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Job-Shop Scheduling 문제에 있어 선별 방법에 따른 유전 알고리즘의 Performance 비교
정호상,정봉주 한국경영과학회 1998 한국경영과학회 학술대회논문집 Vol.- No.2
Job-Shop Scheduling 문제는 전형적인 NP-hard 문제로서 효율적인 발견적 기법을 필요로 한다. 본 연구에서는 이 문제에 대한 유전 알고리즘들의 성능을 비교 분석한다. 유전 알고리즘의 주요 구성 요소들로는 크게 선별, 교자, 돌연변이 등이 존재하는데, 특히 선별은 적자 생존의 자연 법칙에 기초하여, 환경에 대한 적응도에 의해 현 세대의 모집단으로부터 다음 세대에 생존할 개체를 선택하는 과정으로 해의 산출에 중요한 역할을 하는 부분이다. 기존의 많은 연구들이 유전 연산자인 교차, 돌연변이 방법들에 대한 성능 비교에 초점을 맞추었는데, 본 연구에서는 선별 과정에 초점을 맞추어 기존의 알려진 여러 선별 방법 들을 Job-Shop Scheduling 문제에의 적용을 통해 비교 분석하고 새로운 선별 방법을 제안한다.
정호상,김명수,양우일,이상영,최기영 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.9
We study the microwave surface impedance of 170-µm-thick BaFe1.8Co0.2As2 single crystals with a TC of 24 K by using an open-ended sapphire resonator. The surface resistance values measured at two different frequencies of 23.3 and 19.3 GHz revealed exponential behaviors at low temperatures when the residual surface resistance values were subtracted, which was attributed to quasiparticle excitations in the smaller energy gap, Δ1, having an s-wave nature. The measured Δ1 values were (2.1 ± 0.1) meV at 23.3 GHz and (2.3 ± 0.1) meV at 19.3 GHz. A coherence peak was observed at T/TC ∼ 0.85 at 23.3 GHz and at ∼0.71 at 19.3 GHz in the real part of the complex conductivity as a function of temperature, which was consistent with the s-wave nature of the energy gaps in the BaFe1.8Co0.2As2 single crystals. Our results support that the coherence peak, reported earlier for BaFe2−xCoxAs2 films, is indeed due to the intrinsic properties of the BaFe2−xCoxAs2 single crystals, and that, unlike the case in nuclear magnetic resonance experiments, the quasiparticle coherence in BaFe1.8Co0.2As2 single crystals can be detected in microwave experiments.
정호상,양우일,Myung Su Kim,이상영,Brian H. Moeckly,John. H. Claassen 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.3
We study the temperature dependences of the microwave penetration depths at 38 GHz (l(38 GHz)) and 40 GHz (l(40 GHz)) for a YBCO film with a critical temperature (T_C) of 91 K and a MgB_2 film with a T_C of 39 K, respectively, for which two TE_(021)-mode sapphire resonators are used for the measurements. The l(40 GHz) appears to be anomalously suppressed in the MgB_2 film at temperatures below 0.8T_C, with variations in the l(40 GHz) with increasing temperature appearing significantly less than that in the penetration depth measured at 10 kHz (l(10 kHz)) by using the mutual inductance method. The suppressed l(38 GHz) of the MgB_2 film is attributed to enhanced quasiparticle conductivity, which results in significant screening of the electromagnetic waves due to quasiparticles in the MgB_2 film. We discuss the quasiparticle screening effects in the MgB_2 film in comparison with those in a YBCO film.
Two-Resonance Mode 방법용으로 제작된 고온초전도 평행판 사파이어 공진기의 마이크로파 특성
정호상,양우일,이재훈,이상영,Jung, Ho-Sang,Yang, W.I.,Lee, J.H.,Lee, Sang-Young 한국초전도학회 2010 Progress in superconductivity Vol.11 No.2
Sapphire resonators with $YBa_2Cu_3O_{7-\delta}$ (YBCO) endplates have provided a way to realize extremely high quality factor due to the extremely low dielectric loss of sapphire and conductive loss of YBCO films, which enables to measure the low surface resistance of superconductor films at microwave frequencies. We present microwave properties of HTS sapphire resonators designed for measuring the surface resistance of HTS films at millimeter-wave frequencies by using the two-resonance mode dielectric resonator method. Despite enhanced surface resistance ($R_S$) of YBCO films due to the quadratic frequency dependence of the $R_S$, the unloaded quality factor ($Q_0$) of the $TE_{021}$ mode sapphire resonator still appears to be well above $1\;{\times}\;10^6$ at a mm-wave frequency of 38 GHz at 10 K. However, it appears that the $TE_{012}$ mode $Q_0$ is unexpectedly low despite that the corresponding resonance peak looks uncoupled with parasitic modes. We discuss possible reasons for the unexpected results using the surface resistance at the $TE_{021}$, $TE_{012}$, and $TE_{011}$ mode frequencies.
정호상,이윤준,김시원,심승배,정봉주 한국경영과학회 1998 한국경영과학회 학술대회논문집 Vol.- No.1
This study deals with two major issues on work-in-process (WIP) quality: quality forecasting and corrective control of process conditions for achieving a target quality. A causal forecast model that is based on a regression model is used to predict a WIP quality under the current process conditions. In doing this, three problems are raised and solved: (1) to find the reasonable time lags between a set of process conditions and the quality indices of WIP, (2) to find the most significant process variables affecting the quality, and (3) to construct a causal forecast model. The other issue is the corrective control of process conditions for improving WIP qualities. Based on the repeatability property of manufacturing processes, the proposed approach finds the most stable and corrective process conditions for achieving a given target quality. A computerized system was developed to implement these functions.