883 research outputs found
Cartilage can be thicker in advanced osteoarthritic knees: a tridimensional quantitative analysis of cartilage thickness at posterior aspect of femoral condyles.
To test, through tridimensional analysis, whether (1) cartilage thickness at the posterior aspect of femoral condyles differs in knees with medial femorotibial osteoarthritis (OA) compared to non-OA knees; (2) the location of the thickest cartilage at the posterior aspect of femoral condyles differs between OA and non-OA knees.
CT arthrograms of knees without radiographic OA (n = 30) and with severe medial femorotibial OA (n = 30) were selected retrospectively from patients over 50 years of age. The groups did not differ in gender, age and femoral size. CT arthrograms were segmented to measure the mean cartilage thickness, the maximal cartilage thickness and its location in a region of interest at the posterior aspect of condyles.
For the medial condyle, mean and maximum cartilage thicknesses were statistically significantly higher in OA knees compared to non-OA knees [1.66 vs 1.46 mm (p = 0.03) and 2.56 vs 2.14 mm (p = 0.003), respectively]. The thickest cartilage was located in the half most medial aspect of the posterior medial condyle for both groups, without significant difference between groups. For the lateral condyle, no statistically significant difference between non-OA and OA knees was found (p ≥ 0.17).
Cartilage at the posterior aspect of the medial condyle, but not the lateral condyle, is statistically significantly thicker in advanced medial femorotibial OA knees compared to non-OA knees. The thickest cartilage was located in the half most medial aspect of the posterior medial condyle. These results will serve as the basis for future research to determine the histobiological processes involved in this thicker cartilage. Advances in knowledge: This study, through a quantitative tridimensional approach, shows that cartilage at the posterior aspect of the medial condyles is thicker in severe femorotibial osteoarthritic knees compared to non-OA knees. In the posterior aspect of the medial condyle, the thickest cartilage is located in the vicinity of the center of the half most medial aspect of the posterior medial condyle. These results will serve as the basis for future research to determine the histobiological processes involved in this thicker cartilage
Race Matters: Managing Racial Tension when Teaching Multicultural Competence
In this article, the authors suggest using the Mindful Inquiry (Lee, 2009, 2014) to navigate cultural conversations in the counselor education classroom in tandem with the Multicultural and Social Justice Counseling Competencies (MSJCC; Ratts et al., 2015). The authors highlight the literature about racial tension in and outside the classroom, multicultural counseling and social justice, mindfulness and multiculturalism, and teaching multicultural competence. This article concludes with a case example highlighting how to use the Mindful Inquiry (Lee, 2009, 2014) in the classroom while demonstrating how counselors-in-training develop across the MSJCC (Ratts et al., 2015)
Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds
We present 2D MHD simulations of the radiatively driven outflow from a
rotating hot star with a dipole magnetic field aligned with the star's rotation
axis. We focus primarily on a model with moderately rapid rotation (half the
critical value), and also a large magnetic confinement parameter, . The magnetic field
channels and torques the wind outflow into an equatorial, rigidly rotating disk
extending from near the Kepler corotation radius outwards. Even with
fine-tuning at lower magnetic confinement, none of the MHD models produce a
stable Keplerian disk. Instead, material below the Kepler radius falls back on
to the stellar surface, while the strong centrifugal force on material beyond
the corotation escape radius stretches the magnetic loops outwards, leading to
episodic breakout of mass when the field reconnects. The associated dissipation
of magnetic energy heats material to temperatures of nearly K, high
enough to emit hard (several keV) X-rays. Such \emph{centrifugal mass ejection}
represents a novel mechanism for driving magnetic reconnection, and seems a
very promising basis for modeling X-ray flares recently observed in rotating
magnetic Bp stars like Ori E.Comment: 5 pages, 3 figures, accepted by ApJ
Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: II. The Effects of Field-Aligned Rotation
Building upon our previous MHD simulation study of magnetic channeling in
radiatively driven stellar winds, we examine here the additional dynamical
effects of stellar {\em rotation} in the (still) 2-D axisymmetric case of an
aligned dipole surface field. In addition to the magnetic confinement parameter
introduced in Paper I, we characterize the stellar rotation in
terms of a parameter (the ratio of the
equatorial surface rotation speed to orbital speed), examining specifically
models with moderately strong rotation 0.25 and 0.5, and comparing these
to analogous non-rotating cases. Defining the associated Alfv\'{e}n radius
R_{\rm{A}} \approx \eta_{\ast}^{1/4} \Rstar and Kepler corotation radius
R_{\rm{K}} \approx W^{-2/3} \Rstar, we find rotation effects are weak for
models with , but can be substantial and even dominant
for models with R_{\rm{A}} \gtwig R_{\rm{K}}. In particular, by extending our
simulations to magnetic confinement parameters (up to )
that are well above those () considered in Paper I, we are
able to study cases with ; we find that these do
indeed show clear formation of the {\em rigid-body} disk predicted in previous
analytic models, with however a rather complex, dynamic behavior characterized
by both episodes of downward infall and outward breakout that limit the buildup
of disk mass. Overall, the results provide an intriguing glimpse into the
complex interplay between rotation and magnetic confinement, and form the basis
for a full MHD description of the rigid-body disks expected in strongly
magnetic Bp stars like Ori E.Comment: 14 pp, visit this
http://shayol.bartol.udel.edu/massivewiki-media/publications/rotation.pdf for
full figure version of the paper. MNRAS, in pres
Testing magnetically confined wind shock models for Beta Cep using XMM-Newton and Chandra phase-resolved X-ray observations
(abridged) We have performed a set of phase-resolved X-ray observations of
the magnetic B star Beta Cep, for which theoretical models predict the presence
of a confined wind emitting X-rays from stationary shocks.
We obtained four observations spaced in rotational phase with XMM-Newton and
with Chandra. A detailed analysis of the data was performed to derive both
photometric and spectral parameters from the EPIC data, searching for
rotational modulation, and to derive the location of the X-ray plasma from the
line ratios in the He-like triplets of N, O and Ne from the RGS data. The LETG
data were used to constrain the presence of bulk motions in the plasma.
The strong rotational modulation predicted by the early, static magnetically
confined wind model for the X-ray emission is not observed in Beta Cep. The
small modulation present goes in the opposite direction, pointing to the
absence of any optically thick disk of neutral material, and showing a
modulation consistent with the later, dynamic models of magnetically confined
wind models in B stars. The lack of observed bulk motion points to the plasma
being confined by a magnetic field, but the low plasma temperature and lack of
any flaring show that the plasma is not heated by magnetic reconnection.
Therefore, the observations point to X-ray emission from shocks in a
magnetically confined wind, with no evidence of an optically thick, dense disk
at the magnetic equatorComment: Accepted for publication in Astronomy & Astrophysic
The Hanle Effect as a Diagnostic of Magnetic Fields in Stellar Envelopes IV. Application to Polarized P Cygni Wind Lines
The Hanle effect has been proposed as a new diagnostic of circumstellar
magnetic fields for early-type stars, for which it is sensitive to field
strengths in the 1-300 G range. In this paper we compute the polarized P-Cygni
line profiles that result from the Hanle effect. For modeling the polarization,
we employ a variant of the ``last scattering approximation''. For cases in
which the Sobolev optical depths are greater than unity, the emergent line
intensity is assumed to be unpolarized; while for smaller optical depths, the
Stokes source functions for the Hanle effect with optically thin line
scattering are used. For a typical P Cygni line, the polarized emission forms
in the outer wind, because the Sobolev optical depth is large at the inner
wind. For low surface field strengths, weak P Cygni lines are needed to measure
the circumstellar field. For high values of the surface fields, both the Zeeman
and Hanle diagnostics can be used, with the Zeeman effect probing the
photospheric magnetic fields, and the Hanle effect measuring the magnetic field
in the wind flow. Polarized line profiles are calculated for a self-consistent
structure of the flow and the magnetic geometry based on the WCFields model,
which is applicable to slowly rotating stellar winds with magnetic fields drawn
out by the gas flow. For surface fields of a few hundred Gauss, we find that
the Hanle effect can produce line polarizations in the range of a few tenths of
a percent up to about 2 percent.Comment: accepted to the Astrophysical Journa
X-ray Variability in the Young Massive Triple theta2 Ori A
Massive stars rarely show intrinsic X-ray variability. The only O-stars
credited to be intrinsically variable are theta1 Ori C due to effects from
magnetic confinement of its wind, and theta2 Ori A suspected of similar
activity. Early Chandra observations have shown that the most massive star
system in the Orion Trapezium Cluster, theta2 Ori A, shows rapid variability on
time scales of hours. We determine X-ray fluxes and find that the star shows
very strong variability over the last 5 years. We observed a second large X-ray
outburst in November 2004 with the high resolution transmission grating
spectrometer on-board Chandra. In the low state X-ray emissivities indicate
temperatures well above 25 MK. In the high state we find an extended emissivity
distribution with high emissivities in the range from 3 MK to over 100 MK. The
outburst event in stellar terms is one of the most powerful ever observed and
the most energetic one in the ONC with a lower total energy limit of 1.5x10^37
ergs. The line diagnostics show that under the assumption that the line
emitting regions in the low states are as close as within 1 -- 2 stellar radii
from the O-star's photosphere, whereas the hard states suggest a distance of 3
-- 5 stellar radii. The two outbursts are very close to the periastron passage
of the stars. We argue that the high X-ray states are possibly the result of
reconnection events from magnetic interactions of the primary and secondary
stars of the spectroscopic binary. Effects from wind collisions seem unlikely
for this system. The low state emissivity and R-ratios strengthen the
predicament that the X-ray emission is enhanced by magnetic confinement of the
primary wind. We also detect Fe fluorescence indicative of the existence of
substantial amounts of neutral Fe in the vicinity of the X-ray emission.Comment: 11 pages, 8 figures, accepted for publication in The Astrophysical
Main Journa
The Rigidly Rotating Magnetosphere of Sigma Ori E
We attempt to characterize the observed variability of the magnetic
helium-strong star sigma Ori E in terms of a recently developed rigidly
rotating magnetosphere model. This model predicts the accumulation of
circumstellar plasma in two co-rotating clouds, situated in magnetohydrostatic
equilibrium at the intersection between magnetic and rotational equators. We
find that the model can reproduce well the periodic modulations observed in the
star's light curve, H alpha emission-line profile, and longitudinal field
strength, confirming that it furnishes an essentially correct, quantitative
description of the star's magnetically controlled circumstellar environment.Comment: 4 pages, 3 figures, accepted by Ap
An Atlas of K-line Spectra for Cool Magnetic CP Stars: The Wing-Nib Anomaly (WNA)
We present a short atlas illustrating the unusual Ca {\sc ii} K-line profiles
in upper main sequence stars with anomalous abundances. Slopes of the profiles
for 10 cool, magnetic chemically peculiar (CP) stars change abruptly at the
very core, forming a deep "nib." The nibs show the same or nearly the same
radial velocity as the other atomic lines. The near wings are generally more
shallow than in normal stars. In three magnetic CP stars, the K-lines are too
weak to show this shape, though the nibs themselves are arguably present. The
Ca {\sc ii} H-lines also show deep nibs, but the profiles are complicated by
the nearby, strong H absorption. The K-line structure is nearly
unchanged with phase in CrB and Cir. Calculations, including
NLTE, show that other possibilities in addition to chemical stratification may
yield nib-like cores.Comment: 6 pages, 2 figures, and 8 figures; accepted for publication in ApJ
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