The Experts below are selected from a list of 23847 Experts worldwide ranked by ideXlab platform
Lang Shao - One of the best experts on this subject based on the ideXlab platform.
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a new measurement of the spectral lag of gamma ray bursts and its implications for spectral evolution behaviors
The Astrophysical Journal, 2017Co-Authors: Lang Shao, Binbin Zhang, Furi Wang, Yehao Cheng, Xi Zhang, Xue Wang, Huanxue Feng, Meng ZhangAbstract:We carry out a systematical study of the spectral lag properties of 50 single-Pulsed gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor. By dividing the light curves into multiple consecutive energy channels, we provide a new measurement of the spectral lag that is independent of energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the Pulse arrival time and Pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical framework that can fully account for the diverse energy dependencies of both arrival time and Pulse width revealed in this work is still lacking. We also study the spectral evolution behaviors of the GRB Pulses. We find that a GRB Pulse with negligible spectral lag would usually have a shorter Pulse duration and would appear to have a "hardness-intensity tracking" behavior, and a GRB Pulse with a significant spectral lag would usually have a Longer Pulse duration and would appear to have a "hard-to-soft" behavior.
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a new measurement of the spectral lag of gamma ray bursts and its implications for spectral evolution behaviors
arXiv: High Energy Astrophysical Phenomena, 2016Co-Authors: Lang Shao, Binbin Zhang, Furi Wang, Yehao Cheng, Xi Zhang, Xue Wang, Huanxue Feng, Meng ZhangAbstract:We carry out a systematical study of the spectral lag properties of 50 single-Pulsed Gamma-Ray Bursts (GRBs) detected by Fermi/GBM. By dividing the light curves into multiple consecutive energy channels we provide a new measurement of the spectral lag which is independent on energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the Pulse arrival time and Pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical framework that can fully account for the diverse energy dependencies of both arrival time and Pulse width revealed in this work is still missing. We also study the spectral evolution behaviors of the GRB Pulses. We find that the GRB Pulse with negligible spectral lag would usually have a shorter Pulse duration and would appear to have a "hardness-intensity tracking" (HIT) behavior and the GRB Pulse with a significant spectral lag would usually have a Longer Pulse duration and would appear to have a "hard-to-soft" (HTS) behavior.
J V Moloney - One of the best experts on this subject based on the ideXlab platform.
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memory effects in the long wave infrared avalanche ionization of gases a review of recent progress
Reports on Progress in Physics, 2019Co-Authors: E M Wright, S W Koch, M Kolesik, J V MoloneyAbstract:There are currently intense efforts being directed towards extending the range and energy of long distance nonlinear Pulse propagation in the atmosphere by moving to Longer infrared wavelengths, with the purpose of mitigating the effects of turbulence. In addition, picosecond and Longer Pulse durations are being used to increase the Pulse energy. While both of these tacks promise improvements in applications, such as remote sensing and directed energy, they open up fundamental issues regarding the standard model used to calculate the nonlinear optical properties of dilute gases. Amongst these issues is that for Longer wavelengths and Longer Pulse durations, exponential growth of the laser-generated electron density, the so-called avalanche ionization, can limit the propagation range via nonlinear absorption and plasma defocusing. It is therefore important for the continued development of the field to assess the theory and role of avalanche ionization in gases for Longer wavelengths. Here, after an overview of the standard model, we present a microscopically motivated approach for the analysis of avalanche ionization in gases that extends beyond the standard model and we contend is key for deepening our understanding of long distance propagation at long infrared wavelengths. Our new approach involves the mean electron kinetic energy, the plasma temperature, and the free electron density as dynamic variables. The rate of avalanche ionization is shown to depend on the full time history of the Pulsed excitation, as opposed to the standard model in which the rate is proportional to the instantaneous intensity. Furthermore, the new approach has the added benefit that it is no more computationally intensive than the standard one. The resulting memory effects and some of their measurable physical consequences are demonstrated for the example of long-wavelength infrared avalanche ionization and long distance high-intensity Pulse propagation in air. Our hope is that this report in progress will stimulate further discussion that will elucidate the physics and simulation of avalanche ionization at long infrared wavelengths and advance the field.
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memory effects in the long wave infrared avalanche ionization of gases a review of recent progress
arXiv: Optics, 2018Co-Authors: E M Wright, S W Koch, M Kolesik, J V MoloneyAbstract:There are currently intense efforts being directed towards extending the range and energy of long distance nonlinear Pulse propagation in the atmosphere by moving to Longer infrared wavelengths, with the purpose of mitigating the effects of turbulence. In addition, picosecond and Longer Pulse durations are being used to increase the Pulse energy. While both of these tacks promise improvements in applications, such as remote sensing and directed energy, they open up fundamental issues regarding the standard model used to calculate the nonlinear optical properties of dilute gases. Amongst these issues is that for Longer wavelengths and Longer Pulse durations, exponential growth of the laser-generated electron density, the so-called avalanche ionization, can limit the propagation range via nonlinear absorption and plasma defocusing. It is therefore important for the continued development of the field to assess the theory and role of avalanche ionization in gases for Longer wavelengths. Here, after an overview of the standard model, we present a microscopically motivated approach for the analysis of avalanche ionization in gases that extends beyond the standard model and we contend is key for deepening our understanding of long distance propagation at long infrared wavelengths. Our new approach involves the mean electron kinetic energy, the plasma temperature, and the free electron density as dynamic variables. The rate of avalanche ionization is shown to depend on the full time history of the Pulsed excitation, as opposed to the standard model in which the rate is proportional to the instantaneous intensity.
Kâmil Ugurbil - One of the best experts on this subject based on the ideXlab platform.
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multiband multislice ge epi at 7 tesla with 16 fold acceleration using partial parallel imaging with application to high spatial and temporal whole brain fmri
Magnetic Resonance in Medicine, 2010Co-Authors: Steen Moeller, Essa Yacoub, Cheryl A Olman, Edward J Auerbach, John Strupp, Noam Harel, Kâmil UgurbilAbstract:Parallel imaging in the form of multiband radiofrequency excitation, together with reduced k-space coverage in the phase-encode direction, was applied to human gradient echo functional MRI at 7 T for increased volumetric coverage and concurrent high spatial and temporal resolution. Echo planar imaging with simultaneous acquisition of four coronal slices separated by 44mm and simultaneous 4-fold phase-encoding undersampling, resulting in 16-fold acceleration and up to 16-fold maximal aliasing, was investigated. Task/stimulus-induced signal changes and temporal signal behavior under basal conditions were comparable for multiband and standard single-band excitation and Longer Pulse repetition times. Robust, whole-brain functional mapping at 7 T, with 2 x 2 x 2mm(3) (Pulse repetition time 1.25 sec) and 1 x 1 x 2mm(3) (Pulse repetition time 1.5 sec) resolutions, covering fields of view of 256 x 256 x 176 mm(3) and 192 x 172 x 176 mm(3), respectively, was demonstrated with current gradient performance.
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multiband multislice ge epi at 7 tesla with 16 fold acceleration using partial parallel imaging with application to high spatial and temporal whole brain fmri
Magnetic Resonance in Medicine, 2010Co-Authors: Steen Moeller, Essa Yacoub, Cheryl A Olman, Edward J Auerbach, John Strupp, Noam Harel, Kâmil UgurbilAbstract:Parallel imaging in the form of multiband radiofrequency excitation, together with reduced k-space coverage in the phase-encode direction, was applied to human gradient echo functional MRI at 7 T for increased volumetric coverage and concurrent high spatial and temporal resolution. Echo planar imaging with simultaneous acquisition of four coronal slices separated by 44mm and simultaneous 4-fold phase-encoding undersampling, resulting in 16-fold acceleration and up to 16-fold maximal aliasing, was investigated. Task/stimulus-induced signal changes and temporal signal behavior under basal conditions were comparable for multiband and standard single-band excitation and Longer Pulse repetition times. Robust, whole-brain functional mapping at 7 T, with 2 x 2 x 2mm(3) (Pulse repetition time 1.25 sec) and 1 x 1 x 2mm(3) (Pulse repetition time 1.5 sec) resolutions, covering fields of view of 256 x 256 x 176 mm(3) and 192 x 172 x 176 mm(3), respectively, was demonstrated with current gradient performance.
Meng Zhang - One of the best experts on this subject based on the ideXlab platform.
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a new measurement of the spectral lag of gamma ray bursts and its implications for spectral evolution behaviors
The Astrophysical Journal, 2017Co-Authors: Lang Shao, Binbin Zhang, Furi Wang, Yehao Cheng, Xi Zhang, Xue Wang, Huanxue Feng, Meng ZhangAbstract:We carry out a systematical study of the spectral lag properties of 50 single-Pulsed gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor. By dividing the light curves into multiple consecutive energy channels, we provide a new measurement of the spectral lag that is independent of energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the Pulse arrival time and Pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical framework that can fully account for the diverse energy dependencies of both arrival time and Pulse width revealed in this work is still lacking. We also study the spectral evolution behaviors of the GRB Pulses. We find that a GRB Pulse with negligible spectral lag would usually have a shorter Pulse duration and would appear to have a "hardness-intensity tracking" behavior, and a GRB Pulse with a significant spectral lag would usually have a Longer Pulse duration and would appear to have a "hard-to-soft" behavior.
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a new measurement of the spectral lag of gamma ray bursts and its implications for spectral evolution behaviors
arXiv: High Energy Astrophysical Phenomena, 2016Co-Authors: Lang Shao, Binbin Zhang, Furi Wang, Yehao Cheng, Xi Zhang, Xue Wang, Huanxue Feng, Meng ZhangAbstract:We carry out a systematical study of the spectral lag properties of 50 single-Pulsed Gamma-Ray Bursts (GRBs) detected by Fermi/GBM. By dividing the light curves into multiple consecutive energy channels we provide a new measurement of the spectral lag which is independent on energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the Pulse arrival time and Pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical framework that can fully account for the diverse energy dependencies of both arrival time and Pulse width revealed in this work is still missing. We also study the spectral evolution behaviors of the GRB Pulses. We find that the GRB Pulse with negligible spectral lag would usually have a shorter Pulse duration and would appear to have a "hardness-intensity tracking" (HIT) behavior and the GRB Pulse with a significant spectral lag would usually have a Longer Pulse duration and would appear to have a "hard-to-soft" (HTS) behavior.
Huanxue Feng - One of the best experts on this subject based on the ideXlab platform.
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a new measurement of the spectral lag of gamma ray bursts and its implications for spectral evolution behaviors
The Astrophysical Journal, 2017Co-Authors: Lang Shao, Binbin Zhang, Furi Wang, Yehao Cheng, Xi Zhang, Xue Wang, Huanxue Feng, Meng ZhangAbstract:We carry out a systematical study of the spectral lag properties of 50 single-Pulsed gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor. By dividing the light curves into multiple consecutive energy channels, we provide a new measurement of the spectral lag that is independent of energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the Pulse arrival time and Pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical framework that can fully account for the diverse energy dependencies of both arrival time and Pulse width revealed in this work is still lacking. We also study the spectral evolution behaviors of the GRB Pulses. We find that a GRB Pulse with negligible spectral lag would usually have a shorter Pulse duration and would appear to have a "hardness-intensity tracking" behavior, and a GRB Pulse with a significant spectral lag would usually have a Longer Pulse duration and would appear to have a "hard-to-soft" behavior.
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a new measurement of the spectral lag of gamma ray bursts and its implications for spectral evolution behaviors
arXiv: High Energy Astrophysical Phenomena, 2016Co-Authors: Lang Shao, Binbin Zhang, Furi Wang, Yehao Cheng, Xi Zhang, Xue Wang, Huanxue Feng, Meng ZhangAbstract:We carry out a systematical study of the spectral lag properties of 50 single-Pulsed Gamma-Ray Bursts (GRBs) detected by Fermi/GBM. By dividing the light curves into multiple consecutive energy channels we provide a new measurement of the spectral lag which is independent on energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the Pulse arrival time and Pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical framework that can fully account for the diverse energy dependencies of both arrival time and Pulse width revealed in this work is still missing. We also study the spectral evolution behaviors of the GRB Pulses. We find that the GRB Pulse with negligible spectral lag would usually have a shorter Pulse duration and would appear to have a "hardness-intensity tracking" (HIT) behavior and the GRB Pulse with a significant spectral lag would usually have a Longer Pulse duration and would appear to have a "hard-to-soft" (HTS) behavior.
