12,914 research outputs found
Generalised Dice overlap as a deep learning loss function for highly unbalanced segmentations
Deep-learning has proved in recent years to be a powerful tool for image
analysis and is now widely used to segment both 2D and 3D medical images.
Deep-learning segmentation frameworks rely not only on the choice of network
architecture but also on the choice of loss function. When the segmentation
process targets rare observations, a severe class imbalance is likely to occur
between candidate labels, thus resulting in sub-optimal performance. In order
to mitigate this issue, strategies such as the weighted cross-entropy function,
the sensitivity function or the Dice loss function, have been proposed. In this
work, we investigate the behavior of these loss functions and their sensitivity
to learning rate tuning in the presence of different rates of label imbalance
across 2D and 3D segmentation tasks. We also propose to use the class
re-balancing properties of the Generalized Dice overlap, a known metric for
segmentation assessment, as a robust and accurate deep-learning loss function
for unbalanced tasks
Structural investigations on -FeGe at high pressure and low temperature
The structural parameters of -FeGe have been determined at ambient
conditions using single crystal refinement. Powder diffraction have been
carried out to determine structural properties and compressibility for
pressures up to 30 GPa and temperatures as low as 82 K. The discontinuous
change in the pressure dependence of the shortest Fe-Ge interatomic distance
might be interpreted as a symmetry-conserving transition and seems to be
related to a magnetic phase boundary line.Comment: 4 pages, 5 figure
Elastic Registration of Geodesic Vascular Graphs
Vascular graphs can embed a number of high-level features, from morphological
parameters, to functional biomarkers, and represent an invaluable tool for
longitudinal and cross-sectional clinical inference. This, however, is only
feasible when graphs are co-registered together, allowing coherent multiple
comparisons. The robust registration of vascular topologies stands therefore as
key enabling technology for group-wise analyses. In this work, we present an
end-to-end vascular graph registration approach, that aligns networks with
non-linear geometries and topological deformations, by introducing a novel
overconnected geodesic vascular graph formulation, and without enforcing any
anatomical prior constraint. The 3D elastic graph registration is then
performed with state-of-the-art graph matching methods used in computer vision.
Promising results of vascular matching are found using graphs from synthetic
and real angiographies. Observations and future designs are discussed towards
potential clinical applications
Impurity intrusion in radio-frequency micro-plasma jets operated in ambient air
Space and time resolved concentrations of helium metastable atoms in an
atmospheric pressure radio-frequency micro-plasma jet were measured using
tunable diode laser absorption spectroscopy. Spatial profiles as well as
lifetime measurements show significant influences of air entering the discharge
from the front nozzle and of impurities originating from the gas supply system.
Quenching of metastables was used to deduce quantitative concentrations of
intruding impurities. The impurity profile along the jet axis was determined
from optical emission spectroscopy as well as their dependance on the feed gas
flow through the jet.Comment: Journal of Physics D: Applied Physics (accepted), 6 page
Black Hole Cross Section at the Large Hadron Collider
Black hole production at the Large Hadron Collider (LHC) was first discussed
in 1999. Since then, much work has been performed in predicting the black hole
cross section. In light of the start up of the LHC, it is now timely to review
the state of these calculations. We review the uncertainties in estimating the
black hole cross section in higher dimensions. One would like to make this
estimate as precise as possible since the predicted values, or lower limits,
obtain for the fundamental Planck scale and number of extra dimensions from
experiments will depend directly on the accuracy of the cross section. Based on
the current knowledge of the cross section, we give a range of lower limits on
the fundamental Planck scale that could be obtained at LHC energies.Comment: 28 pages, 9 figures, LaTeX; added references, corrected typos,
expanded discussio
BPS black holes, the Hesse potential, and the topological string
The Hesse potential is constructed for a class of four-dimensional N=2
supersymmetric effective actions with S- and T-duality by performing the
relevant Legendre transform by iteration. It is a function of fields that
transform under duality according to an arithmetic subgroup of the classical
dualities reflecting the monodromies of the underlying string compactification.
These transformations are not subject to corrections, unlike the
transformations of the fields that appear in the effective action which are
affected by the presence of higher-derivative couplings. The class of actions
that are considered includes those of the FHSV and the STU model. We also
consider heterotic N=4 supersymmetric compactifications. The Hesse potential,
which is equal to the free energy function for BPS black holes, is manifestly
duality invariant. Generically it can be expanded in terms of powers of the
modulus that represents the inverse topological string coupling constant,
, and its complex conjugate. The terms depending holomorphically on
are expected to correspond to the topological string partition function and
this expectation is explicitly verified in two cases. Terms proportional to
mixed powers of and are in principle present.Comment: 28 pages, LaTeX, added comment
Caracterização fitossociológica do impacto de Pittosporum undutalum VENT. em três Fragmentos de floresta estacional semidecidual (FESD) na encosta da serra do Sudeste, Pelotas, RS.
bitstream/item/43845/1/boletim-127.pd
Electromagnetic radiation from collisions at almost the speed of light: an extremely relativistic charged particle falling into a Schwarzschild black hole
We investigate the electromagnetic radiation released during the high energy
collision of a charged point particle with a four-dimensional Schwarzschild
black hole. We show that the spectra is flat, and well described by a classical
calculation. We also compare the total electromagnetic and gravitational
energies emitted, and find that the former is supressed in relation to the
latter for very high energies. These results could apply to the astrophysical
world in the case charged stars and small charged black holes are out there
colliding into large black holes, and to a very high energy collision
experiment in a four-dimensional world. In this latter scenario the calculation
is to be used for the moments just after the black hole formation, when the
collision of charged debris with the newly formed black hole is certainly
expected. Since the calculation is four-dimensional, it does not directly apply
to Tev-scale gravity black holes, as these inhabit a world of six to eleven
dimensions, although our results should qualitatively hold when extrapolated
with some care to higher dimensions.Comment: 6 pages, 2 figure
Deformation of Curved BPS Domain Walls and Supersymmetric Flows on 2d K\"ahler-Ricci Soliton
We consider some aspects of the curved BPS domain walls and their
supersymmetric Lorentz invariant vacua of the four dimensional N=1 supergravity
coupled to a chiral multiplet. In particular, the scalar manifold can be viewed
as a two dimensional K\"ahler-Ricci soliton generating a one-parameter family
of K\"ahler manifolds evolved with respect to a real parameter, . This
implies that all quantities describing the walls and their vacua indeed evolve
with respect to . Then, the analysis on the eigenvalues of the first
order expansion of BPS equations shows that in general the vacua related to the
field theory on a curved background do not always exist. In order to verify
their existence in the ultraviolet or infrared regions one has to perform the
renormalization group analysis. Finally, we discuss in detail a simple model
with a linear superpotential and the K\"ahler-Ricci soliton considered as the
Rosenau solution.Comment: 19 pages, no figures. Typos corrected. Published versio
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