• 한국인터넷방송통신학회논문지
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• 제16권2호
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• pp.165-170
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• 2016

곡면형 플라즈마 도파로에 기초한 나노 크기의 전력분배기가 다중모드 간섭 결합기의 특성을 이용하여 설계되었다. 플라즈마 곡면형 다중모드 간섭 결합기(PC-MMIC)의 적응 특성을 쉽게 분석하기 위하여 등각변환 해석법을 이용하여 곡면형 구조를 평면형 구조로 등가 변환하였다. 또한, 3D 전송구조의 전파특성과 최적의 설계변수를 선택하기 위하여 유효 유전체 방법과 종방향 모드 전송 선로 해석법을 적용하였다. 설계된 $2{\times}2$ PC-MMIC는 휘어진 구조에 기인하여 quasi-TM 모드에서는 PC-MMIC의 특성이 나타내지 않았으며, quasi-TE 모드의 경우 50%:50%의 비율로 출력되는 3dB 결합특성이 나타나지 않았다. 더욱이, 곡률 반경이 작은 부분 보다 큰 부분에서 입사된 신호가 더욱 좋은 결합특성을 나타내었다.

• Macromolecular Research
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• 제8권3호
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• pp.103-115
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• 2000

The structural changes viewed from the molecular level have been investigated for the isothermal crystallization phenomena of polyethylene (PE) and the solvent-induced crystallization phenomenon of syndiotactic polystyrene (sPS) glassy sample. The data, which were collected by the time-resolved measurements of Fourier-transform infrared spectra, Raman spectra, synchrotron-sourced small-angle X-ray scattering, wide-angle X-ray scattering, and so on, were combined together to extract the detailed structural information in these phase transition phenomena. In the case of PE, the isothermal crystallization from the melt to the orthorhombic form was found to occur via the conformationally-disordered trans chain form, followed by the formation of the lamellar stacking structure of regular orthorhombic-type crystals. In the case of sPS, the amorphous chains in the glassy sample were found to enhance the mobility through the interaction with the injected solvent molecules, which act as a trigger to cause the conformational ordering from the random coil to the regular T$_2$G$_2$-type helical form. The thus created short helical segments were found to grow into longer helices, which gathered together to form the crystallites, as revealed by the organized coupling of the infrared, Raman and X-ray scattering data.

• Journal of Magnetics
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• 제16권1호
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• pp.10-14
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• 2011

This study reports on Co/$Co_2$MnSn two-phase magnets. The Co/$Co_2$MnSn two-phase magnet has Co precipitates in a $Co_2MnSn$ Heusler alloy matrix, in which the two phases are exchange-coupled at the phase boundary. The as-casted Co/$Co_2$MnSn system, which has Co-Mn solid solution precipitates in a $Co_2$MnSn Heusler alloy matrix, showed that the Co solid solution precipitates are crystallographically coherent and there is exchange coupling at the phase boundary. To form pure Co precipitates by removal of Mn solute atoms in Co-Mn solid solution, annealing was carried out 48 hours at $870^{\circ}C$. After annealing, the low $T_c$ and low magnetization phase of the Co-Mn solid solution became a high $T_c$ and high magnetization phase of hexagonal Co.

• Journal of electromagnetic engineering and science
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• 제16권2호
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• pp.126-133
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• 2016

Wireless power transfer (WPT) efficiencies for multiple-input multiple-output (MIMO) systems are formulated with a goal of achieving their maximums using Z matrices. The maximum efficiencies for any arbitrarily given configurations are obtained using optimum loads, which can be determined numerically through adequate optimization procedures in general. For some simpler special cases (single-input single-output, single-input multiple-output, and multiple-input single-output) of the MIMO systems, the efficiencies and optimum loads to maximize them can be obtained using closed-form expressions. These closed-form solutions give us more physical insight into the given WPT problem. These efficiencies are evaluated theoretically based on the presented formulation and also verified with comparisons with circuit- and EM-simulation results. They are shown to lead to a good agreement. This work may be useful for construction of the wireless Internet of Things, especially employed with energy autonomy.

• 마이크로전자및패키징학회지
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• 제25권2호
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• pp.35-39
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• 2018

광결합 효율(Fiber coupling efficiency)을 개선하기 위해서는 Laser diode에서 넓은 각도로 방출된 빛을 광섬유의 중심(Core) 부분으로 모아주는 집광렌즈(Collimating lens)가 필수적이다. 현재 사용되는 집광렌즈는 형틀(Mold)을 이용한 글래스 몰드(Glass mold) 공법이 널리 사용되고 있다. 이 방식은 생산단가가 저렴하지만, 정교한 성형이 어렵고 구면수차와 같은 품질문제가 있다. 본 연구는 기존의 글래스 몰드 공법을 반도체 공정으로 대체함으로써 표면 가공의 정밀도를 높이고, 렌즈의 재질 또한 반도체 공정에 적합한 실리콘으로 변경하였다. 반도체공정은 PR을 이용한 포토리소그래피(Photolithography) 공정과 플라즈마를 이용한 건식 식각(Dry etching) 공정으로 구성된다. 광결합 효율은 실리콘 렌즈의 광학적 특성을 평가하기 위해 초정밀 정렬 시스템을 사용하여 측정되었다. 그 결과, 렌즈 직경 $220{\mu}m$ 일 때의 최대 광결합 효율은 50%로 측정되었고, 렌즈 직경 $210-240{\mu}m$ 범위에서는 최고 광결합 효율 대비 5% 이하의 광결합 특성저하를 보여줌을 확인하였다.

• 한국ITS학회 논문지
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• 제13권1호
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• pp.61-66
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• 2014

본 논문에서는 LTE 700, GSM 850, GSM 900, GSM 1800, GSM 1900, UMTS 대역에서 동작 가능한 안테나를 설계 제작하였다. 작은 크기의 안테나로 광대역 특성을 얻기 위해 다중대역 모노폴 안테나를 기반으로 커플링 구조를 사용하였고 두 개의 slot을 삽입하여 hexa-band 대역폭 특성을 구현하였다. 시뮬레이션에 의한 최적화된 파라미터를 가지고 제작 하였고 제작된 안테나는 $VSWR{\leq}W3:1$에서 Low 주파수대역 410Hz 대역폭 (0.688-1.098GHz)과 High 주파수대역 643MHz 대역폭 (1.607-2.250GHz)이 측정되어 hexa-band(0.698-0.960GHz, 1.710-2.170GHz) 대역폭을 만족하고 높은 이득 (-0.52-4.68dBi) 및 전방향성 (Omni-directional) 방사 패턴을 얻었다.

• 대한전자공학회논문지
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• 제16권2호
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• pp.15-18
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• 1979

집적황학 도파관을 만들기 위해 LiNbO3 substrate 태로 전위원소인 Ti를 확산시켰다. L O out-diffusion 모드를 제거시킴으로써 단일 모드 도파관이 제작 될 구 있었다. 특성 측정에는 He- Ne 레이저(λ= 0.6328μm)와 프리즘 결합 방법이 사용되었다.

• Nuclear Engineering and Technology
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• 제55권1호
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• pp.310-323
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• 2023

The k-eigenvalue neutronics/thermal-hydraulics coupling calculation is a key issue for reactor design and analysis. Jacobian-free Newton-Krylov (JFNK) method, featured with super-linear convergence rate and high efficiency, has been attracting more and more attention to solve the multi-physics coupling problem. However, it may converge to the high-order eigenmode because of the multiple solutions nature of the k-eigenvalue form of multi-physics coupling issue. Based on our previous work, a modified JFNK with a line search method is proposed in this work, which can find the fundamental eigenmode together with thermal-hydraulics feedback in a wide range of initial values. In detail, the existing modified JFNK method is combined with the line search strategy, so that the intermediate iterative solution can avoid a sudden divergence and be adjusted into a convergence basin smoothly. Two simplified 2-D homogeneous reactor models, a PWR model, and an HTR model, are utilized to evaluate the performance of the newly proposed JFNK method. The results show that the performance of this proposed JFNK is more robust than the existing JFNK-based methods.

• 지질공학
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• 제29권4호
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• pp.367-381
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• 2019

We investigate pore pressure conditions and reservoir compaction associated with oil and gas production using 3 different permeability models, which are all based on one-dimensional radial flow diffusion model, but differ in considering permeability evolution during production. Model 1 assumes the most simplistic constant and invariable permeability regardless of production; Model 2 considers permeability reduction associated with reservoir compaction only due to pore pressure drawdown during production; Model 3 also considers permeability reduction but due to the effects of both pore pressure drawdown and coupled pore pressure-stress process. We first derive a unified stress-permeability relation that can be used for various sandstones. We then apply this equation to calculate pore pressure and permeability changes in the reservoir due to fluid extraction using the three permeability models. All the three models yield pore pressure profiles in the form of pressure funnel with different amounts of drawdown. Model 1, assuming constant permeability, obviously predicts the least amount of drawdown with pore pressure condition highest among the three models investigated. Model 2 estimates the largest amount of drawdown and lowest pore pressure condition. Model 3 shows slightly higher pore pressure condition than Model 2 because stress-pore pressure coupling process reduces the effective stress increase due to pore pressure depletion. We compare field data of production rate with the results of the three models. While models 1 and 2 respectively overestimates and underestimates the production rate, Model 3 estimates the field data fairly well. Our result affirms that coupling process between stress and pore pressure occurs during production, and that it is important to incorporate the coupling process in the permeability modeling, especially for tight reservoir having low permeability.

• 한국자기공명학회논문지
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• 제8권1호
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• pp.62-69
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• 2004

Bicyclolactones obtained from the Diels-Alder cycloaddition of 3,5-dibromo-2-pyrone can undergo various palladium catalyzed cross coupling reactions to afford aryl bicyclolactones. The resulting coupled products can be readily converted into various 3-OH cyclohexenes via lactone ring openings, while those bearing dienyl units underwent highly diastereoselective Diels-Alder cycloadditions with selected dienophiles to funish multiply functionalized polycarbocycles. Bromo-bicyclic diene furnished two different diastereomers endo-form (62%) and exo-form (38%) upon cycloadditions with N-Et maleimide (NEM), and their stereochemistries were identified with NMR.