2,646 research outputs found
Cosmological perturbations on local systems
We study the effect of cosmological expansion on orbits--galactic, planetary,
or atomic--subject to an inverse-square force law. We obtain the laws of motion
for gravitational or electrical interactions from general relativity--in
particular, we find the gravitational field of a mass distribution in an
expanding universe by applying perturbation theory to the Robertson-Walker
metric. Cosmological expansion induces an ( force where
is the cosmological scale factor. In a locally Newtonian framework, we
show that the term represents the effect of a continuous
distribution of cosmological material in Hubble flow, and that the total force
on an object, due to the cosmological material plus the matter perturbation,
can be represented as the negative gradient of a gravitational potential whose
source is the material actually present. We also consider the effect on local
dynamics of the cosmological constant. We calculate the perihelion precession
of elliptical orbits due to the cosmological constant induced force, and work
out a generalized virial relation applicable to gravitationally bound clusters.Comment: 10 page
Systems biologists seek fuller integration of systems biology approaches in new cancer research programs
Systems biology takes an interdisciplinary approach to the systematic study of complex interactions in biological systems. This approach seeks to decipher the emergent behaviors of complex systems rather than focusing only on their constituent properties. As an increasing number of examples illustrate the value of systems biology approaches to understand the initiation, progression, and treatment of cancer, systems biologists from across Europe and the United States hope for changes in the way their field is currently perceived among cancer researchers. In a recent EU-US workshop, supported by the European Commission, the German Federal Ministry for Education and Research, and the National Cancer Institute of the NIH, the participants discussed the strengths, weaknesses, hurdles, and opportunities in cancer systems biology
How model sets can be determined by their two-point and three-point correlations
We show that real model sets with real internal spaces are determined, up to
translation and changes of density zero by their two- and three-point
correlations. We also show that there exist pairs of real (even one
dimensional) aperiodic model sets with internal spaces that are products of
real spaces and finite cyclic groups whose two- and three-point correlations
are identical but which are not related by either translation or inversion of
their windows. All these examples are pure point diffractive.
Placed in the context of ergodic uniformly discrete point processes, the
result is that real point processes of model sets based on real internal
windows are determined by their second and third moments.Comment: 19 page
A Uniqueness Theorem for Constraint Quantization
This work addresses certain ambiguities in the Dirac approach to constrained
systems. Specifically, we investigate the space of so-called ``rigging maps''
associated with Refined Algebraic Quantization, a particular realization of the
Dirac scheme. Our main result is to provide a condition under which the rigging
map is unique, in which case we also show that it is given by group averaging
techniques. Our results comprise all cases where the gauge group is a
finite-dimensional Lie group.Comment: 23 pages, RevTeX, further comments and references added (May 26. '99
The prognostic value of Cardiopulmonary Exercise Testing in Idiopathic Pulmonary Fibrosis
Rationale: Idiopathic pulmonary fibrosis (IPF) is characterized by progressive
dyspnea, impaired gas exchange, and ultimate mortality.
Objectives: To test the hypothesis that maximal oxygen uptake
during cardiopulmonary exercise testing at baseline and with
short-term longitudinal measures would predict mortality in
patients with idiopathic pulmonary fibrosis.
Methods: Data from 117 patients with IPF and longitudinal cardiopulmonary
exercise tests were examined retrospectively. Survival
was calculated from the date of the first cardiopulmonary exercise
test.
Measurements and Main Results: Patients with baseline maximal
oxygen uptake less than 8.3 ml/kg/min had an increased risk of
death (n=8; hazard ratio, 3.24; 95% confidence interval, 1.10–9.56;
P = 0.03) after adjusting for age, gender, smoking status, baseline
forced vital capacity, and baseline diffusion capacity for carbon
monoxide. We were unable to define a unit change in maximal
oxygen uptake that predicted survival in our cohort.
Conclusions: We conclude that a threshold maximal oxygen uptake of
8.3 ml/kg/min during cardiopulmonary exercise testing at baseline
adds prognostic information for patients with IPF.Supported by National Institute of Health NHLBI grant P50HL-56402, NHLBI, 2
K24 HL04212, 1 K23 HL68713, and 1K23 HL077719. C.D.F. was supported by
the Alberta Heritage Foundation for Medical Research.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91965/1/2009 AJRCCM The prognostic value of Cardiopulmonary Exercise Testing in Idiopathic Pulmonary Fibrosis.pd
Sex differences in physiological progression of idiopathic pulmonary fibrosis
In idiopathic pulmonary fibrosis, incidence is higher in males, and females may have
better survival. The aim of the present study was to determine whether the rate of increase in
desaturation during serial 6-min walk testing would be greater, and survival worse, for males
versus females.
Serial changes in the percentage of maximum desaturation area (DA) over 1 yr were estimated
using mixed models in 215 patients. DA was defined as the total area above the curve created
using desaturation percentage values observed during each minute of the 6-min walk test.
Multivariate Cox regression assessed survival differences.
Adjusting for baseline DA, 6-min walk distance, change in 6-min walk distance over time and
smoking history, the percentage of maximum DA increased by an average of 2.83 and 1.37% per
month for males and females, respectively. Females demonstrated better survival overall, which
was more pronounced in patients who did not desaturate below 88% on ambulation at baseline
and after additionally adjusting for 6-month relative changes in DA and forced vital capacity.
These data suggest that differences in disease progression contribute to, but do not completely
explain, better survival of females with idiopathic pulmonary fibrosis.This work was supported by National
Institutes of Health grants
5P50HL56402, U10HL080371,
2K24HL04212, K12RR024987 and
K23HL68713, and the Alberta
Heritage Medical Foundation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91966/1/2008 ERJ - Sex Differences in Physiologic Progression of Idiopathic Pulmonary Fibrosis.pd
Random graphs with arbitrary degree distributions and their applications
Recent work on the structure of social networks and the internet has focussed
attention on graphs with distributions of vertex degree that are significantly
different from the Poisson degree distributions that have been widely studied
in the past. In this paper we develop in detail the theory of random graphs
with arbitrary degree distributions. In addition to simple undirected,
unipartite graphs, we examine the properties of directed and bipartite graphs.
Among other results, we derive exact expressions for the position of the phase
transition at which a giant component first forms, the mean component size, the
size of the giant component if there is one, the mean number of vertices a
certain distance away from a randomly chosen vertex, and the average
vertex-vertex distance within a graph. We apply our theory to some real-world
graphs, including the world-wide web and collaboration graphs of scientists and
Fortune 1000 company directors. We demonstrate that in some cases random graphs
with appropriate distributions of vertex degree predict with surprising
accuracy the behavior of the real world, while in others there is a measurable
discrepancy between theory and reality, perhaps indicating the presence of
additional social structure in the network that is not captured by the random
graph.Comment: 19 pages, 11 figures, some new material added in this version along
with minor updates and correction
Clinical Predictors of a Diagnosis of Idiopathic Pulmonary Fibrosis
Rationale: Idiopathic pulmonary fibrosis (IPF) and other idiopathic
interstitial pneumonias (IIPs) have similar clinical and radiographic
features, but their histopathology, response to therapy, and natural
history differ. A surgical lung biopsy is often required to distinguish
between these entities.
Objectives: We sought to determine if clinical variables could predict
a histopathologic diagnosis of IPF in patients without honeycomb
change on high-resolution computed tomography (HRCT).
Methods: Data from 97 patients with biopsy-proven IPF and 38
patients with other IIPs were examined. Logistic regression models
were built to identify the clinical variables that predict histopathologic
diagnosis of IPF.
Measurements and Main Results: Increasing age and average total
HRCT interstitial score on HRCT scan of the chest may predict
a biopsy confirmation of IPF. Sex, pulmonary function, presence
of desaturation, or distance walked during a 6-minute walk test
did not help discriminate pulmonary fibrosis from other IIPs.
Conclusions: Clinical data may be used to predict a diagnosis of IPF
over other IIPs. Validation of these data with a prospective study is
needed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91953/1/2010 AJRCCM Clinical Predictors of a Diagnosis of Idiopathic Pulmonary Fibrosis.pd
A prospective cohort study comparing the reactogenicity of trivalent influenza vaccine in pregnant and non-pregnant women
Background: Influenza vaccination during pregnancy can prevent serious illness in expectant mothers and provide protection to newborns; however, historically uptake has been limited due to a number of factors, including safety concerns. Symptomatic complaints are common during pregnancy and may be mistakenly associated with reactions to trivalent influenza vaccine (TIV). To investigate this, we compared post-vaccination events self-reported by pregnant women to events reported by non-pregnant women receiving TIV.
Methods: A prospective cohort of 1,086 pregnant women and 314 non-pregnant female healthcare workers (HCWs) who received TIV between March-May 2014 were followed-up seven days post-vaccination to assess local and systemic adverse events following immunisation (AEFIs). Women were surveyed by text message regarding perceived reactions to TIV. Those reporting an AEFI completed an interview by telephone or mobile phone to ascertain details. Logistic regression models adjusting for age and residence were used to compare reactions reported by pregnant women and non-pregnant HCWs.
Results: Similar proportions of pregnant women and non-pregnant, female HCWs reported ≥1 reaction following vaccination with TIV (13.0% and 17.3%, respectively; OR = 1.2 [95% CI: 0.8-1.8]). Non-pregnant, female HCWs were more likely to report fever or headache compared to pregnant women (OR: 4.6 [95% CI 2.1-10.3] and OR: 2.2 [95% CI 1.0-4.6], respectively). No other significant differences in reported symptoms were observed. No serious vaccine-associated adverse events were reported, and less than 2% of each group sought medical advice for a reaction.
Conclusions: We found no evidence suggesting pregnant women are more likely to report adverse events following influenza vaccination when compared to non-pregnant female HCWs of similar age, and in some cases, pregnant women reported significantly fewer adverse events. These results further support the safety of TIV administered in pregnant women
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