윈도우 함수를 이용한 2차원 신호의 위상복원

김우식,Kim, Woo-Shik 대한전자공학회 1998 電子工學會論文誌, S Vol.s35 No.10

이 논문에서는 윈도우를 이용한 위상복원에 관하여 다룬다, 구하고자 하는 신호의 푸리에 크기와 이 원하는 신호에 서로 보완 (complementary) 윈도우가 곱해진 신호의 푸리에 크기로부터 원하는 신호를 구하는 문제에 대하여 알아본다. 여기서는 유일 조건을 만족하기 위한 여러 조건을 제시하고 Gerchberg-Saxton 알고리즘을 응용한 새로운 복원 알고리즘을 제시한다. 이 연구의 결과는 광학, 특히 천문학에서 Ground-based Telescope의 성능 개선에 이용할 수 있을 것으로 생각된다. In this paper, we consider the problem of reconstructing a two-dimensional signal from its Fourier intensity and the Fourier intensities of two windowed signals: one by a window w(m,n) and the other by its complementary window [1-w(m,n)]. We develop several conditions under which a signal can be uniquely specified to within several trivial ambiguities such as sign, translation,and time-reversal from the given conditions. We present two possible reconstruction algorithms derived from the Gerchberg-Saxton algorithm.

MPEG-4 동영상 압축에서 비트율과 오류 내성을 고려한 인트라 업데이트

김우식,박래홍,Kim, Woo-Shik,Park, Rae-Hong 대한전자공학회 2002 電子工學會論文誌-SP (Signal processing) Vol.39 No.6

동영상 압축에서 움직임 보상은 뛰어난 압축 효율을 보이는 반면에 어느 한 시점에서 오류가 발생할 경우 그 시점 이후로 계속해서 오류가 확산된다는 단점이 있다. 인트라 업데이트 방법은 이러한 오류의 확산을 차단하는 방법이다. 그러나 인트라 업데이트 방법은 압축의 효율을 떨어뜨린다는 단점이 있다. 본 논문에서는 오류의 영향과 비트율 제어를 함께 고려하여 인트라 업데이트를 할 수 있는 방법을 제안한다. 제안된 방법은 비트율과 왜곡의 값을 추정하고 라그랑지안 최적화를 통해 부호화 모드와 양자화 파라메터를 선택하는 방법으로 MPEG-4 코덱에 적용하여 실험하였다. 실험 결과는 제안된 방법이 기존의 방법보다 패킷 손실과 같은 오류 환경에서 더 좋은 화질을 나타내는 것을 보여준다. Motion compensation is a powerful method to compress an image sequence. Its main drawback is that once an error is occurred, the error propagates through the frames. Recently, the intra update method was proposed to stop the error propagation at the expense of reduction in compression efficiency. This paper proposes an intra update method based on a rate-distortion optimization in error prone environments. The rate and the distortion are estimated using the Lagrangian optimization to select the coding mode and the quantization step size. The proposed method is applied to MPEG-4 codec, and the experimental results show that it is robust to the error such as packet losses comparing with the conventional ones.

HL7과 IEEE 1451 기반 센서 네트워크와의 연동에 관한 연구

김우식,임수영,안진수,나지영,김남현,Kim, Woo-Shik,Lim, Su-Young,Ahn, Jin-Soo,Nah, Ji-Young,Kim, Nam-Hyun 대한의용생체공학회 2008 의공학회지 Vol.29 No.6

HL7(Health Level 7) is a standard for exchanging medical and healthcare data among different medical information systems. As the ubiquitous era is coming, in addition to text and imaging information, a new type of data, i.e., streaming sensor data appear. Since the HL7 is not covering the interfaces among the devices that produces sensor data, it is expected that sooner or later the HL7 needs to include the biomedical sensors and sensor networks. The IEEE 1451 is a family of standards that deals with the sensors, transducers including sensors and actuators, and various wired or wireless sensor networks. In this paper, we consider the possibility of interoperability between the IEEE 1451 and HL7. After we propose a format of messages in HL7 to include the IEEE 1451 TEDS, we present some preliminary results that show the possibility of integrating the two standards.

미립화 및 분무장치 : 다공성 표면에 충돌하는 액적 거동에 대한 실험/수치해석적 연구

김우식 ( Woo Shik Kim ),이상용 ( Sang Yong Lee ) 한국액체미립화학회 2013 한국액체미립화학회 학술강연회 논문집 Vol.2013 No.-

Behavior of a water drop impinging on heated porous surfaces was investigated experimentally and then a numerical solver was developed to predict the spreading/penetrating motion. Four porous substrates were prepared by sintering the glass particles with different sizes (60 - 270 μm in diameter). A water droplet was directed to the porous substrates with the initial wall temperature varying from 60ºC to 300ºC. The impinging Weber numbers ranged from 25 to 200 that correspond to the impact velocities from 0.8 m/s to 2.3 m/s for a water drop of 2.6 mm in diameter. The post-impingement behavior was visualized by using a high-speed camera, and the time variation of the surface temperature distribution was measured with the aid of a high-speed IR camera. The post-impingement regime map was constructed based on the observation. Basically three impingement regimes were identified: full-contact regime in the low temperature range and non-contact regime in the high temperature range, and the partial-contact regime between them. The full-contact regime, in which the drop evaporated or boiled while in contact with the surface without any disintegration, was divided into two sub-regimes: internal evaporation and internal boiling. In the partial-contact regime, a vigorous vapor nucleation was observed at the interface between the drop and the surface, which resulted in formation of the secondary droplets. In the non-contact regime, the drop was levitated but at a lower wall temperature with the larger-bead substrates due to more active nucleation on the rougher surfaces. The increase in the Weber number resulted in the higher transition temperature to the non-contact regime. This is considered to be due to the increase of the dynamic pressure at the liquid-solid interface at the instant of impact. Time variation of the surface temperature was also examined. The temperature sharply decreased right after the drop impact, and then increased with time to reach a thermal equilibrium between the penetrated liquid drop and the porous solid structure (phase I). Then the surface temperature decreased again along with the evaporation of the liquid (phase II), and finally increased up to the initial wall temperature upon completion of evaporation (phase III). The total evaporation time decreased with the larger wet-area diameter, which could be achieved with the larger impact velocity. However, there existed an optimum pore size (or size of particles) to show the maximum wet-area diameter and the shortest evaporation time. The spreading diameter and the wet-area diameter turned out to be the major indicators of the cooling performance, which were strongly influenced by both the impact condition and the characteristics of the porous substrates. In order to examine the spreading/penetrating behavior of the impinging drop against porous substrates in detail, a simulation solver (porousInterFoamWoo) was developed. The solver is based on the open source code, OpenFOAM, but the governing equations were modified from those in a pre-adapted VOF solver (porousInterFoam). The effects of the porosity on the displacement of the liquid-vapor interface and the capillary wicking force were additionally considered in the solver. A capillary-rise experiment and a one-dimensional pressure drop measurement were performed to validate the porousInterFoamWoo solver. Finally, the spreading/penetrating behavior of an impinging water drop against the porous substrates was simulated and compared with the experimental data. The solver predicted the time variations of the spreading and the wet-area diameters with a reasonable accuracy. An improved version of the solver that can predict the temperature distribution as well is currently under construction.

핀-관 열교환기용 분배기에서 유량 분배가 압력손실에 미치는 영향에 대한 실험적 연구

김우식(Woo Shik Kim),조성근(Seong Keun Jo),이상용(Sang Yong Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

In the present study, the effect of flow distribution on pressure loss at distributor for fin-tube heat exchanger was investigated experimentally. Filtered tap water was used as working fluid. The working fluid was flowed into single inlet with 10 ㎜ of inner diameter and distributed to seven axisymmetric outlet ports with 2.5 ㎜ of inner diameter. Inlet flow rate range was from 0.06 to 0.09 ㎏/s and flow distribution ratio, which means flow rate through on outlet tube divided by inlet flow rate, was varied from 0.05 to 0.35. Pressure loss at the distributor was estimated from measured pressure profiles in the inlet and one of the outlet tubes. The value of the loss coefficient calculated from pressure loss decreased with the increase of the both inlet flow rate and flow distribution ratio. Empirical correlation of the loss coefficient was proposed in terms of inlet Reynolds number and the flow distribution ratio.

이중 에너지 영상 방법에 의한 기본 물질의 분리에 관한 연구

김우식(Woo Shik Kim),이태수(Tae Su Lee),민병구(Byoung Goo Min),이충웅(Choong Woong Lee) 대한전자공학회 1985 대한전자공학회 학술대회 Vol.1985 No.6

한국피아노교수법학회논문집 : 협동학습 모형을 적용한 활동중심의 음악수업 지도방안

김우식 ( Woo Shik Kim ),오세규 ( Se Kyu Oh ) 한국피아노교수법학회 2011 음악교수법연구 Vol.7 No.-

본 연구의 목적은 초등 음악수업이 이루어지는 교실 현장에서 쉽게 활용할 수 있으며 최근 들어 그 효용성과 효과성이 입증되고 있는 협동학습의 모형을 이론적인 근거로 하여 제7차 초등학교 음악과 교육과정의 지도내용을 중심으로 개정되는 정신을 반영, 각 모형별로 활용 가능한 예시적 지도안을 구안하여 활동중심으로 구성되어야 하는 음악교육이 현장에서 내실 있게 이루어지기 위한 대안을 마련해보고자 의도된 것이다. 그리하여 본 연구에서는 교과서 제재곡에 대하여, 음악교육에 적용 가능한 협동학습 모형을 제시하고 2008년 4월 28일~6월 28일 (9주)에 걸쳐 5학년 학생들을 대상으로 협동학습 모형을 적용하여 음악수업을 실시하였다. 협동학습을 수업에 적용해본 결과 여러 가지 교육적 장점이 있음을 확인할 수 있었다. Spreading rapidly as a new method for teaching-learning, cooperation learning recently is taking firm root as an alternative to invigorate the area of teaching-learning. Most of all, the reason why cooperation learning is attracting is that it draws students’ interest and is effective for their performance at school, and in addition, it is achieving a variety of educational achievements including improvements in skills for social interactions. In today’s schools, a variety of instructional approaches is required to help all students accomplish educational goals. The object of music education is for students to individually develop their inborn musical talents and creativity, express emotion and thoughts withheld through various musical activities, and furthermore improve the quality of life and become a well-rounded person that is not narrow-minded in any specific specialty. However class in schools consists of an overcrowded class with a teacher centered deliverance of textbook knowledge that take up most of the time and lessons made of an individual and competitive learning structure. Schools are supposed to teach skills including ability to think, communication ability and responsibility for problem-solving, so that students would adopt themselves in a society. Cooperative learning is therefore the most appropriate method to teach such skills. Cooperative learning is a successful teaching strategy in which small teams, each with students of different levels of ability, use a variety of learning activities to improve their understanding of a subject. Each member of a team is responsible not only for learning what is taught but also for helping teammates learn, thus creating an atmosphere of achievement. Students work through the assignment until all group members successfully understand and complete it., So cooperative learning techniques can promote student learning and academic achievement, increase student retention, enhance student satisfaction with their learning experience, help students develop skills in oral communication, develop students’ social skills, promote student self-esteem, and help to promote positive race relations. Although there is no cooperative learning model designed specifically for music subject, it was necessary to apply cooperative learning model for effective music class. Accordingly, this study analyzed the relation between activity-centered music chapters for 5th graders and cooperative learning model. Furthmore, based on the characteristics of the existing cooperative learning model, teaching plans that can be applied for music class are presented as follows: Jigsaw Ⅰ; Group Investigation(GI); Cooperative Learning for Cooperation(Co-op Co-op); Student Teams Achievement Division(STAD); Team Games Tournaments(TGT); Learning Together(LT); Teams Assisted Individualization(TAI); and Illustrative Class Model with cooperative learning structure by Kagan. As a result, it is revealed that cooperative learning in music enables to increase self-esteem and self-discipline for study and establish favorable friendship among students in the course of class learning. The teacher’s role is the most important part for success the ‘Cooperative Learning’ on music. Teachers should know the exact model and design of ‘Cooperative Learning’ so they may guide the students to participate and have positive attitude on music. This study suggests how to take ‘Cooperative Learning’ on music class by searching activity-centered music chapters and it’s model. It is wishful that the application of cooperation learning in the fields of music education would be more activated so that the expected goals of music education could be achieved. And, I believe that the on going study about the new application should be continued to achieve a better class.

지방정부조직에서 멘티의 멘토관계 구조 및 경험과 멘토링효과

김우식(Kim Woo-Shik) 서울행정학회 2005 한국사회와 행정연구 Vol.15 No.4

Researches and studies about mentorship effectiveness in private organizations have filed up. But investigations into mentoring in governmental organizations are starting now in academic arena. The present study focused on the influence of mentor-protege relationship structure and experience factors on perceptions of mentoring functions from the perspective of protege(or mentee). It was examined for 294 samples of public officers in three local governmental organizations(Chungbuk Province, Chongju City, and Chungjoo City) in Chungbuk Area. The mentoring relationship structure(mentor's cognition of protege's mentorship) and experience with mentor (maintaining relationship and number of relationships of protege) significantly affected reports of the amount of career developmental function and psychosocial function which were perceived by proteges.

미립화 및 분무장치 1 : 다공성 물질 표면의 분무 냉각에 관한 연구 동향

김우식 ( Woo Shik Kim ),이상용 ( Sang Yong Lee ) 한국액체미립화학회 2012 한국액체미립화학회 학술강연회 논문집 Vol.2012 No.-

Recently, several attempts have been made to enhance the spray cooling performance by employing porous layers or constructing micro-structures on the target substrates. The impinged drops permeate easily through the porous surfaces and the heat transfer area between the solid and the liquid becomes much larger compared to the non-porous case. Also, the duration of the liquid-solid contact becomes much longer due to retention of the liquid within the substrate by the capillary force. At the same time, the pores on the surface behave as the nucleation sites when the substrate temperature is maintained higher than the boiling point. A few studies showed that existence of the optimum geometry of the porous later/structure but any reasonable criterion based on the physical explanations has yet been proposed. To find the ideal spraying conditions and the optimum configuration of the porous layers/structures for improvement of the cooling performance, the heat transfer mechanism of a single-drop impact on the porous surface should be investigated in detail. The amount of liquid mass deposited onto the surface, time of contact and the vapor release rates in single-drop impact should be obtained as fundamental information in estimating the surface cooling performance of sprays. According to the previous studies on hydrodynamic behavior and cooling performance of a liquid drop impinging on a porous substrate, suppression of Leidenfrost phenomenon, decrease in total evaporation time, absence of receding process, and suppression of splash phenomena were observed in accordance with the penetration of the drop into the porous structures. However, most of the previous studies are limited to the qualitative comparison between the porous and non-porous substrates based on each specific type of porous material. Thus, there should be a systematic study on the effects of the porous characteristics (e.g. porosity, permeability) on the post-impingement behavior and the cooling performance. In other words, effects of the nucleation site density and cavity size (represented by the number density of the surface pores and the size of them) on the boiling phenomena (bubble growth rate), and the relationship between the spreading and penetrating behavior (represented by permeability) should be investigated in detail as the future work.

개혁정책, 최고결정권자, 그리고 정책관료와의 관계

김우식(Kim Woo-Shik) 서울행정학회 2000 한국사회와 행정연구 Vol.11 No.1

개혁은 개인ㆍ집단ㆍ제도ㆍ구조 및 환경의 역동적인 연속적 상호작용과정 속에서 일어난다. 본 논문에서는 환경을 통제하고 개혁정책의 구조적 메카니즘을 ‘사람’에 초점을 맞추어 개혁의 성공적 조건을 탐색하는 데에 연구의 목적을 두고 있다. 따라서 개혁추진 중심인물을 중심으로 개혁 추진자들의 동기, 개혁 추진 세력의 세력화, 최고 의사결정자의 支持를 주요 변수로 선정하여 분석하였다. 본 연구는 세 사례를 중심으로 異時的 비교분석(diachronic comparative analysis)을 시도하였다. 비교의 세 사례는 조선 중종조의 조광조의 개혁과 숙종조의 윤휴의 개혁 그리고 전두환 정권하의 김재익의 경제개혁이며, 그들 개혁의 성패와 관련하여 공통점과 차이점을 비교분석함으로써 개혁성공의 조건(conditions)을 탐색하였다.