1,345 research outputs found
Using the Fundamental Plane to Estimate the Total Binding Mass in A2626
We use fundamental plane (FP) distance estimates to the components of the
double cluster A2626 (cz~17,500 km/s) to constrain cluster kinematics and
estimate total binding mass. The FP coefficients for a sample of 24 early type
and S0 cluster members (alpha=1.30+/-0.36 and beta=0.31+/-0.06) are consistent
with others reported in the literature. We examine the Mg_b distributions
within both subclusters and find them to be indistinguishable. Lacking evidence
for stellar population differences, we interpret the FP zeropoint offset
(\log(D_B/D_A)=-0.037+/-0.046, where D_{cl} is distance to subcluster cl) as a
measure of the distance difference. This measurement is consistent with the
subclusters being at the same distance, and it rules out the Hubble flow
hypothesis (distances proportional to velocity) with 99% confidence; analysis
of the subcluster galaxy magnitude distributions rules out Hubble flow at 93%
confidence. Both results favor a kinematic model where the subclusters are
bound and infalling. We estimate the total cluster binding mass by modelling
the subcluster merger as radial infall. The minimum possible total binding mass
is 1.65 times higher than the sum of the standard virial masses, a difference
statistically significant at the ~3sigma level. We discuss explanations for the
inconsistency including (1) biases in the standard virial mass estimator, (2)
biases in our radial infall mass estimate, and (3) mass beyond the virialized
cluster region; if the standard virial mass is significantly in error, the
cluster has an unusually high mass to light ratio (~1000h). Because
observational signatures of departures from radial infall are absent, we
explore the implications of mass beyond the virialized, core regions.
(abridged)Comment: 14 pages and 5 figures, Latex, Accepted for publication in A
What is More Effective: Corticosteroid Injections or Platelet Rich Plasma Infections in the Treatment of Lateral Epicondylitis?
ABSTRACT
Lateral epicondylitis is a common degenerative tendinopathy that affects a wide variety of individuals. One patient population that often suffers more than others are workers with manual labor jobs that use vibrating tools and repetitive motions.1 Procedural costs and disease burden associated with lateral epicondylitis have increased in recent years.3 Current treatment of lateral epicondylitis using corticosteroid injections is beginning to fall out of favor. Corticosteroid injections help decrease inflammation; however, research looking into the histology of lateral epicondylitis favors more of a degenerative tendinopathy rather than an inflammatory condtion.1 In addition, several studies have found corticosteroid injections to be helpful in the acute phase of lateral epicondylitis but detrimental long-term with rates of relapse in pain and functional impairment.5 Platelet rich plasma (PRP) injections are proving to be an alternative type of injection to treat lateral epicondylitis. PRP contains growth factors and cytokines that help stimulate the healing process.7 Several promising studies have shown that PRP might be more helpful in long-term treatment of lateral epicondylitis. One systematic review found that corticosteroid injections proved to be beneficial for pain relief and function in the short-term (2-8 weeks); whereas PRP injections was shown to be beneficial for long term (8 weeks) pain relief and function.
A Morphology--Cosmology Connection for X--Ray Clusters
We employ N--body/ gas dynamic simulations of the formation of galaxy
clusters to determine whether cluster X--ray morphologies can be used as
cosmological constraints. Confirming the analytic expectations of Richstone,
Loeb, \& Turner, we demonstrate that cluster evolution is sensitive to the
cosmological model in which the clusters form. We further show that
evolutionary differences are echoed in the gross morphological features of the
cluster X--ray emission.
We examine current--epoch X--ray images of models originating from the same
initial density fields evolved in three different cosmologies: (i) an unbiased,
low density universe with \Omega_o \se 0.2; (ii) an unbiased universe
dominated by vacuum energy with \Omega_o \se 0.2 and \lambda_o \se 0.8 and
(iii) a biased Einstein--deSitter model (\Omega \se 1, ).
Using measures of X--ray morphology such as the axial ratio and centroid
shifting, we demonstrate that clusters evolved in the two low models
are much more regular, spherically symmetric, and centrally condensed than
clusters evolved in the Einstein--deSitter model. This morphology--cosmology
connection, along with the availability of a large body of cluster X--ray
observations, makes cluster X--ray morphology both a powerful and a practical
cosmological discriminant.Comment: (uuencoded, compressed postscript, 9 pages including figures),
CFA-370
Detection and Removal of Artifacts in Astronomical Images
Astronomical images from optical photometric surveys are typically
contaminated with transient artifacts such as cosmic rays, satellite trails and
scattered light. We have developed and tested an algorithm that removes these
artifacts using a deep, artifact free, static sky coadd image built up through
the median combination of point spread function (PSF) homogenized, overlapping
single epoch images. Transient artifacts are detected and masked in each single
epoch image through comparison with an artifact free, PSF-matched simulated
image that is constructed using the PSF-corrected, model fitting catalog from
the artifact free coadd image together with the position variable PSF model of
the single epoch image. This approach works well not only for cleaning single
epoch images with worse seeing than the PSF homogenized coadd, but also the
traditionally much more challenging problem of cleaning single epoch images
with better seeing. In addition to masking transient artifacts, we have
developed an interpolation approach that uses the local PSF and performs well
in removing artifacts whose widths are smaller than the PSF full width at half
maximum, including cosmic rays, the peaks of saturated stars and bleed trails.
We have tested this algorithm on Dark Energy Survey Science Verification data
and present performance metrics. More generally, our algorithm can be applied
to any survey which images the same part of the sky multiple times.Comment: 17 pages, 6 figures. Accepted for publication in Astronomy and
Computin
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