325 research outputs found
Volume cross section of auroral radar backscatter and RMS plasma fluctuations inferred from coherent and incoherent scatter data: a response on backscatter volume parameters
Norway and Finland STARE radar measurements in the eastward auroral
electrojet are combined with EISCAT CP-1 measurements of the electron
density and electric field vector in the common scattering volume to
investigate the variation of the auroral radar volume cross section (VCS)
with the flow angle of observations (radar look direction with respect to
the <I><B>E</B></I>×<I><B>B</I></B> electron drift). The data set available consists of ~6000 points
for flow angles of 40–85° and electron drifts between 500
and 2000 m s<sup>−1</sup>. The EISCAT electron density <I>N(h)</I>-profile data are used
to estimate the effective electron density, aspect angle and thickness of
the backscattering layer. It is shown that the flow angle variation of the
VCS is rather weak, only ~5 dB within the range of the considered
flow angles. The VCS values themselves respond almost linearly to the square
of both the electron drift velocity magnitude and the effective electron
density. By adopting the inferred shape of the VCS variation with the flow
angle and the VCS dependence upon wavelength, the relative amplitude of
electrostatic electron density fluctuations over all scales is estimated.
Inferred values of 2–4 percent react nearly linearly to the electron drift
velocity in the range of 500–1000 m s<sup>−1</sup> but the rate of increase slows
down at electron drifts >1000 m s<sup>−1</sup> and density fluctuations of ~5.5
percent due to, perhaps, progressively growing nonlinear wave losses
Comparison of automated video tracking systems in the open field test : ANY-Maze versus EthoVision XT
This project included funding from the Innovative Medicines Initiative 2/EFPIA, European Quality in Preclinical Data (EQIPD) consortium under grant agreement number 777364. We would also like to acknowledge the staff of the Medical Research Facility for their support with animal care, handling and behavioural experiments.Peer reviewedPostprin
On the characterization of magnetic reconnection in global MHD simulations
The conventional definition of reconnection rate as the electric field parallel to an x-line is problematic in global MHD simulations for several reasons: the x-line itself may be hard to find in a non-trivial geometry such as at the magnetopause, and the lack of realistic resistivity modelling leaves us without reliable non-convective electric field. In this article we describe reconnection characterization methods that avoid those problems and are practical to apply in global MHD simulations. We propose that the reconnection separator line can be identified as the region where magnetic field lines of different topological properties meet, rather than by local considerations. The global convection associated with reconnection is then quantified by calculating the transfer of mass, energy or magnetic field across the boundary of closed and open field line regions. The extent of the diffusion region is determined from the destruction of electromagnetic energy, given by the divergence of the Poynting vector. Integrals of this energy conversion provide a way to estimate the total reconnection efficiency
Counterexample Guided Abstraction Refinement Algorithm for Propositional Circumscription
Circumscription is a representative example of a nonmonotonic reasoning
inference technique. Circumscription has often been studied for first order
theories, but its propositional version has also been the subject of extensive
research, having been shown equivalent to extended closed world assumption
(ECWA). Moreover, entailment in propositional circumscription is a well-known
example of a decision problem in the second level of the polynomial hierarchy.
This paper proposes a new Boolean Satisfiability (SAT)-based algorithm for
entailment in propositional circumscription that explores the relationship of
propositional circumscription to minimal models. The new algorithm is inspired
by ideas commonly used in SAT-based model checking, namely counterexample
guided abstraction refinement. In addition, the new algorithm is refined to
compute the theory closure for generalized close world assumption (GCWA).
Experimental results show that the new algorithm can solve problem instances
that other solutions are unable to solve
Ionospheric energy input as a function of solar wind parameters: global MHD simulation results
The magnetotail reconnection region in a global MHD simulation
International audienceThis work investigates the nature and the role of magnetic reconnection in a global magnetohydrodynamic simulation of the magnetosphere. We use the Gumics-4 simulation to study reconnection that occurs in the near-Earth region of the current sheet in the magnetotail. We locate the current sheet surface and the magnetic x-line that appears when reconnection starts. We illustrate the difference between quiet and active states of the reconnection region: variations in such quantities as the current sheet thickness, plasma flow velocities, and Poynting vector divergence are strong. A characteristic feature is strong asymmetry caused by non-perpendicular inflows. We determine the reconnection efficiency by the net rate of Poynting flux into the reconnection region. The reconnection efficiency in the simulation is directly proportional to the energy flux into the magnetosphere through the magnetopause: about half of all energy flowing through the magnetosphere is converted from an electromagnetic into a mechanical form in the reconnection region. Thus, the tail reconnection that is central to the magnetospheric circulation is directly driven; the tail does not exhibit a cycle of storage and rapid release of magnetic energy. We find similar behaviour of the tail in both synthetic and real event runs
The electron drift velocity, ion acoustic speed and irregularity drifts in high-latitude E-region
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