scholarly journals Ultrasonic relaxation of some CdO boro-tellurate glasses

2016 ◽  
Vol 94 (10) ◽  
pp. 1008-1016 ◽  
Author(s):  
M.S. Gaafar ◽  
I.S. Mahmoud
Keyword(s):  
Activation Energy ◽  
Relaxation Process ◽  
Ultrasonic Attenuation ◽  
Operating Frequency ◽  
Thermally Activated ◽  
Different Temperatures ◽  
Standard Linear Solid ◽  
Standard Linear ◽  
Double Well Potential ◽  
Solid Type

50B2O3–(50-x)TeO2–xCdO glass system, with x = 0, 10, 20, 30, 40, and 50 mol% have been prepared, to measure the longitudinal ultrasonic attenuation at frequencies of 2, 4, 6, and 14 MHz in the temperature range from 120 to 300 K. Well-defined broad peaks of the absorption curves were observed at different temperatures depending on the glass composition and the operating frequency. The maximum peaks shifted to higher temperatures with the increase of the operating frequency implying the presence of some kind of relaxation process. This process is suggested as due to the thermally activated relaxation process. The variation of the average activation energy of the process mainly depends on the CdO mol% content. Such dependence was analyzed in terms of the loss of standard linear solid type, with low dispersion and a broad distribution of Arrhenius type relaxation with temperature independent relaxation strength. The obtained acoustic activation energy values were quantitatively interpreted in terms of the number of loss centers (number of oxygen atoms that vibrate in the double well potential).

The Meyer–Neldel Rule in Conduction Mechanism of the Electrospun ZnO Nanofibers

NANO ◽  
2016 ◽  
Vol 11 (03) ◽  
pp. 1650025 ◽  
Author(s):  
Andrzej Stafiniak ◽  
Marek Tłaczała
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Conduction Mechanism ◽  
Deep Level ◽  
Electrical Measurements ◽  
Thermally Activated ◽  
Theoretical Assumptions ◽  
Different Temperatures ◽  
Zno Nanofibers ◽  
Improved Model

An analytical model describing the conductivity of ZnO nanofibers depending on the grains size is proposed. The research is based on the thermal dc electrical measurements of a single electrospun ZnO nanofiber calcined at different temperatures. In the our previous research, we showed that electrical conduction of ZnO nanofibers is mainly thermally activated. The activation energy of conductivity was strongly dependent on the grain size, which in turn depended on the calcination temperature. This could be due to migration of a point defect in the grain of ZnO and could change the carrier concentration. Our recent studies have shown that ZnO nanofibers behavior is consistent with the Meyer–Neldel rule. This indicates an exponential energy distribution of deep level traps in the material. Based on the theoretical assumptions and experimental data, the improved model of conductivity in a single ZnO nanofiber calcined at different temperatures was proposed.

Mössbauer effect study on the mixed valence state of iron in tourmaline

1988 ◽  
Vol 52 (365) ◽  
pp. 221-228 ◽  
Author(s):  
E. A. Ferrow ◽  
H. Annersten ◽  
R. P. Gunawardane
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Valence State ◽  
Mixed Valence ◽  
Effect Study ◽  
High Activation ◽  
Charge Delocalization ◽  
Thermally Activated ◽  
Different Temperatures ◽  
Iron Bearing

AbstractMössbauer spectra of iron-bearing tourmaline, obtained at different temperatures, show the existence of thermally-activated charge delocalization among clusters of iron atoms situated in the Y and Z octahedra of the tourmaline structure. The temperature dependence indicates an unusually high activation energy for the delocalization process which suggests that the process takes place between crystallographically non-equivalent sites. Annealing of the tourmaline in hydrogen is observed to inhibit the delocalization process, thus localizing the electron into the Z-site.

scholarly journals Nearly constant Q models of the generalized standard linear solid type and the corresponding wave equations

Geophysics ◽  
2021 ◽  
pp. 1-125
Author(s):  
Qi Hao ◽  
Stewart Greenhalgh
Keyword(s):  
Quality Factor ◽  
Time Domain ◽  
Inverse Modeling ◽  
Wave Equations ◽  
New Models ◽  
Q Model ◽  
Standard Linear Solid ◽  
Standard Linear ◽  
Forward And Inverse Modeling ◽  
Solid Type

Time-domain seismic forward and inverse modeling for a dissipative medium is a vital research topic to investigate the attenuation structure of the Earth. Constant Q, also called frequency independence of the quality factor, is a common assumption for seismic Q inversion. We propose the first- and second-order nearly constant Q dissipative models of the generalized standard linear solid type, using a novel Q-independent weighting function approach. The two new models, which originate from the Kolsky model (a nearly constant Q model) and the Kjartansson model (an exactly constant Q model), result in the corresponding wave equations in differential form. Even for extremely strong attenuation (e.g., Q = 5), the quality factor and phase velocity for the two new models are close to those for the Kolsky and Kjartansson models, in a frequency range of interest. The wave equations for the two new models involve explicitly a specified Q parameter and have compact and simple forms. We provide a novel perspective on how to build a nearly constant Q dissipative model which is beneficial for time-domain large scale wavefield forward and inverse modeling. This perspective could also help obtain other dissipative models with similar advantages. We also discuss the extension beyond viscoacousticity and other related issues, for example, extending the two new models to viscoelastic anisotropy.

Dielectric Relaxation Studies of Silver Nanoparticles dispersed Liquid Crystal

2015 ◽  
Vol 8 (3) ◽  
pp. 2176-2188 ◽  
Author(s):  
Keisham Nanao Singh
Keyword(s):  
Activation Energy ◽  
Silver Nanoparticles ◽  
Liquid Crystal ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Relaxation Times ◽  
Low Frequency ◽  
Bulk Liquid ◽  
Molecular Rearrangement ◽  
Relaxation Studies

This article reports on the Dielectric Relaxation Studies of two Liquid Crystalline compounds - 7O.4 and 7O.6 - doped with dodecanethiol capped Silver Nanoparticles. The liquid crystal molecules are aligned homeotropically using CTAB. The low frequency relaxation process occurring above 1 MHz is fitted to Cole-Cole formula using the software Dielectric Spectra fit. The effect of the Silver Nanoparticles on the molecular dipole dynamics are discussed in terms of the fitted relaxation times, Cole-Cole distribution parameter and activation energy. The study indicate a local molecular rearrangement of the liquid crystal molecules without affecting the order of the bulk liquid crystal molecules but these local molecules surrounding the Silver Nanoparticles do not contribute to the relaxation process in the studied frequency range. The observed effect on activation energy suggests a change in interaction between the nanoparticles/liquid crystal molecules.

scholarly journals Stable and Efficient Modeling of Anelastic Attenuation in Seismic Wave Propagation

2012 ◽  
Vol 12 (1) ◽  
pp. 193-225 ◽  
Author(s):  
N. Anders Petersson ◽  
Björn Sjögreen
Keyword(s):  
Wave Equation ◽  
Finite Difference ◽  
Half Space ◽  
Material Model ◽  
Second Order ◽  
Finite Difference Approximation ◽  
Difference Approximation ◽  
Space Problem ◽  
Standard Linear Solid ◽  
Standard Linear

AbstractWe develop a stable finite difference approximation of the three-dimensional viscoelastic wave equation. The material model is a super-imposition of N standard linear solid mechanisms, which commonly is used in seismology to model a material with constant quality factor Q. The proposed scheme discretizes the governing equations in second order displacement formulation using 3N memory variables, making it significantly more memory efficient than the commonly used first order velocity-stress formulation. The new scheme is a generalization of our energy conserving finite difference scheme for the elastic wave equation in second order formulation [SIAM J. Numer. Anal., 45 (2007), pp. 1902-1936]. Our main result is a proof that the proposed discretization is energy stable, even in the case of variable material properties. The proof relies on the summation-by-parts property of the discretization. The new scheme is implemented with grid refinement with hanging nodes on the interface. Numerical experiments verify the accuracy and stability of the new scheme. Semi-analytical solutions for a half-space problem and the LOH.3 layer over half-space problem are used to demonstrate how the number of viscoelastic mechanisms and the grid resolution influence the accuracy. We find that three standard linear solid mechanisms usually are sufficient to make the modeling error smaller than the discretization error.

scholarly journals Kinetics and thermodynamic properties related to the drying of 'Cabacinha' pepper fruits

2016 ◽  
Vol 20 (2) ◽  
pp. 174-180 ◽  
Author(s):  
Hellismar W. da Silva ◽  
Renato S. Rodovalho ◽  
Marya F. Velasco ◽  
Camila F. Silva ◽  
Luís S. R. Vale
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Free Energy ◽  
Thermodynamic Properties ◽  
Gibbs Free Energy ◽  
Removal Rate ◽  
Effective Diffusion ◽  
Drying Time ◽  
Three Samples ◽  
Different Temperatures

ABSTRACT The objective of this study was to determine and model the drying kinetics of 'Cabacinha' pepper fruits at different temperatures of the drying air, as well as obtain the thermodynamic properties involved in the drying process of the product. Drying was carried out under controlled conductions of temperature (60, 70, 80, 90 and 100 °C) using three samples of 130 g of fruit, which were weighed periodically until constant mass. The experimental data were adjusted to different mathematical models often used in the representation of fruit drying. Effective diffusion coefficients, calculated from the mathematical model of liquid diffusion, were used to obtain activation energy, enthalpy, entropy and Gibbs free energy. The Midilli model showed the best fit to the experimental data of drying of 'Cabacinha' pepper fruits. The increase in drying temperature promoted an increase in water removal rate, effective diffusion coefficient and Gibbs free energy, besides a reduction in fruit drying time and in the values of entropy and enthalpy. The activation energy for the drying of pepper fruits was 36.09 kJ mol-1.

scholarly journals Asymptotic behaviour for the vibrations modeled by the standard linear solid model with a thermal effect

2013 ◽  
Vol 399 (2) ◽  
pp. 472-479 ◽  
Author(s):  
Margareth S. Alves ◽  
Celene Buriol ◽  
Marcio V. Ferreira ◽  
Jaime E. Muñoz Rivera ◽  
Mauricio Sepúlveda ◽  
...  
Keyword(s):  
Asymptotic Behaviour ◽  
Thermal Effect ◽  
Solid Model ◽  
Standard Linear Solid Model ◽  
Standard Linear Solid ◽  
Standard Linear

scholarly journals Surface Modification of Fly Ash for Active Catalysis

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Deepti Jain ◽  
Renu Hada ◽  
Ashu Rani
Keyword(s):  
Fly Ash ◽  
Heterogeneous Catalysts ◽  
Chemical Activation ◽  
Alumina Content ◽  
Precipitation Method ◽  
Solid Base ◽  
Thermally Activated ◽  
Flame Atomic Absorption ◽  
Flame Atomic Absorption Spectrophotometer ◽  
Different Temperatures

Fly ash based effective solid base catalyst (KF/Al2O3/fly ash473, KF/Al2O3/fly ash673, and KF/Al2O3/fly ash873) was synthesized by loading KF over chemically and thermally activated fly ash. The chemical activation was done by treating fly ash with aluminum nitrate via precipitation method followed by thermal activation at 650°C to increase the alumina content in fly ash. The increased alumina content was confirmed by SEM-EDX analysis. The alumina enriched fly ash was then loaded with KF (10 wt%) and calcined at three different temperatures 473 K, 673 K and 873 K. The amount of loaded KF was monitored by XRD, FTIR spectroscopy, SEM-EDX, TEM and Flame Atomic Absorption Spectrophotometer. The catalytic activities of the catalysts were tested in the Claisen-Schmidt condensation of benzaldehyde and 4-methoxybenzaldehyde with 2′-hydroxyacetophenone to produce 2′-hydroxychalcone and 4-methoxy-2′-hydroxychalcone respectively. Higher conversion (83%) of benzaldehyde and (89%) of 4-methoxybenzaldehyde reveals that among these heterogeneous catalysts KF/Al2O3/fly ash673 is very active.

scholarly journals Superior Degradation Performance of Nanoporous Copper Catalysts on Methyl Orange

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 913
Author(s):  
Jinyi Wang ◽  
Sen Yang
Keyword(s):  
Activation Energy ◽  
Methyl Orange ◽  
High Efficiency ◽  
Low Cost ◽  
Degradation Process ◽  
Copper Catalysts ◽  
Reaction Rate Constant ◽  
Nanoporous Structure ◽  
Intra Particle Diffusion ◽  
Different Temperatures

The development of low-cost and high-efficiency catalysts for wastewater treatment is of great significance. Herein, nanoporous Cu/Cu2O catalysts were synthesized from MnCu, MnCuNi, and MnCuAl with similar ligament size through one-step dealloying. Meanwhile, the comparisons of three catalysts in performing methyl orange degradation were investigated. One of the catalysts possessed a degradation efficiency as high as 7.67 mg·g−1·min−1. With good linear fitting by the pseudo-first-order model, the reaction rate constant was evaluated. In order to better understand the degradation process, the adsorption behavior was considered, and it was divided into three stages based on the intra-particle diffusion model. Three different temperatures were applied to explore the activation energy of the degradation. As a photocatalytic agent, the nanoporous structure of Cu/Cu2O possessed a large surface area and it also had low activation energy, which were beneficial to the excellent degradation performance.

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