5,300 research outputs found
Non-abelian instantons on a fuzzy four-sphere
We study the compatibility between the instanton and the fuzzy
four-sphere algebra. By using the projective module point of view as an
intermediate step, we are able to identify a non-commutative solution of the
matrix model equations of motion which minimally extends the SU(2) instanton
solution on the classical sphere . We also propose to extend the
non-trivial second Chern class with the five-dimensional noncommutative
Chern-Simons term
The Wigner Entropy Production Rate
The characterization of irreversibility in general quantum processes is an
open problem of increasing techno- logical relevance. Yet, the tools currently
available to this aim are mostly limited to the assessment of dynamics induced
by equilibrium environments, a situation that often does not match the reality
of experiments at the microscopic and mesoscopic scale. We propose a theory of
irreversible entropy production that is suited for quantum systems exposed to
general, non-equilibrium reservoirs. We illustrate our framework by addressing
a set of physically relevant situations that clarify both the features and the
potential of our proposal
CHIANTI - An atomic database for emission lines. XI. EUV emission lines of Fe VII, Fe VIII and Fe IX observed by Hinode/EIS
A detailed study of emission lines from Fe VII, Fe VIII and Fe IX observed by
the EUV Imaging Spectrometer on board the Hinode satellite is presented.
Spectra in the ranges 170-212 A and 246-292 A show strongly enhanced lines from
the upper solar transition region (temperatures 5.4 <= log T <= 5.9) allowing a
number of new line identifications to be made. Comparisons of Fe VII lines with
predictions from a new atomic model reveal new plasma diagnostics, however
there are a number of disagreements between theory and observation for emission
line ratios insensitive to density and temperature, suggesting improved atomic
data are required. Line ratios for Fe VIII also show discrepancies with theory,
with the strong 185.21 and 186.60 lines under-estimated by 60-80 % compared to
lines between 192 and 198 A. A newly-identified multiplet between 253.9 and
255.8 A offers excellent temperature diagnostic opportunities relative to the
lines between 185-198 A, however the atomic model under-estimates the strength
of these lines by factors 3-6. Two new line identifications are made for Fe IX
at wavelengths 176.959 A and 177.594 A, while seven other lines between 186 and
200 A are suggested to be due to Fe IX but for which transition identifications
can not be made. The new atomic data for Fe VII and Fe IX are demonstrated to
significantly modify models for the response function of the TRACE 195 A
imaging channel, affecting temperature determinations from this channel. The
data will also affect the response functions for other solar EUV imaging
instruments such as SOHO/EIT, STEREO/EUVI and the upcoming AIA instrument on
the Solar Dynamics Observatory.Comment: 51 pages, submitted to Ap
On the Dirac Eigenvalues as Observables of the on-shell N=2 D=4 Euclidean Supergravity
We generalize previous works on the Dirac eigenvalues as dynamical variables
of the Euclidean gravity and N=1 D=4 supergravity to on-shell N=2 D=4 Euclidean
supergravity. The covariant phase space of the theory is defined as as the
space of the solutions of the equations of motion modulo the on-shell gauge
transformations. In this space we define the Poisson brackets and compute their
value for the Dirac eigenvalues.Comment: 10 pages, LATeX fil
Plasma turbulence at ion scales: a comparison between PIC and Eulerian hybrid-kinetic approaches
Kinetic-range turbulence in magnetized plasmas and, in particular, in the
context of solar-wind turbulence has been extensively investigated over the
past decades via numerical simulations. Among others, one of the widely adopted
reduced plasma model is the so-called hybrid-kinetic model, where the ions are
fully kinetic and the electrons are treated as a neutralizing (inertial or
massless) fluid. Within the same model, different numerical methods and/or
approaches to turbulence development have been employed. In the present work,
we present a comparison between two-dimensional hybrid-kinetic simulations of
plasma turbulence obtained with two complementary approaches spanning about two
decades in wavenumber - from MHD inertial range to scales well below the ion
gyroradius - with a state-of-the-art accuracy. One approach employs hybrid
particle-in-cell (HPIC) simulations of freely-decaying Alfv\'enic turbulence,
whereas the other consists of Eulerian hybrid Vlasov-Maxwell (HVM) simulations
of turbulence continuously driven with partially-compressible large-scale
fluctuations. Despite the completely different initialization and
injection/drive at large scales, the same properties of turbulent fluctuations
at are observed. The system indeed self-consistently
"reprocesses" the turbulent fluctuations while they are cascading towards
smaller and smaller scales, in a way which actually depends on the plasma beta
parameter. Small-scale turbulence has been found to be mainly populated by
kinetic Alfv\'en wave (KAW) fluctuations for , whereas KAW
fluctuations are only sub-dominant for low-.Comment: 18 pages, 4 figures, accepted for publication in J. Plasma Phys.
(Collection: "The Vlasov equation: from space to laboratory plasma physics"
Bright hot impacts by erupted fragments falling back on the Sun: UV redshifts in stellar accretion
A solar eruption after a flare on 7 Jun 2011 produced EUV-bright impacts of
fallbacks far from the eruption site, observed with the Solar Dynamics
Observatory. These impacts can be taken as a template for the impact of stellar
accretion flows. Broad red-shifted UV lines have been commonly observed in
young accreting stars. Here we study the emission from the impacts in the
Atmospheric Imaging Assembly's UV channels and compare the inferred velocity
distribution to stellar observations. We model the impacts with 2D hydrodynamic
simulations. We find that the localised UV 1600A emission and its timing with
respect to the EUV emission can be explained by the impact of a cloud of
fragments. The first impacts produce strong initial upflows. The following
fragments are hit and shocked by these upflows. The UV emission comes mostly
from the shocked front shell of the fragments while they are still falling, and
is therefore redshifted when observed from above. The EUV emission instead
continues from the hot surface layer that is fed by the impacts. Fragmented
accretion can therefore explain broad redshifted UV lines (e.g. C IV 1550A) to
speeds around 400 km/s observed in accreting young stellar objects.Comment: 12 pages, 4 figures (movies available upon request), accepted for
publicatio
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