11,336 research outputs found
The Impulsive Phase in Solar Flares: Recent Multi-wavelength Results and their Implications for Microwave Modeling and Observations
This short paper reviews several recent key observations of the processes
occurring in the lower atmosphere (chromosphere and photosphere) during flares.
These are: evidence for compact and fragmentary structure in the flare
chromosphere, the conditions in optical flare footpoints, step-like variations
in the magnetic field during the flare impulsive phase, and hot, dense
'chromospheric' footpoints. The implications of these observations for
microwaves are also discussed.Comment: 6 pages, 5 figures, presented at 'Solar Physics with Radio
Observations' Symposium, November 2012, Nagoya, Japa
Relativistic deuteron structure function at large Q^2
The deuteron deep inelastic unpolarized structure function F_2^D is
calculated using the Wilson operator product expansion method. The long
distance behaviour, related to the deuteron bound state properties, is
evaluated using the Bethe-Salpeter equation with one particle on mass shell.
The calculation of the ratio F_2^D/F_2^N is compared with other convolution
models showing important deviations in the region of large x. The implications
in the evaluation of the neutron structure function from combined data on
deuterons and protons are discussed.Comment: 7 pages, 1 ps figure, RevTeX source, 1 tar.gz file. Submited to
Physical Letter
The lattice Landau gauge gluon propagator: lattice spacing and volume dependence
The interplay between the finite volume and finite lattice spacing is
investigated using lattice QCD simulations to compute the Landau gauge gluon
propagator. Comparing several ensembles with different lattice spacings and
physical volumes, we conclude that the dominant effects, in the infrared
region, are associated with the use of a finite lattice spacing. The
simulations show that decreasing the lattice spacing, while keeping the same
physical volume, leads to an enhancement of the infrared gluon propagator. In
this sense, the data from simulations, which uses an fm, provides a lower bound for the infinite volume propagator.Comment: Final version to appear in Phys Rev
Impulsive Heating of Solar Flare Ribbons Above 10 MK
The chromospheric response to the input of flare energy is marked by extended
extreme ultraviolet (EUV) ribbons and hard X-ray (HXR) footpoints. These are
usually explained as the result of heating and bremsstrahlung emission from
accelerated electrons colliding in the dense chromospheric plasma. We present
evidence of impulsive heating of flare ribbons above 10 MK in a two-ribbon
flare. We analyse the impulsive phase of SOL2013-11-09T06:38, a C2.6 class
event using data from Atmospheric Imaging Assembly (AIA) on board of Solar
Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) to derive the temperature, emission measure and
differential emission measure of the flaring regions and investigate the
evolution of the plasma in the flaring ribbons. The ribbons were visible at all
SDO/AIA EUV/UV wavelengths, in particular, at 94 and 131 \AA\ filters,
sensitive to temperatures of 8 MK and 12 MK. Time evolution of the emission
measure of the plasma above 10 MK at the ribbons has a peak near the HXR peak
time. The presence of hot plasma in the lower atmosphere is further confirmed
by RHESSI imaging spectroscopy analysis, which shows resolved sources at 11-13
MK associated with at least one ribbon. We found that collisional beam heating
can only marginally explain the necessary power to heat the 10 MK plasma at the
ribbons.Comment: 21 pages, 15 figure
Effect of the curing time on the numerical modelling of the behaviour of a chemically stabilised soft soil
The ability of the Modified Cam Clay (MCC) model combined with the Von Mises (VM) model, considering the effect of curing time on the enhancement of the mechanical properties of a chemically stabilised soft soil is examined. The evolution of the strength and stiffness over time is based on the results of undrained compressive strength (UCS) tests carried out for different curing times (from 28 days to 360 days). Initially, the MCC/VM models associated with the effect of curing time are validated by CIU triaxial tests, for curing times of 28 and 90 days. Finally, the behaviour of an embankment built on a soft soil reinforced with deep mixing columns is predicted based on the previously validated models. The results show that the increase of curing time of the DMCs slightly decreases the settlement obtained with a curing time of 28 days
The spectral content of SDO/AIA 1600 and 1700 \AA\ filters from flare and plage observations
The strong enhancement of the ultraviolet emission during solar flares is
usually taken as an indication of plasma heating in the lower solar atmosphere
caused by the deposition of the energy released during these events. Images
taken with broadband ultraviolet filters by the {\em Transition Region and
Coronal Explorer} (TRACE) and {\em Atmospheric Imaging Assembly} (AIA 1600 and
1700~\AA) have revealed the morphology and evolution of flare ribbons in great
detail. However, the spectral content of these images is still largely unknown.
Without the knowledge of the spectral contribution to these UV filters, the use
of these rich imaging datasets is severely limited. Aiming to solve this issue,
we estimate the spectral contributions of the AIA UV flare and plage images
using high-resolution spectra in the range 1300 to 1900~\AA\ from the Skylab
NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600~\AA\
is { dominated by} the \ion{C}{4} 1550~\AA\ doublet (26\%), \ion{Si}{1}
continua (20\%), with smaller contributions from many other chromospheric lines
such as \ion{C}{1} 1561 and 1656~\AA\ multiplets, \ion{He}{2} 1640~\AA,
\ion{Si}{2} 1526 and 1533~\AA. For the AIA 1700~\AA\ band, \ion{C}{1} 1656~\AA\
multiplet is the main contributor (38\%), followed by \ion{He}{2} 1640 (17\%),
and accompanied by a multitude of other, { weaker} chromospheric lines, with
minimal contribution from the continuum. Our results can be generalized to
state that the AIA UV flare excess emission is of chromospheric origin, while
plage emission is dominated by photospheric continuum emission in both
channels.Comment: Accepted for publication in ApJ Skylab NRL SO82B data used in this
work available at http://dx.doi.org/10.5525/gla.researchdata.68
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