Anisotropic Conductivity Ratio Research Articles

Anisotropic Microwave Conductivity Dispersion of Horizontally Aligned Multi-Walled Carbon- Nanotube Thin Film on Flexible Substrate

In this paper, the anisotropic conductivity dispersion of horizontally aligned multi-walled carbon-nanotube (HA-MWCNT) thin films on a kapton substrate are characterized at microwave range. It is well known that a single carbon nanotube (CNT) presents highly 1-D conduction. For a thin film composed of numerous aligned CNTs, the anisotropic conduction may be preserved to some extent, as this is useful for various applications. In this paper, the anisotropic conduction of HA-MWCNT thin films is investigated in a rectangular waveguide measurement setup. The anisotropic surface conductivities of the films along the nanotube axial and radial directions are extracted from the measured S-parameters. The results reveal an anisotropic conductivity ratio of about 2 for the HA-MWCNTs thin film. Furthermore, it is observed that the real part of the extracted conductivity remains constant over the frequency band while the imaginary part increases almost linearly with frequency.

Synthesis of Ag–Ni core–shell nanowires and their application in anisotropic transparent conductive films

Transparent conductive films with high anisotropic conductivity ratio (>105) were prepared from Ag–Ni core–shell nanowires by applying a magnetic field.

Uplift force, seepage, and exit gradient under diversion dams

Correct estimation of uplift force, seepage discharge and exit gradient is very important in stability analysis of hydraulic structures. In this research, by carrying out a set of experiments on a laboratory model, the application of various methods for estimating uplift pressure and seepage discharge under hydraulic structures, and the exit gradient have been investigated. The results show that for the soil type used in the experiments, the method of Khosla et al. gives a better estimation of seepage effects than creep theories. Moreover, compared with Lane's method, it is found that Bligh's theory has better agreement with the observed data of uplift pressure, seepage discharge and piping. By using the finite-element method, the magnitude of pressure head upon a dam foundation in different conditions is calculated, and a relationship between the anisotropic conductivity ratio and the ratio of coefficients in Lane's creep theory is introduced. It is found that while the accuracy of Lane's theory is reduced by increasing the anisotropic conductivity ratio, the new relation estimates the amount of uplift force very well. Based on the finite-element method, a set of graphs is presented to estimate the exit gradient in different conditions with the presence of a cutoff wall at the downstream end or without any cutoff wall.

Influence of anisotropic conductivity in the skull and white matter on transcranial direct current stimulation via an anatomically realistic finite element head model

To establish safe and efficient transcranial direct current stimulation (tDCS), it is of particular importance to understand the electrical effects of tDCS in the brain. Since the current density (CD) and electric field (EF) in the brain generated by tDCS depend on various factors including complex head geometries and electrical tissue properties, in this work, we investigated the influence of anisotropic conductivity in the skull and white matter (WM) on tDCS via a 3D anatomically realistic finite element head model. We systematically incorporated various anisotropic conductivity ratios into the skull and WM. The effects of anisotropic tissue conductivity on the CD and EF were subsequently assessed through comparisons to the conventional isotropic solutions. Our results show that the anisotropic skull conductivity significantly affects the CD and EF distribution: there is a significant reduction in the ratio of the target versus non-target total CD and EF on the order of 12–14%. In contrast, the WM anisotropy does not significantly influence the CD and EF on the targeted cortical surface, only on the order of 1–3%. However, the WM anisotropy highly alters the spatial distribution of both the CD and EF inside the brain. This study shows that it is critical to incorporate anisotropic conductivities in planning of tDCS for improved efficacy and safety.

비등방 균질 댐의 정상상태에서의 침투면과 신뢰성지수

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. This paper evaluates the effect of anisotropic conductivity on the seepage face and reliability index of an homogeneous dam with and without toe drain. The analysis are conducted under steady state saturated-unsaturated seepage condition using finite element method. Various anisotropic conductivity ratios were interpreted under such conditions as the vertical conductivity is reduced while the horizon conductivity is fixed. The shear strength of soil is defined by the modified Mohr-Coulomb failure criterion. The analysis results demonstrate that the length of seepage face and reliability index at the downstream and upstream of the dam increase with an increasing anisotropic ratio. These results of the seepage face and reliability index, however, depend on the total head difference between the upstream slope and downstream toe. The difference in seepage face and reliability index is attributed to the different equipotential head with different anisotropic ratios of the dam material.

Effect of anisotropic conductivity on suction and reliability index of unsaturated slope exposed to uniform antecedent rainfall

The authors discuss the effect of anisotropic conductivity on the suction and reliability index of an unsaturated embankment for uniform rainfall whose intensity is lower than the saturated hydraulic conductivity. The analysis is performed on good-drainage soil of a specific horizontal conductivity and various anisotropic ratios such that the vertical conductivity is reduced. The initial suction profile for the unsaturated zone is 15 kPa. The effect of the shear strength caused by matric suction in the unsaturated zone is explained by the modified Mohr–Coulomb failure criteria. The uncoupled approach of finite element method and limit equilibrium method is used to evaluate the reliability index at different elapsed time of an antecedent rainfall. The anisotropic conductivity ratios affect the volumetric water content and the suction profile. The reliability index remains practically unchanged at high anisotropic ratios but decreases noticeably at low ratios when the wetting front reaches and elevates the water table level.

A model study of intramural dispersion of action potential duration in the canine pulmonary conus.

Regional gradients of action potential duration (APD) due to electrophysiological differences between endocardial, midmyocardial, and epicardial myocytes may exist across the ventricular wall. In addition, activation sequence-induced gradients of APD may occur if intramural fiber rotation accelerates or decelerates the depolarization wave front. To investigate relative contributions of regional and activation sequence-induced gradients to intramural APD dispersion, we simulated action potential propagation in two-dimensional models with idealized geometries representing the canine pulmonary conus. Ionic currents for endocardial myocytes were described using the Luo-Rudy membrane equations. Modifications to I(Ks) approximated action potentials of epicardial and midmyocardial cells. Spatial coupling was modeled with a bidomain representation of tissue structure that included unequal anisotropic conductivity ratios. Activation sequence-induced gradients reached 69 ms cm(-1) during a nonuniform activation sequence where the change in orientation between endocardial and epicardial fibers accelerated the depolarization wave front. Regional gradients reached 133 ms cm(-1) at the boundary between endocardial and midmyocardial cells. When regional and activation sequence-induced gradients were oriented in opposite directions, overall APD dispersion decreased. When the gradients were oriented in the same direction, overall dispersion measured as high as 202 ms cm(-1). This gradient exceeded values previously estimated as sufficient to induce cardiac arrhythmia during premature stimulation and suggests that regional and activation sequence-induced gradients increase arrhythmia vulnerability in the presence of other arrhythmogenic conditions.