1,213 research outputs found
Does the BICEP2 Observation of Cosmological Tensor Modes Imply an Era of Nearly Planckian Energy Densities?
BICEP2 observations, interpreted most simply, suggest an era of inflation
with energy densities of order (, not far below the
Planck density. However, models of TeV gravity with large extra dimensions
might allow a very different interpretation involving much more modest energy
scales. We discuss the viability of inflation in such models, and conclude that
existing scenarios do not provide attractive alternatives to single field
inflation in four dimensions. Because the detection of tensor modes strengthens
our confidence that inflation occurred, it disfavors models of large extra
dimensions, at least for the moment.Comment: 4 pages, v3: version to appear in JHE
Determination of Nonlinear Genetic Architecture using Compressed Sensing
We introduce a statistical method that can reconstruct nonlinear genetic
models (i.e., including epistasis, or gene-gene interactions) from
phenotype-genotype (GWAS) data. The computational and data resource
requirements are similar to those necessary for reconstruction of linear
genetic models (or identification of gene-trait associations), assuming a
condition of generalized sparsity, which limits the total number of gene-gene
interactions. An example of a sparse nonlinear model is one in which a typical
locus interacts with several or even many others, but only a small subset of
all possible interactions exist. It seems plausible that most genetic
architectures fall in this category. Our method uses a generalization of
compressed sensing (L1-penalized regression) applied to nonlinear functions of
the sensing matrix. We give theoretical arguments suggesting that the method is
nearly optimal in performance, and demonstrate its effectiveness on broad
classes of nonlinear genetic models using both real and simulated human
genomes.Comment: 20 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1408.342
Instability of Quantum de Sitter Spacetime
Quantized fields (e.g., the graviton itself) in de Sitter (dS) spacetime lead
to particle production: specifically, we consider a thermal spectrum resulting
from the dS (horizon) temperature. The energy required to excite these
particles reduces slightly the rate of expansion and eventually modifies the
semiclassical spacetime geometry. The resulting manifold no longer has constant
curvature nor time reversal invariance, and back-reaction renders the classical
dS background unstable to perturbations. In the case of AdS, there exists a
global static vacuum state; in this state there is no particle production and
the analogous instability does not arise.Comment: 3 pages, v2: version to appear in JHE
Repeat prescribing of medications: a system-centred risk management model for primary care organisations
Rationale, aims and objectives:
Reducing preventable harm from repeat medication prescriptions is a patient safety priority worldwide. In the United Kingdom, repeat prescriptions items issued has doubled in the last 20 years from 5.8 to 13.3 items per patient per annum. This has significant resource implications and consequences for avoidable patient harms. Consequently, we aimed to test a risk management model to identify, measure, and reduce repeat prescribing system risks in primary care.
Methods:
All 48 general medical practices in National Health Service (NHS) Lambeth Clinical Commissioning Group (an inner city area of south London in England) were recruited. Multiple interventions were implemented, including educational workshops, a web-based risk monitoring system, and external reviews of repeat prescribing system risks by clinicians. Data were collected via documentation reviews and interviews and subject to basic thematic and descriptive statistical analyses.
Results:
Across the 48 participating general practices, 62 unique repeat prescribing risks were identified on 505 occasions (eg, practices frequently experiencing difficulty interpreting medication changes on hospital discharge summaries), equating to a mean of 8.1 risks per practice (range: 1-33; SD = 7.13). Seven hundred sixty-seven system improvement actions were recommended across 96 categories (eg, alerting hospitals to illegible writing and delays with discharge summaries) with a mean of 15.6 actions per practice (range: 0-34; SD = 8.0).
Conclusions:
The risk management model tested uncovered important safety concerns and facilitated the development and communication of related improvement recommendations. System-wide information on hazardous repeat prescribing and how this could be mitigated is very limited. The approach reported may have potential to close this gap and improve the reliability of general practice systems and patient safety, which should be of high interest to primary care organisations internationally
New Active Asteroid 313P/Gibbs
We present initial observations of the newly-discovered active asteroid
313P/Gibbs (formerly P/2014 S4), taken to characterize its nucleus and
comet-like activity. The central object has a radius 0.5 km (geometric
albedo 0.05 assumed). We find no evidence for secondary nuclei and set (with
qualifications) an upper limit to the radii of such objects near 25 m, assuming
the same albedo. Both aperture photometry and a morphological analysis of the
ejected dust show that mass-loss is continuous at rates 0.2 to 0.4 kg
s, inconsistent with an impact origin. Large dust particles, with radii
50 to 100 m, dominate the optical appearance. At 2.4 AU from the
Sun, the surface equilibrium temperatures are too low for thermal or
desiccation stresses to be responsible for the ejection of dust. No gas is
spectroscopically detected (limiting the gas mass loss rate to 1.8 kg
s). However, the protracted emission of dust seen in our data and the
detection of another episode of dust release near perihelion, in archival
observations from 2003, are highly suggestive of an origin by the sublimation
of ice. Coincidentally, the orbit of 313P/Gibbs is similar to those of several
active asteroids independently suspected to be ice sublimators, including
P/2012 T1, 238P/Read and 133P/Elst-Pizarro, suggesting that ice is abundant in
the outer asteroid belt.Comment: 24 pages, 7 figures, accepted The Astronomical Journa
Synthetic Peptides with Inadvertent Chemical Modifications Can Activate Potentially Autoreactive T Cells
The human CD8+ T cell clone 6C5 has previously been shown to recognize the tert-butyl-modified Bax161–170 peptide LLSY(3-tBu)FGTPT presented by HLA-A*02:01. This nonnatural epitope was likely created as a by-product of fluorenylmethoxycarbonyl protecting group peptide synthesis and bound poorly to HLA-A*02:01. In this study, we used a systematic approach to identify and characterize natural ligands for the 6C5 TCR. Functional analyses revealed that 6C5 T cells only recognized the LLSYFGTPT peptide when tBu was added to the tyrosine residue and did not recognize the LLSYFGTPT peptide modified with larger (di-tBu) or smaller chemical groups (Me). Combinatorial peptide library screening further showed that 6C5 T cells recognized a series of self-derived peptides with dissimilar amino acid sequences to LLSY(3-tBu)FGTPT. Structural studies of LLSY(3-tBu)FGTPT and two other activating nonamers (IIGWMWIPV and LLGWVFAQV) in complex with HLA-A*02:01 demonstrated similar overall peptide conformations and highlighted the importance of the position (P) 4 residue for T cell recognition, particularly the capacity of the bulky amino acid tryptophan to substitute for the tBu-modified tyrosine residue in conjunction with other changes at P5 and P6. Collectively, these results indicated that chemical modifications directly altered the immunogenicity of a synthetic peptide via molecular mimicry, leading to the inadvertent activation of a T cell clone with unexpected and potentially autoreactive specificities
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