11 research outputs found
Can overturning motions in penumbral filaments be detected?
Numerical simulations indicate that the filamentation of sunspot penumbrae
and the associated systematic outflow (the Evershed effect) are due to
convectively driven fluid motions constrained by the inclined magnetic field.
We investigate whether these motions, in particular the upflows in the bright
filaments and the downflows at their edges can be reliably observed with
existing instrumentation. We use a snapshot from a sunspot simulation to
calculate 2D maps of synthetic line profiles for the spectral lines Fe\sci
7090.4 \AA ~ and C\sci 5380.34 \AA. The maps are spatially and spectrally
degraded according to typical instrument properties. Line-of-sight velocities
are determined from line bisector shifts. We find that the detectability of the
convective flows is strongly affected by spatial smearing, particularly so for
the downflows. Furthermore, the line-of-sight velocities are dominated by the
Evershed flow unless the observation is made very near to disk center. These
problems may have compromised recent attempts to detect overturning penumbral
convection. Lines with a low formation height are best suited to detect the
convective flows.Comment: 8 pages, 12 figures, accepted for publication in ApJ on 28th Ju
Enhanced Joule Heating in Umbral Dots
We present a study of magnetic profiles of umbral dots (UDs) and its
consequences on the Joule heating mechanisms. Hamedivafa (2003) studied Joule
heating using vertical component of magnetic field. In this paper UDs magnetic
profile has been investigated including the new azimuthal component of magnetic
field which might explain the relatively larger enhancement of Joule heating
causing more brightness near circumference of UD.Comment: 8 pages, 1 figure, accepted in Solar Physic
Spectropolarimetery of umbral fine structures from Hinode: Evidence for magnetoconvection
We present spectropolarimetric analysis of umbral dots and a light bridge
fragment that show dark lanes in G-band images. Umbral dots show upflow as well
as associated positive Stokes V area asymmetry in their central parts. Larger
umbral dots show down flow patches in their surrounding parts that are
associated with negative Stokes V area asymmetry. Umbral dots show weaker
magnetic field in central part and higher magnetic field in peripheral area.
Umbral fine structures are much better visible in total circularly polarized
light than in continuum intensity. Umbral dots show a temperature deficit above
dark lanes. The magnetic field inclination show a cusp structure above umbral
dots and a light bridge fragment. We compare our observational findings with 3D
magnetohydrodynamic simulations.Comment: Accepted for publication in MNRAS, 6 pages, 6 figure
Probing the Role of Magnetic-Field Variations in NOAA AR 8038 in Producing Solar Flare and CME on 12 May 1997
We carried out a multi-wavelength study of a CME and a medium-size 1B/C1.3
flare occurring on 12 May 1997. We present the investigation of magnetic-field
variations in the NOAA Active Region 8038 which was observed on the Sun during
7--16 May 1997. Analyses of H{\alpha} filtergrams and MDI/SOHO magnetograms
revealed continual but discrete surge activity, and emergence and cancellation
of flux in this active region. The movie of these magnetograms revealed two
important results that the major opposite polarities of pre-existing region as
well as in the emerging flux region (EFR) were approaching towards each other
and moving magnetic features (MMF) were ejecting out from the major north
polarity at a quasi-periodicity of about ten hrs during 10--13 May 1997. These
activities were probably caused by the magnetic reconnection in the lower
atmosphere driven by photospheric convergence motions, which were evident in
magnetograms. The magnetic field variations such as flux, gradient, and sunspot
rotation revealed that free energy was slowly being stored in the corona. The
slow low-layer magnetic reconnection may be responsible for this storage and
the formation of a sigmoidal core field or a flux rope leading to the eventual
eruption. The occurrence of EUV brightenings in the sigmoidal core field prior
to the rise of a flux rope suggests that the eruption was triggered by the
inner tether-cutting reconnection, but not the external breakout reconnection.
An impulsive acceleration revealed from fast separation of the H{\alpha}
ribbons of the first 150 seconds suggests the CME accelerated in the inner
corona, which is consistent with the temporal profile of the reconnection
electric field. In conclusion, we propose a qualitative model in view of
framework of a solar eruption involving, mass ejections, filament eruption,
CME, and subsequent flare.Comment: 8 figures, accepted for publication in Solar Physic
Seroprevalence of transfusion transmitted infections among blood donors at a Tertiary Care Hospital Blood Bank in North India
Background: Blood transfusion service is a sensitive issue as it is covered by “Drug and Cosmetics Act” and has legal implications. Strict criteria are followed while selecting a donor so that proper blood free of all pathogens is available for recipient.
Aim: To study seroprevalence of transfusion-transmitted major infections (HIV, hepatitis B virus [HBV], hepatitis C virus [HCV], syphilis, and malaria) among blood donors at a Tertiary Care Government Hospital Blood Bank in North India and to compare positivity of markers of these infections in voluntary and replacement donors.
Subjects and Methods: This study was conducted over a period of 5 years (July 2010–June 2015). A total number of donors screened during this period was 130,920. Samples were tested for HIV, HBV, HCV, syphilis, and malaria and retested if found positive by third generation ELISA tests (HIV, hepatitis B surface antigen [HBsAg], HCV). Comparative analysis was done using Chi-square for linear trend. Comparison between prevalence rates among voluntary and replacement donors was done using Chi-square tests using Microsoft Excel 2007 software.
Results: Of total 130,920 donors, 114,214 (87%) were voluntary and 16,706 (13%) were replacement donors. Male donors predominated, 128,781 (98.37%) male and female 2139 (1.63%). Average seropositivity of HIV, HBsAg, anti-HCV, syphilis, and malaria was 0.10%, 1.60%, 0.18%, 0.89%, and 0.04% among all donors. Significant difference (P < 0.001) in the seropositivity of HIV, HBsAg, HCV, and syphilis was seen between voluntary and replacement donors. Seroprevalence of HIV, HBsAg, HCV, syphilis, and malaria was 0.08%, 1.56%, 0.13%, 0.71%, 0.03%, and 0.25%, 1.90% 0.51%, 2.12%, and 0.04% in voluntary blood donor and replacement blood donor, respectively.
Conclusion: Comparing a retrospective data over a long period showed decreasing trend in seroprevalence of HIV, HBsAg, anti-HCV, syphilis, and malaria. Results of the study reflect the prevalence of these infections in the healthy population and warrant measures that should be taken to detect these infections and prevent transmission