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최재식(J.S.Choi),성낙원(N.W.Sung) 한국자동차공학회 1994 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1994 No.11_1
A flow model for the intake manifold of an engine was developed by the method of characteristics. The flow model was for l-D, unsteady, non-isentropic compressible flow. The accuracy of the model depends on the boundary conditions in the open end and branches. From this model, the effects of both intake and exhaust valve timings on the mass flow rate into a cylinder were tested and optimum valve timings were verified.<br/>
양방향 송수신모듈 제작을 위한 광결합계수의 계산 및 측정
김종덕,최재식,이상환,조호성,김정수,강승구,이희태,황남,주관종,송민규,Kim, J. D.,Choi, J. S.,Lee, S. H.,Cho, H. S.,Kim, J. S.,Kang, S. G.,Lee, H. T.,Hwang, N.,Joo, G. C.,Song, M. K. 한국광학회 1999 한국광학회지 Vol.10 No.6
레이저 다이오드와 수신광검출기가 집적된 소자를 V-홈을 가진 실리콘 광학벤치에 flip-chip 본딩하고, 경사면을 가진 하나의 단일모드 광섬유와 수동정렬하는 방법을 사용하여 가입자망을 위한 저가의 양방향 송수신 모듈을 설계, 제작하였다. 광섬유의 단면 경사각에 따른 송신광결합 효율과 수신광결합 효율사이의 병목점을 찾기 위해 Gaussian빔 모델을 사용하여 수평정렬거리, 광섬유 단면 경사각, 수직정렬오차등의 변수에 따른 광결합계수를 계산함으로써, 최적의 광정렬조건을 예측하였다. 또한 실리콘 광학벤치에서 광결합효율을 측정하여 광섬유의 수직정렬오차에 따른 광결합계수의 감소가 광섬유의 경사각에 의해 보상될 수 있다는 계산결과의 타당함을 확인하였다. 실제의 sub-module 제작 및 광결합 실험에서 송신빔이 광섬유 단면에 반사되어 PD로 입사되는 것을 최소화하기 위하여 광섬유 단면을 경사절두원추형으로 제작함으로써 PD의 수신 잡음을 $30mu$m 이상의 정렬거리에서 -35dB이하로 유지할 수 있었다. 같은 조건에서 단면 경사각이 $12^{\circ}$인 광섬유에 의해 -12.1dB의 송신출력과 0.2A/W의 responsivity를 얻을 수 있었다. We designed and fabricated a bidirectional optical transceiver module for low cost access network. An integrated chip forming a pin-PD on an 1.3 urn FP-LD was assembled by flip-chip bonding on a Si optical bench, a single mode fiber with an angled end facet was aligned passively with the integrated chip on V-groove of Si-optical bench. Gaussian beam theory was applied to evaluate the coupling coefficients as a function of some parameters such as alignment distance, angle of fiber end facet, vertical alignment error. The theory is also used to search the bottle-neck between transmittance and receiving coupling efficiency in the bi-directional optical system. Tn this paper, we confirmed that reduction of coupling efficiency by the vertical alignment error between laser beam and fiber core axis can be compensated by controlling the fiber facet angle. In the fabrication of sub-module, a'||'&'||' we made such that the fiber facet have a corn shape with an angled facet only core part, the reflection of transmitted laser beam from the fiber facet could be minimized below -35 dE in alignment distance of 2: 30 /J.m. In the same condition, transmitted output power of -12.1 dEm and responsivity of 0.2. AIW were obtained.
PtCeO_x/C와 Pt/CMnO_x의 제조와 메탄올의 전기화학적 산화반응에의 응용
조영진,최재식,하승백,하흥용,오인환,홍성안,이호인 한국공업화학회 2002 응용화학 Vol.6 No.2
This work dealt with the catalytic behavior of PtCeO_x/C catalysts with different Pt:Ce molar ratios. The catalysts were prepared by co-impregnation and their activities on MeOH electro-oxidation were evaluated by dynamic potential methods. Their properties were also investigated by means of physico-chemical characterization(XRD, TPR and BET). Carbon-manganese oxide composite(CMnO_x) as a support in DMFC anode was adopted. CMnO_x with or without heat-treatment was used for supporting Pt, and each of them showed two to three times higher activity on MeOH electro-oxidation, respectively. From the results of various characterizations, CMnO_x was believed to have better properties than carbon but for specific surface area.
기계적 합금화 공정으로 제조한 n 형 Bi2 (Te0.95 Se0.05)3 의 분말 특성과 열전특성
오태성,김희정,최재식,현빈도 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.2
Bi₂(Te_(0. 95)Se_(0. 05)₃ alloy powders have been fabricated by mechanical alloying process, and thermoelectric properties of the hot pressed Bi₂(Te_(0. 95)Se_(0. 05)₃have been investigated. Formation of Bi₂(Te_(0. 95)Se_(0. 05)₃ alloy powders was completed by mechanical alloying of the as-mixed Bi, Te, and Se granules of ∼3.6 ㎜ size for 2 hours at ball-to-material ratio of 5 : 1. Bi₂(Te_(0. 95)Se_(0. 05)₃, fabricated by mechanical alloying and hot pressed for 30minutes in vacuum at temperatures ranged from 300℃ to 550℃, exhibited n-type conduction without addition of donor dopant. When hot pressed at 550℃, figure of merit at 300K was 1.14×10^(-3)/K.