4,539 research outputs found
Simulations of small-scale explosive events on the Sun
Small-scale explosive events or microflares occur throughout the
chromospheric network of the Sun. They are seen as sudden bursts of highly
Doppler shifted spectral lines of ions formed at temperatures in the range
2x10^4 - 5x10^5 K. They tend to occur near regions of cancelling photospheric
magnetic fields and are thought to be directly associated with magnetic field
reconnection. Recent observations have revealed that they have a bi-directional
jet structure reminiscent of Petschek reconnection. In this paper compressible
MHD simulations of the evolution of a current sheet to a steady Petschek,
jet-like configuration are computed using the Versatile Advection Code. We
obtain velocity profiles that can be compared with recent ultraviolet line
profile observations. By choosing initial conditions representative of magnetic
loops in the solar corona and chromosphere, it is possible to explain the fact
that jets flowing outward into the corona are more extended and appear before
jets flowing towards the chromosphere. This model can reproduce the high
Doppler shifted components of the line profiles but the brightening at low
velocities, near the centre of the bi-directional jet, cannot be explained by
this simple MHD model.Comment: 16 pages, 8 figures. To be published in Solar Physic
Energy spectra of 3He-rich solar energetic particles associated with coronal waves
In addition to their anomalous abundances, 3He-rich solar energetic particles
(SEPs) show puzzling energy spectral shapes varying from rounded forms to power
laws where the later are characteristics of shock acceleration. Solar sources
of these particles have been often associated with jets and narrow CMEs, which
are the signatures of magnetic reconnection involving open field. Recent
reports on new associations with large-scale EUV waves bring new insights on
acceleration and transport of 3He-rich SEPs in the corona. We examined energy
spectra for 32 3He-rich SEP events observed by ACE at L1 near solar minimum in
2007-2010 and compared the spectral shapes with solar flare signatures obtained
from STEREO EUV images. We found the events with jets or brightenings tend to
be associated with rounded spectra and the events with coronal waves with power
laws. This suggests that coronal waves may be related to the unknown second
stage mechanism commonly used to interpret spectral forms of 3He-rich SEPs.Comment: Presented at 15th Annual International Astrophysics Conference "The
Science of Ed Stone". Accepted for publication in Journal of Physics:
Conference Serie
Jets or high velocity flows revealed in high-cadence spectrometer and imager co-observations?
We report on active region EUV dynamic events observed simultaneously at
high-cadence with SUMER/SoHO and TRACE. Although the features appear in the
TRACE Fe ix/x 171A images as jets seen in projection on the solar disk, the
SUMER spectral line profiles suggest that the plasma has been driven along a
curved large scale magnetic structure, a pre-existing loop. The SUMER
observations were carried out in spectral lines covering a large temperature
range from 10^4 K to 10^6 K. The spectral analysis revealed that a sudden
heating from an energy deposition is followed by a high velocity plasma flow.
The Doppler velocities were found to be in the range from 90 to 160 km/s. The
heating process has a duration which is below the SUMER exposure time of 25 s
while the lifetime of the events is from 5 to 15 min. The additional check on
soft X-ray Yohkoh images shows that the features most probably reach 3 MK
(X-ray) temperatures. The spectroscopic analysis showed no existence of cold
material during the events
Adiabatic Magnetization of Superconductors as a High-Performance Cooling Mechanism
The adiabatic magnetization of a superconductor is a cooling principle
proposed in the 30s, which has never been exploited up to now. Here we present
a detailed dynamic description of the effect, computing the achievable final
temperatures as well as the process timescales for different superconductors in
various regimes. We show that, although in the experimental conditions explored
so far the method is in fact inefficient, a suitable choice of initial
temperatures and metals can lead to unexpectedly large cooling effect, even in
the presence of dissipative phenomena. Our results suggest that this principle
can be re-envisaged today as a performing refrigeration method to access the
microK regime in nanodevices.Comment: 4 pages, 3 color figure
Multi-Spacecraft Observations of Recurrent 3He-Rich Solar Energetic Particles
We study the origin of 3He-rich solar energetic particles (<1 MeV/nucleon)
that are observed consecutively on STEREO-B, ACE, and STEREO-A spacecraft when
they are separated in heliolongitude by more than 90{\deg}. The 3He-rich period
on STEREO-B and STEREO-A commences on 2011 July 1 and 2011 July 16,
respectively. The ACE 3He-rich period consists of two sub-events starting on
2011 July 7 and 2011 July 9. We associate the STEREO-B July 1 and ACE July 7
3He-rich events with the same sizeable active region producing X-ray flares
accompanied by prompt electron events, when it was near the west solar limb as
seen from the respective spacecraft. The ACE July 9 and STEREO-A July 16 events
were dispersionless with enormous 3He enrichment, lacking solar energetic
electrons and occurring in corotating interaction regions. We associate these
events with a small, recently emerged active region near the border of a
low-latitude coronal hole that produced numerous jet-like emissions temporally
correlated with type III radio bursts. For the first time we present
observations of 1) solar regions with long-lasting conditions for 3He
acceleration and 2) solar energetic 3He that is temporary
confined/re-accelerated in interplanetary space.Comment: accepted for publication in The Astrophysical Journa
Participant recruitment to FiCTION, a primary dental care trial – survey of facilitators and barriers
Objective To identify reasons behind a lower than expected participant recruitment rate within the FiCTION trial, a multi-centre paediatric primary dental care randomised controlled trial (RCT).
Subjects (materials) and methods An online survey, based on a previously published tool, consisting of both quantitative and qualitative responses, completed by staff in dental practices recruiting to FiCTION. Ratings from quantitative responses were aggregated to give overall scores for factors related to participant recruitment. Qualitative responses were independently grouped into themes.
Results Thirty-nine anonymous responses were received. Main facilitators related to the support received from the central research team and importance of the research question. The main barriers related to low child eligibility rates and the integration of trial processes within routine workloads.
Conclusions These findings have directed strategies for enhancing participant recruitment at existing practices and informed recruitment of further practices. The results help provide a profile of the features required of practices to successfully screen and recruit participants. Future trials in this setting should consider the level of interest in the research question within practices, and ensure trial processes are as streamlined as possible. Research teams should actively support practices with participant recruitment and maintain enthusiasm among the entire practice team
Continuous cough monitoring using ambient sound recording during convalescence from a COPD exacerbation
Purpose Cough is common in chronic obstructive pulmonary disease (COPD) and is associated with frequent exacerbations and increased mortality. Cough increases during acute exacerbations (AE-COPD), representing a possible metric of clinical deterioration. Conventional cough monitors accurately report cough counts over short time periods. We describe a novel monitoring system which we used to record cough continuously for up to 45 days during AE-COPD convalescence. Methods This is a longitudinal, observational study of cough monitoring in AE-COPD patients discharged from a single teaching-hospital. Ambient sound was recorded from two sites in the domestic environment and analysed using novel cough classifier software. For comparison, the validated hybrid HACC/LCM cough monitoring system was used on days 1, 5, 20 and 45. Patients were asked to record symptoms daily using diaries. Results Cough monitoring data were available for 16 subjects with a total of 568 monitored days. Daily cough count fell significantly from mean±SEM 272.7±54.5 on day 1 to 110.9±26.3 on day 9 (p<0.01) before plateauing. The absolute cough count detected by the continuous monitoring system was significantly lower than detected by the hybrid HACC/LCM system but normalised counts strongly correlated (r=0.88, p<0.01) demonstrating an ability to detect trends. Objective cough count and subjective cough scores modestly correlated (r=0.46). Conclusions Cough frequency declines significantly following AE-COPD and the reducing trend can be detected using continuous ambient sound recording and novel cough classifier software. Objective measurement of cough frequency has the potential to enhance our ability to monitor the clinical state in patients with COPD
Oscillations in the wake of a flare blast wave
Oscillations of coronal loops in the Sun have been reported in both imaging
and spectral observations at the onset of flares. Images reveal transverse
oscillations, whereas spectra detect line-of-sight velocity or Doppler-shift
oscillations. The Doppler-shift oscillations are commonly interpreted as
longitudinal modes. Our aim is to investigate the relationship between loop
dynamics and flows seen in TRACE 195\AA images and Doppler shifts observed by
SUMER in Si III 1113.2\AA and Fe XIX 1118.1\AA at the time of a C.8-class limb
flare and an associated CME. We carefully co-aligned the sequence of TRACE 195
\AA images to structures seen in the SUMER Si III, Ca X,and Fe XIX emission
lines. Additionally, H-alpha observations of a lifting prominence associated
with the flare and the coronal mass ejection (CME) are available in three bands
around 6563.3 \AA . They give constraints on the timing and geometry.
Large-scale Doppler-shift oscillations in Fe XIX and transverse oscillations in
intensity images were observed over a large region of the corona after the
passage of a wide bright extreme-ultraviolet (EUV) disturbance, which suggests
ionization, heating, and acceleration of hot plasma in the wake of a blast
wave.Comment: 4 pages, 6 figures Astronomy & Astrophysics (accepted
Patchy Reconnection in a Y-Type Current Sheet
We study the evolution of the magnetic field in a Y-type current sheet
subject to a brief, localized magnetic reconnection event. The reconnection
produces up- and down-flowing reconnected flux tubes which rapidly decelerate
when they hit the Y-lines and underlying magnetic arcade loops at the ends of
the current sheet. This localized reconnection outflow followed by a rapid
deceleration reproduces the observed behavior of post-CME downflowing coronal
voids. These simulations support the hypothesis that these observed coronal
downflows are the retraction of magnetic fields reconnected in localized
patches in the high corona.Comment: 4 pages, 3 figure
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