scholarly journals A New Perspective and Explanation to the Formation of Plasmaspheric Shoulder Structure

2020 ◽  
Author(s):  
Hua Zhang ◽  
Guangshuai Peng ◽  
Chao Shen
Keyword(s):  
Extreme Ultraviolet ◽  
Particle Model ◽  
Sharp Reduction ◽  
Subsequent Evolution ◽  
Drift Motion ◽  
Image Satellite ◽  
The Hours ◽  
Speed Up ◽  
New Perspective ◽  
Radial Outflow

Abstract. Over the hours of 5–9 UT on June 8 2001, the extreme ultraviolet (EUV) instrument onboard IMAGE satellite observed a Shoulder-like formation in the morning sector and a Plume-like structure straddling in the between noon and dusk region. Simulation results of the plasmapause formation based on mechanism of drift motion called Test Particle Model (TPM) and have reproduced various plasmapause structures and subsequent evolution of the Shoulder. The analysis indicated that the Shoulder is created by a dawn-dusk convection electric field intensity, sharp reduction and spatial nonuniform manifested. As, combination of the plasmaspheric rotation rate speed up with L-shell increase and plasma flux do radial outflow in the predawn sector to interact, and produce an asymmetric bulge that rotates eastward. The Shoulder-like structure rotates sunward and develops to the single or double Plume structure during active times.

scholarly journals A new perspective and explanation for the formation of plasmaspheric shoulder structures

2021 ◽  
Vol 39 (4) ◽  
pp. 701-707
Author(s):  
Hua Zhang ◽  
Guangshuai Peng ◽  
Chao Shen ◽  
Yewen Wu
Keyword(s):  
Electric Field Intensity ◽  
Extreme Ultraviolet ◽  
Particle Model ◽  
Sharp Reduction ◽  
Active Time ◽  
Drift Motion ◽  
Image Satellite ◽  
Time Period ◽  
The Hours ◽  
New Perspective

Abstract. Over the hours of 05:00–09:00 UT on 8 June 2001, the extreme ultraviolet (EUV) instrument on board the IMAGE satellite observed a shoulder-like formation in the morning sector and a post-noon plume-like structure. The plasmapause formation is simulated using the test particle model (TPM), based on a drift motion theory, which reproduces various plasmapause structures and evolution of the shoulder feature. The analysis indicates that the shoulder is created by sharp reduction and spatial non-uniformity in the dawn–dusk convection electric field intensity. The TPM-modeled event is found to develop an initial pre-dawn asymmetric bulge that becomes a shoulder as a result of increased “corotation” rate with an increasing L-shell that is preceded by localized outward convection. The shoulder structure rotates sunward and develops into a single- or double-plume structure during an active time period in simulation.

scholarly journals Forming a cold electron population at a weakly outgassing comet 

2021 ◽  
Author(s):  
Peter Stephenson ◽  
Marina Galand ◽  
Jan Deca ◽  
Pierre Henri ◽  
Gianluca Carnielli
Keyword(s):  
Test Particle ◽  
Extreme Ultraviolet ◽  
Pure Water ◽  
Particle Model ◽  
Cold Electron ◽  
Electron Population ◽  
Neutral Gas ◽  
Rosetta Mission ◽  
Radial Outflow ◽  
Comet 67P

<p>The Rosetta Mission rendezvoused with comet 67P/Churyumov-Gerasimenko in August 2014 and escorted it for two years along its orbit. The Rosetta Plasma Consortium (RPC) was a suite of instruments, which observed the plasma environment at the spacecraft throughout the escort phase. The Mutual Impedance Probe (RPC/MIP; Wattieaux et al, 2020; Gilet et al., 2020) and Langmuir Probe (RPC/LAP; Engelhardt et al., 2018), both part of RPC, measured the presence of a cold electron population within the coma.</p> <p>Newly born electrons, generated by ionisation of the neutral gas, form a warm population within the coma at ~10eV. Ionisation is either through absorption of extreme ultraviolet photons or through collisions of energetic electrons with the neutral molecules. The cold electron population is formed by cooling the newly born, warm electrons via electron-neutral collisions. Assuming the radial outflow of electrons, the cold population was only expected at comet 67P close to perihelion, where outgassing rate from the nucleus was at its highest (Q > 10<sup>28</sup> s<sup>-1</sup>). However, cold electrons were observed until the end of the Rosetta mission at 3.8au when the outgassing was weak (Q<10<sup>26</sup> s<sup>-1</sup>). Under the radial outflow assumption, there should not have been sufficient neutral gas to efficiently degrade the electron energies.</p> <p>We have developed the first 3D collision model of electrons at a comet. Self-consistently calculated electric and magnetic fields from a collisionless and fully-kinetic Particle-in-Cell model (Deca et al., 2017; 2019) are used as a stationary input for the test particle simulations. We model the neutral coma as a spherically symmetric cloud of pure water, which follows 1/r<sup>2</sup> in cometocentric distance. Electron-neutral collisions are treated as a stochastic process using cross sections from Itikawa and Mason (2005). The model incorporates elastic scattering of electrons and a variety of inelastic collisions, including excitation and ionization of the water molecules.</p> <p>We show that the radial outflow of electrons from the coma is insufficient to generate a cold electron population under weak outgassing conditions. Using our original test particle model, we demonstrate the trapping of electrons in the inner coma by an ambipolar electric field and how this increases the efficiency of the electron cooling.  We also show that, at low outgassing rates, electron-neutral collisions significantly cool electrons within the coma and can lead to the formation of a cold population.</p> <p> </p>

scholarly journals Cooling of Electrons in a Weakly Outgassing Comet

2020 ◽  
Author(s):  
Peter Stephenson ◽  
Marina Galand ◽  
Jan Deca ◽  
Pierre Henri ◽  
Gianluca Carnielli
Keyword(s):  
Solar Wind ◽  
Extreme Ultraviolet ◽  
Pure Water ◽  
Particle Model ◽  
Particle In Cell ◽  
Electron Sources ◽  
Cometary Plasma ◽  
Impedance Probe ◽  
Cold Electrons ◽  
The Impact

<p>The plasma instruments, Mutual Impedance Probe (MIP) and Langmuir Probe (LAP), part of the Rosetta Plasma Consortium (RPC), onboard the Rosetta mission to comet 67P revealed a population of cold electrons (<1eV) (Engelhardt et al., 2018; Wattieaux et al, 2020; Gilet et al., 2020). This population is primarily generated by cooling warm (~10eV) newly-born cometary electrons through collisions with the neutral coma. What is surprising is that the cold electrons were detected throughout the escort phase, even at very low outgassing rates (Q<1e26 s<sup>-1</sup>) at large heliocentric distances (>3 AU), when the coma was not thought to be dense enough to cool the electron population significantly.</p> <p> Using a collisional test particle model, we examine the behaviour of electrons in the coma of a weakly outgassing comet and the formation of a cold population through electron-neutral collisions. The model incorporates three electron sources: the solar wind, photo-electrons produced through ionisation of the cometary neutrals by extreme ultraviolet solar radiation, and secondary electrons produced through electron-impact ionisation.</p> <p>The model includes different electron-water collision processes, including elastic, excitation, and ionisation collisions.</p> <p> The electron trajectories are shaped by electric and magnetic fields, which are taken from a 3D collisionless fully-kinetic Particle-in-Cell (PIC) model of the solar wind and cometary plasma  (Deca 2017, 2019). We use a spherically symmetric coma of pure water, which gives a r<sup>-2</sup> profile in the neutral density. Throughout their lifetime, electrons undergo stochastic collisions with neutral molecules, which can degrade the electrons in energy or scatter them.</p> <p>We first validate our model with comparison to results from PIC simulations. We then demonstrate the trapping of electrons in the coma by an ambipolar electric field and the impact of this trapping on the production of cold electrons.</p>

scholarly journals First ground-based optical analysis of H<sub>β</sub> Doppler profiles close to local noon in the cusp

2006 ◽  
Vol 24 (10) ◽  
pp. 2543-2552 ◽  
Author(s):  
S. C. Robertson ◽  
B. S. Lanchester ◽  
M. Galand ◽  
D. Lummerzheim ◽  
A. B. Stockton-Chalk ◽  
...  
Keyword(s):  
Optical Measurements ◽  
Echelle Spectrograph ◽  
Image Satellite ◽  
High Latitude Region ◽  
The Hours ◽  
Modelling Studies ◽  
Solar Noon ◽  
Latitude Region ◽  
High Throughput Imaging ◽  
Local Noon

Abstract. Observations of hydrogen emissions along the magnetic zenith at Longyearbyen (78.2 N, 15.8 E geographic) are used to investigate the energy and source of protons precipitating into the high latitude region. During the hours around local solar noon (11:00 UT), measurements of the hydrogen Balmer β line are severely affected by sunlight, such that most data until now have been disregarded during these times. Here we use a simple technique to subtract sunlight contamination from such spectral data. An example is shown in which the removal of twilight contamination reveals a brightening of Hβ aurora over Svalbard on 27 November 2000 between 08:00 UT and 10:00 UT, which is centred on magnetic noon (08:48 UT). These data were measured by the High Throughput Imaging Echelle Spectrograph (HiTIES), one instrument on the Southampton-UCL Spectrographic Imaging Facility (SIF). Data from the IMAGE satellite confirms the location of a cusp "spot" over Svalbard at the time of the ground-based measurements, which moved in response to changes in the IMF conditions. A coincident pass of the DMSP F12 satellite provided input spectra for modelling studies of the Hβ profiles, which confirm that the method for removing the twilight contamination is robust. The results described here are the first ground-based optical measurements of Hβ Doppler profiles from the cusp region close to local solar noon, when scattered sunlight swamps the raw data.

scholarly journals Decentralized Distributed Deep Learning with Low-Bandwidth Consumption for Smart Constellations

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Qingliang Meng ◽  
Meiyu Huang ◽  
Yao Xu ◽  
Naijin Liu ◽  
Xueshuang Xiang
Keyword(s):  
Deep Learning ◽  
Parameter Extraction ◽  
Stochastic Gradient Descent ◽  
Network Bandwidth ◽  
Distributed Training ◽  
Intelligent Processing ◽  
Benchmark Datasets ◽  
Speed Up ◽  
New Perspective ◽  
Deep Learning Network

For the space-based remote sensing system, onboard intelligent processing based on deep learning has become an inevitable trend. To adapt to the dynamic changes of the observation scenes, there is an urgent need to perform distributed deep learning onboard to fully utilize the plentiful real-time sensing data of multiple satellites from a smart constellation. However, the network bandwidth of the smart constellation is very limited. Therefore, it is of great significance to carry out distributed training research in a low-bandwidth environment. This paper proposes a Randomized Decentralized Parallel Stochastic Gradient Descent (RD-PSGD) method for distributed training in a low-bandwidth network. To reduce the communication cost, each node in RD-PSGD just randomly transfers part of the information of the local intelligent model to its neighborhood. We further speed up the algorithm by optimizing the programming of random index generation and parameter extraction. For the first time, we theoretically analyze the convergence property of the proposed RD-PSGD and validate the advantage of this method by simulation experiments on various distributed training tasks for image classification on different benchmark datasets and deep learning network architectures. The results show that RD-PSGD can effectively save the time and bandwidth cost of distributed training and reduce the complexity of parameter selection compared with the TopK-based method. The method proposed in this paper provides a new perspective for the study of onboard intelligent processing, especially for online learning on a smart satellite constellation.

scholarly journals Accelerated Battery Lifetime Simulations Using Adaptive Inter-Cycle Extrapolation Algorithm

2021 ◽  
Author(s):  
Valentin Sulzer ◽  
Peyman Mohtat ◽  
Sravan Pannala ◽  
Jason Siegel ◽  
Anna Stefanopoulou
Keyword(s):  
Degradation Mechanism ◽  
Model Development ◽  
Particle Model ◽  
Side Reactions ◽  
Algebraic Equations ◽  
Battery Lifetime ◽  
Extrapolation Algorithm ◽  
Speed Up ◽  
The Difference ◽  
Aging Phenomena

Abstract We propose algorithms to speed up physics-based battery lifetime simulations by one to two orders of magnitude compared to the state-of-the-art. First, we propose a reformulation of the Single Particle Model with side reactions to remove algebraic equations and hence reduce stiffness, with 3x speed-up in simulation time (intra-cycle reformulation). Second, we introduce an algorithm that makes use of the difference between the `fast' timescale of battery cycling and the `slow' timescale of battery degradation by adaptively selecting and simulating representative cycles, skipping other cycles, and hence requires fewer cycle simulations to simulate the entire lifetime (adaptive inter-cycle extrapolation). This algorithm is demonstrated with a specific degradation mechanism but can be applied to various models of aging phenomena. In the particular case study considered, simulations of the entire lifetime are performed in under 5 seconds. This opens the possibility for much faster and more accurate model development, testing, and comparison with experimental data.

Investigating the Jet Comminuting Process in Cuttings Transport by Coupling the CFD/DEM Method and Bonded-Particle Model

SPE Journal ◽  
2019 ◽  
Vol 24 (05) ◽  
pp. 2020-2032 ◽  
Author(s):  
Yongsheng Liu ◽  
Deli Gao ◽  
Xin Li ◽  
Xing Qin ◽  
He Li ◽  
...  
Keyword(s):  
Effective Means ◽  
Element Model ◽  
Secondary Development ◽  
Particle Model ◽  
Compression Tests ◽  
Cuttings Transport ◽  
Horizontal Drilling ◽  
Bonded Particle Model ◽  
Drilling Operations ◽  
New Perspective

Summary Jet comminuting technology has proved to be an effective means of solid particle pulverization, and current research attempts to introduce it for drilling work to reduce cuttings size, because smaller cuttings are easy to circulate out of the bottom, thus can effectively prevent the formation of cuttings bed, especially in horizontal drilling. In this paper, the feasibility of cuttings’ comminution by jet is studied by means of numerical simulation with secondary development. The coupling analysis methods—including the computational–fluid–dynamics/discrete–element–model (CFD/DEM) modeling for the interaction between fluid and cuttings and the particle replacement and bonding modeling for cuttings breakage—are used to characterize the jet comminuting process of cuttings. Input parameters of simulation are reliable and verified by uniaxial compression tests. Case studies presented here indicate that cuttings can be considerably accelerated by 20 to 30 m/s through the throat, which provides a good effective speed for the cuttings. After being accelerated by the fluid and crushed with the target, the vast majority of cuttings results in smaller debris. Also, increasing the inlet speed affects the crushing efficiency. The inclination of the target at near 65° shows good results. This paper proposes a new perspective to introduce the jet comminuting technique for drilling operations, and its findings could help in guiding engineering design in the future.

scholarly journals A Neuron Model with Dendrite Morphology for Classification

Electronics ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 1062
Author(s):  
Shuangbao Song ◽  
Xingqian Chen ◽  
Shuangyu Song ◽  
Yuki Todo
Keyword(s):  
Neuron Model ◽  
Reduction Method ◽  
Classification Performance ◽  
High Dimensional ◽  
Classification Problems ◽  
Dendrite Morphology ◽  
Dimensional Classification ◽  
Proposed Model ◽  
Speed Up ◽  
New Perspective

Recent neurological studies have shown the importance of dendrites in neural computation. In this paper, a neuron model with dendrite morphology, called the logic dendritic neuron model (LDNM), is proposed for classification. This model consists of four layers: a synaptic layer, a dendritic layer, a membrane layer, and a soma body. After training, the LDNM is simplified by proprietary pruning mechanisms and is further transformed into a logic circuit classifier. Moreover, to address the high-dimensional challenge, feature selection is employed as the dimension reduction method before training the LDNM. In addition, the effort of employing a heuristic optimization algorithm as the learning method is also undertaken to speed up the convergence. Finally, the performance of the proposed model is assessed by five benchmark high-dimensional classification problems. In comparison with the other six classical classifiers, LDNM achieves the best classification performance on two (out of five) classification problems. The experimental results demonstrate the effectiveness of the proposed model. A new perspective for solving classification problems by the proposed LDNM is provided in the paper.

scholarly journals Accelerated battery lifetime simulations using adaptive inter-cycle extrapolation algorithm

2021 ◽  
Author(s):  
Valentin Sulzer ◽  
Peyman Mohtat ◽  
Sravan Pannala ◽  
Jason B. Siegel ◽  
Anna G. Stefanopoulou
Keyword(s):  
Degradation Mechanism ◽  
Model Development ◽  
Particle Model ◽  
Side Reactions ◽  
Algebraic Equations ◽  
Battery Lifetime ◽  
Extrapolation Algorithm ◽  
Speed Up ◽  
The Difference ◽  
Aging Phenomena

We propose algorithms to speed up physics-based battery lifetime simulations by one to two orders of magnitude compared to the state-of-the-art. First, we propose a reformulation of the Single Particle Model with side reactions to remove algebraic equations and hence reduce stiffness, with 3x speed-up in simulation time (intra-cycle reformulation). Second, we introduce an algorithm that makes use of the difference between the `fast' timescale of battery cycling and the `slow' timescale of battery degradation by adaptively selecting and simulating representative cycles, skipping other cycles, and hence requires fewer cycle simulations to simulate the entire lifetime (adaptive inter-cycle extrapolation). This algorithm is demonstrated with a specific degradation mechanism but can be applied to various models of aging phenomena. In the particular case study considered, simulations of the entire lifetime are performed in under 5 seconds. This opens the possibility for much faster and more accurate model development, testing, and comparison with experimental data.

Two-dimensional high-latitude thermospheric modeling: A comparison between moderate and extremely disturbed conditions

1991 ◽  
Vol 69 (8-9) ◽  
pp. 1007-1031 ◽  
Author(s):  
C. A. Chang ◽  
J.-P. St.-Maurice
Keyword(s):  
Joule Heating ◽  
Stokes Equations ◽  
Extreme Ultraviolet ◽  
Complex Structure ◽  
Zonal Flow ◽  
Global Scale ◽  
Momentum Equation ◽  
Temperature Fields ◽  
Two Dimensional ◽  
Drift Motion

A set of two-dimensional nonlinear calculations has been done to simulate the auroral region electrojet and to examine the effect of the electric field on the dynamics and thermodynamics of the thermosphere. A large number of physical and dynamical processes in the ionosphere have been considered, including the ion-drag force, the Coriolis force, gravitation, Joule heating, viscous heating and viscous work, solar extreme ultraviolet heating, thermal conduction, and cooling to space owing to infrared radiation of different species. Navier–Stokes equations for a compressible, viscous and thermal conducting fluid flow with source terms have been solved by a MacCormack explicit, alternative forward-backward finite differencing scheme in spherical coordinates. Results have been recorded at various time intervals for three hours simulation time, for altitudes between 80 and 450 km, and from the north pole to the equator. In addition to a strong zonal drift motion and to the basic upward and meridional motion away from the heated region, we obtain a complex structure of waves involving meridional and vertical winds, as well as the density and temperature fields. This computation suggests that waves play a much more important role than ordinary diffusion of energy and momentum is spreading the effects of the disturbances away from the electrojet region. The net result is that there is, strictly speaking, no steady state reached by the neutrals except for the bulk of the zonal flow. A second major feature that we obtain is that nonlinear terms can often dominate the momentum equation, which can reduce the magnitude of the zonal flow by a considerable amount, and can displace the region of maximum neutral flow away from where the electrojet is. The nonlinear terms are also responsible for the formation of a neutral density 'hole' at nonelectrojet latitudes. This hole is found below the region where Joule heating reaches its peak value and is used to enhance the neutral densities at high altitudes on a global scale.

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