231 research outputs found
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Deep learning networks find unique mammographic differences in previous negative mammograms between interval and screen-detected cancers: a case-case study.
BackgroundTo determine if mammographic features from deep learning networks can be applied in breast cancer to identify groups at interval invasive cancer risk due to masking beyond using traditional breast density measures.MethodsFull-field digital screening mammograms acquired in our clinics between 2006 and 2015 were reviewed. Transfer learning of a deep learning network with weights initialized from ImageNet was performed to classify mammograms that were followed by an invasive interval or screen-detected cancer within 12 months of the mammogram. Hyperparameter optimization was performed and the network was visualized through saliency maps. Prediction loss and accuracy were calculated using this deep learning network. Receiver operating characteristic (ROC) curves and area under the curve (AUC) values were generated with the outcome of interval cancer using the deep learning network and compared to predictions from conditional logistic regression with errors quantified through contingency tables.ResultsPre-cancer mammograms of 182 interval and 173 screen-detected cancers were split into training/test cases at an 80/20 ratio. Using Breast Imaging-Reporting and Data System (BI-RADS) density alone, the ability to correctly classify interval cancers was moderate (AUC = 0.65). The optimized deep learning model achieved an AUC of 0.82. Contingency table analysis showed the network was correctly classifying 75.2% of the mammograms and that incorrect classifications were slightly more common for the interval cancer mammograms. Saliency maps of each cancer case found that local information could highly drive classification of cases more than global image information.ConclusionsPre-cancerous mammograms contain imaging information beyond breast density that can be identified with deep learning networks to predict the probability of breast cancer detection
New insights on hadron acceleration at supernova remnant shocks
We outline the main features of nuclei acceleration at supernova remnant
forward shocks, stressing the crucial role played by self-amplified magnetic
fields in determining the energy spectrum observed in this class of sources. In
particular, we show how the standard predictions of the non-linear theory of
diffusive shock acceleration has to be completed with an additional ingredient,
which we propose to be the enhanced velocity of the magnetic irregularities
particles scatter against, to reconcile the theory of efficient particle
acceleration with recent observations of gamma-ray bright supernova remnants.Comment: 7 pages, 2 figures. To apper in "Cosmic-ray induced phenomenology in
star-forming environments: Proceedings of the 2nd Session of the Sant Cugat
Forum of Astrophysics" (April 16-19, 2012), Olaf Reimer and Diego F. Torres
(eds.
Nonthermal Radiation from Type Ia Supernova Remnants
We present calculations of expected continuum emissions from Sedov-Taylor
phase Type Ia supernova remnants (SNRs), using the energy spectra of cosmic ray
(CR) electrons and protons from nonlinear diffusive shock acceleration (DSA)
simulations. A new, general-purpose radiative process code, Cosmicp, was
employed to calculate the radiation expected from CR electrons and protons and
their secondary products. These radio, X-ray and gamma-ray emissions are
generally consistent with current observations of Type Ia SNRs. The emissions
from electrons in these models dominate the radio through X-ray bands. Decays
of \pi^0 s from p-p collisions mostly dominate the gamma-ray range, although
for a hot, low density ISM case (n_{ISM}=0.003 cm^{-3}), the pion decay
contribution is reduced sufficiently to reveal the inverse Compton contribution
to TeV gamma-rays. In addition, we present simple scalings for the contributing
emission processes to allow a crude exploration of model parameter space,
enabling these results to be used more broadly. We also discuss the radial
surface brightness profiles expected for these model SNRs in the X-ray and
gamma-ray bands.Comment: 37 pages, 7 figures, accepted in MNRA
Radio relics in cosmological simulations
Radio relics have been discovered in many galaxy clusters. They are believed
to trace shock fronts induced by cluster mergers. Cosmological simulations
allow us to study merger shocks in detail since the intra-cluster medium is
heated by shock dissipation. Using high resolution cosmological simulations,
identifying shock fronts and applying a parametric model for the radio emission
allows us to simulate the formation of radio relics. We analyze a simulated
shock front in detail. We find a rather broad Mach number distribution. The
Mach number affects strongly the number density of relativistic electrons in
the downstream area, hence, the radio luminosity varies significantly across
the shock surface. The abundance of radio relics can be modeled with the help
of the radio power probability distribution which aims at predicting radio
relic number counts. Since the actual electron acceleration efficiency is not
known, predictions for the number counts need to be normalized by the observed
number of radio relics. For the characteristics of upcoming low frequency
surveys we find that about thousand relics are awaiting discovery.Comment: 10 pages, 4 figures, Invited talk at the conference "Diffuse
Relativistic Plasmas", Bangalore, 1-4 March 2011; in press in special issue
of Journal of Astrophysics and Astronom
High Energy Cosmic Rays From Supernovae
Cosmic rays are charged relativistic particles that reach the Earth with
extremely high energies, providing striking evidence of the existence of
effective accelerators in the Universe. Below an energy around
eV cosmic rays are believed to be produced in the Milky Way while above that
energy their origin is probably extragalactic. In the early '30s supernovae
were already identified as possible sources for the Galactic component of
cosmic rays. After the '70s this idea has gained more and more credibility
thanks to the the development of the diffusive shock acceleration theory, which
provides a robust theoretical framework for particle energization in
astrophysical environments. Afterwards, mostly in recent years, much
observational evidence has been gathered in support of this framework,
converting a speculative idea in a real paradigm. In this Chapter the basic
pillars of this paradigm will be illustrated. This includes the acceleration
mechanism, the non linear effects produced by accelerated particles onto the
shock dynamics needed to reach the highest energies, the escape process from
the sources and the transportation of cosmic rays through the Galaxy. The
theoretical picture will be corroborated by discussing several observations
which support the idea that supernova remnants are effective cosmic ray
factories.Comment: Final draft of a chapter in "Handbook of Supernovae" edited by Athem
W. Alsabti and Paul Murdi
Relics as probes of galaxy cluster mergers
Galaxy clusters grow by mergers with other clusters and galaxy groups. These
mergers create shocks within the intracluster medium (ICM). It is proposed that
within the shocks particles can be accelerated to extreme energies. In the
presence of a magnetic field these particles should then form large regions
emitting synchrotron radiation, creating so-called radio relics. An example of
a cluster with relics is CIZA J2242.8+5301. Here we present hydrodynamical
simulations of idealized binary cluster collisions with the aim of constraining
the merger scenario for this cluster. We conclude that by using the location,
size and width of double radio relics we can set constraints on the mass
ratios, impact parameters, timescales, and viewing geometries of binary cluster
merger events.Comment: Accepted for publication in special issue of Journal of Astrophysics
and Astronomy: conference proceedings of "Diffuse Relativistic Plasmas"
conference, Bangalore, 1-4 March 2011, 4 pages, 2 figure
Cosmic rays and molecular clouds
This paper deals with the cosmic-ray penetration into molecular clouds and
with the related gamma--ray emission. High energy cosmic rays interact with the
dense gas and produce neutral pions which in turn decay into two gamma rays.
This makes molecular clouds potential sources of gamma rays, especially if they
are located in the vicinity of a powerful accelerator that injects cosmic rays
in the interstellar medium. The amplitude and duration in time of the
cosmic--ray overdensity around a given source depend on how quickly cosmic rays
diffuse in the turbulent galactic magnetic field. For these reasons, gamma-ray
observations of molecular clouds can be used both to locate the sources of
cosmic rays and to constrain the properties of cosmic-ray diffusion in the
Galaxy.Comment: To appear in the proceedings of the San Cugat Forum on Astrophysics
2012, 27 pages, 10 figure
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