• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.307-309
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• 2004

분산 서비스 거부 (DDoS) 공격에 대응하기 위한 수많은 연구 결과들이 나와 있지만, 이 공격은 여전히 인터넷 보안의 위협요소 중 하나로 남아있다. 대부분의 분산 서비스 거부 (DDoS) 공격들은 스푸핑한 IP 주소를 이용하여 다량의 패킷을 발생시키기 때문에 정상 패킷과 공격 패킷간의 구분을 어렵게 만든다. 이 공격에 대응하기 위해 기존에 나와있는 연구중 하나인 Pi는 패킷이 지나온 경로를 마킹 하는 방법으로 간단하면서 강건한 대응 방법이었다. 하지만 Pi 마킹 방범은 여러 가지 결점을 갖고 있다. 이 논문에서는 기존의 Pi가 갖고 있는 문제를 개선하기 위한 새로운 패킷 마킹 방법을 제시한다.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.309-310
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• 2014

분산형 전원 시스템과 마이크로그리드에 대한 관심이 증가함에 따라 다수의 병렬 컨버터의 제어가 중요한 이슈가 되었다. 가장 보편화된 분산 전원의 제어 방법 중 하나는 드룹 방식을 이용한 분산형 제어이다. 다중 전원이 연결된 버스의 전압 품질을 향상시키기 위해 본 논문에서는 드룹 제어에 의한 전압 변동을 해결하기 위한 방법이 제안되었다. 제안된 개체 기반의 전압 회복 기술은 모듈 간 통신을 최소화하는 한편 자율적 운용 특성을 유지한다. 시뮬레이션 및 실험 결과를 통해 제안한 방법을 검증하였다.

• Communications for Statistical Applications and Methods
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• v.3 no.2
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• pp.93-102
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• 1996

혼합물 실험에서 실험의 조건이 균질하지 않은 경우, 블럭화를 주로 행한다. 이런 블럭화가 이루어 질때 추정반응값 분산그림을 이용하여 각 구성성분에 제약이 없는 경우와 제약이 있는 경우 각각에 대하여 블럭화가 실험계획의 추정반응값 분산에 어떤 영향을 미치는지 알 수 있는 그래픽 방법을 제안하였다. 이 방법을 통하 여 혼합물 실험에서 블럭화의 효과를 각 구성 성분에 대하여 알아볼 수 있다. 또한, 어떤 블럭화가 추정반응값 분산의 증가를 최소화할 수 있는 지를 그림을 이용하여 비교, 검토할 수 있게 된다.

• Journal of the Korea Computer Graphics Society
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• v.7 no.1
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• pp.11-17
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• 2001

Fractal image coding provides many promising qualities including the high compression ratio. The coding process however suffers from the long search time of domain block pool because the size of the domain block pool is often very large. In this paper, we introduce a hybrid domain block pool search method that combines the block classification and the variance based searching. This hybrid method makes use of the fact that the variance of a block is independent of the block classification. Thus, this hybrid method enhances the search speed by up to an O(number of classes) factor over the purely variance based searching method. An experimental result shows that our method enhances the search speed by up to 17 times over the purely variance based searching method. We also propose an adjustable variance based searching method that further enhances the search speed without noticeable loss of image quality.

• Journal of Broadcast Engineering
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• v.16 no.1
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• pp.144-154
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• 2011

In this paper, we propose a parallel LDPCA encoding method for fast transform-domain Wyner-Ziv video encoding which is suitable in an ultra fast and low power video encoding. The conventional transform-domain Wyner-Ziv video encoding performs LDPCA channel coding of quantized transform coefficients in bitplane-serial fashion, which takes about 60% of total encoding time, and this computational complexity becomes severer as the bitrate increases. The proposed method binds several bitplanes into one packed message and carries out the LDPCA encoding in parallel. The proposed LDPCA encoding method improves the encoding speed by 8 ~ 55 times. In the experiment, the proposed Wyner-Ziv encoder can encode 700 ~ 2,300 QCIF size frames per second with GOP=64. The method can be applied to the pixel-domain Wyner-Ziv encoder using LDPCA, and has a wide scope of application.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.4
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• pp.147-157
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• 1987

Five finite difference schemes (explicit, Bresler, implicit, upstream, and Chaudhari scheme) for the convective dispersion model are analyzed numerically to investigate their characteristics and applicabilities. Camparative study results show that the conditionally stable Chaudhari scheme has the smallest numerical dispersion and that the unconditionally stable Bresler scheme has the overshooting in regions of oscillation. Explicit scheme is the most accurate for a dispersion-dominated flow whereas Chaudhari scheme is for a convection-dominated flow. The computation time (CPU) is the shortest for the explicit or Chaudhari scheme with the same order of magnitude and is always the longest for the Bresler scheme.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.04a
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• pp.1001-1006
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• 2000

90년대 이후 새로운 소프트웨어 개발 방법론으로 객체 지향 방법론이 새로운 패러다임으로 등장한 후 최근에는 컴포넌트 기반 개발 방법 등이 소개되어 다양한 분산 컴포넌트 기술이 태동되었다. 분산 컴퓨팅 환경 하에서의 컴포넌트 기술은 정보 시스템 구축 시 구성요소의 모듈화를 용이하게 하고 인터페이스를 통한 컴포넌트 재사용 성을 가능하게 하여 소프트웨어 생산성 향상에 크게 기여하였다. 본 연구에서는 OMG에 의해 제안된 표준 분산모델로서 코바 프레임워크를 기반으로 정보구조 모델링 방법론을 이용하여 컴포넌트를 구성하고 컴포넌트의 추출을 돕기 위한 컴포넌트 저장소 명세서, 분산 어플리케이션 개발 프로세스 절차를 제안 하고자 한다.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.233-240
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• 2014

In this study, we investigated the dispersion characteristics of guided waves in thin films. Dispersion curves are essential for understanding not only the behavior of ultrasonic waves, but also the mechanical properties of thin films. Matrix techniques are presented for modeling ultrasonic waves in multilayered structures before being used to calculate the dispersion curves for Al-steel and Al-composite specimens. When compared with the dispersion curves obtained using the commercial program (Disperse), the dispersion curves generated from the transfer matrix method show its validity. These developed methods are used to obtain dispersion curves for Al thin films deposited on a Si substrate. The resulting dispersion curves enable observation of both dispersive and non-dispersive behavior for the guided waves, depending on the thickness of the thin films.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.8C
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• pp.795-802
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• 2003

It is very important to construct statistical model in order to exactly estimate the signal variance from a noisy image. In order to estimate variance, information of neighboring region is used generally. The size of neighbor region is varied according to the regional characteristics of image. More accurate estimation of edge variance is due to smaller region of neighbor, on the other hands, larger region of neighbor is used to estimate the variance of flat region. By using estimated variance of original image, in general, Wiener filter is constructed, and it is applied to the noisy image. In this paper, we propose a new method for determining the range of neighbors to estimate the variance in wavelet domain. Firstly, a significance map is constructed using the parent-child relationship of wavelet domain. Based on the number of the significant wavelet coefficients, the range of neighbors is determined and then the variance of the original signal is estimated using ML(maximum likelihood method. Experimental results show that the proposed method yields better results than conventional methods for image denoising.

• The Korean Journal of Applied Statistics
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• v.26 no.6
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• pp.1033-1041
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• 2013

In this paper, we investigate several variance estimators for pps systematic sampling. Unfortunately, there is no unbiased variance estimators for a systematic sample because systematic sampling can be regarded as a random selection of one cluster. This study provides guidance on which variance estimator may be more appropriate than others in several circumstances. We judge the efficiency of variance estimators for systematic sampling based on of their relative biases and relative mean square error. Also, we investigate variance estimation problems for two-stage systematic sampling applied for the Food Raw Material Consumption Survey and the Establishment Labor Force Survey simulation study, in order to consider the popular two-stage pps systematic sample design for establishment and household survey in Korea.