344 research outputs found
The value of clinical judgement analysis for improving the quality of doctors' prescribing decisions
Background Many initiatives are taken to improve prescribing decisions. Educational strategies for doctors have been effective in at least 50% of cases. Some reflection on one's own performance seems to be a common feature of the most effective strategies. So far, such reflections have mainly focused on the observed outcomes of the doctors' decisions, i.e. on what doctors do in practice. Studies in other fields have shown that another form of feedback based on the analysis of judgements may be useful as well. Objectives The objectives of the study were to discuss the principles underlying clinical judgement analysis, give examples of its use in the medical context, and discuss its potential for improving prescribing decisions. Results Clinical judgement analysis can look behind the outcome of a decision to the underlying decision process. Carefully constructed or selected case material is required for this analysis. Combining feedback on outcomes with feedback based on clinical judgement analysis offers doctors insight both in what they do, and why or when they do it. It may reveal determinants of decision making which are not available through unaided introspection. Interventions using this combination of feedback for improving doctors' prescribing behaviour have been (partly) successful in 4 cases and unsuccessful in one case. Conclusions Clinical judgement analysis gives doctors a structured reflection on the decision-making policy, and can help them to improve their future decisions. It may be especially useful for groups of doctors who try to work towards a consensus policy. The approach is not very helpful when simple decision rules are appropriate
De-noising of galaxy optical spectra with autoencoders
Optical spectra contain a wealth of information about the physical properties and formation histories of galaxies. Often though, spectra are too noisy for this information to be accurately retrieved. In this study, we explore how machine learning methods can be used to de-noise spectra and increase the amount of information we can gain without having to turn to sample averaging methods such as spectral stacking. Using machine learning methods trained on noise-added spectra - SDSS spectra with Gaussian noise added - we investigate methods of maximising the information we can gain from these spectra, in particular from emission lines, such that more detailed analysis can be performed. We produce a variational autoencoder (VAE) model, and apply it on a sample of noise-added spectra. Compared to the flux measured in the original SDSS spectra, the model values are accurate within 0.3-0.5 dex, depending on the specific spectral line and S/N. Overall, the VAE performs better than a principle component analysis (PCA) method, in terms of reconstruction loss and accuracy of the recovered line fluxes. To demonstrate the applicability and usefulness of the method in the context of large optical spectroscopy surveys, we simulate a population of spectra with noise similar to that in galaxies at z = 0.1 observed by the Dark Energy Spectroscopic Instrument (DESI). We show that we can recover the shape and scatter of the MZR in this ‘DESI-like’ sample, in a way that is not possible without the VAE-assisted de-noising
The recent star formation history of NGC 628 on resolved scales
Star formation histories (SFHs) are integral to our understanding of galaxy evolution. We can study recent SFHs by comparing the star formation rate (SFR) calculated using different tracers, as each probes a different timescale. We aim to calibrate a proxy for the present-day rate of change in SFR, dSFR/dt, which does not require full spectral energy distribution (SED) modeling and depends on as few observables as possible, to guarantee its broad applicability. To achieve this, we create a set of models in CIGALE and define a SFR change diagnostic as the ratio of the SFR averaged over the past 5 and 200 Myr, ⟨SFR5⟩/⟨SFR200⟩, probed by the Hα −FUV colour. We apply ⟨SFR5⟩/⟨SFR200⟩ to the nearby spiral NGC 628 and find that its star formation activity has overall been declining in the recent past, with the spiral arms, however, maintaining a higher level of activity. The impact of the spiral arm structure is observed to be stronger on ⟨SFR5⟩/⟨SFR200⟩ than on the star formation efficiency (SFEH2). In addition, increasing disk pressure tends to increase recent star formation, and consequently ⟨SFR5⟩/⟨SFR200⟩. We conclude that ⟨SFR5⟩/⟨SFR200⟩ is sensitive to the molecular gas content, spiral arm structure, and disk pressure. The ⟨SFR5⟩/⟨SFR200⟩ indicator is general and can be used to reconstruct the recent SFH of any star-forming galaxy for which Hα, FUV, and either mid- or far-IR photometry is available, without the need of detailed modeling
De-noising of galaxy optical spectra with autoencoders
Optical spectra contain a wealth of information about the physical properties
and formation histories of galaxies. Often though, spectra are too noisy for
this information to be accurately retrieved. In this study, we explore how
machine learning methods can be used to de-noise spectra and increase the
amount of information we can gain without having to turn to sample averaging
methods such as spectral stacking. Using machine learning methods trained on
noise-added spectra - SDSS spectra with Gaussian noise added - we investigate
methods of maximising the information we can gain from these spectra, in
particular from emission lines, such that more detailed analysis can be
performed. We produce a variational autoencoder (VAE) model, and apply it on a
sample of noise-added spectra. Compared to the flux measured in the original
SDSS spectra, the model values are accurate within 0.3-0.5 dex, depending on
the specific spectral line and S/N. Overall, the VAE performs better than a
principle component analysis (PCA) method, in terms of reconstruction loss and
accuracy of the recovered line fluxes. To demonstrate the applicability and
usefulness of the method in the context of large optical spectroscopy surveys,
we simulate a population of spectra with noise similar to that in galaxies at
observed by the Dark Energy Spectroscopic Instrument (DESI). We show
that we can recover the shape and scatter of the MZR in this "DESI-like"
sample, in a way that is not possible without the VAE-assisted de-noising.Comment: 14 pages, 10 figures, 6 tables, accepted for publication in MNRA
Clinical Judgment Analysis
SUMMARY Judgment is central to the practice of medicine and occurs between making clinical observations and taking clinical decisions. Clinical judgment analysis has developed as a method of making statistically firm models of doctors' judgments. Computed models reveal the differential importance attached to items of clinical, social, or other data which are determinants of clinical decisions. These models can both reveal the causes of conflicts of judgment and may help resolve them in a way that unaided discussion cannot. Revealing experts' models to students speeds learning of diagnostic skills. Clinical judgment analysis offers a method of probing the judgments not just of students and doctors but also of patients who have shown systematic differences in their perceptions of risk and benefit. The power and relevance of clinical trials can be improved by the consistent application of judgment policies generated from both the trialists and those who will use their result
A deep search for molecular gas in two massive Lyman break galaxies at z=3 and 4: vanishing CO-emission due to low metallicity
We present deep IRAM Plateau de Bure Interferometer (PdBI) observations, searching for CO-emission toward two massive, non-lensed Lyman break galaxies (LBGs) at z=3.216 and 4.058. With one low significance CO detection (3.5 sigma) and one sensitive upper limit, we find that the CO lines are >~ 3-4 times weaker than expected based on the relation between IR and CO luminosities followed by similarly, massive galaxies at z=0-2.5. This is consistent with a scenario in which these galaxies have low metallicity, causing an increased CO-to-H_2 conversion factor, i.e., weaker CO-emission for a given molecular (H_2) mass. The required metallicities at z>3 are lower than predicted by the fundamental metallicity relation (FMR) at these redshifts, consistent with independent evidence. Unless our galaxies are atypical in this respect, detecting molecular gas in normal galaxies at z>3 may thus remain challenging even with ALMA
Geometrical tests of cosmological models. III. The cosmology-evolution diagram at z=1
The rotational velocity of distant galaxies, when interpreted as a size
(luminosity) indicator, may be used as a tool to select high redshift standard
rods (candles) and probe world models and galaxy evolution via the classical
angular diameter-redshift or Hubble diagram tests. We implement the proposed
testing strategy using a sample of 30 rotators spanning the redshift range
0.2<z<1 with high resolution spectra and images obtained by the VIMOS/VLT Deep
Redshift Survey (VVDS) and the Great Observatories Origins Deep Survey (GOODs).
We show that by applying at the same time the angular diameter-redshift and
Hubble diagrams to the same sample of objects (i.e. velocity selected galactic
discs) one can derive a characteristic chart, the cosmology-evolution diagram,
mapping the relation between global cosmological parameters and local
structural parameters of discs such as size and luminosity. This chart allows
to put constraints on cosmological parameters when general prior information
about discs evolution is available. In particular, by assuming that equally
rotating large discs cannot be less luminous at z=1 than at present (M(z=1) <
M(0)), we find that a flat matter dominated cosmology (Omega_m=1) is excluded
at a confidence level of 2sigma and an open cosmology with low mass density
(Omega_m = 0.3) and no dark energy contribution is excluded at a confidence
level greater than 1 sigma. Inversely, by assuming prior knowledge about the
cosmological model, the cosmology-evolution diagram can be used to gain useful
insights about the redshift evolution of the structural parameters of baryonic
discs hosted in dark matter halos of nearly equal masses.Comment: 14 pages and 11 figures. A&A in pres
Galaxy Zoo and ALFALFA: Atomic Gas and the Regulation of Star Formation in Barred Disc Galaxies
We study the observed correlation between atomic gas content and the
likelihood of hosting a large scale bar in a sample of 2090 disc galaxies. Such
a test has never been done before on this scale. We use data on morphologies
from the Galaxy Zoo project and information on the galaxies' HI content from
the ALFALFA blind HI survey. Our main result is that the bar fraction is
significantly lower among gas rich disc galaxies than gas poor ones. This is
not explained by known trends for more massive (stellar) and redder disc
galaxies to host more bars and have lower gas fractions: we still see at fixed
stellar mass a residual correlation between gas content and bar fraction. We
discuss three possible causal explanations: (1) bars in disc galaxies cause
atomic gas to be used up more quickly, (2) increasing the atomic gas content in
a disc galaxy inhibits bar formation, and (3) bar fraction and gas content are
both driven by correlation with environmental effects (e.g. tidal triggering of
bars, combined with strangulation removing gas). All three explanations are
consistent with the observed correlations. In addition our observations suggest
bars may reduce or halt star formation in the outer parts of discs by holding
back the infall of external gas beyond bar co-rotation, reddening the global
colours of barred disc galaxies. This suggests that secular evolution driven by
the exchange of angular momentum between stars in the bar, and gas in the disc,
acts as a feedback mechanism to regulate star formation in intermediate mass
disc galaxies.Comment: 16 pages, 10 figures. In press at MNRAS. v2 contains corrections
found in proof
An empirical investigation of the interaction manager-task using a human information processing approach. Available in 2 volumes.
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