The Experts below are selected from a list of 132 Experts worldwide ranked by ideXlab platform
Mohamad Shalaby - One of the best experts on this subject based on the ideXlab platform.
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importance of resolving the Spectral Support of beam plasma instabilities in simulations
The Astrophysical Journal, 2017Co-Authors: Mohamad Shalaby, Avery E Broderick, Philip Chang, Christoph Pfrommer, Astrid Lamberts, Ewald PuchweinAbstract:Many astrophysical plasmas are prone to beam-plasma instabilities. For relativistic and dilute beams, the Spectral Support of the beam-plasma instabilities is narrow, i.e., the linearly unstable modes that grow with rates comparable to the maximum growth rate occupy a narrow range of wavenumbers. This places stringent requirements on the box-sizes when simulating the evolution of the instabilities. We identify the implied lower limits on the box size imposed by the longitudinal beam plasma instability, i.e., typically the most stringent condition required to correctly capture the linear evolution of the instabilities in multidimensional simulations. We find that sizes many orders of magnitude larger than the resonant wavelength are typically required. Using one-dimensional particle-in-cell simulations, we show that the failure to sufficiently resolve the Spectral Support of the longitudinal instability yields slower growth and lower levels of saturation, potentially leading to erroneous physical conclusion.
Yoram Bresler - One of the best experts on this subject based on the ideXlab platform.
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optimal sub nyquist nonuniform sampling and reconstruction for multiband signals
IEEE Transactions on Signal Processing, 2001Co-Authors: R Venkataramani, Yoram BreslerAbstract:We study the problem of optimal sub-Nyquist sampling for perfect reconstruction of multiband signals. The signals are assumed to have a known Spectral Support /spl Fscr/ that does not tile under translation. Such signals admit perfect reconstruction from periodic nonuniform sampling at rates approaching Landau's (1967) lower bound equal to the measure of /spl Fscr/. For signals with sparse /spl Fscr/, this rate can be much smaller than the Nyquist rate. Unfortunately the reduced sampling rates afforded by this scheme can be accompanied by increased error sensitivity. In a previous study, we derived bounds on the error due to mismodeling and sample additive noise. Adopting these bounds as performance measures, we consider the problems of optimizing the reconstruction sections of the system, choosing the optimal base sampling rate, and designing the nonuniform sampling pattern. We find that optimizing these parameters can improve system performance significantly. Furthermore, uniform sampling is optimal for signals with /spl Fscr/ that tiles under translation. For signals with nontiling /spl Fscr/, which are not amenable to efficient uniform sampling, the results reveal increased error sensitivities with sub-Nyquist sampling. However, these can be controlled by optimal design, demonstrating the potential for practical multifold reductions in sampling rate.
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perfect reconstruction formulas and bounds on aliasing error in sub nyquist nonuniform sampling of multiband signals
IEEE Transactions on Information Theory, 2000Co-Authors: R Venkataramani, Yoram BreslerAbstract:We examine the problem of periodic nonuniform sampling of a multiband signal and its reconstruction from the samples. This sampling scheme, which has been studied previously, has an interesting optimality property that uniform sampling lacks: one can sample and reconstruct the class /spl Bscr/(/spl Fscr/) of multiband signals with Spectral Support /spl Fscr/, at rates arbitrarily close to the Landau (1969) minimum rate equal to the Lebesgue measure of /spl Fscr/, even when /spl Fscr/ does not tile R under translation. Using the conditions for exact reconstruction, we derive an explicit reconstruction formula. We compute bounds on the peak value and the energy of the aliasing error in the event that the input signal is band-limited to the "span of /spl Fscr/" (the smallest interval containing /spl Fscr/) which is a bigger class than the valid signals /spl Bscr/(/spl Fscr/), band-limited to /spl Fscr/. We also examine the performance of the reconstruction system when the input contains additive sample noise.
Ewald Puchwein - One of the best experts on this subject based on the ideXlab platform.
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importance of resolving the Spectral Support of beam plasma instabilities in simulations
The Astrophysical Journal, 2017Co-Authors: Mohamad Shalaby, Avery E Broderick, Philip Chang, Christoph Pfrommer, Astrid Lamberts, Ewald PuchweinAbstract:Many astrophysical plasmas are prone to beam-plasma instabilities. For relativistic and dilute beams, the Spectral Support of the beam-plasma instabilities is narrow, i.e., the linearly unstable modes that grow with rates comparable to the maximum growth rate occupy a narrow range of wavenumbers. This places stringent requirements on the box-sizes when simulating the evolution of the instabilities. We identify the implied lower limits on the box size imposed by the longitudinal beam plasma instability, i.e., typically the most stringent condition required to correctly capture the linear evolution of the instabilities in multidimensional simulations. We find that sizes many orders of magnitude larger than the resonant wavelength are typically required. Using one-dimensional particle-in-cell simulations, we show that the failure to sufficiently resolve the Spectral Support of the longitudinal instability yields slower growth and lower levels of saturation, potentially leading to erroneous physical conclusion.
R Venkataramani - One of the best experts on this subject based on the ideXlab platform.
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optimal sub nyquist nonuniform sampling and reconstruction for multiband signals
IEEE Transactions on Signal Processing, 2001Co-Authors: R Venkataramani, Yoram BreslerAbstract:We study the problem of optimal sub-Nyquist sampling for perfect reconstruction of multiband signals. The signals are assumed to have a known Spectral Support /spl Fscr/ that does not tile under translation. Such signals admit perfect reconstruction from periodic nonuniform sampling at rates approaching Landau's (1967) lower bound equal to the measure of /spl Fscr/. For signals with sparse /spl Fscr/, this rate can be much smaller than the Nyquist rate. Unfortunately the reduced sampling rates afforded by this scheme can be accompanied by increased error sensitivity. In a previous study, we derived bounds on the error due to mismodeling and sample additive noise. Adopting these bounds as performance measures, we consider the problems of optimizing the reconstruction sections of the system, choosing the optimal base sampling rate, and designing the nonuniform sampling pattern. We find that optimizing these parameters can improve system performance significantly. Furthermore, uniform sampling is optimal for signals with /spl Fscr/ that tiles under translation. For signals with nontiling /spl Fscr/, which are not amenable to efficient uniform sampling, the results reveal increased error sensitivities with sub-Nyquist sampling. However, these can be controlled by optimal design, demonstrating the potential for practical multifold reductions in sampling rate.
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perfect reconstruction formulas and bounds on aliasing error in sub nyquist nonuniform sampling of multiband signals
IEEE Transactions on Information Theory, 2000Co-Authors: R Venkataramani, Yoram BreslerAbstract:We examine the problem of periodic nonuniform sampling of a multiband signal and its reconstruction from the samples. This sampling scheme, which has been studied previously, has an interesting optimality property that uniform sampling lacks: one can sample and reconstruct the class /spl Bscr/(/spl Fscr/) of multiband signals with Spectral Support /spl Fscr/, at rates arbitrarily close to the Landau (1969) minimum rate equal to the Lebesgue measure of /spl Fscr/, even when /spl Fscr/ does not tile R under translation. Using the conditions for exact reconstruction, we derive an explicit reconstruction formula. We compute bounds on the peak value and the energy of the aliasing error in the event that the input signal is band-limited to the "span of /spl Fscr/" (the smallest interval containing /spl Fscr/) which is a bigger class than the valid signals /spl Bscr/(/spl Fscr/), band-limited to /spl Fscr/. We also examine the performance of the reconstruction system when the input contains additive sample noise.
Avery E Broderick - One of the best experts on this subject based on the ideXlab platform.
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importance of resolving the Spectral Support of beam plasma instabilities in simulations
The Astrophysical Journal, 2017Co-Authors: Mohamad Shalaby, Avery E Broderick, Philip Chang, Christoph Pfrommer, Astrid Lamberts, Ewald PuchweinAbstract:Many astrophysical plasmas are prone to beam-plasma instabilities. For relativistic and dilute beams, the Spectral Support of the beam-plasma instabilities is narrow, i.e., the linearly unstable modes that grow with rates comparable to the maximum growth rate occupy a narrow range of wavenumbers. This places stringent requirements on the box-sizes when simulating the evolution of the instabilities. We identify the implied lower limits on the box size imposed by the longitudinal beam plasma instability, i.e., typically the most stringent condition required to correctly capture the linear evolution of the instabilities in multidimensional simulations. We find that sizes many orders of magnitude larger than the resonant wavelength are typically required. Using one-dimensional particle-in-cell simulations, we show that the failure to sufficiently resolve the Spectral Support of the longitudinal instability yields slower growth and lower levels of saturation, potentially leading to erroneous physical conclusion.