65 research outputs found
Cosmic string Y-junctions: a comparison between field theoretic and Nambu-Goto dynamics
We explore the formation of cosmic string Y-junctions when strings of two
different types collide, which has recently become important since string
theory can yield cosmic strings of distinct types. Using a model containing two
types of local U(1) string and stable composites, we simulate the collision of
two straight strings and investigate whether the dynamics matches that
previously obtained using the Nambu-Goto action, which is not strictly valid
close to the junction. We find that the Nambu-Goto action performs only
moderately well at predicting when the collision results in the formation of a
pair of Y-junctions (with a composite string connecting them). However, we find
that when they do form, the late time dynamics matches those of the Nambu-Goto
approximation very closely. We also see little radiative emission from the
Y-junction system, which suggests that radiative decay due to bridge formation
does not appear to be a means via which a cosmological network of such string
would rapidly lose energy.Comment: 17 pages, 17 figures; typo correctio
Radiocephalic and brachiocephalic arteriovenous fistula outcomes in the elderly
BackgroundA recent meta-analysis has suggested that patients aged >65 have worse outcomes with radiocephalic arteriovenous fistulas (RCAVFs) compared with brachiocephalic arteriovenous fistulas (BCAVFs). We hypothesized that outcomes in patients aged ≥80—a rapidly expanding cohort within this elderly group—might be skewing the results, and that age >65 may not be a contraindication to RCAVF formation. This study examined the effect of age group (<65, 65 to 79, ≥80) on functional outcomes (use; primary and secondary functional patency) in RCVAFs and BCAVFs.MethodsWe identified the outcomes of all patients undergoing a first surgical access procedure for a RCAVF or BCVAF between January 1, 2000, and December 31, 2005. We examined the effect of age and other factors including sex, diabetes mellitus, hypertension, late referral (<3 months before dialysis), dialysis before surgical access, preoperative duplex ultrasound imaging, and ethnicity on non-AVF use and primary and secondary functional AVF patency. Logistic regression and Cox proportional hazards regression models were used.ResultsFrom a total of 658 patients, 361 had a RCAVF, and 297 had a BCAVF. Their median age was 68.5 years (interquartile range [IQR], 54.4 to 76.5 years), and 288 (43.8%) were aged <65 years, 274 (41.6%) were 65 to 79, and 96 (14.6%) were ≥80. Age did not influence the site of the first surgical access (P = .874). Only 85.7% of patients actually progressed to hemodialysis, and the RCAVF or BCAVF in 45.7% of those was never used for dialysis. Female sex (hazard ratio [HR], 2.24; 95% confidence interval [CI] 1.387 to 3.643; P = .001) was the only factor associated with an increase risk of RCAVF nonuse, whereas diabetes (HR, 2.095; 95% CI, 1.261 to 3.482; P = .004) was the only factor associated with an increase risk of BCAVF nonuse. The respective primary patency rates at 1 and 2 years for RCAVFs were 46.0% and 27.1% for patients <65, 47.0% and 36.0% for those 65 to 79, and 45.7% and 38.1% for those ≥80. Only female sex (HR, 1.679; 95% CI, 1.261 to 2.236; P = .001) and prior hemodialysis (HR, 1.363; 95% CI, 1.0.29 to 1.804; P = .031) were associated with loss of patency of RCAVFs. The primary functional patency rates for BCAVFs at 1 and 2 years were 39.3% and 31.0% for those <65 years; 53.30% and 37.5% for those 65 to 79, and 46.3% and 42.6% for those ≥80. No factors analyzed were associated with loss of primary functional patency of BCAVFs.ConclusionsAge did not affect usability, primary or secondary patency of either RCAVFs or BCAVFs. Although patient selection is important, even patients ≥80 years who are considered suitable for surgical placement of access should not be denied a RCAVF solely because of age
On the stability of Cosmic String Y-junctions
We study the evolution of non-periodic cosmic string loops containing
Y-junctions, such as may form during the evolution of a network of (p,q) cosmic
superstrings. We set up and solve the Nambu-Goto equations of motion for a loop
with junctions, focusing attention on a specific static and planar initial loop
configuration. After a given time, the junctions collide and the Nambu-Goto
description breaks down. We also study the same loop configuration in a
U(1)xU(1) field theory model that allows composite vortices with corresponding
Y-junctions. We show that the field theory and Nambu-Goto evolution are
remarkably similar until the collision time. However, in the field theory
evolution a new phenomenon occurs: the composite vortices can unzip, producing
in the process new Y-junctions, whose separation may grow significantly,
destabilizing the configuration. In particular, an initial loop with two
Y-junctions may evolve to a configuration with six Y-junctions (all distant
from each other). Setting up this new configuration as an initial condition for
Nambu Goto strings, we solve for its evolution and establish conditions under
which it is stable to the decay mode seen in the field theory case. Remarkably,
the condition closely matches that seen in the field theory simulations, and is
expressed in terms of simple parameters of the Nambu-Goto system. This implies
that there is an easy way to understand the instability in terms of which
region of parameter space leads to stable or unstable unzippings.Comment: 16 pages, 11 figures, typos correcte
Scaling in a SU(2)/Z_3 model of cosmic superstring networks
Motivated by recent developments in superstring theory in the cosmological
context, we examine a field theory which contains string networks with 3-way
junctions. We perform numerical simulations of this model, identify the length
scales of the network that forms, and provide evidence that the length scales
tend towards a scaling regime, growing in proportion to time. We infer that the
presence of junctions does not in itself cause a superstring network to
dominate the energy density of the early Universe.Comment: 12pp, 3 fig
Protocol for an independent patient data meta-analysis of prophylactic mesh placement for incisional hernia prevention after abdominal aortic aneurysm surgery:a collaborative European Hernia Society project (I-PREVENT-AAA)
Introduction Incisional hernia (IH) is a prevalent and potentially dangerous complication of abdominal surgery, especially in high-risk groups. Mesh reinforcement of the abdominal wall has been studied as a potential intervention to prevent IHs. Randomised controlled trials (RCTs) have demonstrated that prophylactic mesh reinforcement after abdominal surgery, in general, is effective and safe. In patients with abdominal aortic aneurysm (AAA), prophylactic mesh reinforcement after open repair has not yet been recommended in official guidelines, because of relatively small sample sizes in individual trials. Furthermore, the identification of subgroups that benefit most from prophylactic mesh placement requires larger patient numbers. Our primary aim is to evaluate the efficacy and effectiveness of the use of a prophylactic mesh after open AAA surgery to prevent IH by performing an individual patient data meta-analysis (IPDMA). Secondary aims include the evaluation of postoperative complications, pain and quality of life, and the identification of potential subgroups that benefit most from prophylactic mesh reinforcement. Methods and analysis We will conduct a systematic review to identify RCTs that study prophylactic mesh placement after open AAA surgery. Cochrane Central Register of Controlled Trials, MEDLINE Ovid, Embase, Web of Science Core Collection and Google Scholar will be searched from the date of inception onwards. RCTs must directly compare primary sutured closure with mesh closure in adult patients who undergo open AAA surgery. Lead authors of eligible studies will be asked to share individual participant data (IPD). The risk of bias (ROB) for each included study will be assessed using the Cochrane ROB tool. An IPDMA will be performed to evaluate the efficacy, with the IH rate as the primary outcome.</p
Protocol for an independent patient data meta-analysis of prophylactic mesh placement for incisional hernia prevention after abdominal aortic aneurysm surgery:a collaborative European Hernia Society project (I-PREVENT-AAA)
Introduction Incisional hernia (IH) is a prevalent and potentially dangerous complication of abdominal surgery, especially in high-risk groups. Mesh reinforcement of the abdominal wall has been studied as a potential intervention to prevent IHs. Randomised controlled trials (RCTs) have demonstrated that prophylactic mesh reinforcement after abdominal surgery, in general, is effective and safe. In patients with abdominal aortic aneurysm (AAA), prophylactic mesh reinforcement after open repair has not yet been recommended in official guidelines, because of relatively small sample sizes in individual trials. Furthermore, the identification of subgroups that benefit most from prophylactic mesh placement requires larger patient numbers. Our primary aim is to evaluate the efficacy and effectiveness of the use of a prophylactic mesh after open AAA surgery to prevent IH by performing an individual patient data meta-analysis (IPDMA). Secondary aims include the evaluation of postoperative complications, pain and quality of life, and the identification of potential subgroups that benefit most from prophylactic mesh reinforcement. Methods and analysis We will conduct a systematic review to identify RCTs that study prophylactic mesh placement after open AAA surgery. Cochrane Central Register of Controlled Trials, MEDLINE Ovid, Embase, Web of Science Core Collection and Google Scholar will be searched from the date of inception onwards. RCTs must directly compare primary sutured closure with mesh closure in adult patients who undergo open AAA surgery. Lead authors of eligible studies will be asked to share individual participant data (IPD). The risk of bias (ROB) for each included study will be assessed using the Cochrane ROB tool. An IPDMA will be performed to evaluate the efficacy, with the IH rate as the primary outcome.</p
A risk-adjusted and anatomically stratified cohort comparison study of open surgery, endovascular techniques and medical management for juxtarenal aortic aneurysms-the UK COMPlex AneurySm Study (UK-COMPASS): a study protocol.
Funder: Health Technology Assessment Programme; Grant(s): Award ID: 15/153/02INTRODUCTION: In one-third of all abdominal aortic aneurysms (AAAs), the aneurysm neck is short (juxtarenal) or shows other adverse anatomical features rendering operations more complex, hazardous and expensive. Surgical options include open surgical repair and endovascular aneurysm repair (EVAR) techniques including fenestrated EVAR, EVAR with adjuncts (chimneys/endoanchors) and off-label standard EVAR. The aim of the UK COMPlex AneurySm Study (UK-COMPASS) is to answer the research question identified by the National Institute for Health Research Health Technology Assessment (NIHR HTA) Programme: 'What is the clinical and cost-effectiveness of strategies for the management of juxtarenal AAA, including fenestrated endovascular repair?' METHODS AND ANALYSIS: UK-COMPASS is a cohort study comparing clinical and cost-effectiveness of different strategies used to manage complex AAAs with stratification of physiological fitness and anatomical complexity, with statistical correction for baseline risk and indication biases. There are two data streams. First, a stream of routinely collected data from Hospital Episode Statistics and National Vascular Registry (NVR). Preoperative CT scans of all patients who underwent elective AAA repair in England between 1 November 2017 and 31 October 2019 are subjected to Corelab analysis to accurately identify and include every complex aneurysm treated. Second, a site-reported data stream regarding quality of life and treatment costs from prospectively recruited patients across England. Site recruitment also includes patients with complex aneurysms larger than 55 mm diameter in whom an operation is deferred (medical management). The primary outcome measure is perioperative all-cause mortality. Follow-up will be to a median of 5 years. ETHICS AND DISSEMINATION: The study has received full regulatory approvals from a Research Ethics Committee, the Confidentiality Advisory Group and the Health Research Authority. Data sharing agreements are in place with National Health Service Digital and the NVR. Dissemination will be via NIHR HTA reporting, peer-reviewed journals and conferences. TRIAL REGISTRATION NUMBER: ISRCTN85731188
New urbanism, crime and the suburbs: a review of the evidence
Sustainability now influences government policy in the UK, Australia and USA and planning policy currently advocates high density, mixed-use residential developments in 'walkable', permeable neighbourhoods, close to public transport, employment and amenities. This clearly demonstrates the growing popularity, influence and application of New Urbanist ideas.This paper reviews the criminological research relating to New Urbanism associated with the three key issues of permeability, rear laneway car parking and mixed-use development. These key issues are discussed from an environmental criminology perspective and challenge New Urbanist assumptions concerning crime. The paper proposes that crime prevention through environmental design (CPTED) and its crime risk assessment model represents a valuable tool for New Urbanists to utilise to reduce opportunities for crime and tackle fear of crime in the community. Recommendations for future research and collaboration are discussed
Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans
Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have
fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in
25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16
regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of
correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP,
while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in
Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium
(LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region.
Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant
enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the
refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa,
an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of
PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent
signals within the same regio
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