37 research outputs found
Wind-Blown Bubbles around Evolved Stars
Most stars will experience episodes of substantial mass loss at some point in
their lives. For very massive stars, mass loss dominates their evolution,
although the mass loss rates are not known exactly, particularly once the star
has left the main sequence. Direct observations of the stellar winds of massive
stars can give information on the current mass-loss rates, while studies of the
ring nebulae and HI shells that surround many Wolf-Rayet (WR) and luminous blue
variable (LBV) stars provide information on the previous mass-loss history. The
evolution of the most massive stars, (M > 25 solar masses), essentially follows
the sequence O star to LBV or red supergiant (RSG) to WR star to supernova. For
stars of mass less than 25 solar masses there is no final WR stage. During the
main sequence and WR stages, the mass loss takes the form of highly supersonic
stellar winds, which blow bubbles in the interstellar and circumstellar medium.
In this way, the mechanical luminosity of the stellar wind is converted into
kinetic energy of the swept-up ambient material, which is important for the
dynamics of the interstellar medium. In this review article, analytic and
numerical models are used to describe the hydrodynamics and energetics of
wind-blown bubbles. A brief review of observations of bubbles is given, and the
degree to which theory is supported by observations is discussed.Comment: To be published as a chapter in 'Diffuse Matter from Star Forming
Regions to Active Galaxies' - A volume Honouring John Dyson. Eds. T. W.
Harquist, J. M. Pittard and S. A. E. G. Falle. 22 pages, 12 figure
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo