• Journal of information and communication convergence engineering
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• 제9권6호
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• pp.725-728
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• 2011

Infrared transmission images from GaAs semi insulating wafers were considered for years as directly related to the quantum absorption by electrons on fundamental states of deep centers, especially EL2. The satisfying correspondence of these images with the dislocations revealed by etching or X ray topography or infrared tomography led to the opinion that a strong concentration of EL2 centers was to be expected in the immediate vicinity of the dislocations. More recent work indicates that contrary to the expected behavior the photoqu$\acute{e}$nching of transmission images at T=80K does not appreciably change the image structure itself but more largely the uniform background level of absorption. Such investigations show that the transmission images of isolated dislocations (Indium doped materials) or cell structures of tangled dislocations (undoped materials) can be partly attributed to scattered light; similar operation at T=10K removes the dark features associated to EL2 but still preserves the skeleton of the pattern which is due to scattering. A result of the measurements is that dislocations must not be considered any longer as inexhaustive EL2 reservoirs. The lifetime of the photoqu$\acute{e}$nching mechanism is shown to vary differently for EL2 centers located close to the dislocations or in the matrix. In this paper we will develop the details of infrared image photoqu$\acute{e}$nching experiments in the vicinity of dislocations; undoped and In doped GaAs materials will be shown. These results will be discussed in the light of surface etching experiments.

• Steel and Composite Structures
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• 제35권5호
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• pp.627-634
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• 2020

The past years were marked by an increase in the use of wood waste in civil and mechanical constructions. Date palm waste remains also one of the most solicited renewable and recyclable natural resources in the composition of composite materials. In Algeria, a great amount of this type of plant wastes accumulates every year. In order to make use of this waste, a new wood-epoxy composite material based on date palm petiole particleboard is developed. It makes use of date palm petiole particleboard as reinforcement and epoxy resin as matrix. The size of the particles reinforcement are between 1~3 mm and proportion of reinforcement used is 37%. In this work, experimental and numerical studies are conducted in order to characterize the wood fibre-epoxy plates. Firstly, experimental modal analysis test was carried out to determine Young's modulus of the elaborated material. Then, in order to validate the results, compression test was conducted. Furthermore, additional information about the shear modulus of this material is obtained by performing an experimental modal analysis to extract the first torsional mode. Moreover, a finite element model is developed using ANSYS software to simulate the vibration behaviour of the plates. The results show a good agreement with the experimental modal analysis, which confirms the values of Young's modulus and shear modulus.

• Steel and Composite Structures
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• 제35권5호
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• pp.671-685
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• 2020

This manuscript presents impacts of gradation of material functions and axial load functions on critical buckling loads and mode shapes of functionally graded (FG) thin and thick beams by using higher order shear deformation theory, for the first time. Volume fractions of metal and ceramic materials are assumed to be distributed through a beam thickness by both sigmoid law and symmetric power functions. Ceramic-metal-ceramic (CMC) and metal-ceramic-metal (MCM) symmetric distributions are proposed relative to mid-plane of the beam structure. The axial compressive load is depicted by constant, linear, and parabolic continuous functions through the axial direction. The equilibrium governing equations are derived by using Hamilton's principles. Numerical differential quadrature method (DQM) is developed to discretize the spatial domain and covert the governing variable coefficients differential equations and boundary conditions to system of algebraic equations. Algebraic equations are formed as a generalized matrix eigenvalue problem, that will be solved to get eigenvalues (buckling loads) and eigenvectors (mode shapes). The proposed model is verified with respectable published work. Numerical results depict influences of gradation function, gradation parameter, axial load function, slenderness ratio and boundary conditions on critical buckling loads and mode-shapes of FG beam structure. It is found that gradation types have different effects on the critical buckling. The proposed model can be effective in analysis and design of structure beam element subject to distributed axial compressive load, such as, spacecraft, nuclear structure, and naval structure.

• Structural Engineering and Mechanics
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• 제63권3호
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• pp.329-345
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• 2017

This paper devoted to study dynamic interaction between crack and inclusion or void by developing the eXtended Finite Element Methods (XFEM). A novel XFEM approximation is presented for these structures containing multi discontinuities (void, inclusion, and crack). The level set methods are used so that elements that include a crack segment, the boundary of a void, or the boundary of an inclusion are not required to conform to discontinuous edges. The investigation covers the effects of a single circular or elliptical void / stiff inclusion, and multi stiff inclusions on the crack propagation path under dynamic loads. Both the void and the inclusion have a significant effect on the dynamic crack propagation path. The crack initially curves towards into the void, then, the crack moves round the void and propagates away the void. If a large void lies in front of crack tip, the crack may propagate into the void. If an enough small void lies in front of crack tip, the void may have a slight or no influence on the crack propagation path. For a stiff inclusion, the crack initially propagates away the inclusion, then, after the crack moves round the inclusion, it starts to propagate along its original path. As ${\delta}$ (the ratio of the elastic modulus of the inclusion to that of the matrix) increases, a larger curvature of the crack path deflection can be observed. However, as ${\delta}$ increases from 2 to 10, the curvature has an evident increase. By comparison, the curvature has a slight increase, as ${\delta}$ increases from 10 to 1000.

• 한국산학기술학회논문지
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• 제16권7호
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• pp.4950-4959
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• 2015

공공시설물의 대형화 및 도심지로의 인구 밀집화에 따라 충돌 또는 폭발과 같은 하중조건 하에서의 구조물 방호성능의 중요성이 대두되고 있다. 그러나, 구조물의 방호설계 및 시공에 있어서 필수적이라 할 수 있는 구조재료 또는 자재에 대한 기술개발은 제대로 이루어지고 있지 않은 실정이다. 이에, 본 연구에서는 고성능 섬유보강 시멘트 복합재로의 기본적인 방호성능 및 방호용 자재로서의 적용 가능성을 파악하고자 40 mm 가스건을 사용한 충격 파괴시험을 수행하였다. 실험 수행 결과, 고성능 섬유보강 시멘트 복합재료에 있어서 시멘트 매트릭스의 강도 및 보강섬유가 방호성능 향상에 도움이 됨을 확인할 수 있었다.

• Steel and Composite Structures
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• 제29권3호
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• pp.405-422
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• 2018

In this research, experimental tensile test and manufacturing of carbon nanotube reinforced composite beam (CNTRC) is presented. Also, bending, buckling, and vibration analysis of CNTRC based on various beam theories such as Euler-Bernoulli, Timoshenko and Reddy beams are considered. At first, the experimental tensile tests are carried out for CNTRC and composite beams in order to obtain mechanical properties and then using Hamilton's principle the governing equations of motion are derived for Euler Bernoulli, Timoshenko and Reddy theories. The results have a good agreement with the obtained results by similar researches and it is shown that adding just two percent of carbon nanotubes increases dimensionless fundamental frequency and critical buckling load as well as decreases transverse deflection of composite beams. Also, the influences of different manufacturing processes such as hand layup and industrial methods using vacuum pump on composite properties are investigated. In these composite beams, glass fibers used in an epoxy matrix and for producing CNTRC, CNTs are applied as reinforcement particles. Applying two percent of CNTs leads to increase the mechanical properties and increases natural frequencies and critical buckling load and decreases deflection. The obtained natural frequencies and critical buckling load by theoretical method are higher than other methods, because there are some inevitable errors in industrial and hand layup method. Also, the minimum deflection occurs for theoretical methods, in bending analysis. In this study, Young's and shear modulli as well as density are obtained by experimental test and have not been used from the results of other researches. Then the theoretical analysis such as bending, buckling and vibration are considered by using the obtained mechanical properties of this research.

• 한국산학기술학회논문지
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• 제16권12호
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• pp.8654-8664
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• 2015

기계, 건축, 토목공학 분야 등에는 불균일 단면을 갖는 보 형태의 구조물들이 널리 사용되고 있다. 본 논문은 양단이 단순 지지된 보 구조물들의 동특성과 진동에 대한 문제를 다루며, 국부좌표를 사용한 지배방정식이 유도된다. 갤러킨의 모드합 방법으로 해가 가정되고, 고유진동수를 구하는 행렬식을 푸는 데는 이분법을 적용하였다. 유한요소법이 단지 기하학적 경계조건만을 만족시키는 허용함수를 사용하는 반면, 본 논문에서는 갤러킨의 모드합 방법을 적용하여, 지배방정식과 경계조건을 모두 만족하는 고유함수를 사용하였다. 계의 동특성을 알기위해, 네 종류의 불균일 단면을 갖는 단순 지지 보에 대해 모달 해석과 시험이 수행되었으며, 해석 결과는 실험 결과와 근사한 일치를 나타내었다.

• 대한화학회지
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• 제44권1호
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• pp.60-67
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• 2000

표면공명흡수는 매질의 유전상수값에 의존한다. 금 나노미립자가 함침된 $TiO_2/SiO_2$ 복합산화물 박막을 $Ti(OPr^i)_4$과 $Si(OEt)_4$, 그리고 $HAuCl_4{\cdot}7H_2O$를 사용하여 졸-겔 방법으로 제조하였다. $TiO_2/SiO_2$ 박막에 함침된 금 나노미립자의 최대 표면 공명 흡수는 $TiO_2/SiO_2$의 몰비에 따라 540 nm에서 615 nm 까지 선형적으로 변하였다. 이러한 박막에 함침된 금 나노미립자의 크기와 구조를 TEM과 XRD로 측정하였다. 그리고 $TiO_2/SiO_2$ 박막의 유전상수값을 실험 data로부터 이론적으로 계산하였다

• 대한두개안면성형외과학회지
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• 제11권2호
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• pp.107-110
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• 2010

Purpose: Chondroid syringoma is a rare mixed tumor of the skin that was first described by Hirsch and Helwig (1961). Characteristically, it is composed of the proliferation of epithelial cells in a myxoid and chondroid matrix. Most lesions occur on the head and neck region, and their size may range from 0.5~3 cm. Since a chondroid syringoma presents similar characteristics to other masses on the head and neck region, it is significantly important to distinguish with other masses by a surgical biopsy. Methods: A 51-year old woman presented with a painless nodular mass ($0.5{\times}0.5{\times}0.5cm$) on the philtrum, which appeared during the previous year. The mass was treated with a laser without a surgical biopsy. However, the size of the mass showed no changes. Surgical excision under local anesthesia was performed and sent for histopathology. Results: Gross examination showed a mass surrounded by a well developed capsule within the dermal layer. After complete excision without injury to the orbicularis oris muscle, the wound was covered with a local flap. The histology examination revealed numerous cuboid epithelial cells with tuboalveolar structures and keratinous cysts within a chondroid stroma. No recurrence or metastasis was observed at the follow-up visits. Conclusion: Chondroid syringoma is a rare mass on the face. An accurate diagnosis is essential for optimal treatment. This paper reports a case of a chondroid syringoma on the philtrum with a brief review of the relevant literature.

• 한국언어정보학회지:언어와정보
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• 제18권1호
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• pp.33-52
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• 2014

This paper proposes a unified structural account of some instances of the English Modals and Semi-auxiliaries. The classification and the syntactic/structural description of the English Modal auxiliary verbs and verb-related elements have long been the center for many proposals in the history of generative syntax. According to van Gelderen (1993) and Lightfoot (2002), it was sometime around 1380 that the Tense-node (T) appeared in the phrasal structures of the English language, and the T-node is under which the English Modal auxiliaries occupy. Closely related is the existing evidence that English Modals were used as main verbs up to the early sixteenth century (Lightfoot 1991, Han 2000). This paper argues for a bi-clausal approach to English Modal auxiliaries with the infinitival particle 'to' such as 'ought to' 'used to' and 'dare (to)' 'need (to)', etc. and Semi-auxiliaries including 'be to' and 'have to'. More specifically, 'ought' in 'ought to' constructions, for instance, undergoes V-to-T movement within the matrix clause, just like 'HAVEAux' and all instances of 'BE', whereas 'to' occupies the T position of the embedded complement clause. By proposing the bi-clausal account, Radford's (2004, 2009) problems can be solved. Further, the historical motivation for the account takes a stance along with Norde (2009) and Brinton & Traugott (2005) in that Radford's (2004, 2009) syncretization of the two positions of the infinitival particle 'to' is no different from the 'boundary loss' in the process of Grammariticalization. This line of argument supports Krug's (2011), and in turn Bolinger's(1980) generalization on Auxiliaryhood, while providing a novel insight into Head movement of V-to-T in Present Day English.