Jet Acceleration by Tangled Magnetic Fields

We explore the possibility that extragalactic radio jets might be accelerated by highly disorganized magnetic fields that are strong enough to dominate the dynamics until the terminal Lorentz factor is reached. Following the twin-exhaust model by Blandford & Rees (1974), the collimation under this scenario is provided by the stratified thermal pressure from an external medium. The acceleration efficiency then depends on the pressure gradient of that medium. In order for this mechanism to work there must be continuous tangling of the magnetic field, changing the magnetic equation of state away from pure flux freezing (otherwise conversion of Poynting flux to kinetic energy flux is suppressed). This is a complementary approach to models in which the plasma is accelerated by large scale ordered fields. We include a simple prescription for magnetic dissipation, which leads to tradeoffs among conversion of magnetic energy into bulk kinetic energy, random particle energy, and radiation. We present analytic dynamical solutions of such jets, assess the effects of radiation drag, and comment on observational issues, such as the predicted polarization and synchrotron brightness. Finally, we try to make the connection to observed radio galaxies and gamma-ray bursts.Comment: 15 pages, 10 figures, accepted for publication in Ap

Dynamics of Warm-Absorbing Gas in Seyfert Galaxies: NGC 5548

A hydromagnetic (MHD) wind from a clumpy molecular accretion disk is invoked to explain observations of warm absorbing (WA) gas in UVX from Sy galaxies. This paper focuses on two issues: (1) compatibility of kinematics and dynamics of MHD wind with the observed properties of WAs; and (2) relationship between the UVX absorptions. We provide an in-depth comparison between the MHD model and the Sy 1 galaxy NGC 5548, which at high spectral resolution exhibits a number of discrete UV absorption components. We find that: (1) the total column densities of Ovii, Oviii and H, are reproduced by constraining the UV ion column densities of Civ and Nv in each component to lie within a factor of 2 of their observed values and optimizing over the possible sets of component ionization states and Civ column densities; (2) the WA exists in the outer part of the wind and is not a continuation of the flow in the BLR; and (3) the WA extends in radial and polar directions and is ionization-stratified. X-ray absorption is found to be heavily biased towards smaller r, and UV absorption originates at larger distances from the central continuum source. We show that the discrete absorption components along the line-of-sight are intrinsically clumpy. Density differences between kinematic components result in a range of ionization and recombination timescales. We further test the applicability of the MHD wind to WAs in general, by constructing a quasi-continuous flow model, and extending it to arbitrary aspect angles. We estimate the fraction of Sy 1s having detectable WAs with larger Ovii column density than Oviii, and the range of total H column densities. We also find that the ratio of Ovii to Oviii optical depths can serve as a new diagnostic of AGN aspect angle.Comment: Latex, 8 postscript figures. Astrophysical Journal, 536, June 10, in pres

The initiation of Dutch newly qualified hospital-based midwives in practice, a qualitative study

In the Netherlands, a percentage of newly qualified midwives start work in maternity care as a hospital-based midwife, although prepared particularly for working autonomously in the community. Aim: This study aimed to explore newly qualified Dutch midwives' perceptions of their job demands and resources during their initiation to hospital-based practice. Design: We conducted a qualitative study with semi structured interviews using the Job Demands-Resources model as theoretical framework. Methods: Twenty-one newly qualified midwives working as hospital-based midwives in the Netherlands were interviewed individually between January and July 2018. Transcripts were analyzed using thematic content analysis. Findings: High workload, becoming a team member, learning additional medical procedures and job insecurity were perceived demands. Participants experienced the variety of the work, the teamwork, social support, working with women, and employment conditions as job resources. Openness for new experiences, sociability, calmness and accuracy were experienced as personal resources, and perfectionism, self-criticism, and fear of failure as personal demands. Conclusion: Initiation to hospital-based practice requires from newly qualified midwives adaptation to new tasks: working with women in medium and high-risk care, managing tasks, as well as often receiving training in additional medical skills. Sociability helps newly qualified midwives in becoming a member of a multidisciplinary team; neuroticism and perfectionism hinders them in their work. Clear expectations and a settling-in period may help newly qualified midwives to adapt to practice. The initiation phase could be better supported by preparing student midwives for working in a hospital setting and helping manage expectations about the settling-in period

National cross-sectional study of the sociodemographic characteristics of Aotearoa New Zealand's regulated health workforce pre-registration students: A mirror on society?

Objectives To provide a sociodemographic profile of students enrolled in their first year of a health professional pre-registration programme offered within New Zealand (NZ) tertiary institutions. Design Observational, cross-sectional study. Data were sought from NZ tertiary education institutions for all eligible students accepted into the first ar of a health professional programme for the 5-year period 2016-2020 inclusive. Variables of interest: gender, citizenship, ethnicity, rural classification, socioeconomic deprivation, school type and school socioeconomic scores. Analyses were carried out using the R statistics software. Setting Aotearoa NZ. Participants All students (domestic and international) accepted into the first ar of a health professional programme leading to registration under the Health Practitioners Competence Assurance Act 2003. Results NZ's health workforce pre-registration students do not reflect the diverse communities they will serve in several important dimensions. There is a systematic under-representation of students who identify as Māori and Pacific, and students who come from low socioeconomic and rural backgrounds. The enrolment rate for Māori students is about 99 per 100 000 eligible population and for some Pacific ethnic groups is lower still, compared with 152 per 100 000 for NZ European students. The unadjusted rate ratio for enrolment for both Māori students and Pacific students versus Other' students is approximately 0.7. Conclusions We recommend that: (1) there should be a nationally coordinated system for collecting and reporting on the sociodemographic characteristics of the health workforce pre-registration; (2) mechanisms be developed to allow the agencies that fund tertiary education to base their funding decisions directly on the projected health workforce needs of the health system and (3) tertiary education funding decisions be based on Te Tiriti o Waitangi (the foundational constitutional agreement between the Indigenous people, Māori and the British Crown signed in 1840) and have a strong pro-equity focus

The long-lived Type IIn SN 2015da: Infrared echoes and strong interaction within an extended massive shell star star star

In this paper we report the results of the first similar to four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy greater than or similar to 10(51) erg. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be similar or equal to 8 M-circle dot, with an extreme mass-loss rate for the progenitor star similar or equal to 0.6 M-circle dot yr(-1), suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a fluxexcess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass greater than or similar to 0.4 x 10(-3) M-circle dot for the dustSpanish MICINN gran

Chemical Abundances in the Secondary Star in the Black Hole Binary A0620-00

Using a high resolution spectrum of the secondary star in the black hole binary A0620-00, we have derived the stellar parameters and veiling caused by the accretion disk in a consistent way. We have used a chi^2 minimization procedure to explore a grid of 800 000 LTE synthetic spectra computed for a plausible range of both stellar and veiling parameters. Adopting the best model parameters found, we have determined atmospheric abundances of Fe, Ca, Ti, Ni and Al. The Fe abundance of the star is [Fe/H]=0.14 +- 0.20. Except for Ca, we found the other elements moderately over-abundant as compared with stars in the solar neighborhood of similar iron content. Taking into account the small orbital separation, the mass transfer rate and the mass of the convection zone of the secondary star, a comparison with element yields in supernova explosion models suggests a possible explosive event with a mass cut comparable to the current mass of the compact object. We have also analyzed the Li abundance, which is unusually high for a star of this spectral type and relatively low mass.Comment: 32 pages, 5 tables and 11 figures, uses rotate.st