The Experts below are selected from a list of 109083 Experts worldwide ranked by ideXlab platform
Tingao Tang - One of the best experts on this subject based on the ideXlab platform.
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formulization of long time domain switching around the coercive Field from imprint measurements on ferroelectric thin films
Journal of Applied Physics, 2008Co-Authors: An Quan Jiang, J W Fei, Y Y Lin, Tingao TangAbstract:The time interval for the completion of slow polarization reversal in ferroelectric thin films measured in the order of magnitude of 10−9–100s is broadened by more than two decades as the applied Field approaches the coercive Field of domain switching. The domain-switching kinetics is conjectured to change from the classical Kolmogorov–Avrami–Ishibashi (KAI) model at high Fields to nucleation-limited-switching (NLS) model at low Fields. However, the true voltage drop across the film from the real-time measurement of the oscilloscope remains constant at a coercive voltage Vc during polarization reversal irrespective of the applied voltage. Therefore, the above high-Field Assumption for KAI does not exist. From our measurements, a long-time effect of imprint can occur for any slow processes of physical phenomena, even if the imprint Field is very weak. The imprinted Vc can be estimated either from the voltage shift in the curve of switched polarization versus the applied voltage or directly from the height ...
Mathieu Perton - One of the best experts on this subject based on the ideXlab platform.
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A computer code for forward calculation and inversion of the H/V spectral ratio under the diffuse Field Assumption
Computers & Geosciences, 2016Co-Authors: Antonio García-jerez, José Piña-flores, Francisco J. Sánchez-sesma, Francisco Luzón, Mathieu PertonAbstract:During a quarter of a century, the main characteristics of the horizontal-to-vertical spectral ratio of ambient noise HVSRN have been extensively used for site effect assessment. In spite of the uncertainties about the optimum theoretical model to describe these observations, over the last decade several schemes for inversion of the full HVSRN curve for near surface surveying have been developed.In this work, a computer code for forward calculation of H/V spectra based on the diffuse Field Assumption (DFA) is presented and tested. It takes advantage of the recently stated connection between the HVSRN and the elastodynamic Green's function which arises from the ambient noise interferometry theory.The algorithm allows for (1) a natural calculation of the Green's functions imaginary parts by using suitable contour integrals in the complex wavenumber plane, and (2) separate calculation of the contributions of Rayleigh, Love, P-SV and SH waves as well. The stability of the algorithm at high frequencies is preserved by means of an adaptation of the Wang's orthonormalization method to the calculation of dispersion curves, surface-waves medium responses and contributions of body waves.This code has been combined with a variety of inversion methods to make up a powerful tool for passive seismic surveying. H/V spectral ratios of ambient seismic noise are modeled by using full waveField.The theoretical framework is consistent with ambient noise interferometry.The method provides separate calculations of different wave modes.The software is also suitable for coda waves and any other diffuse-like waveFields.It supports joint inversion of seismic velocity models from H/V and dispersion curves.
An Quan Jiang - One of the best experts on this subject based on the ideXlab platform.
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formulization of long time domain switching around the coercive Field from imprint measurements on ferroelectric thin films
Journal of Applied Physics, 2008Co-Authors: An Quan Jiang, J W Fei, Y Y Lin, Tingao TangAbstract:The time interval for the completion of slow polarization reversal in ferroelectric thin films measured in the order of magnitude of 10−9–100s is broadened by more than two decades as the applied Field approaches the coercive Field of domain switching. The domain-switching kinetics is conjectured to change from the classical Kolmogorov–Avrami–Ishibashi (KAI) model at high Fields to nucleation-limited-switching (NLS) model at low Fields. However, the true voltage drop across the film from the real-time measurement of the oscilloscope remains constant at a coercive voltage Vc during polarization reversal irrespective of the applied voltage. Therefore, the above high-Field Assumption for KAI does not exist. From our measurements, a long-time effect of imprint can occur for any slow processes of physical phenomena, even if the imprint Field is very weak. The imprinted Vc can be estimated either from the voltage shift in the curve of switched polarization versus the applied voltage or directly from the height ...
Douglas S. Luther - One of the best experts on this subject based on the ideXlab platform.
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Comparison of methods of estimating mean synoptic current structure in “stream coordinates” reference frames with an example from the Antarctic Circumpolar Current
Deep Sea Research Part I: Oceanographic Research Papers, 2003Co-Authors: Christopher S. Meinen, Douglas S. LutherAbstract:Abstract Stream coordinates techniques, that is, methods of deriving the mean “synoptic” structures of narrow meandering ocean currents from Eulerian measurements, have been in use for nearly two decades and have resulted in improvements in our understanding of the dynamics and transports of such currents. A 2-year experiment in the Sub-Antarctic Front (SAF) southwest of Tasmania, involving overlapping arrays of inverted echo sounders and horizontal electric Field recorders, has provided an opportunity to test various stream coordinates methods. The methods differ significantly in how well, or even if, they can reveal divergence or convergence of the meandering current, and whether they accurately reproduce the current's horizontal structure and transport. Cross-stream distance was determined either via a frozen-Field Assumption or as the distance to an optimally interpolated (OI) origin contour; downstream direction was determined either as the local direction which maximized the vertical shear of horizontal velocity or as the tangent line to the OI mapped core contour. All combinations of these distance and direction definitions were tested. The use of a frozen Field Assumption in determining cross-stream distance yields overly smooth along-stream velocity cross-sections and overestimated transports. The vertical shear definition of downstream direction results in a false rotation of cross-stream flows into along-stream flows near the flanks of the current. The preferred methods define the horizontal location of the front with 2-D arrays of instruments (e.g., inverted echo sounders or moored current meters). Methods employing the Assumptions of a meandering “frozen-Field” baroclinic structure or the use of the local vertical shear of the horizontal velocity to determine the downstream direction should be avoided, if possible, particularly in the SAF.
Antonio García-jerez - One of the best experts on this subject based on the ideXlab platform.
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A computer code for forward calculation and inversion of the H/V spectral ratio under the diffuse Field Assumption
Computers & Geosciences, 2016Co-Authors: Antonio García-jerez, José Piña-flores, Francisco J. Sánchez-sesma, Francisco Luzón, Mathieu PertonAbstract:During a quarter of a century, the main characteristics of the horizontal-to-vertical spectral ratio of ambient noise HVSRN have been extensively used for site effect assessment. In spite of the uncertainties about the optimum theoretical model to describe these observations, over the last decade several schemes for inversion of the full HVSRN curve for near surface surveying have been developed.In this work, a computer code for forward calculation of H/V spectra based on the diffuse Field Assumption (DFA) is presented and tested. It takes advantage of the recently stated connection between the HVSRN and the elastodynamic Green's function which arises from the ambient noise interferometry theory.The algorithm allows for (1) a natural calculation of the Green's functions imaginary parts by using suitable contour integrals in the complex wavenumber plane, and (2) separate calculation of the contributions of Rayleigh, Love, P-SV and SH waves as well. The stability of the algorithm at high frequencies is preserved by means of an adaptation of the Wang's orthonormalization method to the calculation of dispersion curves, surface-waves medium responses and contributions of body waves.This code has been combined with a variety of inversion methods to make up a powerful tool for passive seismic surveying. H/V spectral ratios of ambient seismic noise are modeled by using full waveField.The theoretical framework is consistent with ambient noise interferometry.The method provides separate calculations of different wave modes.The software is also suitable for coda waves and any other diffuse-like waveFields.It supports joint inversion of seismic velocity models from H/V and dispersion curves.