the adhesive layer owing to the difference in elastic modulus.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.1
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• pp.291-298
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• 1995

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. This paper studied the directivity of shear waves emitted from angle probes and scattered from surface defects by using visualization method. These experimental results were compared with the theory which was based on the continuous wave. The applicability of continuous wave theory was discussed in terms of the parameter $d/{\lambda}$; where d is transducer or defect size and ${\lambda}$ is the wavelength. In the case of angle probes, the experimental results show good agreement with theoretical directivity on the principal lobe. When defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. In the case of the same ratio of defect size to wavelength, the directivity of reflected waves from the defect show almost the same directivity in spite of frequency differences. When the $d/{\lambda}$ is greater than 1.5, measured directivities almost agreed with the theoretical one.

• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.34-39
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• 2010

Due to big demand for satellite and communication service using personal handheld terminals, demand for satellites with huge antennas is increasing correspondingly. While such large antennas are realized by various types of deployable antennas, the reflecting surface is made by many facets irrespective of deploying mechanisms. In order to analyze the faceted-reflector more accurately, an existing ray-tracing method is improved. The algorithm allows the rays to cross each other, which is the main characteristic of the faceted-reflector, and takes unevenness of amplitude and phase over the aperture plane into consideration. For the study of the effect of facet configuration, facet generating algorithm is devised. From the analysis algorithm and the facet-generating algorithm, it has been found that the number of facets in a radial direction affects both directivity and sidelobe level. On the other hand, the number of facets in a circumferential direction affects sidelobe level only.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.1
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• pp.57-62
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• 1990

This paper deals with the flow caused by a two-dimensional pulsating source, which moves with a constant horizontal speed beneath the free surface. The analysis is based on lincar potential theory including surface tension effects. In the case of subcritical reduced frequencies $\tau<1/4(\tau=U_{\omega}/g$, U=constant speed, $\omega$=circular frequency, g=gravitational acceleration), six wave components arc found. Two of them are largely affected by surface tension, which propagate ahead of the source in the direction of and opposite to the steady translation, respectively. The rest are almost identical with those found by Haskind(1954), i.e. for which the surface tension effect is negligible. For low oscillation frequencies, the resonant frequency still exists at $\tau$ only slightly greater than 1/4. For oscillation frequencies greater than $\nu(={\omega}^2/g)>20$, the surface tension effect is so significant that it disperses generated waves and consequently the singular phenomenon is removed. However, in addition to the gravity breaking, capillary breakings occur when the translation speed coincides with the minimum capillary celerity.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.161-167
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• 2001

It is difficult to obtain accurate fracture toughness values using three point bending test(TPB) proposed by RILEM committees because the shape of load-deflection curve is irregular and final crack propagation occurs after some slow stable cracking. However, fracture toughness is easily obtained from crack initiation load in the disk test. In this paper, the fracture properties of high strength concrete disks with center-crack was investigated. For this purpose, the experimental results were compared with the results by finite element analysis(FEA). And the experimental fracture locus was compared with theoretical fracture locus. Also, the results of fracture properties for the degree of concrete strength are presented. It is concluded from this study that results from FEA with maximum stress theory were compared well with the results from experiment. And the degree of concrete strength was contributed to the crack initiation load and fracture toughness, but was not contributed to the failure angle. Also, The discrepancy of fracture locus between the maximum stress theory and the experiment for concrete is considered to depend upon a large energy requirement for inducing the mixed-mode and sliding mode fractures.

• Information and Communications Magazine
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• v.30 no.1
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• pp.24-32
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• 2012

우리는 지금 스마트 사회에 살아가고 있다. 언제 어디서든 스마트 디바이스를 통해 기존에 PC에서 하던 작업들을 손쉽게 하고 있다. 한편 스마트폰의 확산으로 이용자 수가 급증하고 있는 소셜네트워크 서비스(SNS)는 이용자들이 자신의 일상적인 이야기를 사이버공간에 게시함으로 인해 개인의 사생활 정보들이 노출되고, 그러한 정보들이 범죄에 악용되는 사례들이 눈에 띄게 증가하고 있다. 또한 SNS를 이용한 악성코드의 유포 및 빠른 전파 등도 새로운 보안위협으로 나타나고 있다. 그 밖에 스마트 기기를 대상으로 한 해킹 및 악성코드 감염 등 위협이 증가하고 있는 형편이다. 본고에서는 스마트 사회의 주요 보안위협을 살펴보고 미국, 유럽, 일본, 호주 등 선진국의 관련 정책 동향과 국내 정책과 실태를 분석하여 새로운 정보보호 정책 수립 방향을 제언하고자 한다. 스마트 사회 위험 요소로 가장 보편적으로 사용되고 있는 스마트폰과 스마트폰을 통해 이용되고 있는 소셜네트워크 서비스, 클라우드 서비스의 보안위협을 제기하고 최근 글로벌 이슈로 떠오르고 있는 빅 데이터 환경의 보안위협을 분석하였다. 스마트 사회의 위협을 대비하고 있는 주요국 정책을 살펴보면, 미국의 경우 사회적 합의를 바탕으로한 감시와 통제를 강화하는 정책을 추진 중에 있으며 유럽의 5개국 EU5(영국, 독일, 프랑스, 스페인, 이탈리아)는 스마트폰 위협을 중심으로 공동 대응 방안을 마련하고 있다. 일본은 스마트 워크중심의 보안대책을 강구하고 있으며 호주는 스마트 사회 보안위협에 대한 국민의 인식제고에 주력하고 있다. 국내의 경우도 스마트 사회의 보안위협에 선제적 대응을 위하여 "스마트 모바일 시큐리티 종합계획"을 수립하여 추진중에 있다. 하지만 보안 실태를 보면 스마트 사회 보안위협에 대한 이용자들의 우려는 높은 반면 기업의 보안 대책 마련에 대한 투자는 여전히 미흡한 상황이다. 향후 우리 사회가 디바이스간 융합을 넘어 모든 사물이 연결되는 초(超)연결(Hyper-Connectivity) 시대로 진화되어 가면 편리성이 증대되는 만큼 더 많은 위협에 우리의 일상이 노출되는 문제가 발생하게 될 것이다. 안전한 미래 사회로 진입하기 위해서는 보다 체계적이고 종합적인 정보보호 정책마련이 필요하다. 본고에서는 이를 위한 정책수립의 방향을 제언했다.

• Journal of Korea Society of Industrial Information Systems
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• v.5 no.3
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• pp.117-124
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• 2000

A systolic array is a parallel processing system which consists of processing elements of basic computation capabilities, connected with regular and local communication lines. It has been known that a systolic array is on of effective systems to solve complicated communication problems occurred between densely connected neurons on ANN(Artificial Neural Network). In this paper, a systolic array simulator for the back-propagation ANN, which automatically constructs the proper systolic array for a given number of neurons of the ANN, is designed and constructed. With animation techniques of the simulators, it is easy for users to be able to examine the execution of the back-propagation algorithm on the designed systolic array step by step. Moreover the simulator can perform forward and backward operations of the back-propagation algorithm either in sequence or in parallel on the designed systolic array. Parallel execution can be performed by feeding continuous input patterns and by executing bidirectional propagations on all of processing elements of a systolic array at the same time.

• Journal of Advanced Navigation Technology
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• v.26 no.5
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• pp.350-357
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• 2022

With the recent prediction of 'Cycle 25', the importance of space weather research increases. Accordingly, the World Radiocommunication Conference (WRC)-23 has adopted Agenda Item 9.1a) and carried out sharing researches between active/passive space weather observation systems and existing services. Therefore, in this paper, in order to increase the precision of space weather environment data and secure the frequency spectrum for observation systems, the direct interference effect from the weather radar in Gosan, Jeju on the space weather observation receiver in Hallim, Jeju, and the indirect interference on the observation receiver by diffraction and scattering from the radar target have been analyzed. As a result, it can be known that the radar direction, the propagation direction diffracted and scattered from the target, and the Rradar Cross Section (RCS) of the radar target, the reception area of the space weather observation antenna, and the antenna off-boresight are important parameters for the interference effect analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6B
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• pp.543-550
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• 2009

The traditional simple extrapolation type short term quantitative rainfall forecast can not realize the evolution of rainfall generating weather system. To overcome the drawback of the linear extrapolation type rainfall forecasting model, the history of a weather system from sequential weather radar information and a polynomial regression technique were used to generate forecast fileds of x-directional, y-directional velocities and radar reflectivity which considered the nonlinear behavior related to the evolution of weather systems. Results demonstrated that test statistics of forecasts using the developed model is better than that of 2-CAPPI forecast. However there is still a large room to improve the forecast of spatial and temporal evolution of local storms since the model is not based on a fully physical approach but a statistical approach.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.6
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• pp.157-162
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• 2023

A highly sensitive refractive index bio-sensor based on grating-assisted strip directional coupler (GASDC) is proposed. The sensor is designed using two asymmetric strip waveguides with a top-loaded grating structure in one of the waveguides. Maximum light couples from one waveguide to the other at the resonance wavelength satisfying phase-matching condition (PMC), and it shows that the change in phase-matching condition with the change in refractive index of the analyte medium in the cover region can be used as a measure of the sensitivity. The proposed sensor will be an on-chip device with a high refractive index sensitivity, and the sensor configuration offers a low propagation loss, thereby enhancing the sensitivity. Furthermore, variation of the sensitivity with the waveguide parameters of sensor is evaluated to optimize the design.