558 research outputs found
A one-parameter family of interpolating kernels for Smoothed Particle Hydrodynamics studies
A set of interpolating functions of the type f(v)={(sin[v pi/2])/(v pi/2)}^n
is analyzed in the context of the smoothed-particle hydrodynamics (SPH)
technique. The behaviour of these kernels for several values of the parameter n
has been studied either analytically as well as numerically in connection with
several tests carried out in two dimensions. The main advantage of this kernel
relies in its flexibility because for n=3 it is similar to the standard widely
used cubic-spline, whereas for n>3 the interpolating function becomes more
centrally condensed, being well suited to track discontinuities such as shock
fronts and thermal waves.Comment: 36 pages, 12 figures (low-resolution), published in J.C.
The Optimal Size and Progressivity of Old-Age Social Security
Almost every public pension system shares two attributes: earning deductions
to finance benefits, and benefits that depend on earnings. This paper analyzes
theoretically and empirically the trade-off between social insurance and
incentive provision faced by reforms to these two attributes. First, I combine
the social insurance and the optimal linear-income literature to build a model
with a flexible pension contribution rate and benefits' progressivity that
incorporates inter-temporal and inter-worker types of redistribution and
incentive distortion. The model is general, allowing workers to be
heterogeneous on productivity and retirement preparedness, and they exhibit
present-focused bias. I then estimate the model by leveraging three
quasi-experimental variations on the design of the Chilean pension system and
administrative data merged with a panel survey. I find that taxable earnings
respond to changes in the benefit-earnings link, future pension payments, and
net-of-tax rate, which increases the costs of reforms. I also find that
lifetime payroll earnings have a strong positive relationship with productivity
and retirement preparedness, and that pension transfers are effective in
increasing retirement consumption. Therefore, there is a large inter-worker
redistribution value through the pension system. Overall, there are significant
social gains from marginal reforms: a 1% increase in the contribution rate and
in the benefit progressivity generates social gains of 0.08% and 0.29% of the
GDP, respectively. The optimal design has a pension contribution rate of 17%
and focuses 42% of pension public spending on workers below the median of
lifetime earnings
Neutrino-driven winds from neutron star merger remnants
We present a detailed, 3D hydrodynamics study of the neutrino-driven winds
that emerge from the remnant of a NS merger. Our simulations are performed with
the Newtonian, Eulerian code FISH, augmented by a detailed, spectral neutrino
leakage scheme that accounts for heating due to neutrino absorption in
optically thin conditions. Consistent with the 2D study of Dessart et al.
(2009), we find that a strong baryonic wind is blown out along the original
binary rotation axis within ms after the merger. We compute a lower limit
on the expelled mass of , large enough to be
relevant for heavy element nucleosynthesis. The physical properties vary
significantly between different wind regions. For example, due to stronger
neutrino irradiation, the polar regions show substantially larger than
those at lower latitudes. This has its bearings on the nucleosynthesis: the
polar ejecta produce interesting r-process contributions from to
about 130, while the more neutron-rich, lower-latitude parts produce also
elements up to the third r-process peak near . We also calculate the
properties of electromagnetic transients that are powered by the radioactivity
in the wind, in addition to the macronova transient that stems from the dynamic
ejecta. The high-latitude (polar) regions produce UV/optical transients
reaching luminosities up to , which peak around 1
day in optical and 0.3 days in bolometric luminosity. The lower-latitude
regions, due to their contamination with high-opacity heavy elements, produce
dimmer and more red signals, peaking after days in optical and
infrared. Our numerical experiments indicate that it will be difficult to infer
the collapse time-scale of the HMNS to a BH based on the wind electromagnetic
transient, at least for collapse time-scales larger than the wind production
time-scale.Comment: 25 pages, 4 tables, 22 figures. Submitted to MNRA
Few Shot Learning in Histopathological Images:Reducing the Need of Labeled Data on Biological Datasets
Although deep learning pathology diagnostic algorithms are proving comparable results with human experts in a wide variety of tasks, they still require a huge amount of well annotated data for training. Generating such extensive and well labelled datasets is time consuming and is not feasible for certain tasks and so, most of the medical datasets available are scarce in images and therefore, not enough for training. In this work we validate that the use of few shot learning techniques can transfer knowledge from a well defined source domain from Colon tissue into a more generic domain composed by Colon, Lung and Breast tissue by using very few training images. Our results show that our few-shot approach is able to obtain a balanced accuracy (BAC) of 90% with just 60 training images, even for the Lung and Breast tissues that were not present on the training set. This outperforms the finetune transfer learning approach that obtains 73% BAC with 60 images and requires 600 images to get up to 81% BAC.This study has received funding from the European
Union’s Horizon 2020 research and innovation programme
under grant agreement No. 732111 (PICCOLO project)
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