1,214 research outputs found
Neural networks for gamma-hadron separation in MAGIC
Neural networks have proved to be versatile and robust for particle
separation in many experiments related to particle astrophysics. We apply these
techniques to separate gamma rays from hadrons for the MAGIC Cerenkov
Telescope. Two types of neural network architectures have been used for the
classi cation task: one is the MultiLayer Perceptron (MLP) based on supervised
learning, and the other is the Self-Organising Tree Algorithm (SOTA), which is
based on unsupervised learning. We propose a new architecture by combining
these two neural networks types to yield better and faster classi cation
results for our classi cation problem.Comment: 6 pages, 4 figures, to be published in the Proceedings of the 6th
International Symposium ''Frontiers of Fundamental and Computational
Physics'' (FFP6), Udine (Italy), Sep. 26-29, 200
Modellare lo scavo archeologico: esperienze e tecniche a confronto
By examining the potential offered by the digital survey, the article aims at encourag¬ing archaeologists to undertake a more rational approach towards three-dimensional data acquisition and management. Data was derived from excavations at Aveia (AQ - Italy) and Seglamen (Ethiopia). The 3D data-capture was achieved with the laser scanner and structure from motion techniques that make it possible to obtain a point cloud of an object from a sequence of photographic images, which are neither ordered nor calibrated. The conclusions reflect the role of digital technologies in the field of stratigraphic survey. Independence from scale and the ability to extract profiles and contours of stratigraphic units are factors of great importance for a virtual reconstruction of archaeological excavations
A 3D environment to rebuild virtually the so-called Augusteum in Herculaneum
Computer graphics and three-dimensional modelling techniques have extended the possibilities of archaeologists in the creation of virtual reconstruction of ancient sites and monuments. Modern computational systems allow the implementation of computer-generated scenarios tailored on human cognitive capacities. Although Virtual Archaeology is not a novelty in the panorama of archaeological methods, there is no agreement among scholars on the minimal parameters necessary to virtually rebuild an ancient context, nor is there any requirement needed to guarantee the accuracy and the effectiveness of the final reconstruction; the strength of a model is based mainly on the capacity of the archaeologist to check the final result in terms of comparison between interpretations and hypotheses. The paper aims at exploring how the archaeologists could perform their work in a computational laboratory thanks to shared 3D models. The case study selected is the recent virtual reconstruction of the so-called Basilica in Herculaneum, a monument - 250 years after its discovery - still largely unexplained. The building is completely buried by volcanic lava save for part of its entrance porch. It was extensively explored using tunnels and looted by its early excavators. Different scholars have rebuilt the monument mainly on the basis of two plans, drawn in the 18th century, and few notes taken by the archaeologists during the exploration. The 3D model, carried out by integrating cad modelling with close-range photogrammetry, is intended to highlight some controversial parts of the reconstructions. Metadata associated to the digital replica describe the physical object and register all phases from data-acquisition to data-visualization in order to allow the validation of the model and the use or re-use of the digital resource
The luminous late-time emission of the type Ic supernova iPTF15dtg - evidence for powering from a magnetar?
iPTF15dtg is a Type Ic supernova (SN) showing a broad light curve around
maximum light, consistent with massive ejecta if we assume a
radioactive-powering scenario. We study the late-time light curve of iPTF15dtg,
which turned out to be extraordinarily luminous for a stripped-envelope (SE)
SN. We compare the observed light curves to those of other SE SNe and also with
models for the Co decay. We analyze and compare the spectra to nebular
spectra of other SE SNe. We build a bolometric light curve and fit it with
different models, including powering by radioactivity, magnetar powering, as
well as a combination of the two. Between 150 d and 750 d past explosion,
iPTF15dtg's luminosity declined by merely two magnitudes instead of the six
magnitudes expected from Co decay. This is the first
spectroscopically-regular SE SN showing this behavior. The model with both
radioactivity and magnetar powering provides the best fit to the light curve
and appears to be the more realistic powering mechanism. An alternative
mechanism might be CSM interaction. However, the spectra of iPTF15dtg are very
similar to those of other SE SNe, and do not show signs of strong CSM
interaction. iPTF15dtg is the first spectroscopically-regular SE SN whose light
curve displays such clear signs of a magnetar contributing to the powering of
the late time light curve. Given this result, the mass of the ejecta needs to
be revised to a lower value, and therefore the progenitor mass could be
significantly lower than the previously estimated 35 .Comment: 9 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Induced gravitational collapse at extreme cosmological distances: the case of GRB 090423
CONTEXT: The induced gravitational collapse (IGC) scenario has been
introduced in order to explain the most energetic gamma ray bursts (GRBs),
Eiso=10^{52}-10^{54}erg, associated with type Ib/c supernovae (SNe). It has led
to the concept of binary-driven hypernovae (BdHNe) originating in a tight
binary system composed by a FeCO core on the verge of a SN explosion and a
companion neutron star (NS). Their evolution is characterized by a rapid
sequence of events: [...]. AIMS: We investigate whether GRB 090423, one of the
farthest observed GRB at z=8.2, is a member of the BdHN family. METHODS: We
compare and contrast the spectra, the luminosity evolution and the
detectability in the observations by Swift of GRB 090423 with the corresponding
ones of the best known BdHN case, GRB 090618. RESULTS: Identification of
constant slope power-law behavior in the late X-ray emission of GRB 090423 and
its overlapping with the corresponding one in GRB 090618, measured in a common
rest frame, represents the main result of this article. This result represents
a very significant step on the way to using the scaling law properties, proven
in Episode 3 of this BdHN family, as a cosmological standard candle.
CONCLUSIONS: Having identified GRB 090423 as a member of the BdHN family, we
can conclude that SN events, leading to NS formation, can already occur already
at z=8.2, namely at 650 Myr after the Big Bang. It is then possible that these
BdHNe originate stem from 40-60 M_{\odot} binaries. They are probing the
Population II stars after the completion and possible disappearance of
Population III stars.Comment: 9 pages, 9 figures, to appear on A&
A field survey on the presence of prednisolone and prednisone in urine samples from untreated cows
Archaeological Expedition at Aksum (Ethiopia) of the Università degli Studi di Napoli “L’Orientale” - 2011 Field Season: Seglamen
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