1,183 research outputs found
Possible Contribution to Electron and Positron Fluxes from Pulsars and their Nebulae
The AMS-02 experiment confirms the excess of positrons in cosmic rays (CRs)
for energy above 10 GeV with respect to the secondary production of positrons
in the interstellar medium. This is interpreted as evidence of the existence of
a primary source of these particles. Possible candidates are dark matter or
astrophysical sources. In this work we discuss the possible contribution due to
pulsars and their nebulae. Our key assumption is that the primary spectrum of
electrons and positrons at the source is the same of the well known photon
spectrum observed from gamma-rays telescopes. Using a diffusion model in the
Galaxy we propagate the source spectra up to the Solar System. We compare our
results with the recent experiments and with the LIS modelComment: To appear in the Proceedings of the 14th ICATPP Conference, Villa
Olmo 23-27 September 201
Pulsar Wind Nebulae as a source of the observed electron and positron excess at high energy: the case of Vela-X
We investigate, in terms of production from pulsars and their nebulae, the
cosmic ray positron and electron fluxes above GeV, observed by the
AMS-02 experiment up to 1 TeV. We concentrate on the Vela-X case. Starting from
the gamma-ray photon spectrum of the source, generated via synchrotron and
inverse Compton processes, we estimated the electron and positron injection
spectra. Several features are fixed from observations of Vela-X and unknown
parameters are borrowed from the Crab nebula. The particle spectra produced in
the pulsar wind nebula are then propagated up to the Solar System, using a
diffusion model. Differently from previous works, the omnidirectional intensity
excess for electrons and positrons is obtained as a difference between the
AMS-02 data and the corresponding local interstellar spectrum. An equal amount
of electron and positron excess is observed and we interpreted this excess
(above 100 GeV in the AMS-02 data) as a supply coming from Vela-X. The
particle contribution is consistent with models predicting the gamma-ray
emission at the source. The input of a few more young pulsars is also allowed,
while below 100 GeV more aged pulsars could be the main contributors.Comment: Accepted for publication in Journal of High Energy Astrophysics
(2015
Evolution and strengthening of the Calabrian Regional Seismic Network
The Calabrian Arc is an area of high seismic hazard,
in the past often affected by destructive earthquakes. The
seismicity of the Calabrian region is monitored by the Italian
National Seismic Network integrated by the Calabrian Regional
one and, in the last three years, by the Pollino temporary
array. We have applied the Seismic Network Evaluation
through Simulation to assess the individual contribution of
each network in locating earthquakes with epicentres in the
Calabrian region and surrounding. We shows that the Calabrian
Regional Seismic Network greatly improves the quality
of the coverage in almost the Calabria territory except in
the Crotone Basin, in the Serre and in the offshore areas. We
show that the contribution of the Pollino temporary array is
instead restricted to a very small area centred on the Pollino
Chain. Due to the presence in the Serre of important seismogenic
volumes, which in the past have generated destructive
earthquakes, it would be opportune to add at least several
seismic stations in this area and surrounding to improve the
seismic monitoring
La rete sismica della Calabria
L’installazione e gestione di una rete di sismografi finalizzata al monitoraggio della sismicità della Calabria risale agli inizi degli anni ‘70, quando furono attribuiti come compiti prima all’IRPI-CNR e quindi al Dipartimento di Scienze della Terra
dell’Università della Calabria (UniCal). Tuttavia le prime stazioni furono attivate solo a partire dal 1978, sostanzialmente nell’ambito del Progetto Finalizzato Geodinamica (PFG). La crescita della
struttura fu rallentata dalla carenza di personale tecnico, problema che tuttora rappresenta una difficoltà e, dopo la chiusura del PFG, anche di risorse finanziarie
A dual output polarimeter devoted to the study of the Cosmic Microwave Background
We have developed a correlation radiometer at 33 GHz devoted to the search
for residual polarization of the Cosmic Microwave Background (CMB). The two
instruments`s outputs are linear combination of two Stokes Parameters (Q and U
or U and V). The instrument is therefore directly sensitive to the polarized
component of the radiation (respectively linear and circular). The radiometer
has a beam-width oif 7 or 14 deg, but it can be coupled to a telescope
increasing the resolution. The expected CMB polarization is at most a part per
milion. The polarimeter has been designed to be sensitive to this faint signal,
and it has been optimized to improve its long term stability, observing from
the ground. In this contribution the performances of the instrument are
presented, together with the preliminary test and observations.Comment: 12 pages, 6 figures, in print on the Proc. SPIE Conf. - August 200
Three years of gravity continous obsevations in the Calabria Arc System: a model of the gravity tide and the tidal field
Remarkable mass displacements of different origin and nature are currently active in the
geological domain known as Calabrian-Peloritani Arc and in the adjacent Tyrrhenian and Ionian Seas. Geophysical, geological and archeological evidence exists that the Ionian coasts
are interested by intense subsidence phenomena(e.g. Marino et al., 2010; Minelli et al., 2013; Stanley and Bernasconi, 2012). However, over geological times, the whole Calabrian region has been rapidly rising relatively to the sea level. The region can be subdivided into several blocks that move upwards with different mean vertical velocities, estimated in some areas up to
about 2 mm/yr in the last 700,000 years (e.g. Sorriso-Valvo, 1993; Westaway, 1993; Antonioli al., 2006). Finally, as shown by the intermediate and deep local seismicity the subduction under the Tyrrhenian Sea is still active and should be taken into account, whatever its stage of
development (e.g. Monna et al., 2013; Piana Agostinetti et al., 2009, and reference therein).
Although since over a century the Calabrian region is going through a period of relative seismic quietness, its seismic hazard is at the highest levels in the Mediterranean basin due to several catastrophic earthquakes present in the historical records
A Logical Approach to Cooperative Information Systems
``Cooperative information system management'' refers to the capacity of several computing systems to communicate and cooperate in order to acquire, store, manage, query data and knowledge. Current solutions to the problem of cooperative information management are still far from being satisfactory. In particular, they lack the ability to fully model cooperation among heterogeneous systems according to a declarative style. The use of a logical approach to model all aspects of cooperation seems very promising. In this paper, we de®ne a logical language able to support cooperative queries, updates and update propagation. We model the sources of information as deductive databases, sharing the same logical language to ex- press queries and updates, but containing independent, even if possibly related, data. We use the Obj-U-Datalog (E. Bertino, G. Guerrini, D. Montesi, Toward deductive object data- bases, Theory and Practice of Object Systems 1 (1) (1995) 19±39) language to model queries and transactions in each source of data. Such language is then extended to deal with active rules in the style of Active-U-Datalog (E. Bertino, B. Catania, V. Gervasi, A. Ra aet a, Ac- tive-U-Datalog: Integrating active rules in a logical update language, in: B. Freitag, H. Decker, M. Kifer, A. Voronkov (Eds.), LBCS 1472: Transactions and Change in Login Databases, 1998, pp. 106±132), interpreted according to the PARK semantics proposed in G. Gottlob, G. Moerkotte, V.S. Subrahmanian (The PARK semantics for active rules, in: P.M.G. Apers, M. Bouzeghoub, G. Gardarin (Eds.), LNCS 1057: Proceedings of the Fifth International Con- ference on Extending Database Technology, 1996, pp. 35±55). By using active rules, a system can e ciently perform update propagation among di erent databases. The result is a logical environment, integrating active and deductive rules, to perform update propagation in a cooperative framework
TRIS I: Absolute Measurements of the Sky Brightness Temperature at 0.6, 0.82 and 2.5 GHz
At frequencies close to 1 GHz the sky diffuse radiation is a superposition of
radiation of Galactic origin, the 3 K Relic or Cosmic Microwave Background
Radiation, and the signal produced by unresolved extragalactic sources. Because
of their different origin and space distribution the relative importance of the
three components varies with frequency and depends on the direction of
observation. With the aim of disentangling the components we built TRIS, a
system of three radiometers, and studied the temperature of the sky at , and GHz using geometrically scaled antennas
with identical beams (HPBW = ). Observations
included drift scans along a circle at constant declination
which provided the dependence of the sky signal on the
Right Ascension, and absolute measurement of the sky temperature at selected
points along the same scan circle. TRIS was installed at Campo Imperatore (lat.
= N, long.= , elevation = 2000 m a.s.l.) in
Central Italy, close to the Gran Sasso Laboratory.Comment: Accepted for publication in The Astrophysical Journa
Continuous gravity and tilt observations in an active geodynamic area of southern Italy: the Calabrian Arc system
Calabria (southern Italy) is a site of considerable seismic activity related to the ongoing evolution of the Calabrian Arc system, where a complex lithospheric structure is present. For over a century the Calabrian region has been going through a period of relative seismic quietness, yet its seismic hazard is at the highest levels in the Mediterranean basin due to several catastrophic earthquakes present in the historical records. In order to strengthen the geophysical monitoring of this region, a gravity and tilt recording station was set up in the premises of the University of Calabria. The recorded signals should allow to estimate a tidal anomaly, possibly correlated with the difference between some local feature of the lithosphere or geodynamic activity and the corresponding characteristics of the model used to calculate the reference gravity tide. We report here on the results obtained by the analysis of more than two years of continuous gravity and tilt observations at a site in the northern part of the region. The tidal analysis of the gravity records, covering the time interval May 2011 - September 2013, has provided amplitudes, amplification factors and phases of the main lunar and solar gravity tidal waves. A reliable model of the gravity tide is necessary for accurate processing of discrete absolute and relative gravimetric
measurements and to detect in the gravity signals possible components correlated to
major seismic activity. The Ocean Tide Load (OTL) effect was accounted for in the
determination of the tidal field spectral parameters. The most widespread DDW99/
NH Earth’s model, adopted here as reference, fits the obtained results well enough.
The tidal residual vectors do not highlight any significant anomaly ascribable to the
complex structure of the lithosphere beneath the region. The analysis of the tilt records
points out a manifest influence of the fluctuations of the air temperature on ground
slope, at annual and diurnal periods. The spectral analysis highlights the presence, on
both E-W and N-S components, of a significant S1 solar wave. Values of the thermal admittance, at diurnal period, have been estimated for both tilt components. A weak energy at the frequency of 1.932 cycles/day, at the limit of statistical significance, is also observed, identifiable as the main semidiurnal lunar wave M2 of the crustal tide. The amplitude and the amplification factors of such a wave are consistent with the values expected by the DDW99/NH model. Beyond everything, the obtained results of the analyses of gravity and tilt records have provided models for the gravity tide and tidal field in the Calabrian region. Moreover, it turns out that the response of the complex lithospheric structure in the Calabrian Arc system to the tidal stress field does not produce any significant anomaly related to the adopted model. Moreover, the absolute measurements of the gravity acceleration, carried out in 1994 and 2013, yielded coinciding values, implying that during the time interval of 20 years not any significant vertical movement and/or mass redistribution in the underground occurred
in the area, despite its intense geodynamic activity
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