• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술대회 논문집 전문대학교육위원
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• pp.124-126
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• 2003

The results of investigations of $Ag_2Se$ single crystal is presented. $Ag_2Se$ crystal was grown by the Bridgman method. The $Ag_2Se$ single crystal was an orthorhombic structure with lattice constance a=4.1686 $\AA$, b=9.0425 $\AA$, c=8.0065 $\AA$. Hall effect shows a n-type conductivity in the $Ag_2Se$ single crystal. The electrical resistivity values was $1.25{\times}10^3ohm^{-1}cm^{-1}$ and electron mobility was $-5.48{\times}10^3cm^2/V{\cdot}sec$ at room temperature(RT).

• 한국전자파학회논문지
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• 제23권4호
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• pp.415-423
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• 2012

본 논문에서는 유전 알고리즘을 이용한 광대역 부배열 최적화 설계에 대해 기술하였다. 먼저 무한 주기 구조의 삼각 배열을 이용하여 광대역 복사 소자를 설계하였다. 너치 구조의 복사 소자로 정면 빔 조향 시 능동 반사 계수 -10 dB 이하를 만족하는 최대 및 최소 주파수 비가 약 2:1 정도로 광대역 특성을 가지고 있다. 이러한 광대역 배열 소자 1,100여개로 이루어진 안테나 구조의 부배열 최적화를 위해 유전 알고리즘을 이용하였다. 대조군인 규칙 부배열 안테나 구조와 비교해서 최적화(불규칙) 부배열 안테나 구조의 최대 부엽 준위가 4.5-5.5dB 정도 개선되었음을 확인하였다.

• Journal of Magnetics
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• 제14권3호
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• pp.117-119
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• 2009

Polycrystalline samples of LaFe$O_3$-BaTi$O_3$ were synthesized to examine the structural and magnetic behavior. X-ray diffraction confirmed that the ceramics had tetragonal symmetry with less tetragonal strain (c/a) than BaTi$O_3$. The magnetic hysteresis measured at room temperature suggested that the magnetic nature deviates from that of the parent LaFe$O_3$, which has antiferromagentic with a G-type spin structure. Improved magnetic behavior of the solid solution compound might be due to the increase in the canting angle of the spin. The presence of oxygen vacancies and fluctuating Fe valence, arising from the substitution of $Ba^{2+}$ and $Ti^{4+}$ at the A- and B-sites of the lattice, might contribute to bulk magnetization. The temperature dependent magnetization indicated that magnetization was higher at low temperatures and showed a decreasing trend with increasing temperature to room temperature. The magnetic transition temperature of these samples was 665 K and 743 K for the mixed system and LaFe$O_3$, respectively.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.732-739
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• 2005

The determination of sound pressure radiated from periodic plate structures is fundamental in the estimation of noise level in aircraft fuselages or ship hull structures. As a robust approach to this problem, here a very general and comprehensive analytical model is developed for predicting the sound radiated by a vibrating plate stiffened by periodically spaced orthogonal symmetrical beams subjected to a sinusoidally time varying point load. In this these, we experiment with the numerical analysis using the space harmonic series and the SYSNOISE for measuring the vibration mode and character of response caused by sound radiation with adding the harmonic point force in the thin isotropic plate supported by the rectangular lattice reinforcement. We used the reinforcements, beams of open type section like the style of 'ㄷ' letter; the space of the beams were chosen to be 0.2m, 0.3m, 0.4m. We studied the behavior of sound pressure levels, analysis of vibration mode between support points, connection between frequency function and sound pressure levels, and connection between position function and sound pressure levels.

• 대한건축학회논문집:구조계
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• 제35권8호
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• pp.123-130
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• 2019

Recently, it is required to develop a monitoring technology that combines an FBG sensor as a means for continuously monitoring whether reinforcing effect of FRP is maintained on FRP reinforced structural members. However, most existing researches focus on the insertion of FBG sensors into bar-shaped FRPs, and there is insufficient study on the details strip-type FRPs combined with FBG sensors. Therefore, in this paper, it is studied to develop a reinforcement in which a FBG sensor is combined with a FRP strip. Especially, combination of FRP and FBG sensor. For this, a series of experiments were performed to find the adhesive strength of fiber-FRP-epoxy joints, the tensile strength of FBG sensor part with reflection-lattice, and the performance depending on the connection method of FRF and FBG sensor. As a result of the study, it was found that a minimum strength of $216.15N/mm^2$ is required for incorporating FBG sensors in FRP using epoxy. It is considered that the adhesion length of epoxy joints should be more than 50mm. When the FBG sensor is attached to the FRP strip as an epoxy, it is considered appropriate to use the complete attachment and the sensor non-attachment method.

• 대한금속재료학회지
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• 제49권11호
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• pp.900-904
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• 2011

We have synthesized core-shell structured nanocrystals based on chalcopyrite-type $Cu_{0.2}InS_2$. The photoluminescence of the nanocrystals shows a significant blueshift in the emission wavelength by shell capping with ZnS layers. This shift can be explained with the compressive stress to core nanocrystals applied by the formation of a ZnS shell layer with a large lattice mismatch with the core. In this study, the emission wavelength could be tuned by changing the composition of the shell layers. Nanocrystals with emission wavelength ranging from 575 nm through 630 nm were synthesized by varying the portion of cadmium compared with zinc in the shell layers.

• Wind and Structures
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• 제36권4호
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• pp.263-275
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• 2023

As a new kind of construction facility for high rise buildings, the integral steel platform scaffold system (ISPS) consisting of the steel skeleton and suspended scaffold faces high wind during the construction procedure. The lattice structure type and existence of core tubes both make it difficult to estimate the wind load and calculate the wind-induced responses. In this study, an aeroelastic model with a geometry scale ratio of 1:25 based on the ISPS for Shanghai Tower, with the representative square profile, is manufactured and then tested in a wind tunnel. The first mode of the prototype ISPS is a torsional one with a frequency of only 0.68 Hz, and the model survives under extreme wind speed up to 50 m/s. The static wind load and wind vibration factors are derived based on the test result and supplementary finite element analysis, offering a reference for the following ISPS design. The spacer at the bottom of the suspended scaffold is suggested to be long enough to touch the core tube in the initial status to prevent the collision. Besides, aerodynamic wind loads and cross-wind loads are suggested to be included in the structural design of the ISPS.

• Bulletin of the Korean Chemical Society
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• 제25권4호
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• pp.511-516
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• 2004

A Li$[Co_{0.17}Li_{0.28}Mn_{0.55}]O_2$ cathode compound was prepared by a simple combustion method. The X-ray diffraction pattern showed that this compound could be classified as ${\alpha} -NaFeO_2$ structure type with the lattice constants of a = 2.8405(9) ${\AA}$ and c = 14.228(4) ${\AA}$. According to XANES analysis, the oxidation state of Mn and Co ions in the compound were 4+ and 3+, respectively. During the first charge process, the irreversible voltage plateau at around 4.65 V was observed. The similar voltage-plateau was observed in the initial charge profile of other solid solution series between $Li_2MnO_3\;and\;LiMnO_2$ (M=Ni, Cr...). The first discharge capacity was 187 mAh/g and the second discharge capacity increased to 204 mAh/g. As the increase of cycling number, one smooth discharge profile was converted to two distinct sub-plateaus and the discharge capacity was slowly decreased. From the Co and Mn K-edge XANES spectra measured at different cyclic process, it can be concluded that irreversible transformation of phase is occurred during continuous cycling process.

• 대한화학회지
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• 제48권1호
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• pp.46-52
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• 2004

층상구조를 갖는 망간산화물에서 결정성과 구조적 안정도 간의 관계에 대해 조사하였다. 좋은 결정성을 갖는 망간산화물은 고상합성법-이온교환법을 이용하여 합성하였으며, 나노결정 망간산화물은 실온에서의 Chimie-Douce 반응을 통해 얻어졌다. 마이크로 라만 분광과 X선 흡수분광 결과는 결정성에 상관없이 이들 화합물에 존재하는 망간이온이 공통적으로 층상구조의 팔면체 자리에 안정화되어 있음을 보여준다. 미분전하용량 분석 결과는 나노결정 화합물의 층상구조가 전기화학적 충방전 과정 동안 안정하다는 사실을 보여주며, 이와는 대조적으로 좋은 결정성을 갖는 층상구조 화합물의 경우 현저한 구조변화를 겪는다는 사실을 보여준다. 마이크로 라만 분광 결과는 이러한 구조전이가 층상 구조로부터 스핀넬 타입 구조로의 변화에 해당함을 보여준다. 위 실험 결과로부터 나노결정성이 층상구조의 안정도를 향상시킨다는 결론을 얻을 수 있었다.

• 한국전산구조공학회논문집
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• 제34권5호
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• pp.287-292
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• 2021

본 논문에서는 CAD 시스템에서 사용하는 NURBS 기저함수를 사용하는 아이소-지오메트릭 해석(Isogeometric analysis) 방법과 기하학적으로 엄밀한 빔 모델링(geometrically exact beam model)을 활용하여 회전과 병진 운동이 결합된 새로운 형태의 메타물질(metamaterial)에 대한 해석을 진행하였다. 이차원 셀 구조는 자유형상변환(Free-form deformation) 법과 적절한 내삽법(Interpolation)을 통해 원통 위에 입혀졌다. 원통의 치수와 셀 개수가 비틀림 각도에 미치는 영향이 매개변수 연구(parametric study)를 통해 확인되었다. 비틀림과 병진 운동이 결합된 구조의 메커니즘에 대해 수치 예제를 통해 알아보았다.