An OCDMA Scheme to Reduce Multiple Access Interference and Enhance Performance for Optical Subscriber Access Networks

Sangjo Park,김봉규,김병휘 한국전자통신연구원 2004 ETRI Journal Vol.26 No.1

We propose a new optical code division multiple access (OCDMA) scheme for reducing multiple access interference (MAI) and enhancing performance for optical subscriber access networks using modified pseudorandom noise (PN)-coded fiber Bragg gratings with bipolar OCDMA decoders. Through the bipolar OCDMA decoder and the modified PN codes, MAI among users is effectively depressed. As the data are encoded either by a unipolar signature sequence of the modified PN code or its complement according to whether the data bit is 1 or 0, the bit error ratio (BER) can be more improved with the same signal to interference plus noise ratio over the conventional on-off shift keying-based OCDMA system. We prove by numerical analysis that the BER of the proposed bipolar OCDMA system is better than the conventional unipolar OCDMA system. We also analyze the spectral power distortion effects of the broadband light source.

Linear Dependence of Energy Band-gap on the Composition of MgxZn1-xTe Single Crystals Studied by Photocurrent Measurements

Chung sangjo,Jun yongki,Suh eunkyung 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.4

Single crystals structures of MgxZn1−xTe (0 < x< 0.48) were grown for various Mg mole compositions by using a vertical Bridgman method. The optical properties of the grown crystal were characterized using photocurrent (PC) and persistent photoconductivity (PPC) measurements. As a result of the PC spectra, single crystalline MgxZn1−xTe (x = 0) showed an energy band gap of 2.380 and 2.260 eV at 4.2 and 294 K, respectively. The PC peak blue-shifts with increasing Mg mole fraction and shows linear dependence of energy band gap, Eg(x) = b + (0.8)x. The extrapolation shows the energy band gaps of MgTe as 3.18 and 3.06 eV at temperatures of 4.2 and 294 K, respectively. Furthermore, the PC peak red-shifts with increasing temperature, and the temperature coefficient is given by a value of dEg/dT = – (5.6 6.1) × 10−4 eV/K for the temperature range above 100 K. In the PPC measurements, the decay times of the PPC spectra strongly depended on the Mg content. These results clearly indicate a change in crystal structure with increasing Mg mole fraction.

마음챙김 관점에서 본 대학 정보화 프로젝트

오상조(Sangjo Oh),김용영(Yong-Young Kim),김범수(Beomsoo Kim) 한국전자거래학회 2011 한국전자거래학회지 Vol.16 No.3

대학은 지속가능성을 확보하기 위해 대학 정보화에 꾸준히 투자하고 있고, 이러한 노력 덕분에 학생들이나 교직원들은 언제 어디서나 대학의 정보시스템에 접속하여 효율적으로 업무를 처리할 수 있게 되었다. 최근 대학은 정보기술 수요 환경의 변화에 대응하여 다양한 서비스를 제공하기 위해 대학 행정 정보화 프로젝트에서 나서고 있다. 그 중 일부 대학은 계획한 성과를 달성하였지만, 새롭게 개발된 시스템의 이용을 중단하여야 할 것인가를 고민중인 대학도 있다. 대학 정보화는 어느 정도의 실패 요인을 안고 출발하기 마련이다. 예측하지 못한 사태로 인해 난관에 봉착하기도 하고, 구성원들의 지혜를 모아 문제를 슬기롭게 극복하기도 한다. 마음챙김 이론은 이러한 시스템 개발 및 운영 과정을 심도있게 살펴볼 수 있는 관점을 제공한다. 본 연구는 대학 행정 정보시스템 개발 프로젝트 사례를 마음챙김 관점에서 분석하고, 그 파급효과와 시사점 등을 정리하였다. Universities have been investing in their information systems to keep their management functions working efficiently and effectively. Thanks to these efforts, faculty members and other university employees can perform their tasks efficiently almost anywhere and anytime. Several universities embarked upon information systems projects to take advantage of emerging information technologies in their administration and management. Only a limited number of universities have achieved their objectives; some others have been even tinkering with the idea of abandoning their newly developed academic information systems. The development of academic information systems often start with a relatively high risk of system failure. Sometimes, these systems encounter unforeseen obstacles or fail in systems development. These universities with problems also can overcome these issues by collecting their wisdom. The mindfulness theory is suitable for dealing with implementing academic information systems. This research analyzes an academic information systems development case from a mindfulness perspective, and also addresses its research implications and theoretical contributions.

Fold recognition by combining profile–profile alignment and support vector machine

Han, Sangjo,Lee, Byung-chul,Yu, Seung Taek,Jeong, Chan-seok,Lee, Soyoung,Kim, Dongsup Oxford University Press 2005 Bioinformatics Vol.21 No.11

<P><B>Motivation:</B> Currently, the most accurate fold-recognition method is to perform profile–profile alignments and estimate the statistical significances of those alignments by calculating <I>Z</I>-score or <I>E</I>-value. Although this scheme is reliable in recognizing relatively close homologs related at the family level, it has difficulty in finding the remote homologs that are related at the superfamily or fold level.</P><P><B>Results:</B> In this paper, we present an alternative method to estimate the significance of the alignments. The alignment between a query protein and a template of length <I>n</I> in the fold library is transformed into a feature vector of length <I>n</I> + 1, which is then evaluated by support vector machine (SVM). The output from SVM is converted to a posterior probability that a query sequence is related to a template, given SVM output. Results show that a new method shows significantly better performance than PSI-BLAST and profile–profile alignment with <I>Z</I>-score scheme. While PSI-BLAST and <I>Z</I>-score scheme detect 16 and 20% of superfamily-related proteins, respectively, at 90% specificity, a new method detects 46% of these proteins, resulting in more than 2-fold increase in sensitivity. More significantly, at the fold level, a new method can detect 14% of remotely related proteins at 90% specificity, a remarkable result considering the fact that the other methods can detect almost none at the same level of specificity.</P><P><B>Contact:</B> kds@kaist.ac.kr</P>

혼합 흐름 터보팬 엔진의 성능해석 모델링

김상조(Sangjo Kim),김동현(Donghyun Kim),김귀순(Kuisoon Kim),손창민(Changmin Son),김유일(YouIl Kim),민성기(Seongki Min) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.5

항공기 성능해석을 하기 위해서는 엔진 상세 데이터가 필수적으로 요구된다. 하지만 이러한 엔진 상세 데이터는 항공회사의 경험으로 축적된 자산이기 때문에 엔진 성능 정보를 구하기 어렵다. 본 연구에서는 일반적으로 공개된 자료와 문헌정보를 이용하여 혼합흐름 터보팬 엔진 성능 모델을 구축하고 결과를 비교하였다. The details of engine data are essentially needed for engine modeling and simulation. But, the engine data are kept secret because the information is company’s experiential property. In this paper performed the performance modeling of the mixed flow turbofan engine cycles from the general available engine data, and verify the validity.

가스터빈 엔진의 축류압축기 성능선도 생성방법에 대한 비교 연구

김상조(Sangjo Kim),김동현(Donghyun Kim),손창민(Changmin Son),김귀순(Kuisoon Kim),김유일(YouIl Kim),민성기(Seongki Min) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11

가스터빈 엔진의 성능모사를 위해서는 구성품의 유량, 회전수, 압력비 그리고 효율 변화를 나타내는 성능선도를 이용하는 것이 필수적이다. 본 연구에서는 축류 압축기 성능선도 생성 방법인 유사성능선도 축척법(scaling method), 단 성능선도를 이용한 단 축적법(stage-stacking method), 3차원 전산해석, 3차원 전산해석과 단 축적법을 복합적으로 이용하는 방법들을 적용하였다. 그리고 서지 지점을 예측하기 위해 두 가지 방법을 적용하였다. 각각의 방법들을 사용하여 구성한 축류 압축기 성능 선도를 성능시험결과와 비교하였다. In the performance analysis of gas turbine engines, it is essential to use a performance map that represents the variation in mass flow rate, rpm, pressure ratio and efficiency. In this paper, The performance map is generated by the methods such as scaling method, stage-stacking method, 3-D CFD analysis and combined application of stage-stacking and 3-D CFD analysis. And the surge point was estimated within this work using two different models. The performance maps using the methods mentioned above were compared with the experimental data.

신용장 서류심사의 일치성 판단기준

김상조(Sangjo Kim),이재달(Jaedal Lee) 한국항만경제학회 2013 韓國港灣經濟學會誌 Vol.29 No.2

본 연구는 신용장 서류심사의 일치성 판단기준에 대해 우리나라 대법원의 실무적 판례를 중심으로 고찰하고자 한다. 대법원의 서류심사의 일치성 판단기준은 엄격일치의 원칙이 지지되고 있다. 그리고 대법원이 서류심사에서 그 판단이 구체적인 경우는 신용장과의 차이가 국제적 표준은행관행에 비추어 용인될 수 있는가의 여부를 따른다. 이 경우 대법원은 국제표준은행관행으로 국제상업회의소(ICC)의견이나 결정을 참고하기도 하고, ICC의 의견이나 결정이 없는 경우는 국제표준은행관행을 탐구하여 인정하기도 할 것이다. 그러나 은행 서류심사자들이 서류심사를 할 경우 고도의 높은 식견과 지식이 없으므로 짧은 시간에 이를 찾아 판단하는 것이 지극히 어려운 일이 될 것이다. 본 연구의 사례에서 보듯이 신용장의 엄격일치의 원칙은 계속 완화되어 가고, 최근의 판례는 거의 대부분 엄격일치의 예외로 판시하고 있다. 그러므로 은행 서류심사자들은 이와 같은 일치성판단이 어렵기 때문에 자의적 서류심사행위를 하는 것이 불가피하게 될 것이다. 그 결과 은행과 개설의뢰인은 서류상의 엄격성을 확보하는 것이 어렵게 되고, 국제거래에서 신용장의 자유로운 사용을 기피하게 될 것이다. 따라서 은행실무자의 신용장 서류심사의 일치성 판단기준에 대한 다양한 실무적 적용에 본 연구가 활용되기를 기대한다. The purpose of the study is to examine compliance criteria for documents of the Letter of Credit(L/C) by the Korean Supreme Court in practical use. The judgement criteria of the court in documents" examination is supported by the doctrine of strict compliance. And, in examination of documents by the Supreme Court, the difference between documents presented and the credit should be followed by the allowance of international standard banking practices. In this case, the Supreme Court makes a reference for ICC"s opinion or decision proposed as the international standard banking practices, or otherwise admit by exploring the practices. However, when documents reviewing by the bankers" auditors, it is very difficult for them to judge in a short time due to the lack of high level of knowledges and insights. As shown the cases of this study, the doctrine of strict compliance of an L/C be relaxed, and most of the recent precedents be ruled by the exception of the doctrine. Because, therefore, it is difficult for to documents reviewers of bank to judge these consistencies, conducting arbitrary document review will be inevitable. As a result, it will be difficult for banks and applicants to ensure the strictness of the documents, and free use of L/Cs in international transactions will be avoided. Finally, the expanded usage of the electronic negotiation system that simplifies the highly difficult compliance criteria to ensure the strictness of documents will be needed, and not only be eradicated the acts of arbitrary documents examination practices, but also be promoted the freely usage of L/Cs.

A W-Shaped Antenna With Spatial Polarization Variation for Direction Finding

Choi, Sangjo,Sarabandi, Kamal IEEE 2018 IEEE antennas and wireless propagation letters Vol.17 No.12

<P>A compact impedance-matched W-shaped antenna is presented that can radiate a perfect circular polarization (CP) at its boresight and distinct polarization states at different propagating directions in the far-field. The antenna structure consists of a horizontal dipole, a vertical dipole, and two elliptical loops connecting the adjacent arms of the dipole elements. The arc length and geometry of the loops are designed to produce the perfect CP at the boresight of the antenna. Using a single feed point, the antenna has an isotropic radiation pattern and is capable of producing distinct polarization states in different directions except for the plane of the antenna. Also, the symmetrical polarization characteristics with respect to the axes of the antenna symmetry are shown in the same propagating direction. This ambiguity of polarization can be resolved by using a pair of the proposed antennas operating at slightly different frequencies as a transmitter and triad dipoles to realize an azimuth-polar direction finding system. To demonstrate the validity of the antenna design, an antenna structure operating at 2.58 GHz is fabricated over a ground plane and measured. The measured radiation pattern shows the perfect CP at the boresight and 6.2% for the 3 dB axial ratio bandwidth.</P>

터보팬 엔진 개발에서의 성능 해석 프로그램 활용

김상조(Sangjo Kim),김유일(Youil Kim),이수창(Suchang Lee),김명호(Myung Ho Kim) 한국추진공학회 2020 한국추진공학회 학술대회논문집 Vol.2020 No.11

수소 액화용 다단 터보 팽창기 개발

한상조(Sangjo Han),최범석(Bum Seog Choi),박무룡(Moo Ryong Park) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

The paper discusses the development of hydrogen liquefaction turbine. Hydrogen gas has good energy density by weight, but has poor energy density compared with hydrocarbons. To get same energy with hydrocarbon, hydrogen needs large storage tanks. Liquefaction of hydrogen can solve this problem. In Claude cycle, the liquefaction system requires a turbo-expander which is not developed domestically. This research covers the process of developing the hydrogen liquefaction turbo-expander from meridional designs to 3D CFD. Off-design performance is checked in different rotating speed and expansion ratio. To check the performance of the turbo-expander, 3D fully CFD simulation is conducted to check the flow and thermal performance using ANSYS CFX. Due to high expansion ratio(5) required for a hydrogen liquefaction system, multi-stage design is employed in this study.