31,345 research outputs found
Killing the Straw Man: Does BICEP Prove Inflation at the GUT Scale?
The surprisingly large value of , the ratio of power in tensor to scalar
density perturbations in the CMB reported by the BICEP2 Collaboration, if
confirmed, provides strong evidence for Inflation at the GUT scale. While the
Inflationary signal remains the best motivated source, a large value of
alone would still allow for the possibility that a comparable gravitational
wave background might result from a self ordering scalar field (SOSF)
transition that takes place later at somewhat lower energy. We find that even
without detailed considerations of the predicted BICEP signature of such a
transition, simple existing limits on the isocurvature contribution to CMB
anisotropies would definitively rule out a contribution of more than to
,. We also present a general relation for the allowed fractional
SOSF contribution to as a function of the ultimate measured value of .
These results point strongly not only to an inflationary origin of the BICEP2
signal, if confirmed, but also to the fact that if the GUT scale is of order
then either the GUT transition happens before Inflation or the
Inflationary transition and the GUT transition must be one and the same.Comment: 3 pages 2 figures, accepted for publication in Physics Letters B .
Accepted version revised slightly in response to referee's comment
Long-term study of the impact of methotrexate on serum cytokines and lymphocyte subsets in patients with active rheumatoid arthritis: correlation with pharmacokinetic measures
Objective To describe changes in immune parameters observed during long-term methotrexate (MTX) therapy in patients with active rheumatoid arthritis (RA) and explore correlations with simultaneously measured MTX pharmacokinetic (PKC) parameters.
Design Prospective, open-label, long-term mechanism of action study.
Setting University clinic.
Methods MTX was initiated at a single weekly oral dose of 7.5 mg and dose adjusted for efficacy and toxicity for the duration of the study. Standard measures of disease activity were performed at baseline and every 6–36 months. Serum cytokine measurements in blood together with lymphocyte surface immunophenotypes and stimulated peripheral blood mononuclear cell (PBMC) cytokine production were assessed at each clinical evaluation.
Results Cytokine concentrations exhibited multiple significant correlations with disease activity measures over time. The strongest correlations observed were for interleukin (IL)-6 (r=0.45, p<0.0001 for swollen joints and r=0.32, p=0.002 for tender joints) and IL-8 (r=0.25, p=0.01 for swollen joints). Significant decreases from baseline were observed in serum IL-1B, IL-6 and IL-8 concentrations. The most significant changes were observed for IL-6 (p<0.001). Significant increases from baseline were observed in IL-2 release from PBMCs ex vivo (p<0.01). In parallel, multiple statistically significant correlations were observed between MTX PKC measures and immune parameters. The change in swollen joint count correlated inversely with the change in area under the curve (AUC) for MTX (r=−0.63, p=0.007).
Conclusions MTX therapy of patients with RA is accompanied by a variety of changes in serum cytokine expression, which in turn correlate strongly with clinical disease activity and MTX pharmacokinetics (PKCs). These data strongly support the notion that MTX mediates profound and functionally relevant effects on the immunological hierarchy in the RA lesion
The Bulge-Halo Connection in Galaxies: A Physical Interpretation of the Vcirc-sigma_0 Relation
We explore the dependence of the ratio of a galaxy's circular velocity,
Vcirc, to its central velocity dispersion, sigma_0, on morphology, or
equivalently total light concentration. Such a dependence is expected if light
traces the mass. Over the full range of galaxy types, masses and brightnesses,
and assuming that the gas velocity traces the circular velocity, we find that
galaxies obey the relation log(Vcirc/sigma_0)= 0.63-0.11*C28 where
C28=5log(r80/r20) and the radii are measured at 80 percent and 20 percent of
the total light. Massive galaxies scatter about the Vcirc = sqrt(2)*sigma_0
line for isothermal stellar systems. Disk galaxies follow the simple relation
Vcirc/sigma_0=2(1-B/T), where B/T is the bulge-to-total light ratio. For pure
disks, C28~2.8, B/T -> 0, and Vcirc~=2*sigma_0. Self-consistent equilibrium
galaxy models from Widrow & Dubinski (2005) constrained to match the
size-luminosity and velocity-luminosity relations of disk galaxies fail to
match the observed Vcirc/sigma_0 distribution. Furthermore, the matching of
dynamical models for Vcirc(r)/sigma(r) with observations of dwarf and
elliptical galaxies suffers from limited radial coverage and relatively large
error bars; for dwarf systems, however, kinematical measurements at the galaxy
center and optical edge suggest Vcirc(Rmax) > 2*sigma_0 (in contrast with past
assumptions that Vcirc = sqrt(2)*sigma_0 for dwarfs.) The Vcirc-sigma_0-C28
relation has direct implications for galaxy formation and dynamical models,
galaxy scaling relations, the mass function of galaxies, and the links between
respective formation and evolution processes for a galaxy's central massive
object, bulge, and dark matter halo.Comment: Accepted for publication in ApJL. Current version matches ApJL page
requiremen
Delayed Sampling and Automatic Rao-Blackwellization of Probabilistic Programs
We introduce a dynamic mechanism for the solution of analytically-tractable
substructure in probabilistic programs, using conjugate priors and affine
transformations to reduce variance in Monte Carlo estimators. For inference
with Sequential Monte Carlo, this automatically yields improvements such as
locally-optimal proposals and Rao-Blackwellization. The mechanism maintains a
directed graph alongside the running program that evolves dynamically as
operations are triggered upon it. Nodes of the graph represent random
variables, edges the analytically-tractable relationships between them. Random
variables remain in the graph for as long as possible, to be sampled only when
they are used by the program in a way that cannot be resolved analytically. In
the meantime, they are conditioned on as many observations as possible. We
demonstrate the mechanism with a few pedagogical examples, as well as a
linear-nonlinear state-space model with simulated data, and an epidemiological
model with real data of a dengue outbreak in Micronesia. In all cases one or
more variables are automatically marginalized out to significantly reduce
variance in estimates of the marginal likelihood, in the final case
facilitating a random-weight or pseudo-marginal-type importance sampler for
parameter estimation. We have implemented the approach in Anglican and a new
probabilistic programming language called Birch.Comment: 13 pages, 4 figure
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