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- 저자 : Woo-Shik Kim(김우식) (검색결과 113 건)
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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.
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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.
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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.
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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.
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김우식(Woo Shik Kim),김병호(Byung Ho Kim),박철영(Chul Young Park),김경진(Kyeong Jin Kim),오주형(Joo Hyeong Oh),동석호(Seok Ho Dong),장영운(Young Woon Chang),이정일(Jeoung Il Lee),장린(Rin Chang) 대한내과학회 1998 대한내과학회지 Vol.54 No.6
Intrahepatic arterioportal fistulae are rare, but can induce serious complications such as portal hypertension. We present a patient who developed portal hypertension secondary to an intrahepatic arterioportal fistula which was successfully embolized with occlusive balloon and microcoils. A 47-year-old previously healthy male was admitted to our hospital following an episode of melena and abdominal distension. The noteworthy feature in his previous medical history was a hepatic injury caused by a traffic accident when he was aged 9. He didn`t drink liquor at all. General appearance was pale and acutely ill. The abdomen was markedly distended and a very noisy bruit over the liver area was continously heard. Laboratory findings, including liver function tests were completely normal except for anemia (Hb 57g/dL) and hepatitis viral markers were all negative. Endoscopy demonstrated gastroesophageal varices as the source of bleeding which was treated with variceal ligation. Computed tomography showed a dilated vascular structure in the periphery of the liver at the arterial phase, which suggested a intrahepaic arterioportal fistula. The fistula was also subsequently identified with duplex ultrasound and angiography. Occlusion of the right hepatic artery was performed with occlusive balloon and microcoils. Ascites was rapidly corrected in accordance with a large amount of diuresis and gastrcsophageal varices were also completely disappeared whithin a month. On follow-up examination months after hepatic embolization, duplex ultrasound and selective angiography revealed a minute flow of blood through this fistula, but the patient remains well with no recurrence of signs of portal hypertension.
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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.
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김우식(Woo Shik Kim),하민철(Min Cheol Ha) 서울행정학회 2007 한국사회와 행정연구 Vol.18 No.2
Mentoring as a knowledge transfer and translation is useful for newcomers to organizations. Newcomers could get formal and tacit knowledge through mentoring in organization context. Mentoring is good for individuals' career development and psychological support. It is also important for organizational effectiveness. Through mentoring relationships, mentor and mentee interact f or k nowledge t ransfer, which i s important t o them f or f ulfilling t heir n eeds a nd organizational success as a whole. On this position, this study was to investigate differences between public and private organizations in structure, process, and functional effectiveness of mentoring relationships. From outcomes of our study, we gained several informations about similarities and differences between two sectors. And for preparing formal mentoring program in public sector, some policy implications were discussed.
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