The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Qiugang Zong - One of the best experts on this subject based on the ideXlab platform.
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relativistic electron flux Dropouts in the outer radiation belt associated with corotating interaction regions
Journal of Geophysical Research, 2015Co-Authors: C J Yuan, Qiugang Zong, H Zhang, Aimin DuAbstract:Understanding how the relativistic electron fluxes drop out in the outer radiation belt under different conditions is of great importance. To investigate which mechanisms may affect the Dropouts under different solar wind conditions, 1.5–6.0 MeV electron flux Dropout events associated with 223 corotating interaction regions (CIRs) from 1994 to 2003 are studied using the observations of Solar, Anomalous, Magnetospheric Particle Explorer satellite. According to the superposed epoch analysis, it is found that high solar wind dynamic pressure with the peak median value of about 7 nPa is corresponding to the Dropout of the median of the radiation belt content (RBC) index to 20% of the level before stream interface arrival, whereas low dynamic pressure with the peak median value of about 3 nPa is related to the Dropout of the median of RBC index to 40% of the level before stream interface arrival. Furthermore, the influences of Russell-McPherron effect with respect to interplanetary magnetic field orientation on Dropouts are considered. It is pointed out that under positive Russell-McPherron effect (+RM effect) condition, the median of RBC index can drop to 23% of the level before stream interface arrival, while for negative Russell-McPherron effect (−RM effect) events, the median of RBC index only drops to 37% of the level before stream interface arrival. From the evolution of phase space density profiles, the effect of +RM on Dropouts can be through nonadiabatic loss.
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relativistic electron fluxes Dropout in the outer radiation belt under different solar wind conditions
Journal of Geophysical Research, 2013Co-Authors: C J Yuan, Qiugang ZongAbstract:[1] In this study, we apply superposed epoch analysis to the 1.5–6.0 MeV electron flux Dropout events observed on Solar, Anomalous, Magnetospheric Particle Explorer satellite for 110 magnetic storms related to coronal mass ejections (CMEs) associated with interplanetary shocks during 1998–2003, which can help to study one of the scientific objectives of the recently launched Van Allen Probe—to determine and quantify the mechanisms of the losses in the outer radiation belt. Results obtained in this paper show that the impact of high solar wind dynamic pressure (Pdy) on the magnetosphere would lead to much larger electron flux Dropout than low dynamic pressure. Furthermore, it is shown that southward interplanetary magnetic field (IMF) condition can result in more significant Dropout compared with northward IMF condition. In addition, the largest local Dropout is caused by high Pdy with northward IMF at L∼5.1. Dropouts under high Pdy and southward IMF conditions are the largest, whereas Dropouts under low Pdy and northward IMF conditions are the smallest. Our study tackles the problem of quantifying the Dropouts of electrons by calculating the radiation belt content index and finding the spatial distribution of Dropout and the location of maximum Dropout. Another finding is that Pdy and IMF affect the Dropouts in CME-driven storms. These new findings provide insight into which mechanisms play a more important role in different Dropout events.
C J Yuan - One of the best experts on this subject based on the ideXlab platform.
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relativistic electron flux Dropouts in the outer radiation belt associated with corotating interaction regions
Journal of Geophysical Research, 2015Co-Authors: C J Yuan, Qiugang Zong, H Zhang, Aimin DuAbstract:Understanding how the relativistic electron fluxes drop out in the outer radiation belt under different conditions is of great importance. To investigate which mechanisms may affect the Dropouts under different solar wind conditions, 1.5–6.0 MeV electron flux Dropout events associated with 223 corotating interaction regions (CIRs) from 1994 to 2003 are studied using the observations of Solar, Anomalous, Magnetospheric Particle Explorer satellite. According to the superposed epoch analysis, it is found that high solar wind dynamic pressure with the peak median value of about 7 nPa is corresponding to the Dropout of the median of the radiation belt content (RBC) index to 20% of the level before stream interface arrival, whereas low dynamic pressure with the peak median value of about 3 nPa is related to the Dropout of the median of RBC index to 40% of the level before stream interface arrival. Furthermore, the influences of Russell-McPherron effect with respect to interplanetary magnetic field orientation on Dropouts are considered. It is pointed out that under positive Russell-McPherron effect (+RM effect) condition, the median of RBC index can drop to 23% of the level before stream interface arrival, while for negative Russell-McPherron effect (−RM effect) events, the median of RBC index only drops to 37% of the level before stream interface arrival. From the evolution of phase space density profiles, the effect of +RM on Dropouts can be through nonadiabatic loss.
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relativistic electron fluxes Dropout in the outer radiation belt under different solar wind conditions
Journal of Geophysical Research, 2013Co-Authors: C J Yuan, Qiugang ZongAbstract:[1] In this study, we apply superposed epoch analysis to the 1.5–6.0 MeV electron flux Dropout events observed on Solar, Anomalous, Magnetospheric Particle Explorer satellite for 110 magnetic storms related to coronal mass ejections (CMEs) associated with interplanetary shocks during 1998–2003, which can help to study one of the scientific objectives of the recently launched Van Allen Probe—to determine and quantify the mechanisms of the losses in the outer radiation belt. Results obtained in this paper show that the impact of high solar wind dynamic pressure (Pdy) on the magnetosphere would lead to much larger electron flux Dropout than low dynamic pressure. Furthermore, it is shown that southward interplanetary magnetic field (IMF) condition can result in more significant Dropout compared with northward IMF condition. In addition, the largest local Dropout is caused by high Pdy with northward IMF at L∼5.1. Dropouts under high Pdy and southward IMF conditions are the largest, whereas Dropouts under low Pdy and northward IMF conditions are the smallest. Our study tackles the problem of quantifying the Dropouts of electrons by calculating the radiation belt content index and finding the spatial distribution of Dropout and the location of maximum Dropout. Another finding is that Pdy and IMF affect the Dropouts in CME-driven storms. These new findings provide insight into which mechanisms play a more important role in different Dropout events.
Wen-an Zhang - One of the best experts on this subject based on the ideXlab platform.
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moving horizon estimation for networked systems with quantized measurements and packet Dropouts
IEEE Transactions on Circuits and Systems, 2013Co-Authors: Andong Liu, Wen-an Zhang, Michael Z Q ChenAbstract:This paper is concerned with the moving horizon estimation (MHE) problem for linear discrete-time systems with limited communication, including quantized measurements and packet Dropouts. The measured output is quantized by a logarithmic quantizer and the packet Dropout phenomena is modeled by a binary switching random sequence. The main purpose of this paper is to design an estimator such that, for all possible quantized errors and packet Dropouts, the state estimation error sequence is convergent. By choosing a stochastic cost function, the optimal estimator is obtained by solving a regularized least-squares problem with uncertain parameters. The proposed method can be used to deal with the estimation and prediction problems for systems with quantized errors and packet Dropouts in a unified framework. The stability properties of the optimal estimator are also studied. The obtained stability condition implicitly establishes a relation between the upper bound of the estimation error and two parameters, namely, the quantization density and the packet Dropout probability. Moreover, the maximum quantization density and the maximum packet Dropout probability are given to ensure the convergence of the upper bound of the estimation error sequence. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed method.
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CDC - Moving horizon estimation for networked systems with packet Dropouts
2012 IEEE 51st IEEE Conference on Decision and Control (CDC), 2012Co-Authors: Andong Liu, Wen-an ZhangAbstract:The moving horizon estimation (MHE) problem is investigated in this paper for a class of networked systems with packet Dropouts. The packet Dropout is described by a binary switching random sequence. The main purpose of this paper is to design a estimator such that, for all possible packet Dropouts, the state estimation error sequence is convergent. By choosing a stochastic cost function, the optimal solution of the MHE optimization problem with packet Dropouts is given. Moreover, the convergence properties of the estimator are studied, and the maximum packet Dropout probability is given to ensure the convergence of the state estimation error. Finally, the performance of the proposed estimator is evaluated and an example is given to demonstrate the effectiveness of the proposed method.
Andong Liu - One of the best experts on this subject based on the ideXlab platform.
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moving horizon estimation for networked systems with quantized measurements and packet Dropouts
IEEE Transactions on Circuits and Systems, 2013Co-Authors: Andong Liu, Wen-an Zhang, Michael Z Q ChenAbstract:This paper is concerned with the moving horizon estimation (MHE) problem for linear discrete-time systems with limited communication, including quantized measurements and packet Dropouts. The measured output is quantized by a logarithmic quantizer and the packet Dropout phenomena is modeled by a binary switching random sequence. The main purpose of this paper is to design an estimator such that, for all possible quantized errors and packet Dropouts, the state estimation error sequence is convergent. By choosing a stochastic cost function, the optimal estimator is obtained by solving a regularized least-squares problem with uncertain parameters. The proposed method can be used to deal with the estimation and prediction problems for systems with quantized errors and packet Dropouts in a unified framework. The stability properties of the optimal estimator are also studied. The obtained stability condition implicitly establishes a relation between the upper bound of the estimation error and two parameters, namely, the quantization density and the packet Dropout probability. Moreover, the maximum quantization density and the maximum packet Dropout probability are given to ensure the convergence of the upper bound of the estimation error sequence. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed method.
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CDC - Moving horizon estimation for networked systems with packet Dropouts
2012 IEEE 51st IEEE Conference on Decision and Control (CDC), 2012Co-Authors: Andong Liu, Wen-an ZhangAbstract:The moving horizon estimation (MHE) problem is investigated in this paper for a class of networked systems with packet Dropouts. The packet Dropout is described by a binary switching random sequence. The main purpose of this paper is to design a estimator such that, for all possible packet Dropouts, the state estimation error sequence is convergent. By choosing a stochastic cost function, the optimal solution of the MHE optimization problem with packet Dropouts is given. Moreover, the convergence properties of the estimator are studied, and the maximum packet Dropout probability is given to ensure the convergence of the state estimation error. Finally, the performance of the proposed estimator is evaluated and an example is given to demonstrate the effectiveness of the proposed method.
Rajarshi Roy - One of the best experts on this subject based on the ideXlab platform.
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Effect of Spontaneous Emission Noise and Modulation on Semiconductor Lasers Near Threshold with Optical Feedback
International Journal of Modern Physics B, 2003Co-Authors: Wing-shun Lam, Parvez N. Guzdar, Rajarshi RoyAbstract:The dynamical behavior of power Dropouts in a semiconductor laser with optical feedback, pumped near threshold current, is strongly influenced by quantum noise. This is clearly demonstrated by experiments with modulations on the pumping current or the feedback strength. For the cases without modulation and with only current modulation, the Dropouts occur randomly. However the feedback strength modulation locks the Dropout events periodically. By numerically modeling these three cases using the Lang–Kobayashi equations with a stochastic term to take into account spontaneous emission noise, it is shown that the observed behavior of the Dropouts can be readily reproduced for all three cases. Noise plays a signifcant role in explaining the observed Dropout events. A simple explanation of the observed Dropout phenomenon is presented, based on the adiabatic motion of the ellipse formed by the steady state solutions of the rate equations due to slow time modulations of the injection current or the feedback strength.
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Determinism and stochasticity of power-Dropout events in semiconductor lasers with optical feedback.
Optics letters, 1995Co-Authors: Angela Hohl, H. J. C. Van Der Linden, Rajarshi RoyAbstract:Semiconductor lasers with optical feedback can display sudden power-Dropout events at irregular time intervals. We show numerically that, in some parameter regimes, spontaneous emission noise qualitatively influences the nature and statistics of the Dropouts. Experimental measurements of the mean time between Dropout events and its dependence on feedback strength agree well with analytic predictions made by Henry and Kazarinov [IEEE J. Quantum Electron. QE-22, 294 (1986)] based on the assumption that spontaneous emission noise induces these Dropout events.
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Dynamics of power Dropout events in semiconductor lasers with optical feedback
Conference Proceedings LEOS'96 9th Annual Meeting IEEE Lasers and Electro-Optics Society, 1Co-Authors: Angela Hohl, H. J. C. Van Der Linden, Rajarshi RoyAbstract:Semiconductor lasers are extremely sensitive to optical feedback, which can cause power Dropout events (often called low-frequency fluctuations (LFF)) near the solitary laser threshold. In this phenomenon, the laser power suddenly drops to almost zero and then recovers in a stepwise manner to its original power level, only to drop out again at irregular time intervals. Previous attempts to explain the origin of these power Dropout events employed either solely deterministic or stochastic models. However, power Dropout events occur near the solitary laser threshold, where stochastic fluctuations due to spontaneous emission noise typically have a large influence on the dynamical behavior of a laser. In this paper, we have therefore included both deterministic and stochastic mechanisms in our numerical computations to provide a comprehensive model for the Dropout events. We show numerically that in some parameter regimes, spontaneous emission noise qualitatively influences the nature and statistics of the Dropouts. Experimental measurements of the mean time between Dropout events and its dependence on feedback strength agree well with analytic predictions made by Henry and Kazarinov (1986) based on the assumption that spontaneous emission noise induces these Dropout events.
