2,019 research outputs found
The contribution of statistical physics to evolutionary biology
Evolutionary biology shares many concepts with statistical physics: both deal
with populations, whether of molecules or organisms, and both seek to simplify
evolution in very many dimensions. Often, methodologies have undergone parallel
and independent development, as with stochastic methods in population genetics.
We discuss aspects of population genetics that have embraced methods from
physics: amongst others, non-equilibrium statistical mechanics, travelling
waves, and Monte-Carlo methods have been used to study polygenic evolution,
rates of adaptation, and range expansions. These applications indicate that
evolutionary biology can further benefit from interactions with other areas of
statistical physics, for example, by following the distribution of paths taken
by a population through time.Comment: 18 pages, 3 figures, glossary. Accepted in Trend in Ecology and
Evolution (to appear in print in August 2011
Attributable costs of surgical site infection and endometritis after low transverse cesarean delivery
BACKGROUND: Accurate data on costs attributable to hospital-acquired infections are needed in order to determine their economic impact and the cost-benefit of potential preventive strategies. OBJECTIVE: Determine the attributable costs of surgical site infection (SSI) and endometritis (EMM) after cesarean section using two different methods. DESIGN: Retrospective cohort. SETTING: Barnes-Jewish Hospital, a 1250-bed academic tertiary care hospital. PATIENTS: 1,605 women who underwent low transverse cesarean section from 7/1999 – 6/2001. METHODS: Attributable costs of SSI and EMM were determined by generalized least squares (GLS) and propensity score matched-pairs using administrative claims data to define underlying comorbidities and procedures. For the matched-pairs analyses, uninfected control patients were matched to patients with SSI or with EMM based on their propensity to develop infection, and the median difference in costs calculated. RESULTS: The attributable total hospital cost of SSI calculated by GLS was 2,852. The attributable total hospital cost of EMM calculated by GLS was 3,842. The majority of excess costs were associated with room and board and pharmacy costs. CONCLUSIONS: The costs of SSI and EMM were lower than SSI costs reported after more extensive operations. The attributable costs of EMM calculated using the two methods were very similar, while the costs of SSI calculated using propensity score matched-pairs were lower than the costs calculated by GLS. The difference in costs determined by the two methods needs to be considered by investigators performing cost analyses of hospital-acquired infections
Respiratory Physiology and the Impact of Different Modes of Ventilation on the Photoplethysmographic Waveform
The photoplethysmographic waveform sits at the core of the most used, and arguably the most important, clinical monitor, the pulse oximeter. Interestingly, the pulse oximeter was discovered while examining an artifact during the development of a noninvasive cardiac output monitor. This article will explore the response of the pulse oximeter waveform to various modes of ventilation. Modern digital signal processing is allowing for a re-examination of this ubiquitous signal. The effect of ventilation on the photoplethysmographic waveform has long been thought of as a source of artifact. The primary goal of this article is to improve the understanding of the underlying physiology responsible for the observed phenomena, thereby encouraging the utilization of this understanding to develop new methods of patient monitoring. The reader will be presented with a review of respiratory physiology followed by numerous examples of the impact of ventilation on the photoplethysmographic waveform
Decoupling in an expanding universe: boundary RG-flow affects initial conditions for inflation
We study decoupling in FRW spacetimes, emphasizing a Lagrangian description
throughout. To account for the vacuum choice ambiguity in cosmological
settings, we introduce an arbitrary boundary action representing the initial
conditions. RG flow in these spacetimes naturally affects the boundary
interactions. As a consequence the boundary conditions are sensitive to
high-energy physics through irrelevant terms in the boundary action. Using
scalar field theory as an example, we derive the leading dimension four
irrelevant boundary operators. We discuss how the known vacuum choices, e.g.
the Bunch-Davies vacuum, appear in the Lagrangian description and square with
decoupling. For all choices of boundary conditions encoded by relevant boundary
operators, of which the known ones are a subset, backreaction is under control.
All, moreover, will generically feel the influence of high-energy physics
through irrelevant (dimension four) boundary corrections. Having established a
coherent effective field theory framework including the vacuum choice
ambiguity, we derive an explicit expression for the power spectrum of
inflationary density perturbations including the leading high energy
corrections. In accordance with the dimensionality of the leading irrelevant
operators, the effect of high energy physics is linearly proportional to the
Hubble radius H and the scale of new physics L= 1/M.Comment: LaTeX plus axodraw figures. v2: minor corrections; refs added. JHEP
style: 34 pages + 18 pages appendi
Arecibo 430 MHz Pulsar Polarimetry: Faraday Rotation Measures and Morphological Classifications
We have measured Faraday Rotation Measures (RMs) at Arecibo Observatory for
36 pulsars, 17 of them new. We combine these and earlier measurements to study
the galactic magnetic field and its possible temporal variations. Many RM
values have changed significantly on several-year timescales, but these
variations probably do not reflect interstellar magnetic field changes. By
studying the distribution of pulsar RMs near the plane in conjunction with the
new NE2001 electron density model, we note the following structures in the
first galactic longitude quadrant: (1) The local field reversal can be traced
as a null in RM in a 0.5-kpc wide strip interior to the Solar Circle, extending
\~7 kpc around the Galaxy. (2) Steadily increasing RMs in a 1-kpc wide strip
interior to the local field reversal, and also in the wedge bounded by 42<l<52
deg, indicate that the large-scale field is approximately steady from the local
reversal in to the Sagittarius arm. (3) The RMs in the 1-kpc wide strip
interior to the Sagittarius arm indicate another field reversal in this strip.
(4) The RMs in a final 1-kpc wide interior strip, straddling the Scutum arm,
also support a second field reversal interior to the Sun,between the
Sagittarius and Scutum arms. (5) Exterior to the nearby reversal, RMs from
60<l<78 deg show evidence for two reversals, on the near and far side of the
Perseus arm. (6) In general, the maxima in the large-scale fields tend to lie
along the spiral arms, while the field minima tend to be found between them. We
have also determined polarized profiles of 48 pulsars at 430 MHz. We present
morphological pulse profile classifications of the pulsars, based on our new
measurements and previously published data.Comment: Accepted by Astrophysical Journal Supplement, 56 pages, 22 fig
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