The Experts below are selected from a list of 2550 Experts worldwide ranked by ideXlab platform
T Gryba - One of the best experts on this subject based on the ideXlab platform.
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legendre Polynomial approach for modeling free ultrasonic waves in multilayered plates
Journal of Applied Physics, 1999Co-Authors: J E Lefebvre, Victor Y Zhang, J Gazalet, T GrybaAbstract:Modeled on the Laguerre Polynomial approach used for surface acoustic waves, a formulation is presented for the study of free-acoustic wave propagation in layered plates. It uses the Legendre Polynomials. Each layer can be of arbitrary anisotropy and piezoelectricity with arbitrary crystal orientation with the only restriction that the parameters of the constituent materials are close to each other. Formulations are given for open-circuit and short-circuit surfaces. Phase velocity dispersion curves, attenuations, power distributions, and field profiles are easily obtained from an algorithm easily implemented on a computer using commercial software. Numerical results are given for AlAs/GaAs multilayered structures which illustrate the capabilities of the described method. Its major advantages are: (i) in a unified formulation, all types of modes, surface modes, interface modes, and plate modes are naturally encompassed. (ii) Large values of the frequency-thickness product as compared to the values allowed by the usual methods may be dealt with. (iii) For propagation loss calculation, the usual multivariable search is avoided since the proposed method naturally works in the complex plane.
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conceptual advantages and limitations of the Laguerre Polynomial approach to analyze surface acoustic waves in semi infinite substrates and multilayered structures
Journal of Applied Physics, 1998Co-Authors: J E Lefebvre, Victor Y Zhang, J Gazalet, T GrybaAbstract:Laguerre Polynomial approach is used to calculate velocities, coupling coefficients, and field distributions of surface acoustic waves in both semi-infinite substrates and multilayered structures. Approximation used in boundary conditions for applying the Laguerre Polynomial method is investigated. Effectiveness of the method to calculate the coupling coefficient is checked. Its capabilities with regard to the various types of waves are reviewed. It is shown that Laguerre Polynomial method cannot be used to study leaky surface acoustic waves. For true surface acoustic waves it can, but for deep penetration, computing time becomes prohibitive. Laguerre Polynomial method is interesting for true surface acoustic waves modes if decay length is of the order of one acoustic wavelength: velocities, coupling coefficient and, continuous field profiles are quite well returned. However, for multilayered structures, very dissimilar parameters of the constituent materials give rise to significant field level discontinuities at the interfaces. It is shown that the Laguerre Polynomial method does not return, within reasonable computing time and required memory, these discontinuities of which multiple quantum well-based devices can take advantage.
J E Lefebvre - One of the best experts on this subject based on the ideXlab platform.
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legendre Polynomial approach for modeling free ultrasonic waves in multilayered plates
Journal of Applied Physics, 1999Co-Authors: J E Lefebvre, Victor Y Zhang, J Gazalet, T GrybaAbstract:Modeled on the Laguerre Polynomial approach used for surface acoustic waves, a formulation is presented for the study of free-acoustic wave propagation in layered plates. It uses the Legendre Polynomials. Each layer can be of arbitrary anisotropy and piezoelectricity with arbitrary crystal orientation with the only restriction that the parameters of the constituent materials are close to each other. Formulations are given for open-circuit and short-circuit surfaces. Phase velocity dispersion curves, attenuations, power distributions, and field profiles are easily obtained from an algorithm easily implemented on a computer using commercial software. Numerical results are given for AlAs/GaAs multilayered structures which illustrate the capabilities of the described method. Its major advantages are: (i) in a unified formulation, all types of modes, surface modes, interface modes, and plate modes are naturally encompassed. (ii) Large values of the frequency-thickness product as compared to the values allowed by the usual methods may be dealt with. (iii) For propagation loss calculation, the usual multivariable search is avoided since the proposed method naturally works in the complex plane.
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conceptual advantages and limitations of the Laguerre Polynomial approach to analyze surface acoustic waves in semi infinite substrates and multilayered structures
Journal of Applied Physics, 1998Co-Authors: J E Lefebvre, Victor Y Zhang, J Gazalet, T GrybaAbstract:Laguerre Polynomial approach is used to calculate velocities, coupling coefficients, and field distributions of surface acoustic waves in both semi-infinite substrates and multilayered structures. Approximation used in boundary conditions for applying the Laguerre Polynomial method is investigated. Effectiveness of the method to calculate the coupling coefficient is checked. Its capabilities with regard to the various types of waves are reviewed. It is shown that Laguerre Polynomial method cannot be used to study leaky surface acoustic waves. For true surface acoustic waves it can, but for deep penetration, computing time becomes prohibitive. Laguerre Polynomial method is interesting for true surface acoustic waves modes if decay length is of the order of one acoustic wavelength: velocities, coupling coefficient and, continuous field profiles are quite well returned. However, for multilayered structures, very dissimilar parameters of the constituent materials give rise to significant field level discontinuities at the interfaces. It is shown that the Laguerre Polynomial method does not return, within reasonable computing time and required memory, these discontinuities of which multiple quantum well-based devices can take advantage.
S Nishimura - One of the best experts on this subject based on the ideXlab platform.
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a convergence study for the Laguerre expansion in the moment equation method for neoclassical transport in general toroidal plasmas
Physics of Plasmas, 2010Co-Authors: S Nishimura, H Sugama, H Maassberg, C D Beidler, S Murakami, Y Nakamura, S HirookaAbstract:The dependence of neoclassical parallel flow calculations on the maximum order of Laguerre Polynomial expansions is investigated in a magnetic configuration of the Large Helical Device [S. Murakami, A. Wakasa, H. Maassberg, et al., Nucl. Fusion 42, L19 (2002)] using the monoenergetic coefficient database obtained by an international collaboration. On the basis of a previous generalization (the so-called Sugama-Nishimura method [H. Sugama and S. Nishimura, Phys. Plasmas 15, 042502 (2008)]) to an arbitrary order of the expansion, the 13 M, 21 M, and 29 M approximations are compared. In a previous comparison, only the ion distribution function in the banana collisionality regime of single-ion-species plasmas in tokamak configurations was investigated. In this paper, the dependence of the problems including electrons and impurities in the general collisionality regime in an actual nonsymmetric toroidal configuration is reported. In particular, qualities of approximations for the electron distribution function are investigated in detail.
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moment equation methods for calculating neoclassical transport coefficients in general toroidal plasmas
Physics of Plasmas, 2008Co-Authors: H Sugama, S NishimuraAbstract:A detailed comparison is made between moment-equation methods presented by H. Sugama and S. Nishimura [Phys. Plasmas 9, 4637 (2002)] and by M. Taguchi [Phys. Fluids B 4, 3638 (1992)] for calculating neoclassical transport coefficients in general toroidal plasmas including nonsymmetric systems. It is shown that these methods can be derived from the drift kinetic equation with the same collision model used for correctly taking account of collisional momentum conservation. In both methods, the Laguerre Polynomials of the energy variable are employed to expand the guiding-center distribution function and to obtain the moment equations, by which the radial neoclassical transport fluxes and the parallel flows are related to the thermodynamic forces. The methods are given here in the forms applicable for an arbitrary truncation number of the Laguerre-Polynomial expansion so that their accuracies can be improved by increasing the truncation number. Differences between results from the two methods appear when the ...
Rogerio Jorge - One of the best experts on this subject based on the ideXlab platform.
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theory of the drift wave instability at arbitrary collisionality
Physical Review Letters, 2018Co-Authors: Rogerio Jorge, Paolo Ricci, Nuno LoureiroAbstract:A numerically efficient framework that takes into account the effect of the Coulomb collision operator at arbitrary collisionalities is introduced. Such a model is based on the expansion of the distribution function on a Hermite-Laguerre Polynomial basis to study the effects of collisions on magnetized plasma instabilities at arbitrary mean-free path. Focusing on the drift-wave instability, we show that our framework allows retrieving established collisional and collisionless limits. At the intermediate collisionalities relevant for present and future magnetic nuclear fusion devices, deviations with respect to collision operators used in state-of-the-art turbulence simulation codes show the need for retaining the full Coulomb operator in order to obtain both the correct instability growth rate and eigenmode spectrum, which, for example, may significantly impact quantitative predictions of transport. The exponential convergence of the spectral representation that we propose makes the representation of the velocity space dependence, including the full collision operator, more efficient than standard finite difference methods.
Victor Y Zhang - One of the best experts on this subject based on the ideXlab platform.
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legendre Polynomial approach for modeling free ultrasonic waves in multilayered plates
Journal of Applied Physics, 1999Co-Authors: J E Lefebvre, Victor Y Zhang, J Gazalet, T GrybaAbstract:Modeled on the Laguerre Polynomial approach used for surface acoustic waves, a formulation is presented for the study of free-acoustic wave propagation in layered plates. It uses the Legendre Polynomials. Each layer can be of arbitrary anisotropy and piezoelectricity with arbitrary crystal orientation with the only restriction that the parameters of the constituent materials are close to each other. Formulations are given for open-circuit and short-circuit surfaces. Phase velocity dispersion curves, attenuations, power distributions, and field profiles are easily obtained from an algorithm easily implemented on a computer using commercial software. Numerical results are given for AlAs/GaAs multilayered structures which illustrate the capabilities of the described method. Its major advantages are: (i) in a unified formulation, all types of modes, surface modes, interface modes, and plate modes are naturally encompassed. (ii) Large values of the frequency-thickness product as compared to the values allowed by the usual methods may be dealt with. (iii) For propagation loss calculation, the usual multivariable search is avoided since the proposed method naturally works in the complex plane.
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conceptual advantages and limitations of the Laguerre Polynomial approach to analyze surface acoustic waves in semi infinite substrates and multilayered structures
Journal of Applied Physics, 1998Co-Authors: J E Lefebvre, Victor Y Zhang, J Gazalet, T GrybaAbstract:Laguerre Polynomial approach is used to calculate velocities, coupling coefficients, and field distributions of surface acoustic waves in both semi-infinite substrates and multilayered structures. Approximation used in boundary conditions for applying the Laguerre Polynomial method is investigated. Effectiveness of the method to calculate the coupling coefficient is checked. Its capabilities with regard to the various types of waves are reviewed. It is shown that Laguerre Polynomial method cannot be used to study leaky surface acoustic waves. For true surface acoustic waves it can, but for deep penetration, computing time becomes prohibitive. Laguerre Polynomial method is interesting for true surface acoustic waves modes if decay length is of the order of one acoustic wavelength: velocities, coupling coefficient and, continuous field profiles are quite well returned. However, for multilayered structures, very dissimilar parameters of the constituent materials give rise to significant field level discontinuities at the interfaces. It is shown that the Laguerre Polynomial method does not return, within reasonable computing time and required memory, these discontinuities of which multiple quantum well-based devices can take advantage.
