910 research outputs found
Genomic relatedness within five common Finnish Campylobacter jejuni pulsed-field gel electrophoresis genotypes studied by amplified fragment length polymorphism analysis, ribotyping and serotyping
Thirty-five Finnish Campylobacter jejuni strains with five SmaI/SacII pulsed-field gel electrophoresis (PFGE) genotypes selected among human and chicken isolates from 1997 and 1998 were used for comparison of their PFGE patterns, amplified fragment length polymorphism (AFLP) patterns, HaeIII ribotypes, and heat-stable (HS) serotypes. The discriminatory power of PFGE, AFLP, and ribotyping with HaeIII were shown to be at the same level for this selected set of strains, and these methods assigned the strains into the same groups. The PFGE and AFLP patterns within a genotype were highly similar, indicating genetic relatedness. The same HS serotypes were distributed among different genotypes, and different serotypes were identified within one genotype. HS serotype 12 was only associated with the combined genotype G1 (PFGE-AFLP-ribotype). These studies using polyphasic genotyping methods suggested that common Finnish C. jejuni genotypes form genetic lineages which colonize both humans and chickens
Type III Radio Burst Duration and SEP Events
Long-duration (>15 min), low-frequency (25 MeV. The 1-MHz duration of the type III burst (28 rein) is near the median value of type III durations found for gradual SEP events and ground level enhancement (GLE) events. Yet, there was no sign of SEP events. On the other hand, two other type III bursts from the same active region had similar duration but accompanied by WAVES type 11 bursts; these bursts were also accompanied by SEP events detected by SOHO/ERNE. This study suggests that the type III burst duration may not be a good indicator of an SEP event, consistent with the statistical study of Cliver and Ling (2009, ApJ )
Ground Level Enhancement in the 2014 January 6 Solar Energetic Particle Event
We present a study of the 2014 January 6 solar energetic particle (SEP)
event, which produced a small ground level enhancement (GLE), making it the
second GLE of this unusual solar cycle 24. This event was primarily observed by
the South Pole neutron monitors (increase of ~2.5%) whereas a few other neutron
monitors recorded smaller increases. The associated coronal mass ejection (CME)
originated behind the western limb and had the speed of 1960 km/s. The height
of the CME at the start of the associated metric type II radio burst, which
indicates the formation of a strong shock, was measured to be 1.61 Rs using a
direct image from STEREO-A/EUVI. The CME height at the time of GLE particle
release (determined using the South Pole neutron monitor data) was directly
measured as 2.96 Rs, from the STEREO-A/COR1 white-light observations. These CME
heights are consistent with those obtained for the GLE71, the only other GLE of
the current cycle as well as cycle-23 GLEs derived using back-extrapolation.
GLE72 is of special interest because it is one of the only two GLEs of cycle
24, one of the two behind-the-limb GLEs and one of the two smallest GLEs of
cycles 23 and 24
CME Interaction with Coronal Holes and Their Interplanetary Consequences
A significant number of interplanetary (IP) shocks (-17%) during cycle 23 were not followed by drivers. The number of such "driverless" shocks steadily increased with the solar cycle with 15%, 33%, and 52% occurring in the rise, maximum, and declining phase of the solar cycle. The solar sources of 15% of the driverless shocks were very close the central meridian of the Sun (within approx.15deg), which is quite unexpected. More interestingly, all the driverless shocks with their solar sources near the solar disk center occurred during the declining phase of solar cycle 23. When we investigated the coronal environment of the source regions of driverless shocks, we found that in each case there was at least one coronal hole nearby suggesting that the coronal holes might have deflected the associated coronal mass ejections (CMEs) away from the Sun-Earth line. The presence of abundant low-latitude coronal holes during the declining phase further explains why CMEs originating close to the disk center mimic the limb CMEs, which normally lead to driverless shocks due to purely geometrical reasons. We also examined the solar source regions of shocks with drivers. For these, the coronal holes were located such that they either had no influence on the CME trajectories. or they deflected the CMEs towards the Sun-Earth line. We also obtained the open magnetic field distribution on the Sun by performing a potential field source surface extrapolation to the corona. It was found that the CMEs generally move away from the open magnetic field regions. The CME-coronal hole interaction must be widespread in the declining phase, and may have a significant impact on the geoeffectiveness of CMEs
Major Solar Eruptions and High Energy Particle Events during Solar Cycle 24
We report on a study of all major solar eruptions that occurred on the
front-side of the Sun during the rise to peak phase of cycle 24 (first 62
months) in order to understand the key factors affecting the occurrence of
large solar energetic particle events (SEPs) and the ground levels enhancement
(GLE) events. The eruptions involve major flares with soft X-ray peak flux >/=
5.0 x10-5 Wm-2 (i.e., flare size >/= M5.0) and accompanying coronal mass
ejections (CMEs). The selection criterion was based on the fact that the only
front-side GLE in cycle 24 (GLE 71) had a flare size of M5.1. Only ~37% of the
major eruptions from the western hemisphere resulted in large SEP events.
Almost the same number of large SEP events was produced in weaker eruptions
(flare size <M5.0), suggesting that the soft X-ray flare is not a good
indicator of SEP or GLE events. On the other hand, the CME speed is a better
indicator of SEP and GLE events because it is consistently high supporting the
shock acceleration mechanism for SEPs and GLEs. We found the CME speed,
magnetic connectivity to Earth, and ambient conditions as the main factors that
contribute to the lack of high energy particle events during cycle 24. Several
eruptions poorly connected to Earth (eastern-hemisphere or behind-the-west-limb
events) resulted in very large SEP events detected by the STEREO spacecraft.
Some very fast CMEs, likely to have accelerated particles to GeV energies, did
not result in a GLE event because of poor latitudinal connectivity. The
stringent latitudinal requirement suggests that the highest energy particles
are likely accelerated in the nose part of shocks. There were also
well-connected fast CMEs, which did not seem to have accelerated high energy
particles due to possible unfavorable ambient conditions (high Alfven speed,
overall reduction in acceleration efficiency in cycle 24).Comment: 29 pages, 5 figures, 5 tables, to be published in a special issue of
Earth, Planets, and Spac
Depletion of Mediator Kinase Module Subunits Represses Superenhancer-Associated Genes in Colon Cancer Cells
In cancer, oncogene activation is partly mediated by acquired superenhancers, which therefore represent potential targets for inhibition. Superenhancers are enriched for BRD4 and Mediator, and both BRD4 and the Mediator MED12 subunit are disproportionally required for expression of superenhancer-associated genes in stem cells. Here we show that depletion of Mediator kinase module subunit MED12 or MED13 together with MED13L can be used to reduce expression of cancer-acquired superenhancer genes, such as the MYC gene, in colon cancer cells, with a concomitant decrease in proliferation. Whereas depletion of MED12 or MED13/MED13L caused a disproportional decrease of superenhancer gene expression, this was not seen with depletion of the kinases cyclin-dependent kinase 9 (CDK8) and CDK19. MED12-MED13/MED13L-dependent superenhancer genes were coregulated by beta-catenin, which has previously been shown to associate with MED12. Importantly, beta-catenin depletion caused reduced binding of MED12 at the MYC superenhancer. The effect of MED12 or MED13/MED13L depletion on cancer-acquired superenhancer gene expression was more specific than and partially distinct from that of BRD4 depletion, with the most efficient inhibition seen with combined targeting. These results identify a requirement of MED12 and MED13/MED13L for expression of acquired superenhancer genes in colon cancer, implicating these Mediator subunits as potential therapeutic targets for colon cancer, alone or together with BRD4.Peer reviewe
Front-Side Type II Radio Bursts Without Shocks Near Earth
Type II radio bursts are due to shocks driven by coronal mass ejections (CMEs), so the shocks are expected to arrive at Earth in 2-3 days if the source is on the front-side of the Sun. However, a significant fraction of front-side CMEs producing type II bursts did not result in shocks at 1 AU. On can think of several possibilities for the lack of shocks: (1) CMEs originating at large central meridian distances may be driving a shock, but the shock may not be extended sufficiently to reach to the Sun-Earth line. (2) CME cannibalism results in the merger of shocks so that one observes a single shock at Earth even though there are two type II bursts near the Sun. (3) CME-driven shocks may become weak and dissipate before reaching 1 AU. We examined a set of 30 type II bursts observed by the Wind/WAVES experiment that had the solar sources very close to the disk center (within a CMD of 15 degrees), but did not have shock at Earth. We find that the near-Sun speeds of the associated CMEs average to approx.600 km/s, only slightly higher than the average speed of CM Es associated with radio-quiet shocks. However, the fraction of halo CMEs is only -28%, compared to 40% for radio-quiet shocks and 72% for all radio-loud shocks. We conclude that the disk-center radio loud CMEs with no shocks at 1 AU are generally of lower energy and they drive shocks only close to the Sun
Sun-to-Earth Propagation of the 2015 June 21 Coronal Mass Ejection Revealed by Optical, EUV, and Radio Observations
We investigate the propagation of the 2015 June 21 CME-driven shock as
revealed by the type II bursts at metric and longer wavelengths and coronagraph
observations. The CME was associated with the second largest geomagnetic storm
of solar cycle 24 and a large solar energetic particle (SEP) event. The
eruption consisted of two M-class flares, with the first one being confined,
with no metric or interplanetary radio bursts. However, there was intense
microwave burst, indicating accelerated particles injected toward the Sun. The
second flare was eruptive that resulted in a halo CME. The CME was deflected
primarily by an equatorial coronal hole that resulted in the modification of
the intensity profile of the associated SEP event and the duration of the CME
at Earth. The interplanetary type II burst was particularly intense and was
visible from the corona all the way to the vicinity of the Wind spacecraft with
fundamental-harmonic structure. We computed the shock speed using the type II
drift rates at various heliocentric distances and obtained information on the
evolution of the shock that matched coronagraph observations near the Sun and
in-situ observations near Earth. The depth of the geomagnetic storm is
consistent with the 1-AU speed of the CME and the magnitude of the southward
component.Comment: 34 pages, 13 figures, 3 tables, Accepted for publication in JAST
Extreme Kinematics of the 2017 September 10 Solar Eruption and the Spectral Characteristics of the Associated Energetic Particles
We report on the 2017 September 10 ground level enhancement (GLE) event
associated with a coronal mass ejection (CME) whose initial acceleration
(~9.1km s^-2) and initial speed (~4300 km/s) were among the highest observed in
the SOHO era. The GLE event was of low intensity (~4.4% above background) and
softer-than-average fluence spectrum. We suggest that poor connectivity
(longitudinal and latitudinal) of the source to Earth compounded by the weaker
ambient magnetic field contributed to these GLE properties. Events with similar
high initial speed either lacked GLE association or had softer fluence spectra.
The shock-formation height inferred from the metric type II burst was ~1.4 Rs,
consistent with other GLE events. The shock height at solar particle release
(SPR) was ~4.4+/-0.38 Rs, consistent with the parabolic relationship between
the shock height at SPR and source longitude. At SPR, the eastern flank of the
shock was observed in EUV projected on the disk near the longitudes
magnetically connected to Earth: W60 to W45.Comment: 13 pages, 5 figures, to appear in the Astrophysical Journal Letter
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