Error rates in SARS-CoV-2 testing examined with Bayes' theorem.

The SARS-CoV-2 pandemic has created a demand for large scale testing, as part of the effort to understand and control transmission. It is important to quantify the error rates of test equipment under field conditions, which might differ significantly from those obtained in the laboratory. A literature review on SARS-CoV-2 reverse-transcription polymerase chain reaction (RT-PCR) is used to construct a clinical test confusion matrix. A simple correction method for bulk test results is then demonstrated with examples. The required sensitivity and specificity of a test are explored for societal needs and use cases, before a sequential analysis of common example scenarios is explored. The analysis suggests that many of the people with mild symptoms and positive test results are unlikely to be infected with SARS-CoV-2 in some regions. It is concluded that current and foreseen alternative tests can not be used to "clear" people as being non-infected. Recommendations are given that regional authorities must establish a programme to monitor operational test characteristics before launching large scale testing; and that large scale testing for tracing infection networks in some regions is not viable, but may be possible in a focused way that does not exceed the working capacity of the laboratories staffed by competent experts. RT-PCR tests can not be solely relied upon as the gold standard for SARS-CoV-2 diagnosis at scale, instead clinical assessment supported by a range of expert diagnostic tests should be used.

A time dependent kinetic small angle neutron scattering study of a novel YFe phase.

Crystallization of amorphous Y67Fe33 into the YFe2 C15 Laves phase via a novel 'YFe' intermediate phase has been observed through to completion using time-resolved small angle neutron scattering (SANS). The nucleation and growth kinetics of the phase transformations have been studied at annealing temperatures below the crystallization temperatures for both the 'YFe' phase and the YFe2 phase. The SANS results agree with previously reported neutron diffraction and SANS data. At the annealing temperatures of 360, 370 and 380 °C, changes in the scattering intensity I(Q) occur as a result of the contrast between the amorphous matrix and the nucleating and growing Y and 'YFe' phases. Critical scattering occurs during each of the isotherms, relating to the full crystallization of Y67Fe33, and extrapolation gives a crystallization temperature of 382 °C. Beyond critical scattering, isotherms at 435, 450, and 465 °C reveal the details of the continuing transformation of the 'YFe' intermediate phase into the YFe2 C15 Laves phase.

Chiral paramagnetic skyrmion-like phase in MnSi.

We present a comprehensive study of chiral fluctuations in the reference helimagnet MnSi by polarized neutron scattering and neutron spin echo spectroscopy, which reveals the existence of a completely left-handed and dynamically disordered phase. This phase may be identified as a spontaneous Skyrmion phase: it appears in a limited temperature range just above the helical transition T_{C} and coexists with the helical phase at T_{C}.

Evidence for a spin emulsion.

Magnetic small-angle neutron scattering from the itinerant electron magnet, Y(Mn1-xFex)2, in which ferromagnetic and antiferromagnetic spin correlations compete, is found to follow an anomalous Q(-6) dependence (Q = 4pisintheta/lambda). It is suggested that this scattering is the magnetic analogue of that predicted for a structural microemulsion by Teubner's extension of conventional Kirste-Porod scattering to well-defined interfaces with extreme differences between mean and Gaussian curvatures. The "spin-emulsion-like" morphology of magnetic interfaces in Y(Mn1-xFex)2 is confirmed both qualitatively and quantitatively by a simple model based upon reported near neighbor Mn and Fe spin correlations.

Kinetic neutron diffraction and SANS studies of phase formation in bioactive machinable glass ceramics.

Bioactive fluormica-fluorapatite glass-ceramic materials offer a very encouraging solution to the problem of efficient restoration and reconstruction of hard tissues. To produce material with the desired crystalline phases, a five-stage heat treatment must be performed. This thermal processing has a large impact on the microstructure and ultimately the final mechanical properties of the materials. We have examined the thermal processing of one of our most promising machinable biomaterials, using time-resolved small angle neutron scattering and neutron diffraction to study the nucleation and growth of crystallites. The processing route had already been optimized by studying the properties of quenched samples using x-ray diffraction, mechanical measurements and differential thermal analysis. However these results show that the heat treatment can be further optimized in terms of crystal nucleation, and we show that these techniques are the only methods by which a truly optimized thermal processing route may be obtained.

Determination of hyperfine field distributions in amorphous magnets.

We present an overview of two leading methods of determining probability distributions from Mössbauer spectra, using the model amorphous magnet Fe(80)B(20). A comparison is made between the maximum-entropy method, which permits analysis using truly arbitrary parameter probability distributions, and a Voigtian-based analysis, which uses a sum of Gaussian components to create parameter distributions of pseudo-arbitrary shape. Our results indicate that, in Fe(80)B(20), a Gaussian distribution of magnetic hyperfine fields is a very good approximation, although small deviations from a Gaussian shape are evident. We find that the apparent existence of correlations between the isomer shift and magnetic hyperfine field parameters, as found using Voigt-based analyses, may be an artefact of imposing a Gaussian shape on the parameter distributions. We conclude that maximum entropy and Voigtian analyses together provide a very powerful means of characterizing magnetic materials with Mössbauer spectroscopy.

Time-frequency and time-scale techniques for the classification of native and bioprosthetic heart valve sounds.

The determination of diagnostic features in recorded heart sounds was investigated with Carpentier-Edwards (CE) bioprosthetic valves. Morphological features, extracted using the Choi-Williams distribution, achieved between 96 and 61% correct classification. The time-scale wavelet-transform feature set achieved 100% correct classification with native valve populations, and 87% with the CE replacements.