3,984 research outputs found
Characterizing the magnetic fields of the first tau Sco analogues
The B0.2 V magnetic star tau Sco stands out from the larger population of
massive OB stars due to its high X-ray activity, peculiar wind diagnostics and
complex magnetic field. Recently, Petit et al. 2011 presented the discovery of
the first two tau Sco analogues -- HD 66665 and HD 63425, identified by the
striking similarity of their UV spectra to that of tau Sco. ESPaDOnS and Narval
spectropolarimetric observations were obtained by the Magnetism in Massive
Stars CFHT and TBL Large Programs, in order to characterize the stellar and
magnetic properties of these stars. A magnetic field of similar surface
strength was found on both stars, reinforcing the connection between the
presence of a magnetic field and wind peculiarities. We present additional
phase-resolved observations secured by the MiMeS collaboration for HD 66665 in
order to measure its magnetic geometry, and correlate that geometry with
diagnostics of mass-loss.Comment: to appear in the proceedings of Stellar polarimetry: From birth to
death, Madison, USA, June 27 - June 30, 2011 (version 2 was updated to
correct a typo in the arXiv metadata
Quenching across quantum critical points in periodic systems: dependence of scaling laws on periodicity
We study the quenching dynamics of a many-body system in one dimension
described by a Hamiltonian that has spatial periodicity. Specifically, we
consider a spin-1/2 chain with equal xx and yy couplings and subject to a
periodically varying magnetic field in the z direction or, equivalently, a
tight-binding model of spinless fermions with a periodic local chemical
potential, having period 2q, where q is a natural number. For a linear quench
of the magnetic field strength (or potential strength) at rate 1/\tau across a
quantum critical point, we find that the density of defects thereby produced
scales as 1/\tau^{q/(q+1)}, deviating from the 1/\sqrt{\tau} scaling that is
ubiquitous to a range of systems. We analyze this behavior by mapping the
low-energy physics of the system to a set of fermionic two-level systems
labeled by the lattice momentum k undergoing a non-linear quench as well as by
performing numerical simulations. We also find that if the magnetic field is a
superposition of different periods, the power law depends only on the smallest
period for very large values of \tau although it may exhibit a cross-over at
intermediate values of \tau. Finally, for the case where a zz coupling is also
present in the spin chain, or equivalently, where interactions are present in
the fermionic system, we argue that the power associated with the scaling law
depends on a combination of q and interaction strength.Comment: 13 pages including 11 figure
Children of prisoners: exploring the impact of families' reappraisal of the role and status of the imprisoned parent on children's coping strategies
Qualitative data from a larger study on the impact of parental imprisonment in four countries found that children of prisoners face fundamentally similar psychological and social challenges. The ways that children cope, however, are influenced by the interpretative frame adopted by the adults around them, and by how issues of parental imprisonment are talked about in their families. This article argues that families have to reappraise their view of the imprisoned parent and then decide on their policy for how to deal with this publicly. Their approach may be based on openness and honesty or may emphasise privacy and secrecy, or a combination of these. Children are likely to be influenced by their parents'/carers' views, although these may cause conflict for them. Where parents/carers retain a positive view of the imprisoned parent, children are likely to benefit; where parents/carers feel issues of shame and stigma acutely, this is likely to be transmitted to their children. This is important for social workers and practitioners involved in supporting prisoners' families and for parenting programmes
Inverting the handedness of circularly polarized luminescence from light-emitting polymers using film thickness
The emission of circularly polarized light is central to many applications, including data storage, optical quantum computation, biosensing, environmental monitoring, and display technologies. An emerging method to induce (chiral) circularly polarized (CP) electroluminescence from the active layer of polymer light-emitting diodes (polymer OLEDs; PLEDs) involves blending achiral polymers with chiral small-molecule additives, where the handedness/sign of the CP light is controlled by the absolute stereochemistry of the small molecule. Through the in-depth study of such a system we report an interesting chiroptical property: the ability to tune the sign of CP light as a function of active layer thickness for a fixed enantiomer of the chiral additive. We demonstrate that it is possible to achieve both efficient (4.0 cd/A) and bright (8000 cd/m2) CP-PLEDs, with high dissymmetry of emission of both left-handed (LH) and right-handed (RH) light, depending on thickness (thin films, 110 nm: gEL = 0.51, thick films, 160 nm: gEL = -1.05, with the terms "thick" and "thin" representing the upper and lower limits of the thickness regime studied), for the same additive enantiomer. We propose that this arises due to an interplay between localized CP emission originating from molecular chirality and CP light amplification or inversion through a chiral medium. We link morphological, spectroscopic, and electronic characterization in thin films and devices with theoretical studies in an effort to determine the factors that underpin these observations. Through the control of active layer thickness and device architecture, this study provides insights into the mechanisms that result in CP luminescence and high performance from CP-PLEDs, as well as demonstrating new opportunities in CP photonic device design
Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei
We present an investigation of H-alpha emission line variations observed in
the massive Algol binary, RY Per. We give new radial velocity data for the
secondary based upon our optical spectra and for the primary based upon high
dispersion UV spectra. We present revised orbital elements and an estimate of
the primary's projected rotational velocity (which indicates that the primary
is rotating 7 times faster than synchronous). We use a Doppler tomography
algorithm to reconstruct the individual primary and secondary spectra in the
region of H-alpha, and we subtract the latter from each of our observations to
obtain profiles of the primary and its disk alone. Our H-alpha observations of
RY Per show that the mass gaining primary is surrounded by a persistent but
time variable accretion disk. The profile that is observed outside-of-eclipse
has weak, double-peaked emission flanking a deep central absorption, and we
find that these properties can be reproduced by a disk model that includes the
absorption of photospheric light by the band of the disk seen in projection
against the face of the star. We developed a new method to reconstruct the disk
surface density distribution from the ensemble of H-alpha profiles observed
around the orbit, and this method accounts for the effects of disk occultation
by the stellar components, the obscuration of the primary by the disk, and flux
contributions from optically thick disk elements. The resulting surface density
distribution is elongated along the axis joining the stars, in the same way as
seen in hydrodynamical simulations of gas flows that strike the mass gainer
near trailing edge of the star. This type of gas stream configuration is
optimal for the transfer of angular momentum, and we show that rapid rotation
is found in other Algols that have passed through a similar stage.Comment: 39 pages, 12 figures, ApJ in press, 2004 June 20 issu
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