130 research outputs found
Stochastic reserving with a stacked model based on a hybridized Artificial Neural Network
Currently, legal requirements demand that insurance companies increase their
emphasis on monitoring the risks linked to the underwriting and asset
management activities. Regarding underwriting risks, the main uncertainties
that insurers must manage are related to the premium sufficiency to cover
future claims and the adequacy of the current reserves to pay outstanding
claims. Both risks are calibrated using stochastic models due to their nature.
This paper introduces a reserving model based on a set of machine learning
techniques such as Gradient Boosting, Random Forest and Artificial Neural
Networks. These algorithms and other widely used reserving models are stacked
to predict the shape of the runoff. To compute the deviation around a former
prediction, a log-normal approach is combined with the suggested model. The
empirical results demonstrate that the proposed methodology can be used to
improve the performance of the traditional reserving techniques based on
Bayesian statistics and a Chain Ladder, leading to a more accurate assessment
of the reserving risk
Chemical enrichment and star formation in the Milky Way disk III. Chemodynamical constraints
In this paper, we investigate some chemokinematical properties of the Milky
Way disk, by using a sample composed by 424 late-type dwarfs. We show that the
velocity dispersion of a stellar group correlates with the age of this group,
according to a law proportional to t^0.26, where t is the age of the stellar
group. The temporal evolution of the vertex deviation is considered in detail.
It is shown that the vertex deviation does not seem to depend strongly on the
age of the stellar group. Previous studies in the literature seem to not have
found it due to the use of statistical ages for stellar groups, rather than
individual ages. The possibility to use the orbital parameters of a star to
derive information about its birthplace is investigated, and we show that the
mean galactocentric radius is likely to be the most reliable stellar birthplace
indicator. However, this information cannot be presently used to derive radial
evolutionary constraints, due to an intrinsic bias present in all samples
constructed from nearby stars. An extensive discussion of the secular and
stochastic heating mechanisms commonly invoked to explain the age-velocity
dispersion relation is presented. We suggest that the age-velocity dispersion
relation could reflect the gradual decrease in the turbulent velocity
dispersion from which disk stars form, a suggestion originally made by Tinsley
and Larson (1978) and supported by several more recent disk evolution
calculations. A test to distinguish between the two types of models using
high-redshift galaxies is proposed.Comment: 20 pages, 10 encapsulated postscript figures, LaTeX, uses Astronomy
and Astrophysics macro aa.cls, graphicx package, to be published in Astronomy
and Astrophysics (2004), Also available at:
http://www.astro.iag.usp.br/~macie
Research priorities for maintaining biodiversity’s contributions to people in Latin America
Maintaining biodiversity is crucial for ensuring human well-being. The authors participated in a workshop held in Palenque, Mexico, in August 2018, that brought together 30 mostly early-career scientists working in different disciplines (natural, social and economic sciences) with the aim of identifying research priorities for studying the contributions of biodiversity to people and how these contributions might be impacted by environmental change. Five main groups of questions emerged: (1) Enhancing the quantity, quality, and availability of biodiversity data; (2) Integrating different knowledge systems; (3) Improved methods for integrating diverse data; (4) Fundamental questions in ecology and evolution; and (5) Multi-level governance across boundaries. We discuss the need for increased capacity building and investment in research programmes to address these challenges
Design and implementation of the AMIGA embedded system for data acquisition
The Auger Muon Infill Ground Array (AMIGA) is part of the AugerPrime upgrade
of the Pierre Auger Observatory. It consists of particle counters buried 2.3 m
underground next to the water-Cherenkov stations that form the 23.5 km
large infilled array. The reduced distance between detectors in this denser
area allows the lowering of the energy threshold for primary cosmic ray
reconstruction down to about 10 eV. At the depth of 2.3 m the
electromagnetic component of cosmic ray showers is almost entirely absorbed so
that the buried scintillators provide an independent and direct measurement of
the air showers muon content. This work describes the design and implementation
of the AMIGA embedded system, which provides centralized control, data
acquisition and environment monitoring to its detectors. The presented system
was firstly tested in the engineering array phase ended in 2017, and lately
selected as the final design to be installed in all new detectors of the
production phase. The system was proven to be robust and reliable and has
worked in a stable manner since its first deployment.Comment: Accepted for publication at JINST. Published version, 34 pages, 15
figures, 4 table
Extraction of the Muon Signals Recorded with the Surface Detector of the Pierre Auger Observatory Using Recurrent Neural Networks
The Pierre Auger Observatory, at present the largest cosmic-ray observatory
ever built, is instrumented with a ground array of 1600 water-Cherenkov
detectors, known as the Surface Detector (SD). The SD samples the secondary
particle content (mostly photons, electrons, positrons and muons) of extensive
air showers initiated by cosmic rays with energies ranging from eV up
to more than eV. Measuring the independent contribution of the muon
component to the total registered signal is crucial to enhance the capability
of the Observatory to estimate the mass of the cosmic rays on an event-by-event
basis. However, with the current design of the SD, it is difficult to
straightforwardly separate the contributions of muons to the SD time traces
from those of photons, electrons and positrons. In this paper, we present a
method aimed at extracting the muon component of the time traces registered
with each individual detector of the SD using Recurrent Neural Networks. We
derive the performances of the method by training the neural network on
simulations, in which the muon and the electromagnetic components of the traces
are known. We conclude this work showing the performance of this method on
experimental data of the Pierre Auger Observatory. We find that our predictions
agree with the parameterizations obtained by the AGASA collaboration to
describe the lateral distributions of the electromagnetic and muonic components
of extensive air showers.Comment: 23 pages, 15 figures. Version accepted for publication in JINS
Deep-Learning based Reconstruction of the Shower Maximum using the Water-Cherenkov Detectors of the Pierre Auger Observatory
The atmospheric depth of the air shower maximum is an
observable commonly used for the determination of the nuclear mass composition
of ultra-high energy cosmic rays. Direct measurements of are
performed using observations of the longitudinal shower development with
fluorescence telescopes. At the same time, several methods have been proposed
for an indirect estimation of from the characteristics of
the shower particles registered with surface detector arrays. In this paper, we
present a deep neural network (DNN) for the estimation of .
The reconstruction relies on the signals induced by shower particles in the
ground based water-Cherenkov detectors of the Pierre Auger Observatory. The
network architecture features recurrent long short-term memory layers to
process the temporal structure of signals and hexagonal convolutions to exploit
the symmetry of the surface detector array. We evaluate the performance of the
network using air showers simulated with three different hadronic interaction
models. Thereafter, we account for long-term detector effects and calibrate the
reconstructed using fluorescence measurements. Finally, we
show that the event-by-event resolution in the reconstruction of the shower
maximum improves with increasing shower energy and reaches less than
at energies above .Comment: Published version, 29 pages, 12 figure
Calibration of the underground muon detector of the Pierre Auger Observatory
To obtain direct measurements of the muon content of extensive air showers with energy above 10 eV, the Pierre Auger Observatory is currently being equipped with an underground muon detector (UMD), consisting of 219 10 m-modules, each segmented into 64 scintillators coupled to silicon photomultipliers (SiPMs). Direct access to the shower muon content allows for the study of both of the composition of primary cosmic rays and of high-energy hadronic interactions in the forward direction. As the muon density can vary between tens of muons per m2 close to the intersection of the shower axis with the ground to much less than one per m2 when far away, the necessary broad dynamic range is achieved by the simultaneous implementation of two acquisition modes in the read-out electronics: the binary mode, tuned to count single muons, and the ADC mode, suited to measure a high number of them. In this work, we present the end-to-end calibration of the muon detector modules: first, the SiPMs are calibrated by means of the binary channel, and then, the ADC channel is calibrated using atmospheric muons, detected in parallel to the shower data acquisition. The laboratory and field measurements performed to develop the implementation of the full calibration chain of both binary and ADC channels are presented and discussed. The calibration procedure is reliable to work with the high amount of channels in the UMD, which will be operated continuously, in changing environmental conditions, for several years
A Catalog of the Highest-energy Cosmic Rays Recorded during Phase I of Operation of the Pierre Auger Observatory
A catalog containing details of the highest-energy cosmic rays recorded through the detection of extensive air-showers at the Pierre Auger Observatory is presented with the aim of opening the data to detailed examination. Descriptions of the 100 showers created by the highest-energy particles recorded between 1 January 2004 and 31 December 2020 are given for cosmic rays that have energies in the range 78 EeV to 166 EeV. Details are also given of a further nine very-energetic events that have been used in the calibration procedure adopted to determine the energy of each primary. A sky plot of the arrival directions of the most energetic particles is shown. No interpretations of the data are offered
- …