Tangled Magnetic Fields in Solar Prominences

Solar prominences are an important tool for studying the structure and evolution of the coronal magnetic field. Here we consider so-called "hedgerow" prominences, which consist of thin vertical threads. We explore the possibility that such prominences are supported by tangled magnetic fields. A variety of different approaches are used. First, the dynamics of plasma within a tangled field is considered. We find that the contorted shape of the flux tubes significantly reduces the flow velocity compared to the supersonic free fall that would occur in a straight vertical tube. Second, linear force-free models of tangled fields are developed, and the elastic response of such fields to gravitational forces is considered. We demonstrate that the prominence plasma can be supported by the magnetic pressure of a tangled field that pervades not only the observed dense threads but also their local surroundings. Tangled fields with field strengths of about 10 G are able to support prominence threads with observed hydrogen density of the order of 10^(11) cm^(-3). Finally, we suggest that the observed vertical threads are the result of Rayleigh-Taylor instability. Simulations of the density distribution within a prominence thread indicate that the peak density is much larger than the average density. We conclude that tangled fields provide a viable mechanism for magnetic support of hedgerow prominences.Comment: 14 pages (emulateapj style), 10 figures, ApJ, in pres

Estimation of solar prominence magnetic fields based on the reconstructed 3D trajectories of prominence knots

We present an estimation of the lower limits of local magnetic fields in quiescent, activated, and active (surges) promineces, based on reconstructed 3-dimensional (3D) trajectories of individual prominence knots. The 3D trajectories, velocities, tangential and centripetal accelerations of the knots were reconstructed using observational data collected with a single ground-based telescope equipped with a Multi-channel Subtractive Double Pass imaging spectrograph. Lower limits of magnetic fields channeling observed plasma flows were estimated under assumption of the equipartition principle. Assuming approximate electron densities of the plasma n_e = 5*10^{11} cm^{-3} in surges and n_e = 5*10^{10} cm^{-3} in quiescent/activated prominences, we found that the magnetic fields channeling two observed surges range from 16 to 40 Gauss, while in quiescent and activated prominences they were less than 10 Gauss. Our results are consistent with previous detections of weak local magnetic fields in the solar prominences.Comment: 14 pages, 12 figures, 1 tabl

Injury during pregnancy and nervous system birth defects: Texas, 1999 to 2003

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/100279/1/bdra23143.pd

Physics of Solar Prominences: II - Magnetic Structure and Dynamics

Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape

Calcium-dependent neuroepithelial contractions expel damaged cells from the developing brain

Both developing and adult organisms need efficient strategies for wound repair. In adult mammals, wounding triggers an inflammatory response that can exacerbate tissue injury and lead to scarring. In contrast, embryonic wounds heal quickly and with minimal inflammation, but how this is achieved remains incompletely understood. Using in vivo imaging in the developing brain of Xenopus laevis, we show that ATP release from damaged cells and subsequent activation of purinergic receptors induce long-range calcium waves in neural progenitor cells. Cytoskeletal reorganization and activation of the actomyosin contractile machinery in a Rho kinase-dependent manner then lead to rapid and pronounced apical-basal contractions of the neuroepithelium. These contractions drive the expulsion of damaged cells into the brain ventricle within seconds. Successful cell expulsion prevents the death of nearby cells and an exacerbation of the injury. Cell expulsion through neuroepithelial contraction represents a mechanism for rapid wound healing in the developing brain

Language endangerment and language documentation in Africa

Non peer reviewe

The association between developmental handicaps and traumatic brain injury during pregnancy: An issue that deserves more systematic evaluation

Aims: Trauma during pregnancy is commonly viewed as benign for the foetus when the delivery occurs normally. This study revisits that point of view. Method: We included eighteen patients having a neurological handicap with an anamnesis of an accident during pregnancy and a follow-up sufficient to determine a definite outcome. Results: Pregnancy outcome and observed management. Foetal abnormalities were detected in six cases between the first and the thirteenth day after the trauma. Emergency delivery or rapid birth after signs of foetal distress occurred in five cases. One baby died soon after birth. One-third of cases were not submitted to any investigation. Various neurological handicaps were recorded: Congenital microcephaly (three patients), congenital hydrocephalus (three), Infantile cerebral hemiplegy (six), quadriplegy with severe encephalopathy (four), diplegy (one), clumsiness with cerebellar atrophy (one), Moebius syndrome (one), mental retardation with autistic features (two), learning disability (one) auditory agnosia (one).Cerebral imaging showed macroscopic abnormalities in fourteen patients, evoking various pathogenetic hypotheses. Conclusion: The association between maternal trauma and foetal brain lesions lacks sufficient investigation in many cases. Prospective studies are needed to clarify both medical and legal issues. Guidelines are proposed for obstetrical and paediatric management after significant maternal trauma