798,926 research outputs found
GNA: new framework for statistical data analysis
We report on the status of GNA --- a new framework for fitting large-scale
physical models. GNA utilizes the data flow concept within which a model is
represented by a directed acyclic graph. Each node is an operation on an array
(matrix multiplication, derivative or cross section calculation, etc). The
framework enables the user to create flexible and efficient large-scale lazily
evaluated models, handle large numbers of parameters, propagate parameters'
uncertainties while taking into account possible correlations between them, fit
models, and perform statistical analysis. The main goal of the paper is to give
an overview of the main concepts and methods as well as reasons behind their
design. Detailed technical information is to be published in further works.Comment: 9 pages, 3 figures, CHEP 2018, submitted to EPJ Web of Conference
Evolution, nucleosynthesis and yields of AGB stars at different metallicities (III): intermediate mass models, revised low mass models and the ph-FRUITY interface
We present a new set of models for intermediate mass AGB stars (4.0, 5.0 and,
6.0 Msun) at different metallicities (-2.15<=Fe/H]<=+0.15). This integrates the
existing set of models for low mass AGB stars (1.3<=M/M<=3.0) already included
in the FRUITY database. We describe the physical and chemical evolution of the
computed models from the Main Sequence up to the end of the AGB phase. Due to
less efficient third dredge up episodes, models with large core masses show
modest surface enhancements. The latter is due to the fact that the interpulse
phases are short and, then, Thermal Pulses are weak. Moreover, the high
temperature at the base of the convective envelope prevents it to deeply
penetrate the radiative underlying layers. Depending on the initial stellar
mass, the heavy elements nucleosynthesis is dominated by different neutron
sources. In particular, the s-process distributions of the more massive models
are dominated by the \nean~reaction, which is efficiently activated during
Thermal Pulses. At low metallicities, our models undergo hot bottom burning and
hot third dredge up. We compare our theoretical final core masses to available
white dwarf observations. Moreover, we quantify the weight that intermediate
mass models have on the carbon stars luminosity function. Finally, we present
the upgrade of the FRUITY web interface, now also including the physical
quantities of the TP-AGB phase of all the models included in the database
(ph-FRUITY).Comment: Accepted for publication on ApJ
Fitness-dependent topological properties of the World Trade Web
Among the proposed network models, the hidden variable (or good get richer)
one is particularly interesting, even if an explicit empirical test of its
hypotheses has not yet been performed on a real network. Here we provide the
first empirical test of this mechanism on the world trade web, the network
defined by the trade relationships between world countries. We find that the
power-law distributed gross domestic product can be successfully identified
with the hidden variable (or fitness) determining the topology of the world
trade web: all previously studied properties up to third-order correlation
structure (degree distribution, degree correlations and hierarchy) are found to
be in excellent agreement with the predictions of the model. The choice of the
connection probability is such that all realizations of the network with the
same degree sequence are equiprobable.Comment: 4 Pages, 4 Figures. Final version accepted for publication on
Physical Review Letter
DOBBS: Towards a Comprehensive Dataset to Study the Browsing Behavior of Online Users
The investigation of the browsing behavior of users provides useful
information to optimize web site design, web browser design, search engines
offerings, and online advertisement. This has been a topic of active research
since the Web started and a large body of work exists. However, new online
services as well as advances in Web and mobile technologies clearly changed the
meaning behind "browsing the Web" and require a fresh look at the problem and
research, specifically in respect to whether the used models are still
appropriate. Platforms such as YouTube, Netflix or last.fm have started to
replace the traditional media channels (cinema, television, radio) and media
distribution formats (CD, DVD, Blu-ray). Social networks (e.g., Facebook) and
platforms for browser games attracted whole new, particularly less tech-savvy
audiences. Furthermore, advances in mobile technologies and devices made
browsing "on-the-move" the norm and changed the user behavior as in the mobile
case browsing is often being influenced by the user's location and context in
the physical world. Commonly used datasets, such as web server access logs or
search engines transaction logs, are inherently not capable of capturing the
browsing behavior of users in all these facets. DOBBS (DERI Online Behavior
Study) is an effort to create such a dataset in a non-intrusive, completely
anonymous and privacy-preserving way. To this end, DOBBS provides a browser
add-on that users can install, which keeps track of their browsing behavior
(e.g., how much time they spent on the Web, how long they stay on a website,
how often they visit a website, how they use their browser, etc.). In this
paper, we outline the motivation behind DOBBS, describe the add-on and captured
data in detail, and present some first results to highlight the strengths of
DOBBS
The Pisa Stellar Evolution Data Base for low-mass stars
The last decade showed an impressive observational effort from the
photometric and spectroscopic point of view for ancient stellar clusters in our
Galaxy and beyond. The theoretical interpretation of these new observational
results requires updated evolutionary models and isochrones spanning a wide
range of chemical composition. With this aim we built the new "Pisa Stellar
Evolution Database" of stellar models and isochrones by adopting a well-tested
evolutionary code (FRANEC) implemented with updated physical and chemical
inputs. In particular, our code adopts realistic atmosphere models and an
updated equation of state, nuclear reaction rates and opacities calculated with
recent solar elements mixture. A total of 32646 models have been computed in
the range of initial masses 0.30 - 1.10 Msun for a grid of 216 chemical
compositions with the fractional metal abundance in mass, Z, ranging from
0.0001 to 0.01, and the original helium content, Y, from 0.25 to 0.42. Models
were computed for both solar-scaled and alpha-enhanced abundances with
different external convection efficiencies. Correspondingly, 9720 isochrones
were computed in the age range 8 - 15 Gyr, in time steps of 0.5 Gyr. The whole
database is available to the scientific community on the web. Models and
isochrones were compared with recent calculations available in the literature
and with the color-magnitude diagram of selected Galactic globular clusters.
The dependence of relevant evolutionary quantities on the chemical composition
and convection efficiency were analyzed in a quantitative statistical way and
analytical formulations were made available for reader's convenience.Comment: Accepted for publication in A&
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