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김우식,정운수,조창래 한국화학공학회 1973 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.11 No.5
本硏究는 第2報로써 非定常狀態下에서의 回分蒸留工程의 있어서 Holdup ratio의 효과를 규명하려 한 것이다. 操作時間의 따른 Still pot內의 濃度變化를 蒸留速度로 定義하여 다음과 같은 理論式을 誘導했다. (수식) 試料는 Benzene-Carbontetrachloride와 Methanol-Ethanol 等의 二成分系를 使用했으며 實驗値와 比較검토 結果 上記 理論式과 잘 一致했다. 한편, Reflux ratio가 낮을 때는 Holdup ratio가 증가할수록 분리효과는 증가하였고, Reflux ratio가 높을 경우는 Holdup ratio가 증가할수록 분리효과는 감소했다. 따라서 다른 모든 變數를 일정하게 유지시켰을 때 Holdup ratio의 분리효과는 Reflux ratio의 의존함을 알았다. 또 Holdup ratio의 분리효과가 뚜렷이 나타나지 않았을 때의 Reflux ratio를 Critical Reflux ratio라 하였으며 本 硏究에서 Benzene-Carbontetrachloride의 Critical Reflux ratio는 9였고 Methanol-Ethanol系에서는 2였다. This study is concerned with the separation of binary mixtures in the fractional batch distillation under various conditions of Holdup to charge ratio at constant reflux ratio. The rate of separation is defined as the rate of change in the still composition with respect to the operating time elapsed. Under proper assumption a theoretical equation relating the still composition with the operating time was derived as; (수식) The equation was compared with experimental results obtained with two binary mixtures, i.e., Benzene-CTC(carbontetrachloride) and Methanol-Ethanol, in a Oldershaw-type batch distillation apparatus. Consequently the equation was found to be substantially agreed with the experimental results, especially for the Methanol-Ethanol system. For the benzene-CTC system the equation tended to agree with experimental results. Meanwhile, holdup ratio was found experimently to have two counteracting effects on the separation of binary mixtures. Namely, in a series of experimental works, as the reflux ratio was increased above the critical reflux ratio the effect of increased holdup ratio become increasingly unfavorable to sharpness of separation. At reflux ratio below the critical reflux ratio the effect of increasing holdup ratio was favorable. For the Benzene-CTC system (30 plates) the critical reflux ratio was 9, at the Methanol-Ethanol system was 2.
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Closed-form Algorithms for Phase Retrieval with an Additive Linear Phase Signal
김우식 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.4
The phase retrieval problem is a problem of reconstruction of a signal from the magnitude of its Fourier transform. In this paper, we consider the problem of reconstructing an unknown onedimensional signal from the magnitude of its Fourier transform and the magnitude of the Fourier transform of another signal that is made by the addition of a linear phase signal at the center of the original signal. Since there are two kinds of linear phase signals, i.e., symmetric and antisymmetric, we consider the two cases separately. After showing that there are exactly two solution signals that satisfy the given condition, we develop a closed-form algorithm that may reconstruct the two solution signals.
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Phase Retrieval By Enforcing the Off-Axis Holographic Condition
김우식 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2
The phase retrieval problem is concerned with the reconstruction of a Fourier transform phase or the signal itself from its Fourier transform magnitude and occurs in various physical fields, including astronomy, optics, X-ray crystallography, etc. In this paper, we address a one-dimensional phase retrieval by using a window function to enforce an off-axis holographic condition. We show that, by choosing an appropriate window function, we can make the windowed signal satisfy the off-axis holographic condition and reconstruct the unknown signal from the magnitudes of two Fourier transforms; the magnitude of the Fourier transform of an original unknown signal and that of the windowed signal. We show that this problem has a unique solution to within a sign ambiguity and present a closed-form solution. The phase retrieval problem is concerned with the reconstruction of a Fourier transform phase or the signal itself from its Fourier transform magnitude and occurs in various physical fields, including astronomy, optics, X-ray crystallography, etc. In this paper, we address a one-dimensional phase retrieval by using a window function to enforce an off-axis holographic condition. We show that, by choosing an appropriate window function, we can make the windowed signal satisfy the off-axis holographic condition and reconstruct the unknown signal from the magnitudes of two Fourier transforms; the magnitude of the Fourier transform of an original unknown signal and that of the windowed signal. We show that this problem has a unique solution to within a sign ambiguity and present a closed-form solution.
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Two-Dimensional Phase Retrieval by Enforcing the Off-Axis Holographic Condition
김우식 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.II
The phase retrieval problem is concerned with the reconstruction of a Fourier transform phase or the signal itself from its Fourier transform magnitude and involves various physical fields, including astronomy, optics, X-ray crystallography, {\it etc.} Among many approaches to solve this non-unique problem, the off-axis holography technique is most fundamental and well known. The implementation of this technique, however, is very difficult. In this paper, we propose a simple and easy method of implementing an off-axis holography technique for a two-dimensional signal such as the image obtained by using a specially designed window. We address a phase retrieval by enforcing an off-axis holographic condition for a two dimensional signal, show that this problem has a unique solution to within a sign ambiguity, and present a closed form solution.
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PVA 섬유보강 시멘트 혼합토의 압축강도 특성에 관한 연구
김우식,정두회,조일묵 한국방재학회 2012 한국방재학회논문집 Vol.12 No.3
The characteristics of compressive strength of PVA fiber reinforced soil-cement mixture has been evaluated through unconfined compressive strength tests. Test specimens were prepared with a variety of cement contents, fiber contents,fiber lengths, and curing periods to investigate the effect of these parameters on the strength characteristics of PVA fiber reinforced soil-cement mixture. In addition, a compresso-meter has been revised to measure the internal strain of test specimen during the process of loading. The internal strain was used to evaluate the secant moduli (E50) of soilcement mixtures. The PVA fiber reinforced soil-cement mixture showed a ductile failure whereas the unreinforced soilcement mixture showed a brittle failure. The inclusion of PVA fiber in soil-cement mixtures improved the compressive strength characteristics of soil-cement mixtures in several aspects. 본 연구는 DCM공법으로 조성된 시멘트 혼합토의 역학적 특성을 개선시키기 위한 일환으로 시멘트 슬러리와 함께 PVA 섬유를 교반혼합한 PVA 섬유보강 시멘트 혼합토에 대한 일축압축시험을 통하여 PVA 섬유보강 혼합토의 시멘트 함유량, PVA 섬유 혼입율 및 섬유 길이, 그리고 양생기간에 따른 응력-변형률 거동과 일축압축강도 특성을 평가하였다. 무보강 시멘트 혼합토와 PVA 섬유보강 시멘트 혼합토는 시멘트 첨가량이 증가할수록 일축압축강도가 증가하였고, 무보강 시멘트 혼합토는 취성파괴의 거동을 보이는 반면에 PVA 섬유보강 시멘트 혼합토는 연성파괴의 거동을 보이는 것으로 나타났다. 또한 시멘트 첨가량,PVA 섬유 혼입량과 섬유의 길이는 PVA 섬유보강 시멘트 혼합토의 응력-변형률 거동과 일축압축강도의 크기에 중요한 영향을미치는 인자로 평가되었다.
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