135 research outputs found
Dynamics of isolated magnetic bright points derived from Hinode/SOT G-band observations
Small-scale magnetic fields in the solar photosphere can be identified in
high-resolution magnetograms or in the G-band as magnetic bright points (MBPs).
Rapid motions of these fields can cause magneto-hydrodynamical waves and can
also lead to nanoflares by magnetic field braiding and twisting. The MBP
velocity distribution is a crucial parameter for estimating the amplitudes of
those waves and the amount of energy they can contribute to coronal heating.
The velocity and lifetime distributions of MBPs are derived from solar G-band
images of a quiet sun region acquired by the Hinode/SOT instrument with
different temporal and spatial sampling rates. We developed an automatic
segmentation, identification and tracking algorithm to analyse G-Band image
sequences to obtain the lifetime and velocity distributions of MBPs. The
influence of temporal/spatial sampling rates on these distributions is studied
and used to correct the obtained lifetimes and velocity distributions for these
digitalisation effects. After the correction of algorithm effects, we obtained
a mean MBP lifetime of (2.50 +- 0.05) min and mean MBP velocities, depending on
smoothing processes, in the range of (1 - 2) km/s. Corrected for temporal
sampling effects, we obtained for the effective velocity distribution a
Rayleigh function with a coefficient of (1.62 +- 0.05) km/s. The x- and y-
components of the velocity distributions are Gaussians. The lifetime
distribution can be fitted by an exponential function.Comment: Astronomy and Astrophysics (in press
Structural Invariance of Sunspot Umbrae Over the Solar Cycle: 1993-2004
Measurements of maximum magnetic flux, minimum intensity, and size are
presented for 12 967 sunspot umbrae detected on the NASA/NSO
spectromagnetograms between 1993 and 2004 to study umbral structure and
strength during the solar cycle. The umbrae are selected using an automated
thresholding technique. Measured umbral intensities are first corrected for a
confirming observation of umbral limb-darkening. Log-normal fits to the
observed size distribution confirm that the size spectrum shape does not vary
with time. The intensity-magnetic flux relationship is found to be steady over
the solar cycle. The dependence of umbral size on the magnetic flux and minimum
intensity are also independent of cycle phase and give linear and quadratic
relations, respectively. While the large sample size does show a low amplitude
oscillation in the mean minimum intensity and maximum magnetic flux correlated
with the solar cycle, this can be explained in terms of variations in the mean
umbral size. These size variations, however, are small and do not substantiate
a meaningful change in the size spectrum of the umbrae generated by the Sun.
Thus, in contrast to previous reports, the observations suggest the equilibrium
structure, as testified by the invariant size-magnetic field relationship, as
well as the mean size (i.e. strength) of sunspot umbrae do not significantly
depend on solar cycle phase.Comment: 17 pages, 6 figures. Published in Solar Physic
Carnosine Prevents Apoptosis of Glomerular Cells and Podocyte Loss in STZ Diabetic Rats
Background/Aims: We identified carnosinase-1 (CN-1) as risk-factor for diabetic nephropathy (DN). Carnosine, the substrate for CN-1, supposedly is a protective factor regarding diabetic complications. In this study, we hypothesized that carnosine administration to diabetic rats might protect the kidneys from glomerular apoptosis and podocyte loss. Methods: We examined the effect of oral L-carnosine administration (1g/kg BW per day) on apoptosis, podocyte loss, oxidative stress, AGEs and hexosamine pathway in kidneys of streptozotocin-induced diabetic Wistar rats after 3 months of diabetes and treatment. Results: Hyperglycemia significantly reduced endogenous kidney carnosine levels. In parallel, podocyte numbers significantly decreased (-21% compared to non-diabetics,
Stokes Diagnostis of 2D MHD-simulated Solar Magnetogranulation
We study the properties of solar magnetic fields on scales less than the
spatial resolution of solar telescopes. A synthetic infrared
spectropolarimetric diagnostics based on a 2D MHD simulation of
magnetoconvection is used for this. We analyze two time sequences of snapshots
that likely represent two regions of the network fields with their immediate
surrounding on the solar surface with the unsigned magnetic flux density of 300
and 140 G. In the first region we find from probability density functions of
the magnetic field strength that the most probable field strength at logtau_5=0
is equal to 250 G. Weak fields (B < 500 G) occupy about 70% of the surface,
while stronger fields (B 1000 G) occupy only 9.7% of the surface. The magnetic
flux is -28 G and its imbalance is -0.04. In the second region, these
parameters are correspondingly equal to 150 G, 93.3 %, 0.3 %, -40 G, and -0.10.
We estimate the distribution of line-of-sight velocities on the surface of log
tau_5=-1. The mean velocity is equal to 0.4 km/s in the first simulated region.
The averaged velocity in the granules is -1.2 km/s and in the intergranules is
2.5 km/s. In the second region, the corresponding values of the mean velocities
are equal to 0, -1.8, 1.5 km/s. In addition we analyze the asymmetry of
synthetic Stokes-V profiles of the Fe I 1564.8 nm line. The mean values of the
amplitude and area asymmetry do not exceed 1%. The spatially smoothed amplitude
asymmetry is increased to 10% while the area asymmetry is only slightly varied.Comment: 24 pages, 12 figure
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
The Effect of Age on the Gingival Crevicular Fluid Composition During Experimental Gingivitis. A Pilot Study
Management practices for control of ragwort species
The ragwort species common or tansy ragwort (Jacobaea vulgaris, formerly Senecio jacobaea), marsh ragwort (S. aquaticus), Oxford ragwort (S. squalidus) and hoary ragwort (S. erucifolius) are native in Europe, but invaded North America, Australia and New Zealand as weeds. The abundance of ragwort species is increasing in west-and central Europe. Ragwort species contain different groups of secondary plant compounds defending them against generalist herbivores, contributing to their success as weeds. They are mainly known for containing pyrrolizidine alkaloids, which are toxic to grazing cattle and other livestock causing considerable losses to agricultural revenue. Consequently, control of ragwort is obligatory by law in the UK, Ireland and Australia. Commonly used management practices to control ragwort include mechanical removal, grazing, pasture management, biological control and chemical control. In this review the biology of ragwort species is shortly described and the different management practices are discussed
Sunspots: from small-scale inhomogeneities towards a global theory
The penumbra of a sunspot is a fascinating phenomenon featuring complex
velocity and magnetic fields. It challenges both our understanding of radiative
magneto-convection and our means to measure and derive the actual geometry of
the magnetic and velocity fields. In this contribution we attempt to summarize
the present state-of-the-art from an observational and a theoretical
perspective.Comment: Accepted for publication in Space Science Review
- …