The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Anatoly Spitkovsky - One of the best experts on this subject based on the ideXlab platform.
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Particle in cell simulations of a nonlinear transverse electromagnetic wave in a pulsar wind termination shock
The Astrophysical Journal, 2005Co-Authors: Olaf Skjaeraasen, A Melatos, Anatoly SpitkovskyAbstract:A 2.5-dimensional Particle-in-cell code is used to investigate the propagation of a large-amplitude, superluminal, nearly transverse electromagnetic (TEM) wave in a relativistically streaming electron-positron plasma with and without a shock. In the freestreaming, unshocked case, the analytic TEM dispersion relation is verified, and the streaming is shown to stabilize the wave against parametric instabilities. In the confined, shocked case, the wave induces strong, Coherent Particle oscillations, heats the plasma, and modifies the shock density profile via ponderomotive effects. The wave decays over {approx}> 10{sup 2} skin depths; the decay length scale depends primarily on the ratio between the wave frequency and the effective plasma frequency, and on the wave amplitude. The results are applied to the termination shock of the Crab pulsar wind, where the decay length-scale ({approx}> 0.05''?) might be comparable to the thickness of filamentary, variable substructure observed in the optical and X-ray wisps and knots.
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Particle in cell simulations of a nonlinear transverse electromagnetic wave in a pulsar wind termination shock
arXiv: Astrophysics, 2005Co-Authors: Olaf Skjaeraasen, A Melatos, Anatoly SpitkovskyAbstract:A 2.5-dimensional Particle-in-cell code is used to investigate the propagation of a large-amplitude, superluminal, nearly transverse electromagnetic (TEM) wave in a relativistically streaming electron-positron plasma with and without a shock. In the freestreaming, unshocked case, the analytic TEM dispersion relation is verified, and the streaming is shown to stabilize the wave against parametric instabilities. In the confined, shocked case, the wave induces strong, Coherent Particle oscillations, heats the plasma, and modifies the shock density profile via ponderomotive effects. The wave decays over $\gtrsim 10^2$ skin depths; the decay length scale depends primarily on the ratio between the wave frequency and the effective plasma frequency, and on the wave amplitude. The results are applied to the termination shock of the Crab pulsar wind, where the decay length-scale (at least 0.05") might be comparable to the thickness of filamentary, variable substructure observed in the optical and X-ray wisps and knots.
Gerhard Baur - One of the best experts on this subject based on the ideXlab platform.
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Coherent Particle production in relativistic heavy ion collisions
Nuclear Physics A, 1992Co-Authors: Gerhard BaurAbstract:Abstract Coherent Particle production via the γ-γ mechanism occurs in disruptive as well as non-disruptive relativistic heavy ion collisions. Due to the enhancement factor of Z4, relativistic heavy ion colliders may compete with e+e− colliders in the study of γ-γ physics. To reduce the strong backgroun, non-disruptive collisions must be selected. In disruptive collisions, the dilepton production via Coherent γ-γ processes is calculated, as a function of the impact parameter. Cross-sections are large, comparable to those expected from thermal and Drell-Yan mechanisms. However, the very low p⊥-values will allow a discrimination.
Tony J Prescott - One of the best experts on this subject based on the ideXlab platform.
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hippocampus as unitary Coherent Particle filter
International Joint Conference on Neural Network, 2010Co-Authors: Charles Fox, Tony J PrescottAbstract:We present a mapping of the hippocampal formation onto a Temporal Restricted Boltzmann Machine [1] based architecture, running a deterministic version of Gibbs sampling, and extended with a lostness detection and recovery circuit modelled on subiculum and septal acetylcholine (ACh). The mapping approximates Bayesian filtering, which infers both auto-associative de-noised percepts and temporal sequences, the latter including sequences of places during navigation. Inference may be viewed as a neurally implemented Particle filter with a single Particle - as suggested previously [2] as a purely behavioural animal model.
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IJCNN - Hippocampus as unitary Coherent Particle filter
The 2010 International Joint Conference on Neural Networks (IJCNN), 2010Co-Authors: Charles Fox, Tony J PrescottAbstract:We present a mapping of the hippocampal formation onto a Temporal Restricted Boltzmann Machine [1] based architecture, running a deterministic version of Gibbs sampling, and extended with a lostness detection and recovery circuit modelled on subiculum and septal acetylcholine (ACh). The mapping approximates Bayesian filtering, which infers both auto-associative de-noised percepts and temporal sequences, the latter including sequences of places during navigation. Inference may be viewed as a neurally implemented Particle filter with a single Particle - as suggested previously [2] as a purely behavioural animal model.
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Hippocampal formation as unitary Coherent Particle filter
BMC Neuroscience, 2009Co-Authors: Charles Fox, Tony J PrescottAbstract:A standard approach to localization, recall and prediction from sensors is the Hidden Markov Model (HMM, [1]), with location as hidden state and sense data as observations. Assuming that hippocampus performs a similar task, we present a new top-down mapping of this function onto its anatomy. In localization models of CA3 [2], firing rates of individual place cells encode probabilities over current location and recurrent connections may represent transitions probabilities between them. In auto-associative models [3], recurrent connections bring the network into a vector-coded memorized state. The existence of cells encoding rewards and locations of external objects supports this view [3].
Olaf Skjaeraasen - One of the best experts on this subject based on the ideXlab platform.
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Particle in cell simulations of a nonlinear transverse electromagnetic wave in a pulsar wind termination shock
The Astrophysical Journal, 2005Co-Authors: Olaf Skjaeraasen, A Melatos, Anatoly SpitkovskyAbstract:A 2.5-dimensional Particle-in-cell code is used to investigate the propagation of a large-amplitude, superluminal, nearly transverse electromagnetic (TEM) wave in a relativistically streaming electron-positron plasma with and without a shock. In the freestreaming, unshocked case, the analytic TEM dispersion relation is verified, and the streaming is shown to stabilize the wave against parametric instabilities. In the confined, shocked case, the wave induces strong, Coherent Particle oscillations, heats the plasma, and modifies the shock density profile via ponderomotive effects. The wave decays over {approx}> 10{sup 2} skin depths; the decay length scale depends primarily on the ratio between the wave frequency and the effective plasma frequency, and on the wave amplitude. The results are applied to the termination shock of the Crab pulsar wind, where the decay length-scale ({approx}> 0.05''?) might be comparable to the thickness of filamentary, variable substructure observed in the optical and X-ray wisps and knots.
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Particle in cell simulations of a nonlinear transverse electromagnetic wave in a pulsar wind termination shock
arXiv: Astrophysics, 2005Co-Authors: Olaf Skjaeraasen, A Melatos, Anatoly SpitkovskyAbstract:A 2.5-dimensional Particle-in-cell code is used to investigate the propagation of a large-amplitude, superluminal, nearly transverse electromagnetic (TEM) wave in a relativistically streaming electron-positron plasma with and without a shock. In the freestreaming, unshocked case, the analytic TEM dispersion relation is verified, and the streaming is shown to stabilize the wave against parametric instabilities. In the confined, shocked case, the wave induces strong, Coherent Particle oscillations, heats the plasma, and modifies the shock density profile via ponderomotive effects. The wave decays over $\gtrsim 10^2$ skin depths; the decay length scale depends primarily on the ratio between the wave frequency and the effective plasma frequency, and on the wave amplitude. The results are applied to the termination shock of the Crab pulsar wind, where the decay length-scale (at least 0.05") might be comparable to the thickness of filamentary, variable substructure observed in the optical and X-ray wisps and knots.
Charles Fox - One of the best experts on this subject based on the ideXlab platform.
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hippocampus as unitary Coherent Particle filter
International Joint Conference on Neural Network, 2010Co-Authors: Charles Fox, Tony J PrescottAbstract:We present a mapping of the hippocampal formation onto a Temporal Restricted Boltzmann Machine [1] based architecture, running a deterministic version of Gibbs sampling, and extended with a lostness detection and recovery circuit modelled on subiculum and septal acetylcholine (ACh). The mapping approximates Bayesian filtering, which infers both auto-associative de-noised percepts and temporal sequences, the latter including sequences of places during navigation. Inference may be viewed as a neurally implemented Particle filter with a single Particle - as suggested previously [2] as a purely behavioural animal model.
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IJCNN - Hippocampus as unitary Coherent Particle filter
The 2010 International Joint Conference on Neural Networks (IJCNN), 2010Co-Authors: Charles Fox, Tony J PrescottAbstract:We present a mapping of the hippocampal formation onto a Temporal Restricted Boltzmann Machine [1] based architecture, running a deterministic version of Gibbs sampling, and extended with a lostness detection and recovery circuit modelled on subiculum and septal acetylcholine (ACh). The mapping approximates Bayesian filtering, which infers both auto-associative de-noised percepts and temporal sequences, the latter including sequences of places during navigation. Inference may be viewed as a neurally implemented Particle filter with a single Particle - as suggested previously [2] as a purely behavioural animal model.
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Hippocampal formation as unitary Coherent Particle filter
BMC Neuroscience, 2009Co-Authors: Charles Fox, Tony J PrescottAbstract:A standard approach to localization, recall and prediction from sensors is the Hidden Markov Model (HMM, [1]), with location as hidden state and sense data as observations. Assuming that hippocampus performs a similar task, we present a new top-down mapping of this function onto its anatomy. In localization models of CA3 [2], firing rates of individual place cells encode probabilities over current location and recurrent connections may represent transitions probabilities between them. In auto-associative models [3], recurrent connections bring the network into a vector-coded memorized state. The existence of cells encoding rewards and locations of external objects supports this view [3].