• Geomechanics and Engineering
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• 제17권6호
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• pp.527-534
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• 2019

There have been developed a number of methods to assess the abrasivity of rock materials with the increased use of mechanized rock excavation. These methods range from determination of abrasive and hard mineral content using petrographic thin section analysis to weight loss or development of wear flat on a specified cutting tool. The Cerchar abrasivity index (CAI) test has been widely accepted for the assessment of rock abrasiveness. This test has been considered to provide a reliable indication of rock abrasiveness for isotropic rocks. However, a great amount of rocks in nature are anisotropic. Hence, viability assessment of Cerchar abrasivity test for the anisotropic rocks is investigated in this research. The relationship between CAI value and quartz content for the isotropic rocks is well known in literature. However, a correlation between EQ, F-Schimazek value, Rock Abrasivity Index (RAI) and CAI of anisotropic rocks such as phyllite was done first time in literature with this research. The results obtained with this research show F-Schimazek values and RAI values should be considered when determination of the abrasivity of anisotropic rocks instead of just using Cerchar scratch test.

• 한국지반공학회논문집
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• 제28권4호
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• pp.35-42
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• 2012

균질한 재료로 설계된 댐에서 수직 수평 투수계수가 서로 다를 경우에 이 비등방성 비율이 침투수의 침투면과 신뢰성지수에 어떤 영향을 주는지를 분석하였다. 정상상태에 있는 포화-불포화 침투수 현상을 유한요소법을 사용하여 분석하였다. 수평방향 투수계수를 고정한 상태에서 수직방향 투수계수만을 줄여주는 방법으로 여러가지 다른 비등방성 비율을 해석하였다. 댐제체의 전단강도는 수정된 모어-쿨롱 파괴기준을 사용하여 결정하였다. 해석 결과에 따르면 비등방성 비율이 증가함에 따라 침투면의 거리와 신뢰성지수는 증가하는 것으로 나타났으나 댐 상하류의 전체 수두차에 따라 차이를 보였다. 이러한 침투면과 신뢰성지수의 차이는 비등방성 비율이 변동함에 따라 등가수두선도 변화하는 현상에 의한 것으로 판단된다.

• Journal of the Optical Society of Korea
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• 제1권2호
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• pp.67-73
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• 1997

Light wave diffraction from multiple superposed volume gratings is inestigated using a perturbative iteration method of the integral equation of Maxwell's wave equation. The host material and index gratings are anisotropic and non-coplanar multiple volume gratings are considered. In this method, the paraxial approximation and lack of backward scattering in conventional coupled mode theory are not assumed. Systematic analysis of anisotropic wave diffraction due to multiple noncoplanar volume index gratings is performed in increasing level of diffraction orders corresponding to successive iterations.

• Journal of Astronomy and Space Sciences
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• 제28권2호
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• pp.117-122
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• 2011

In this paper, the anisotropic nature of the magnetic turbulence associated with magnetic dipolarizations in the Earth's plasma sheet is examined. Specifically, we determine the power spectral indices for the perpendicular and parallel components of the fluctuating magnetic field with respect to the background magnetic field, and compare them in order to identify possible anisotropic features. For this study, we identify a total of 47 dipolarization events in February 2008 using the magnetic field data observed by the THEMIS A, D and E satellites when they are situated near the neutral sheet in the near-Earth tail. For the identified events, we estimate the spectral indices for the frequency range from 1.3 mHz to 42 mHz. The results show that the degree of anisotropy, as defined by the ratio of the spectral index of the perpendicular components to that of the parallel component, can range from ~0.2 to ~2.6, and there are more events associated with the ratio greater than unity (i.e., the perpendicular index being greater than the parallel index) than those which are anisotropic in the opposite sense. This implies that the dipolarization-associated turbulence of the magnetic field is often anisotropic, to some non-negligible degree. We then discuss how this result differs from what the theory of homogeneous, anisotropic, magnetohydrodynamic turbulence would predict.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.150-155
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• 2003

Fractures in the form of micro cracks are commonly found in natural rocks. A rock behaves in a complex way due to fracture; in particular, the anisotropic strength of a rock material is significantly influenced by the presence of these fractures. Therefore, it is essential to understand the failure mechanism of a fractured rock. In this study, a fractured rock is formulated in terms of fabric tensor based on geometric and mechanical simplifications. In this way, position, density and shape of fractures can be determined by the fabric tensor so that rocks containing multi-fractures can successfully be modeled. Also an index to evaluate the degree of anisotropy of a fractured rock is proposed. Hence, anisotropic strength of a rock containing fractures under uniaxial compression condition is estimated through a series of numerical analyses for the multi-fractured model. Numerical investigations are carried out by varying the fracture angle from $0^{\circ}\;to\;90^{\circ}$ and relationship between uniaxial compression strength and the degree of anisotropy is investigated. By comparing anisotropic strength of numerical analysis with analytic solution, this study attempts to understand the failure mechanism of rock containing fractures.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.195-195
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• 2010

In recent years, Anodic aluminum oxide(AAO) has become popular and attractive materials. It can be easily fabricated and self-organized pore structures. It has been widely used as a biosensor membrane, photonic crystal for optical circuit and template for nanotube growth etc. In previous papers, the theory was developed that AAO shows anisotropic optical properties, since it has anisotropic structure with numerous cylindrical pores. It gives rise to the anisotropy of the refractive index called as birefringence. It can be used as conventional polarizing elements with high efficiency and low cost. Therefore, we would like to compare the theory and experimental results in this study. One method which can measure effective refractive index of thin film is the prism coupling technique. It can give accurate results fast and simply. Furthermore, we can also measure separately the refractive index with different polarization using polarization of the laser (TE mode and TM mode). We calculated the effective refractive index with effective medium approximations (EMAs) by pore size in the SEM image. EMAs are physical models that describe the macroscopic system as the homogeneous and typical method of all mean field theories.

• 한국지반환경공학회 논문집
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• 제10권3호
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• pp.37-45
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• 2009

대구지역에 분포하는 고유이방성 셰일(shale)의 점재하지수 및 일축․압축강도 특성을 평가하기 위한 일련의 실험실 시험을 수행하였다. 또한 시험시편의 크기효과 및 형태효과를 조사하기 위하여 축방향 및 직경방향으로 점재하지수를 측정하였다. 일반적으로 직경방향의 점재하지수는 길이/직경(L/D)비가 대략 1.0 이상일때 일정한 값을 보이고 축방향 점재하 시험 결과 L/D비의 증가에 따라 평균 점재하지수가 약간 감소하는 경향을 보였으며 L/D비가 1.0 이상이면 corner파괴가 발생하였다. 최소의 점재하지수는 층리면이 연직과 이루는 각 ($\beta$)이 $15^{\circ}{\sim}30^{\circ}$에서 나타났고 ${\beta}=30^{\circ}$에서 최소의 일축압축강도가 얻어졌다. $\beta$ 값의 범위가 $0^{\circ}{\sim}90^{\circ}$인 시편의 점재하지수와 일축압축강도를 측정하여 이들의 상호관계를 회귀분석하였다. 층리면을 $0^{\circ}$에서 $90^{\circ}$까지 변화시키면서 측정한 점재하지수는 일축압축강도와 선형적인 관계인 ${\sigma}_c=25.0 I_{s(50)}$로 나타났다. 한편, 층리각($\beta$)를 90${^{\circ}}$로 고정시킨 상태에서의 이들의 상관성은 ${\sigma}_c=14.4 I_{s(50)}$로 나타났는데, 이는 ISRM(1985)에서 추천하는 층리가 없는 무결암 시료에 대한 일반적인 상관성, ${\sigma}_c=22 I_{s(50)}$과는 많은 차이가 있음을 확인하였다. 일축압축강도의 이방성 모형은 기존의 Ramamurthy(1993)이론에 지수 'n'을 도입하여 n= 3을 적용 했을때 측정결과와 잘 부합되는 결과를 얻었다.

• 터널과지하공간
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• 제14권4호
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• pp.261-268
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• 2004

The main objectives of this study are to investigate the anisotropic characteristics of rocks and to evaluate the relationships between physical properties. A series of experiments were performed in three mutually perpendicular directions for three rock types, which are granite, granitic gneiss and limestone. The relationships of measured physical properties were evaluated. The results of ultrasonic wave velocity measurement show that granite of three rock types gives the largest directional difference, and that the wave velocity in a plane parallel to a transversely isotropic one is dominantly faster than that in a subvertical or vertical plane. It implies that ultrasonic wave velocity for rock could be used as a useful tool for estimating the degree of anisotropy. The ratio of uniaxial compressive strength to Brazilian tensile strength ranges approximately from 13 to 16 for granite. from 8 to 9 for granite gneiss, and from 9 to 18 for limestone. The directional differences for granite and granitic gneiss are very small, and on the other hand, is relatively large for limestone. It is suggested that strength of rock makes quite difference depending on the rock types and loading directions, especially for the anisotropic rocks such as transversely isotropic or orthotropic rocks. The ratio of uniaxial compressive strength to point load strength index ranges from 18 to 20 for granite, from 17 to 19 for granitic gneiss, and from 21 to 24 for limestone. These results show that point load strength index makes also a difference depending on rock types and directions. Therefore. it should be noted that the ratio of uniaxial compressive strength to point load strength index could be applied to all rock types. Uniaxial compressive strength shows relatively good relationship with point load strength index, Schmidt hammer rebound value, and tensile strength. In particulat, point load strength index is shown to be the best comparative relationship. It is indicated that point load test is the most useful tool to estimate an uniaxial compressive strength indirectly.

• 전자공학회논문지D
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• 제34D권10호
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• pp.77-84
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• 1997

The refractive index changes due to the electroptic effect are discussed when external electric fields $E_x, E_y, E_2$ are applied on $LiNbO_3$, a typical anisotropic material. Derived are approximate equations for principal axis' rotations and index changes, results of which are compared with exact results by te computer simulations. In each useful application of $LiNbO_3$substrate, the results of the approximate equations are confirmed to agree with exact solutions.

• 한국광학회:학술대회논문집
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• 한국광학회 2007년도 동계학술발표회 논문집
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• pp.96-97
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• 2007