1,234 research outputs found
Bayesian evidence-driven diagnosis of instrumental systematics for sky-averaged 21-cm cosmology experiments
We demonstrate the effectiveness of a Bayesian evidence-based analysis for
diagnosing and disentangling the sky-averaged 21-cm signal from instrumental
systematic effects. As a case study, we consider a simulated REACH pipeline
with an injected systematic. We demonstrate that very poor performance or
erroneous signal recovery is achieved if the systematic remains unmodelled.
These effects include sky-averaged 21-cm posterior estimates resembling a very
deep or wide signal. However, when including parameterised models of the
systematic, the signal recovery is dramatically improved in performance. Most
importantly, a Bayesian evidence-based model comparison is capable of
determining whether or not such a systematic model is needed as the true
underlying generative model of an experimental dataset is in principle unknown.
We, therefore, advocate a pipeline capable of testing a variety of potential
systematic errors with the Bayesian evidence acting as the mechanism for
detecting their presence
Bayesian evidence-driven likelihood selection for sky-averaged 21-cm signal extraction
We demonstrate that the Bayesian evidence can be used to find a good
approximation of the true likelihood function of a dataset, a goal of the
likelihood-free inference (LFI) paradigm. As a concrete example, we use forward
modelled sky-averaged 21-cm signal antenna temperature datasets where we
artificially inject noise structures of various physically motivated forms. We
find that the Gaussian likelihood performs poorly when the noise distribution
deviates from the Gaussian case e.g. heteroscedastic radiometric or
heavy-tailed noise. For these non-Gaussian noise structures, we show that the
generalised normal likelihood is on a similar Bayesian evidence scale with
comparable sky-averaged 21-cm signal recovery as the true likelihood function
of our injected noise. We therefore propose the generalised normal likelihood
function as a good approximation of the true likelihood function if the noise
structure is a priori unknown
A Bayesian approach to RFI mitigation
Interfering signals such as Radio Frequency Interference from ubiquitous
satellite constellations are becoming an endemic problem in fields involving
physical observations of the electromagnetic spectrum. To address this we
propose a novel data cleaning methodology. Contamination is simultaneously
flagged and managed at the likelihood level. It is modeled in a Bayesian
fashion through a piecewise likelihood that is constrained by a Bernoulli prior
distribution. The techniques described in this paper can be implemented with
just a few lines of code.Comment: 6 pages, 4 figures, accepted by Physical Review D (APS
A Research-Based Curriculum for Teaching the Photoelectric Effect
Physics faculty consider the photoelectric effect important, but many
erroneously believe it is easy for students to understand. We have developed
curriculum on this topic including an interactive computer simulation,
interactive lectures with peer instruction, and conceptual and mathematical
homework problems. Our curriculum addresses established student difficulties
and is designed to achieve two learning goals, for students to be able to (1)
correctly predict the results of photoelectric effect experiments, and (2)
describe how these results lead to the photon model of light. We designed two
exam questions to test these learning goals. Our instruction leads to better
student mastery of the first goal than either traditional instruction or
previous reformed instruction, with approximately 85% of students correctly
predicting the results of changes to the experimental conditions. On the
question designed to test the second goal, most students are able to correctly
state both the observations made in the photoelectric effect experiment and the
inferences that can be made from these observations, but are less successful in
drawing a clear logical connection between the observations and inferences.
This is likely a symptom of a more general lack of the reasoning skills to
logically draw inferences from observations.Comment: submitted to American Journal of Physic
A novel, high-sensitivity, bacteriophage-based assay identifies low level Mycobacterium tuberculosis bacteraemia in immunocompetent patients with active and incipient tuberculosis
Haematogenous dissemination of M. tuberculosis (Mtb) is critical to pathogenesis of progressive tuberculous infection in animal models. Using a novel phage-based blood assay, we report the first concordant evidence in well-characterised immunocompetent human cohorts, demonstrating associations of Mtb bacteraemia with progressive phenotypes of latent infection and active pulmonary TB respectively
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