The NANOGrav 15 yr Data Set: Search for Transverse Polarization Modes in the Gravitational-wave Background

\ua9 2024. The Author(s). Published by the American Astronomical Society.Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These correlations describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more general metric theories of gravity can have additional polarization modes, which produce different interpulsar correlations. In this work, we search the NANOGrav 15 yr data set for evidence of a gravitational-wave background with quadrupolar HD and scalar-transverse (ST) correlations. We find that HD correlations are the best fit to the data and no significant evidence in favor of ST correlations. While Bayes factors show strong evidence for a correlated signal, the data does not strongly prefer either correlation signature, with Bayes factors ∼2 when comparing HD to ST correlations, and ∼1 for HD plus ST correlations to HD correlations alone. However, when modeled alongside HD correlations, the amplitude and spectral index posteriors for ST correlations are uninformative, with the HD process accounting for the vast majority of the total signal. Using the optimal statistic, a frequentist technique that focuses on the pulsar-pair cross-correlations, we find median signal-to-noise ratios of 5.0 for HD and 4.6 for ST correlations when fit for separately, and median signal-to-noise ratios of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While the signal-to-noise ratios for each of the correlations are comparable, the estimated amplitude and spectral index for HD are a significantly better fit to the total signal, in agreement with our Bayesian analysis

How to Detect an Astrophysical Nanohertz Gravitational Wave Background

\ua9 2023. The Author(s). Published by the American Astronomical Society.Analyses of pulsar timing data have provided evidence for a stochastic gravitational wave background in the nanohertz frequency band. The most plausible source of this background is the superposition of signals from millions of supermassive black hole binaries. The standard statistical techniques used to search for this background and assess its significance make several simplifying assumptions, namely (i) Gaussianity, (ii) isotropy, and most often, (iii) a power-law spectrum. However, a stochastic background from a finite collection of binaries does not exactly satisfy any of these assumptions. To understand the effect of these assumptions, we test standard analysis techniques on a large collection of realistic simulated data sets. The data-set length, observing schedule, and noise levels were chosen to emulate the NANOGrav 15 yr data set. Simulated signals from millions of binaries drawn from models based on the Illustris cosmological hydrodynamical simulation were added to the data. We find that the standard statistical methods perform remarkably well on these simulated data sets, even though their fundamental assumptions are not strictly met. They are able to achieve a confident detection of the background. However, even for a fixed set of astrophysical parameters, different realizations of the universe result in a large variance in the significance and recovered parameters of the background. We also find that the presence of loud individual binaries can bias the spectral recovery of the background if we do not account for them

Repaired tetralogy of Fallot: the roles of cardiovascular magnetic resonance in evaluating pathophysiology and for pulmonary valve replacement decision support

Surgical management of tetralogy of Fallot (TOF) results in anatomic and functional abnormalities in the majority of patients. Although right ventricular volume load due to severe pulmonary regurgitation can be tolerated for many years, there is now evidence that the compensatory mechanisms of the right ventricular myocardium ultimately fail and that if the volume load is not eliminated or reduced by pulmonary valve replacement the dysfunction might be irreversible. Cardiovascular magnetic resonance (CMR) has evolved during the last 2 decades as the reference standard imaging modality to assess the anatomic and functional sequelae in patients with repaired TOF. This article reviews the pathophysiology of chronic right ventricular volume load after TOF repair and the risks and benefits of pulmonary valve replacement. The CMR techniques used to comprehensively evaluate the patient with repaired TOF are reviewed and the role of CMR in supporting clinical decisions regarding pulmonary valve replacement is discussed

Effects of therapy for dysphagia in Parkinson's disease: systematic review

This systematic review explores the effects of dysphagia treatment for Parkinson's disease. The review includes rehabilitative, surgical, pharmacologic, and other treatments. Only oropharyngeal dysphagia is selected for this literature search, excluding dysphagia due to esophageal or gastric disorders. The effects of deep brain stimulation on dysphagia are not included. In general, the literature concerning dysphagia treatment in Parkinson's disease is rather limited. Most effect studies show diverse methodologic problems. Multiple case studies and trials are identified by searching biomedical literature databases PubMed and Embase, and by hand-searching reference lists. The conclusions of most studies cannot be compared with one another because of heterogeneous therapy methods and outcome measures. Further research based on randomized controlled trials to determine the effectiveness of different therapies for dysphagia in Parkinson's disease is required

Living with oropharyngeal dysphagia: effects of bolus modification on health-related quality of life—a systematic review

Purpose - Difficulty swallowing, oropharyngeal dysphagia, is widespread among many patient populations (such as stroke and cancer groups) and aged community-dwelling individuals. It is commonly managed with bolus modification: altering food (usually cutting, mashing or puréeing) or fluids (typically thickening) to make them easier or safer to swallow. Although this treatment is ubiquitous, anecdotal evidence suggests patients dislike this management, and this may affect compliance and well-being. This review aimed to examine the impact of bolus modification on health-related quality of life. Methods - A systematic review of the literature was conducted by speech pathologists with experience in oropharyngeal dysphagia. The literature search was completed with electronic databases, PubMed and Embase, and all available exclusion dates up to September 2012 were used. The search was limited to English-language publications which were full text and appeared in peer-reviewed journals. Results - Eight studies met the inclusion criteria. Generally, bolus modification was typically associated with worse quality of life. Modifications to foods appeared to be more detrimental than modifications to fluids, but this may be due to the increased severity of dysfunction that is implied by the necessity for significant alterations to foods. The number of studies retrieved was quite small. The diverse nature of methodologies, terminologies and assessment procedures found in the studies makes the results difficult to generalise. Conclusion - Overall, even though the severity of dysphagia may have been a confounding factor, the impact of bolus modification on health-related quality of life in patients with oropharyngeal dysphagia appears to be negative, with increased modification of food and fluids often correlating to a decreased quality of life. Further, associated disease factors, such as decreased life expectancy, may also have affected health-related quality of life. More research is needed