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Particle-in-cell (PIC) simulations are focusing on the individual trajectories of a very large number of particles in self-consistent and external electric and magnetic fields; they are widely used in the study of plasma jets, for example. The main disadvantage of PIC simulations is the large simulation runtime, which often requires a parallel implementation of the algorithm. The current paper focuses on a PIC1d3v simulation algorithm  and describes the successful implementation of adoi:10.15439/2020f130 dblp:conf/fedcsis/SuciuHMJVE20 fatcat:jlvcfyyfyzaujitvktrmzcu6m4
more »... lel version of it on a multicore architecture, using OpenMP, with very promising experimental and theoretical results.
<p><strong>Abstract.</strong> In this paper we investigate quantitatively the effect of data gaps for four methods of estimating the amplitude spectrum of a time series: fast Fourier transform (FFT), discrete Fourier transform (DFT), <i>Z</i> transform (ZTR) and the Lomb–Scargle algorithm (LST). We devise two tests: the single-large-gap test, which can probe the effect of a single data gap of varying size and the multiple-small-gaps test, used to study the effect of numerous small gaps ofdoi:10.5194/angeo-34-437-2016 fatcat:tosxkqbgfzaw7guldexx7npmu4
more »... le size distributed within the time series. The tests are applied on two data sets: a synthetic data set composed of a superposition of four sinusoidal modes, and one component of the magnetic field measured by the <i>Venus Express</i> (VEX) spacecraft in orbit around the planet Venus. For single data gaps, FFT and DFT give an amplitude monotonically decreasing with gap size. However, the shape of their amplitude spectrum remains unmodified even for a large data gap. On the other hand, ZTR and LST preserve the absolute level of amplitude but lead to greatly increased spectral noise for increasing gap size. For multiple small data gaps, DFT, ZTR and LST can, unlike FFT, find the correct amplitude of sinusoidal modes even for large data gap percentage. However, for in-situ data collected in a turbulent plasma environment, these three methods overestimate the high frequency part of the amplitude spectrum above a threshold depending on the maximum gap size, while FFT slightly underestimates it.</p>
For an extensive review of the existing kinetic and fluid solar wind models see Echim, Lemaire and Lie-Svendsen (2011) . ...arXiv:1410.3597v1 fatcat:imuep2yzuzdl7in6nbw5he33nm
The analysis of data variability from in-situ observations is essential for scientists and space mission controllers. Given the limited resources available on-board a spacecraft as well as the presence of the Field-Programmable Gate Arrays (FPGA) devices in modern spacecraft architectures, an efficient realtime monitoring solution should be deployed on these devices to use minimal computational and energy resources, and to reduce the main on-board computer utilization, thus making it availabledoi:10.1109/access.2022.3143239 fatcat:kiuhr632ffelvbnpyuizcjsplq
more »... or other tasks. This paper describes the implementation of an algorithm for computing a local stationarity measure (LSM) on FPGA devices. The algorithm tests weak stationarity from the convergence of the partial means of the signal computed on subsets of increasing length, compared to the overall mean of the signal over a fixed-length running window; the window spans the entire signal. The algorithm is designed for an on-board implementation which monitors and detects changes of variables measured in-situ by scientific instruments (e.g., magnetometers). The design was tested with synthetic and real-time signals and provides results in very good agreement with a dedicated data analysis library specifically designed for the analysis of satellite data. INDEX TERMS FPGA-based design, high-level synthesis (HLS), local stationarity measure (LSM), magnetic field monitoring, satellites on-board processing, weak stationarity test.
Recent results of numerical magnetohydrodynamic simulations suggest that in collisionless space plasmas turbulence can spontaneously generate thin current sheets. These coherent structures can partially explain intermittency and the non-homogenous distribution of localized plasma heating in turbulence. In this Letter Cluster multi-point observations are used to investigate the distribution of magnetic field discontinuities and the associated small-scale current sheets in the terrestrialdoi:10.3847/2041-8205/819/1/l15 fatcat:ce5atia7hbehpauq4uhyb6ejgq
more »... heath downstream of a quasi-parallel bow shock. It is shown experimentally, for the first time, that the strongest turbulence generated current sheets occupy the long tails of probability distribution functions (PDFs) associated with extremal values of magnetic field partial derivatives. During the analyzed one hour long time interval, about a hundred strong discontinuities, possibly proton-scale current sheets were observed.
Simone Benella, Giuseppe Consolini, Fabio Giannattasio, Tom Chang and Marius Echim contributed to the results' interpretation and theoretical discussions. ...doi:10.3390/e19080383 fatcat:cgdt6ezrtnbalfz65hpl46h244
., 2009) numerical simulations (see also the review by Echim and Lemaire, 2000) . ... For consistency, we consider the same satellite S1 as in Voitcu and Echim (2017) . ...doi:10.5194/angeo-36-1521-2018 fatcat:xpiqdlicjbh5zbeeabgt33kipa
In this paper we perform a comparative study of the forward and backward Liouville mapping applied to the modeling of ring-shaped and non-gyrotropic velocity distribution functions of particles injected in a sheared electromagnetic field. The test-kinetic method is used to compute the velocity distribution function in various areas of a proton cloud moving in the vicinity of a region with a sharp transition of the magnetic field and a non-uniform electric field. In the forward approach thedoi:10.1016/j.cpc.2012.07.005 fatcat:xeerqyoryrdylpw7mzsh2fa3sy
more »... ity distribution function is computed for a two-dimensional spatial bin, while in the backward approach the distribution function is averaged over a spatial bin with the same size as for the forward method and using a two-dimensional trapezoidal integration scheme. It is shown that the two approaches lead to similar results for spatial bins where the velocity distribution function varies smoothly. On the other hand, with bins covering regions of configuration space characterized by sharp spatial gradients of the velocity distribution function, the forward and backward approaches will generally provide different results.
Echim thanks the staff of the Belgian Institute for Space Aeronomy for long-term and efficient support, and acknowledges financial support from the Belgian Solar Terrestrial Center of Excellence (STCE) ... An expression for the parallel electric field sustained by two-dimensional cross-B sheared plasma flows has been derived by Echim and Lemaire (2005) . ... After several decades of fluid and kinetic solar wind modeling, often leading to controversies, scientists now realize that both approaches are complementary and not opposed (Lemaire and Echim 2008; Parker ...doi:10.1007/s10712-010-9106-y fatcat:rko3to7nerbnbiqkokmhuddclu
., Teodorescu and Echim, 2020) . ...doi:10.3389/fspas.2020.617113 fatcat:jmvporu73fcyneprjeyu4b7fei
We investigate Venus Express (VEX) observations of magnetic field fluctuations performed systematically in the solar wind at 0.72 Astronomical Units (AU), between 2007 and 2009, during the deep minimum of the solar cycle 24. The Power Spectral Densities (PSD) of the magnetic field components have been computed for the time intervals that satisfy data integrity criteria and have been grouped according to the type of wind, fast and slow defined for speeds larger and respectively smaller than 450doi:10.1088/2041-8205/804/2/l41 fatcat:fkyouyjg3vb7nbrrfw73wd5rnu
more »... m/s. The PSDs show higher levels of power for the fast than for the slow wind. The spectral slopes estimated for all PSDs in the frequency range 0.005-0.1 Hz exhibit a normal distribution. The average value of the trace of the spectral matrix is -1.60 for fast solar wind and -1.65 for slow wind. Compared to the corresponding average slopes at 1 AU, the PSDs are shallower at 0.72 AU for slow wind conditions suggesting a steepening of the solar wind spectra between Venus and Earth. No significant time variation trend is observed for the spectral behavior of both slow and fast wind.
(Echim et al., 2007 ). ... (Echim and Lamy, private communication, 2010; Chang et al., 2010) . Fig. 4 . 4 (a) PDF of v for hydrodynamic turbulence at 64 in units of bin size. ...doi:10.1007/s00024-014-0874-z fatcat:ejct7ddnwrfjnl5renzc6ze43m
Echim and Lemaire, 2003; Echim, 2004; . ... Note that similar findings have been obtained by kinetic modelling (Echim and Lemaire, 2005; Echim et al., 2005) and reported from spacecraft observations (Lundin et al., 2005) . ...doi:10.1002/2015ja021973 fatcat:yw2tzxdz55hzjdjzaznpjxwx4e
Aims Our goal is to develop and provide an open end-to-end (Sun to Earth) space weather modeling system, enabling to combine ("couple") various space weather models in an integrated tool, with the models located either locally or geographically distributed, so as to better understand the challenges in creating such an integrated environment. Methods The physics-based models are installed on different compute clusters and can be run interactively and remotely and that can be coupled over thedoi:10.1051/swsc/2020012 fatcat:qakjbdmaijcv3hqqzok4q7b2oa
more »... rnet, using open source 'high-level architecture' software, to make complex modeling chains involving models from the Sun to the Earth. Visualization tools have been integrated as 'models' that can be coupled to any other integrated model with compatible output. Results The first operational version of the VSWMC is accessible via the SWE Portal and demonstrates its end-to-end simulation capability. Users interact via the front-end GUI and can interactively run complex coupled simulation models and view and retrieve the output, including standard visualizations, via the GUI. Hence, the VSWMC provides the capability to validate and compare model outputs.
Physics of Plasmas
In this paper, we discuss the formation of ring-shaped and gyro-phase restricted velocity distribution functions (VDFs) at the edges of a cloud of protons injected into non-uniform distributions of the electromagnetic field. The velocity distribution function is reconstructed using the forward test-kinetic method. We consider two profiles of the electric field: (1) a non-uniform E-field obtained by solving the Laplace equation consistent with the conservation of the electric drift and (2) adoi:10.1063/1.3686134 fatcat:6a6x52emrncpvagvar3ifgbmia
more »... tant and uniform E-field. In both cases, the magnetic field is similar to the solutions obtained for tangential discontinuities. The initial velocity distribution function is Liouville mapped along numerically integrated trajectories. The numerical results show the formation of an energy-dispersed structure due to the energy-dependent displacement of protons towards the edges of the cloud by the gradient-B drift. Another direct effect of the gradient-B drift is the formation of ring-shaped velocity distribution functions within the velocity-dispersed structure. Higher energy particles populate the edges of the proton beam, while smaller energies are located in the core. Non-gyrotropic velocity distribution functions form on the front-side and trailing edge of the cloud; this effect is due to remote sensing of energetic particles with guiding centers inside the beam. The kinetic features revealed by the test-kinetic solutions have features similar to in-situ velocity distribution functions observed by Cluster satellites in the magnetotail, close to the neutral sheet.
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