2,950 research outputs found
Relativistic models of magnetars: the twisted-torus magnetic field configuration
We find general relativistic solutions of equilibrium magnetic field
configurations in magnetars, extending previous results of Colaiuda et al.
(2008). Our method is based on the solution of the relativistic Grad-Shafranov
equation, to which Maxwell's equations can be reduced in some limit. We obtain
equilibrium solutions with the toroidal magnetic field component confined into
a finite region inside the star, and the poloidal component extending to the
exterior. These so-called twisted-torus configurations have been found to be
the final outcome of dynamical simulations in the framework of Newtonian
gravity, and appear to be more stable than other configurations. The solutions
include higher order multipoles, which are coupled to the dominant dipolar
field. We use arguments of minimal energy to constrain the ratio of the
toroidal to the poloidal field.Comment: 13 pages, 12 figures. Minor changes to match the version published on
MNRA
Structure and deformations of strongly magnetized neutron stars with twisted torus configurations
We construct general relativistic models of stationary, strongly magnetized
neutron stars. The magnetic field configuration, obtained by solving the
relativistic Grad-Shafranov equation, is a generalization of the twisted torus
model recently proposed in the literature; the stellar deformations induced by
the magnetic field are computed by solving the perturbed Einstein's equations;
stellar matter is modeled using realistic equations of state. We find that in
these configurations the poloidal field dominates over the toroidal field and
that, if the magnetic field is sufficiently strong during the first phases of
the stellar life, it can produce large deformations.Comment: 10 pages, 5 figures. Minor changes to match the version published on
MNRA
Paths to Positivity: Relational Trajectories and Interaction in Positive Stepparent-Stepchild Dyads
Stepfamilies are inherently complex family systems, marked by change, flexible boundaries, and early conflict. But the developmental pathways by which long-term stepparent relationships become positive require more study. We interviewed 38 stepchildren who had reached adulthood, to understand how their relationships with a stepparent became positive. Four relational trajectories defined these positive relationships: punctuated, consistent positive, progressive incline, and modulated turbulent. Distinctive communicative practices were associated with each trajectory, such as communicating assurances, “siding,” or revelations of character. In addition, the trajectories shared three common processes: responsiveness to stepchild vulnerability, stepparent “adding value” to the family, and maturation/ reframing of the past. Findings support the existence of multiple pathways to positivity and suggest that major fluctuations are experienced along the way. Findings are interpreted in light of existing research on stepfamily development and Afifi’s theory of resilience and relational load. Recommendations are offered for stepfamilies and professionals who serve them
Asteroseismology can reveal strong internal magnetic fields in red giant stars
Internal stellar magnetic fields are inaccessible to direct observations, and little is known about their amplitude, geometry, and evolution. We demonstrate that strong magnetic fields in the cores of red giant stars can be identified with asteroseismology. The fields can manifest themselves via depressed dipole stellar oscillation modes, arising from a magnetic greenhouse effect that scatters and traps oscillation-mode energy within the core of the star. The Kepler satellite has observed a few dozen red giants with depressed dipole modes, which we interpret as stars with strongly magnetized cores. We find that field strengths larger than ~10^5 gauss may produce the observed depression, and in one case we infer a minimum core field strength of ≈10^7 gauss
Technique for producing highly planar Si/SiO0.64Ge0.36/Si metal–oxide–semiconductor field effect transistor channels
Si/Si0.64Ge0.36/Si heterostructures have been grown at low temperature (450 °C) to avoid the strain-induced roughening observed for growth temperatures of 550 °C and above. The electrical properties of these structures are poor, and thought to be associated with grown-in point defects as indicated in positron annihilation spectroscopy. However, after an in situ annealing procedure (800 °C for 30 min) the electrical properties dramatically improve, giving an optimum 4 K mobility of 2500 cm2 V – 1 s – 1 for a sheet density of 6.2 × 1011 cm – 2. The low temperature growth yields highly planar interfaces, which are maintained after anneal as evidenced from transmission electron microscopy. This and secondary ion mass spectroscopy measurements demonstrate that the metastably strained alloy layer can endure the in situ anneal procedure necessary for enhanced electrical properties. Further studies have shown that the layers can also withstand a 120 min thermal oxidation at 800 °C, commensurate with metal–oxide–semiconductor device fabrication
Health practitioners' perceptions of the barriers and enablers to the implementation of reproductive genetic carrier screening: A systematic review.
BACKGROUND: As interest in reproductive genetic carrier screening rises, with increased availability, the role of healthcare practitioners is central in guiding uptake aligned with a couples' values and beliefs. Therefore, practitioners' views on implementation are critical to the success of any reproductive genetic carrier screening programme. AIM: To explore healthcare practitioners' perceptions of the barriers and enablers to implementation. MATERIALS & METHODS: We undertook a systematic review of the literature searching seven databases using health practitioner, screening and implementation terms returning 490 articles. RESULTS: Screening led to the inclusion of 26 articles for full-text review. We found three interconnected themes relating to reproductive genetic carrier screening: (i) use and impact, (ii) practitioners' beliefs and expectations and (iii) resources. DISCUSSION: Barriers and enablers to implementation were present within each theme and grouping these determinants by (a) community for example lack of public interest, (b) practitioner for example lack of practitioner time and (c) organisation for example lack of effective metrics, reveals a preponderance of practitioner barriers and organisational enablers. Linking barriers with potential enablers leaves several barriers unresolved (e.g., costs for couples) implying additional interventions may be required. CONCLUSION: Future research should draw on the findings from this study to develop and test strategies to facilitate appropriate offering of reproductive genetic carrier screening by healthcare practitioners
CP and related phenomena in the context of Stellar Evolution
We review the interaction in intermediate and high mass stars between their
evolution and magnetic and chemical properties. We describe the theory of
Ap-star `fossil' fields, before touching on the expected secular diffusive
processes which give rise to evolution of the field. We then present recent
results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that
magnetic fields of the kind seen on the main-sequence already exist during the
pre-main sequence phase, in agreement with fossil field theory, and that the
origin of the slow rotation of Ap/Bp stars also lies early in the pre-main
sequence evolution; we also present results confirming a lack of stars with
fields below a few hundred gauss. We then seek which macroscopic motions
compete with atomic diffusion in determining the surface abundances of AmFm
stars. While turbulent transport and mass loss, in competition with atomic
diffusion, are both able to explain observed surface abundances, the interior
abundance distribution is different enough to potentially lead to a test using
asterosismology. Finally we review progress on the turbulence-driving and
mixing processes in stellar radiative zones.Comment: Proceedings of IAU GA in Rio, JD4 on Ap stars; 10 pages, 7 figure
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