• Steel and Composite Structures
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• 제26권4호
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• pp.513-531
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• 2018

In this article, static, buckling and free vibration analyses of a sinusoidal micro composite beam reinforced by single-walled carbon nanotubes (SWCNTs) with considering temperature-dependent material properties embedded in an elastic medium in the presence of magnetic field under transverse uniform load are presented. This system is used at micro or sub micro scales to enhance the stiffness of micro composite structures such as bar, beam, plate and shell. In the present work, the size dependent effects based on surface stress effect and modified strain gradient theory (MSGT) are considered. The generalized rule of mixture is employed to predict temperature-dependent mechanical and thermal properties of micro composite beam. Then, the governing equations of motions are derived using Hamilton's principle and energy method. Numerical results are presented to investigate the influences of material length scale parameters, elastic foundation, composite fiber angle, magnetic intensity, temperature changes and carbon nanotubes volume fraction on the bending, buckling and free vibration behaviors of micro composite beam. There is a good agreement between the obtained results by this research and the literature results. The obtained results of this study demonstrate that the magnetic intensity, temperature changes, and two parameters elastic foundations have important effects on micro composite stiffness, while the magnetic field has greater effects on the bending, buckling and free vibration responses of micro composite beams. Moreover, it is shown that the effects of surface layers are important, and observed that the changes of carbon nanotubes volume fraction, beam length-to-thickness ratio and material length scale parameter have noticeable effects on the maximum deflection, critical buckling load and natural frequencies of micro composite beams.

• Geomechanics and Engineering
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• 제13권5호
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• pp.861-879
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• 2017

Coal and gas outburst is a serious dynamic disaster that occurs during coal mining and threatens the lives of coal miners. Currently, coal and gas outburst is commonly predicted using single indicator and its critical value. However, single indicator is unable to fully reflect all of the factors impacting outburst risk and has poor prediction accuracy. Therefore, a more accurate prediction method is necessary. In this work, we first analyzed on-site impacting factors and precursors of coal and gas outburst; then, we constructed a Fisher discriminant analysis (FDA) index system using the gas adsorption index of drilling cutting ${\Delta}h_2$, the drilling cutting weight S, the initial velocity of gas emission from borehole q, the thickness of soft coal h, and the maximum ratio of post-blasting gas emission peak to pre-blasting gas emission $B_{max}$; finally, we studied an FDA-based multiple indicators discriminant model of coal and gas outburst, and applied the discriminant model to predict coal and gas outburst. The results showed that the discriminant model has 100% prediction accuracy, even when some conventional indexes are lower than the warning criteria. The FDA method has a broad application prospects in coal and gas outburst prediction.

• Earthquakes and Structures
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• 제26권3호
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• pp.203-218
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• 2024

Beam-column joints in the frame structure are at high risk of brittle shear failure which would lead to significant residual deformation and even the collapse of the structure during an earthquake. In order to improve the damage issue and enhance the recoverability of the beam-column joints, a sector lead rubber damper (SLRD) has been developed. The SLRD can increase the bearing capacity and energy dissipation capacity, and also demonstrating recoverability of seismic performance following cyclic loading. In this paper, the hysteretic behavior of SLRD was experimentally investigated in terms of the regular hysteretic behavior, large deformation behavior and fatigue behavior. Furthermore, a parametric analysis was performed to study the influence of the primary design parameters on the hysteretic behavior of SLRD. The results show that SLRD resist the exerted loading through the shear capacity of both rubber parts coupled with the lead cores in the pre-yielding stage of lead cores. In the post-yielding phase, it is only the rubber parts of the SLRD that provide the shear capacity while the lead cores primarily dissipate the energy through shear deformation. The SLRD possesses a robust capacity for large deformation and can sustain hysteretic behavior when subjected to a loading rotation angle of 1/7 (equivalent to 200% shear strain of the rubber component). Furthermore, it demonstrates excellent fatigue resistance, with a degradation of critical behavior indices by no more than 15% in comparison to initial values even after 30 cycles. As for the designing practice of SLRD, it is recommended to adopt the double lead core scheme, along with a rubber material having the lowest possible shear modulus while meeting the desired bearing capacity and a thickness ratio of 0.4 to 0.5 for the thin steel plate.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.104-104
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• 2009

Critical dimensions has rapidly shrunk to increase the degree of integration and to reduce the power consumption. However, it is accompanied with several problems like direct tunneling through the gate insulator layer and the low conductivity characteristic of poly-silicon. To cover these faults, the study of new materials is urgently needed. Recently, high dielectric materials like $Al_2O_3$, $ZrO_2$ and $HfO_2$ are being studied for equivalent oxide thickness (EOT). However, poly-silicon gate is not compatible with high-k materials for gate-insulator. To integrate high-k gate dielectric materials in nano-scale devices, metal gate electrodes are expected to be used in the future. Currently, metal gate electrode materials like TiN, TaN, and WN are being widely studied for next-generation nano-scale devices. The TaN gate electrode for metal/high-k gate stack is compatible with high-k materials. According to this trend, the study about dry etching technology of the TaN film is needed. In this study, we investigated the etch mechanism of the TaN thin film in an inductively coupled plasma (ICP) system with $O_2/BCl_3/Ar$ gas chemistry. The etch rates and selectivities of TaN thin films were investigated in terms of the gas mixing ratio, the RF power, the DC-bias voltage, and the process pressure. The characteristics of the plasma were estimated using optical emission spectroscopy (OES). The surface reactions after etching were investigated using X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES).

• Geomechanics and Engineering
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• 제34권5호
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• pp.491-505
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• 2023

The practical usage of underground space and demand for vehicular tunnels necessitate the construction of non-circular wide rectangular tunnels. However, constructing large tunnels in soft clayey soil conditions with no ground improvement can lead to excessive ground deformations and collapse. In recent years, in situ ground improvement techniques such as jet grouting and deep cement mixing are often utilized to perform cement-stabilisation around the tunnel boundary to prevent large deformations and failure. This paper discusses the stability characteristics and failure behaviour of a wide rectangular tunnel in cement-treated soft clays. First, the plane strain finite element model is developed and validated with the results of centrifuge model tests available in the past literature. The critical tunnel support pressures computed from the numerical study are found to be in good agreement with those of centrifuge model tests. The influence of varying strength and thickness of improved soil surround, and cover depth are studied on the stability and failure modes of a rectangular tunnel. It is observed that the failure behaviour of the tunnel in improved soil surround depends on the ratio of the strength of improved soil surround to the strength of surrounding soil, i.e., q_ui/q_us, rather than just q_ui. For low q_ui/q_us ratios,the stability increases with the cover; however, for the high strength improved soil surrounds with q_ui >> q_us, the stability decreases with the cover. The failure chart, modified stability equation, and stability chart are also proposed as preliminary design guidelines for constructing rectangular tunnels in the improved soil surrounded by soft clays.

• 한국초전도ㆍ저온공학회논문지
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• 제15권4호
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• pp.15-20
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• 2013

We investigated the flux pinning properties of both 10 mol% Zr-and Sn-doped $YBa_2Cu_3O_{7-{\delta}}$ (YBCO) films with the same thickness of ~350 nm for a comparative purpose. The films were prepared on the $SrTiO_3$ (STO) single crystal substrate by the metal-organic deposition (MOD) process. Compared with Sn-doped YBCO film, Zr-doped one exhibited a significant enhancement in the critical current density ($J_c$) and pinning force density ($F_p$). The anisotropic $J_{c,min}/J_{c,max}$ ratio in the field-angle dependence of $J_c$ at 77 K for 1 T was also improved from 0.23 for Sn-doped YBCO to 0.39 for Zr-doped YBCO. Thus, the highest magnetic $J_c$ values of 9.0 and $2.9MA/cm^2$ with the maximum $F_p$ ($F_{p,max}$) values of 19 and $5GN/m^3$ at 65 and 77 K for H // c, respectively, could be achieved from Zr-doped YBCO film. The stronger pinning effect in Zr-doped YBCO film is attributable to smaller $BaZrO_3$ (BZO) nanoparticles (the average size ${\approx}28.4$ nm) than $YBa_2SnO_{5.5}$ (YBSO) nanoparticles (the average size ${\approx}45.0$ nm) incorporated in Sn-doped YBCO film since smaller nanoparticles can generate more defects acting as effective flux pinning sites due to larger incoherent interfacial area for the same doping concentration.

• 센서학회지
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• 제13권2호
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• pp.101-109
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• 2004

This paper presents a novel z-axis accelerometer with perfectly aligned vertical combs fabricated using the extended sacrificial bulk micromachining (extended SBM) process. The z-axis accelerometer is fabricated using only one (111) SOI wafer and two photo masks without wafer bonding or CMP processes as used by other research efforts that involve vertical combs. In our process, there is no misalignment in lateral gap between the upper and lower comb electrodes, because all critical dimensions including lateral gaps are defined using only one mask. The fabricated accelerometer has the structure thickness of $30{\mu}m$, the vertical offset of $12{\mu}m$, and lateral gap between electrodes of $4{\mu}m$. Torsional springs and asymmetric proof mass produce a vertical displacement when an external z-axis acceleration is applied, and capacitance change due to the vertical displacement of the comb is detected by charge-to-voltage converter. The signal-to-noise ratio of the modulated and demodulated output signal is 80 dB and 76.5 dB, respectively. The noise equivalent input acceleration resolution of the modulated and demodulated output signal is calculated to be $500{\mu}g$ and $748{\mu}g$. The scale factor and linearity of the accelerometer are measured to be 1.1 mV/g and 1.18% FSO, respectively.

• 한국작물학회지
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• 제36권4호
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• pp.319-323
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• 1991

벼의 도복에 관련하는 형질들의 포장도복과의 관련정도를 밝혀 벼의 이도복성육종의 기초자료를 제공코져 1900년대에서 1980년대에 재배 또는 육성된 10품종을 재배하여 실험한 결과를 요약하면 다음과 같다. 1 포장도복정도와 관련정도가 높은 형질들은 간장, 단위간하중(W/l), 단위 직경휨모멘트(W1/d), 도복지수(L), 하중비(W1/P), 임계도 복하중지수 (Ws$^2$/l$^4$)등 이었다. 2. 간장은 포장도복과 높은 상관(r=0.7607)을 보이나 간장만으로 품종의 도복정도를 판정하기는 미흡하였다 3. 측정의 난역도와 소모되는 시간을 고찰해 볼 때 도복저항성을 판정하는데 유용할 형질들은 간장, W/l, W1/d, Ws$^2$/l$^4$이었다. 4. 간경, 줄기단면적, 간벽의 두께, 줄기단면의 2차 관성 모멘트는 포장도복과 아무런 상관관계를 보이지 않았다. 5. 좌절강도(S)는 포장도복과 유의한 부의 상관 (r=-0.3986)을 보였다.

• 한국항공우주학회지
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• 제44권8호
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• pp.649-656
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• 2016

두꺼운 복합재료 회전원판은 경량화와 고속화가 요구되는 터빈 디스크, 플라이휠 등에 다양한 기계요소도 활용되고 있다. 본 연구에서는 회전속도가 두꺼운 복합재료 원판의 동적특성에 미치는 영향을 살펴보았다. 이를 위해 두꺼운 복합재료 회전원판의 동적 운동방정식을 유도하고 유한요소 정식화를 수행하였다. 등방성 원판, 원주강화 복합재료 원판, 그리고 반경강화 복합재료 원판에 대한 수치해석을 수행하였다. 횡전단변형과 회전관성의 고려는 원판이 회전할 때에도 고유진동수를 감소시킬 뿐만 아니라 임계속도를 낮추는 역할을 한다. 원판의 회전속도가 증가함에 따라 횡전단변형과 회전관성 효과가 감소한다는 이전의 연구결과와는 달리 탄성계수의 이방성, 두께비, 모우드에 따라 그 효과가 감소 또는 증가할 수 있는 것으로 나타났다.

• 한국정보과학회논문지:소프트웨어및응용
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• 제31권7호
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• pp.911-921
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• 2004

지문영상으로부터 특징점을 정확하게 추출하는 것은 효과적인 지문인식 시스템의 구축에 매우 중요하다. 하지만 지문영상의 품질에 따라 특징점 추출의 정확도가 달라지기 때문에 지문인식 시스템에서의 영상 전처리 과정은 시스템의 성능에 크게 영향을 미친다. 본 논문에서는 지문영상으로부터 명암값의 평균 및 분산, 블록 방향성 차, 방향성 변화도, 융선과 골의 두께 비율 등의 5가지 특징을 추출하고 계층적 클러스터링 알고리즘으로 클러스터링하여 영상의 품질 특성을 분석한 후 습성(oily), 보통(neutral), 건성(dry)의 특성에 적합하게 영상을 개선하는 지식기반 전처리 방법을 제안한다. NIST DB 4와 인하대학교 데이타를 이용하여 실험한 결과, 클러스터링 기법이 영상의 특성을 제대로 구분함을 확인할 수 있었다. 또한 제안한 방법의 성능 평가를 위해 품질 지수와 블록 방향성 차이를 측정하여 일반적인 전처리 방법보다 지식기반 전처리 방법이 품질 지수와 블록 방향성 차이를 향상시킴을 확인할 수 있었다.