• 에너지공학
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• 제10권3호
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• pp.278-285
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• 2001

본 연구에서는 경수로 사용후핵연료를 모사하는 모의 핵연료 제조 공정 중 소결체 특성에 미치는 변수들의 영향에 관하여 기술하였다. 주로 성형압, 소결 온도 및 시간이 소결체의 밀도에 미치는 영향에 관하여 분석하였다. 성형압은 1 ton/$\textrm{cm}^2$에서 4ton/$\textrm{cm}^2$, 소결 온도는 167$0^{\circ}C$, 173$0^{\circ}C$, 178$0^{\circ}C$, 소결 시간은 4시간, 8시간, 24시간으로 변화시키면서 실험을 수행하였다. 성형밀도는 성형압의 1/3승에 비례하며, 이론 밀도의 약 90.5%에서 99.6%까지의 소결 밀도를 갖는 모의 핵연료를 제조하였다. 결정립 성장지수와 활성화에너지는 각각 2.5와 287.97kJ/mo1 이었다.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1081-1090
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• 2019

Detailed pulse shape analysis of a Geiger-$M{\ddot{u}}ller$ counter is performed to understand the pulse shape dependence on operating voltage. New data is presented to demonstrate that not all pulses generated in a GM counter are identical. In fact, there is a strong correlation between the operating voltage and the pulse shape. Similar to detector deadtime, pulse shapes fall in three distinct regions. For low voltage region, where deadtime was reported to reduce with increasing voltage, pulse generated in this region was observed to have a fixed pulse width with a variable tail. The pulse width and fall time of the tail was observed to be a function of applied voltage; exponentially reducing with increasing voltage with an exponent of negative 6E-04 and 2E-03 respectively. The second region showed a pulse without any significant tail. During this time the detector deadtime was earlier reported to be at its minimum. The highest voltage region demonstrated a different deadtime mechanism where the second pulse was reduced in width. During this time the deadtime seemed to be increasing with increasing voltage. This data allows us to gain some unique insight into the phenomenon of GM detector deadtime not reported thus far.

• Structural Engineering and Mechanics
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• 제70권1호
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• pp.55-66
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• 2019

This work deals with the size-dependent wave propagation analysis of functionally graded (FG) anisotropic nanoplates based on a nonlocal strain gradient refined plate model. The present model incorporates two scale coefficients to examine wave dispersion relations more accurately. Material properties of FG anisotropic nanoplates are exponentially varying in the z-direction. In order to solve the governing equations for bulk waves, an analytical method is performed and wave frequencies and phase velocities are obtained as a function of wave number. The influences of several important parameters such as material graduation exponent, geometry, Winkler-Pasternak foundation parameters and wave number on the wave propagation of FG anisotropic nanoplates resting on the elastic foundation are investigated and discussed in detail. It is concluded that these parameters play significant roles on the wave propagation behavior of the nanoplates. From the best knowledge of authors, it is the first time that FG nanoplate made of anisotropic materials is investigated, so, presented numerical results can serve as benchmarks for future analysis of such structures.

• Steel and Composite Structures
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• 제43권1호
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• pp.117-127
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• 2022

This study investigates the wave propagation in porous functionally graded (FG) sandwich plates subjected to hygrothermal environments. A new simple three-unknown first-ordershear deformation theory (FSDT) incorporating an integral term is utilized in this paper. Only three unknowns are used to formulate the governing differential equation by applying the Hamilton principle. The FG layer of the sandwich plate is modeled using the power-law function with evenly distributed porosities to represent the defects of the manufacturing process. The plate is subjected to nonlinear hygrothermal changes across the thickness. The effects of the power-law exponent, core to thickness ratios, porosity volume, and the relations between volume fraction and wave properties of porous FG plate under the hygrothermal environment are investigated. The results showed that the waves' phase velocities increase linearly with the waves number in the FGM plate. The porosity of the FG materials plate has a noticeable impact on the phase velocity when considering the high ratios of the core layer. It has a negligible effect on small core layers. Finally, it is observed that changing temperatures and moistures do not influence the relationship between the power law and the phase velocity.

• Advances in materials Research
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• 제5권4호
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• pp.279-298
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• 2016

Present disquisition proposes an analytical solution method for exploring the buckling characteristics of porous magneto-electro-elastic functionally graded (MEE-FG) plates with various boundary conditions for the first time. Magneto electro mechanical properties of FGM plate are supposed to change through the thickness direction of plate. The rule of power-law is modified to consider influence of porosity according to two types of distribution namely even and uneven. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. The variation of pores along the thickness direction influences the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM plate under magneto-electrical field via Hamilton's principle. An analytical solution procedure is exploited to achieve the non-dimensional buckling load of porous FG plate exposed to magneto-electrical field with various boundary condition. A parametric study is led to assess the efficacy of material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage, boundary conditions, aspect ratio and side-to-thickness ratio on the non-dimensional buckling load of the plate made of magneto electro elastic FG materials with porosities. It is concluded that these parameters play remarkable roles on the dynamic behavior of porous MEE-FG plates. The results for simpler states are confirmed with known data in the literature. Presented numerical results can serve as benchmarks for future analyses of MEE-FG plates with porosity phases.

• 융합신호처리학회논문지
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• 제8권3호
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• pp.143-148
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• 2007

영상처리에 있어서 갑작스러운 신호와 불확실한 시스템의 특징을 정확하게 표현하기 위하여 많은 연구가 수행되어 왔다. 많이 알려진 퓨리어 변환은 임의 신호의 주파수 해석에 폭넓게 사용되어 왔다. 그러나 이 방법은 시간 축에서 발생하는 갑작스러운 신호 변환과 비정상적인 신호를 주파수 변환 영역에서 나타낼 수 없으므로 유용하지 않다. 본 논문은 이산 웨이브렛을 이용한 영상해석을 하였다. 이는 웨이브렛 영역에서의 극대치는 Lipschitz 지수 표현이 가능하고, 또한 극대치만 사용하여 영상 데이터의 윤곽선 및 데이터 특성을 표현하는 유용함을 나타내었다. 더욱이 적은 극대치만을 사용하여 본래 영상을 재생하는 것도 가능하게 되었다. fractal 해석은 예로서 적용되었다. 그리고, 모형 배에서 기름 띠의 가시화 영상이 해석되었다. 극대치 해석으로 fractal 변수를 구하고, 가시화 영상 해석의 실험으로 양호한 결과를 얻었다.

• 한국전자파학회논문지
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• 제11권1호
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• pp.124-135
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• 2000

본 논문에서는 공간영역 closed -form 그런함수를 사용하여 마이크로스트립 구조를 효율적으로 수치해석할 수 있는 방법을 고려해 보고자 한다, 모벤트법을 가용하여 임피던스 행렬의 요소를 구할 때 closed -form 그린함수 를 사용하여 그 계산시간을 현저히 줄일 수 있다는 것은 이미 잘 알려진 사실이다. 그러나 행렬의 대각요소를 구하는 과정에서 그 계산결과가 여전히 느리게 수렴한다는 문제점이 발견되었고, 그 이유는 closed -form 그런함 수에 포함되어 있는 복소지수의 작은 항때문인 것으로 사료된다. 따라서 대각요소 계산시 느린 수렴도의 문제점 을 해소하기 위해 좌표계 변환에 의한 수치적분기법을 고려해 보고자 한다. 본 논문에서 제시한 수치기법들의 타당성을 확인하기 위해 동축선 급전에 의한 마이크로스트립 안테나 산란문제의 해석에 적용하여 기존 논문의 결과와 비교해 볼 때 비교적 잘 일치함을 확인할 수 있었다.

• Advances in nano research
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• 제8권1호
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• pp.83-94
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• 2020

An analytical formulation and solution process for the buckling analysis of porous magneto-electro-elastic functionally graded (MEE-FG) beam via different thermal loadings and various boundary conditions is suggested in this paper. Magneto electro mechanical coupling properties of FGM beam are taken to vary via the thickness direction of beam. The rule of power-law is changed to consider inclusion of porosity according to even and uneven distribution. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. Change in pores along the thickness direction stimulates the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM beam under magneto-electrical field via Hamilton's principle. An analytical model procedure is adopted to achieve the non-dimensional buckling load of porous FG beam exposed to magneto-electrical field with various boundary conditions. In order to evaluate the influence of thermal loadings, material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage and boundary conditions on the critical buckling temperature of the beam made of magneto electro elastic FG materials with porosities a parametric study is presented. It is concluded that these parameters play remarkable roles on the buckling behavior of porous MEE-FG beam. The results for simpler states are proved for exactness with known data in the literature. The proposed numerical results can serve as benchmarks for future analyses of MEE-FG beam with porosity phases.

• Computers and Concrete
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• 제32권1호
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• pp.61-74
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• 2023

This article investigates the wave propagation analysis of the imperfect functionally graded (FG) sandwich plates based on a novel simple four-variable integral quasi-3D higher-order shear deformation theory (HSDT). The thickness stretching effect is considered in the transverse displacement component. The presented formulation ensures a parabolic variation of the transverse shear stresses with zero-stresses at the top and the bottom surfaces without requiring any shear correction factors. The studied sandwich plates can be used in several sectors as areas of aircraft, construction, naval/marine, aerospace and wind energy systems, the sandwich structure is composed from three layers (two FG face sheets and isotropic core). The material properties in the FG faces sheet are computed according to a modified power law function with considering the porosity which may appear during the manufacturing process in the form of micro-voids in the layer body. The Hamilton principle is utilized to determine the four governing differential equations for wave propagation in FG plates which is reduced in terms of computation time and cost compared to the other conventional quasi-3D models. An eigenvalue equation is formulated for the analytical solution using a generalized displacements' solution form for wave propagation. The effects of porosity, temperature, moisture concentration, core thickness, and the material exponent on the plates' dispersion relations are examined by considering the thickness stretching influence.

• 한국전기전자재료학회논문지
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• 제17권6호
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• pp.683-689
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• 2004

The microstructure and electrical characteristics of A ∼ C's ZnO varistors fabricated according to variable sintering condition, which sintering temperature was 1130 $^{\circ}C$ and speeds of pusher were A: 2 mm/min, B: 4 mm/min, C: 6 mm/min, respectively, were investigated. The experimental results obtained from this study were summarized as follows: The sintering density of A ∼C's ZnO varistors sintered at 1130 $^{\circ}C$ were decreased by sintering keep time to shorten, such as A: 9hour, B: 4.5hour and C: 3hour. A's ZnO varistor exhibited good densification nearly 98 % of theory density. In the microstructure, A∼C's ZnO varistors fabricated variable sintering condition was consisted of ZnO grain(ZnO), spinel phase(Z $n_{2.33}$S $b_{0.67}$ $O_4$), Bi-rich phasc(B $i_2$ $O_3$), wholly. Varistor voltage of A∼C's ZnO varistors sintered at 1130 $^{\circ}C$ increased in order A