7,945 research outputs found
Discussion of: A statistical analysis of multiple temperature proxies: Are reconstructions of surface temperatures over the last 1000 years reliable?
Discussion of "A statistical analysis of multiple temperature proxies: Are
reconstructions of surface temperatures over the last 1000 years reliable?" by
B.B. McShane and A.J. Wyner [arXiv:1104.4002]Comment: Published in at http://dx.doi.org/10.1214/10-AOAS398F the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A reconnaissance of the possible donor stars to the Kepler supernova
The identity of Type Ia supernova progenitors remains a mystery, with various
lines of evidence pointing towards either accretion from a non-degenerate
companion, or the rapid merger of two degenerate stars leading to the
thermonuclear destruction of a white dwarf. In this paper we spectroscopically
scrutinize 24 of the brightest stars residing in the central 38" x 38" of the
SN 1604 (Kepler) supernova remnant to search for a possible surviving companion
star. We can rule out, with high certainty, a red giant companion star - a
progenitor indicated by some models of the supernova remnant. Furthermore, we
find no star that exhibits properties uniquely consistent with those expected
of a donor star down to L>10Lsun. While the distribution of star properties
towards the remnant are consistent with unrelated stars, we identify the most
promising candidates for further astrometric and spectroscopic follow-up. Such
a program would either discover the donor star, or place strong limits on
progenitor systems to luminosities with L<<Lsun.Comment: accepted by Ap
Discretized vs. continuous models of p-wave interacting fermions in 1D
We present a general mapping between continuous and lattice models of Bose-
and Fermi-gases in one dimension, interacting via local two-body interactions.
For s-wave interacting bosons we arrive at the Bose-Hubbard model in the weakly
interacting, low density regime. The dual problem of p-wave interacting
fermions is mapped to the spin-1/2 XXZ model close to the critical point in the
highly polarized regime. The mappings are shown to be optimal in the sense that
they produce the least error possible for a given discretization length. As an
application we examine the ground state of a interacting Fermi gas in a
harmonic trap, calculating numerically real-space and momentum-space
distributions as well as two-particle correlations. In the analytically known
limits the convergence of the results of the lattice model to the continuous
one is shown.Comment: 7 pages, 5 figure
Hybrid Deterministic-Stochastic Methods for Data Fitting
Many structured data-fitting applications require the solution of an
optimization problem involving a sum over a potentially large number of
measurements. Incremental gradient algorithms offer inexpensive iterations by
sampling a subset of the terms in the sum. These methods can make great
progress initially, but often slow as they approach a solution. In contrast,
full-gradient methods achieve steady convergence at the expense of evaluating
the full objective and gradient on each iteration. We explore hybrid methods
that exhibit the benefits of both approaches. Rate-of-convergence analysis
shows that by controlling the sample size in an incremental gradient algorithm,
it is possible to maintain the steady convergence rates of full-gradient
methods. We detail a practical quasi-Newton implementation based on this
approach. Numerical experiments illustrate its potential benefits.Comment: 26 pages. Revised proofs of Theorems 2.6 and 3.1, results unchange
An overview of the Salish Sea Marine Survival Project: U.S.-Canada integration
The Salish Sea Marine Survival Project (Project) is a multi-year transboundary effort to determine the primary factors affecting juvenile salmon and steelhead survival in the Salish Sea. The Project, coordinated by nonprofits Long Live the Kings (U.S.) and the Pacific Salmon Foundation (Canada), brings together multidisciplinary expertise from over 20 Federal and State agencies, Tribes, academia and nonprofit organizations on both sides of the U.S.-Canada border. Through the development of a comprehensive, ecosystem-based research framework; coordinated data collection and standardization; and improved information sharing, the Project will help managers better understand the critical relationship between salmon and the Salish Sea. This transboundary initiative began in 2012 and will last seven years. Foundational reports include the Pacific Salmon Foundation’s Strait of Georgia Chinook and Coho Proposal (2009) and subsequently the Hypotheses and Preliminary Research Recommendations for Puget Sound (2012). In November 2012, a workshop with 90 participants was held to receive feedback from the broader scientific community regarding the critical elements of a US-Canada research program. The foundational and workshop summary reports are available at the Project web site (www.marinesurvivalproject.org). Science teams are now using this information to develop and implement the necessary research. We will present an overview of the Salish Sea Marine Survival Project, describing its history, leading hypotheses for poor survival, current status in research development and implementation, and how this work will contribute to Salish Sea sustainable resource management and recovery efforts. We will highlight the multi-disciplinary, collaborative nature of this project and the role of non-governmental organizations in aiding this large-scale initiative
Kinetic models reveal the in vivo mechanisms of mutagenesis in microbes and man
This review summarizes the evidence indicating that mutagenic mechanisms in vivo are essentially the same in all living cells. Unique metabolic reactions to a particular environmental stress apparently target specific genes for increased rates of transcription and mutation, resulting in higher mutation rates for those genes most likely to solve the problem. Kinetic models which have demonstrated predictive value are described and are shown to simulate mutagenesis in vivo in Escherichia coli, the p53 tumor suppressor gene, and somatic hypermutation. In all three models, direct correlations are seen between mutation frequencies and transcription rates. G and C nucleosides in single-stranded DNA (ssDNA) are intrinsically mutable, and G and C silent mutations in p53 and in VH framework regions provide compelling evidence for intrinsic mechanisms of mutability, since mutation outcomes are neutral and are not selected. During transcription, the availability of unpaired bases in the ssDNA of secondary structures is rate-limiting for, and determines the frequency of mutations in vivo. In vitro analyses also verify the conclusion that intrinsically mutable bases are in fact located in ssDNA loops of predicted stem-loop structures (SLSs)
Post-Pancreatoduodenectomy Outcomes and Epidural Analgesia: A 5-Year Single Institution Experience
Introduction
Optimal pain control post-pancreatoduodenectomy is a challenge. Epidural analgesia (EDA) is increasingly utilized despite inherent risks and unclear effects on outcomes.
Methods
All pancreatoduodenectomies (PD) performed from 1/2013-12/2017 were included. Clinical parameters were obtained from retrospective review of a prospective clinical database, the ACS NSQIP prospective institutional database and medical record review. Chi-Square/Fisher’s Exact and Independent-Samples t-Tests were used for univariable analyses; multivariable regression (MVR) was performed.
Results
671 consecutive PD from a single institution were included (429 EDA, 242 non-EDA). On univariable analysis, EDA patients experienced significantly less wound disruption (0.2% vs. 2.1%), unplanned intubation (3.0% vs. 7.9%), pulmonary embolism (0.5% vs. 2.5%), mechanical-ventilation >48hrs (2.1% vs. 7.9%), septic shock (2.6% vs. 5.8%), and lower pain scores. On MVR accounting for baseline group differences (gender, hypertension, pre-operative transfusion, labs, approach, pancreatic duct size), EDA was associated with less superficial wound infections (OR 0.34; CI 0.14-0.83; P=0.017), unplanned intubations (OR 0.36; CI 0.14-0.88; P=0.024), mechanical ventilation >48 hrs (OR 0.22; CI 0.08-0.62; P=0.004), and septic shock (OR 0.39; CI 0.15-1.00; P=0.050). EDA improved pain scores post-PD days 1-3 (P<0.001). No differences were seen in cardiac or renal complications; pancreatic fistula (B+C) or delayed gastric emptying; 30/90-day mortality; length of stay, readmission, discharge destination, or unplanned reoperation.
Conclusion
Based on the largest single institution series published to date, our data support the use of EDA for optimization of pain control. More importantly, our data document that EDA significantly improved infectious and pulmonary complications
The SkyMapper Transient Survey
The SkyMapper 1.3 m telescope at Siding Spring Observatory has now begun
regular operations. Alongside the Southern Sky Survey, a comprehensive digital
survey of the entire southern sky, SkyMapper will carry out a search for
supernovae and other transients. The search strategy, covering a total
footprint area of ~2000 deg2 with a cadence of days, is optimised for
discovery and follow-up of low-redshift type Ia supernovae to constrain cosmic
expansion and peculiar velocities. We describe the search operations and
infrastructure, including a parallelised software pipeline to discover variable
objects in difference imaging; simulations of the performance of the survey
over its lifetime; public access to discovered transients; and some first
results from the Science Verification data.Comment: 13 pages, 11 figures; submitted to PAS
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