623 research outputs found
Magnetic Non-Potentiality of Solar Active Regions and Peak X-Ray Flux of the Associated Flares
Predicting the severity of the solar eruptive phenomena like flares and
Coronal Mass Ejections (CMEs) remains a great challenge despite concerted
efforts for several decades. The advent of high quality vector magnetograms
obtained from Hinode (SOT/SP) has increased the possibility of meeting this
challenge. In particular, the Spatially Averaged Signed Shear Angle (SASSA)
seems to be an unique parameter to quantify the non-potentiality of the active
regions. We demonstrate the usefulness of SASSA for predicting the flare
severity. For this purpose we present case studies of the evolution of magnetic
non-potentiality using 115 vector magnetograms of four active regions namely
ARs NOAA 10930, 10960, 10961 and 10963 during December 08-15, 2006, June 03-10,
2007, June 28-July 5, 2007 and July 10-17, 2007 respectively. The NOAA ARs
10930 and 10960 were very active and produced X and M class flares
respectively, along with many smaller X-ray flares. On the other hand, the NOAA
ARs 10961 and 10963 were relatively less active and produced only very small
(mostly A and B-class) flares. For this study we have used a large number of
high resolution vector magnetograms obtained from Hinode (SOT/SP). The analysis
shows that the peak X-ray flux of the most intense solar flare emanating from
the active regions depends on the magnitude of the SASSA at the time of the
flare. This finding of the existence of a lower limit of SASSA for a given
class of X-ray flare will be very useful for space weather forecasting. We have
also studied another non-potentiality parameter called mean weighted shear
angle (MWSA) of the vector magnetograms along with SASSA. We find that the MWSA
does not show such distinction as the SASSA for upper limits of GOES X-Ray flux
of solar flares, however both the quantities show similar trends during the
evolution of all active regions studied.Comment: 25 pages, 5 figures, accepted for publication in the Astrophysical
Journa
Anomalous flows in a sunspot penumbra
High-resolution spectropolarimetric observations of active region NOAA 11271
were obtained with the spectro-polarimeter on board Hinode to analyze the
properties of an anomalous flow in the photosphere in a sunspot penumbra. We
detect a blue-shifted feature that appeared on the limb-side penumbra of a
sunspot and that was present intermittently during the next two hours. It
exhibited a maximum blue-shift of 1.6 km/s, an area of 5.2 arcsec^2, and an
uninterrupted lifetime of 1 hr. The blue-shifted feature, when present, lies
parallel to red-shifts. Both blue and red shifts flank a highly
inclined/horizontal magnetic structure that is radially oriented in the
penumbra. The low-cadence SP maps reveal changes in size, radial position in
the penumbra and line-of-sight velocity of the blue-shifted feature, from one
scan to the other. There was an increase of nearly 500 G in the field strength
and a marginal reduction in the field inclination of about 10 deg with the
onset of the blue-shifts. In the chromosphere, intense, arc-shaped brightenings
were observed close to the location of the blue-shifts, that extend from the
edge of the umbral core to the penumbra-quiet Sun boundary. The strongest and
largest brightenings were observed about 30 min after the strongest blue-shifts
were detected at the photosphere. The close spatial proximity of the two
phenomenon strongly suggests a causal relationship. The blue-shifted feature
represents plasma motion that could be related to a magnetic structure that
rises in the solar atmosphere and subsequently reconnects with the ambient
chromospheric magnetic field of the sunspot or an inverse Evershed flow, which
would be unique in the photosphere. This transient phenomena is presumably
related to the dynamic stability of the sunspot because the corresponding
umbral core separated two days later at the location of the blue-shifts and
fragmented subsequently.Comment: Accepted for publication in A&A: 8 pages, 8 figure
Role of sialic acid in brachyspira hyodysenteriae adhesion to pig colonic mucins
Infection with Brachyspira hyodysenteriae results in mucoid hemorrhagic diarrhea. This pathogen is associated with the colonic mucus layer, mainly composed of mucins. Infection regulates mucin O-glycosylation in the colon and increases mucin secretion as well as B. hyodysenteriae binding sites on mucins. Here, we analyzed potential mucin epitopes for B. hyodysenteriae adhesion in the colon, as well as the effect of colonic mucins on bacterial growth. Associations between B. hyodysenteriae binding to pig colonic mucins and mucin glycan data showed that B. hyodysenteriae binding was associated with the presence of N-glycolylneuraminic acid (NeuGc) on mucins. The role of sialic acid in B. hyodysenteriae adhesion was analyzed after the removal of sialic acid residues on the mucins by enzymatic treatment with sialidase A, which decreased bacterial binding to the mucins. The effect of pig colonic mucins on B. hyodysenteriae growth was determined in carbohydrate-free medium. B. hyodysenteriae growth increased in the presence of mucins from two out of five infected pigs, suggesting utilization of mucins as a carbon source for growth. Additionally, bacterial growth was enhanced by free sialic acid and N-acetylglucosamine. The results highlight a role of sialic acid as an adhesion epitope for B. hyodysenteriae interaction with colonic mucins. Furthermore, the mucin response and glycosylation changes exerted in the colon during B. hyodysenteriae infection result in a potentially favorable environment for pathogen growth in the intestinal mucus layer
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