2,088 research outputs found
Comparing persistence diagrams through complex vectors
The natural pseudo-distance of spaces endowed with filtering functions is
precious for shape classification and retrieval; its optimal estimate coming
from persistence diagrams is the bottleneck distance, which unfortunately
suffers from combinatorial explosion. A possible algebraic representation of
persistence diagrams is offered by complex polynomials; since far polynomials
represent far persistence diagrams, a fast comparison of the coefficient
vectors can reduce the size of the database to be classified by the bottleneck
distance. This article explores experimentally three transformations from
diagrams to polynomials and three distances between the complex vectors of
coefficients.Comment: 11 pages, 4 figures, 2 table
Sphinx measurements of the 2009 solar minimum x-ray emission
The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured
soft X-ray emission in the 1-15 keV energy range during the deep solar minimum
of 2009 with a sensitivity much greater than GOES. Several intervals are
identified when the X-ray flux was exceptionally low, and the flux and solar
X-ray luminosity are estimated. Spectral fits to the emission at these times
give temperatures of 1.7-1.9 MK and emission measures between 4 x 10^47 cm^-3
and 1.1 x 10^48 cm^-3. Comparing SphinX emission with that from the Hinode
X-ray Telescope, we deduce that most of the emission is from general coronal
structures rather than confined features like bright points. For one of 27
intervals of exceptionally low activity identified in the SphinX data, the
Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT
(0.1-2.4 keV) was less than most nearby K and M dwarfs.Comment: Astrophysical Journal, in press. 14 pp, 3 figure
A solar spectroscopic absolute abundance of argon from RESIK
Observations of He-like and H-like Ar (Ar XVII and Ar XVIII) lines at 3.949
Angstroms and 3.733 Angstroms respectively with the RESIK X-ray spectrometer on
the CORONAS-F spacecraft, together with temperatures and emission measures from
the two channels of GOES, have been analyzed to obtain the abundance of Ar in
flare plasmas in the solar corona. The line fluxes per unit emission measure
show a temperature dependence like that predicted from theory, and lead to
spectroscopically determined values for the absolute Ar abundance, A(Ar) = 6.44
pm 0.07 (Ar XVII) and 6.49 pm 0.16 (Ar XVIII) which are in agreement to within
uncertainties. The weighted mean is 6.45 pm 0.06, which is between two recent
compilations of the solar Ar abundance and suggest that the photospheric and
coronal abundances of Ar are very similar.Comment: 4 figure
The Solar Photospheric-to-Coronal Fe abundance from X-ray Fluorescence Lines
The ratio of the Fe abundance in the photosphere to that in coronal flare
plasmas is determined by X-ray lines within the complex at 6.7~keV (1.9~\AA)
emitted during flares. The line complex includes the He-like Fe (\fexxv)
resonance line (6.70~keV) and Fe K lines (6.39, 6.40~keV), the
latter being primarily formed by the fluorescence of photospheric material by
X-rays from the hot flare plasma. The ratio of the Fe K lines to the
\fexxv\ depends on the ratio of the photospheric-to-flare Fe abundance,
heliocentric angle of the flare, and the temperature of the
flaring plasma. Using high-resolution spectra from X-ray spectrometers on the
{\em P78-1} and {\em Solar Maximum Mission} spacecraft, the Fe abundance in
flares is estimated to be and times the photospheric
Fe abundance, the {\em P78-1} value being preferred as it is more directly
determined. This enhancement is consistent with results from X-ray spectra from
the {\em RHESSI} spacecraft, but is significantly less than a factor 4 as in
previous work.Comment: Accepted for publication by MNRA
Testing EUV/X-ray Atomic Data for the Solar Dynamics Observatory
The Atmospheric Imaging Assembly (AIA) and the Exteme-ultraviolet Variability
Experiment (EVE) onboard the Solar Dynamics Observatory include spectral
windows in the X-ray/EUV band. Accuracy and completeness of the atomic data in
this wavelength range is essential for interpretation of the spectrum and
irradiance of the solar corona, and of SDO observations made with the AIA and
EVE instruments. Here we test the X-ray/EUV data in the CHIANTI database to
assess their completeness and accuracy in the SDO bands, with particular focus
on the 94A and 131A AIA passbands. Given the paucity of solar observations
adequate for this purpose, we use high-resolution X-ray spectra of the
low-activity solar-like corona of Procyon obtained with the Chandra Low Energy
Transmission Grating Spectrometer (LETGS). We find that while spectral models
overall can reproduce quite well the observed spectra in the soft X-ray range
ll 130A, they significantly underestimate
the observed flux in the 50-130A wavelength range. The model underestimates the
observed flux by a variable factor ranging from \approx 1.5, at short
wavelengths below \sim50A, up to \approx5-7 in the \sim 70-125A range. In the
AIA bands covered by LETGS, i.e. 94A and 131A, we find that the observed flux
can be underestimated by large factors (\sim 3 and \sim 1.9 respectively, for
the case of Procyon presented here). We discuss the consequences for analysis
of AIA data and possible empirical corrections to the AIA responses to model
more realistically the coronal emission in these passbands.Comment: 11 pages, 9 figures, accepted for publication on Ap
The Steps to Managerial Excellence
Without any doubt, relaunching Romanian economy depends very much on SME sector getting out of the crisis, sector which has the main contribution to GDP production, to state budget income and human resources employment. Starting from these premises, based on scientific research performed in the framework of the VALAD* project, we present in the following a group of coordinates and markers which, in our opinion, are capable to relaunch indigenous SME sector. Elements contained in this study are complementary to the ones presented in the article “Policy coordinates concerning SME sector development in Romania”, published in the previous issue of this magazine.crisis; SME sector; SME’s management; entrepreneurship.
Temperature distribution of a non-flaring active region from simultaneous Hinode XRT and EIS observations
We analyze coordinated Hinode XRT and EIS observations of a non-flaring
active region to investigate the thermal properties of coronal plasma taking
advantage of the complementary diagnostics provided by the two instruments. In
particular we want to explore the presence of hot plasma in non-flaring
regions. Independent temperature analyses from the XRT multi-filter dataset,
and the EIS spectra, including the instrument entire wavelength range, provide
a cross-check of the different temperature diagnostics techniques applicable to
broad-band and spectral data respectively, and insights into cross-calibration
of the two instruments. The emission measure distribution, EM(T), we derive
from the two datasets have similar width and peak temperature, but show a
systematic shift of the absolute values, the EIS EM(T) being smaller than XRT
EM(T) by approximately a factor 2. We explore possible causes of this
discrepancy, and we discuss the influence of the assumptions for the plasma
element abundances. Specifically, we find that the disagreement between the
results from the two instruments is significantly mitigated by assuming
chemical composition closer to the solar photospheric composition rather than
the often adopted "coronal" composition (Feldman 1992). We find that the data
do not provide conclusive evidence on the high temperature (log T[K] >~ 6.5)
tail of the plasma temperature distribution, however, suggesting its presence
to a level in agreement with recent findings for other non-flaring regions.Comment: 14 pages, 15 figures. Accepted for publication in the Astrophysical
Journa
Modeling UV and X-Ray Emission in a Post-CME Current Sheet
A post-CME current sheet (CS) is a common feature developed behind an
erupting flux rope in CME models. Observationally, white light observations
have recorded many occurrences of a thin ray appearing behind a CME eruption
that closely resembles a post-CME CS in its spatial correspondence and
morphology. UV and X-ray observations further strengthen this interpretation by
the observations of high temperature emission at locations consistent with
model predictions. The next question then becomes whether the properties inside
a post-CME CS predicted by a model agree with observed properties. In this
work, we assume that the post-CME CS is a consequence of Petschek-like
reconnection and that the observed ray-like structure is bounded by a pair of
slow mode shocks developed from the reconnection site. We perform
time-dependent ionization calculations and model the UV line emission. We find
that such a model is consistent with SOHO/UVCS observations of the post-CME CS.
The change of Fe XVIII emission in one event implies an inflow speed of ~10
km/s and a corresponding reconnection rate of M_A ~ 0.01. We calculate the
expected X-ray emission for comparison with X-ray observations by Hinode/XRT,
as well as the ionic charge states as would be measured in-situ at 1 AU. We
find that the predicted count rate for Hinode/XRT agree with what was observed
in a post-CME CS on April 9, 2008, and the predicted ionic charge states are
consistent with high ionization states commonly measured in the interplanetary
CMEs. The model results depend strongly on the physical parameters in the
ambient corona, namely the coronal magnetic field, the electron density and
temperature during the CME event. It is crucial to obtain these ambient coronal
parameters and as many facets of the CS properties as possible by observational
means so that the post-CME current sheet models can be scrutinized more
effectively
Hinode/EIS spectroscopic validation of very hot plasma imaged with Solar Dynamics Observatory in non-flaring active region cores
We use coronal imaging observations with SDO/AIA, and Hinode/EIS spectral
data, to explore the potential of narrow band EUV imaging data for diagnosing
the presence of hot (T >~5MK) coronal plasma in active regions. We analyze
observations of two active regions (AR 11281, AR 11289) with simultaneous AIA
imaging, and EIS spectral data, including the CaXVII line (at 192.8A) which is
one of the few lines in the EIS spectral bands sensitive to hot coronal plasma
even outside flares. After careful coalignment of the imaging and spectral
data, we compare the morphology in a 3 color image combining the 171, 335, and
94A AIA spectral bands, with the image obtained for CaXVII emission from the
analysis of EIS spectra. We find that in the selected active regions the CaXVII
emission is strong only in very limited areas, showing striking similarities
with the features bright in the 94A (and 335A) AIA channels and weak in the
171A band. We conclude that AIA imaging observations of the solar corona can be
used to track hot plasma (6-8MK), and so to study its spatial variability and
temporal evolution at high spatial and temporal resolution.Comment: 10 pages, 2 figures, accepted for publication on ApJ Letter
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