30 research outputs found
Modeling coronal magnetic field using spherical geometry: cases with several active regions
The magnetic fields in the solar atmosphere structure the plasma, store free
magnetic energy and produce a wide variety of active solar phenomena, like
flare and coronal mass ejections(CMEs). The distribution and strength of
magnetic fields are routinely measured in the solar surface(photosphere).
Therefore, there is considerable interest in accurately modeling the 3D
structure of the coronal magnetic field using photospheric vector magnetograms.
Knowledge of the 3D structure of magnetic field lines also help us to interpret
other coronal observations, e.g., EUV images of the radiating coronal plasma.
Nonlinear force-free field (NLFFF) models are thought to be viable tools for
those task. Usually those models use Cartesian geometry. However, the spherical
nature of the solar surface cannot be neglected when the field of view is
large. In this work, we model the coronal magnetic field above multiple active
regions using NLFFF extrapolation code using vector magnetograph data from the
Synoptic Optical Long-term Investigations of the Sun survey (SOLIS)/ Vector
Spectromagnetograph (VSM) as a boundary conditions. We compare projections of
the resulting magnetic field lines solutions with their respective coronal
EUV-images from the Atmospheric Imaging Assembly (SDO/AIA) observed on October
11, 2011 and November 13, 2012. This study has found that the NLFFF model in
spherical geometry reconstructs the magnetic configurations for several active
regions which agrees with observations. During October 11, 2011 observation,
there are substantial number of trans-equatorial loops carrying electric
current.Comment: 3 Figures, Submitted to Astrophysics and Space Science Journa
Magnetic Connectivity between Active Regions 10987, 10988, and 10989 by Means of Nonlinear Force-Free Field Extrapolation
Extrapolation codes for modelling the magnetic field in the corona in
cartesian geometry do not take the curvature of the Sun's surface into account
and can only be applied to relatively small areas, \textit{e.g.}, a single
active region. We apply a method for nonlinear force-free coronal magnetic
field modelling of photospheric vector magnetograms in spherical geometry which
allows us to study the connectivity between multi-active regions. We use vector
magnetograph data from the Synoptic Optical Long-term Investigations of the Sun
survey (SOLIS)/Vector Spectromagnetograph(VSM) to model the coronal magnetic
field, where we study three neighbouring magnetically connected active regions
(ARs: 10987, 10988, 10989) observed on 28, 29, and 30 March 2008, respectively.
We compare the magnetic field topologies and the magnetic energy densities and
study the connectivities between the active regions(ARs). We have studied the
time evolution of magnetic field over the period of three days and found no
major changes in topologies as there was no major eruption event. From this
study we have concluded that active regions are much more connected
magnetically than the electric current.Comment: Solar Physic
Coronal Magnetic Field Structure and Evolution for Flaring AR 11117 and its Surroundings
In this study, photospheric vector magnetograms obtained with the Synoptic
Optical Long-term Investigations of the Sun survey (SOLIS), are used as
boundary conditions to model the three-dimensional nonlinear force-free (NLFF)
coronal magnetic fields as a sequence of nonlinear force-free equilibria in
spherical geometry. We study the coronal magnetic field structure inside active
regions and its temporal evolution. We compare the magnetic field configuration
obtained from NLFF extrapolation before and after flaring event in active
region (AR) 11117 and its surroundings observed on 27 October 2010. We compare
the magnetic field topologies and the magnetic energy densities and study the
connectivities between AR 11117 and its surroundings. During the investigated
time period, we estimate the change in free magnetic energy from before to
after the flare to be 1.74x10^{32}erg which represents about 13.5% of nonlinear
force-free magnetic energy before the flare. In this study, we find that
electric currents from AR 11117 to its surroundings were disrupted after the
flare.Comment: 14 pages, 14 figures, Accepted by Solar Physics Journa
Urban malaria and associated risk factors in Jimma town, south-west Ethiopia
<p>Abstract</p> <p>Background</p> <p>Malaria kills millions around the world. Until recently it was believed to be a disease of rural areas, since the <it>Anopheles </it>mosquito, which transmits <it>Plasmodium </it>species breeds in rural areas. Urban malaria is emerging as a potential, but "avertable" crisis, in Africa. In view of the rapidly growing number of small and medium-sized towns in Ethiopia there is a pressing need to improve the understanding of the epidemiology of malaria. Therefore, the aim of this study was to determine malaria prevalence and associated risk factors in Jimma town.</p> <p>Methods</p> <p>A cross-sectional study was carried out in Jimma town from April 1 to May 28, 2010. 804 study participants were included from 291 households for microscopic examination of malaria parasites. Socio-demography data and risk factors were collected using structured questionnaires. Logistic regression analysis was done using SPSS 15.0 statistical software.</p> <p>Results</p> <p>From a total of 804 study participants in current survey only 42 (5.2%) were positive for malaria parasites. <it>Plasmodium vivax, Plasmodium falciparum </it>and mixed infection accounted 71.4%, 26.2% and 2.4%, respectively. Higher malaria prevalence rate was observed among under-five children (11%). Those who do not use insecticide-treated bed nets (ITN) were more likely to be infected with malaria (OR = 13.6; 95% CI 4.9-37.2, p < 0.001) compared with those who use the ITN. Living in areas where stagnant water existed (OR = 2.1; 95% CI 1.00-4.2, p = 0.047) and its distance of existence <1 km from the house(OR = 2.1; 95% CI 2.0-15.8, p = 0.001) were more likely to be infected with malaria parasite compared with those who live away from stagnant at a distance greater than 1 km.</p> <p>Conclusion</p> <p>Malaria is a major health problem with <it>P. vivax </it>becoming a predominant species in the town. The prevalence was strongly associated with proximity of residence to potential mosquito breeding sites. Malaria is affecting significant proportions of the urban settlers and human activities nevertheless play an important role in bringing the mosquito breeding sites closer to residences.</p
Information, Externalities and Socioeconomics of Malaria in Honduras: A Preliminary Analysis
Zoonotic tuberculosis in a high bovine tuberculosis burden area of Ethiopia
BackgroundTuberculosis (TB) is a major cause of ill health and one of the leading causes of death worldwide, caused by species of the Mycobacterium tuberculosis complex (MTBC), with Mycobacterium tuberculosis being the dominant pathogen in humans and Mycobacterium bovis in cattle. Zoonotic transmission of TB (zTB) to humans is frequent particularly where TB prevalence is high in cattle. In this study, we explored the prevalence of zTB in central Ethiopia, an area highly affected by bovine TB (bTB) in cattle.MethodA convenient sample of 385 patients with pulmonary tuberculosis (PTB, Nâ=â287) and tuberculous lymphadenitis (TBLN, Nâ=â98) were included in this cross-sectional study in central Ethiopia. Sputum and fine needle aspirate (FNA) samples were obtained from patients with PTB and TBLN, respectively, and cultures were performed using BACTEC⢠MGIT⢠960. All culture positive samples were subjected to quantitative PCR (qPCR) assays, targeting IS1081, RD9 and RD4 genomic regions for detection of MTBC, M. tuberculosis and M. bovis, respectively.ResultsTwo hundred and fifty-five out of 385 sampled patients were culture positive and all were isolates identified as MTBC by being positive for the IS1081 assay. Among them, 249 (97.6%) samples had also a positive RD9 result (intact RD9 locus) and were consequently classified as M. tuberculosis. The remaining six (2.4%) isolates were RD4 deficient and thereby classified as M. bovis. Five out of these six M. bovis strains originated from PTB patients whereas one was isolated from a TBLN patient. Occupational risk and the widespread consumption of raw animal products were identified as potential sources of M. bovis infection in humans, and the isolation of M. bovis from PTB patients suggests the possibility of human-to-human transmission, particularly in patients with no known contact history with animals.ConclusionThe detected proportion of culture positive cases of 2.4% being M. bovis from this region was higher zTB rate than previously reported for the general population of Ethiopia. Patients with M. bovis infection are more likely to get less efficient TB treatment because M. bovis is inherently resistant to pyrazinamide. MTBC species identification should be performed where M. bovis is common in cattle, especially in patients who have a history of recurrence or treatment failure