120 research outputs found
Combining galaxy and 21cm surveys
Acoustic waves traveling through the early Universe imprint a characteristic
scale in the clustering of galaxies, QSOs and inter-galactic gas. This scale
can be used as a standard ruler to map the expansion history of the Universe, a
technique known as Baryon Acoustic Oscillations (BAO). BAO offer a
high-precision, low-systematics means of constraining our cosmological model.
The statistical power of BAO measurements can be improved if the `smearing' of
the acoustic feature by non-linear structure formation is undone in a process
known as reconstruction. In this paper we use low-order Lagrangian perturbation
theory to study the ability of cm experiments to perform reconstruction
and how augmenting these surveys with galaxy redshift surveys at relatively low
number densities can improve performance. We find that the critical number
density which must be achieved in order to benefit cm surveys is set by
the linear theory power spectrum near its peak, and corresponds to densities
achievable by upcoming surveys of emission line galaxies such as eBOSS and
DESI. As part of this work we analyze reconstruction within the framework of
Lagrangian perturbation theory with local Lagrangian bias, redshift-space
distortions, -dependent noise and anisotropic filtering schemes.Comment: 10 pages, final version to appear in MNRAS, helpful suggestions from
referee and others include
A Signature of Cosmic Strings Wakes in the CMB Polarization
We calculate a signature of cosmic strings in the polarization of the cosmic
microwave background (CMB). We find that ionization in the wakes behind moving
strings gives rise to extra polarization in a set of rectangular patches in the
sky whose length distribution is scale-invariant. The length of an individual
patch is set by the co-moving Hubble radius at the time the string is
perturbing the CMB. The polarization signal is largest for string wakes
produced at the earliest post-recombination time, and for an alignment in which
the photons cross the wake close to the time the wake is created. The maximal
amplitude of the polarization relative to the temperature quadrupole is set by
the overdensity of free electrons inside a wake which depends on the ionization
fraction inside the wake. The signal can be as high as
in degree scale polarization for a string at high redshift (near recombination)
and a string tension given by .Comment: 8 pages, 3 figure
Impacts of Dark Stars on Reionization and Signatures in the Cosmic Microwave Background
We perform a detailed and systematic investigation of the possible impacts of
dark stars upon the reionization history of the Universe, and its signatures in
the cosmic microwave background (CMB). We compute hydrogen reionization
histories, CMB optical depths and anisotropy power spectra for a range of
stellar populations including dark stars. If dark stars capture large amounts
of dark matter via nuclear scattering, reionization can be substantially
delayed, leading to decreases in the integrated optical depth to last
scattering and large-scale power in the EE polarization power spectrum. Using
the integrated optical depth observed by WMAP7, in our canonical reionization
model we rule out the section of parameter space where dark stars with high
scattering-induced capture rates tie up more than ~90% of all the first
star-forming baryons, and live for over ~250 Myr. When nuclear scattering
delivers only moderate amounts of dark matter, reionization can instead be sped
up slightly, modestly increasing the CMB optical depth. If dark stars do not
obtain any dark matter via nuclear scattering, effects upon reionization and
the CMB are negligible. The effects of dark stars upon reionization and its CMB
markers can be largely mimicked or compensated for by changes in the existing
parameters of reionization models, making dark stars difficult to disentangle
from astrophysical uncertainties, but also widening the range of standard
parameters in reionization models that can be made consistent with
observations.Comment: Small changes in response to referee's comments; matches version
accepted for publication in ApJ. 14 pages, 9 figure
Information and choice of residential care provider for older people: a comparative study in England, the Netherlands and Spain
This study compared how older people use quality information to choose residential care providers in England, the Netherlands and Spain (Catalonia). The availability of information varies between each country, from detailed inspection and survey information in the Netherlands, through to a lack of publicly available information in Catalonia. We used semi-structured interviews and group workshops with older people, families and professionals to compare experiences of the decision-making process and quality information, and also to explore what quality information might be used in the future. We found that most aspects of the decision-making experience and preferences for future indicators were similar across the three countries. The use of quality information was minimal across all three, even in England and the Netherlands where information was widely available. Differences arose mainly from factors with the supply of care. Older people were most interested in the subjective experiences of other residents and relatives, rather than 'hard' objective indicators of aspects such as clinical care. We find that the amount of publicly available quality information does not in itself influence the decisions or the decision-making processes of older people and their carers. To improve the quality of decisions, more effort needs to be taken to increase awareness and to communicate quality in more accessible ways, including significant support from professionals and better design of quality information
An Application of Using Support Vector Machine Based on Classification Technique for Predicting Medical Data Sets
© 2019, Springer Nature Switzerland AG. This paper illustrates the utilise of various kind of machine learning approaches based on support vector machines for classifying Sickle Cell Disease data set. It has demonstrated that support vector machines generate an essential enhancement when applied for the pre-processing of clinical time-series data set. In this aspect, the objective of this study is to present discoveries for a number of classes of approaches for therapeutically associated problems in the purpose of acquiring high accuracy and performance. The primary case in this study includes classifying the dosage necessary for each patient individually. We applied a number of support vector machines to examine sickle cell data set based on the performance evaluation metrics. The result collected from a number of models have indicated that, support vector Classifier demonstrated inferior outcomes in comparison to Radial Basis Support Vector Classifier. For our Sickle cell data sets, it was found that the Parzen Kernel Support Vector Classifier produced the highest levels of performance and accuracy during training procedure accuracy 0.89733, AUC 0.94267. Where the testing set process, accuracy 0.81778, the area under the curve with 0.86556
Length of carotid stenosis predicts peri-procedural stroke or death and restenosis in patients randomized to endovascular treatment or endarterectomy.
BACKGROUND: The anatomy of carotid stenosis may influence the outcome of endovascular treatment or carotid endarterectomy. Whether anatomy favors one treatment over the other in terms of safety or efficacy has not been investigated in randomized trials.
METHODS: In 414 patients with mostly symptomatic carotid stenosis randomized to endovascular treatment (angioplasty or stenting; n = 213) or carotid endarterectomy (n = 211) in the Carotid and Vertebral Artery Transluminal Angioplasty Study (CAVATAS), the degree and length of stenosis and plaque surface irregularity were assessed on baseline intraarterial angiography. Outcome measures were stroke or death occurring between randomization and 30 days after treatment, and ipsilateral stroke and restenosis ≥50% during follow-up. RESULTS: Carotid stenosis longer than 0.65 times the common carotid artery diameter was associated with increased risk of peri-procedural stroke or death after both endovascular treatment [odds ratio 2.79 (1.17-6.65), P = 0.02] and carotid endarterectomy [2.43 (1.03-5.73), P = 0.04], and with increased long-term risk of restenosis in endovascular treatment [hazard ratio 1.68 (1.12-2.53), P = 0.01]. The excess in restenosis after endovascular treatment compared with carotid endarterectomy was significantly greater in patients with long stenosis than with short stenosis at baseline (interaction P = 0.003). Results remained significant after multivariate adjustment. No associations were found for degree of stenosis and plaque surface.
CONCLUSIONS: Increasing stenosis length is an independent risk factor for peri-procedural stroke or death in endovascular treatment and carotid endarterectomy, without favoring one treatment over the other. However, the excess restenosis rate after endovascular treatment compared with carotid endarterectomy increases with longer stenosis at baseline. Stenosis length merits further investigation in carotid revascularisation trials
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