The Experts below are selected from a list of 13737 Experts worldwide ranked by ideXlab platform
Haruo Sato - One of the best experts on this subject based on the ideXlab platform.
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Parabolic equation and envelope synthesis based on the markov Approximation
2012Co-Authors: Haruo Sato, Michael Fehler, Takuto MaedaAbstract:The inhomogeneity of the earth’s lithosphere has a broad spectrum compared with the wavelength of regional seismic waves. We will now present a model for wave propagation through random media having long-wavelength components of velocity inhomogeneity compared with the dominant wavelength of seismic waves. We focus on diffraction and multiple forward-scattering effects upon the waveform formation. In such a case we can apply the Parabolic Approximation for the wave equation.
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seismic wave propagation and scattering in the heterogeneous earth
1997Co-Authors: Haruo Sato, Michael FehlerAbstract:Introduction.- Heterogeneity in the Lithosphere.- Phenomenological Approaches to Seismogram Envelopes in short-periods.- Born Approximation for Wave Scattering in Random Media.- Attenuation of High-Frequency Seismic Waves.- Synthesis of Three-Component Seismogram Envelopes for Earthquakes Using Scattering Amplitudes from the Born Approximation.- Envelope Synthesis Based on the Radiative Transfer Theory: Multiple Scattering Models.- Parabolic Approximation and Envelope Synthesis based on the Markov Approximation. Summary and Epilogue.
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regional differences of random inhomogeneities around the volcanic front in the kanto tokai area japan revealed from the broadening of s wave seismogram envelopes
Journal of Geophysical Research, 1995Co-Authors: Kazushige Obara, Haruo SatoAbstract:Broadening of seismogram envelopes around direct S waves of deep earthquakes that occurred in a lithospheric slab reveals random inhomogeneities in the upper mantle and crust. Regional differences in the character of envelope broadening were studied in relation to the volcanic front in the central part of Japan. A total of 58 earthquakes that occurred along the subducting Pacific plate ranging from 80 to 500 km in depth were observed at 73 stations of the Kanto-Tokai seismic observation network and used in this analysis. Time lags of the maximum peak arrival and the half-maximum arrival were measured from the onset of the direct S wave on root-mean-squared traces of horizontal component seismograms in frequency bands of 1, 2, 4, and 8 Hz. The envelope broadening is weak at stations located along the coastline of the Pacific Ocean, however, the dependence of time lags on the hypocentral distance and frequency becomes strong at stations near the volcanic front. Moreover, the time lags become very long with increasing hypocentral distances and frequencies west of the volcanic front. This broadening of the seismogram envelope can be interpreted as the effect of the diffraction and multiple forward scattering on the seismic wave propagation through random inhomogeneities. The Parabolic Approximation is applied to simulate the envelope broadening when the correlation distance of velocity inhomogeneities is longer than the seismic wavelength. The numerical simulation indicates that the dependence of the envelope broadening on the travel distance and frequency depends greatly on the type of the autocorrelation function for the randomness. By comparing the observed frequency dependence of the envelope broadening with the result of the numerical simulation, the type of the autocorrelation function was estimated to be close to Gaussian at stations east of the volcanic front and close to exponential west of the volcanic front. The regional difference in the randomness on both sides of the volcanic front might reflect the difference in the short-wavelength component inhomogeneities.
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inversion of full seismogram envelopes based on the Parabolic Approximation estimation of randomness and attenuation in southeast honshu japan
Journal of Geophysical Research, 1991Co-Authors: Frank Scherbaum, Haruo SatoAbstract:The envelope shape around the arrival of the direct waves of seismic signals traveling in a randomly inhomogeneous medium has been predicted, based on the Parabolic Approximation, to be a measure of the long-wavelength components of the randomness as well as the attenuation properties of the medium. We use a nonlinear Marquardt-Levenberg inversion technique in order to model the SH wave envelopes of 119 earthquakes in the frequency band 2–6 Hz for lapse times less than 1.5 times the shear wave travel time. We attempted to obtain the ratio of the mean square fractional velocity fluctuation to the correlation length (e2V/a) estimates as well as estimates of attenuation Qs−1. For the majority of the events we found a good correlation between the envelope shape and the hypocentral distances. The resultant e2V/a of 10−3.27±0.32 km−1 is independent of frequency. It agrees well with the choice of the Gaussian autocorrelation function for the long-wavelength components of the random velocity fluctuations. The resultant attenuation Qs−1 is roughly proportional to the reciprocal of frequency. We may interpret it as either the scattering loss due to short-wavelength components of randomness or intrinsic loss. We have performed numerical simulations of the inversion process to quantify the model parameter uncertainties and to obtain a better understanding of the model parameter resolution. By modeling the wave envelopes as a superposition of noise-free wave envelopes and band-pass-filtered Gaussian noise we were able to reproduce the visual appearance of the observed envelopes as well as the observed features in the model parameter dependency. We find that for long hypocentral distances the envelope shape is controlled by the attenuation coefficient, while for short hypocentral distances the velocity fluctuations contribute dominantly.
Amir M. Sodagar - One of the best experts on this subject based on the ideXlab platform.
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a pipelined rom less architecture for sine output direct digital frequency synthesizers using the second order Parabolic Approximation
IEEE Transactions on Circuits and Systems Ii: Analog and Digital Signal Processing, 2001Co-Authors: Amir M. Sodagar, G.r. LahijiAbstract:A mathematical Approximation for the sine function is proposed which is so close to the sine function that it satisfies the accuracy requirements for sine computation in a typical sine-output direct digital frequency synthesizers (DDS). Then, it is shown that the proposed Approximation is realizable by standard digital circuitry, so, a novel ROM-less architecture for sine-output DDS is developed, optimized, and implemented. Experimental results for the implemented ROM-less sine-output DDS are in complete agreement with simulation results in showing that the Approximation error will cause harmonic levels below the spurious levels associated with the output quantization error. Another important advantage of the proposed architecture is that it dispenses with ROM, so it can be easily pipelined in order to be as fast as is required.
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mapping from phase to sine amplitude in direct digital frequency synthesizers using Parabolic Approximation
IEEE Transactions on Circuits and Systems Ii: Analog and Digital Signal Processing, 2000Co-Authors: Amir M. Sodagar, Roientan G LahijiAbstract:This paper describes a new approach in sine-amplitude Approximation for sine-output direct digital frequency synthesizers, which provides an initial guess much closer to the target sine amplitude than previous Approximations. Another important advantage of the proposed idea is that it can be simply implemented using full-digital circuitry. Gate- and transistor-level simulations demonstrate the feasibility of the idea, and the simulation results are in complete agreement with the experimental results for the implemented test architecture.
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a novel architecture for rom less sine output direct digital frequency synthesizers by using the 2 sup nd order Parabolic Approximation
International Frequency Control Symposium, 2000Co-Authors: Amir M. Sodagar, G RoientanAbstract:An extended form of the Parabolic Approximation, which was previously introduced by the authors, is proposed. The proposed form of the Approximation is so close to the sine function that satisfies the accuracy requirements for a typical sine-output DDFS. Then, the Approximation is used to develop a novel ROM-less architecture for sine-output direct digital frequency synthesizers. Based on the optimized architecture, an experimental test system is developed. Experimental results for the implemented ROM-less sine-output Parabolic DDFS show that the Approximation error will cause harmonic levels below the spurious level associated with the output quantization.
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Parabolic Approximation a new method for phase to amplitude conversion in sine output direct digital frequency synthesizers
International Symposium on Circuits and Systems, 2000Co-Authors: Amir M. Sodagar, G.r. LahijiAbstract:A new approach in sine amplitude Approximation for sine-output direct digital frequency synthesizers "Parabolic Approximation" is presented. The proposed Approximation provides an initial guess, which is much closer to the target sine amplitude than previous Approximations and can be simply implemented using full-digital circuitry.
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a new initial guess for sine function dedicated to sine output direct digital frequency synthesizers
IEEE International Caracas Conference on Devices Circuits and Systems, 2000Co-Authors: Amir M. Sodagar, G.r. LahijiAbstract:A new approach in sine amplitude Approximation for sine-output direct digital frequency synthesizers "Parabolic Approximation" is presented. The proposed Approximation provides an initial guess, which is very much closer to the target sine amplitude than previous Approximations and can be simply implemented using full-digital circuitry.
G.r. Lahiji - One of the best experts on this subject based on the ideXlab platform.
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a pipelined rom less architecture for sine output direct digital frequency synthesizers using the second order Parabolic Approximation
IEEE Transactions on Circuits and Systems Ii: Analog and Digital Signal Processing, 2001Co-Authors: Amir M. Sodagar, G.r. LahijiAbstract:A mathematical Approximation for the sine function is proposed which is so close to the sine function that it satisfies the accuracy requirements for sine computation in a typical sine-output direct digital frequency synthesizers (DDS). Then, it is shown that the proposed Approximation is realizable by standard digital circuitry, so, a novel ROM-less architecture for sine-output DDS is developed, optimized, and implemented. Experimental results for the implemented ROM-less sine-output DDS are in complete agreement with simulation results in showing that the Approximation error will cause harmonic levels below the spurious levels associated with the output quantization error. Another important advantage of the proposed architecture is that it dispenses with ROM, so it can be easily pipelined in order to be as fast as is required.
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Parabolic Approximation a new method for phase to amplitude conversion in sine output direct digital frequency synthesizers
International Symposium on Circuits and Systems, 2000Co-Authors: Amir M. Sodagar, G.r. LahijiAbstract:A new approach in sine amplitude Approximation for sine-output direct digital frequency synthesizers "Parabolic Approximation" is presented. The proposed Approximation provides an initial guess, which is much closer to the target sine amplitude than previous Approximations and can be simply implemented using full-digital circuitry.
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a new initial guess for sine function dedicated to sine output direct digital frequency synthesizers
IEEE International Caracas Conference on Devices Circuits and Systems, 2000Co-Authors: Amir M. Sodagar, G.r. LahijiAbstract:A new approach in sine amplitude Approximation for sine-output direct digital frequency synthesizers "Parabolic Approximation" is presented. The proposed Approximation provides an initial guess, which is very much closer to the target sine amplitude than previous Approximations and can be simply implemented using full-digital circuitry.
A Fiasconaro - One of the best experts on this subject based on the ideXlab platform.
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single particle spectrum and binding energy of nuclear matter
Physics Letters B, 2000Co-Authors: M Baldo, A FiasconaroAbstract:Abstract In non-relativistic Brueckner calculations of nuclear matter, the self-consistent single particle potential is strongly momentum dependent. To simplify the calculations, a Parabolic Approximation is often used in the literature. The variation in the binding energy value introduced by the Parabolic Approximation is quantitatively analyzed in detail. It is found that the Approximation can introduce an uncertainty at best of 1–2 MeV already around the saturation density, and therefore it should be avoided in Brueckner calculations.
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single particle spectrum and binding energy of nuclear matter
arXiv: Nuclear Theory, 2000Co-Authors: M Baldo, A FiasconaroAbstract:In non-relativistic Brueckner calculations of nuclear matter, the self-consistent single particle potential is strongly momentum dependent. To simplify the calculations, a Parabolic Approximation is often used in the literature. The variation in the binding energy value introduced by the Parabolic Approximation is quantitatively analyzed in detail. It is found that the Approximation can introduce an uncertainty of 1-2 MeV near the saturation density.
M Baldo - One of the best experts on this subject based on the ideXlab platform.
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single particle spectrum and binding energy of nuclear matter
Physics Letters B, 2000Co-Authors: M Baldo, A FiasconaroAbstract:Abstract In non-relativistic Brueckner calculations of nuclear matter, the self-consistent single particle potential is strongly momentum dependent. To simplify the calculations, a Parabolic Approximation is often used in the literature. The variation in the binding energy value introduced by the Parabolic Approximation is quantitatively analyzed in detail. It is found that the Approximation can introduce an uncertainty at best of 1–2 MeV already around the saturation density, and therefore it should be avoided in Brueckner calculations.
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single particle spectrum and binding energy of nuclear matter
arXiv: Nuclear Theory, 2000Co-Authors: M Baldo, A FiasconaroAbstract:In non-relativistic Brueckner calculations of nuclear matter, the self-consistent single particle potential is strongly momentum dependent. To simplify the calculations, a Parabolic Approximation is often used in the literature. The variation in the binding energy value introduced by the Parabolic Approximation is quantitatively analyzed in detail. It is found that the Approximation can introduce an uncertainty of 1-2 MeV near the saturation density.
