131 research outputs found
Plasma flows and magnetic field interplay during the formation of a pore
We studied the formation of a pore in AR NOAA 11462. We analysed data
obtained with the IBIS at the DST on April 17, 2012, consisting of full Stokes
measurements of the Fe I 617.3 nm lines. Furthermore, we analysed SDO/HMI
observations in the continuum and vector magnetograms derived from the Fe I
617.3 nm line data taken from April 15 to 19, 2012. We estimated the magnetic
field strength and vector components and the LOS and horizontal motions in the
photospheric region hosting the pore formation. We discuss our results in light
of other observational studies and recent advances of numerical simulations.
The pore formation occurs in less than 1 hour in the leading region of the AR.
The evolution of the flux patch in the leading part of the AR is faster (< 12
hour) than the evolution (20-30 hour) of the more diffuse and smaller scale
flux patches in the trailing region. During the pore formation, the ratio
between magnetic and dark area decreases from 5 to 2. We observe strong
downflows at the forming pore boundary and diverging proper motions of plasma
in the vicinity of the evolving feature that are directed towards the forming
pore. The average values and trends of the various quantities estimated in the
AR are in agreement with results of former observational studies of steady
pores and with their modelled counterparts, as seen in recent numerical
simulations of a rising-tube process. The agreement with the outcomes of the
numerical studies holds for both the signatures of the flux emergence process
(e.g. appearance of small-scale mixed polarity patterns and elongated granules)
and the evolution of the region. The processes driving the formation of the
pore are identified with the emergence of a magnetic flux concentration and the
subsequent reorganization of the emerged flux, by the combined effect of
velocity and magnetic field, in and around the evolving structure.Comment: Accepted for publication in Astronomy and Astrophysic
Coronagraphic observations of Si X 1430 nm acquired by DKIST/Cryo-NIRSP with methods for telluric absorption correction
We report commissioning observations of the Si X 1430 nm solar coronal line
observed coronagraphically with the Cryogenic Near-Infrared Spectropolarimeter
(Cryo-NIRSP) at the National Science Foundation's Daniel K. Inouye Solar
Telescope (DKIST). These are the first known spatially resolved observations of
this spectral line, which has strong potential as a coronal magnetic field
diagnostic. The observations target a complex active region located on the
solar northeast limb on 4 March 2022. We present a first analysis of this data,
which extracts the spectral line properties through a careful treatment of the
variable atmospheric transmission that is known to impact this spectral window.
Rastered images are created and compared with EUV observations from the SDO/AIA
instrument. A method for estimating the electron density from the Si X
observations is then demonstrated that makes use of the forbidden line's
density-sensitive emissivity and an emission-measure analysis of the SDO/AIA
bandpass observations. In addition, we derive an effective temperature and
non-thermal line width across the region. This study informs the calibration
approaches required for more routine observations of this promising diagnostic
line.Comment: 12 pages, 9 figures, Accepted for publication in Ap
Phase diversity restoration of sunspot images I. Relations between penumbral and photospheric features
We investigate the dynamics of and the relations between small-scale
penumbral and photospheric features near the outer penumbral boundary:
penumbral grains (PGs), dark penumbral fibrils, granules, and photospheric
G-band bright points. The analysis is based on a 2 h time sequence of a sunspot
close to disc center, taken simultaneously in the G-band and in the blue
continuum at 450.7 nm. Observations were performed at the Swedish Vacuum Solar
Telescope (La Palma) in July 1999. A total of 2564 images (46 arcsec x 75
arcsec) were corrected for telescope aberrations and turbulence perturbations
by applying the inversion method of phase diversity. Our findings can by
summarized as follows: (a) One third of the outward-moving PGs pass through the
outer penumbral boundary and then either continue moving as small bright
features or expand and develop into granules. (b) Former PGs and G-band bright
points next to the spot reveal a different nature. The latter have not been
identified as a continuation of PGs escaping from the penumbra. The G-band
bright points are mostly born close to dark penumbral fibrils where the
magnetic field is strong, whereas PGs stem from the less-magnetized penumbral
component and evolve presumably to non-magnetic granules or small bright
features.Comment: Accepted by A&A, 9 pages and 5 figure
Radiative emission of solar features in the Ca II K line: comparison of measurements and models
We study the radiative emission of various types of solar features, such as
quiet Sun, enhanced network, plage, and bright plage regions, identified on
filtergrams taken in the Ca II K line. We analysed fulldisk images obtained
with the PSPT, by using three interference filters that sample the Ca II K line
with different bandpasses. We studied the dependence of the radiative emission
of disk features on the filter bandpass. We also performed a NLTE spectral
synthesis of the Ca II K line integrated over the bandpass of PSPT filters. The
synthesis was carried out by utilizing both the PRD and CRD with the most
recent set of semi empirical atmosphere models in the literature and some
earlier atmosphere models. We measured the CLV of intensity values for various
solar features identified on PSPT images and compared the results obtained with
those derived from the synthesis. We find that CRD calculations derived using
the most recent quiet Sun model, on average, reproduce the measured values of
the quiet Sun regions slightly more accurately than PRD computations with the
same model. This may reflect that the utilized atmospheric model was computed
assuming CRD. Calculations with PRD on earlier quiet Sun model atmospheres
reproduce measured quantities with a similar accuracy as to that achieved here
by applying CRD to the recent model. We also find that the median contrast
values measured for most of the identified bright features, disk positions, and
filter widths are, on average, a factor 1.9 lower than those derived from PRD
simulations performed using the recent bright feature models. The discrepancy
between measured and modeled values decreases by 12% after taking into account
straylight effects on PSPT images. PRD computations on either the most recent
or the earlier atmosphere models of bright features reproduce measurements from
plage and bright plage regions with a similar accuracy.Comment: 14 pages, 18 figures, accepted by A&
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Efficacy and Safety of Antioxidant Treatment With α-Lipoic Acid Over 4 Years in Diabetic Polyneuropathy
Objective: To evaluate the efficacy and safety of α-lipoic acid (ALA) over 4 years in mild-to-moderate diabetic distal symmetric sensorimotor polyneuropathy (DSPN). Research Design and Methods: In a multicenter randomized double-blind parallel-group trial, 460 diabetic patients with mild-to-moderate DSPN were randomly assigned to oral treatment with 600 mg ALA once daily (n = 233) or placebo (n = 227) for 4 years. Primary end point was a composite score (Neuropathy Impairment Score [NIS]âLower Limbs [NIS-LL] and seven neurophysiologic tests). Secondary outcome measures included NIS, NIS-LL, nerve conduction, and quantitative sensory tests (QSTs). Results: Change in primary end point from baseline to 4 years showed no significant difference between treatment groups (P = 0.105). Change from baseline was significantly better with ALA than placebo for NIS (P = 0.028), NIS-LL (P = 0.05), and NIS-LL muscular weakness subscore (P = 0.045). More patients showed a clinically meaningful improvement and fewer showed progression of NIS (P = 0.013) and NIS-LL (P = 0.025) with ALA than with placebo. Nerve conduction and QST results did not significantly worsen with placebo. Global assessment of treatment tolerability and discontinuations due to lack of tolerability did not differ between the groups. The rates of serious adverse events were higher on ALA (38.1%) than on placebo (28.0%). Conclusions: Four-year treatment with ALA in mild-to-moderate DSPN did not influence the primary composite end point but resulted in a clinically meaningful improvement and prevention of progression of neuropathic impairments and was well tolerated. Because the primary composite end point did not deteriorate significantly in placebo-treated subjects, secondary prevention of its progression by ALA according to the trial design was not feasible
Two-Dimensional Spectroscopy of Photospheric Shear Flows in a Small delta Spot
In recent high-resolution observations of complex active regions,
long-lasting and well-defined regions of strong flows were identified in major
flares and associated with bright kernels of visible, near-infrared, and X-ray
radiation. These flows, which occurred in the proximity of the magnetic neutral
line, significantly contributed to the generation of magnetic shear. Signatures
of these shear flows are strongly curved penumbral filaments, which are almost
tangential to sunspot umbrae rather than exhibiting the typical radial
filamentary structure. Solar active region NOAA 10756 was a moderately complex,
beta-delta sunspot group, which provided an opportunity to extend previous
studies of such shear flows to quieter settings. We conclude that shear flows
are a common phenomenon in complex active regions and delta spots. However,
they are not necessarily a prerequisite condition for flaring. Indeed, in the
present observations, the photospheric shear flows along the magnetic neutral
line are not related to any change of the local magnetic shear. We present
high-resolution observations of NOAA 10756 obtained with the 65-cm vacuum
reflector at Big Bear Solar Observatory (BBSO). Time series of
speckle-reconstructed white-light images and two-dimensional spectroscopic data
were combined to study the temporal evolution of the three-dimensional vector
flow field in the beta-delta sunspot group. An hour-long data set of consistent
high quality was obtained, which had a cadence of better than 30 seconds and
sub-arcsecond spatial resolution.Comment: 23 pages, 6 gray-scale figures, 4 color figures, 2 tables, submitted
to Solar Physic
Magnetic Coupling in the Quiet Solar Atmosphere
Three kinds of magnetic couplings in the quiet solar atmosphere are
highlighted and discussed, all fundamentally connected to the Lorentz force.
First the coupling of the convecting and overshooting fluid in the surface
layers of the Sun with the magnetic field. Here, the plasma motion provides the
dominant force, which shapes the magnetic field and drives the surface dynamo.
Progress in the understanding of the horizontal magnetic field is summarized
and discussed. Second, the coupling between acoustic waves and the magnetic
field, in particular the phenomenon of wave conversion and wave refraction. It
is described how measurements of wave travel times in the atmosphere can
provide information about the topography of the wave conversion zone, i.e., the
surface of equal Alfv\'en and sound speed. In quiet regions, this surface
separates a highly dynamic magnetic field with fast moving magnetosonic waves
and shocks around and above it from the more slowly evolving field of high-beta
plasma below it. Third, the magnetic field also couples to the radiation field,
which leads to radiative flux channeling and increased anisotropy in the
radiation field. It is shown how faculae can be understood in terms of this
effect. The article starts with an introduction to the magnetic field of the
quiet Sun in the light of new results from the Hinode space observatory and
with a brief survey of measurements of the turbulent magnetic field with the
help of the Hanle effect.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Models and Observations of Sunspot Penumbrae
The mysteries of sunspot penumbrae have been under an intense scrutiny for
the past 10 years. During this time, some models have been proposed and
refuted, while the surviving ones had to be modified, adapted and evolved to
explain the ever-increasing array of observational constraints. In this
contribution I will review two of the present models, emphasizing their
contributions to this field, but also pinpointing some of their inadequacies to
explain a number of recent observations at very high spatial resolution. To
help explaining these new observations I propose some modifications to each of
them. These modifications bring those two seemingly opposite models closer
together into a general picture that agrees well with recent 3D
magneto-hydrodynamic simulations.Comment: 9 pages, 1 color figure. Review talk to appear in the proceedings of
the International Workshop of 2008 Solar Total Eclipse: Solar Magnetism,
Corona and Space Weather--Chinese Space Solar Telescope Scienc
Racial differences in the outcome of patients with urothelial carcinoma of the upper urinary tract: an international study
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86897/1/j.1464-410X.2011.10188.x.pd
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