3,889 research outputs found
Horizontal flow fields observed in Hinode G-band images. I. Methods
Context: The interaction of plasma motions and magnetic fields is an
important mechanism, which drives solar activity in all its facets. For
example, photospheric flows are responsible for the advection of magnetic flux,
the redistribution of flux during the decay of sunspots, and the built-up of
magnetic shear in flaring active regions. Aims: Systematic studies based on
G-band data from the Japanese Hinode mission provide the means to gather
statistical properties of horizontal flow fields. This facilitates comparative
studies of solar features, e.g., G-band bright points, magnetic knots, pores,
and sunspots at various stages of evolution and in distinct magnetic
environments, thus, enhancing our understanding of the dynamic Sun. Methods: We
adapted Local Correlation Tracking (LCT) to measure horizontal flow fields
based on G-band images obtained with the Solar Optical Telescope on board
Hinode. In total about 200 time-series with a duration between 1-16 h and a
cadence between 15-90 s were analyzed. Selecting both a high-cadence (dt = 15
s) and a long-duration (dT = 16 h) time-series enabled us to optimize and
validate the LCT input parameters, hence, ensuring a robust, reliable, uniform,
and accurate processing of a huge data volume. Results: The LCT algorithm
produces best results for G-band images having a cadence of 60-90 s. If the
cadence is lower, the velocity of slowly moving features will not be reliably
detected. If the cadence is higher, the scene on the Sun will have evolved too
much to bear any resemblance with the earlier situation. Consequently, in both
instances horizontal proper motions are underestimated. The most reliable and
yet detailed flow maps are produced using a Gaussian kernel with a size of 2560
km x 2560 km and a full-width-at-half-maximum (FWHM) of 1200 km (corresponding
to the size of a typical granule) as sampling window.Comment: 12 pages, 8 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
Modeling of Social Transitions Using Intelligent Systems
In this study, we reproduce two new hybrid intelligent systems, involve three
prominent intelligent computing and approximate reasoning methods: Self
Organizing feature Map (SOM), Neruo-Fuzzy Inference System and Rough Set Theory
(RST),called SONFIS and SORST. We show how our algorithms can be construed as a
linkage of government-society interactions, where government catches various
states of behaviors: solid (absolute) or flexible. So, transition of society,
by changing of connectivity parameters (noise) from order to disorder is
inferred
DOT tomography of the solar atmosphere. IV. Magnetic patches in internetwork areas
We use G-band and Ca II H image sequences from the Dutch Open Telescope (DOT)
to study magnetic elements that appear as bright points in internetwork parts
of the quiet solar photosphere and chromosphere. We find that many of these
bright points appear recurrently with varying intensity and horizontal motion
within longer-lived magnetic patches. We develop an algorithm for detection of
the patches and find that all patches identified last much longer than the
granulation. The patches outline cell patterns on mesogranular scales,
indicating that magnetic flux tubes are advected by granular flows to
mesogranular boundaries. Statistical analysis of the emergence and
disappearance of the patches points to an average patch lifetime as long as
530+-50 min (about nine hours), which suggests that the magnetic elements
constituting strong internetwork fields are not generated by a local turbulent
dynamo.Comment: 8 pages, 6 figure
Do quasi-regular structures really exist in the solar photosphere? I. Observational evidence
Two series of solar-granulation images -- the La Palma series of 5 June 1993
and the SOHO MDI series of 17--18 January 1997 -- are analysed both
qualitatively and quantitatively. New evidence is presented for the existence
of long-lived, quasi-regular structures (first reported by Getling and Brandt
(2002)), which no longer appear unusual in images averaged over 1--2-h time
intervals. Such structures appear as families of light and dark concentric
rings or families of light and dark parallel strips (``ridges'' and
``trenches'' in the brightness distributions). In some cases, rings are
combined with radial ``spokes'' and can thus form ``web'' patterns. The
characteristic width of a ridge or trench is somewhat larger than the typical
size of granules. Running-average movies constructed from the series of images
are used to seek such structures. An algorithm is developed to obtain, for
automatically selected centres, the radial distributions of the azimuthally
averaged intensity, which highlight the concentric-ring patterns. We also
present a time-averaged granulation image processed with a software package
intended for the detection of geological structures in aerospace images. A
technique of running-average-based correlations between the brightness
variations at various points of the granular field is developed and indications
are found for a dynamical link between the emergence and sinking of hot and
cool parcels of the solar plasma. In particular, such a correlation analysis
confirms our suggestion that granules -- overheated blobs -- may repeatedly
emerge on the solar surface. Based on our study, the critical remarks by Rast
(2002) on the original paper by Getling and Brandt (2002) can be dismissed.Comment: 21 page, 8 figures; accepted by "Solar Physics
O/Fe in metal-poor main sequence and subgiant stars
A study of the O/Fe ratio in metal-poor main sequence and subgiant stars is
presented using the [OI] 6300A line, the OI 7774A triplet, and a selection of
weak FeII lines observed on high-resolution spectra acquired with the VLT UVES
spectrograph. The [OI] line is detected in the spectra of 18 stars with -0.5 <
[Fe/H] < -2.4, and the triplet is observed for 15 stars with [Fe/H] ranging
from -1.0 to -2.7. The abundance analysis was made first using standard model
atmospheres taking into account non-LTE effects on the triplet: the [OI] line
and the triplet give consistent results with [O/Fe] increasing quasi-linearly
with decreasing [Fe/H] reaching [O/Fe] ~ +0.7 at [Fe/H] = -2.5. When
hydrodynamical model atmospheres representing stellar granulation in dwarf and
subgiant stars replace standard models, the [O/Fe] from the [OI] and FeII lines
is decreased by an amount which increases with decreasing [Fe/H]. The [O/Fe] vs
[Fe/H] relation remains quasi-linear extending to [O/Fe] ~ +0.5 at [Fe/H] =
-2.5, but with a tendency of a plateau with [O/Fe] ~ +0.3 for -2.0 < [Fe/H] <
-1.0, and a hint of cosmic scatter in [O/Fe] at [Fe/H] ~ -1.0. Use of the
hydrodynamical models disturbs the broad agreement between the oxygen
abundances from the [OI], OI, and OH lines, but 3D non-LTE effects may serve to
erase these differences.Comment: ps file, 18 pages (including 10 figures) - Accepted for publication
in A&
Automated Detection of Solar Eruptions
Observation of the solar atmosphere reveals a wide range of motions, from
small scale jets and spicules to global-scale coronal mass ejections.
Identifying and characterizing these motions are essential to advancing our
understanding the drivers of space weather. Both automated and visual
identifications are currently used in identifying CMEs. To date, eruptions near
the solar surface (which may be precursors to CMEs) have been identified
primarily by visual inspection. Here we report on EruptionPatrol (EP): a
software module that is designed to automatically identify eruptions from data
collected by SDO/AIA. We describe the method underlying the module and compare
its results to previous identifications found in the Heliophysics Event
Knowledgebase. EP identifies eruptions events that are consistent with those
found by human annotations, but in a significantly more consistent and
quantitative manner. Eruptions are found to be distributed within 15Mm of the
solar surface. They possess peak speeds ranging from 4 to 100 km/sec and
display a power-law probability distribution over that range. These
characteristics are consistent with previous observations of prominences.Comment: 6 pages, 4 figures, 7th Solar Information Processing Workshop, to
appear in Space Weather and Space Climat
Asteroseismology from multi-month Kepler photometry: the evolved Sun-like stars KIC 10273246 and KIC 10920273
The evolved main-sequence Sun-like stars KIC 10273246 (F-type) and KIC
10920273 (G-type) were observed with the NASA Kepler satellite for
approximately ten months with a duty cycle in excess of 90%. Such continuous
and long observations are unprecedented for solar-type stars other than the
Sun.
We aimed mainly at extracting estimates of p-mode frequencies - as well as of
other individual mode parameters - from the power spectra of the light curves
of both stars, thus providing scope for a full seismic characterization.
The light curves were corrected for instrumental effects in a manner
independent of the Kepler Science Pipeline. Estimation of individual mode
parameters was based both on the maximization of the likelihood of a model
describing the power spectrum and on a classic prewhitening method. Finally, we
employed a procedure for selecting frequency lists to be used in stellar
modeling.
A total of 30 and 21 modes of degree l=0,1,2 - spanning at least eight radial
orders - have been identified for KIC 10273246 and KIC 10920273, respectively.
Two avoided crossings (l=1 ridge) have been identified for KIC 10273246,
whereas one avoided crossing plus another likely one have been identified for
KIC 10920273. Good agreement is found between observed and predicted mode
amplitudes for the F-type star KIC 10273246, based on a revised scaling
relation. Estimates are given of the rotational periods, the parameters
describing stellar granulation and the global asteroseismic parameters
and .Comment: 15 pages, 15 figures, to be published in Astronomy & Astrophysic
Parallel memetic algorithms for independent job scheduling in computational grids
In this chapter we present parallel implementations of Memetic Algorithms (MAs) for the problem of scheduling independent jobs in computational grids. The problem of scheduling in computational grids is known for its high demanding computational time. In this work we exploit the intrinsic parallel nature of MAs as well as the fact that computational grids offer large amount of resources, a part of which could be used to compute the efficient allocation of jobs to grid resources.
The parallel models exploited in this work for MAs include both fine-grained and coarse-grained parallelization and their hybridization. The resulting schedulers have been tested through different grid scenarios generated by a grid simulator to match different possible configurations of computational grids in terms of size (number of jobs and resources) and computational characteristics of resources. All in all, the result of this work showed that Parallel MAs are very good alternatives in order to match different performance requirement on fast scheduling of jobs to grid resources.Peer ReviewedPostprint (author's final draft
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