1,041 research outputs found
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Elicitation and representation of expert knowledge for computer aided diagnosis in mammography
To study how professional radiologists describe, interpret and make decisions about micro-calcifications in mammograms. The purpose was to develop a model of the radiologists' decision making for use in CADMIUM II, a computerized aid for mammogram interpretation that combines symbolic reasoning with image processing
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Use of computer-aided detection (CAD) tools in screening mammography: a multidisciplinary investigation
We summarise a set of analyses and studies conducted to assess the effects of the use of a computer-aided detection (CAD) tool in breast screening. We have used an interdisciplinary approach that combines: (a) statistical analyses inspired by reliability modelling in engineering; (b) experimental studies of decisions of mammography experts using the tool, interpreted in the light of human factors psychology; and (c) ethnographic observations of the use of the tool both in trial conditions and in everyday screening practice. Our investigations have shown patterns of human behaviour and effects of computer-based advice that would not have been revealed by a standard clinical trial approach. For example, we found that the negligible measured effect of CAD could be explained by a range of effects on experts' decisions, beneficial in some cases and detrimental in others. There is some evidence of the latter effects being due to the experts using the computer tool differently from the intentions of the developers. We integrate insights from the different pieces of evidence and highlight their implications for the design, evaluation and deployment of this sort of computer tool
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CAD in mammography: lesion-level versus case-level analysis of the effects of prompts on human decisions
Object: To understand decision processes in CAD-supported breast screening by analysing how prompts affect readers’ judgements of individual mammographic features (lesions). To this end we analysed hitherto unexamined details of reports completed by mammogram readers in an earlier evaluation of a CAD tool.
Material and methods: Assessments of lesions were extracted from 5,839 reports for 59 cancer cases. Statistical analyses of these data focused on what features readers considered when recalling a cancer case and how readers reacted to CAD prompts.
Results: About 13.5% of recall decisions were found to be caused by responses to features other than those indicating actual cancer. Effects of CAD: lesions were more likely to be examined if prompted; the presence of a prompt on a cancer increased the probability of both detection and recall especially for less accurate readers in subtler cases; lack of prompts made cancer features less likely to be detected; false prompts made non-cancer features more likely to be classified as cancer.
Conclusion: The apparent lack of impact reported for CAD in some studies is plausibly due to CAD systematically affecting readers’ identification of individual features, in a beneficial way for certain combinations of readers and features and a damaging way for others. Mammogram readers do not ignore prompts. Methodologically, assessing CAD by numbers of recalled cancer cases may be misleading
Properties of bow-shock sources at the Galactic center
There are an enigmatic population of massive stars around the Galactic Center
(GC) that were formed some Ma ago. A fraction of these stars has been found to
orbit the supermassive black hole, SgrA*, in a projected clockwise disk, which
suggests that they were formed in a formerly existing dense disk around SgrA*.
We focus on the extended, near-infrared (NIR) sources IRS1W, IRS5, IRS10W, and
IRS21 that have been suggested to be young, massive stars that form bow-shocks
through their interaction with the ISM. Their nature has impeded accurate
determination of their orbital parameters. We aim at establishing their nature
and kinematics to test whether they form part of the clockwise disk. We
performed NIR multi-wavelength imaging using adaptive optics (AO) and sparse
aperture masking (SAM). We introduce a new method for self-calibration of the
SAM PSF in dense stellar fields. The emission mechanism, morphology and
kinematics of the targets were examined via 3D bow-shock models. We confirm
previous findings that IRS21, IRS1W, and IRS5 are bow-shocks created by the
interaction between mass-losing stars and the interstellar gas. The nature of
IRS10W remains unclear. Our modeling shows that the bow-shock-emission is
caused by thermal emission while the scattering of stellar light does not play
any significant role. IRS 1W appears to be a bow-shock produced by an
anisotropic stellar wind or by locally inhomogeneous ISM density. Our best-fit
models provide an estimate of the local proper motion of the ISM in the NA in
agreement with the published models. Assuming that all of the sources are tied
to SgrA*, their orbital planes were obtained via a Monte-Carlo simulation. Our
orbital analysis suggests that they are not part of any of the clockwise disk.
We thus add more evidence to recent findings that a large part of the massive
stars show apparently random orbital orientations.Comment: accepted for publication by A&A, 17 pages, 11 figures, 1 appendi
Direct Detection of the Tertiary Component in the Massive Multiple HD 150 136 with VLTI
Massive stars are of fundamental importance for almost all aspects of
astrophysics, but there still exist large gaps in our understanding of their
properties and formation because they are rare and therefore distant. It has
been found that most O-stars are multiples. HD 150 136 is the nearest system to
Earth with >100 M_sol, and provides a unique opportunity to study an extremely
massive system. Recently, evidence for the existence of a third component in HD
150 136, in addition to the tight spectroscopic binary that forms the main
component, was found in spectroscopic observations. Our aim was to image and
obtain astrometric and photometric measurements of this component using long
baseline optical interferometry to further constrain the nature of this
component. We observed HD150136 with the near-infrared instrument AMBER
attached to the ESO VLT Interferometer. The recovered closure phases are robust
to systematic errors and provide unique information on the source asymmetry.
Therefore, they are of crucial relevance for both image reconstruction and
model fitting of the source structure. The third component in HD 150 136 is
clearly detected in the high-quality data from AMBER. It is located at a
projected angular distance of 7.3 mas, or about 13 AU at the line-of-sight
distance of HD 150 136, at a position angle of 209 degrees East of North, and
has a flux ratio of 0.25 with respect to the inner binary. We resolved the
third component of HD 150 136 in J, H and K filters. The luminosity and color
of the tertiary agrees with the predictions and shows that it is also an O
main-sequence star. The small measured angular separation indicates that the
tertiary may be approaching the periastron of its orbit. These results, only
achievable with long baseline near infrared interferometry, constitute the
first step towards the understanding of the massive star formation mechanisms
Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A with sparse aperture masking and spectroastrometry
Contemporary theory holds that massive stars gather mass during their initial
phases via accreting disk-like structures. However, conclusive evidence for
disks has remained elusive for the most massive young objects. This is mainly
due to significant observational challenges. Incisive studies, even targeting
individual objects, are therefore relevant to the progression of the field. NGC
3603 IRS 9A* is a young massive stellar object still surrounded by an envelope
of molecular gas. Previous mid-infrared observations with long-baseline
interferometry provided evidence for a disk of 50 mas diameter at its core.
This work aims at a comprehensive study of the physics and morphology of IRS 9A
at near-infrared wavelengths. New sparse aperture masking interferometry data
taken with NACO/VLT at Ks and Lp filters were obtained and analysed together
with archival CRIRES spectra of the H2 and BrG lines. The calibrated
visibilities recorded at Ks and Lp bands suggest the presence of a partially
resolved compact object of 30 mas at the core of IRS 9A, together with the
presence of over-resolved flux. The spectroastrometric signal of the H2 line
shows that this spectral feature proceeds from the large scale extended
emission (300 mas) of IRS 9A, while the BrG line appears to be formed at the
core of the object (20 mas). This scenario is consistent with the brightness
distribution of the source for near- and mid-infrared wavelengths at various
spatial scales. However, our model suffers from remaining inconsistencies
between SED modelling and the interferometric data. Moreover, the BrG
spectroastrometric signal indicates that the core of IRS 9A exhibits some form
of complexity such as asymmetries in the disk. Future high-resolution
observations are required to confirm the disk/envelope model and to flesh out
the details of the physical form of the inner regions of IRS 9A.Comment: Accepted to be published in Astronomy & Astrophysics, 13 pages, 14
figure
Radio continuum and X-ray emission from the most extreme FIR-excess galaxy NGC 1377: An extremely obscured AGN revealed
Galaxies which strongly deviate from the radio-far IR correlation are of
great importance for studies of galaxy evolution as they may be tracing early,
short-lived stages of starbursts and active galactic nuclei (AGNs). The most
extreme FIR-excess galaxy NGC1377 has long been interpreted as a young dusty
starburst, but millimeter observations of CO lines revealed a powerful
collimated molecular outflow which cannot be explained by star formation alone.
We present new radio observations at 1.5 and 10 GHz obtained with the Jansky
Very Large Array (JVLA) and Chandra X-ray observations towards NGC1377. The
observations are compared to synthetic starburst models to constrain the
properties of the central energy source. We obtained the first detection of the
cm radio continuum and X-ray emission in NGC1377. We find that the radio
emission is distributed in two components, one on the nucleus and another
offset by 4.5 to the South-West. We confirm the extreme FIR-excess of the
galaxy, with a 4.2, which deviates by more than
7- from the radio-FIR correlation. Soft X-ray emission is detected on
the off-nucleus component. From the radio emission we estimate for a young
( Myr) starburst a star formation rate SFR0.1 M yr. Such
a SFR is not sufficient to power the observed IR luminosity and to drive the CO
outflow. We find that a young starburst cannot reproduce all the observed
properties of the nucleus of NGC1377. We suggest that the galaxy may be
harboring a radio-quiet, obscured AGN of 10M, accreting at
near-Eddington rates. We speculate that the off-nucleus component may be
tracing an hot-spot in the AGN jet.Comment: 14 pages, accepted for publication on Astronomy and Astrophysics on
08/07/201
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Why Are People's Decisions Sometimes Worse with Computer Support?
In many applications of computerised decision support, a recognised source of undesired outcomes is operators' apparent over-reliance on automation. For instance, an operator may fail to react to a potentially dangerous situation because a computer fails to generate an alarm. However, the very use of terms like "over-reliance" betrays possible misunderstandings of these phenomena and their causes, which may lead to ineffective corrective action (e.g. training or procedures that do not counteract all the causes of the apparently "over-reliant" behaviour). We review relevant literature in the area of "automation bias" and describe the diverse mechanisms that may be involved in human errors when using computer support. We discuss these mechanisms, with reference to errors of omission when using "alerting systems", with the help of examples of novel counterintuitive findings we obtained from a case study in a health care application, as well as other examples from the literature
On the Enhanced Interstellar Scattering Toward B1849+005
(Abridged) This paper reports new Very Large Array (VLA) and Very Long
Baseline Array (VLBA) observations of the extragalactic source B1849+005 at
frequencies between 0.33 and 15 GHz and the re-analysis of archival VLA
observations at 0.33, 1.5, and 4.9 GHz. The structure of this source is complex
but interstellar scattering dominates the structure of the central component at
least to 15 GHz. An analysis of the phase structure functions of the
interferometric visibilities shows the density fluctuations along this line of
sight to be anisotropic (axial ratio = 1.3) with a frequency-independent
position angle, and having an inner scale of roughly a few hundred kilometers.
The anisotropies occur on length scales of order 10^{15} cm (D/5 kpc), which
within the context of certain magnetohydrodynamic turbulence theories indicates
the length scale on which the kinetic and magnetic energy densities are
comparable. A conservative upper limit on the velocity of the scattering
material is 1800 km/s. In the 0.33 GHz field of view, there are a number of
other sources that might also be heavily scattered. Both B1849+005 and PSR
B1849+00 are highly scattered, and they are separated by only 13'. If the lines
of sight are affected by the same ``clump'' of scattering material, it must be
at least 2.3 kpc distant. However, a detailed attempt to account for the
scattering observables toward these sources does not produce a self-consistent
set of parameters for such a clump. A clump of H\alpha emission, possibly
associated with the H II region G33.418-0.004, lies between these two lines of
sight, but it seems unable to account for all of the required excess
scattering.Comment: 23 pages, LaTeX2e AASTeX, 13 figures in 14 PostScript files, accepted
for publication in Ap
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