1,307 research outputs found
Nonlinear Force-Free Field Modeling of the Solar Magnetic Carpet and Comparison with SDO/HMI and Sunrise/IMaX Observations
In the quiet solar photosphere, the mixed polarity fields form a magnetic
carpet, which continuously evolves due to dynamical interaction between the
convective motions and magnetic field. This interplay is a viable source to
heat the solar atmosphere. In this work, we used the line-of-sight (LOS)
magnetograms obtained from the Helioseismic and Magnetic Imager (HMI) on the
\textit{Solar Dynamics Observatory} (\textit{SDO}), and the Imaging
Magnetograph eXperiment (IMaX) instrument on the \textit{Sunrise} balloon-borne
observatory, as time dependent lower boundary conditions, to study the
evolution of the coronal magnetic field. We use a magneto-frictional relaxation
method, including hyperdiffusion, to produce time series of three-dimensional
(3D) nonlinear force-free fields from a sequence of photospheric LOS
magnetograms. Vertical flows are added up to a height of 0.7 Mm in the modeling
to simulate the non-force-freeness at the photosphere-chromosphere layers.
Among the derived quantities, we study the spatial and temporal variations of
the energy dissipation rate, and energy flux. Our results show that the energy
deposited in the solar atmosphere is concentrated within 2 Mm of the
photosphere and there is not sufficient energy flux at the base of the corona
to cover radiative and conductive losses. Possible reasons and implications are
discussed. Better observational constraints of the magnetic field in the
chromosphere are crucial to understand the role of the magnetic carpet in
coronal heating.Comment: Accepted for publication in The Astrophysical Journal (13 pages, 10
figures
Polarization Sensitive Optical Coherence Tomography for Blood Glucose Monitoring in Human Subjects
A device based on Polarization sensitive optical coherence tomography is
developed to monitor blood glucose levels in human subjects. The device was
initially tested with tissue phantom. The measurements with human subjects for
various glucose concentration levels are found to be linearly dependent on the
degree of circular polarization obtainable from the PS-OCT.Comment: 12 pages, 5 figure
First Stereoscopic Coronal Loop Reconstructions from Stereo Secchi Images
We present the first reconstruction of the three-dimensional shape of
magnetic loops in an active region from two different vantage points based on
simultaneously recorded images. The images were taken by the two EUVI
telescopes of the SECCHI instrument onboard the recently launched STEREO
spacecraft when the heliocentric separation of the two space probes was 12
degrees. We demostrate that these data allow to obtain a reliable
three-dimensional reconstruction of sufficiently bright loops. The result is
compared with field lines derived from a coronal magnetic field model
extrapolated from a photospheric magnetogram recorded nearly simultaneously by
SOHO/MDI. We attribute discrepancies between reconstructed loops and
extrapolated field lines to the inadequacy of the linear force-free field model
used for the extrapolation.Comment: 6 pages, 5 figure
Stellar winds, dead zones, and coronal mass ejections
Axisymmetric stellar wind solutions are presented, obtained by numerically
solving the ideal magnetohydrodynamic (MHD) equations. Stationary solutions are
critically analysed using the knowledge of the flux functions. These flux
functions enter in the general variational principle governing all axisymmetric
stationary ideal MHD equilibria. The magnetized wind solutions for
(differentially) rotating stars contain both a `wind' and a `dead' zone. We
illustrate the influence of the magnetic field topology on the wind
acceleration pattern, by varying the coronal field strength and the extent of
the dead zone. This is evident from the resulting variations in the location
and appearance of the critical curves where the wind speed equals the slow,
Alfven, and fast speed. Larger dead zones cause effective, fairly isotropic
acceleration to super-Alfvenic velocities as the polar, open field lines are
forced to fan out rapidly with radial distance. A higher field strength moves
the Alfven transition outwards. In the ecliptic, the wind outflow is clearly
modulated by the extent of the dead zone. The combined effect of a fast stellar
rotation and an equatorial `dead' zone in a bipolar field configuration can
lead to efficient thermo-centrifugal equatorial winds. Such winds show both a
strong poleward collimation and some equatorward streamline bending due to
significant toroidal field pressure at mid-latitudes. We discuss how coronal
mass ejections are then simulated on top of the transonic outflows.Comment: scheduled for Astrophys. J. 530 #2, Febr.20 2000 issue. 9 figures (as
6 jpeg and 8 eps files
A study of habits of tobacco use among medical students and influence of various factors including medical education
Background: Tobacco use is a major preventable cause of morbidity and mortality. Tobacco usage among medical professionals should be reduced. It is important that they are aware regarding effects/ill effects of tobacco use, anti tobacco strategies, tobacco cessation technique to reduce tobacco usage among population. Authors undertook this study to understand tobacco use among medical students.Methods: Authors conducted cross sectional, descriptive study by collecting anonymous data of 414 undergraduate medical students of medical college, Jamnagar in predesigned forms. Data were analysed using MS-excel and graphpad prism. Authors used Fagerstrom test for nicotine dependence to assess nicotine dependence.Results: Tobacco users were 19.57%, among them 83.95% were smokers. Prevalence was higher in male (34.35% in male and 1.09% in female subgroup) and students with positive family history (36.81% in positive and 6.03% in negative family history subgroup). Current users were 7.73%. They were 8.20% in hosteller and 2.78% day scholar subgroups. Authors didn’t find statistical significant association of medical education with habit. Leading causes of starting tobacco use were curiosity/recreational purpose (35.8%), peer group pressure (32.10%) and stress (25.93%). Most of current user had low nicotine dependence (73.33%).Conclusions: Tobacco use among medical students is a significant problem. Important factors affecting it are gender, family history, current living status, stress, peer group pressure, media influences. Authors recommend that special awareness programme and specific training regarding tobacco cessation should be given to medical students
Bulk viscous fluid in symmetric teleparallel cosmology: theory versus experiment
The standard formulation of General Relativity Theory, in the absence of a
cosmological constant, is unable to explain the responsible mechanism for the
observed late-time cosmic acceleration. On the other hand, by inserting the
cosmological constant in Einstein's field equations it is possible to describe
the cosmic acceleration, but the cosmological constant suffers from an
unprecedented fine-tunning problem. This motivates one to modify Einstein's
space-time geometry of General Relativity. The modified theory of
gravity is an alternative theory to General Relativity, where the non-metricity
scalar is the responsible candidate for gravitational interactions. In the
present work we consider a Friedmann-Lem\^aitre-Robertson-Walker cosmological
model dominated by bulk viscous cosmic fluid in gravity with the
functional form , where and are free parameters
of the model. We constrain our model with the recent Pantheon supernovae data
set of 1048 data points, Hubble data set of 31 data points and baryon acoustic
oscillations data set consisting of six points. For higher values of redshift,
it is clear that the cosmology better fits data than standard cosmology.
We present the evolution of our deceleration parameter with redshift and it
properly predicts a transition from decelerated to accelerated phases of the
universe expansion. Also, we present the evolution of density, bulk viscous
pressure and the effective equation of state parameter with redshift. Those
show that bulk viscosity in a cosmic fluid is a valid candidate to acquire the
negative pressure to drive the cosmic expansion efficiently.We also examine the
behavior of different energy conditions to test the viability of our
cosmological model. Furthermore, the statefinder diagnostics are also
investigated in order to distinguish among different dark energy models.Comment: Comments are welcom
Pseudotumor cerebri syndrome in childhood : incidence, clinical profile and risk factors in a national prospective population-based cohort study
Aim To investigate the epidemiology, clinical profile and risk factors of pseudotumor cerebri syndrome (PTCS) in children aged 1-16 years. Methods A national prospective population-based cohort study over 25 months. Newly diagnosed PTCS cases notified via British Paediatric Surveillance Unit (BPSU) were ascertained using classical diagnostic criteria and categorised according to 2013 revised diagnostic criteria. We derived national age, sex and weight-specific annual incidence rates and assessed effects of sex and weight category. Results We identified 185 PTCS cases of which 166 also fulfilled revised diagnostic criteria. The national annual incidence (95% CI) of childhood PTCS aged 1-16 years was 0.71 (0.57- 0.87) per 100,000 population increasing with age and weight to 4.18 and 10.7 per 100,000 in obese 12-15 year old boys and girls respectively. Incidence rates under 7 years were similar in both sexes. From 7 years onwards, the incidence in girls was double that in boys, but only in overweight (including obese) children. In 12-15 year old children, an estimated 82% of the incidence of PTCS was attributable to obesity. Two subgroups of PTCS were apparent: 168 (91%) cases aged from 7 years frequently presented on medication and with headache, and were predominantly female and obese. The remaining 17 (9%) cases under 7 years often lacked these risk factors and commonly presented with new onset squint. Conclusions This uniquely largest population-based study of childhood PTCS will inform the design of future intervention studies. It suggests that weight reduction is central to the prevention of PTCS
The Influence of Magnetic Field on Oscillations in the Solar Chromosphere
Two sequences of solar images obtained by the Transition Region and Coronal
Explorer in three UV passbands are studied using wavelet and Fourier analysis
and compared to the photospheric magnetic flux measured by the Michelson
Doppler Interferometer on the Solar Heliospheric Observatory to study wave
behaviour in differing magnetic environments. Wavelet periods show deviations
from the theoretical cutoff value and are interpreted in terms of inclined
fields. The variation of wave speeds indicates that a transition from dominant
fast-magnetoacoustic waves to slow modes is observed when moving from network
into plage and umbrae. This implies preferential transmission of slow modes
into the upper atmosphere, where they may lead to heating or be detected in
coronal loops and plumes.Comment: 8 pages, 6 figures (4 colour online only), accepted for publication
in The Astrophysical Journa
- …