• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.5
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• pp.1111-1116
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• 2000

The mixed $H_2/ H_\infty$ control method is one of positive approaches to design a controller having both the$H_2$-performance and the $H_\infty$-robust stability. In this paper, Firstly, The tracking Performance to be designed has been represented as $H_2$-norms for the plants with uncertainties. Secondly, $H_\infty$-norm have been set up in order to ensure the robust stabilities. The mixed digital controllers have been designed for an inverted system. The mixed $H_2/ H_\infty$digital controller for the inverted pendulum system was intended to stabilize the unstability of the plant together with the good tracking Performance.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.2
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• pp.185-192
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• 2013

In this paper, proposed to improve the performance of speech and mixed content signal classification using MFCC based on GMM probability model used for the MPEG USAC(Unified Speech and Audio Coding) standard. For effective pattern recognition, the Gaussian mixture model (GMM) probability model is used. For the optimal GMM parameter extraction, we use the expectation maximization (EM) algorithm. The proposed classification algorithm is divided into two significant parts. The first one extracts the optimal parameters for the GMM. The second distinguishes between speech and mixed content signals using MFCC feature parameters. The performance of the proposed classification algorithm shows better results compared to the conventionally implemented USAC scheme.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.3
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• pp.67-75
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• 2013

The numerical analysis for the verification of preburner's cooling characteristics applying to kerosene-LOx rocket engine has been fulfilled. The distribution of combustion gas properties in primary combustion zone was calculated by the mixture ratio based on head injector arrangement, the properties of oxygen flowing in wall channels as coolant were applied under real-gas conditions, and multi-phase mixing model was employed to calculate the mixing process of primary combustion zone with liquid oxygen which was used for wall cooling. The results of numerical analysis were compared with the experimental results, hence thermo-physical properties in cooling channels and a combustor could be quantitatively identified.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.81-84
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• 2010

In this study, a coaxial swirl injector using hydrogen peroxide and kerosene was designed and combustion performance tests were performed to evaluate combustion characteristic according to mixture ratio. Spray characteristic of the injector was verified by cold flow test and combustion performances according to mixture ratio were evaluated by the characteristic exhaust velocity. Test results showed that the combustion efficiency at the design condition was about 95% and the pressure fluctuation was very small.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10A
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• pp.847-851
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• 2011

In this paper, we reported on a high performance MMIC star mixer for millimeter-wave applications. The star mixer was fabricated using drain-source-connected pseudomorphic high electron mobility transistor (PHEMT) diodes considering the PHEMT MMIC full process on 2 mil thick GaAs substrate. The average conversion loss of 13 dB was measured in the RF frequency range of 81 GHz to 86 GHz at LO frequency of 75 GHz with LO power of 10 dBm. The RF-LO isolation characteristics are greater than 30 dB and the input 1-dB compression are approximately 4 dBm. The total chip size is 0.8 mm ${\times}$ 0.8 mm.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.1
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• pp.41-47
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• 2002

Fractal image compression can reduce the size of image data by the contractive mapping that is affine transformation to find the block(called as range block) which is the most similar to the original image. Even though fractal image compression is regarded as an efficient way to reduce the data size, it has high distortion rate and requires long encoding time. In this paper, we presented a hybrid fractal image compression system with the modified SOFM Vector Quantizer which uses improved competitive learning method. The simulation results showed that the VQ hybrid fractal using improved competitive loaming SOFM has better distortion rate than the VQ hybrid fractal using normal SOFM.

• Journal of Life Science
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• v.21 no.11
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• pp.1599-1606
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• 2011

To evaluate the effects of microorganism agents on oil biodegradation, treatability and microcosm studies were conducted. Petroleum oil degrading bacteria were isolated from enriched cultures of oil-contaminated sediment samples using a mineral salts medium (MSM) containing 0.5% Arabian heavy crude oil as the sole carbon source. After a 5 day-incubation period using MSM, mixed microorganisms of three species (strains BS1, BS2 and BS4) degraded 48.4% of aliphatic hydrocarbons and 30.5% of aromatic hydrocarbons. Treatability and microcosm tests were performed in the three different treatment conditions (AO: Arabian heavy crude oil, AO+IN: Arabian heavy crude oil+inorganic nutrient, AO+IN+MM: Arabian heavy crude oil+inorganic nutrient+mixed microorganism agents). Among these, significantly enhanced biodegradation of aliphatic hydrocarbons were observed in AO+IN and AO+IN+MM conditions, without showing any different biodegradation rates in either condition. However, the degradation rates of aromatic hydrocarbons in an AO+IN+MM condition were increased by 50% in the treatability test and by 13% in the microcosm test compared to those in an AO+IN condition. Taken together, it can be concluded that mixed microorganism agents enhance the biodegradation of aliphatic and aromatic hydrocarbons in laboratory, a treatability test, and a microcosm test. This agent could especially be a useful tool in the application of bioremediation for removal of aromatic hydrocarbons.

• Annual Conference on Human and Language Technology
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• 2003.10d
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• pp.101-107
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• 2003

최근의 웹 문서는 텍스트 위주의 구성이 아닌 이미지, 사운드, 동영상 등의 다양한 타입으로 구성되는 추세이다. 이에 따라 단순히 웹 문서 내의 단어 정보추출 만으로는 좋은 성능의 클러스터링을 기대하기 어렵다. 본 논문은 전통적인 문서 클러스터링 기법인 단어기반 클러스터링 기법의 취약점을 제시하고, 웹 문서간의 링크구조정보 중 동시인용 정보를 이용하여 웹 문서 클러스터링 성능향상의 가능성을 보이고자 한다. 실험에서는 네이버디렉토리 중 '자연과학' 범주에 포함된 문서를 대상으로 위의 두 가지 방식과 이 두 가지를 혼합한 단어-링크 혼합 클러스터링을 통해 기존의 방식보다 더 낳은 성능을 얻을 수 있었다.

• Journal of KIISE:Software and Applications
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• v.26 no.1
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• pp.25-39
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• 1999

지리 정보 시스템에서 공간 분석을 위해 사용되는 중요한 연산인 공간 조인은 대상이 되는 공간 객체의 수가 증가함에 따라서 연산 시간이 지수적으로 증가하는 특징을 가지고 있다. 그러므로 다량의 공간 데이터에 대해서 공간 연산시간을 줄이기 위한 병렬처리가 필요하다. 이 논문에서는 비겹침 정규분할 방식의 사분트리를 이용한 공간 조인 알고리즘을 제시하고 MIMD 구조 및 공유 디스크 방식의 병렬 처리시스템에 적용하여 성능을 평가한다. 사분트리를 이용한 공간조인 방법으로서 중복 표현된 공간객체를 줄이기 위한 사분면(quadrant)의 병합 방법,영역 제한을 통해 연산 대상 객체를 줄이기 위한 사분면의 분할 방법, 그리고 병합 및 분할 방법을 혼용하여 공간 조인 연산의 숫자를 최소화하는 혼합 방법을 제시한다. 실험 평가에서는 각 방법들을 병렬 처리 시스템에 적용하여 여과단계 및 정제단계에서의 연산량과 수행 시간을 통해 성능을 비교 평가한다. 실험결과, 여과 단계에서는 분할 방법이 가장 우수했지만, 정제 단계에서는 병합 방법이 가장 우수했다. 따라서 전체적인 고려할 때 두 방법의 장점을 수용한 혼합 방법이 가장 우수한 성능을 나타냈다.

• Information and Communications Magazine
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• v.13 no.8
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• pp.103-122
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• 1996

초고속정보통신망의 구축이 효율적이고 신뢰성 있는 서비스를 제공하기 위하여 위성/지상망을 통합한 혼합망 구조로 개발됨에 따라 지상 광파이버를 기반으로 개발된 ATM 전송프로토콜을 위성망에 직접적으로 적용하기 위한 기술개발이 요구된다. 이러한 점을 고려하여 본 고에서는 위성 ATM(Asynchronous Transfer Mode) 전송에 따른 문제점 분석, 개선방안 및 성능평가를 수행하였다. 혼합망 구성에 따른 위성망의 구조를 접속된 지상노드의 유형 및 위성시스템 특성에 따라 3가지 유형으로 분류하여 제시하였고, 위성 ATM 전송에 따른 기술적인 문제점을 채널 BER과 위성지연 측면으로 분류하여 제시하였다. 위성채널 BER 성능개선을 위한 2가지 방안(인터리빙, HEC 보강)을 제시하였으며 위성지연분석은 고정지연(Fixed delay)과 셀지연변이(CDV : Cell Delay Variation) 측면에서 성능평가를 수행하였다.