74 research outputs found
Cosmic string loop distribution on all length scales and at any redshift
We analytically derive the expected number density distribution of Nambu-Goto
cosmic string loops at any redshift soon after the time of string formation to
today. Our approach is based on the Polchinski-Rocha model of loop formation
from long strings which we adjust to fit numerical simulations and complement
by a phenomenological modelling of gravitational backreaction. Cosmological
evolution drives the loop distribution towards scaling on all length scales in
both the radiation and matter era. Memory of any reasonable initial loop
distribution in the radiation era is shown to be erased well before Big Bang
Nucleosynthesis. In the matter era, the loop distribution reaches full scaling,
up to some residual loops from the radiation era which may be present for
extremely low string tension. Finally, the number density of loops below the
gravitational cutoff is shown to be scale independent, proportional to a
negative power of the string tension and insensitive to the details of the
backreaction modelling. As an application, we show that the energy density
parameter of loops today cannot exceed 10^(-5) for currently allowed string
tension values, while the loop number density cannot be less than 10^(-6) per
Mpc^3. Our result should provide a more robust basis for studying the
cosmological consequences of cosmic string loops.Comment: 24 pages, 4 figures, uses iopart. References added, matches published
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On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection
A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries
Vitamin D deficiency is associated with respiratory symptoms and airway wall thickening in smokers with and without COPD: a prospective cohort study
Contains fulltext :
220742.pdf (publisher's version ) (Open Access)BACKGROUND: Previous studies have established a higher prevalence of vitamin D deficiency in patients with COPD, but the relationship between vitamin D levels and COPD exacerbations remains controversial. In addition, the effect of vitamin D levels on imaging characteristics remains mostly unexplored. Using cross-sectional and longitudinal follow up data from the COPDGene Study, we assessed the association between vitamin D levels on respiratory symptoms, exacerbations, and imaging characteristics. We hypothesized that vitamin D deficiency will be associated with worse respiratory-related outcomes. METHODS: Current and former smokers between ages 45-80 were enrolled the COPDGene Study. Subjects completed questionnaires, spirometry, six-minute walk test, and chest computed tomography scans. A subset of subjects had measurement of serum concentration of 25-hydroxyvitamin D (25(OH)D). Vitamin D deficiency was defined as serum concentration less than 20 ng/mL. Longitudinal follow up was conducted via a web-based or telephone questionnaire. RESULTS: Vitamin D levels were measured on 1544 current and former smokers, of which 981 subjects had sufficient vitamin D levels and 563 subjects had vitamin D deficiency. Subjects with vitamin D deficiency were younger with increased likelihood of being African American, being current smokers, having a lower percent predicted FEV1, and having COPD. Vitamin D deficiency was associated with worse quality of life, increased dyspnea, decreased exercise tolerance, and increased frequency of severe exacerbations. Vitamin D deficiency was also associated with increased segmental airway wall thickness on chest CT scans. CONCLUSION: Vitamin D deficiency was associated with increased respiratory symptoms, decreased functional status, increased frequency of severe exacerbations, as well as airway wall thickening on chest CT scans. Further research is needed to determine the potential impact of vitamin D supplementation to improve disease outcomes
Duration of androgen deprivation therapy for high-risk prostate cancer: application of randomized trial data in a tertiary referral cancer center
Epub: Dec 17, 2015Abstract not availableVinayak Muralidhar, Meredith M. Regan, Lillian Werner, Mari Nakabayashi, Carolyn P. Evan, Joaquim Bellmunt, Toni K. Choueiri, Aymen A. Elfiky, Lauren C. Harshman, Rana R. McKay, Mark M. Pomerantz, Christopher J. Sweeney, Mary-Ellen Taplin, Philip W. Kantoff, Paul L. Nguye
Machine Learning Characterization of COPD Subtypes: Insights From the COPDGene Study
Contains fulltext :
220804.pdf (Publisher’s version ) (Closed access)COPD is a heterogeneous syndrome. Many COPD subtypes have been proposed, but there is not yet consensus on how many COPD subtypes there are and how they should be defined. The COPD Genetic Epidemiology Study (COPDGene), which has generated 10-year longitudinal chest imaging, spirometry, and molecular data, is a rich resource for relating COPD phenotypes to underlying genetic and molecular mechanisms. In this article, we place COPDGene clustering studies in context with other highly cited COPD clustering studies, and summarize the main COPD subtype findings from COPDGene. First, most manifestations of COPD occur along a continuum, which explains why continuous aspects of COPD or disease axes may be more accurate and reproducible than subtypes identified through clustering methods. Second, continuous COPD-related measures can be used to create subgroups through the use of predictive models to define cut-points, and we review COPDGene research on blood eosinophil count thresholds as a specific example. Third, COPD phenotypes identified or prioritized through machine learning methods have led to novel biological discoveries, including novel emphysema genetic risk variants and systemic inflammatory subtypes of COPD. Fourth, trajectory-based COPD subtyping captures differences in the longitudinal evolution of COPD, addressing a major limitation of clustering analyses that are confounded by disease severity. Ongoing longitudinal characterization of subjects in COPDGene will provide useful insights about the relationship between lung imaging parameters, molecular markers, and COPD progression that will enable the identification of subtypes based on underlying disease processes and distinct patterns of disease progression, with the potential to improve the clinical relevance and reproducibility of COPD subtypes
Is this trail too crowded? A choice experiment to evaluate tradeoffs and preferences of park visitors in Garibaldi Park, British Columbia
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