The time-averaged 30 ks Chandra AO1 High Energy Transmission Grating Spectrometer observation of the microquasar GRS 1915]105 in the low hard state reveals for the Ðrst time in this source neutral K absorption edges from iron, silicon, magnesium, and sulphur. Ionized resonance (r) absorption from H-and He-like species of Fe (XXV, XXVI) and possibly Ca XX are also seen as well as possible emission from neutral Fe Ka and ionized Fe XXV (forbidden or the resonance emission component of a P Cygni proÐle). We report the tentative detection of the Ðrst astrophysical signature of X-ray absorption Ðne structure in the photoelectric edge of Si (and possibly Fe and Mg) attributed to material in grains. The large column densities measured from the neutral edges reveal anomalous Si and Fe abundances and illustrate the importance of high-resolution X-ray measurements for assessing material that surrounds bright X-ray sources, especially if depletion onto grains plays a prominent role. Scenarios for which the anomalous abundances can be attributed to surrounding cold material associated with GRS 1915]105 and/or for which the enrichment may signify either a highly unusual supernova/hypernova or external supernova activity local to the binary are discussed. We attribute the ionized features to a hot disk, disk wind, or corona environment. Based on H-and He-like Fe (XXV, XXVI), we estimate constraints on the ionization parameter temperature (T [ 2.4 ] 106 K), and hydrogen equivalent number (log m Z 4.15), density cm~3) for this region. Variability studies with the simultaneous RXT E data show that (n Z 1012 the light-curve count rate tracks the changes in the disk blackbody as well as the power-law Ñux, with the most signiÐcant variations observed in the former. The Chandra data show spectral changes that also track the behavior of the light curve and may point to changes in both the ionizing Ñux and density of the absorber. A 3.69 Hz quasi-periodic oscillation and weak Ðrst harmonic are seen in the RXT E data.

A significant fraction of planetary nebulae (PNe) and protoplanetary nebulae (PPNe) exhibit aspherical, axisymmetric structures, many of which are highly collimated. The origin of these structures is not entirely understood, however, recent evidence suggests that many observed PNe harbour binary systems, which may play a role in their shaping. In an effort to understand how binaries may produce such asymmetries, we study the effect of low‐mass (<0.3 M⊙) companions (planets, brown dwarfs and low‐mass main‐sequence stars) embedded into the envelope of a 3.0‐M⊙ star during three epochs of its evolution [red giant branch, asymptotic giant branch (AGB), interpulse AGB]. We find that common envelope evolution can lead to three qualitatively different consequences: (i) direct ejection of envelope material resulting in a predominately equatorial outflow, (ii) spin‐up of the envelope resulting in the possibility of powering an explosive dynamo‐driven jet and (iii) tidal shredding of the companion into a disc which facilitates a disc‐driven jet. We study how these features depend on the secondary's mass and discuss observational consequences.

We supplement the mean field dynamo growth equation with the total magnetic helicity evolution equation. This provides an explicitly time dependent model for alpha quenching in dynamo theory. For dynamos without shear, this approach accounts for the observed large scale field growth and saturation in numerical simulations. After a significant kinematic phase, the dynamo is resistively quenched, i.e. the saturation time depends on the microscopic resistivity. This is independent of whether or not the turbulent diffusivity is resistively quenched. We find that the approach is also successful for dynamos that include shear and exhibit migratory waves (cycles). In this case however, whether or not the cycle period remains of the order of the dynamical time scale at large magnetic Reynolds numbers does depend how on how the turbulent magnetic diffusivity quenches. Since this is unconstrained by magnetic helicity conservation, the diffusivity is presently an input parameter. Comparison to current numerical experiments suggests a turbulent diffusivity that depends only weakly on the magnetic Reynolds number, but higher resolution simulations are needed.

We develop a new nonlinear mean field dynamo theory that couples field growth to the time evolution of the magnetic helicity and the turbulent electromotive force, E. We show that the difference between kinetic and current helicities emerges naturally as the growth driver when the time derivative of E is coupled into the theory. The solutions predict significant field growth in a kinematic phase and a saturation rate/strength that is magnetic Reynolds number dependent/independent in agreement with numerical simulations. The amplitude of early time oscillations provides a diagnostic for the closure.

IntroductionRepetitive head impacts (RHI) sustained in contact sports are thought to be necessary for the long-term development of chronic traumatic encephalopathy (CTE). Our objectives were to: 1) characterize the magnitude and persistence of RHI-induced white matter (WM) changes; 2) determine their relationship to kinematic measures of RHI; and 3) explore their clinical relevance.MethodsProspective, observational study of 10 Division III college football players and 5 non-athlete controls during the 2011-12 season. All subjects underwent diffusion tensor imaging (DTI), physiologic, cognitive, and balance testing at pre-season (Time 1), post-season (Time 2), and after 6-months of no-contact rest (Time 3). Head impact measures were recorded using helmet-mounted accelerometers. The percentage of whole-brain WM voxels with significant changes in fractional anisotropy (FA) and mean diffusivity (MD) from Time 1 to 2, and Time 1 to 3 was determined for each subject and correlated to head impacts and clinical measures.ResultsTotal head impacts for the season ranged from 431–1,850. No athlete suffered a clinically evident concussion. Compared to controls, athletes experienced greater changes in FA and MD from Time 1 to 2 as well as Time 1 to 3; most differences at Time 2 persisted to Time 3. Among athletes, the percentage of voxels with decreased FA from Time 1 to 2 was positively correlated with several helmet impact measures. The persistence of WM changes from Time 1 to 3 was also associated with changes in serum ApoA1 and S100B autoantibodies. WM changes were not consistently associated with cognition or balance.ConclusionsA single football season of RHIs without clinically-evident concussion resulted in WM changes that correlated with multiple helmet impact measures and persisted following 6 months of no-contact rest. This lack of WM recovery could potentially contribute to cumulative WM changes with subsequent RHI exposures.

The acknowledgement of risks for traumatic brain injury in American football players has prompted studies for sideline concussion diagnosis and testing for neurological deficits. While concussions are recognized etiological factors for a spectrum of neurological sequelae, the consequences of sub-concussive events are unclear. We tested the hypothesis that blood-brain barrier disruption (BBBD) and the accompanying surge of the astrocytic protein S100B in blood may cause an immune response associated with production of auto-antibodies. We also wished to determine whether these events result in disrupted white matter on diffusion tensor imaging (DT) scans. Players from three college football teams were enrolled (total of 67 volunteers). None of the players experienced a concussion. Blood samples were collected before and after games (n = 57); the number of head hits in all players was monitored by movie review and post-game interviews. S100B serum levels and auto-antibodies against S100B were measured and correlated by direct and reverse immunoassays (n = 15 players; 5 games). A subset of players underwent DTI scans pre- and post-season and after a 6-month interval (n = 10). Cognitive and functional assessments were also performed. After a game, transient BBB damage measured by serum S100B was detected only in players experiencing the greatest number of sub-concussive head hits. Elevated levels of auto-antibodies against S100B were elevated only after repeated sub-concussive events characterized by BBBD. Serum levels of S100B auto-antibodies also predicted persistence of MRI-DTI abnormalities which in turn correlated with cognitive changes. Even in the absence of concussion, football players may experience repeated BBBD and serum surges of the potential auto-antigen S100B. The correlation of serum S100B, auto-antibodies and DTI changes support a link between repeated BBBD and future risk for cognitive changes.

The origin, evolution and role of magnetic fields in the production and shaping of protoplanetary nebulae (PPNe) and planetary nebulae (PNe) are a subject of active research. Most PNe and PPNe are axisymmetric with many exhibiting highly collimated outflows; however, it is important to understand whether such structures can be generated by isolated stars or require the presence of a binary companion. Towards this end, we study a dynamical, large-scale α − interface dynamo operating in a 3.0 M Asymptotic Giant Branch (AGB) star in both an isolated setting and a setting in which a low-mass companion is embedded inside the envelope. The back reaction of the fields on the shear is included and differential rotation and rotation deplete via turbulent dissipation and Poynting flux. For the isolated star, the shear must be resupplied in order to sufficiently sustain the dynamo. Furthermore, we investigate the energy requirements that convection must satisfy to accomplish this by analogy to the Sun. For the common envelope case, a robust dynamo results, unbinding the envelope under a range of conditions. Two qualitatively different types of explosion may arise: (i) magnetically induced, possibly resulting in collimated bipolar outflows and (ii) thermally induced from turbulent dissipation, possibly resulting in quasi-spherical outflows. A range of models is presented for a variety of companion masses.

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