• 대한토목학회논문집
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• 제33권2호
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• pp.409-422
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• 2013

부재간의 연결조건에 따른 다양하고 복잡한 강구조물의 P-${\Delta}$ 해석 및 좌굴 거동특성을 파악하기 위하여, 본 연구에서는 부재의 연결이 회전 및 이동스프링으로 구성된 부분강절(semi-rigid) 뼈대요소의 일반화된 접선강도 행렬을 유도하였고 이로부터 다시 Taylor 전개를 적용하여 탄성강도 행렬과 기하학적 강도행렬을 일반화된 형태로 제시하였다. 이를 위하여, 보-기둥부재의 좌굴조건을 만족시키는 처짐함수로부터 안정함수(stability function)를 유도하였고, 횡변위(sway)를 고려한 힘-변위관계와 적합조건을 고려하여 엄밀한 부분강절 뼈대요소의 접선강도행렬을 제시하였다. 다양한 수치해석 예제에 대해 타 연구자의 해석 결과 및 본 연구의 선형 및 비선형 해석이론을 통한 좌굴해석 결과를 비교하여 본 연구의 타당성과 부분강절 뼈대구조물의 좌굴거동 특성을 제시하였다.

• 대한기계학회논문집B
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• 제41권4호
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• pp.285-291
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• 2017

본 연구에서는 무인 항공 장비에 장착되는 전자 장비에 상변화 물질을 적용한 방열 설계를 수치적으로 진행하였다. 상변화 물질에 대한 열특성 실험을 통해 용융점($T_m$), 용융시 온도 증분(${\Delta}T_m$) 및 체적 팽창을 확인하였으며, 이를 통해 해석 모델 검증을 진행하였다. 용융시 용융점에서 발생하는 온도 정체 현상을 모사하기 위해 등가 비열법으로 계산한 열 물성치를 상변화 물질의 해석 모델 물성치로 입력하였으며, 실험 결과와의 비교를 통해 해석 모델의 신뢰성을 검증하였다. 검증된 해석 모델을 통해 핀과 함께 상변화 물질이 충진된 장비 하우징의 방열 성능을 향상시키고, 이를 통해 장비의 열적 안정성을 확보하였다. 현재 상변화 물질이 충진된 하우징의 방열 성능 극대화를 위해 핀 최적 설계에 대한 추가적인 연구가 진행 중에 있다.

• 대한기계학회논문집
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• 제12권5호
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• pp.952-958
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• 1988

본 연구에서는 폭방향 불균일 냉각에 따른 열응력이 판변형 및 잔류응력의 주 요원인이라는 고려하에 냉각중에 압연판의 온도분포 및 열응력을 예측할 수 있는 수치 해석 모델을 구성하였다. 온도와 응력 계산에 상변태 현상을 고려하였으며, 판변형 은 압축성분 열응력에 의한 좌굴현상으로 고려하여 해석하였다.

• Ocean and Polar Research
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• 제41권2호
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• pp.89-97
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• 2019

Long chain plant waxes (n-alkanes, n-alkanoic acids, and n-alcohols) and their carbon isotopic compositions (${\delta}^{13}C$) in geologic archives are valuable tools for paleovegetation reconstruction. However, the sensitivity of different plant wax constituents to vegetation shift is not well understood. This study explores controls on the variation in ${\delta}^{13}C$ values of long-chain n-alkanes ($C_{27}$ to $C_{33}$) and n-alkanoic acids ($C_{26}-C_{30}$) in the Gulf of Mexico core sediments (ODP 625B) near the Mississippi River delta. n-Alkanoic acids' ${\delta}^{13}C$ values were higher than those of n-alkanes by 1-2‰ on average and such a pattern is the opposite from their isotope fractionation observed in living plants: 1-2‰ smaller in n-alkanes than n-alkanoic acids. We attribute this offset to contributions from aquatic plants or microbes that produce high concentrations of $^{13}C-enriched$ long-chain n-alkanoic acids. The sensitivity of n-alkanes and n-alkanoic acids to vegetation and climate varied among chain lengths. The $n-C_{33}$ alkanes were most sensitive to $C_4$ grassland expansion among n-alkane homologues, while no specific trend was observed in n-alkanoic acids. This is due to the similarity in n-alkanoic acid concentrations between $C_3$ and $C_4$ plants by homologues and low terrestrial plant-derived n-alkanoic acid contributions to the sediments. The results of this study suggest that long chain n-alkanoic acids' ${\delta}^{13}C$ values in sediments may be influenced by contributions from different sources such as aquatic plants or microbial inputs and therefore interpretations regarding this matter should be cautiously formulated. We suggest that there is a need for further studies on characterizing long-chain n-alkanoic acids ($C_{26}-C_{34}$) in aquatic plants and microbes from various climates and environments in order to investigate their production and integration into sedimentary archives.

• Communications for Statistical Applications and Methods
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• 제15권2호
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• pp.147-159
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• 2008

We consider using ranked set sampling methods to draw inference about the three well-known measures of overlap, namely Matusita's measure $\rho$, Morisita's measure $\lambda$ and Weitzman's measure $\Delta$. Two exponential populations with different means are considered. Due to the difficulties of calculating the precision or the bias of the resulting estimators of overlap measures, because there are no closed-form exact formulas for their variances and their exact sampling distributions, Monte Carlo evaluations are used. Confidence intervals for those measures are also constructed via the bootstrap method and Taylor series approximation.

• 한국농공학회지
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• 제38권2호
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• pp.133-144
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• 1996

To get accurate results, the realistic stress-strain relationships of soils are dependent on a number of factors such as soil types, density, stress levels and stress path. Such attempts are continuously being made by the developement of analytical models for soils incorporating all such factors. Isotropic compression-expansion test and a series of drained conventional triaxial tests with several stress path for Baekma river sand were performed to investigate parameters characteristics of Lade's single work hardening model dependant on the stress path. Using the computer program based on the regression analysis, the values of parameters for the model were determined. In conclusion, the parameters of Lade's model are little influenced by the stress paths. Though yield criterion parameters ( h, ${\alpha}$a) are much influenced by stress level and stress path, the parameters don't have influence on stress-strain behavior.

• Journal of Magnetics
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• 제20권2호
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• pp.110-113
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• 2015

Two kinds of magnetic fluids with different volume fractions are symmetrically filled into the W0.9 photonic crystal waveguide structure. The 2D plane-wave expansion method is used to investigate the slow light properties numerically. The constant group index criterion is employed to evaluate the slow light performance. The wavelength bandwidth ${\Delta}{\lambda}$ centering at ${\lambda}_0=1550nm$ varies from 32.4 to 44.2 nm when the magnetic field factor ${\alpha}_{\parallel}$ changes from 0 to 1. And the corresponding normalized delay bandwidth product can be tuned from 0.221 to 0.258. For comparison and optimization, two infiltration cases are investigated and the more advantageous infiltration scheme is found.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.18-20
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• 2003

Land cover change detection is one of the most important trends in which remote sensing data could be used to assist strategists and the planners to decide the best land use policy. Two images of NOAA-AVHRR and SPOT vegetation acquired in November 1992 and 2002 were used to assess the changes of Agricultural lands in Egypt. A supervised classification together with two change images derived from classification result and NDVI were used to evaluate the trend and form of the change. It was found that agricultural areas increased by about 14.3 % during the study period in particular around the River Nile Delta and near the Northern Lakes of Egypt. The new cultivated lands were extracted mainly from the desert and from the salt marches areas. At the same time, parts of the agricultural lands were turned into non-cultivated land because of the urban expansion and soil degradation.

• Bulletin of the Korean Chemical Society
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• 제12권6호
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• pp.618-625
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• 1991

A general expression adopting a nonmultipole expansion method is derived for pseudocontact contribution to the NMR chemical shift arising from the electron orbital angular momentum and electron spin dipolar-nuclear spin angular momentum interaction of $3d^9$ system in a strong crystal field of tetragonally distorted tetrahedral symmetry. From this expression all the multipolar term are determined and the exact solution of ${\Delta}$B/B(ppm) is compared with the multipolar term. The $1/R^5$ term in the multipolar terms contributes dominantly to the NMR chemical shift but the other terms are certainly significant except that of the <111> axis. In addition, an analysis of the temperature dependence of the NMR chemical shift further illustrates that considerable care must be taken in interpeting NMR results in paramagnetic system.

• Bulletin of the Korean Chemical Society
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• 제7권3호
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• pp.231-235
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• 1986

MNDO and ab initio calculations for gas phase reactions of alkoxide-exchange at silicon and carbon centers have been performed. Results show that MNDO values of ${\Delta}$E's of these reactions closely parallel those of the STO-3G method. The alkoxide-exchange at silicon is shown to be facile due to the formation of stable five-coordinate intermediate while the reaction at carbon is predicted to proceed with high barrier; the difference in this substitution behavior between carbon and silicon is shown to be due to an easy valence shell expansion of silicon in accommodating an extra bond in the formation of stable five-coordinate intermediates.