• Review of KIISC
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• v.16 no.2
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• pp.71-78
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• 2006

인터넷 주소 고갈 문제를 해결하고 QoS를 효과적으로 제공하기 위하여 IPv6가 개발되었다. IPv6는 IPSec이라는 자체의 보안 요소를 탑재하고 있기 때문에 보안의 중요성이 강조되는 유비쿼터스 사회에서 기존의 IPv4가 가지고 있든 문제점을 해결할 수 있을 것으로 기대한다. 그러나 IPv6의 도입에 따른 IPv4/IPv6 전환 시 보안 문제와 IPv6 자체의 보안 특성 등에 대하여 분석할 필요가 있다. 본고에서는 IPv6 환경에서 침입탐지 및 웜의 전파 특성에 대하여 기술하고자 한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.7
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• pp.733-740
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• 2008

In this paper, an indoor propagation model based on 3d ray tracing is presented for wireless communications. In case of indoor propagation models, various radio propagation paths such as wall-transmitted wave and scattered wave from ceilings, pillars, and furnitures arises and 3-D formulation is needed. To accommodate such scatterers, objects are modeled by triangulated surfaces and ray tubes using those surfaces are introduced and efficient calculation methods using the tubes are presented.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.27-33
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• 1995

The microwave absorbing characteristics and complex permeability of $Ni_{2-x}Zn_{x}Y$ - rubber composites with variation of composition and particle size were investigated. With a ferrite particle with a diameter of about $1\mu\textrm{m}$, only spin rotational resonance was observed. This behavior probably due to the particle being sufficiently small to approach single domain characteristics so that only spin rotations can occur. The first matching frequency, found in $Ni_{2-x}Zn_{x}Y$ - rubber composites, which was higher than that of spin rotational resonance, increased with spin rotational resonance frequency. It is also found that the second matching frequency is independent of spin rotational resonance frequency. Based on these findings, it could be concluded that the microwave absorbing characteristics were caused by only one type of resonance, the spin rotational resonance.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.4
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• pp.44-51
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• 2017

An experimental results on the dynamic characteristics of hydrocarbon/air premixed flames with ultrasonic standing waves are presented and compared. Images of the propagating flames were acquired by using a high-speed camera, and the flame behavior of methane/air and propane/air premixed flame were closely scrutinized through the image post-processing. At the fuel-lean conditions, the flame propagation velocity increased due to the intervention of the ultrasonic standing wave and vice versa at the fuel-rich conditions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.3
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• pp.440-448
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• 1999

This paper describes a full wave analysis of the scattering from electromagnetic absorbers which can be approximated as infinite periodic structure using hybrid finite element method. By introducing fictitious boundaries, equivalent finite region is defined and proper boundary conditions of each boundary are obtained by Floquet theorem. Since higher-order Floquet modes are employed, the method presented in this paper can be readily applied to the periodic structure haying a relatively long period. To reduce difficulty in evaluating the surface integral, the normal component to the surface were represented with the tangential component to the surface. Comparisons of calculated results with analytical or published ones show the validation of the method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.12C
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• pp.1677-1685
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• 2004

Recently, FD (Frame Dropping)-CD (Coefficient Dropping) transcoding is considered due to the low computational complexity and simple implementation. The conventional FD-CD transcoding schemes have not considered the CD errors that tend to be propagated and accumulated. In this paper, we derive the error characteristics incurred by the CD errors and, through computer simulations, we show that the CD errors are propagated and not negligible to the decoded qualities of the next frames within single GOP. Then, we propose an exponential-decaying model that describes well the characteristics of propagation/accumulation errors. Finally, it is shown that the proposed model can be effectively used for estimating the overall distortions incurred by the CD errors.

• The Journal of the Korea Contents Association
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• v.6 no.12
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• pp.155-162
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• 2006

It was well known that how much seriously the Internet worm such as the Code Red had an effect on our daily activities. Recently the rapid growth of the Internet speed will produce more swift damage us in a short term period. In order to defend against future worm, we need to understand the propagation pattern during the lifetime of worms. In this paper, we analyze the propagation pattern of the Code Red worm by a computer simulation. In particular, we show that an existing simulation result about the number of infectious hosts does not match the observed data, and then we introduce a factor of revised human countermeasures into the simulation. We also show the simulation results presenting the importance of patching and pre-patching of the Internet worm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.11
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• pp.1224-1230
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• 2007

Recently, wireless LAN are often applied in home or office because of its various of convenience. Frequency rage of wireless LAN specified by IEEE 802.11a is at 5.2 GHz and IEEE 802.11b is 2.4 GHz. But in offices with wireless LAN devices, reflection of waves against walls, ceilings, floors and desks made of metal creates multipath problems that reduce communication speed and lose data. These problems can be solved by using EM wave absorber. In this paper, we designed and fabricated EM wave absorbers using MnZn-ferrite, sendust, carbon and CPE(Chlorinated Polyethylene). The EM wave absorber with the ratio of MnZn-Ferrite : sendust : CPE=64 : 16 : 20 wt.% has thickness of 3.7 mm and absorption ability more than 17 dB at 2.4 GHz and the EM wave absorber with the ratio of MnZn-ferrite : carbon : CPE=40 : 15 : 45 wt.% has thickness of 3.8 mm and absorption ability more than 23 dB at 5.2 GHz.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.537-544
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• 2017

An experimental study was carried out to investigate the characteristics of the propagation distance of a flood wave considering the levee failure speed in a flat inundation area. The Ritter solution for one dimensional flow was considered to formulate the experimental results and a representative form with coefficients of k and m, which consider the three dimensional flow characteristics, was applied. The experiments showed that the propagation velocity of the wave front in the inundation area was influenced by the levee breach speed as well as the initial water level, which is a significant variable representing the flood wave behavior. In addition, coefficients k and m are not constants, but variables that vary with levee breach speed. An empirical formula was also suggested using the experimental results in the form of the relationships between k and m. In this study, a large-scale experiment for flood inundation was carried out to examine the behavior of flooding in the inundated area and the relationships between the levee breach speed and wave-front propagation velocity were suggested based on the experimental results. These research results are expected to be used as the baseline data to draw a flow inundation map, establish an emergency action plan, and verify the two-dimensional numerical model.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.3
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• pp.222-229
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• 2009

In this paper, we designed and fabricated the EM wave absorbers for preventing the reduction of the communication range when RFID Tag is approached to a metal plate. The EM wave absorber samples were fabricated with difference composition ratios of Amorphous metal powder and CPE, the absorption abilities of which were simulated by substituting different thicknesses of the EM wave absorbers. Then the EM wave absorbers are manufactured based on the simulated results. By using the EM wave absorbers, we have confirmed the improvement effect of RFID tag antenna and the increase of communication range of RFID system. As a result, it was cleary shown that the communication range of RFID system is improved by adopting the EM wave absorber with the composition ratio of Amorphous metal powder:CPE=80:20 wt.% and the thickness of 4 mm. Thus, it was confirmed that the proposed EM wave absorber can increase the communication range of RFID system from 0.8 m to 5.2 m in UHF band.