962 research outputs found
Formation and eruption of sigmoidal structure from a weak field region of NOAA 11942
Using observations from Solar Dynamics Observatory, we studied an interesting
example of a sigmoid formation and eruption from small-scale flux canceling
regions of active region (AR) 11942. Analysis of HMI and AIA observations infer
that initially the AR is compact and bipolar in nature, evolved to sheared
configuration consisting of inverse J-shaped loops hosting a filament channel
over a couple of days. By tracking the photospheric magnetic features, shearing
and converging motions are observed to play a prime role in the development of
S-shaped loops and further flux cancellation leads to tether-cutting
reconnection of J-loops. This phase is co-temporal with the filament rise
motion followed by sigmoid eruption at 21:32 UT on January 6. The flux rope
rises in phases of slow (v = 26 km~s) and fast (a= 55
ms) rise motion categorizing the CME as slow with an associated weak
C1.0 class X-ray flare. The flare ribbon separation velocity peaks at around
peak time of the flare at which maximum reconnection rate (2.14 Vcm)
occurs. Further, the EUV light-curves of 131, 171\AA~have delayed peaks of 130
minutes compared to 94\AA~and is explained by differential emission measure.
Our analysis suggests that the energy release is proceeded in a much long time
duration, manifesting the onset of filament rise and eventual eruption driven
by converging and canceling flux in the photosphere. Unlike strong eruption
events, the observed slow CME and weak flare are indications of slow runway
tether-cutting reconnection where most of the sheared arcade is relaxed during
the extended post phase of the eruption.Comment: Accepted for Publication in The Astrophysical journal on 19 February,
2019. It has 17 pages including 12 figure
Statistical study of magnetic non-potential measures in confined and eruptive flares
Using the HMI/SDO vector magnetic field observations, we studied the relation
of degree of magnetic non-potentiality with the observed flare/CME in active
regions. From a sample of 77 flare/CME cases, we found a general relation that
degree of non-potentiality is positively correlated with the flare strength and
the associated CME speeds. Since the magnetic flux in the flare-ribbon area is
more related to the reconnection, we trace the strong gradient polarity
inversion line (SGPIL), Schrijver's R value manually along the flare-ribbon
extent. Manually detected SGPIL length and R values show higher correlation
with the flare strength and CME speed than the automatically traced values
without flare-ribbon information. It highlights the difficulty of predicting
the flare strength and CME speed a priori from the pre-flare magnetograms used
in flare prediction models. Although the total, potential magnetic energy
proxies show weak positive correlation, the decrease in free energy exhibits
higher correlation (0.56) with the flare strength and CME speed. Moreover, the
eruptive flares have threshold of SGPIL length (31Mm), R value
(Mx), free-energy decrease (erg) compared to
confined ones. In 90\% eruptive flares, the decay-index curve is steeper
reaching within 42Mm, whereas it is beyond 42Mm in %
confined flares. While indicating the improved statistics in the predictive
capability of the AR eruptive behavior with the flare-ribbon information, our
study provides threshold magnetic properties for a flare to be eruptive.Comment: 12 pages, 9 figures, accepted in Ap
Center to limb observations and modeling of the Ca I 4227 A line
The observed center-to-limb variation (CLV) of the scattering polarization in
different lines of the Second Solar Spectrum can be used to constrain the
height variation of various atmospheric parameters, in particular the magnetic
fields via the Hanle effect. Here we attempt to model non-magnetic CLV
observations of the profiles of the Ca I 4227 A line recorded with the
ZIMPOL-3 at IRSOL. For modeling, we use the polarized radiative transfer with
partial frequency redistribution with a number of realistic 1-D model
atmospheres. We find that all the standard FAL model atmospheres, used by us,
fail to simultaneously fit the observed (, ) at all the limb distances
(). However, an attempt is made to find a single model which can provide a
fit at least to the CLV of the observed instead of a simultaneous fit to
the (, ) at all . To this end we construct a new 1-D model by
combining two of the standard models after modifying their temperature
structures in the appropriate height ranges. This new combined model closely
reproduces the observed at all the , but fails to reproduce the
observed rest intensity at different . Hence we find that no single 1-D
model atmosphere succeeds in providing a good representation of the real Sun.
This failure of 1-D models does not however cause an impediment to the magnetic
field diagnostic potential of the Ca I 4227 A line. To demonstrate this we
deduce the field strength at various positions without invoking the use
of radiative transfer.Comment: 20 pages, 10 figures, Accepted for publication in Ap
Finding the critical decay index in solar prominence eruptions
The background field is assumed to play prime role in the erupting structures
like prominences. In the flux rope models, the critical decay index () is
a measure of the rate at which background field intensity decreases with height
over the flux rope or erupting structure. In the real observations, the
critical height of the background field is unknown, so a typical value of
is adopted from the numerical studies. In this study, we determined
the of 10 prominence eruptions (PEs). The prominence height in 3D is
derived from two-perspective observations of \textit{Solar Dynamics
Observatory} and \textit{Solar TErrestrial RElations Observatory}. Synoptic
maps of photospheric radial magnetic field are used to construct the background
field in the corona. During the eruption, the height-time curve of the sample
events exhibits the slow and fast-rise phases and is fitted with the
linear-cum-exponential model. From this model, the onset height of fast-rise
motion is determined and is considered as the critical height for the onset of
the torus-instability because the erupting structure is allowed to expand
exponentially provided there is no strapping background field. Corresponding to
the critical height, the values of our sample events are varied to be in
the range of 0.8-1.3. Additionally, the kinematic analysis suggests that the
acceleration of PEs associated with flares are significantly enhanced compared
to flare-less PEs. We found that the flare magnetic reconnection is the
dominant contributor than the torus-instability to the acceleration process
during the fast-rise phase of flare-associated PEs in low corona
().Comment: 12 pages, 6 figures and 2 table
Theoretical Study of Physisorption of Nucleobases on Boron Nitride Nanotubes: A New Class of Hybrid Nano-Bio Materials
We investigate the adsorption of the nucleic acid bases, adenine (A), guanine
(G), cytosine (C), thymine (T) and uracil (U) on the outer wall of a high
curvature semiconducting single-walled boron nitride nanotube (BNNT) by first
principles density functional theory calculations. The calculated binding
energy shows the order: G>A\approxC\approxT\approxU implying that the
interaction strength of the (high-curvature) BNNT with the nucleobases, G being
an exception, is nearly the same. A higher binding energy for the G-BNNT
conjugate appears to result from a stronger hybridization of the molecular
orbitals of G and BNNT, since the charge transfer involved in the physisorption
process is insignificant. A smaller energy gap predicted for the G-BNNT
conjugate relative to that of the pristine BNNT may be useful in application of
this class of biofunctional materials to the design of the next generation
sensing devices.Comment: 17 pages 6 figure
Physisorption of Nucleobases on Graphene
We report the results of our first-principles investigation on the
interaction of the nucleobases adenine (A), cytosine (C), guanine (G), thymine
(T), and uracil (U) with graphene, carried out within the density functional
theory framework, with additional calculations utilizing Hartree--Fock plus
second-order Moeller-Plesset perturbation theory. The calculated binding energy
of the nucleobases shows the following hierarchy: G > T ~ C ~ A > U, with the
equilibrium configuration being very similar for all five of them. Our results
clearly demonstrate that the nucleobases exhibit significantly different
interaction strengths when physisorbed on graphene. The stabilizing factor in
the interaction between the base molecule and graphene sheet is dominated by
the molecular polarizability that allows a weakly attractive dispersion force
to be induced between them. The present study represents a significant step
towards a first-principles understanding of how the base sequence of DNA can
affect its interaction with carbon nanotubes, as observed experimentally.Comment: 7 pages, 3 figure
Metabolic and anthropometric influences on nerve conduction parameters in patients with peripheral neuropathy: a retrospective chart analysis
Background and Aims: Nerve conduction study (NCS) measures how fast an electrical impulse moves through the nerve and is a standard technique for diagnosing and assessing neurological diseases. Despite diabetes and obesity being a common accompaniment of peripheral neuropathy, their effects on NCS patterns have not been elucidated conclusively. Our study aimed to assess several anthropometric and metabolic factors with NCS outcomes to address this gap. Research
Design and Methods: This retrospective chart analysis study was conducted on subjects who underwent NCS between 1 January 2009 and 31 December 2019 at a regional hospital. Metabolic, anthropometric, demographical and NCS data were collected from patients’ health records.
Results: In total, 120 subjects presenting with sensorimotor peripheral neuropathy symptoms were included in the study. Age, HbA1c, urea and ESR variables were significantly negatively associated with nerve conduction outcomes (Spearman’s correlation rho between −0.210 and −0.456, p < 0.038). HbA1c and age consistently had the most substantial contribution to velocity and amplitude in all regression models (beta coefficients between −0.157 and 0.516, p < 0.001). Urea also significantly account for a large amount of variance in amplitude and velocity in the lower limbs.
Conclusion: This study suggests that the severity of sensorimotor neuropathy is influenced by glycaemic control, age and uraemia. The interpretation of NCS results must consider these factors suggesting that improved glycaemic and uraemic control may improve nerve conduction outcomes
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