669 research outputs found
Effects of activated ceria and zirconia nanoparticles on the protective behaviour of silane coatings in chloride solutions
This work investigates the effect of CeO2 and ZrO2 nanoparticles on the corrosion protection performance of non-inhibited and cerium inhibited silane coatings in 3.5% and 5% NaCl solutions on electro-galvanized steel substrates. Atomic force microscopy (AFM) results show relatively uniform coating thickness and varying nanoparticle distribution depending on coating composition. The corrosion behaviour of the sol–gel coatings revealed that CeO2-ZrO2 nanoparticles reinforce the barrier properties of the silane films and seem to act as nano-reservoirs providing a prolonged release of cerium ions. This prolonged release of inhibitor from oxide nanoreservoirs confers longer protection to the metallic substrate
Automated Double Cantilever Beam test system – A two-axis moving camera setup controlled by image analysis for crack recognition
SAXJ1712.6-3739: a persistent hard X-ray source as monitored with INTEGRAL
The X-ray source SAXJ1712.6-3739 is a very weak Low Mass X-ray Binary
discovered in 1999 with BeppoSAX and located in the Galactic Center. This
region has been deeply investigated by the INTEGRAL satellite with an
unprecedented exposure time, giving us an unique opportunity to study the hard
X-ray behavior also for weak objects. The spectral results are based on the
systematic analysis of all INTEGRAL observations covering the source position
performed between February 2003 and October 2006. SAXJ1712.6-3739 did not shows
any flux variation along this period as well as compared to previous BeppoSAX
observation. Hence, to better constrain the physical parameters we combined
both instrument data. Long INTEGRAL monitoring reveals, for the first time,
that this X-ray burster is a weak persistent source, displaying a X-ray
spectrum extended to high energy and spending most of the time in a low
luminosity hard state. The broad-band spectrum is well modeled with a simple
Comptonized model with a seed photons temperature of ~0.5keV and an electron
temperature of ~24keV. The low mass accretion rate (~2x10^{-10} Msun/yr), the
long bursts recurrence time, the small sizes of the region emitting the seed
photons consisting with the inner disk radius and the high luminosity ratio in
the 40-100keV and 20-40keV band, are all features common to the Ultra Compact
source class.Comment: accepted A&
INTEGRAL high energy monitoring of the X-ray burster KS 1741-293
KS 1741-293, discovered in 1989 by the X-ray camera TTM in the Kvant module
of the Mir space station and identified as an X-ray burster, has not been
detected in the hard X band until the advent of the INTEGRAL observatory.
Moreover this source has been recently object of scientific discussion, being
also associated to a nearby extended radio source that in principle could be
the supernova remnant produced by the accretion induced collapse in the binary
system. Our long term monitoring with INTEGRAL, covering the period from
February 2003 to May 2005, confirms that KS 1741-293 is transient in soft and
hard X band. When the source is active, from a simultaneous JEM-X and IBIS data
analysis, we provide a wide band spectrum from 5 to 100 keV, that can be fit by
a two component model, a multiple blackbody for the soft emission and a
Comptonized or a cut-off power law model for the hard component. Finally, by
the detection of two X-ray bursters with JEM-X, we confirm the bursting nature
of KS 1741-293, including this source in the class of the hard tailed X-ray
bursters.Comment: 7 pages, accepted for publication on MNRA
The complete catalogue of gamma-ray bursts observed by the Wide Field Cameras on board BeppoSAX
We present the complete on-line catalogue of gamma-ray bursts observed by the
two Wide Field Cameras on board \sax in the period 1996-2002. Our aim is to
provide the community with the largest published data set of GRB's prompt
emission X-ray light curves and other useful data. This catalogue
(BS-GRBWFCcat) contains data on 77 bursts and a collection of the X-ray light
curves of 56 GRB discovered or noticed shortly after the event and of other
additional bursts detected in subsequent searches. Light curves are given in
the three X-ray energy bands (2-5, 5-10, 10-26 keV). The catalogue can be
accessed from the home web page of the ASI Science Data Center-ASDC
(http://www.asdc.asi.it)Comment: 4 pages, 3 figure
A comparative study of the X-ray afterglow properties of optically bright and dark GRBs
We have examined the complete set of X-ray afterglow observations of dark and
optically bright GRBs performed by BeppoSAX until February 2001. X-ray
afterglows are detected in 90% of the cases. We do not find significant
differences in the X-ray spectral shape, in particular no higher X-ray
absorption in GRBs without optical transient (dark GRBs) compared to GRBs with
optical transient (OTGRBs). Rather, we find that the 1.6-10 keV flux of OTGRBs
is on average about 5 times larger than that of the dark GRBs. A K-S test shows
that this difference is significant at 99.8% probability. Under the assumption
that dark and OTGRB have similar spectra, this could suggest that the first are
uncaught in the optical band because they are just faint sources. In order to
test this hypothesis, we have determined the optical-to-X ray flux ratios of
the sample. OTGRBs show a remarkably narrow distribution of flux ratios, which
corresponds to an average optical-to-x spectral index 0.794\pm 0.054. We find
that, while 75% of dark GRBs have flux ratio upper limits still consistent with
those of OT GRBs, the remaining 25% are 4 - 10 times weaker in optical than in
X-rays. The significance of this result is equal to or higher than 2.6 sigma.
If this sub-population of dark GRBs were constituted by objects assimilable to
OTGRBs, they should have shown optical fluxes higher than upper limits actually
found. We discuss the possible causes of their behaviour, including a possible
occurrence in high density clouds or origin at very high redshift and a
connection with ancient, Population III stars.Comment: 19 pages, 5 figures. To be published in The Astrophysical Journa
X-ray spectral study of the hot gas in three Clusters of Galaxies
We study the physical properties of three clusters of galaxies, selected from
a BeppoSAX Wide Field Camera (WFC) survey. These sources are identified as 1RXS
J153934.7-833535, 1RXS J160147.6-754507, and 1RXS J081232.3-571423 in the ROSAT
All-Sky Survey catalogue. We obtained XMM-Newton follow-up observations for
these three clusters. We fit single and multi-temperature models to spectra
obtained from the EPIC-pn camera to determine the temperature, the chemical
composition of the gas and their radial distribution. Since two observations
are contaminated by a high soft-proton background, we develop a new method to
estimate the effect of this background on the data. For the first time, we
present the temperature and iron abundance of two of these three clusters. The
iron abundance of 1RXS J153934.7-33535 decreases with radius. The fits to the
XMM-Newton and Chandra data show that the radial temperature profile within 3'
towards the centre either flattens or lowers. A Chandra image of the source
suggests the presence of X-ray cavities. The gas properties in 1RXS
J160147.6-754507 are consistent with a flat radial distribution of iron and
temperature within 2' from the centre. 1RXS J081232.3-571423 is a relatively
cool cluster with a temperature of about 3 keV. The radial temperature and iron
profiles suggest that 1RXS J153934.7-833535 is a cool core cluster. The Chandra
image shows substructure which points toward AGN feedback in the core. The flat
radial profiles of the temperature and iron abundance in 1RXS J160147.6-754507
are similar to the profiles of non-cool-core clusters.Comment: Accepted for publication in A&A, 8 pages, 8 figures; corrected typos,
added data points on which fig 1 and 2 are based as comment to source file
High-Resolution X-ray Spectroscopy of the Interstellar Medium
The interstellar medium (ISM) has a multiphase structure characterized by
gas, dust and molecules. The gas can be found in different charge states:
neutral, low-ionized (warm) and high-ionized (hot). It is possible to probe the
multiphase ISM through the observation of its absorption lines and edges in the
X-ray spectra of background sources. We present a high-quality RGS spectrum of
the low-mass X-ray binary GS 1826-238 with an unprecedent detailed treatment of
the absorption features due to the dust and both the neutral and ionized gas of
the ISM. We constrain the column density ratios within the different phases of
the ISM and measure the abundances of elements such as O, Ne, Fe and Mg. We
found significant deviations from the proto-Solar abundances: oxygen is
over-abundant by a factor 1.23 +/- 0.05, neon 1.75 +/- 0.11, iron 1.37 +/- 0.17
and magnesium 2.45 +/- 0.35. The abundances are consistent with the measured
metallicity gradient in our Galaxy: the ISM appears to be metal-rich in the
inner regions. The spectrum also shows the presence of warm/hot ionized gas.
The gas column has a total ionization degree less than 10%. We also show that
dust plays an important role as expected from the position of GS 1826-238: most
iron appears to be bound in dust grains, while 10-40% of oxygen consists of a
mixture of dust and molecules
Evidence for chromatic X-ray light-curve breaks in Swift GRB afterglows and their theoretical implications
The power-law decay of the X-ray emission of GRB afterglows 050319, 050401,
050607, 050713A, 050802 and 050922C exhibits a steepening at about 1--4 hours
after the burst which, surprisingly, is not accompanied by a break in the
optical emission. If it is assumed that both the optical and X-ray afterglows
arise from the same outflow then, in the framework of the standard forward
shock model, the chromaticity of the X-ray light-curve breaks indicates that
they do not arise solely from a mechanism related to the outflow dynamics (e.g.
energy injection) or the angular distribution of the blast-wave kinetic energy
(structured outflows or jets). The lack of a spectral evolution accompanying
the X-ray light-curve breaks shows that these breaks do not arise from the
passage of a spectral break (e.g. the cooling frequency) either. Under these
circumstances, the decoupling of the X-ray and optical decays requires that the
microphysical parameters for the electron and magnetic energies in the forward
shock evolve in time, whether the X-ray afterglow is synchrotron or
inverse-Compton emission. For a steady evolution of these parameters with the
Lorentz factor of the forward shock and an X-ray light-curve break arising from
cessation of energy injection into the blast-wave, the optical and X-ray
properties of the above six Swift afterglows require a circumburst medium with
a r^{-2} radial stratification, as expected for a massive star origin for long
GRBs. Alternatively, the chromatic X-ray light-curve breaks may indicate that
the optical and X-ray emissions arise from different outflows. Neither feature
(evolution of microphysical parameters or the different origin of the optical
and X-ray emissions) were clearly required by pre-Swift afterglows.Comment: 6 pages, sumbitted to MNRA
The Role of Neurophysiology in Managing Patients with Chiari Malformations
Chiari type 1 malformation; Electromyography; SyringomyeliaMalformación de Chiari tipo 1; Electromiografía; SiringomieliaMalformació de Chiari tipus 1; Electromiografia; SiringomieliaChiari malformation type 1 (CM1) includes various congenital anomalies that share ectopia of the cerebellar tonsils lower than the foramen magnum, in some cases associated with syringomyelia or hydrocephalus. CM1 can cause dysfunction of the brainstem, spinal cord, and cranial nerves. This functional alteration of the nervous system can be detected by various modalities of neurophysiological tests, such as brainstem auditory evoked potentials, somatosensory evoked potentials, motor evoked potentials, electromyography and nerve conduction studies of the cranial nerves and spinal roots, as well as brainstem reflexes. The main goal of this study is to review the findings of multimodal neurophysiological examinations in published studies of patients with CM1 and their indication in the diagnosis, treatment, and follow-up of these patients, as well as their utility in intraoperative monitoring.This study was partially supported by grants FIS PI22/01082, which was co-financed by the European Regional Development Fund (ERDF), awarded to M.A. Poca and Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR), Spain, grant 2021SGR/00810. The following nongovernmental associations have generously donated funding to support this research: (1) Asociación Nacional de Amigos de Arnold-Chiari (ANAC, http://www.arnoldchiari.es (accessed on 5 October 2023)), (2) Asociación Chiari y Siringomielia del Principado de Asturias (Ch.y.S.P.A., https://chyspa.org (accessed on 5 October 2023)), (3) Federación Española de Malformación de Chiari y Patologías Asociadas (FEMACPA), and (4) Mariana Dañobeitia https://vhir.vallhebron.com/es/sociedad/noticias/la-hija-de-una-paciente-con-malformacion-de-chiari-dona-21840-euros-para-impulsar-la-investigacion (accessed on 5 October 2023))
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