144 research outputs found
Spectral features in isolated neutron stars induced by inhomogeneous surface temperatures
The thermal X-ray spectra of several isolated neutron stars display
deviations from a pure blackbody. The accurate physical interpretation of these
spectral features bears profound implications for our understanding of the
atmospheric composition, magnetic field strength and topology, and equation of
state of dense matter. With specific details varying from source to source,
common explanations for the features have ranged from atomic transitions in the
magnetized atmospheres or condensed surface, to cyclotron lines generated in a
hot ionized layer near the surface. Here we quantitatively evaluate the X-ray
spectral distortions induced by inhomogeneous temperature distributions of the
neutron star surface. To this aim, we explore several surface temperature
distributions, we simulate their corresponding general relativistic X-ray
spectra (assuming an isotropic, blackbody emission), and fit the latter with a
single blackbody model. We find that, in some cases, the presence of a spurious
'spectral line' is required at a high significance level in order to obtain
statistically acceptable fits, with central energy and equivalent width similar
to the values typically observed. We also perform a fit to a specific object,
RX J0806.4-4123, finding several surface temperature distributions able to
model the observed spectrum. The explored effect is unlikely to work in all
sources with detected lines, but in some cases it can indeed be responsible for
the appearance of such lines. Our results enforce the idea that surface
temperature anisotropy can be an important factor that should be considered and
explored also in combination with more sophisticated emission models like
atmospheres.Comment: 11 pages, 7 figures; accepted for publication in MNRA
Modelling of the Surface Emission of the Low-Magnetic Field Magnetar SGR 0418+5729
We perform a detailed modelling of the post-outburst surface emission of the
low magnetic field magnetar SGR 0418+5729. The dipolar magnetic field of this
source, B=6x10^12 G estimated from its spin-down rate, is in the observed range
of magnetic fields for normal pulsars. The source is further characterized by a
high pulse fraction and a single-peak profile. Using synthetic temperature
distribution profiles, and fully accounting for the general-relativistic
effects of light deflection and gravitational redshift, we generate synthetic
X-ray spectra and pulse profiles that we fit to the observations. We find that
asymmetric and symmetric surface temperature distributions can reproduce
equally well the observed pulse profiles and spectra of SGR 0418. Nonetheless,
the modelling allows us to place constraints on the system geometry (i.e. the
angles and that the rotation axis makes with the line of sight and
the dipolar axis, respectively), as well as on the spot size and temperature
contrast on the neutron star surface. After performing an analysis iterating
between the pulse profile and spectra, as done in similar previous works, we
further employed, for the first time in this context, a Markov-Chain
Monte-Carlo approach to extract constraints on the model parameters from the
pulse profiles and spectra, simultaneously. We find that, to reproduce the
observed spectrum and flux modulation: (a) the angles must be restricted to
or ; (b) the
temperature contrast between the poles and the equator must be at least a
factor of , and (c) the size of the hottest region ranges between
0.2-0.7 km (including uncertainties on the source distance). Last, we interpret
our findings within the context of internal and external heating models.Comment: 13 pages, 10 figures. Accepted for publication in MNRA
Non-Gaussianity from the Cross-correlation of the Astrophysical Gravitational Wave Background and the Cosmic Microwave Background
Since the first LIGO/Virgo detection, Gravitational Waves (GWs) have been
very promising as a new complementary probe to understand our Universe. One of
the next challenges of GW search is the detection and characterization of the
stochastic gravitational wave background (SGWB), that is expected to open a
window on the very early Universe (cosmological background) and to provide us
new information on astrophysical source populations (astrophysical background).
One way to characterize the SGWB and to extract information about its origin is
through the cross-correlation with other cosmological probes. To this aim, in
this paper, we explore the cross-correlation between the astrophysical
background anisotropies and the Cosmic Microwave Background (CMB) ones. Such a
signal is sensitive to primordial non-Gaussianity (nG) through the GW bias.
Thus, we study the capability of next generation space-based interferometers to
detect such a cross-correlation signal and to constrain primordial nG.Comment: 13 pages, 5 figure
Magnetic winding and turbulence in ultra-hot Jupiters
While magnetism in exoplanets remains largely unknown, Hot Jupiters have been
considered as natural candidates to harbour intense magnetic fields, both due
to their large masses and their high energy budgets coming from irradiation as
a consequence of their vicinity to their host stars. In this work we perform
MHD simulations of a narrow day-side atmospheric column of ultra-hot Jupiters,
suitable for very high local temperatures (T > 3000 K). Since the conductivity
in this regime is very high, the dominant effect is winding due to the intense
zonal winds. By including a forcing that mimics the wind profiles obtained in
global circulation models, the shear layer induces a strong toroidal magnetic
field (locally reaching hundreds of gauss), supported by meridional currents.
Such fields and the sustaining currents dont depend on the internally
generated field, but are all confined in the thin (less than a scale-height)
shear layer around 1 bar. Additionally, we add random perturbations that induce
turbulent motions, which lead to further (but much smaller) magnetic field
generation to a broader range of depths. These results allow an evaluation of
the currents induced by the atmospheric dynamo. Although here we use ideal MHD
and the only resistivity comes from the numerical scheme, we estimate
a-posteriori the amount of Ohmic heat deposited in the outer layers, which
could be employed in evolutionary models for Hot Jupiters' inflated radii.Comment: submitted for publication in MNRA
Multiobjective Optimization of a Rotman Lens through the QLWS Minimization
We address the multiobjective optimization of a Rotman lens by means of a recently proposed method based on the minimization of a properly defined global cost function named Quantized Lexicographic Weighted Sum (QLWS). More specifically, we have considered three different objectives concurring during the optimal synthesis of the lens. First, the difference between actual and desired delay among the excitations of the array elements fed by the lens needs to be lower than a given threshold. Second, gain losses of the beams scanned by the array fed by the lens need to be lower than a given threshold. Third, lens insertion losses should be as low as possible. Exploitation of the QLWS based approach allowed us to obtain in a few minutes a Rotman lens fulfilling these three concurring objectives and to improve the starting result obtained by a commercial software
On the Rate of Crustal Failures in Young Magnetars
The activity of magnetars is powered by their intense and dynamic magnetic fields and has been proposed as the trigger to extragalactic fast radio bursts. Here we estimate the frequency of crustal failures in young magnetars, by computing the magnetic stresses in detailed magnetothermal simulations including Hall drift and ohmic dissipation. The initial internal topology at birth is poorly known but is likely to be much more complex than a dipole. Thus, we explore a wide range of initial configurations, finding that the expected rate of crustal failures varies by orders of magnitude depending on the initial magnetic configuration. Our results show that this rate scales with the crustal magnetic energy, rather than with the often used surface value of the dipolar component related to the spin-down torque. The estimated frequency of crustal failures for a given dipolar component can vary by orders of magnitude for different initial conditions, depending on how much magnetic energy is distributed in the crustal nondipolar components, likely dominant in newborn magnetars. The quantitative reliability of the expected event rate could be improved by a better treatment of the magnetic evolution in the core and the elastic/plastic crustal response, not included here. Regardless of that, our results are useful inputs in modeling the outburst rate of young Galactic magnetars, and their relation with the fast radio bursts in our and other galaxies.C.D., D.V., N.R., and A.G.G. are supported by the ERC Consolidator Grant “MAGNESIA” (No. 817661) and acknowledge funding from grants SGR2017-1383 and PGC2018-095512-BI00. J.A.P. acknowledges support by the Generalitat Valenciana (PROMETEO/2019/071) and by AEI grant PGC2018-095984-BI00. R.P. acknowledges support from NSF award AST-1616157. We acknowledge support from the PHAROS COST Action (CA16214)
Conducting interfaces between band insulating oxides: the LaGaO3/SrTiO3
We show that the growth of the heterostructure LaGaO3/SrTiO3 yields the
formation of a highly conductive interface. Our samples were carefully analyzed
by high resolution electron microscopy, in order to assess their crystal
perfection and to evaluate the abruptness of the interface. Their carrier
density and sheet resistance are compared to the case of LaAlO3/SrTiO3 and a
superconducting transition is found. The results open the route to widening the
field of polar-non polar interfaces, pose some phenomenological constrains to
their underlying physics and highlight the chance of tailoring their properties
for future applications by adopting suitable polar materials.Comment: in press Appl. Phys. Lett. 97, 1 (2010
Is vitamin D-fortified yogurt a value-added strategy for improving human health? A systematic review and meta-analysis of randomized trials.
Yogurt is a good source of probiotics, calcium, and proteins, but its content of vitamin D is low. Therefore, yogurt could be a good choice for vitamin D fortification to improve the positive health outcomes associated with its consumption. The primary aim of this systematic review and meta-analysis was to investigate the effect of vitamin D-fortified yogurt compared with plain yogurt on levels of serum 25-hydroxy vitamin D (25OHD). The secondary aim was to evaluate the effect of fortified yogurt on parathyroid hormone, anthropometric parameters, blood pressure, glucose metabolism, and lipid profile. We searched PubMed, Scopus, and Google Scholar for eligible studies; that is, randomized controlled trials (RCT) that compared vitamin D-fortified yogurt with control treatment without any additional supplement. Random-effects models were used to estimate pooled effect sizes and 95% confidence intervals. Findings from 9 RCT (n = 665 participants) that lasted from 8 to 16 wk are summarized in this review. The meta-analyzed mean differences for random effects showed that vitamin D-fortified yogurt (from 400 to 2,000 IU) increased serum 25OHD by 31.00 nmol/L. In addition, vitamin D-fortified yogurt decreased parathyroid hormone by 15.47 ng/L, body weight by 0.92 kg, waist circumference by 2.01 cm, HOMA-IR by 2.18 mass units, fasting serum glucose by 22.54 mg/dL, total cholesterol by 13.38 mg/dL, and triglycerides by 30.12 mg/dL compared with the controlled treatments. No publication bias was identified. Considerable between-study heterogeneity was observed for most outcomes. Vitamin D-fortified yogurt may be beneficial in improving serum 25OHD, lipid profile, glucose metabolism, and anthropometric parameters and decreasing parathyroid hormone level in pregnant women and adult and elderly subjects with or without diabetes, prediabetes, or metabolic syndrome
Chapter Didattica immersiva nell’Ingegneria Agraria. Un caso d’uso nel Laboratorio di Agricoltura Digitale e di Alta Tecnologia
The chapter describes experiences of 360° videos use by the Agrismart Lab Group of the University of Florence. The Agrismart Lab Group focuses on the technological transfer of information obtained during the research phase to provide the greatest possible diffusion and dissemination of discoveries regarding the technological-digital revolution in the agricultural sector. Dissemination, applications, and teaching are the main outcomes of our research activities, and we have fully utilized the SEPA360 project's resources. In particular, the student will be able to see smart farming examples both in the field and in the immersive teaching lab having clearer theoretical notions by 360° viewers. Two case studies (tractor 4.0 and Agrobot) are included in the interactive videos, which are utilized both for learning and verification
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