• 한국세라믹학회지
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• 제23권6호
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• pp.59-65
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• 1986

Flexural strength fracture toughness and strengthening mechanisms of cordierite ceramics reinforced by SiC whiskers up to 40vol% were investigated. The specimens were hot pressed at Ar atmosphere. The porosity increased with the SiC whisker content. Flexural strength and single edge notch beam fracture toughness were measured up to 1,000$^{\circ}C$. Extrapolating to zero porosity the reinforced composites exhibited in-creasings in flexural strength and fracture toughness with the SiC whisker content. The composites were strengthened mainly by load transfer crack impediment and partially by crack deflection mechanisms. Impurities played an important role in determining the mechanical properties of the composites.

• 한국레이저가공학회지
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• 제11권1호
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• pp.25-31
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• 2008

The characteristics of femtosecond laser ablation of $Al_2O_3$ for prescision microfabrication are studied experimentally. Specifically, the process time during femtosecond laser drilling of microholes with $sub-100{\mu}m$ diameter are investigated for varying laser fluence, scan speed and beam path designs like trepanning with continuously changed start points. The accumulation of sub-micrometer size particles within the hole and the deterioration of edge clarity and roundness for decreasing hole diameter are examined and through process optimization the microdrilling with good hole quality is achieved using a femtosecond laser system (repetitionrate 1 kHz, wavelength 785 nm, pulse duration 185 fs)

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 춘계학술대회 논문집
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• pp.72-73
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• 2010

In this paper, the main noise sources and its radiated noise levels of upwind horizontal-axis wind turbines are experimentally and theoretically investigated. Theoretical predictions for indentifying the dominant source locations are made by using the empirical noise prediction model of Brooks et al. (1989) for the airfoil self noise. Through the comparison of theoretical results with the experimental results, turbulence-boundary-layer-trailing-edge (TBL-TE) noise is revealed to be the dominant source over all frequency range and separation and stall (S-S) noise is possibly important in the relative lower frequency range compared with TBL-TE noise.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.98-103
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• 2004

This paper presents modeling and simulation of the bump foil bearings with consideration of the elastic behavior of the foil and gas compressibility. Heshmat had originally introduced the simple compliance model to estimate the EHL(elasto-hydrodynamic lubrication) performance. But this approach can not consider the deflection of top foil at the edge of bearing, so model is insufficient to analyze in case that the eccentricity ratio is greater than I. So the top foil is considered as a simple beam model supported by linear spring elements, and the bump foil deflection can be simple compliance model. The EHL calculations are performed for convention rigid type, classical foil type, variable pitch type and double bump type toil bearings. This paper presents that 2nd or 3rd generation bearings have excellent performance in every speeds.

• 한국광학회지
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• 제8권1호
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• pp.19-25
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• 1997

Agfa 8E75HD 사진건판에서 얻은 dichromated gelatin(DCG) 박막에 구면파와 평면파를 간섭시켜 holographic zone plate(HZP)를 만들었다. DCG박막의 비서형적인 광학특성들을 고려하여 HZP의 이론식을 유도하였다. 이 이론식에 의한 HZP의 초점거리를 거리는 f. f/2, f/3, f/4, ... 였으며, 실험적으로도 평면파를 입사하여 6개까지의 해당 초점들을 관측하였다. 칼날 주사 방법으로 측정한 첫 번째 재생 초점 근처에서의 빔의 모양은 Gaussian 분포를 가짐을 확인하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 가을 학술발표회 논문집
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• pp.59-66
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• 2001

The post-peak analysis of concrete structures is carried out using a nine-node Reissner-Mindlin(RM) shell element which is formulated by using degenerated solid concepts. In order to avoid element deficiencies inherited in the standard RM shell element, assumed strains are adopted in the present shell element. A microscopic material model is adopted to represent the inelastic characteristic of concrete material. In particular, a concrete softening model is introduced to this material model. The arc-length control method is used to trace the post-peak behaviour of concrete structures. From the numerical test of the single-edge-notched beam, the present shell element shows a reasonable agreement with experimental data.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2002년도 추계기술심포지움논문집
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• pp.177-179
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• 2002

A1$_2$ $O_3$기판재료의 $K_{IC}$ 증가를 위한 재료설계를 시도하였다. 먼저 A1$_2$ $O_3$기판을 구성하는 A1$_2$ $O_3$다층구조물에 적절한 다공성 중간층을 삽입하는 샌드위치 구조물을 제조하였다. 제조된 A1$_2$ $O_3$구조물의 미세구조를 관찰하였고, Vickers 경도와 three-point bending test를 통해서 단일조성 구조물과 샌드위치 구조물의 경도와 인성 측정치를 비교하였다. 다공층을 삽입한 A1$_2$ $O_3$샌드위치 구조물의 Single-Edge Notched Beam이 단일 조성의 구조물에 비해 파괴강도와 인성이 향상되는 결과를 얻었다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.63-66
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• 2008

The bridge deck section composed of a concrete slab resting on two I-beam girders are known to be susceptible to flutter instability and vortex shedding. Moreover, the cable stayed bridge in construction is more vulnerable to wind rather than in service when the free cantilever construction method is applied. This paper describes the effect of the dynamic wind loads on the bridge during construction and the effect of alternative temporary stabilizing measures. Therefore, a series of wind tunnel tests and numerical analysis were carried out to determine if any countermeasures were required.

• 한국통신학회논문지
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• 제25권10A호
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• pp.1521-1528
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• 2000

In this paper we analyze the performance of a DS/CDMA system in LEO mobile satellite channels. The channel uses the Extended Suzuki model which is the product of a Rician distribution having a LOS component and a lognormal distribution due to shadowing. We assume that the signal transmitted from the satellite to the mobile undergoes the same fading for the whole coverage of signal's beam. The average bit error probabilities of double coverage system is calculated in this paper. The interference resulting from the reference satellite is calculated for mobile located in the middle of the double coverage region whereas the additive interference from next-satellite is included for mobile located in the edge of the double coverage region. The performance of the mobile's receiving signal is dependent on shadowing and the interference of the next-satellite. We can obtain an obtain an improved average bit error probability by using dual diversity over the conventional correlated receiver for similar shadowing conditions in the coverage area of the satellite channel.

• Current Optics and Photonics
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• 제4권4호
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• pp.353-360
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• 2020

Adopting an elaborately designed reflective objective consisting of four mirrors, we have developed a rotating-polarizer-type microspot spectroscopic ellipsometer (SE) with an ultra-small spot size. The diameter of the focused beam, whether evaluated using a direct-image method or a knife-edge method, is less than 8.4 ㎛. After proper correction for the polarizing effect of the mirrors in the reflective objective, we unambiguously determine the dispersion of the complex refractive index and the thickness of monolayer MoS₂ using the measured microspot-spectroellipsometric data. The measured ellipsometric spectra are sensitive enough to identify small variations in thickness of MoS₂ flakes, which ranged from 0.48 nm to 0.67 nm.