126,505 research outputs found
Chromospheric evaporation in sympathetic coronal bright points
{Chromospheric evaporation is a key process in solar flares that has
extensively been investigated using the spectroscopic observations. However,
direct soft X-ray (SXR) imaging of the process is rare, especially in remote
brightenings associated with the primary flares that have recently attracted
dramatic attention.} {We intend to find the evidence for chromospheric
evaporation and figure out the cause of the process in sympathetic coronal
bright points (CBPs), i.e., remote brightenings induced by the primary CBP.}
{We utilise the high-cadence and high-resolution SXR observations of CBPs from
the X-ray Telescope (XRT) aboard the Hinode spacecraft on 2009 August 23.} {We
discover thermal conduction front propagating from the primary CBP, i.e., BP1,
to one of the sympathetic CBPs, i.e., BP2 that is 60\arcsec away from BP1.
The apparent velocity of the thermal conduction is 138 km s.
Afterwards, hot plasma flowed upwards into the loop connecting BP1 and BP2 at a
speed of 76 km s, a clear signature of chromospheric evaporation.
Similar upflow was also observed in the loop connecting BP1 and the other
sympathetic CBP, i.e., BP3 that is 80\arcsec away from BP1, though less
significant than BP2. The apparent velocity of the upflow is 47 km
s. The thermal conduction front propagating from BP1 to BP3 was not well
identified except for the jet-like motion also originating from BP1.} {We
propose that the gentle chromospheric evaporation in the sympathetic CBPs were
caused by thermal conduction originating from the primary CBP.}Comment: 9 pages, 5 figure
Blobs in recurring EUV jets
In this paper, we report our discovery of blobs in the recurrent and
homologous jets that occurred at the western edge of NOAA active region 11259
on 2011 July 22. The jets were observed in the seven extreme-ultraviolet (EUV)
filters of the Atmospheric Imaging Assembly (AIA) instrument aboard the Solar
Dynamics Observatory (SDO). Using the base-difference images of the six filters
(94, 131, 171, 211, 193, and 335 {\AA}), we carried out the differential
emission measure (DEM) analyses to explore the thermodynamic evolutions of the
jets. The jets were accompanied by cool surges observed in the H line
center of the ground-based telescope in the Big Bear Solar Observatory. The
jets that had lifetimes of 2030 min recurred at the same place for three
times with interval of 4045 min. Interestingly, each of the jets
intermittently experienced several upward eruptions at the speed of 120450
km s. After reaching the maximum heights, they returned back to the
solar surface, showing near-parabolic trajectories. The falling phases were
more evident in the low- filters than in the high- filters, indicating
that the jets experienced cooling after the onset of eruptions. We identified
bright and compact blobs in the jets during their rising phases. The
simultaneous presences of blobs in all the EUV filters were consistent with the
broad ranges of the DEM profiles of the blobs (),
indicating their multi-thermal nature. The median temperatures of the blobs
were 2.3 MK. The blobs that were 3 Mm in diameter had lifetimes of
2460 s. To our knowledge, this is the first report of blobs in coronal jets.
We propose that these blobs are plasmoids created by the magnetic reconnection
as a result of tearing-mode instability and ejected out along the jets.Comment: 22 pages, 10 figure
Helicity Observation of Weak and Strong Fields
We report in this letter our analysis of a large sample of photospheric
vector magnetic field measurements. Our sample consists of 17200 vector
magnetograms obtained from January 1997 to August 2004 by Huairou Solar
Observing Station of the Chinese National Astronomical Observatory. Two
physical quantities, and current helicity, are calculated and their
signs and amplitudes are studied in a search for solar cycle variations.
Different from other studies of the same type, we calculate these quantities
for weak () fields separately. For
weak fields, we find that the signs of both and current helicity are
consistent with the established hemispheric rule during most years of the solar
cycle and their magnitudes show a rough tendency of decreasing with the
development of solar cycle. Analysis of strong fields gives an interesting
result: Both and current helicity present a sign opposite to that of
weak fields. Implications of these observations on dynamo theory and helicity
production are also briefly discussed.Comment: accepted for publication in ApJ Lette
Knowledge discovery for friction stir welding via data driven approaches: Part 2 – multiobjective modelling using fuzzy rule based systems
In this final part of this extensive study, a new systematic data-driven fuzzy modelling approach has been developed, taking into account both the modelling accuracy and its interpretability (transparency) as attributes. For the first time, a data-driven modelling framework has been proposed designed and implemented in order to model the intricate FSW behaviours relating to AA5083 aluminium alloy, consisting of the grain size, mechanical properties, as well as internal process properties. As a result, ‘Pareto-optimal’ predictive models have been successfully elicited which, through validations on real data for the aluminium alloy AA5083, have been shown to be accurate, transparent and generic despite the conservative number of data points used for model training and testing. Compared with analytically based methods, the proposed data-driven modelling approach provides a more effective way to construct prediction models for FSW when there is an apparent lack of fundamental process knowledge
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