4,725 research outputs found
Ac losses in type 2 superconductors
Electrical, and calorimetric measurements on alternating current loss in niobium zirconium, niobium titanium, and niobium stannide superconductor
METODO INNOVATIVO PER CREARE UN LAYER NANOSTRUTTURATO HONEYCOMB DI TITANIA, AUTOGENERATO SULLE SUPERFICI DI MATERIALI A BASE TITANIO, DESTINATI AL DOMINIO MEDICALE E CHIRURGICO DEGLI IMPIANTI DENTALI, DELLE PROTESI ORTOPEDICHE E DELLE OSTEOSINTESI.
NANOTECNOLOGIA, TITANIO, PROTESI ORTOPEDICHE, OSTEOSINTESI, NANOSTRUTTUR
Blood Lead Levels In Nevada Children
The purpose of this study was to assess the prevalence of plumbism in children one to six years of age in Nevada. During a four-year period from 1992 – 1996, 10,700 children were screened for evidence of blood lead intoxication. The capillary specimens were analyzed by atomic absorption spectrometry. All children with a lead level =\u3e 10 ug/L were retested using venous blood. Ninety three percent of the children had blood lead levels \u3c 10 µg/d
The Noether Symmetry Approach: Foundation and Applications: The Case of Scalar-Tensor Gauss–Bonnet Gravity
We sketch the main features of the Noether Symmetry Approach, a method to reduce and solve dynamics of physical systems by selecting Noether symmetries, which correspond to conserved quantities. Specifically, we take into account the vanishing Lie derivative condition for general canonical Lagrangians to select symmetries. Furthermore, we extend the prescription to the first prolongation of the Noether vector. It is possible to show that the latter application provides a general constraint on the infinitesimal generator xi, related to the spacetime translations. This approach can be used for several applications. In the second part of the work, we consider a gravity theory, including the coupling between a scalar field phi and the Gauss-Bonnet topological term G. In particular, we study a gravitational action containing the function F(G,phi) and select viable models by the existence of symmetries. Finally, we evaluate the selected models in a spatially flat cosmological background and use symmetries to find exact solutions
Updating the orbital ephemeris of the dipping source XB 1254-690 and the distance to the source
XB 1254-690 is a dipping low mass X-ray binary system hosting a neutron star
and showing type I X-ray bursts. We aim at obtaining more accurate orbital
ephemeris and at constraining the orbital period derivative of the system for
the first time. In addition, we want to better constrain the distance to the
source in order to locate the system in a well defined evolutive scenario. We
apply for the first time an orbital timing technique to XB 1254-690, using the
arrival times of the dips present in the light curves that have been collected
during 26 years of X-ray pointed observations performed from different space
missions. We estimate the dip arrival times using a statistical method that
weights the count-rate inside the dip with respect to the level of the
persistent emission outside the dip. We fit the obtained delays as a function
of the orbital cycles both with a linear and a quadratic function. We infer the
orbital ephemeris of XB 1254-690 improving the accuracy of the orbital period
with respect to previous estimates. We infer a mass of M
M for the donor star, in agreement with the estimations already
present in literature, assuming that the star is in thermal equilibrium while
it transfers part of its mass via the inner Lagrangian point, and assuming a
neutron star mass of 1.4 M. Using these assumptions, we also
constrain the distance to the source, finding a value of 7.6 kpc.
Finally, we discuss the evolution of the system suggesting that it is
compatible with a conservative mass transfer driven by magnetic braking.Comment: 13 pages, 5 figures, accepted for publication in Research in
Astronomy and Astrophysics (RAA
A re-analysis of the NuSTAR and XMM-Newton broad-band spectrum of Ser~X-1
Context: Ser X-1 is a well studied LMXB which clearly shows a broad iron
line. Recently, Miller et al. (2103) have presented broad-band, high quality
NuSTAR data of SerX-1.Using relativistically smeared self-consistent reflection
models, they find a value of R_in close to 1.0 R_ISCO (corresponding to 6 R_g),
and a low inclination angle, less than 10 deg. Aims: The aim of this paper is
to probe to what extent the choice of reflection and continuum models (and
uncertainties therein) can affect the conclusions about the disk parameters
inferred from the reflection component. To this aim we re-analyze all the
available public NuSTAR and XMM-Newton. Ser X-1 is a well studied source, its
spectrum has been observed by several instruments, and is therefore one of the
best sources for this study. Methods: We use slightly different continuum and
reflection models with respect to those adopted in literature for this source.
In particular we fit the iron line and other reflection features with
self-consistent reflection models as reflionx (with a power-law illuminating
continuum modified with a high energy cutoff to mimic the shape of the incident
Comptonization spectrum) and rfxconv. With these models we fit NuSTAR and
XMM-Newton spectra yielding consistent spectral results. Results: Our results
are in line with those already found by Miller et al. (2013) but less extreme.
In particular, we find the inner disk radius at about 13 R_g and an inclination
angle with respect to the line of sight of about 27 deg. We conclude that,
while the choice of the reflection model has little impact on the disk
parameters, as soon as a self-consistent model is used, the choice of the
continuum model can be important in the precise determination of the disk
parameters from the reflection component. Hence broad-band X-ray spectra are
highly preferable to constrain the continuum and disk parameters.Comment: 13 pages including 8 figures. Accepted for publication in A&
Advanced superconducting magnets investigation
Mathematical models for steady state behavior of composite superconductors and experimental verification using magnet coi
Optical pulsations from a transitional millisecond pulsar
Weakly magnetic, millisecond spinning neutron stars attain their very fast
rotation through a 1E8-1E9 yr long phase during which they undergo
disk-accretion of matter from a low mass companion star. They can be detected
as accretion-powered millisecond X-ray pulsars if towards the end of this phase
their magnetic field is still strong enough to channel the accreting matter
towards the magnetic poles. When mass transfer is much reduced or ceases
altogether, pulsed emission generated by particle acceleration in the
magnetosphere and powered by the rotation of the neutron star is observed,
preferentially in the radio and gamma-ray bands. A few transitional millisecond
pulsars that swing between an accretion-powered X-ray pulsar regime and a
rotationally-powered radio pulsar regime in response to variations of the mass
in-flow rate have been recently identified. Here we report the detection of
optical pulsations from a transitional pulsar, the first ever from a
millisecond spinning neutron star. The pulsations were observed when the pulsar
was surrounded by an accretion disk and originated inside the magnetosphere or
within a few hundreds of kilometres from it. Energy arguments rule out
reprocessing of accretion-powered X-ray emission and argue against a process
related to accretion onto the pulsar polar caps; synchrotron emission of
electrons in a rotation-powered pulsar magnetosphere seems more likely.Comment: 32 pages, 7 figures. The first two authors contributed equally to
this wor
A possible solution of the puzzling variation of the orbital period of MXB 1659-298
MXB 1659-298 is a transient neutron star Low-Mass X-ray binary system that
shows eclipses with a periodicity of 7.1 hr. The source went to outburst in
August 2015 after 14 years of quiescence. We investigate the orbital properties
of this source with a baseline of 40 years obtained combining the eight eclipse
arrival times present in literature with 51 eclipse arrival times collected
during the last two outbursts. A quadratic ephemeris does not fit the delays
associated with the eclipse arrival times and the addition of a sinusoidal term
with a period of yr is required. We infer a binary orbital
period of hr and an orbital period derivative of
s s. We show that the large orbital
period derivative can be explained with a highly non conservative mass transfer
scenario in which more than 98\% of the mass provided by the companion star
leaves the binary system. We predict an orbital period derivative value of
s s and constrain the companion star
mass between 0.3 and M. Assuming that the
companion star is in thermal equilibrium the periodic modulation can be due to
either a gravitational quadrupole coupling due to variations of the oblateness
of the companion star or with the presence of a third body of mass M
Jovian masses.Comment: 10 pages, 6 figures. Accepted by MNRA
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