41 research outputs found
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Observational diagnostics of gas in protoplanetary disks
Protoplanetary disks are composed primarily of gas (99% of the mass).
Nevertheless, relatively few observational constraints exist for the gas in
disks. In this review, I discuss several observational diagnostics in the UV,
optical, near-IR, mid-IR, and (sub)-mm wavelengths that have been employed to
study the gas in the disks of young stellar objects. I concentrate in
diagnostics that probe the inner 20 AU of the disk, the region where planets
are expected to form. I discuss the potential and limitations of each gas
tracer and present prospects for future research.Comment: Review written for the proceedings of the conference "Origin and
Evolution of Planets 2008", Ascona, Switzerland, June 29 - July 4, 2008. Date
manuscript: October 2008. 17 Pages, 6 graphics, 134 reference
Accretion, Outflows, and Winds of Magnetized Stars
Many types of stars have strong magnetic fields that can dynamically
influence the flow of circumstellar matter. In stars with accretion disks, the
stellar magnetic field can truncate the inner disk and determine the paths that
matter can take to flow onto the star. These paths are different in stars with
different magnetospheres and periods of rotation. External field lines of the
magnetosphere may inflate and produce favorable conditions for outflows from
the disk-magnetosphere boundary. Outflows can be particularly strong in the
propeller regime, wherein a star rotates more rapidly than the inner disk.
Outflows may also form at the disk-magnetosphere boundary of slowly rotating
stars, if the magnetosphere is compressed by the accreting matter. In isolated,
strongly magnetized stars, the magnetic field can influence formation and/or
propagation of stellar wind outflows. Winds from low-mass, solar-type stars may
be either thermally or magnetically driven, while winds from massive, luminous
O and B type stars are radiatively driven. In all of these cases, the magnetic
field influences matter flow from the stars and determines many observational
properties. In this chapter we review recent studies of accretion, outflows,
and winds of magnetized stars with a focus on three main topics: (1) accretion
onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and
(3) winds from isolated massive magnetized stars. We show results obtained from
global magnetohydrodynamic simulations and, in a number of cases compare global
simulations with observations.Comment: 60 pages, 44 figure
Domestic Violence and Health Care: Opening Pandora¿s Box ¿ Challenges and Dilemmas
In this article we take a critical stance toward the rational progressive narrative
surrounding the integration of domestic violence within health care. Whilst changes in
recent UK policy and practice have resulted in several tangible benefits, it is argued that
there may be hidden dilemmas and challenges. We suggest that the medical model of care
and its discursive practices position women as individually accountable for domestic
violence-related symptoms and injuries. This may not only be ineffective in terms of
service provision but could also have the potential to reduce the political significance of
domestic violence as an issue of concern for all women. Furthermore, it is argued that the
use of specific metaphors enables practitioners to distance themselves from interactions
that may prove to be less comfortable and provide less than certain outcomes. Our analysis
explores the possibilities for change that might currently be available. This would
appear to involve a consideration of alternative discourses and the reformulation of power
relations and subject positions in health care
The 14-kDa Dynein Light Chain-Family Protein Dlc1 Is Required for Regular Oscillatory Nuclear Movement and Efficient Recombination during Meiotic Prophase in Fission Yeast
A Schizosaccharomyces pombe spindle pole body (SPB) protein interacts in a two-hybrid system with Dlc1, which belongs to the 14-kDa Tctex-1 dynein light chain family. Green fluorescent protein-tagged Dlc1 accumulated at the SPB throughout the life cycle. During meiotic prophase, Dlc1 was present along astral microtubules and microtubule-anchoring sites on the cell cortex, reminiscent of the cytoplasmic dynein heavy chain Dhc1. In a dlc1-null mutant, Dhc1-dependent nuclear movement in meiotic prophase became irregular in its duration and direction. Dhc1 protein was displaced from the cortex anchors and the formation of microtubule bundle(s) that guide nuclear movement was impaired in the mutant. Meiotic recombination in the dlc1 mutant was reduced to levels similar to that in the dhc1 mutant. Dlc1 and Dhc1 also have roles in karyogamy and rDNA relocation during the sexual phase. Strains mutated in both the dlc1 and dhc1 loci displayed more severe defects in recombination, karyogamy, and sporulation than in either single mutant alone, suggesting that Dlc1 is involved in nuclear events that are independent of Dhc1. S. pombe contains a homolog of the 8-kDa dynein light chain, Dlc2. This class of dynein light chain, however, is not essential in either the vegetative or sexual phases