• 한국진공학회지
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• 제8권1호
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• pp.36-42
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• 1999

이온빔 스퍼터링 방법으로 n-type si 기판에 고팅된, 수소를 함유하지 않은 다이아몬드성 카본 필름의 전계 방출 특성을 조사하였다. 필름의 구조나 두께에 관계없이 전계 방출 전류는 양극과 시편의 표면사이에서 발생하는 electrical breakdown에 의해 현저히 증가하였으며, 이때의 effective work function은 약 0.1eV의 작은 값을 가지고 있었다. 텅스텐 tip을 이용하여 breakdown에 의해 발생한 시편표면의 손상수위 근처를 scanning 하면서 전계 방출 전류를 측정하여, 전계 방출이 일어나는 정확한 위치를 확인하였다. 전계 방출은 breakdown에 의해 발생한 표면 손상 부위의 모든 곳에서 균일하게 일어나는 것이 아니라 특정 부위에서 집중적으로 관찰되었다. Auger electron spectroscopy와 SEM을 이용한 분석을 통해 손상 부위 중 Si과 C의 화합물이 형성된 곳에서만 절계 방출이 일어나고 있음을 알 수 있었으며, 손상부위의 형상변화는 전계 방출의 충분조건이 아니었다. 본 연구의 결과는 breakdown에 의한 전기 방출 전류의 증가는 시편 표면의 형상 변화에 의한 전계증진의 효과보다는 표면에서 발생하는 화학적 결합의 변화에 기인하고 있음을 보여준다.

• 한국근적외분광분석학회:학술대회논문집
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• 한국근적외분광분석학회 2001년도 NIR-2001
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• pp.1182-1182
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• 2001

In this study, the newly constructed optical measurement system, which was mainly composed of a parametric tunable laser and a near infrared photoelectric multiplier, was introduced to clarify the optical characteristics of wood as discontinuous body with anisotropic cellular structure from the viewpoint of the time-of-flight near infrared spectroscopy (TOF-NIRS). The combined effects of the cellular structure of wood sample, the wavelength of the laser beam λ, and the detection position of transmitted light on the time resolved profiles were investigated in detail. The variation of the attenuance of peak maxima At, the time delay of peak maxima Δt and the variation of full width at half maximum Δw were strongly dependent on the feature of cellular structure of a sample and the wavelength of the laser beam. The substantial optical path length became about 30 to 35 times as long as sample thickness except the absorption band of water. Δt ${\times}$ Δw representing the light scattering condition increased exponentially with the sample thickness or the distance between the irradiation point and the end of sample. Around the λ=900-950 nm, there may be considerable light scattering in the lumen of tracheid, which is multiple specular reflection and easy to propagate along the length of wood fiber. Such tendency was remarkable for soft wood with the aggregate of thin layers of cell walls. When we apply TOF-NIRS to the cellular structural materials like wood, it is very important to give attention to the difference in the light scattering within cell wall and the multiple specular-like reflections between cell walls. We tried to express the characteristics of the time resolved profile on the basis of the optical parameters for light propagation determined by the previous studies, which were absorption coefficient K and scattering coefficient S from Kubelka-Munk theory and n from nth power cosine model of radiant intensity. The wavelength dependency of the product of K/S and n, which expressed the light-absorbing and -scattering condition and the degree of anisotropy, respectively, was similar to that of the time delay of peak maxima Δt. The variation of the time resolved profile is governed by the combination of these parameters. So, we can easily find the set of parameters for light propagation synthetically from Δt.

• EDISON SW 활용 경진대회 논문집
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• 제5회(2016년)
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• pp.167-174
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• 2016

Recently laminated plates like composite materials has been used in a various field to grow the specific strength of the composition. However, delamination area caused by barely visible impact damage has potential risk that it can raise buckling of the delaminated plate. Because it can interrupt compressive behavior of laminated plates and reduce their strength, the whole structure can't be constituted by these materials. Many studies assume that behavior of the delaminated plate which is in lamanated plates equals theoretical buckling but their actual motion doesn't coincide because of initial imperfections of materials like deflection, residual stress, eccentricity and so on. In this paper, we change laminated plates with initial delamination into a beam of rectangular cross section with the initial crack and analyze compressive behavior according to initial imperfections through finite element method(FEM). Consequently analysis results show that behavior of laminated plates involving delamination differs from ideal buckling of the delaminated plate in actual conditions and we can predict its motion through imperfections relationship.

• 한국정밀공학회지
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• 제17권8호
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• pp.172-179
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• 2000

In this paper a technology for the fabrication of the oblique structure using the LIGA process will be presented. The fabricated microstructure is a tetrahedral 3- facet mirror. The mirror has an equilateral triangular base of hundreds ${\mu}m$ length mirror-like three side-facets inclined to the base at 45$^{\circ}$ and knife edges. Two regular triangles of 45$^{\circ}$ and tan-12. After development the shaded part of the PMMA the tetrahedral mirror remains, The completed mirror shows excellent aspects of mirror-like facets and knife-edges. By controlling the gap between the mask and the substrate the size of mirror easily can be changed. This mirror would be used as a laser beam splitter for the feedback control of the HDD slider.

• 한국강구조학회 논문집
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• 제13권4호
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• pp.419-431
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• 2001

본 연구에서는 단부 RC 중앙보 S조 혼합보에 대해 RC부 주근의 정착방법(플랜지 위에 직접 용접, 스터드 볼트 용접 정착) 과 이질구조부 (SRC 부)의 보강 방법에 따른 구조적 거동 분석을 고찰하였다. 이질구조부 보강방법으로는 무보강, 수직전단보강근 보강[D10-@50], 경사보강(X자형 보강), 수평보강1[웨브보강(0.3L)], 수평보강2[웨브보강(0.3L)], 수직보강[플랜지보강(0.3L)]과 같은 보강방법을 주요변수로 하여 구조적 특성을 상호 비교 분석하였다. 그 결과 보 주근의 정착방법에 따른 연성능력 및 내력 등과 같은 구조적 특성에는 큰 차이가 없었으며, 혼합구조보의 구조적 특성을 극대화시키기 위해서는 이질구조부를 수직보강한 경우와 2열 수평으로 보강한 방법이 가장 효과적인 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제52권2호
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• pp.307-322
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• 2014

A two-step procedure to detect and quantify damages in structures from changes in curvature mode shapes is presented here. In the first step the maximum difference in curvature mode shapes of the undamaged and damaged structure are used for visual identification of the damaged internal-substructure. In the next step, the identified substructures are searched using unified particle swarm optimization technique for exact identification of damage location and amount. Efficiency of the developed procedure is demonstrated using beam like structures. This methodology may be extended for identifying damages in general frame structures.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 제5회 학술대회 논문집 일렉트렛트 및 응용기술연구회
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• pp.45-48
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• 2003

BiSrCaCuO thin films were fabricated by atomic layer-by-layer deposition using an ion beam sputtering method. 10 wt% and 90 wt% ozone mixed with oxygen were used with ultraviolet light irradiation to assist oxidation. At early stages of the atomic layer by layer deposition, two dimensional epitaxial growth which covers the substrate surface would be suppressed by the stress and strain caused by the lattice misfit, then three dimensional growth takes place. Since Cu element is the most difficult to oxidize, only Sr and Bi react with each other predominantly, and forms a buffer layer on the substrate in an amorphous-like structure, which is changed to $SrBi_2O_4$ by in-situ anneal.

• International Journal of Aeronautical and Space Sciences
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• 제13권3호
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• pp.323-331
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• 2012

A simple and robust methodology is presented to determine the location and amount of crack in beam like structures based on the incremental particle swarm optimization technique. A comparison is made for assessing the performance of standard particle swarm optimization and the incremental particle swarm optimization technique for detecting crack in structural members. The objective function is formulated using the measured natural frequency of the intact structure and the frequency obtained from the finite element simulation. The outcomes of the simulated results demonstrate that the developed method is capable of detecting and estimating the extent of damages with satisfactory precision.

• International Journal of Aeronautical and Space Sciences
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• 제13권2호
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• pp.199-209
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• 2012

An advanced aeroelastic formulation for flutter analyses is presented in this paper. Refined 1D structural models were coupled with the doublet lattice method, and the g-method was used for flutter analyses. Structural models were developed in the framework of the Carrera Unified Formulation (CUF). Higher-order 1D structural models were obtained by using Taylor-like expansions of the cross-section displacement field of the structure. The order (N) of the expansion was considered as a free parameter since it can be arbitrarily chosen as an input of the analysis. Convergence studies on the order of the structural model can be straightforwardly conducted in order to establish the proper 1D structural model for a given problem. Flutter analyses were conducted on several wing configurations and the results were compared to those from literature. Results show the enhanced capabilities of CUF 1D in dealing with the flutter analysis of typical wing structures with high accuracy and low computational costs.

• 한국산업융합학회 논문집
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• 제11권2호
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• pp.93-98
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• 2008

Steel fibre reinforced concrete (SFRC) were considered a new technology for the construction industry. However today this technology has found wider acceptance among the construction industry. Currently, steel fibres are used in varied segments in many application areas across different segments in the construction industry, especially in tunneling, airports, warehouses, etc. Time and safety are the main factors are among the various advantages which renders steel fibres superior to the competing product. For fibers reinforcing, The maximum load carrying capacity is controlled by fibers pulling out of the composite because fiber reinforcing does not have a deformed surface like larger steel reinforcing bars. The study demonstrated that above concept is applicable and effective in concrete structure by analytical study. The analytical result appears that SFRP have the potential to significantly increase the strength of existing concrete structures, while at the same time dramatically improving their fracture energy characteristics.