972 research outputs found
Brane-world Cosmologies with non-local bulk effects
It is very common to ignore the non-local bulk effects in the study of
brane-world cosmologies using the brane-world approach. However, we shall
illustrate through the use of three different scenarios, that the non-local
bulk-effect does indeed have significant impact on both the
initial and future behaviour of brane-world cosmologies.Comment: 17 pages, no figures, iopart.cls, submitted to CQ
Direct Awards in Germany – Design And Effects
Institute of Transport and Logistics Studies. Faculty of Economics and Business. The University of Sydne
Scalar Field Cosmologies with Barotropic Matter: Models of Bianchi class B
We investigate in detail the qualitative behaviour of the class of Bianchi
type B spatially homogeneous cosmological models in which the matter content is
composed of two non-interacting components; the first component is described by
a barotropic fluid having a gamma-law equation of state, whilst the second is a
non-interacting scalar field (phi) with an exponential potential V=Lambda exp(k
phi). In particular, we study the asymptotic properties of the models both at
early and late times, paying particular attention on whether the models
isotropize (and inflate) to the future, and we discuss the genericity of the
cosmological scaling solutions.Comment: 18 pages, 1 figure, uses revtex and epsf to insert figur
The Dynamics of Multi-Scalar Field Cosmological Models and Assisted Inflation
We investigate the dynamical properties of a class of spatially homogeneous
and isotropic cosmological models containing a barotropic perfect fluid and
multiple scalar fields with independent exponential potentials. We show that
the assisted inflationary scaling solution is the global late-time attractor
for the parameter values for which the model is inflationary, even when
curvature and barotropic matter are included. For all other parameter values
the multi-field curvature scaling solution is the global late-time attractor
(in these solutions asymptotically the curvature is not dynamically
negligible). Consequently, we find that in general all of the scalar fields in
multi-field models with exponential potentials are non-negligible in late-time
behaviour, contrary to what is commonly believed. The early-time and
intermediate behaviour of the models is also studied. In particular, n-scalar
field models are investigated and the structure of the saddle equilibrium
points corresponding to inflationary m-field scaling solutions and
non-inflationary m-field matter scaling solutions are also studied (where m<n),
leading to interesting transient dynamical behaviour with new physical
scenarios of potential importance.Comment: 27 pages, uses REVTeX Added an appendix illustrating some of the
details needed to compute the stability of the assisted inflationary solutio
Local and non-local measures of acceleration in cosmology
Current cosmological observations, when interpreted within the framework of a
homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) model,
strongly suggest that the Universe is entering a period of accelerating
expansion. This is often taken to mean that the expansion of space itself is
accelerating. In a general spacetime, however, this is not necessarily true. We
attempt to clarify this point by considering a handful of local and non-local
measures of acceleration in a variety of inhomogeneous cosmological models.
Each of the chosen measures corresponds to a theoretical or observational
procedure that has previously been used to study acceleration in cosmology, and
all measures reduce to the same quantity in the limit of exact spatial
homogeneity and isotropy. In statistically homogeneous and isotropic
spacetimes, we find that the acceleration inferred from observations of the
distance-redshift relation is closely related to the acceleration of the
spatially averaged universe, but does not necessarily bear any resemblance to
the average of the local acceleration of spacetime itself. For inhomogeneous
spacetimes that do not display statistical homogeneity and isotropy, however,
we find little correlation between acceleration inferred from observations and
the acceleration of the averaged spacetime. This shows that observations made
in an inhomogeneous universe can imply acceleration without the existence of
dark energy.Comment: 19 pages, 10 figures. Several references added or amended, some minor
clarifications made in the tex
Disparities in kidney transplantation accessibility among immigrant populations in Europe: A systematic review and meta-analysis
Background and objectives: Disparities in access to healthcare for patients with an immigration background are well-known. The aim of this study was to determine whether disparities among immigrant populations translate into a relative difference in the number of kidney transplants (KT) performed in documented immigrant patients (first and second generation) relative to native-born patients in Europe. Methods: A literature search was performed in PubMed from inception to 11-10-2022. Studies were eligible if: (1) written in English, (2) included immigrant and native-born KT patients, (3) performed in countries registered as Council of Europe members, (4) focused on documented first- and second-generation immigrant populations [1]. Systematic reviews, literature reviews, and case reports or articles about emigration, non-KT, and undocumented immigrants were excluded. The outcome measurement was a relative percentage of KTs to the total population per 100.000 residents. By dividing the immigrant percentages by the native-born resident percentages, the odds ratio (OR) was calculated in a meta-analysis. The risk of bias was assessed; articles with high risk of bias were excluded in a second meta-analysis. Results: Out of 109 articles, 5 were included (n = 24,614). One Italian study (n = 24,174) had a ratio below 1, being 0.910 (95%CI 0.877-0.945). The other four articles (n = 196, n = 283, n = 77, n = 119) had ratios above 1: 1.36 (95%CI 0.980-1.87), 2.04 (95%CI 1.56-2.68), 2.23 (95%CI 1.53-3.25) and 2.64 (95%CI 1.68-4.15). After performing a meta-analysis, the OR did not show a significant difference: 1.68 (95%CI 1.03-2.75). After bias correction, this remained unchanged: 1.78 (95%CI 0.961-3.31). Conclusions: In our meta-analysis we did not find a significant difference in the relative number of KTs performed in immigrant versus native-born populations in Europe. However, a lesser likelihood for immigrants to receive a pre-emptive kidney transplantation was found. Large heterogeneity between studies (e.g. different sample size, patient origins, study duration, adult vs children patients) was a shortcoming to our analysis. Nevertheless, our article is the first review in this understudied topic. As important questions (e.g. on ethnicity, living donor rate) remain, future studies are needed to address them
Protocolized Versus Nonprotocolized Weaning to Reduce the Duration of Invasive Mechanical Weaning in Neonates A Systematic Review of All Types of Studies
Mechanical ventilation is one of the most commonly used
treatments in neonatology. Prolonged mechanical ventilation is associated with deleterious outcomes. To reduce
the ventilation duration, weaning protocols have been developed to achieve extubation in adult and pediatric care
in a safe and uniform manner. We performed a systematic
review to obtain all available evidence on the effect of protocolized versus nonprotocolized weaning on the duration
of invasive mechanical ventilation in critically ill neonates.
The Cochrane Central Register of Controlled Trials,
MEDLINE, EMBASE, CINAHL, Web of Science, and the
International Clinical Trial Registry Platform were searched
until January 2018. Quantitative and qualitative studies
involving neonates that investigated or described protocolized versus nonprotocolized weaning were included.
Primary outcome was the difference in weaning duration.
A total of 2099 potentially relevant articles were retrieved.
Three stud
Disparities in kidney transplantation accessibility among immigrant populations in Europe:A systematic review and meta-analysis
Background and objectives: Disparities in access to healthcare for patients with an immigration background are well-known. The aim of this study was to determine whether disparities among immigrant populations translate into a relative difference in the number of kidney transplants (KT) performed in documented immigrant patients (first and second generation) relative to native-born patients in Europe. Methods: A literature search was performed in PubMed from inception to 11-10-2022. Studies were eligible if: (1) written in English, (2) included immigrant and native-born KT patients, (3) performed in countries registered as Council of Europe members, (4) focused on documented first- and second-generation immigrant populations [1]. Systematic reviews, literature reviews, and case reports or articles about emigration, non-KT, and undocumented immigrants were excluded. The outcome measurement was a relative percentage of KTs to the total population per 100.000 residents. By dividing the immigrant percentages by the native-born resident percentages, the odds ratio (OR) was calculated in a meta-analysis. The risk of bias was assessed; articles with high risk of bias were excluded in a second meta-analysis. Results: Out of 109 articles, 5 were included (n = 24,614). One Italian study (n = 24,174) had a ratio below 1, being 0.910 (95%CI 0.877–0.945). The other four articles (n = 196, n = 283, n = 77, n = 119) had ratios above 1: 1.36 (95%CI 0.980–1.87), 2.04 (95%CI 1.56–2.68), 2.23 (95%CI 1.53–3.25) and 2.64 (95%CI 1.68–4.15). After performing a meta-analysis, the OR did not show a significant difference: 1.68 (95%CI 1.03–2.75). After bias correction, this remained unchanged: 1.78 (95%CI 0.961–3.31). Conclusions: In our meta-analysis we did not find a significant difference in the relative number of KTs performed in immigrant versus native-born populations in Europe. However, a lesser likelihood for immigrants to receive a pre-emptive kidney transplantation was found. Large heterogeneity between studies (e.g. different sample size, patient origins, study duration, adult vs children patients) was a shortcoming to our analysis. Nevertheless, our article is the first review in this understudied topic. As important questions (e.g. on ethnicity, living donor rate) remain, future studies are needed to address them.</p
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