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구속된 고강도 콘크리트 기둥의 휨 거동에 관한 실험적 연구
양근혁,이영호,곽노현,정헌수 중앙대학교 기술과학연구소 1998 기술과학연구소 논문집 Vol.28 No.-
본 실험적 연구의 목적은 콘크리트 강도, 띠근 배근형태, 띠근 량, 축하중비가 축하증과 횡하증을 받는 구속된 콘크리트 기둥의 휨 내력과 연성에 미치는 영향을 팡가하기 위한 것이다. 구속된 기둥의 휨 거동을 시험하기 위하여 200×200×800mm 크기의 시험체 14개를 2축 하중하에서 실험하였다. 시험결과로서, 저축력에서 콘크리트 구속으로 인한 휨 강도의 증가는 비교적 작게 있지만, 고축력에서 콘크리트 구속으로 인한 휨 강도 증가는 크게 있다. 그리고, 고축력, 고강도 콘크리트에서 내부 cross-ties가 있으면 휨 연성의 증가가 보였으며, 구속된 콘크리트 기둥의 연성은 단순한 띠근 량보다는 구속지수에 관계되었다. The purpose of this experimental study was to investigate the effects of concrete strength, the configuration of lateral ties, the amount of lateral ties, and level of axial loads on flexural strength and ductility of confined of reinforced concrete columns subjected to combined axial and lateral loads. To simulate the flexural behavior of confined columns, fourteen reinforced concrete columns, 200×200×800mm, were tested under bi-axial loads. Test results indicate that for low axial load levels, the enhancement of the flexural strength due to concrete confinement is relatively small, but that for high axial load levels, the enhancement of the flexural strength due to concrete confinement can be very high. Considerable enhancement of ductility was observed in columns confined by cross-ties, even for high strength concrete columns and under high axial loads. Ductility of confined columns are found to be more related to confinement index (ρ??f??/??) than the amount of lateral ties(ρ??)
RGB 성분을 갖는 24비트 이미지의 무손실 압축 기법
박노혁(No-Hyeok Park),진서현(Suh-Hyun Cheon) 한국정보과학회 1996 한국정보과학회 학술발표논문집 Vol.23 No.1A
무손실 JPEG 압축 표준은 RGB성분을 갖는 24비트 칼라 이미지를 압축할 때 RGB 이미지를 YUV 이미지로 변환하는 과정에서 손실이 발생하고, 7개의 예측 선택값중에서 사용자가 하나를 지정하여 사용해야 하며, RGB 성분간의 중복성을 고려하지 않는다는 문제점을 가지고 있다. 본 논문에서는 RGB 이미지를 그대로 사용하여 YUV 이미지로의 변환에 의한 손실을 방지하고, 예측 선택값의 적응 선택으로 예측 선택값 선택의 어려움을 제거하였으며 기준 성분을 선택하여 RGB 성분간의 중복성을 제거함으로써 압축 효율을 증대시킬 수 있는 압축 기법을 제시하고 있다. 제안한 방법으로 JPEG 표준 테스트 이미지와 이미지프로세싱에 많이 사용되는 24비트 RGB 이미지로 실험한 결과 표준 방법보다 평균 7 - 12%의 향상을 보였다.
명노훈(No Hoon Myoung),이억섭(Ouk Sub Lee),김동혁(Dong Hyeok Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
The thermal stresses induced by difference in Coefficient of Thermal Expansion between FR-4 board and 63Sn-37Pb solder joint directly affect the reliability of 63Sn-37Pb solder joint. This research, thus, focuses to investigate the change resistance and crack propagation behavior around solder joint by imposing a designed Acceleration Life Test Procedure on solder joint by using a newly manufactured Thermal Impact Experimental Apparatus. The fracture mechanism of the solder joint was found to be highly influenced by thermal stresses. The reliability of solder joint was evaluated by using a weibull distribution.
Ball Grid Array 63Sn-37Pb Solder joint 의 건전성 평가
명노훈(No-Hoon Myoung),이억섭(Ouk Sub Lee),김동혁(Dong-Hyeok Kim) 한국정밀공학회 2004 한국정밀공학회 학술발표대회 논문집 Vol.2004 No.10월
Generally, component and FR-4 board are connected by solder joint. Because material properties of components and FR-4 board are different, component and FR-4 board show different coefficients of thermal expansion (CTE) and thus strains in component and board are different when they are heated. That is, the differences in CTE of component and FR-4 board cause the dissimilarity in shear strain and BGA solder joint’s failure. The first order Taylor series expansion of the limit state function incorporating with thermal fatigue models is used in order to estimate the failure probability of solder joints under heated condition. A model based on plastic-strain rate such as the Coffin-Manson Fatigue Model is utilized in this study. The effects of random variables such as frequency, maximum temperature, and temperature variations on the failure probability of the BGA solder joint are systematically investigated by using a failure probability model with the first order reliability method(FORM).
명노훈(No-Hoon Myoung),이억섭(Ouk-Sub Lee),김동혁(Dong-Hyeok Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
Generally, component and FR-4 board are connected by solder joint. Because material properties of components and FR-4 board are different, component and FR-4 board show different coefficients of thermal expansion (CTE) and thus strains in component and board are different when they are heated. That is, the differences in CTE of component and FR-4 board cause the dissimilarity in shear strain and solder joint’s failure. The first order Taylor series expansion of the limit state function incorporating with Tresca failure criterion is used in order to estimate the failure probability of solder joints under heated condition. Using shear stresses and shear strains appeared on the solder joint, we estimate the failure probability of solder joints with the Tresca failure criterion. The effects of random variables such as CTE, distance of the solder joint from the neutral point(DNP), temperature variation and height of solder on the failure probability of the solder joint are systematically studied by using the failure probability model with first order reliability method(FORM).
Multi-Layer SnSe Nanoflake Field-Effect Transistors with Low-Resistance Au Ohmic Contacts
Cho, Sang-Hyeok,Cho, Kwanghee,Park, No-Won,Park, Soonyong,Koh, Jung-Hyuk,Lee, Sang-Kwon SPRINGER SCIENCE + BUSINESS MEDIA 2017 NANOSCALE RESEARCH LETTERS Vol.12 No.1
<P>We report p-type tin monoselenide (SnSe) single crystals, grown in double-sealed quartz ampoules using a modified Bridgman technique at 920 °C. X-ray powder diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) measurements clearly confirm that the grown SnSe consists of single-crystal SnSe. Electrical transport of multi-layer SnSe nanoflakes, which were prepared by exfoliation from bulk single crystals, was conducted using back-gated field-effect transistor (FET) structures with Au and Ti contacts on SiO<SUB>2</SUB>/Si substrates, revealing that multi-layer SnSe nanoflakes exhibit p-type semiconductor characteristics owing to the Sn vacancies on the surfaces of SnSe nanoflakes. In addition, a strong carrier screening effect was observed in 70−90-nm-thick SnSe nanoflake FETs. Furthermore, the effect of the metal contacts to multi-layer SnSe nanoflake-based FETs is also discussed with two different metals, such as Ti/Au and Au contacts.</P>