scholarly journals Anisotropic Diffusion and the Townsend?Huxley Experiment

1973 ◽  
Vol 26 (4) ◽  
pp. 469 ◽  
Author(s):  
JJ Lowke
Keyword(s):  
Experimental Data ◽  
Electric Field ◽  
Electron Mobility ◽  
Diffusion Coefficients ◽  
Applied Electric Field ◽  
Anisotropic Diffusion ◽  
Diffusion Tubes ◽  
New Formula ◽  
The Relationship ◽  
Diffusion Tube

The relationship between current ratios and electron diffusion coefficients for the Townsend-Huxley experiment is reanalysed with the assumption that diffusion can be represented by two coefficients DT and DL for diffusion transverse and parallel respectively to the applied electric field. When the new formula is used to interpret previous experimental data obtained with a diffusion tube of length 2 cm, the derived values of DT/fl become independent of pressure (fl being the electron mobility). For longer diffusion tubes (~ 6 cm), current ratios are insensitive to DL and the results differ insignificantly from those obtained using the formula previously derived on the assumption that diffusion is isotropic.

The breathers in nematic liquid crystals under applied electric field

2019 ◽  
Vol 33 (26) ◽  
pp. 1950319
Author(s):  
Yan Li ◽  
Xiaobo Lu ◽  
Chunfeng Hou
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Field ◽  
Nematic Liquid Crystal ◽  
Dynamic Equation ◽  
Applied Electric Field ◽  
Deflection Angle ◽  
Breather Solution ◽  
The Relationship ◽  
Sg Equation

In this paper, we study the twist of the nematic liquid crystal molecules under the applied electric field. The dynamic equation of the twisted molecules is derived. It is proved to be a kind of sine-Gordon (SG) equation. We obtain the breather solution of the equation and confirm that the deflection angles of the twisted molecules can distribute in the form of breathers. We give the relationship between the molecular deflection angle and the breather frequency, and discuss the effect of electric field on breather shape and breather frequency.

STUDY OF THE RELATIONSHIP BETWEEN STRUCTURE AND O-17 ELECTRIC FIELD GRADIENT PARAMETERS IN SOME ALUMINOSILICATES

2005 ◽  
Vol 19 (24) ◽  
pp. 1213-1221 ◽  
Author(s):  
ERDEM KAMIL YILDIRIM ◽  
RAY DUPREE
Keyword(s):  
Experimental Data ◽  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Local Structure ◽  
Asymmetry Parameter ◽  
Bond Angle ◽  
Theoretical Work ◽  
The Relationship ◽  
Oxygen Site

The relation between O-17 quadrupolar parameters and the local structure in silicates is of considerable interest if these parameters are to be used as a local probe. Although there are a number of investigations and some theoretical work on Si—O—Si bonds, there seems to be very little experimental data on Si—O—Al bonds. We have therefore investigated a number of sodalites with a general formula of M 8 [AlSiO 4 ]Cl 2 where M is an alkali cation. They have only one oxygen site and a Si:Al ratio of one. By varying the alkali we were able to change the Si—O—Al bond angle about five degrees steps from 125 to 152 degrees. The value of the electric field gradient (EFG), CQ of O-17, followed a roughly similar angular dependence to that found for Si—O—Si bonds with CQ180= 4.2 MHz . The asymmetry parameter of O-17 also behaved in a similar fashion to that found for Si—O—Si bonds although it increased more rapidly at small angles.

Combined Edge and Anisotropy Effects on Fickian Mass Diffusion in Polymer Composites

2004 ◽  
Vol 126 (4) ◽  
pp. 427-435 ◽  
Author(s):  
Levent Aktas ◽  
Youssef K. Hamidi ◽  
M. Cengiz Altan
Keyword(s):  
Experimental Data ◽  
Diffusion Equation ◽  
Polymer Composites ◽  
Diffusion Coefficients ◽  
Anisotropic Diffusion ◽  
Rectangular Domain ◽  
Least Square ◽  
Fickian Diffusion ◽  
Finite Sample ◽  
Time Curve

The common methods used to determine the diffusion coefficients of polymer composites are based on the solution of Fickian diffusion equation in one-dimensional (1D) rectangular domain. However, these diffusivities usually involve errors primarily due to finite sample dimensions and anisotropy introduced by fiber reinforcements. In this study, the solution of transient, three-dimensional (3D) anisotropic Fickian diffusion equation is nondimensionalized using six parameters. The solution is then used to analyze the combined contribution of finite sample dimensions and anisotropy to the errors involved in diffusion constants calculated by 1D methods. The small time solution of the Fickian diffusion equation in 3D domain is used to analyze the slope used in diffusivity calculations. It is shown that the diffusion coefficient calculated by the 1D approach is exact only if the correct slope of percent mass gain versus root square time curve at t=0 is used. However, it has also been shown that depending on the part geometry and degree of anisotropy, there might be considerable differences between the measured slope from the experimental data and the actual slope at t=0. The mismatch between the slopes results in as much as 50% errors in estimates of diffusion coefficients. Using the 3D solution in nondimensional form, the magnitudes of these errors are studied. A least-square curve-fit method, which yields accurate anisotropic diffusion coefficients, is proposed. The method is demonstrated on artificially generated experimental data for a polymer composite containing 50% unidirectional reinforcement. The anisotropic diffusion coefficients used to generate the data are recovered with less than 1% error.

scholarly journals A Note on the Longitudinal Diffusion of Electrons in Argon

1972 ◽  
Vol 25 (5) ◽  
pp. 637 ◽  
Author(s):  
AG Robertson ◽  
JA Rees
Keyword(s):  
Electric Field ◽  
Momentum Transfer ◽  
Cross Section ◽  
Diffusion Coefficients ◽  
Applied Electric Field ◽  
Longitudinal Diffusion ◽  
Marked Influence ◽  
Momentum Transfer Cross Section

It has been shown both experimentally and theoretically that the diffusion of electrons subject to the influence of an applied electric field is often significantly different in directions parallel and normal to the electric field (Wagner, Davis, and Hurst 1967; Parker and Lowke 1969; Lowke and Parker 1969; Skullerud 1969). Lowke and Parker (1969) showed that the ratio of the diffusion coefficients (DL parallel to the electric field and DT normal to the field) is particularly sensitive to rapid variations with energy of the momentum transfer cross section of the electrons. It is to be expected therefore that for electrons in argon the Ramsauer?Townsend minimum in the momentum transfer cross section at energies of ~ 0�3 eV will have a marked influence on the value of DL.

Investigation on Multiple Piezoelectric Effect of Piezoelectric Crystal Under Applied Electric Field

2008 ◽  
Author(s):  
Baoyuan Sun ◽  
Yinhui Shi ◽  
Min Qian ◽  
Jun Zhang ◽  
Zhonghua Zhang
Keyword(s):  
Electric Field ◽  
Applied Electric Field ◽  
Piezoelectric Effect ◽  
Field Analysis ◽  
Experimental Result ◽  
Analysis Software ◽  
Element Analysis ◽  
The Finite Element Analysis ◽  
Converse Piezoelectric Effect ◽  
The Relationship

Based on the theory of classical piezoelectricity, the relationship between the generation of multiple piezoelectric effect under applied electric field and boundary conditions is analyzed. The generating process of multiple piezoelectric effect is elaborated and the formulas of secondary direct and tertiary converse piezoelectric effect are deduced. The displacement or voltage generated by primary converse, secondary direct and tertiary converse piezoelectric effect is calculated by using coupled-field analysis function in the Finite Element Analysis software-ANSYS. Experimental research of multiple piezoelectric effect under applied electric field is performed through PZT-5 stack. The experimental result verifies the existence of multiple piezoelectric effect. Experimental data shows that voltage and displacement generated by secondary direct and tertiary converse piezoelectric effect respectively are linear with the applied voltage. Both the simulation and experimental results prove that the theoretical analysis is accurate.

Combined Edge and Anisotropy Effects on Fickian Mass Diffusion in Polymer Composites

2003 ◽  
Author(s):  
Levent Aktas ◽  
Youssef K. Hamidi ◽  
M. Cengiz Altan
Keyword(s):  
Experimental Data ◽  
Diffusion Equation ◽  
Polymer Composites ◽  
Diffusion Coefficients ◽  
Anisotropic Diffusion ◽  
Three Dimensional ◽  
Least Square ◽  
Fickian Diffusion ◽  
Finite Sample ◽  
One Dimensional

The common methods used to determine the diffusion coefficients of polymer composites are based on the solution of Fickian diffusion equation in one-dimensional rectangular domain. However, these diffusivities usually involve errors primarily due to finite sample dimensions and anisotropy introduced by fiber reinforcements. In this study, the solution of transient, three-dimensional anisotropic Fickian diffusion equation is non-dimensionalized using six parameters. The solution is then used to analyze the combined contribution of finite sample dimensions and anisotropy to the errors involved in diffusion constants calculated by one-dimensional methods. The small time solution of the Fickian diffusion equation in three-dimensional domain is used to analyze the slope used in diffusivity calculations. It is shown that the diffusion coefficient calculated by one-dimensional approach is exact only if the correct slope of percent mass gain versus root square time curve at t=0 is used. However, it has also been shown that depending on the part geometry and degree of anisotropy, there might be considerable differences between the measured slope from the experimental data and the actual slope at t=0. The mismatch between the slopes results in as much as 50% errors in estimates of diffusion coefficients. Using the three-dimensional solution in non-dimensional form, the magnitudes of these errors are studied. A least square curve fit method, which yields accurate anisotropic diffusion coefficients, is proposed. The method is demonstrated on artificially generated experimental data for a polymer composite containing 50% unidirectional reinforcement. The anisotropic diffusion coefficients used to generate the data are recovered with less than 1% error.

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