189 research outputs found
Energy and helicity budgets of solar quiet regions
We investigate the free magnetic energy and relative magnetic helicity
budgets of solar quiet regions. Using a novel non-linear force-free method
requiring single solar vector magnetograms we calculate the instantaneous free
magnetic energy and relative magnetic helicity budgets in 55 quiet-Sun vector
magnetograms. As in a previous work on active regions, we construct here for
the first time the (free) energy-(relative) helicity diagram of quiet-Sun
regions. We find that quiet-Sun regions have no dominant sense of helicity and
show monotonic correlations a) between free magnetic energy/relative helicity
and magnetic network area and, consequently, b) between free magnetic energy
and helicity. Free magnetic energy budgets of quiet-Sun regions represent a
rather continuous extension of respective active-region budgets towards lower
values, but the corresponding helicity transition is discontinuous due to the
incoherence of the helicity sense contrary to active regions. We further
estimate the instantaneous free magnetic-energy and relative magnetic-helicity
budgets of the entire quiet Sun, as well as the respective budgets over an
entire solar cycle. Derived instantaneous free magnetic energy budgets and, to
a lesser extent, relative magnetic helicity budgets over the entire quiet Sun
are comparable to the respective budgets of a sizeable active region, while
total budgets within a solar cycle are found higher than previously reported.
Free-energy budgets are comparable to the energy needed to power fine-scale
structures residing at the network, such as mottles and spicules
A persistent quiet-Sun small-scale tornado. II. Oscillations
Recently, the characteristics, and dynamics of a persistent 1.7 h vortex
flow, resembling a small-scale tornado, have been investigated with ground-base
and space-based observations and for the first time in the Ha line centre. The
vortex flow showed significant substructure in the form of several intermittent
chromospheric swirls.
We investigate the oscillatory behaviour of various physical parameters in
the vortex area, with a 2D wavelet analysis performed within the vortex flow
area and in a quiet-Sun region (for comparison), using the same high spatial
and temporal resolution Ha and Ca II 8542 CRISP observations, as well as
Doppler velocities and FWHM derived from the Ha line profiles.
The vortex flow shows significant oscillatory power in the 3-5 min range that
peaks around 4 min and behaves differently than the reference quiet-Sun region.
Oscillations reflect the cumulative action of different components such as
swaying motions, rotation, and waves. The derived swaying motion periods are in
the range of 200-220 s, and the rotation periods are ~270 s for Ha and ~215 s
for Ca II. Periods increase with atmospheric height and seem to decrease with
radial distance from the vortex centre, suggesting a deviation from a rigid
rotation. The behaviour of power within the vortex flow as a function of period
and height implies the existence of evanescent waves and the excitation of
different types of waves, such as magnetoacoustic (e.g. kink) or Alfven waves.
The vortex flow seems to be dominated by two motions: a transverse (swaying)
motion, and a rotational motion while oscillations point to the propagation of
waves within it. Nearby fibril-like flows could play an important role in the
rotational modulation of the vortex flow. Indirect evidence exists that the
structure is magnetically supported while the central swirl seems to be acting
as a "central engine" to the vortex flow
Comprehension and Maintenance of Large Scale Multi-Language Software Applications: Open Issues and Challenges
During the last decade, the number of software applications that have been deployed as a collection of components implemented in different programming languages and paradigms has increased considerably. When such applications are maintained, traditional program comprehension and reengineering techniques may not be adequate. In this context, this working session aims to stimulate discussion around key issues relating to the comprehension, reengineering, and maintenance of multi-language software applications. Such issues include, but are not limited to, the formalization, management, exploration, and presentation of multi-language program dependencies, as well as the development of practical toolsets for automating and easing the comprehension and maintenance of multi-language software
Chromospheric swirls I. Automated detection in H observations and their statistical properties
Chromospheric swirls are considered to play a significant role in the
dynamics and heating of the upper solar atmosphere. It is important to
automatically detect and track them in chromospheric observations and determine
their properties. We applied a recently developed automated chromospheric swirl
detection method to time-series observations of a quiet region of the solar
chromosphere obtained in the H-0.2 \r{A} wavelength of the H
spectral line by the CRISP instrument at the Swedish 1-m Solar Telescope. The
algorithm exploits the morphological characteristics of swirling events in high
contrast chromospheric observations and results in the detection of these
structures in each frame of the time series and their tracking over time. We
conducted a statistical analysis to determine their various properties,
including a survival analysis for deriving the mean lifetime. A mean number of
146 9 swirls was detected within the FOV at any given time. The mean
surface density is found equal to 0.08 swirlsMm and the
occurrence rate is 10 swirlsMm min. These values
are much higher than those previously reported from chromospheric observations.
The radii of the detected swirls range between 0.5 and 2.5 Mm, with a mean
value equal to 1.3 0.3 Mm, which is slightly higher than previous
reports. The lifetimes range between 1.5 min and 33.7 min with an arithmetic
mean value of 8.5 min. A survival analysis of the lifetimes, however,
using the Kaplan-Meier estimator in combination with a parametric model results
in a mean lifetime of 10.3 0.6 min. An automated method sheds more light
on their abundance than visual inspection, while higher cadence, higher
resolution observations will most probably result in the detection of a higher
number of such features on smaller scales and with shorter lifetimes
Emergence of small-scale magnetic flux in the quiet Sun
We study the evolution of a small-scale emerging flux region (EFR) in the
quiet Sun, from its emergence to its decay. We track processes and phenomena
across all atmospheric layers, explore their interrelations and compare our
findings with recent numerical modelling studies. We used imaging, spectral and
spectropolarimetric observations from space-borne and ground-based instruments.
The EFR appears next to the chromospheric network and shows all characteristics
predicted by numerical simulations. The total magnetic flux of the EFR exhibits
distinct evolutionary phases, namely an initial subtle increase, a fast
increase and expansion of the region area, a more gradual increase, and a slow
decay. During the initial stages, bright points coalesce, forming clusters of
positive- and negative-polarity in a largely bipolar configuration. During the
fast expansion, flux tubes make their way to the chromosphere, producing
pressure-driven absorption fronts, visible as blueshifted chromospheric
features. The connectivity of the quiet-Sun network gradually changes and part
of the existing network forms new connections with the EFR. A few minutes after
the bipole has reached its maximum magnetic flux, it brightens in soft X-rays
forming a coronal bright point, exhibiting episodic brightenings on top of a
long smooth increase. These coronal brightenings are also associated with
surge-like chromospheric features, which can be attributed to reconnection with
adjacent small-scale magnetic fields and the ambient magnetic field. The
emergence of magnetic flux even at the smallest scales can be the driver of a
series of energetic phenomena visible at various atmospheric heights and
temperature regimes. Multi-wavelength observations reveal a wealth of
mechanisms which produce diverse observable effects during the different
evolutionary stages of these small-scale structures.Comment: Accepted for publication in Astronomy & Astrophysics 14 pages, 14
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Arrhythmias in Chronic Kidney Disease.
Arrhythmias cause disability and an increased risk of premature death in the general population but far more so in patients with renal failure. The association between the cardiac and renal systems is complex and derives in part from common causality of renal and myocardial injury from conditions including hypertension and diabetes. In many cases, there is a causal relationship, with renal dysfunction promoting arrhythmias and arrhythmias exacerbating renal dysfunction. In this review, the authors expand on the challenges faced by cardiologists in treating common and uncommon arrhythmias in patients with renal failure using pharmacological interventions, ablation and cardiac implantable device therapies. They explore the most important interactions between heart rhythm disorders and renal dysfunction while evaluating the ways in which the coexistence of renal dysfunction and cardiac arrhythmia influences the management of both
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