176 research outputs found
Why and When to Expect Gaussian Error Distributions in Epoch of Reionization 21-cm Power Spectrum Measurements
We explore error distributions in Epoch of Reionization 21-cm power spectrum
estimators using a combination of mathematical analysis and numerical
simulations. We provide closed form solutions for the error distributions of
individual bins in 3d-power spectra for two estimators currently in use in the
field, which we designate as ``straight-square" and ``cross-multiply"
estimators. We then demonstrate when the corresponding spherically binned power
spectra should (and should not) have Gaussian error distributions, which
requires appealing to nonstandard statements of the central limit theorem. This
has important implications for how upper limits are reported, as well as how
cosmological inferences are performed based on power spectrum measurements.
Specifically, assuming a Gaussian error distribution can over or underestimate
the upper limit depending on the type of estimator, and produces overly compact
likelihood functions for the power spectrum
Statistical recovery of 21cm visibilities and their power spectra with Gaussian constrained realisations and Gibbs sampling
Radio interferometers designed to probe the 21cm signal from Cosmic Dawn and
the Epoch of Reionisation must contend with systematic effects that make it
difficult to achieve sufficient dynamic range to separate the 21cm signal from
foreground emission and other effects. For instance, the instrument's chromatic
response modulates the otherwise spectrally smooth foregrounds, making them
difficult to model, while a significant fraction of the data must be excised
due to the presence of radio frequency interference (RFI), leaving gaps in the
data. Errors in modelling the (modulated and gappy) foregrounds can easily
generate spurious contamination of what should otherwise be 21cm
signal-dominated modes. Various approaches have been developed to mitigate
these issues by (e.g.) using non-parametric reconstruction of the foregrounds,
in-painting the gaps, and weighting the data to reduce the level of
contamination. We present a Bayesian statistical method that combines these
approaches, using the coupled techniques of Gaussian constrained realisations
(GCR) and Gibbs sampling. This provides a way of drawing samples from the joint
posterior distribution of the 21cm signal modes and their power spectrum in the
presence of gappy data and an uncertain foreground model in a computationally
scalable manner. The data are weighted by an inverse covariance matrix that is
estimated as part of the inference, along with a foreground model that can then
be marginalised over. We demonstrate the application of this technique on a
simulated HERA-like delay spectrum analysis, comparing three different
approaches for accounting for the foreground components.Comment: Updated to match accepted version. Note minor changes to power
spectrum plots due to a small bugfi
Diabetes reduces bone marrow and circulating porcine endothelial progenitor cells, an effect ameliorated by atorvastatin and independent of cholesterol
Bone marrow derived endothelial progenitor cells (EPCs) are early precursors of mature endothelial cells which replenish aging and damaged endothelial cells. The authors studied a diabetic swine model to determine if induction of DM adversely affects either bone marrow or circulating EPCs and whether a HMG-CoA reductase inhibitor (statin) improves development and recruitment of EPCs in the absence of cholesterol lowering. Streptozotocin was administered to Yorkshire pigs to induce DM. One month after induction, diabetic pigs were treated with atorvastatin (statin, n = 10), ezetimibe (n = 10) or untreated (n = 10) and evaluated for number of bone marrow and circulating EPCs and femoral artery endothelial function. There was no effect of either medication on cholesterol level. One month after induction of DM prior to administration of drugs, the number of bone marrow and circulating EPCs significantly decreased (P < 0.0001) compared to baseline. Three months after DM induction, the mean proportion of circulating EPCs significantly increased in the atorvastatin group, but not in the control or ezetimibe groups. The control group showed progressive reduction in percentage of flow mediated vasodilatation (no dilatation at 3 months) whereas the atorvastatin group and ezetimibe exhibited vasodilatation, 6% and 4% respectively. DM results in significant impairment of bone marrow and circulating EPCs as well as endothelial function. The effect is ameliorated, in part, by atorvastatin independent of its cholesterol lowering effect. These data suggest a model wherein accelerated atherosclerosis seen with DM may, in part, result from reduction in EPCs which may be ameliorated by treatment with a statin
Bridging Alone: Religious Conservatism, Marital Homogamy, and Voluntary Association Membership
This study characterizes social insularity of religiously conservative American married couples by examining patterns of voluntary associationmembership. Constructing a dataset of 3938 marital dyads from the second wave of the National Survey of Families and Households, the author investigates whether conservative religious homogamy encourages membership in religious voluntary groups and discourages membership in secular voluntary groups. Results indicate that couplesâ shared affiliation with conservative denominations, paired with beliefs in biblical authority and inerrancy, increases the likelihood of religious group membership for husbands and wives and reduces the likelihood of secular group membership for wives, but not for husbands. The social insularity of conservative religious groups appears to be reinforced by homogamyâparticularly by wives who share faith with husbands
International Veterinary Epilepsy Task Force consensus proposal: Medical treatment of canine epilepsy in Europe
In Europe, the number of antiepileptic drugs (AEDs) licensed for dogs has grown considerably over the last years. Nevertheless, the same questions remain, which include, 1) when to start treatment, 2) which drug is best used initially, 3) which adjunctive AED can be advised if treatment with the initial drug is unsatisfactory, and 4) when treatment changes should be considered. In this consensus proposal, an overview is given on the aim of AED treatment, when to start long-term treatment in canine epilepsy and which veterinary AEDs are currently in use for dogs. The consensus proposal for drug treatment protocols, 1) is based on current published evidence-based literature, 2) considers the current legal framework of the cascade regulation for the prescription of veterinary drugs in Europe, and 3) reflects the authorsâ experience. With this paper it is aimed to provide a consensus for the management of canine idiopathic epilepsy. Furthermore, for the management of structural epilepsy AEDs are inevitable in addition to treating the underlying cause, if possible
Cheating on the Edge
We present the results of an individual agent-based model of antibiotic resistance in bacteria. Our model examines antibiotic resistance when two strategies exist: âproducersââwho secrete a substance that breaks down antibioticsâand nonproducers (âcheatsâ) who do not secrete, or carry the machinery associated with secretion. The model allows for populations of up to 10,000, in which bacteria are affected by their nearest neighbors, and we assume cheaters die when there are no producers in their neighborhood. Each of 10,000 slots on our grid (a torus) could be occupied by a producer or a nonproducer, or could (temporarily) be unoccupied. The most surprising and dramatic result we uncovered is that when producers and nonproducers coexist at equilibrium, nonproducers are almost always found on the edges of clusters of producers
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