605 research outputs found
Population Synthesis of Isolated Neutron Stars with magneto-rotational evolution II: from radio-pulsars to magnetars
Population synthesis studies constitute a powerful method to reconstruct the
birth distribution of periods and magnetic fields of the pulsar population.
When this method is applied to populations in different wavelengths, it can
break the degeneracy in the inferred properties of initial distributions that
arises from single-band studies. In this context, we extend previous works to
include -ray thermal emitting pulsars within the same evolutionary model as
radio-pulsars. We find that the cumulative distribution of the number of X-ray
pulsars can be well reproduced by several models that, simultaneously,
reproduce the characteristics of the radio-pulsar distribution. However, even
considering the most favourable magneto-thermal evolution models with fast
field decay, log-normal distributions of the initial magnetic field
over-predict the number of visible sources with periods longer than 12 s. We
then show that the problem can be solved with different distributions of
magnetic field, such as a truncated log-normal distribution, or a binormal
distribution with two distinct populations. We use the observational lack of
isolated NSs with spin periods P>12 s to establish an upper limit to the
fraction of magnetars born with B > 10^{15} G (less than 1\%). As future
detections keep increasing the magnetar and high-B pulsar statistics, our
approach can be used to establish a severe constraint on the maximum magnetic
field at birth of NSs.Comment: 12 pages, 11 figures, 5 table
Pushing context-awareness down to the core: moreflexibility for the PerLa language
Information technology is increasingly pervading our envi-
ronment, making real Mark Weiserâs vision of a âdisappear-
ing technologyâ. The work described in this paper focuses
on using context to enable pervasive system personaliza-
tion, allowing context-aware sensor-data tailoring. Since
sensor networks, besides data collection, are also able to pro-
duce active behaviours, the tailoring capabilities are also ex-
tended to these, thus applying context-awareness to generic
system operations. Moreover, because the number of pos-
sible context can grow rapidly with the complexity of the
application, the design phase is also supported by the possi-
bility to speed-up and modularize the definition of the data
and operations associated with each specific context, pro-
ducing a support tool that eases the job of the designers of
modern context-aware pervasive systems
Towards autonomic pervasive systems: the PerLa context language
The property of context-awareness, inherent to a Pervasive
System, requires a clear definition of context and of how the
context parameter values must be extracted from the real
world. Since often the same variables are common to the
operational system and to the context it operates into, the
usage of the same language to manage both the application
and the context can lead to substantial savings in application
development time and costs. In this paper we propose a
context-management extension to the PerLa language and
middleware that allows for declarative gathering of context
data from the environment, feeding this data to the internal
context model and, once a context is active, acting on the
relevant resources of the pervasive system, according to the
chosen contextual policy
From Display to Labelled Proofs for Tense Logics
We introduce an effective translation from proofs in the display calculus to proofs in the labelled calculus in the context of tense logics. We identify the labelled calculus proofs in the image of this translation as those built from labelled sequents whose underlying directed graph possesses certain properties. For the basic normal tense logic Kt, the image is shown to be the set of all proofs in the labelled calculus G3Kt
The influence of magnetic field geometry on magnetars X-ray spectra
Nowadays, the analysis of the X-ray spectra of magnetically powered neutron
stars or magnetars is one of the most valuable tools to gain insight into the
physical processes occurring in their interiors and magnetospheres. In
particular, the magnetospheric plasma leaves a strong imprint on the observed
X-ray spectrum by means of Compton up-scattering of the thermal radiation
coming from the star surface. Motivated by the increased quality of the
observational data, much theoretical work has been devoted to develop Monte
Carlo (MC) codes that incorporate the effects of resonant Compton scattering in
the modeling of radiative transfer of photons through the magnetosphere. The
two key ingredients in this simulations are the kinetic plasma properties and
the magnetic field (MF) configuration. The MF geometry is expected to be
complex, but up to now only mathematically simple solutions (self-similar
solutions) have been employed. In this work, we discuss the effects of new,
more realistic, MF geometries on synthetic spectra. We use new force-free
solutions in a previously developed MC code to assess the influence of MF
geometry on the emerging spectra. Our main result is that the shape of the
final spectrum is mostly sensitive to uncertain parameters of the
magnetospheric plasma, but the MF geometry plays an important role on the
angle-dependence of the spectra.Comment: 6 pages, 4 figures To appear in Proceedings of II Iberian Nuclear
Astrophysics Meeting held in Salamanca, September 22-23, 201
Calcareous nannofossils across the Eocene-Oligocene transition:Preservation signals and biostratigraphic remarks from ODP Site 1209 (NW Pacific, Shatsky Rise) and IODP Hole U1411B (NW Atlantic Ocean, Newfoundland Ridge)
Endometriosis of the ureteral stump: An entity with severe manifestations
A 50-year-old woman on continuous oral estroprogestin therapy and with a history of endometriosis presented with gross hematuria and right reno-ureteral colic pain. Fifteen years before she had undergone total nephrectomy for loss of function of her right kidney due to an ureteral endometriotic nodule resulting in ureteral obstruction. The ureter had not been removed. For the following 15 years-period she had not manifested symptoms or signs of endometriosis. Although imaging investigations allowed to suspect endometriosis of the ureteral stump, urothelial cancer or carcinoma arising in endometriosis nodule could not be excluded. A laparoscopic hysterosalpingo- oophorectomy with the residual ureteral stump removal was performed. Some endometriotic implants on the ureteral stump wall were histologically detected. Proximal ureterectomy should be recommended in patients affected by ureteral endometriosis with a non-functioning kidney since long-term severe complications could derive from the residual stump. A continuous estroprogestin therapy does not totally prevent these complications
On Deriving Nested Calculi for Intuitionistic Logics from Semantic Systems
This paper shows how to derive nested calculi from labelled calculi for propositional intuitionistic logic and first-order intuitionistic logic with constant domains, thus connecting the general results for labelled calculi with the more refined formalism of nested sequents. The extraction of nested calculi from labelled calculi obtains via considerations pertaining to the elimination of structural rules in labelled derivations. Each aspect of the extraction process is motivated and detailed, showing that each nested calculus inherits favorable proof-theoretic properties from its associated labelled calculus
Calcareous Nannofossils and Paleoclimatic Evolution Across the Eocene-Oligocene Transition at IODP Site U1509, Tasman Sea, Southwest Pacific Ocean
The EoceneâOligocene transition (EOT; âź34 Ma) was one of the most prominent global cooling events of the Cenozoic, coincident with the emergence of continentalâscale iceâsheets on Antarctica. Calcareous nannoplankton experienced significant assemblage turnover at a time of longâterm surface ocean cooling and trophic conditions, suggesting causeâeffect relationships between Antarctic glaciation, broader climate changes, and the response of phytoplankton communities. To better evaluate the timing and nature of these relationships, we generated calcareous nannofossil and geochemical data sets (δ18O, δ13C and %CaCO3) over a âź5 Myr stratigraphic interval recovered across the EOT from IODP Site U1509 in the Tasman Sea, South Pacific Ocean. Based on trends observed in the calcareous nannofossil assemblages, there was an overall decline of warmâoligotrophic communities, with a shift toward taxa better adapted to cooler more eutrophic conditions. Assemblage changes indicate four distinct phases caused by temperature decrease and variations in paleocurrents: late Eocene warmâoligotrophic phase, precursor diversityâdecrease phase, early Oligocene coldâeutrophic phase, and a steadyâstate cosmopolitan phase. The most prominent shift in the assemblages occurred during the âź550 kyrâlong precursor diversityâdecrease phase, which has relatively high bulk δ18O and %CaCO3 values, and predates the phase of maximum glacial expansion (Earliest Oligocene Glacial MaximumâEOGM)
The X-ray outburst of the Galactic Centre magnetar SGR J1745-2900 during the first 1.5 year
In 2013 April a new magnetar, SGR 1745-2900, was discovered as it entered an
outburst, at only 2.4 arcsec angular distance from the supermassive black hole
at the Centre of the Milky Way, Sagittarius A*. SGR 1745-2900 has a surface
dipolar magnetic field of ~ 2x10^{14} G, and it is the neutron star closest to
a black hole ever observed. The new source was detected both in the radio and
X-ray bands, with a peak X-ray luminosity L_X ~ 5x10^{35} erg s^{-1}. Here we
report on the long-term Chandra (25 observations) and XMM-Newton (8
observations) X-ray monitoring campaign of SGR 1745-2900, from the onset of the
outburst in April 2013 until September 2014. This unprecedented dataset allows
us to refine the timing properties of the source, as well as to study the
outburst spectral evolution as a function of time and rotational phase. Our
timing analysis confirms the increase in the spin period derivative by a factor
of ~2 around June 2013, and reveals that a further increase occurred between
2013 Oct 30 and 2014 Feb 21. We find that the period derivative changed from
6.6x10^{-12} s s^{-1} to 3.3x10^{-11} s s^{-1} in 1.5 yr. On the other hand,
this magnetar shows a slow flux decay compared to other magnetars and a rather
inefficient surface cooling. In particular, starquake-induced crustal cooling
models alone have difficulty in explaining the high luminosity of the source
for the first ~200 days of its outburst, and additional heating of the star
surface from currents flowing in a twisted magnetic bundle is probably playing
an important role in the outburst evolution.Comment: 16 pages, 12 figures; accepted for publication on MNRA
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