A Note on the Radiative and Collisional Branching Ratios in Polarized Radiation Transport with Coherent Scattering

We discuss the implementation of physically meaningful branching ratios between the CRD and PRD contributions to the emissivity of a polarized multi-term atom in the presence of both inelastic and elastic collisions. Our derivation is based on a recent theoretical formulation of partially coherent scattering, and it relies on a heuristic diagrammatic analysis of the various radiative and collisional processes to determine the proper form of the branching ratios. The expression we obtain for the emissivity is $\varepsilon=\left[\varepsilon^{\tiny (1)}-\varepsilon^{\tiny (2)}_{\rm f.s.} \right]+\varepsilon^{\tiny (2)}$, where $\varepsilon^{\tiny (1)}$ and $\varepsilon^{\tiny (2)}$ are the emissivity terms for the redistributed and partially coherent radiation, respectively, and where "f.s." implies that the corresponding term must be evaluated assuming a flat-spectrum average of the incident radiation

On the Influence of Magnetic Fields on the Structure of Protostellar Jets

We here present the first results of fully three-dimensional (3-D) MHD simulations of radiative cooling pulsed (time-variable) jets for a set of parameters which are suitable for protostellar outflows. Considering different initial magnetic field topologies in approximate $equipartition$ with the thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which permeating the jet and the ambient medium; and (iii) a purely toroidal field permeating only the jet, we find that the overall morphology of the pulsed jet is not very much affected by the presence of the different magnetic field geometries in comparison to a nonmagnetic calculation. Instead, the magnetic fields tend to affect essentially the detailed structure and emission properties behind the shocks at the head and at the pulse-induced internal knots, particularly for the helical and toroidal geometries. In these cases, we find, for example, that the $H_\alpha$ emissivity behind the internal knots can be about three to four times larger than that of the purely hydrodynamical jet. We also find that some features, like the nose cones that often develop at the jet head in 2-D calculations involving toroidal magnetic fields, are smoothed out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections (for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar

Dispositional Optimism and Autonomic Reactivity During Passive-Coping and Active-Coping Stress Tasks

Optimism is a positive psychological factor that has been associated with improved mental and physical health outcomes. To better understand the mechanism through which optimism results in improved health, researchers have examined whether autonomic reactivity to stress moderates this relation. While many studies have examined the relation between optimism and autonomic reactivity to stress, findings are mixed. Although some studies have found optimism to be associated with reductions in heart rate and blood pressure responses to acute stress presentations, many studies exploring this relation have found optimism to be associated with greater blood pressure responses to stress. However, most of these studies have used active-coping versus passive-coping stress tasks to assess autonomic reactivity. This study aimed to investigate the relation between optimism and autonomic reactivity using both active-coping and passive-coping stress tasks to examine whether observed differences in reactivity to stress in previous studies is moderated by this task dimension. Participants with high and low scores on a standardized measure of optimism completed both an active- and passive-coping stress task. Various reactivity measures, including blood pressure, heart rate, and heart rate variability were monitored to assess cardiovascular reactivity to the tasks. It was hypothesized that participants with high optimism would demonstrate higher cardiovascular reactivity during the active-coping stress task than participants low in optimism, while there would be no significant differences in cardiovascular reactivity between the two groups during the passive-coping stress task. Findings revealed that task type did not moderate the relation between optimism and reactivity. There was a significant main effect of optimism on DBP reactivity to stress, though this effect disappeared when controlling for social anxiety. Findings support future examination of the relation between optimism and autonomic reactivity, and subsequently, the relation between optimism and health